THE FEDERAL DEMOCRATIC REPIRUC IF ETHIOPIA
MINISTRY OF WATER RESOURCES
ArjoDedessa Irrigation Project Feasibility Study Report
VOLUME - III
Water Resources
VOLUME - III (a)
Annexure - 7 Meteorological And Hydrological Studies
Annexure - 8 Hydrogeological Studies
May. JOO?
Addis Ababa
CJ1
WATER WORKS OESIGN & SUPERVISION ENTERPRISE
IN ASSOCIATION WITH
INHHCONTINENTM CONSDITMTS IND HCHNDCMTSINDIA PVT 1TD
P () Box 2S() I Addis Ababa Ethiopia
To! (2^1)1 614501/6^IK9(i Tax (125I)I 61517IF.-mail u h d scaiclccom netdARJO-DEDESSA irrigation project
FEASIBILITY STUDY REPORT
CONTENTS OF THE REPORT
SERIAL NO,
1
2
3
VOLUME NO,
PARTICULARS EXECUTIVE SUMMARY MAIN REPORT
Pan I - Report
Part ri - Maps i Drawings
ANNEXURES
VOLUME -1
SURVEY AND INVETIGATION (ANNEXURES - 1 to 3)
4
volume -1
Topoyaprxc Survey Geomorphoiog»cai Studies &
Geological & Geolecnmcai investigation
Part I - Report
5
Volume -1 (Pi
Part ii - Appendices
6
VOLUME -II
NATURAL  RESOURCES  (ANNEXURES  -  4  Io 8|
Forestry Energy & Catchment Development Plan
VOLUME -in
WATER RESOURCES (ANNEXURES - 7 to 11)
Volume - III (al
Meteorological & Hydrological & Hydrogeological Studies
Dam & Appurtenant WcX*$
Par. - Repon
B
volume • III (b)
9
Part II - Drawings
irogation & Drainage
10
volume - ill (cj
Pan I - Report
11
■2
13
14
Part H - Drawings
Myorauiic Structures 
volume • ill idi
Pan • Repon
Part ll • Drawings
VOLUME rv
AGRICUTLRUE (ANNEXURES - 12 to 18)
voiume - EV k,ai
So* Survey & Land Evaluation
15
Volume * IV (bj
Agricultural Planning
Volume • IV (cj
Livestock. Fishenes Agricultural Mechanization &
Agricultural Marketing
VOLUME - V
ENVIRONMENTAL  AND  SOCIO  -  ECONOMIC  ASPECTS
(ANNEXURES-19 to 25)
17
Volume-v (8)
Environment Health & Sooo-econcmic Aspecn
18
Volume-v(b)
Organization 5 Management Physical infrastructure
Resettlement. Financial S Economic AnalysisI
I I I I
IAnnexure - 7
METEOROLOGICAL AND
HYDROLOGICAL STUDIESAr}o Dcd«sa Irrigation Pn>)BCl Meteorological and Hydrological Aspects
M*y 3007
Table of Contents
Ta BL f Uf CONTENTS------------- .------ - ----- ------------------------*------------ --- ------------------------- ----- —
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2. REVIEW OF PRE VIOLS STUDIES------------------ -----—-------------------- -----------------------------------------.----- - --------- S
2  1 LaJJMAYEA ]9ft2 STUDY .................. ...................... . ..
3
22
Land and Water Resources of the Bl u e Njle B *isd- E thkjpia
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GOl^TRY wffjf Mas rfcR Pl Ah STUDIES EV DS A ’ W APCOS J19S&-VUJ 
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STldy by BCEOM - (n association fcirMSL an(j EiRG Hfw
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25
STUDY B t MBffISTR Y W WATER RE SOURCES FOR LOWf K Df.DESSa (2 MH J. . .. 15
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UtilitywEajljerStudies .
16
Climatological Data .. Rain fall
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meteorological Data......................................................
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RAINFALL ANALYSIS------------ ----------
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INTRODUCTION
Ranfall Internal and external CtMKiwni Estimation of Rainf.ab i Rfb lability Level Estimation of maximi m Rainfall Fplfq* f srnv
MONTHLY STREAMFLOW ANALYSIS.™—.
40
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HYDROLOGICAL OBSERVATION STATIONS
EXTEhSki\ OF RECORDS
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synthetic  Flows
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estimation of floods for lingauged catchments
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RrtTICfrAL METHOD
72
SCS Method
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Transferring Gauged Data
Estimation of Weighted as erase
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SYNDtR ME THOD OF CONSUL CljNr SVNTHETJT HVDROGRaFH
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FL OOD FREQUENCY ANALYSIS
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Water Works Design & Supervision Enterprise
[a Associate with hn«XdntiiienLaJ Cemulunis and TeetiBOcrau Pit LtdArju Messi ImfsUQo Project
Meteorological and Hydrological Aspects
H I        IS TRHiHX i'TH>S
s i       estimation or Proc ABfi-rr> ft lighted mome >1 s fi J       Ge> F taLtZf ft £xn?f ME \ al l t De trihl rlWh
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probable maximi m flood
SEDIMENT ANALYSIS
10 1 Estimation of SEftiMZNf tiEijD
JD.2 DISTRIRlTPOS OF 'SEDIMENT lh DIE REST* VW
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REFERENCES
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Water Works Design & Supervision Eourprise
In Associate with kttrtiiatinHitai EonsirtMta Ud IttiuiDEriti Pn UdArjo-Dedessi Irrigation Project Meteorological and Hydrological Aspects
May aw?
LIST OF TABLES
Table l i
T^slL4 i Table * 2
Table 4 3- Table 4 4 Table 4 5 Table 5 i Table 5.2 Table 5 3 Tables*
Table. 5.5
Table. 5 6
Table 5 7
Table  56
Tables? Table 5.10
Table 6 1
Table 6.2
Table 6 3
Tables*
Table 6 5
Table 6 6
Table 6.7
Table a 1 Tables 2 Table? l TaBlE 9 2 Table 10 1 Table 10 2. Table 10 3 Table iO a
Table 11 1
Table 12 1
Table 12 2
TaBlE 12 J Table  12* Table  12A Table 4-3 1 Table  *32 Table 13 3 Table 14 1 Table 14.2.
flREAK UP OF AjhBav BaSiN AREA
4
TaBlE Details CF METEORDlOGKTK. OlBSLta * T'CN STaTiQnS  QCaT£c iN an. AROUND IHE
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FKUECTaREa
.......... ■■■
........................... 26
TYPES OF CUMATic DATA AVAILABLE AT TnF va»Ou5 MFTEQRQlOG’Cal OBSERvaTiOa
STATIONS
....... .
Summary OF METFOftQtOGtCAL ChaRACTBRlSTlCS AT PROJECT ARE* SUMMARY OF ESTIMATED MEAN ETC QF ARJQ DEDESSA PROJECT AREA
MAQNrnUDE DP ETo AT GWEN PO*-£iEED*a*CE PTOBABadTY LEVEL CROSS Correlation Matrix df Annual Rain* al .
MeanMonThl* Rah#all ...
. ..
Parameter Estimates or wubull &stri&ution
MONTHLY Rain*al„S CQ«tf SPCWING TD DIFFERENT Re_lABAtfTY LEVELS
parameter Estimates Of half-momthl* RajmfAu.
Half-Monthly Rainfall Magnitude t at Different Ae .jJulitv LEvElS
HAi F-Month; y Ra'NFAu MAGNITUDES IN PERCENT &F THE MEAN CORRESPONDING TQ Different Reliability levels
27
28
2#
Mi
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3?
38
maximum annual 2*-hr Rajnfa^l
Maximum RainFalu MaGniTuOES anC FREQUENCES
Maximum Rainfalu Magnitudes for Higher Durations
Availability of Streamf low Data in the Region
M£An MONThlt FlQW (iN MM'7SEC,i
Coefficient of varjaton of monthly Discharges
Summary OF REGIONAL MCHTl*.* FlOW CHARACTERISTICS
table Statistics of monthly fiqws at Arjd Deoessa dam sjte
RfL'AftLITY LEVS I V5 Monthly StR£ amFlGwS AT DAM SlTE CHAftACTEHiSTiCS OF RanOOm INUWERS ^SEDFDR FlOW GenfRA^pQN estimated Flood Guanthjes Based on GEv OsTmauTioN
Estimated FlOO© Ov*n* aEs Based oh LuG Distribution
Table Cumulative v'Dljme cf Probable Maximum F^qqo
De sign f loot Hydrograph Derated from Estimated Pmf
RekA*IDNSHIPS between WATE R Discharge AhiC SEGMENT load Monthly total sediment load at the Reservoir Site ACCUMULATED Total. SEDIMENT Load at the Reservoir Site DiSTRIBuTbOn of SEDlME NY in THE ARJO DED£S$a RESERvChR water quAu:Tv re slats for sites oh the Oeqcssa r»ver
Catchment Characteristics
....... SO
ROTTED Design Flood at FRL CpfiflESPOKJiNG TO 1152 M
Rou TED Design Koot at FRl GorrespokunG td 1555 m
Rex. TED Design Flood at FRl Corresponding tq * JSGm Routed Design Floooat Coffer Dam of arjd Didessa Reservoir irrigation water Acquirements for various SC€nW»s Reservoir Characteristics at dead storage level .
Storage Reservoir Characteristics and Reliabl .tv levels
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CONSIDERED ....
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AAfriuAu ENFRGY GEhCRATiCJHSAT DE O?SSa Gam FQft THE V4SIOU5 OPTiQn$
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Water Works Design & Supervision Enterprise
In Amciilt with LutereonttosoUJ CoDsuJluiUi ul Teebooenm Ptl LidAjjg Dedessa JitIjiaJdu Project MeieorotogicaJ and Hydrological Aspects
MkX MW7
list of annexure
AmEx A
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A3
AA
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Results obtained from the M£nEOftOLOGuc*.u Analvw
Estimated Mean Temperature at ARzj DcdessaP^jCCt are.*, (in*C) Estimated Minimum Temperature at Arjg De dessa Project Area i,in Cj Estimated Maximum TcMPERaKiRE at ARX2 DEOESSA Project Area 1 INX) Estimated Relative. HuMiornr at Arjq OLDE SS* Project area (in perze nt i Estimated Mean Dajlt Sunshine Duration at Arjo De dessa Project area EsriMATED mean OaaE7oo* Aftjo Dedessa project are*
Estimated Mean Monthly ETa of Arjd Dedessa ProjeCT Area Estimated MEat, MONTMlv RaAiFA^l at ARjO DEDESSa PROJECT AR£a Estimated Mean h**/-mohthlt Rainfal at the Project Area i.in mwhrj Results obtained from the fivdrologhza,. Ana*. *sis
estimated monthly Flws *t arjq dedessaOm She
Regional uomtul* C0Eff«mi of varlations |CV)
Regional mOnIml* goEfkent OF SKEGNESS . .
16 Regional nkinthlt coefficient of correlations (Rj
Standardized probability weighted moments
ME.AN MQNThlt Total i.S JS0EnO€D and 6edj Se dime NT -OW1 ElEvEaTiOn-Area-Capacit* Relationships C* Ar jo &EOE 5Sa Reservoir Sample Simulation Re Sul ts of AhjO OEOESS* Resejivchr
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103
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Standards
...... —......................................... „...... ..................... ............................................121
Commonly USED values 0* RUNOFF COEFFICIENTS .
. ^_...
RuMXF COEFFICIENT for PERVKXIS SURFACES ST SELECTED rtYOUcxoGC SOIL SCS CuRvt NUMBE RS FDR VaRiOuS COKXThXS '
RjESERvc** Flood Standards
______ I2j
Ratios of the basc 9*j€n5iOh£S5 hygrograph of the SCS GuOEtlNES FOR INTEftPfltTAFrONS OF WaTE R QUALITY FOR IRRIGATION
i?l
121
122
i 25
126
METEQROUOGICM Bata................................................................................... ....................................... .. 127
□ETajlS of meteorological Obse RvaTiQn Statkjms
TYPES Of Climatic Data avmlaBlE AT The various METEORQlCGiCaj.
mean Monthly Rajm=all at BeO£l£ Station Mean Monthly Rain*al^ a: J=mma Station Mean Momtmi v Raiw al^ at Dedessa st atk>
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Mfan Temperature AT BfQfLESTA-xm             .......... ................................ . bi
Relative humid,nr at BFmi Static*, ia/% f
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W«D S*tEO AT J'MUA Static*.
J4
Sunshine Uuratiomat 6t DE lie Station
hydrological Data
list of selected hydrological obse rv a non Stations
MEAa MQMThlv S TREAMFLDA at OEDtSSAN NEAR AR JO ST Al ■□*, Mean MQMTnlT S~REAm FLOW AT OtDESSAN rfAR DCmBi STATKMx Aniajaa Maximum F.ooqs
MEASURED SEOIMF NT COMCEHTCATlOh AT GuMXRA GAuQfcG STATION
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Water Works Design & Supervision Enterprise
In Ass eclair with InierconltitttLii CeutilluiU ud TecJnftcrita Pvi LidAru DEdes5*Jrrlff*tlOD Project Meteorological and Hydrological Aspects
May LW
LIST OF FIGURES
Figure 4 1         MEam MOWThl* TEMPFRaTUHE at F«WRE 4 2' MEANMDMTHLV RElATrVF MumiDiTv *T    30
figure 4 3          meam monthly wino Speed at Figure 4 * mean monthly SumSmwe hours at Figure *.5          mean Mourn t etq at ar jq Deoe ssa project a«ea
Figure 5i|a>'      TREnC1 Analysis of Annua. Rainfall at jimmaStaticn Figure 5              Trend Analysis OF Annual RawFalk at BEDEl lE STaTKW Figure 5 1<C)     Trend Analysis of Annual Rawau at Pewssa Static* Figure 5 2Jai      Single Mase Curve of jimma Rainfall
30
31
42
42
45
4?
Figure S.zjhj.   Sacle mass Curve of Bedel_e Raw ................................................................................................ w
Figure 5 ?<C)     SinglC Mass Curve of Dedessa Rainfall
Figure 5 3 Mean Mdnthlv Rainfall at arju Oedessa Prdjetct Area
44
45
Figure 12 T
ElEVATiOn-AAea-CaPACITf Curves of ARjC DECCSSA Re SERVER
K4
Figure i2 2
iw low and Outflow Flood hvdhographs at Ajr >c Dedessa Reservoir
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FiGuftE 12.3.
IMFlCMw ANO O^'TFLOwr FlDOO HVDHOCAaPkS AT AP.JO DEDESSa RESERVOIR
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Figure t 2 a
Average hy daografh or maximum flows at Ar jo Of dessa Dam Site
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Figure 14 i
Power Duration Curves
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■-------------------------------- -- --------------- ------------------- --- -----------------  V
Water Works Design & Supervision Enterprise
Id Aseocbicc Hlh Intmoatinenul CodeuMmu ui Tecfraocrits Ptl Ltd.M3 Arjo Dcdessa Imfxtion Prujrct
Meteorological and Hydrological Aspects
1. INTRODUCTION
1.1 The Nile Basin
May 2007
Having a length of 6.625 km , the Nite River takes  the rank  of number one with respect to length, in the world It drams  a total drainage area oi 2 96 M.Km4 with its  annual total flow of aooul 64 0.t.3 As  one could appreciate, lhe discnarge per Km4' is  small when comparea lo oLher large rrvers  of lhfl world From lhe Lake Victoria, to the Mediterranean Sea. Lhe river crosses  very  many  different areas  associated with different climate relief ano geology The main sources  ol the river are the equatorial lake ptateau and lhe Ethiopian Highlands The three maior tributaries  which emanate from the Ethiopian Highlands  are. from south to the no<1h, the Bara Axabo. lhe Blue Nile, familiarly known as Abbay ana the Tekeze -Atbara System
1,2 Abbay Basin
The AbD3y  Basin is  one Of the most important basims, Ih Ethiopia It accounts  lor abaul 17 5% of Ethiopian land area 25% of its  population ana 50% of its  annua^ average Surface water resources  in me Law Tana, it has  the country  s  largest fresh water ia*e. covering an extent of 3000 km1 The Anbay  nas  an average annual run off of about 50 H m’ The overs of Abbay contribute on an average 62% of Nile nver flows in Aswan dam
The climate of the Aooay  Basrn is  dominated by  two features, namely, it s  near equaional location ano in altitude range aetween 590 m amsi. to 4000 m amsi These influences resun in rich variety  ol local climates  rangmg rrom nobdesert like along (he Sudan OOrder to the temperate type on the high plateau with depiction of cold ir>1he rugn mouniams  The Basin can generally  tie d escribed as 5 emperate a t n igher elevation and tropical a t lower etevanons  However due 10 the distinctive aspects  of the highland climate, it <S perhaps better to describe it using the iocsi Climatic  zones, that have oean established wdn elevation (and -esultant temperature^ as Controlling factors
The Qoaa zone l«s  teiow i860 meters  and has  annual temperature range from 2CcC to 2fi‘C The lAioma Oega zone lies  between 1800 meters  ano 240D maters  ano has  annual average temperature ranging horn 16’C to 20'1C The Uega zone, above 2400 meters  has average annual temperalure ranging from If^C to 16’C The major portion of the population inhabit in me more climatically  pieasant ano healthier upper two zones  which leaves the lower Oolla zone sparsely populated
Waler Works Design & Supervision Enterprise
I
la Associate with [ntereootln ratal Coasultiati and Tecimotrats |*vi Lid4rjo Dtdetift imeauDn Project MeieorgJcigicaJ and Hydrological Aspects
May 200?
There are mainly  3 rainy  seasons  The main one (kireml) lasts  generally  from June lo Septemoer. during which. the south was! winos  bring rams  from the Atlantic  Ocean About 70% to even up to 90% ot the rainfall occurs  during this  season This  season obviou&iy  is associated wdh minimum levels  of sunshine, low variations  in aaily  temperature and high relative humidity  A dry  season (Begaj lasts  from October to January, during which clear skies  are associated with maximum sunshine hours, high daily  temperature variation and low relative humidity  F malSy  the m mor rainy  season (Belgjiasls  from February  Io May. dunng which south east Winds  tinng the small rains  from lhe Indian Ocean The temperature range is  very  high in this  season Tne precise timing and duration of these seasons  vary  cons-deratily  depending upon location wilhm Aobay  Basm. and to some lesser extent, yesr to year as well
Generally  speaking, the low aiidude depicts  the patfern of "1 5 to even 12 5 hours  of sunshine and temperature varying only  for a small range from 3?C to 7“C through out the year
The mean annual rainfall over the entire oasm COukt De reckoned at 1400 millimeters, where as  the mean e vapoiranspiration is  acout l 300 millimeter Broadly, based on the ramfall pattern, a different areas  have been id&nlifieti by  lhe earlier Master Plan study (Abbay  River Basin Inlegrateo Master Plan Prated - 6CEOM in association with BRGM. 30 IS*, consulting Engineers - 1998). These are
i)  Soul  hem  area  covering  East  ana  West  VVetlega,  Jimma  and  llluoabor  Zanes  with relatively h»gn rainfall (1400*2200 millimeters, and a long wet season
u)  A  central  area  covering  most  of  Western  Goiam  and  parts  of  neignoaring  zones  as weal  characterized  by  reualivety  high  rainfall  .1400  -  2200  milhrnelersj  Bui  there  is a   more   pronounced   seasonal   pattern   associated   with   snort   wet   ano   longer   dTy seasons
III)  An  area  covering  most  of  me  eastern  pan  pf  me  basin  including  North  ano  Soulh lWello  Eastern  oart  of  EasL  Gajam  ana  South  Gpnoar  and  much  of  Norin  and  North West   Shewa   region,   excluding   small   proportion   al   mountain   areas   This   area   is characterized  by  relatively  low  rainfall  (less  man  1200  m<lkmet&r  j  distnbutea  irt  both the rainy seasons, depicting bimudality
Water Works Design & Supervision Enterprise
2
In Auscuic with totircOBUncntal CnogaluaLs sod TtcbnocTwPj Ptl LidHi
■BArj® Deaessa ImeaUfin Project MeteorDiogical and Hydrological Aspects
May 2007
tvj The West ana North West area covering North Gondar region. The rainfall rs about 1200 millimeters falling predominantly, m the main rainy season associated with tiagr average rales of evapotranspiration.
Wrth respect to the hydrographic scenario, the Basin is dominated Dy Aooay River which nses *n the tenter of the catchment and develops its course in a clock wise spinal 11 collects tributaries all along rts 992 km journey up to Sudan border As said earlier, the Abbay Basin catchment area of 199.812 km2 is encompassing the br&a& up as beiow
As Gilgei Aboay the mam nver flows north (ram its source near Sekela into the w»de and shallow Lame Tana The tane also receives other tributaries from a catchment of 15.054 km" including tn butanes Megecn. Ribb andi Gumara. Shortly after leaving the lake the mar reaches the celebrated1 Tis Abbay fatlfi, thereafter flowing in a deep and rugged gorge on its way to Suoan Border The break-up of Abay oasm catchment area r$ available in Table i 1
1.3    The Deaessa Catchments
The DOdessa River is the larges! tributary of the Aboay in terms ot the volume oi waler contribution to the lots- flow of AObay at [he Sudan boraer Draining nearly an area of 34.000 s quare kilo meters, t he D edessa nver originates m "he Mt.Venmo and Mt Wacne ranges, flowing in an easteny direction lor about 75 kilo meters, then turning rattier sharply to the north until it reaches the Aopay River The major tributaries of lhe Dedessa nver are the Wama. entering from lhe east, the Dabana from the west, and lhe Angar from the east.
Dedessa Catchment vs sduaieo in lhe south-west pan of Abbay Basin The catch mem area
at a gauging station near Arja town is 9.981 um ’ The climate of
-
the Dedessa Catchment
results  from its  location and elevation (1220 to 3012 meters  } The catchment vs cnaractenzed by mountainous, highly rugged and dissected topography with deep slopes The iowest part of the catchment rs characterized by valley floor with flat to gentle scopes
Must or the rainfall in the Dedessa Catchment is ooncentrated in the June to September period with virtual draught from Novemopr through February Annual totals, average from ies4 than 15C centimeters to more than 200 centimeters The Dedessa catchment, bes-des reflecting a marked rainfall increase with higher elevation, also receives heavier annual quantities  than most of the catchments  in the Abbay  basin Examination or the rainfall records from this area shows that this is due to a longer (May through October i rainy season rather than heavier maximum monthly quantities
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The mein annual flo^ of Odessa rtw at ArjO jtg-txjn
19 about 3.800 million ffl* having #3
majumum flow in August and September (52 percent of the annual] and mmunum (low hd February and March (J&ss than 1,5 percsnl or the annual)
Further  vwip  desonplian  □(  the  Climatic  (actors  ramfaU  and  hydrological  parameters  an made Jrt 1he ensuing respective sections of til repon
Table I, j:          Break up Of AOna y Basin Area
System Tribulary
Joining
From
Catchment
Area (Km1)
Lake Tana
—
North Goiam                    Right side
Beshilo
'/veieka
jemma
Left side
-i
■
South Gojam                    Rignt side
Muger Guder Fincha Deaessa Angar Wonbera Dabus Beles Onder Ranad
Left side
n
■
■
Rignt side
Left side
Rignt side
—
—
Total
15.054 14.389
13.242
6.415
15.782
16 762
8.188
7,011
4 089
19.630
7.901
12.957
21.032
14,200
14.891
8.269
199,812
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2, REVIEW OF PREVIOUS STUDIES
Ml? 2007
Because of rhe importance of ine Abbay, very many  studies had been earned out m the past concerning lhe oasm Though, ihere Wfisl not any  specific  study  lor the development of Dedessa suo basm exclusively, all lhe studies  under taken, ptrlarrnng to Abbay  or the country as  a whole spoke q1 Dedessa development Hence though such a review has  to be more exhaustive, it is  necessary  to undertake such a review defore attempting Dedessa sub basin development especiarly  lhe aspects  connected with hydrology  in 1ms  sectoral study  Such a review is presented in me following suo paragraphs
2.1 Lahmayer 1962 Study
This was mainly concerned With Gilgei An-Hay Scheme Although, 1: was HQl having adequate data base, the study  provided interesting information about Gilgci Aooay  and its  tributaries, wtircr. couio be considered as a cars base for review ano up dating m the light of lhe raw data
2.2 Land and Water Resources of the Blue Nile Basin Ethiopia
Th? study  was  jnoer tanen py  rne unded States  Department of lhe inienor Bureau erf Reclamation during 195S - 1964 This  detailed study  on Hand ano water resources development gl Lhe Agbay  basm is  worth mentioning imponaoL sludy  Even ai 3 time, when there was a Irftle o< no data, very exhaustive analysis erf the available data nac been carried oui Loesiaofisn nydroiogicai studies  Intact the pioneering works  undertaken during that tune, has made Aosay  basin m Ethiopia, to be u<oud of a possessing a good net work  of hydrometric Stations  lor making reliable estimates. The nycnoiogicai aspects  nave been coverec  in Appendix  IP of the report. In 4 differed i sections  of this  Appendix, the various  facets  ol nyorpiggical analysis nave oeen pul forth as be*ow
• Section 1;         A  general  oascnptipn  on  ciimaie  availability  of  waler,  sedimentation  rates and possible *rrhgalton requirements
• Section II          A presentation of the status of historical stream flow ano their elaborations.
• Section III.         A presentation on flow flows and the analysis attempted
• Section IV         A presemaljon on waler jse
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In  lhe  Section  I.  on  giving  an  account  gf  the  synoptic  anti  climatic  situations,  the  22  stations 
with  long  care  nave  been  analyzed  tor  precipitation  and  temperature  The  basm  iSOLherm  and
precijutauon   maps   have   been   prepared   based   on   above   analysis   The   waler   avaiUDHiiy 
aspects  nave  been  also  addressed  m  this  Secnon  I  The  samples  analyzed  al  5  stations 
indicated  a  igw  sodium  hazard;  mgsl  of  them  showed  low  to  medium  salimly  hazard,  some
samples  contained  from  none  to  a  maximum  d  0  2  ppm  ol  Boron,  which  was  found  to  be
(oieratxe  by  most  sensitive  crops  The  samples  showing  highest  salinity  w  ere  irom  Mugger
and  Dinner  With  respect  to  sedimentation,  ratings  were  established  at  4  starions  and  based
on  extrapolation  me  sediment  rate  was  computed  at  all  the  identified  potential  dam  sues  The
panerr  of  sediment  distribution  in  reservoirs  expected  alter  50  years  of  useful  lite  was  adopted
uniformly n a water o aiance t ype ol simuiation, 1 c* e stabhshing i ne success of e act of the
identified   projects   in   me   seclFon   3   regions   have   oeen   identified   for   development   wnh
respective   crop   projections,   cropping   calendar   and   trap   water   requirement   The   WfllfiT 
requirements varied from 7S2 millimeters rn Gdgel Abbay to 1375 millimeters tn Dmder area
The  section  H  has  addressee  the  srream  How  development  for  loeanoos  of  ihe  identified  dam
Sites  by  p  0SSib!&  b«l  sei  or  analysis  available  al  the  lime  In  [he  study  period  59  g  augifiy 
stations  were  eslablishen.  including  74  stations  With  automatic  SLage  records  By  the  various 
analysis  including  graphical  rainfall  runoff  correlations,  tee  Row  senes  were  built  up  ai  all  dam
tcrcauorte  ana  ai  salient  Jocanons  The  annual  mean  flows  at  Sudan  border  was  estimates  at
50 Bm’
For  the  Dadessa  at  Arjo.  ihe  correlated  flows  were  established  for  3  years  r7911  tn  tgi  7  ang
I932j.  The  mean  annual  how  estimate  was  4332  32  Mm   [eaten  men,  area  9436  Square  kfo
1
rnetsn)
For  ihe  Daoana  at  Mum  the  mean  annual  flow  was  establisn&d  al  1757.26  Mm   (calcnmem
3
area 3030 Square Kilometers}
For  tne  Angar  near  Nekamte.  the  How  estimate  ai  annua  mean  level  was  2523  33  Mm3
iCatcnment area 4350 square xiiometersj
Th
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For the proposed Deoessa dam, with a catchment area of 3360 square kilo meters, the How was estimated to be 1533 75 Mm Similady. for the cam sue at Dabana. with a catchment area ot 2654 kilo meters, the annual flow al mean level was  estimated al 1515 63 Mm" For the Angar. 2 dam sues had been idanlifi&d. one at a location with a catchmenl area of 1780 square kilo meters | aG-2 D amj a nd a nolher a 11 ocation with a c atcnment a rea of 4 523 s quare k ilo meters  iAG-6 Dam) The mean annual flows  estimated respectively  at these two locations were, 983.125 and 2251.26 MmJ
The section ill, addresses  toe causalive factors  or floods  >n Abbay  The design raintoll for the basin was  estimated cased on 6 representative station s  data. These are presented below
which are forming a data base worth for revLtw and up dating for adoplion
1 day design rainfall
=
87 Midi meters
2 day design rainfall
-
126    '
5 day design rainfall
=
185  *
10 aay design rainfall
=
251  *
15 nay desigr rainfall
=
321  *
The design flood was  estimated by  phystoai approach using unit hydrograph, storm analysis and design t toed n ydrograpn convolution I or 21 dam sites F or t he others, f tooa i requency analysis based statistical return penod floods were estimatea
For the Deaessa DD-2 reservoir toe PMF was computed as  5390 m3/sec with a base penoa of 99 hours. For the Dabana storage reservoir. The PMF estimate was al 4860 m^sec with a case penod of 91 hours. For the Angar-2 reservoir with a catcnmem area of 1780 square Kilometers the PMF  ana the duration of toe nydrograpr were 3970 m’rsec  and 80 hours  respectively  For the Angar-6 reservoir, the above respective figures were 6180 rr?/sec ano 111 hours.
For toe Dedessa storage aam. tne 5. 10 25. 50 100, year floods  were estimated io be 1700.
i960  2100  2300  and  2400  m i'sec  respectively  These
3
formed  a  gora  oata
base  tor  review  in
me present study
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The section FV as indicated m the beginning oeais with lhe water use studies The 19€0 water use status was reviewed along with such water uses in villages. Then, the run oil estimates have oeen aoopied considering the envisaged irngation and power developments ki respective simulation study Due io Oedessa dam USBR study, estimated a reduction o1 about 139 M ru in DedesM flows io me Aooay .
On me whole, tors USSR siudy is a useful one for lhe Oasm as a whole, tnougn wi1h paucity of data, because u1 ns systematic treatment of hydrological and simulation aspects
2.3   Country wide Master Plan studies - EVDSA/WAPCOS (1908-90}
These siudies  were carried out during 19S0-9O for country  wide water and tend resources development. covering all river basins. These were primarily  desk  studies  for identifying potential imgakon and hydropower sites based on Country woe data ColtediDn and analysis, coupled with detailed map studies The study was addressing the Abbay basin also aiong with orher basins. The USSR studies  were reviewed in detail far the Abbay  basin. ana subsequently  This  study  came out with modifications  in me USER sites  in some cases  and proposed many other sites as well Though desk study the data ease availaDle to this study on nyorological and hyoro meteorological aspects were fairly adequate because of the earlier pioneering works by USER m esiabksning a good net work of such data observation stations
In this study, the rainfall as well as run off aaia for the vicinity of the identilied projects were
collected ana analyzed even though elaborate consistency checks were no1 uneer Lgnen The
oala gaps idling and extrapolation of aala nave been done using statistical regression analysis using mostly orvanate linear as welt non tmear correlations in certain major dams, syntheiic 
Data generation by single sue multi season stochastic models as well nas been under taken
With respect ip floods, the flood frequency anatysrs of the annual maximum flood senes has been cameo ou1 for the observation stahons, in the vicinity of all identified potential cam sites The EVi distribution with the methoa of maximum likelihood fitting has  been followed in the above flood frequency  analysis  On deciding the approonate design cnfena for the inflow design flood for each loentifieo dam site, the flood peaks at the nearest gauging station nave been transferred to the dam sue by empirical formula. For deriving the shape of the complete design inflow hydrograph at the dam site the procedure as indicaied below nas been follower?
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For the neares-l gauging station, lhe observed maxrmum flood hydrograph were iw.aled Far these a <e'ai*onship between lime ana Q/QP cartip were established 11 again sl Q/QP) where t represents  time Q represents  the discharge ai I and QP 15 the pea* discharge Using trus pattern of relationship the aam site hydrograph has  been oeveiopea using the pea*, as estimated by flood frequency analysts.
Simulation studies  nave been systematical earned oul to judge me success  of a scheme at criteria based rehaailiiy  levels. Climatic  data otner than raintatl have aiso been documented though without detailed processing or elaborations The sediment rates as Quoted by various previous  studies  of different easins  have been acopled ana used in simulation studies, considering Ide expectancy of projecis as 50 years
The data case on (he geomeiry of identified studies could be considered to be only 
approximate, as were oasea on purely topographic maps The hyjroiogica. ana hyarc metearotogicai data were also not put into rigorous analysis, which is called tor design of
identified projects, riowever this study along with USBR study beck up gave a very good data
base/ irweniory of an possible exploitable dam sites in Aboay oasm This EVDSA/WAPCO-S
study has cameo out such exercise m all 1he other river basins of the country as welt
The oams  loenufied m me Dedessa sub basin by  this  study  is  the Arp Dedessa irrigation preyed. This  proposal envisaged a dam. a chute spillway, an irrigation ouiiet with in take structure ano a canal taking off on the right Side The project envisaged irrigation over 135.000 hectares with 160% irrigation intensity The inflow in a 75% rehaDle year was estimated to oe 776 00 Mm3 The 10.000 year flood witn a peak of 090 cubit meters per second was getting moderated to an out flow hydrograph of peak  of 642 cubic  meters  per second The Oeao storage was fixed as 93 Mm , an the basis of annual rate of around 1 9 Mn?
2.4    Study by BCEOM - in association with ISL and BRG 1999
The  study  entitled  'Aobay  River  Basin  integrated  development  Master  Plan  Projecf  has  beer, cameo out with the following water resources onentec objectives
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•     Preparation  of  the  rwer  basin  development  master  pian  thai  will  guide  the  development of  ihe  resources  of  tne  Basin  potentially  with  respect  10  occurrence,  distribution,  quality and quaniity of waler resources for ihe coming 30 1o 50 years
•       To   prepare   water   allocation   and   utilisation   plans   under   alternative   development scenarios  and  io  generate  data  information  and  knowledge  that  will  contribute  io  ihe future water allocation negotiations with downstream countries
The  hydroiogicai  and  hydro  meteorological  siudies  are  more  relevant  for  review  in  this  section These aspects nave beer covered in Section ll, volume ill of Ihe Masler Plan Study report.
The oasic  climatic  features  and the climaloiogicai oata of the Abbay  river basin are discussed first. The rainfall data procured by the study was for 173 stations, the data lengln vanea from 3 to 40 years, with associated monthly  gaps. The dala for oiner climatic  factors  were availatre for 10B stations. Trie field verficanon oi these siations  and equipments  has  also been under taken The dala is  said io nave been subiected to analysis  ano some errors  connecter) wiln observations  or processing were identified The study  has  perhaps  noi attempted io improve me quality  of sucn aaia on the plea ttiat it was  outside the consonants  capacity  or responsibility  As  such, me data base after screening and omitting such erroneous  data is staled io be good
With  respect  to  Hydrology  in  the  pan  2of  ihe  BDOve  volume  III,  the  following  aspects  nave been covered systematically.
*    Sasic i-iydrograpmc Features
•    The Hydrometric nei work
■ Review of previous studies
•    Data collection ano Analysis
*    Sectoral mettiMpiogy
bn the basic hydrographic aspects, a good wont of prepanng a map of Ihe basin has been
presented dividing the basin tn to reasonably nomogeneous areas, named 'Basin Units 
representing each of the caichment or one tributary or of several minor ones wilh similar
behaviors. With respect to the hydrometric net worn, it has been considered to oe adequate as
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pe< WMO norms, taxing m to consideration 116 effective stations  The list of staiion, therr locations. and drainage areas  controlled have been well documented in T  spies. appendices and maps The master plan nas found that the spatial distnbution of the stations is not even or equitable The pans  of Besmlo, Weleka and Jemma were not adequacy  represenied Based on visit to all accessible observation stations itie master plan could identify.
* In many  cases  those stations  which have been abandoned are nd worth reconstruction either they  hao not been installed at oplimal locations  or the catchment area controlled toy tnem was too smalt
* The numbers  of automatic  water level recorders  still operational at the study  time were low ihough most of the stations  had been equipped with such recorders  at the time of tneir installations
*    tn many gauges stations the cables of bank operaied cable way were missing
*      On  tne  other  hana  most  stall  gauges  were  m  good  condition  ana  water  level  data  was considered to oe quite reasonable.
There   upon   recommendations   nave   oeer   spell   put   to   be   executed  as   and  when   budget, equipmem and man power are made available
in the first observation, it is fell that wnat is meant as optimum could have been indicated As 
tor as hydroioaicai net warns are concernea, optimality vanes Depending upon the purpose of
the net work It could be a general purpose nel work or could be a specific purpose nei work 
it is not ctear that wnat is the master pian ascribed optimality Funner, since because a
gauging station controts a small catcnment. it seems they have been ignored by Ine masier
plan study
Measurement of discharges  have a multipurpose oriented utilities  like ascertaining the sensitive ar non sensitive areas  flood rate estimation or for a specific  purpose including community  based waler harvesting schemes  etc  Hence, the approach of ignoring stations with smai- catchments does not seem to pe nased on analysis of vivid concepts
Subsequently,   the   Master   Plan   has   made   a   very   brief   review   of   nydroiogicpi   aspects   of previous stuoies Again n is felt that a Masier Plan of the magnitude couid have reviewed in a
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■Tiare  eiacoraie  manner   The  review  courtf  have  brought  out  each  aspect  oi  hydrdiogiptil  ano nytfra  m&c&omiogicai  a  no  simulation  studies  attempted  by  the  earner  studies  Only  such oelailec review would hare formed the natum to appreciate the Further studies taken up by rhe Master Plan.
N6X1, tne data collection ana analysis part is discussed m the report The data sets processed were mean dany  levels, discharge measurements  and suspended sediment concentration Paia With respeci to data processing me major Study  earned out seems  to oe review and reestablishing rating curves  The details  on very  many  nydrcuogicaL analysis  which should have been carneo out odone rinai use of he data in oasm simulation are not finding a piace in the hydrotogy venume (not explicitly eescii bed'
With  respect  to  rating  curve  analysis,  detailed  exploration  ol  the  discharge  dala  of  121   stations have oeen made and eqvaiion erf the form
Q = a (H-H f
o
have been fitted, wnicfi is  common practice m Hydrology  It is  a good thing mat Master plan has  used both analytical ano graphical methods  m parallel m establishing such rating curves Pot ail the stations  analyzed, a total of 25U equations  have been arnv&o with gooc  correlation coefficients of 0 50 ana above ir of the pairs at oata.
The  discharges  have  wen  estimated  using  these  equations.  Then  Master  Plan  stucy  states thal on checxmg homogeneity, the monthly values wee extracted
it  would  have  been  better  to  appreciate  if  the  nomenclature  erf  Homogeneity  with  justifications nau been inchcsied in the repon.
It  .s  aiso  stated  funner  m  me  waster  Plan  that  the  discharges  were  compared  with  earlier studies ano the results dig not nave major vacations.
Again  it  is  leit  that  better  appreciation  could  have  been  made  if  me  concept  of  major  variation had been spelt out.
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Subsequently, water Balance model ol the basin has  tiean formulated Lakmg only representative s rations so a s t o m sue i ne m odd c wnprehensve iwlhodt p ver icadi ng T he selection criteria used for inenlificetiOfl and inclusion of hydttmeinc  stations  m me mooei seem to be appropriate. The mpur hydrological discharges  were Bsiabiksned on daily  time resolution
level for the period of 33 years (1960-1992The gap................... ng techniques seem to have in bull subjective inferences.
Wrin reaped to assessment ot water availability a map has been prepare^ ar a scale of
1  1D00  000  co  estimate  Ihs  glo&a.  water  amiability  to  be  applied  in  all  pocentrai  water resources oevetopmerit sues in Abbay bpsm.
This map ceuid no of use just for a preliminary estimate of annual flows at pre-teasibihty tevci The water availability has been further estimated by retailed watar balance mwtei In tins. m the first runL tne present scenario nas been m built ano for IB net work stations, end water availability nas been estimated The salient findings of this run are as oeidw which era in order
» The annu^L average volume [Towing across me border from Abbay River is 50.30 Bn?
*    Adoui S3% of tne average annual vgrume ai border is ripwing m 4 monihs I July -
October),  while  the  4  months  trom
February 
1o
May 
ac
count
for
le
ss  than  4
%o
f
tne
mean annual flow
• 
The average annual flow al the out iel
from Tana
rep
resent
s a
DOui
7% o
f
the above
annual flaws a1 border
Floods::
The   highest  flood   Hydrographs 
recorded
ai
each
of
the
wate
r
baiance
net
w
ork 
stations nave Deen put io analyses 1o establish lne relation between time and QiQm ratios
Then Hood frequency  analysis  of the annual maximum discharges  has  been cameo out by Gumbei's  EVl distribution to estimate the return psnoci flood peaks  (It is  noi clear whether the annuaL maximum observed peaks  were convened in to instantaneous  peaks) Further enatner reiationsmp connecting catchment size lo flood peak  has  oeen derived lor 2 groups  of eaten meat sizes  one for catchment groups  having catchment area less  than 10 Odd kfn1 ano another one 'or catehmenl sizes  more than 10,000 km7 It has  been concluded that tee formulae denied so can be used for pre-feasteiiity  level studies  only  Master Plan has 
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arlempied io i nk slope ai tfffwwiE catchmenls win flood discharge rates w*ncr- a s& d-d o
r
exhifcn any correlation ir has been opined m the Masier Plan mat ram'aii runoff crxrtul^i
were nol applicable
Ng data or study results pn flood side Will M di any use Lo me pTMenl project speci-c Study Ths  flood slubies  adopted by  rne Master Plan m qhr be uselb to preliminary nbmales  ie*e only
Sodimetit  iransppnation  For  96  stations  sediment  rating  cunts  have  bee-  analyzed  with available data, on me basis, of following iype pi relationships
QL = 3 (H-Hb) ’ unking water level wnh How
OS - ftQLn linking sediment
discharge OS with tipuio discharge QL with a and p as parameters
The KUI sedimentation Iran sported is acc&untM 3S Ute Sum <rt su spendeo sediment load ar.d bed load For bed ioau estimation. 3 drfferem options  are indicated, with a toft or recommendation on Meyer Peter egualton However at the eixt of sediment deliberations Master Plan study hu +e<r mal a global estimate of bed looo transport for the whole Abbey basin gr for any of me large sub basins has no meaning; Hence the siudy nas tunner staled lhal at Master Plan level, considering the amount of bed road transport tefinriMy being small comparotr co suspended load ana considering the sue oi the Abbay  basin it w?s  not necessary to proceed with data coileclxm for evaluation oi bed load estimaiKm
The  above  statement  oi  Master  Plan  is  not  able  to  be  appreciated  witnoul  c<ucidBlicm Subsequenity, lhe Master Plan has prepared maps raoied to erosion
The other studies oonnecled with water balance and water resources modeling seem rc be m
order Software WATBAL has been used in lhe modeling to vanous scenarios T development
after initial calibration to me present scenario
Tnese have been done io*
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» present situation
■ Future situauon encompassing
ci  Scenario  N“  1
a  Scenario  N°  2
o  Scenario  N*  3
□ Scenario N  4
c
(identified projects 1i
(ioenlified projects 2 including Tana Beles} (idemifito projects in main stream)
if all development)
The  results  could  be  utilized  For  comparing  tne  results  of  specific  sub  basin  oriented  modeling studies, like tn& one under isken in the present sfoay
2,5 Study by Ministry of Water resources far Lower Dedessa (2001)
Tins is a reconnaissance level study for the Lower Deoessa Medium hydro power project This gives a vivid analysis of the data and the Hydroiogicai features oi the Oedessa sun basin The oam ate controlling a eatenmant area of 1fl,200 square Kilo meters, has the following water resources poientia. according rp this stuoy
Mean annual flow
“7290 MmJ
Annual Flow tn 75% exceedance year-6300 Mm1 Annual Flow m 30% exceedance year=6l 00 MmJ Annual Flow in 90% exceedance year=5230 MmJ Annual Flow in 95% exceedance year=46O0 tuTm]
The following are the lrequency floods ecHmates
10 Year return penoo (food 20 Year rtf urn penod <!OOC
i00 Year return penoo i'opn 1000 tear return period Tlood 10D00 Year return period flood
=1977 cubic  meter per second =2210 cubic  mater per sewng -2735 cubic  meter per second =3460 cubic  meter per secono =4224 cubic meter per second
A sedimem rate of SOOtons  per square silo meter per year has  been adapted This  gives annual sediment load ol 9 1 million tons  per year The SO year sediment volume of 329 MmJ hac been accounted for reservoir sizing
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and Hydrological Aspects
mij 2Q<r.'
The  siudy  had
analyzed  me  energy  generation  with
a  net
head  of
133  meters  and  wim  toe
assumption  of
regulation  of  70%  of  lhe  mean  annual
llow  T
he  energ
y  that  could  be  generated
so, was estimated to De 1580 GWh per year, with an installed capacity of 299 MW. on adopting a plant factor of 0 6 This  is  very  relevant to Dedessa sub basin and the present study  The useful data were taken m to account
2.6 Utility of Earlier Studies
All the earner sludies  reviewed have some useful daia base Alt itie useful information (data o1 all tne above studies  have been reviewed and utilized as  per need and appropriateness}. However, lhe present study  is  specific  sub basm (Dedessa) development study, and as  such, systematic  hydrological ano modeling studies  are warranted wilh modern tools  Df analysis. This sectoral report narrates these specific sludies
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Hi; 2007
For  the  study  towards  itie  development  of  1he  Defl&ssa  sub  basin,  tne  data  on  climate  river flows and sedimentation oecome relevant with respect Io Hydrological Modeling and Vv alec
Resources Planning
3.1    Climatological Data
The climatological data like sunshine duration, relative humidity  wind speeds  temperalure in 1he resolution levels  or monthly  means  of daily  means, monthly  mean of oaily  maximum and monthly  mean of daily  minimum become very  important parameters  with respect to lhe proposed command area development These in association with command area rainfall form the basic  inputs  for the estimation of lhe crop water requirement exercise A vivid analysts follows on these important parameters in the section 4 of this report
3,2.   Rainfall
The rainfall requires  cnticai analysis  lor the dam site ano the upstream lor appreciating and developing floods  either as  a full hyorograpn or in the form ol flood peak  rale, expected at different Exceedance probability  ieveis  return penods) The rainfall oata needs  to oe analyzed m ns various forms, like maximum of observed 1 day/2 aay or 3 to 15 days vames or as a time senes  of observeo annual maximum 1 day  rainfall or as  monthly  / fonmgntly  tolars  as  per analysis  at different stages  The analysis  has  io under take tne gambit of snort duration ramfall intensities  as  well, m connection wiih design ol drainages  ano return period rainfall peaks  lor the design of flood control worxs, m the downstream of the dam m ana m the vicinity  of the proposed commano area.
3.3.   River Discharge
Likewise 1he river flows  data time senes, preferably  on monthly  or fortnightly  time resolution ieveis. forms  the fore runner ior establishing water resources  availability  lor performing simulator whether as  basic  hisioncai time series  or indirectly  ihrougn synthetically  generated time senes  (mostly  generated by  a stochastic  generation scheme}, where as  the same flow oata nas  to be analyzed in a dif'erent form as  discharge (flow rates  instead ol flow volumes} with resDect to flood analysis
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3.4.     Sedment Data
Ttie sedmenl data is  obviously  required co piar. the size of ine storages. for apponionmg itie active andindcuve storage spaces  and for determining lite revised g eomietry  of the storage after certain design life, (revised elevation - area capacdy  relationship) as  tins  revised relation is  used m ihe simulation modeling Toe water quality  is  another aspect which needs  10
□e  addressed  in  Hydrological  study  along  wdn  low  flaw  analysis  Tor  mandatory  downsream releases, aosety associaiee witn me concerns ci environmental and ecological aspects
With suer, appreciation of the frame work  of hydrological slmlies  and modeling. the data base was established, as  elaborately  discussed in the intenm report. However in the Tallowing seclioas and m the annexufe enclosed with this report, the dais base an chrnaHKogy. Hydrology including sedimentalror floods  are indicated All the data availaDle m a regional sense up to dace i2(XMj were Drought to analysis cesn and appropriately inciuaea
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4. ESTIMATION OF REFERENCE EVAPOTRANSPIRATION
4.1
Introduction
Th*  climate  of  the  Ago
Didessa
catchmen
t  results  ham
ns  location  a
nd  el
evation
(i  300  to
3012
meters}
The  list  of  stations  for
observa
tions  of
meteorological
data  along
with
iength
of  records
and
availability of data types
is given
in Table
4. 1 AH relev
ant types of
data
nave b
een record
ed al
Jtrruna (located very  close to the neao of the Didessa catchment) stations  since <953 Rainfall arw temperature have been ooserved al Didessa and Bedele Rainfall ana temperature nave been arso recorned al Demb> and Agara stations
Climatic  data for the project area such as  temperature, relative humidily. sunshine hours, wind speed and rainfall have beer, collected ano reviewed Consistency  tests, data rectification and other adjustments  have Deen performed as  necessary  oata gaps  have been filled using interpolation ano correlations methods as appropriate
The FAO Penman-Monteith method is  maintained as  the soie standard method tor the computation of crop reference evapoteanspiration (ETO) from meteorological data. This  section describes  how [he monthly  ETU is  determined from temperature humidity, wind-speed and sunsnme hours  data collected at Banir Oar station The ETe calculation nas  beer earned out by means of a computer
The FAO Penman-Momeith equation determines  the evapotranspiration from the hypothetical grass  reference surface ano provides  a standard to which evapotranspiration lor various  crops growing in the Aryo-Dedessa project command area can be related
The melhoas  for calculating evapotranspiration from meteorological aata require various dimeioHjgicai and physical parameters. Some of the data are measured directly  in Banir Dar meteorological station. Other parameters  are related to commonly  measured data and can be derived wiih the nelp of a direct or empmcai relationship. This  section discusses  the source and computation of all oata required for the calculation of the reference evapotranspiration by means of the FAQ Penman-Monteith method
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The meieorol&gicai factors  determining evapoiranspiration are weather parameters  which provide energy  for vaponzaifori and remove *aier vapour From the evaporating surface The principal weather parameters  to consider are presented below. The data abiained from (he Beoeie, Cedessa and Jim ma stations  are assumed directly  applicable to lhe Aijo Dedessa irrigation Project wilhapplicauon 01 appropriate information transfer mechanisms
4.2    Meteorological Data
4.2.1 Meteorological Observation Stations
Five meteorological observation stations ere locateo in ano around the Arjo-Dedessa irrigation
Project area These meteorological data are obtained irgm the National Meteorological
Senncss Agency (NMSA) Out of these Jimma is Class i station that include opservations ol
rainfall, temperature relative humidily sunshine duration wind sjieec and evaporation
Bettae and Dedessa are also Class 1 stations but do not include sunshine duration in
addition Agars ano Demtn are Class 3 stations that include observations ot rgmlall and
temperature. The longest record that covers 50 years of meteorological data is available ai
Jimma station that Includes ramtail ana temperature data since 1952
Agaro ano Dembi stations  are located withm the cachmenl area ot lh& proposed dam site Jimma station is  located at approximately  at 10 kmfrom me divide oi Oeaessa catchment Sedelle station is  located close to the proposed irrigation tom mend area of the project Dedessa station is  located further downstream gl lhe command area. The details  like location, allituoe year of esibblisnmem aipng wild lfieir ciass are available rn Table 4 '
Meieonciogicai cars available at the five PoservauciTi stations locai&a in and a<ounu Itie project area fiava Deen collected The types  Df meiearoiogical daiEa available at Ihese sEasions  along wrtti lhe lenglh of data are given m Table 4.2.
Jimma Airport meteorttogical ssaupn is taken to be the mosi reliable Class I sialron From which meieorologzcai information relevant 10 the project area has  been derived The data trom Jimma station has  been used lor noth the catchment study  ang estimation or mereoroiogieai variables at lhe irrigaiion command area. The necessary  adjustment for lhe differences  in elevation has peer made in translernng the data. Meteorological information from Agara and Oempi stations
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whicn ate totaled within the oam site catchment have Deen used for caccnmeni study  m addition tp Jimma station. Similarly, meteorological data ol Bcdelle and Dedessa have oeen jsm in addition 10 the data obtained from Jimma station lor estimating rainfall and evapotranspiration al lhe proposed irrigation command
In summary  climatological I data obtained from Bedete. Deoessa and Jimma stations  were found to De me most reliable and relevant for use in me analysis of rainfall lor Ine Ago Dedessa imgatinn project Bedeie is  geographically  the closesl station to rhe command area Oedcssa station and the command area are located 31 the same elevation (i e, both 1330 m asl) Jimma station (which is  Class  Ij nas  the longest record of all me stations  within the neighbourhood ol the command area so as  to oe index  station in extrapolating and interpolating missing and snort term of climatic data relevant to the Ago Dedessa catchment and command area
4.2.2 Air temperature
In the projed farm area, lhe mean monthly  temperature variations  inrougnoui the year are minor, oemg 20 0°C in December to 25 4°C in March The mean monthly  temperatures  of lhe command area >s given in Taoie 4 3 ana graphically illustrated by Figure 4.1 Temperalure data nave oeen jsed in estimating evapotranspiration rates from reference crops
Agmmeteorology  rs  concerned with lite air temperature near the level of the crop canopy  In traditional ana moaerr automatic  weather stations  the air temperature is  measured Inside shelters  (Stevenson screens  or ventilated radiation smeidsj placed in line with World Meteorological Organization (WMO) standards  al 2 m above the ground Minimum and maximum tnermometers  record the minimum and maximum air temperature over a 24-hour period
Due Io the non-linearity  of numidity  data nequireo in the FAO Penman-Monteite equation, the vapour p ressure for a certain period should be computed as  the mean between the vapour pressure ei the daily  maximum and minimum air temperatures  of that period The daily maximum air temperature (Tmil) ano daily  minimum air temperature (Tw) are. resoectiveiy. (tie maximum and minimum air temperature observed dunng the 24-hour period The mean daily air temperature (T^^j rs only employed in the FAO Penman-Monteith equation co calculate the
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slope  of  the  saiuration  vapour  pressure  curves  (4)  estimating  saiuraticn  vapour  pressure
■eTRancl aT/ (Steten-BDitzmann iaw)
The so a.' radiation aosarneo by the BtmosphMe and me tieul emilied by trie earth increase me air lemperaiure. The senjibte neat ol rhe surrounding gm Iransfws  energy  10 the crap and exerts  as  such a controlling influence on the rate af evapotranspiration In sunny  warm weather the loss Of water by evapotranspiration <5 greater man m cloudy and cool weather
4.2.3 Air humidity
Mean humility values vary between 56 63 percent tn March to 88 63 percent in September The mean monthly  numidrty  ol the command ares  ts  given m Table 4.S and grapmcalty 
Iluslrgted  by  Figure  4  2  Data  pf  humidity  have  been  used  m  eslimalmg  evapotranspiration rates from reference craps
The reUbve humidity (RH) expresses the degree ol saturation of the an as a ratio of the actual te,) to the saturation (e‘(T>) vapour pressure ar the same temperature (Ti Reiaiive humidity it
the rabp Between the amount ol water the amDiont air actually hekfe ano the amount it ctwkl
n&d at the same temperalure. » is fl imensioniess ana is commonly given ass percentage
Although ine actual vapour pressure might tw relatively constant throughout the day. trie
relative humidity fluctuates between a maomum near sunrise ana a mmimum around early afternoon TTie trartefwn of the relative humidity is lhe resull cl the ted mat the saturation
vapour pressure m aetermmec d> lhe air temperature As lhe tomporaLure cnanges ounng the
day Lhe rpiaiive humidity also changes substantially
While me energy  supply  from tee sun ana surrounding air is  ine main dnwrvg force for the vaporization of water, the deference between the waler vapour pressure sl the evaparenspinng surface ano ine surrounding air is  the determining factor for the vapour removal Well-watereo ft&kis in hot dry arid areas consume targe amounts pt water due to tee abundance of energy ana lhe desiccating power of the atmosphere, tn humid tropical regions, fflcuwrtnslandmg ine high energy  input, trie fugn humidity  of the air wtl reduce the evapotranspiration demand, in sucn an environment, lhe air is already ciose to saturation, so that »ss additional water can be stored ano hence the evapotranspiration rate is lower than in and regions.
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4.2.4 Wind $ pee fl
My
Mean wind speeo values vary between 0 48 meter per second in November to 1 Gfi meler per second m April The mean monthly  wind speeds  ol me command area are given m Table 4 3 and graphically  illustrated Dy  Figure 4 3 Average wmd speed recorded at Jimma station n meters  per second (m/s) is  taken as  wind speed information relevant for me Ago-Dedessa command area as there is no reliable data at oiner climatic stations nearby. Time senes aspect of the wmd data rs  not considered as  it exhibits  unacceptable erratic  variation within the record penod. Using the mean values  against the lime senes  data has  been tested for Sahir Dar station and resulted in equal result for monthly  and annual evapoiranspriation estimates However the mean wind values  produced an estimated coefficient of variation (CV) of 2 2% insreaa of 2.4% estimated from the time senes
Wind is  charactenzed by  its  direction and velocity. Wind direction reiers  to the direction from wmcn the wmd is  blowing. For the computation qI evapotranspiration, wind speed is  the relevant vanaDie. Wind speed is  measureo with anemometers- The anemometers  commonly 
□sea  in  weather  stations  are  composed  ol  cups  or  propellers  which  are  turned  by  the  torce  oi the  wine  By  counting  ine  number  of  revolutions  over  a  given  time  penod.  the  average  wind speed over the measunng pence is computed
The process  of vapour removal depends  to a large extent on wind and air turtmtence which transfers  targe quantities  of air over the evaporating surface. When vaporizing water the air above the evaporating surface becomes  gradually  saturated with water vapour If this  air is  not continuously  replaced wiLn doer air the driving force lor water vapour removal arid me evapotranspiration rate decreases.
4.2.5 Solar radiation
Mean sunshine duralron is 8 3 hours in December and is reduced io 3.7 hours during July The mean monthly  sunshine durations  of the command area are giver, in Table 4 3 ana graphically illustrated by  Figure 4 4 Data of sunshine hours  nave been used in estimating evapotranspiration rates from reference crops
i   he  relative  sunsnme  duration  tn/N)  is  another  ratio  that  expresses  the  cloudiness  of  me atmosphere. It is the ratio ol the actual duration ot sunshine, n, to the maximum possible
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duration of sunshine or daylrght hours  N In the absence of any  clouds, the actual duration of sunshine is equal 10 the daylight hours (n = N} and the ratio is one. while on cloudy days n and consequently  ine ratio may  oe zero. In the absence of a direct measuremeni of FL. the relative sunsnme duration, n/N. is  often jsed to derive solar radiation from extraterrestrial radiation As with extraterrestrial radiation, the day length N depends on the position of the sun and is hence a function of latitude ano oate
The evapotranspiration process  is  determined by  the amount o! energy  available to vaporize water Solar radiation is  the largest energy  source and is  able to change large quantities  of liquid water into water vapour The potential amount of radiation that can reach the evaporating surface is  determined by  its  location and Sime ol the year Due to differences  in the position ol the sun. the potential radiavon differs  al vanous  latitudes  and in different seasons. The actual solar radiation reaching the evaporating surface depends  on the turtudity  of the atmosphere and (he presence of aouds  whicn reflect ana absorb ma^or parts  of the radiation When assessing the effect or solar radiation on evapotranspiration, one shoe la also bear in mind that not all available energy  is  used to vaponze water Part of the soiar energy  is  used to heat up the atmosphere ana tne soil prdlile
4.3 Pen mart-Monteith Equation
From the anginal      Penman-Montetth   equation   and   the   equations   of   (he   aerodynamic   ana canopy resistance    the FAO Penman-Monteilh equation can be expressed as follows
ETd = gjQ£Al£.
r 27311
(2 1)
i + T(I + D.34 uj
where
ETO = reference evapotranspiration [mm Oay ]
1
R  = net radiation at the crop surface [MJ m'
n
2 da/1],
D
1
G = sod heat flux density [MJ m'3 day''].
T = air temperature at 2 m ne»ght [ C],
u 2 = wino speed ai 2 m height [m s' ],
e & = saturation vapour pressure [kPa],
e  = actual vapour pressure [kPa] = e, RH^.
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and
6^' e» = saturation vapour pressure deficit (kPa|. i          - slope vapour pressure curve [kPa ‘C‘’|. 7               = psychrometric constant (kPa C’’|
RH = relative humidity divided by WO
R.’      = Rra " RrJ
RPi = 0 7T Rs
Rs      = (025 + 0 50 n/M)R,
RrJ         = rT/(0 34-0 14 e.0 5)^ 135 Rs’Ro-0 R„ =(0 75*2 ( Altitude X1 D0000| R»
(2 2)
(2.3)
(2 4)
(2 5)
(2 B)
The calculation procedure consisls ot the following slaps
1 Derivation ol some climatic parameters from i he o aily maximurn (Tm) and minimum (T „) air temperature, altituoe (zj ano mean wind speed (uj).
r
2   Calculation of tne vapour pressure deficit (e,. * e ). The saturation vapour pressure (e,j
A
is derived from T^,, ana T™^ while the actual vapour pressure (e^j can oe derived irom the dewpoint temperature (T^j. from maximum (Rb^j and minimum fRb-^.i relative humidity from the maximum (RH™*,). or Irom mean relative humidity (RH „J.
m
3   Determination of the net radiation (R„j as the difference between the nei shortwave radiation (RnJ and the net longwave radiation (R™). tn the calculation sheet, the effect of ml hesi flux (G> is ignored tor oaily calculations as tne magnitude of the flux in this 
caw is reratively small The net radiation, expressed in MJ m'2 day'1, is converted io
mm/day i equivalent evaporation) in the FaO Penman-Monteilh equation by using D 40B
as tne conversion factor wiLhin me equation
4. ET0 is obtained Oy combining the results of the previous sieps.
The following values were selected from FAG 1990 (Crop Evapolranspiralibn - Guidelines ior computing crap water requirements - FAC Imgation and drainage paper 56)
□ Psychometnc constant (y) for differeni allitudes (z),
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□    Slope of vapour pressure curve i.^) for different temperatures (T).
o  Saturation  vapour  pressure  [(e'(T)l  for  different  temperatures  (T),
c Daly extraterrestrial radiation (R>) for different latitudes.
o Mean maximum possible daylight hours (N) for different latitudes,
□   oT/ uStelan-BoiLzmann Sawj ai different temperatures (T)
The estimated mean daily  and monthly  reference crop evapotranspiration magnitudes  (in mm) from 1991 to 2004. oased on Penman-Monuenn Equation, are presented by Tames 4.3 arm 4 4. respectively anc graphically illustrated by Figure 4 5
The results at the meteorological analysis including the rainfail are provided in the annexlure A Tanle 4.1 Tabic Mwte o* Meiwwogical Observation Slations located in and around the proiec? area
S.No    Station Name
Latitude
North
Longitude
East
Altitude
(m|
Period
n&g,      Um        D’fl     Min.
1 Agaro 07 51 36 36
t700          19SO-20O4
2
Bedeile
08
27
36
20
2005
1967-2004
3
Dedessa
09
33
36
06
1300
1971*2004
4
Demo.
08
04
36
37
i960
1954-2004
5
Ji mm a.
07
40
36
50
1725
1952-2004
Tien? 4.2- Types of Clmatc Data available ai the various Meteorological Observation Stalrons
NO        Siauon name            Yrs        RF       Tm          RH       ws    StJ       1 hr 1 da  Relay
i Dioessa 30 X X X X
2 Bedeie 26 X X X X
¥
3      Dembi
20         X          X
4      Agaro                  21         X          X
5      Jimma                 50         X         X          X        X       X              XXX                   1
Yr$      refer tc rairfal! senes
cu»
1
1
3
3
RF       monthly rainfall
Tm
average Temperature
SO       sunshine duration
1 hr
RH
relative humidity
maximum 1-hour rainfall
W5
wino space
1 day
maximum i .-oay rainfall
Rday
number 01 rain days
2b
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Table 4.3:           Summary of Meteordoflitsi CtvaracterulKS at Project Area
Jan         Feb     March    April      May        June        July         Aug         Sept
Monthly Mean Temperature m oC
Serene 21.9 23.15 25 4 25.05 24.03 22 09 21 32 21.19 21 83
cv       0 048   0.044  0 036   0.065   0071    0 029   0 028   0.031   0.027
Skew    0.071   -0 58   0.067  -3 628   -3.23   0117    0275    0 007     0.93
May 2007
Oct Nov Dec
Mm
Max
19.5
20 44
23 63
16 26
15.89
20.96
19.99
19 88
21.06
24 6
24 9
27 37
27 72
26 19
23 41
22 72
2234
23 2
22 35 22144 19 99 0.036 0 0544 0 066 0.353 -0 118 -0 02 20 19 19.081 16 92 24.25 25.051 22.68
R«nUjfiive Humidity (*/•)
Average  64 77   58.97   56.63   67 97   75.72   61 07   87 46   88.52   86 63      84.55 79 366 72 44 CV       0.099   0 127   0.084   0 073   0 053   0.047   0061    0.048     0.03       0 053 0 0705 0 089
SrCw      ■0 27  ■0?7   -0.37   0474       0 2    -0.87    ■2 92      '2      □ 249           019 0 287 -0 13
Min        51.5     43 2    4509    57 42   65.23    65 8    61.77   72.23   8249       74 24 67.667 55 37
Max        77.3   71 68   64 08   62.17   86.18    90.3     98.1    97 53   95 67      94.73 93 187 85 13
kVino' Speed
082      0.8       1.0      1.06     1 04    0.86     062      0.51       05      0 51     0 48     0 51
Suns/woe Hours 'hrsvoay)
Average   8.155   7.638   7 452   7.28?   7.624   6 061   3 703   4 059   6 164       7.855 8.3245 8.306 CV        0 125  0.166   0.145   0165    0157    0 189   0 243    0.23     0 22       C 139 0.2139 0 104
Skew -047 -0.36 -0.27 -1.12 0.141 -0.36 0.248 -0 42 -0.27 0.138 3 525 0.971 Min 6.05 4 905 4 592 3.304 5 428 3.364 2.277 16 2.622 5 778 01121 5 634 Max 10 9919 9.744 9 44 10 15 8 12 5 445 6.2 9 12 10 08 10 201 11 02
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Table 4.4. Summary of Esllnulted Mean Eld Of Afjo Dedessa Project Area
May 2007
Jin Feb              March April         May      June     July       Aug        Sept      act      Ngw      Dec
Daily: Estimated ETa \mm/day)
Average    3.7     4.11     4.62 4.51          4 33     3 58     2 96     3 11     3.81    4 03   3 79    3 44 CV       0.05 0.06         0.05     0.07     0 06     0.08     0 08     0.08     0.09     0 06    0 12    0.05
Skew    <l 47 -0.77         4)      -0.05    -0.55    -019     0 33    -0 51    -D 18  -0.27  -3 11    0 88
Mir       3.23 336          3.90     344      3 35     2.97     2.58     2.44      2 88     3.5    1.95    3 11
Max      4.03    4.49     5.24     5 13     5.06     4 15      3 46     3 59     4 49    4 4?   4.24    3.96
Wonf/?ly Esfrmaitfd ETo
mm/rnonth
Average     115     115     143      136      134      107     91.8     96 5      114     125    114     107 C\/       0 05 0.00         0 05     0 07   O-QS     0 08     0 08     0 08     0 09    0 06   0 12    0 05
Skew    -0.47 -0.77 -O -0.95
-0.65   -0 19    a.33   -0.51    -0 18   -0 27  -3.11    0 88
Min 100 94 6 124 103 104 09 80 75 7 86 5 W9 58 6 96.4
Max 125 125 162 164 15? 125 107 in 135 139 127 123
Estimated Eto (mm/day)
i form avers-je values of data
1
Average    3.69    4.06     4.66 4lfl            4 2B     3.57     2.95     3 10     3 75    4.00    3 79    344
Estimated" Eto (/nm/monitfy form ivtrage values of data/
Average     114      114     142      134      133      107       92        96       113     124    114     107
Mote? ^oui annua E7<j = 1397 nvr
2S
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May 2007
T»Wt 4,5;     Magnrlude or £ To at gwgfl non .exwnanre ?rQtwUi
My Jav
el
PY&tMJitex Jin Fit)    Mar   April      May    Jun*   July    Av0
S*P<
Oei
Nov
Oat
55      3 72  4 14  4.05   4.56   4.37  3 61  2 99  3.14
3 05
4 06
384
3.40
60      3 75  4 16   4 63  4.60   4.42  365   3 02    3.ta
3 89
409
3.90
3 49
G5     3 77  4.21 4 71   4 64   447   3 66  3.05  3.21
194
4 12
396
3 51
70      3JW  4.25  4 75   4 69   4.52  3 72  3.09  3.24
399
4 15
4 02
3 53
75     3-63  4.29  479    4 74   4.57  3 77  3 12  3 28
4 04
4 19
4.09
3.56
£0      3 06  4.33  4 33   4.00   4.63  3.01  3 16  3 32
4.09
4.23
4 16
3.59
35      3 90  4.36   4 98   466    4 70  3.87  3 21  337
4 16
4 28
4.25
3.63
90      3.95  4.45  4.94   4 95   479   3.93  3.27   3.44
4.24
434
4.35
3 67
95      4.02  4 54  5 03   5 07   4 93  4.04  3 35  3.53
4 36
4 43
4 51
3.74
A*-g     370  471      4.62   451        4.33  3.58  2.96  311
3.31
4.03
379
344
fmm/mouTffy
FWBy Ja n    F«n  Mar   Appill     May   JynaJuly   Aug
Sapt
oct No
r
D-ec Annul!
55       115   116   144     137     136   ioe    93    97 4
116
126
115
107   1405
00      116    117   145    138    137   109   94    98 4
117
127
117
108   1412
65       117   110   145    139      ’30   111   95    99.5
118
128
119
109   1420
70       110    119   147    141     140   112   96     10T
120
129
121
110   1423
75       119    120   148    142     14?   113   97     102
121
130
123
110   1436
B0      120   121   150    144      144    114   98     103
123
13T
125
111   1446
85      121    T23  151     146     146   1 is   99     105
125
133
127
112   1457
90      T22   125  153    148     149   116  101    107
127
135
131
^14   1471
95       125   127   156     152     153  121   104    109
131
13?
135
116   1492
Avg      115    115   143     135     134   107   92    96.5
114
125
H4
107   1397
hu.ifu
Growrtft factor (Xp)
FraUMy Jl-n    Fab  Mar   April      May   Juna July     Aug Sapi   □ci      Nov  free  Arrnp^l w
55     1.01  TOT  1.01    101    1 01 1.01   1.01   1 01 1.01    i-Oi     l 01 1 01   1.005
60      1.01  1 02  1.01    1.02    1 02  1.02   102    1 02 1 02    l 02    1 031 01    1.01
«5     1 02   -.02  1 02   1.03     103  1.03   1 03   1 03 1 03    1.02   T 04 1.02   1 016
70      1.03  T 03   103   1.04    1 04 1.04   1.04   1 04 1 05    1.03   1 06 1 03   1.022
75       l 04   1 04  1 (U    105    1 05 1 05   1.05   too   1 06    1 04   1 08 1 04   1.028
60      1 34   105    i 05   1 06    1 07  1.07    1.07   1 07 1.07    1 05   1 1   104  1.035
85       1.05  1 07  1.06   1 08    1 09  1.00   1 08   1 08 1 09    1.06   1 12 t 05   1.043
«        1 07  1 08  1.07    1 1     T 11   1 1    1 1     1 1  1 11    1.08   1 15 1.07  1 053
95      1 09    t.1     l 09   1 12    1 14  1.13   1.13   1 13 1 14     1 1    1 191 09   1.068
11l1111111111
29
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Figine 41 Meih Monthly T«mpM*tur» at
Arjo Dcdessj* Project Area
Itiy 3007
Figure 4.2: Main Monthly Relative Humidity at Arjo Dedessa Project Area
Figure 4.3: Mean Monthly Wind Speed at Arjo Dideaa Project Area
Figure 4.4. Mean Monthly Sunsnine Hours Arjo Dedess a Project Area
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F<»ure 4.5:
Mean Monthly ETa it Arjo Didnss Project Area
U
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5. RAINFALL ANALYSIS
5x1 Introduction
Miy 2007
The rainfall data attained from Bedele. Dedessa and Jimma stations  were founu to be the mosi rehaole and relevant for use m me analysis  of ramlall for the Arp Dedessa irrigation project Beoele is  geographically  me closest station to me command area. Dedessa station ano Ine c Dmmand a res are located a 11 he same elevation ( l e. o otn 1 330 m a si) Jimma station (whicn is  Class  I) has  the longest record of all the stations  within the neighbourhood qI the command area so as  to tie index  station m extrapolating 3nd interpolating missing and shortage ol rainfall data relevant 10 the Arjo Dedessa catchment and command area
The ramlall in me Arjo Diflessa Catchment as welt as in its surrounding i$ uni-modal type Mosi ol  ihe  rainfall  is  concentrated  in  the  May  to  September  covering  with  virtual  drought  from November  tnrbugn  March  The  five  wettesl  months  cover  63  percent  of  the  total  annual  ramfall The  dry  season,  being  from  November  to  February  (four  months)  has  a  total  rainfall  of  about 7% ol ihe mean annual rainfall
The mean monthly rainfall for stations m the project area is given in Tabic S 1 and their pattern is  graphically  illusiratea m Figure 5 3 The length of rainfall data collected from Jimma is relatively  more retiaoie compared to the oata set collected from other stations  because of its long record length and shorter time interval of ooservation. Didessa ana Bedeie statrons  also provide more relevant rainfall data IhaT cap be adopted for the command area since Bedele is dose to Ihe projeci area and Diaessa station is located within the same dimatic zone as that ol the project area
5.2 Rainfall Internal and External Consistency
Though a good oata base has  oeen established lor rainfall. considering the data of the ihree stations  namely  Dedessa, Jimma ana Sedeie, it is  customary  ir. Hyoro-meteoroiogical studies to firm up the consistency wilh statistical analysis.
The trend in the annual rainfall pattern is  a relevant aspect with respeci to me behavior of the rainfall and to compare sucn Dehavior wilh those ol other relevant stations involved in the study with a view 1o firm up external consistency. Accordingly, a 3 year moving average anafysis
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was taxen up for each of the 3 stations The results are shown in the figures 5 1 ( a|. (b„■ arg .
These show similar trends
Similarly  an analysis  wiUi respect IO the cross  correlation structure among the 3 Matrons  was earned oui The cross correlation main* depots the fol owing status 4 Table 5.2} al annual tune resolution level, wmeh is not abnormal
Then the single mass curve analysis was taken up for each Bf these 3 slatons (Figures 6 2
(a), (b) and (c)
These also do nor indicate any abnormality to reject this data set
As such, these ramfali dais were used m Hs different forms rcr various speeffums of me
analysis
53 Estimation of Rainfall Reliability Level
Using ine rainfall ana irrigation waler available for the command area requires  tne magnitude and reliability  level of rainfall corresponding Ic  various  rainfall time mlervals. Annual, monthly and half monthly intervals are chosen durations for the Arjo-Dedessa irrigation prgjeci
Ramfati reliability  level and magnitude can De analyzed by  making use of theoretical distributions  in this  study  Ine Extreme yaiue Type III (minimum) distribution was  utilized The dislnbulian is  aiso known as  (he Weibull distribution or aS GumbEi S Limited distnbution of ltie Smallest Value Naturally  rainfalls  are ocuna by  zero or olher higher values  on ihe itfi The W«buB (c* EV3j distnbution can be expressed as
(5.1)
when
Xp =E*(D-F>i-lri(1-p)rJl
Xp = magmtuae ol rainfall corresponding to probability level of p
The  moment  estimates  of  Ihe  parameters  E  (the  lower  limit),  U  ana  a  (te.,  E,  and  A)  «n  pe obtained from the following equation
U = Xm * Cv.Xm Y(a)
E = \j - Cv.Xm.Z(aj
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where
Xm = mean value,
Cv = coefficient of ^nation = starward devianan di video by the mean
Y(a) = {2-Csy6
Z(a) = [8+(3-Cs)>9
and
A = 3/(1 +Cs)
Cs - snew coetticieni calculated from data
The estimated moninly ano half-monthly parameters of Weibull Distribution are given m Tabe
5 3 arid 5 5. respectively
The  following  algorithm  were  used  in  the  derivation  ol  annual,  monlhly.  and  half-month  55  to  95 percent reliability levels.
1.  Averages, standard deviations, standard Deviation, skew coefficient of annual, monthly 
ano half-monthly averages were calculated
2.  Weibulf Distribution parameters (namely Id. E and A) corresponding io annual, monthly 
ano naif-monthly rainfalls were calculated from the statistics
3 Magnitudes of rainfalls corresponding to 55 to 95 percent reliability levels were
estimated
The results so obtained are given in Tapies 5 4 and 5.6 for monthly and half-monthly time intervals, respectively
The   naff   monthly   ramtafl   magnitudes   as   a   percentage   or   mean,   corresponding   io   various reliability levers are shown in Table 5 7
5.4 Estimation of Maximum Rainfall Frequencies
For  imemal  drams  ano  smaller  control  works,  the  need  for  various  return  period  rainfall  ano with different durations were 1ound tc be necessary In general, maximum rainfall magnitudes
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Hay 2t»r
of  intensity  corresponding  to  various  relum  periods  [or  probability  levels)  can  tut  est-matec  by applying ‘he lollowing form
It = Im [1+ CV.K(TH
(54>
where
It  =  rainiari  intensity  corresponding  io  return  per-od  at  T  years  (mmj, lm = rnean of annual maximum intensity of ramfail (mm'hr).
CV = coefficient of variation of annual intensity of rainfall KfT) = frequency factor
For Extreme Value Type i (ocGumoef) Distrrbutioc,
K(T) = *0 779 (0.577 + ln.ln[T/{(T -1}])
The maximum annual 24hr rainfall service is given in Tattle 5.8.
(5.5)
The results of lhe maximum 24-hr and 1’hr rainfall frequencies are presented in Table 5 9 The 1-nr ramlall intensities were estimated by 1he formula derived for Ethiopia expressed as
= 1^40.523 + O.lSln D;
(3,6)
where
l P - maximum ramlall intensity correspond mg to curation D (mm/hr),
in - natural logarithm
D = duration of lh (hr),
In = maximum rainfall intensity corresponding to duration 24 hours (mm/hrl
.  tie  amfail  rnagnrtuoes  for  higher  durations,  2  aays  &  3  oays  have  also  been  analysed using lhe EVI frequency distribution, The results for vanous return periods are shown m Table 5 10
Mora  details  ol  me  analysis  are  available  ir  me  annexure  A  "Results  obtained  from meleorologrcai Analysis'
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The annual rainfall available at differenl years are given below
suy SM?
hear year
=
1453  mm
75 % year
=
114S mm
80 % year
=
1090  mm
95 % year
■
653 mm
Table 5.1: Mean Monlbty Rainfall
Dticripttafi
Jan
Fe&
March A
pril May
June
July
Aufl
Sep
0.1      Nov Dec      Tfllal
□idessa
3
6
26
49    158
274
312
277
209
104    28      8       1454
Oedele
18
23
65
105   239
291
310
303
302
156   41     12      1864
Dembi
25
44
101
128   223
303
307
367
290
145    52     29     2013
Agaro
24
36
SB
93    149
232
234
231
174
127    54     30     1471
Jimma
33
49
88
133   172
219
208
210
182
103    68     36      1502
Table 5.2: Cross Correlation Matrix of Annual Rainfall
—--------------------——r-—
Dedessa
Jimma
B edele
Dedes&a
1
0)1
0 24
Jimma
1
0 48
Bedeie
1
Table 5.3: Parameter Estimate* of Weibuil D istribution
Jin Feb Mir April May June July Aug Sept Oct Nov Dec Annual
y(a) 0 5 06 06 04 0.5 05 08 04 04 05 11 08 0.4 i(a| 02 0.2 02 0.3 0.2 0.3 0 1 0.3 03 0.2 -01 0 1 0-3
□  24     2 1 22         3.6     2.4     2.9     1.3     37      34      24 09 13                3,2
E    183   21 9 61 2    81.5 201.1 267 3 252 9 257 7 245.0 1 31 0 30 0 13.9         1541
■12.9-15 0-17 4  -55.3   -9 6      73   154 l   35 9 60 9 -29 9 3 8 -4 4               575
D - Xm *Cv'Xm -/fa, E = U - Cv*Xnj-jfa; X = E + n>E; Y-frif?- VT)*f f/ej
•6
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Table 5* Monthly Rainfall* Corresponding to Difffirflhl RtliabUity teve Is Reliability
LeveiJ an Feb Mar April May June July Aug Sep! Oct Now Doc Annuat
(%)
55
10 B 12.2 40 9 58 1
150
213    219    221    212   91 65 18.6 7.58
1353
6C
8 84 9 79 35 8 51.7
13?
198    211    210    203   81 66 16.36 12
1304
65
6 92 7.4 30 8 45.3
124
184    204    200    194   71 76 14 24 74
1253
70
5 5 03 25.8 38 6
ill
169    197    190    184   61 82 122343
1202
75
3 04263207 31.5
97 9
154     190    178    174  51 68 10.42 16
1148
80
0 990 16155 23 8
84 2
138     183    166    164   41 13883092
1090
85
0      0 9 97 15.2
69 4
120    177    152    152  29 86 7 36 0
1025
90
0      0 3 87 4 84
529
997    170    135    138   1729602 0
951
95
0000
32 7
73.7    163    113    119   1 974 4 82 0
853
Avg 15.31 SA 53.6 69.5 180 8 2*3-0 Z45-9 238.3 229 6115.531.412.7 1453 Table 5.5:         Parameter Estimates of Hal ('Monthly Rainfall
JWoofh Parameters of Weibuii distribution
1fa         XW                    U
— - - H
1.1
0.8
0.1
1.5
8.6
-43
1.2
0.9
0.0
1.1
8.1
-2-6
2.1
12
-0.1
0.9
77
-4{J
2.2
08
01
1.5
11 0
-6 1
J.1
0.6
0.2
16
24 3
-14,8
32
06
0.2
20
37.7
-11 7
4.1
06
02
19
26 5
■135
4.2
OS
G.2
24
54 5
25 6
5.1
06
02
19
87.6
-11 2
52
06
0.2
20
112.7
75
6.1
05
0.3
2.6
134.3
•19 8
62
05
02
2.5
135
10 4
7.1
07
0.2
17
130
40 7
7.2
09
0.1
1.2
126
809
8.1
0.5
03
2.9
128
8.2
5.2
05
03
2.7
131
37 4
91
0.6
0.2
22
128
49 2
9.2
0.4
0.3
3.6
1196
•6.2
10 1
0.6
0.2
24
83 5
-17 7
10.2
0.7
01
l6
47 1
-11 7
11.1
0.8
01
1.3
21 5
-3 2
11.2
12
-01
0-9
10 3
30
12.1
11
0.0
10
58
-3 3
12.2
1.3
’O.1
0.9
5.1
-3 7
Annual
0.4
0.3
3.2
1541.2
575.1
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labia 5.6: Half-Monthly Rainfill Magnitudes at Different Reliability Level*
■ay 2007
Month
Avg
Rettebtfity level
___
55%      60%     65%     70%     75%    80%    05%    90%      95%
7 5      4.41      3 43     2.49     1 56    0 69       0         0         0          0
1,1            7.6         4        3 09     2 24     1 45     07        0         0         0          0
1.2            88        2 46      1.38     0.41       0         0         0         0         0          0
2.1            96       5 52      4.22      2.98     1 77      06        0         0         0          0
2.2           20.6      13.2       10.5     7.87     5 25    2 64       0         0         0          0
3.1           33.0      24 4     21 1       179     14 6    11 4    8.08    4.61    0 62        o 3.2          22.7      15.2      124      9 67     699     4.32    1.61       0         0          0
4.1           46.7      34.9       30       251      20 1    15.1    9 86    4 25       0          0
4.2           76.2      59 6     52.8     46.1     39.5      33      263     19.4    11.9     3.32
5-1          102 6    34 27    77.2     70 28   63 42  56 51  4943   42 02  33 96    24 5
3J          119.6     101      92 5      83 9     751     65 9    56.3    45 7     33.6     18 3
6.1          123.2     106       982      90,7     63.2    75 5    67.4    58.7    48.9     36 8 6.2           122      1039    97 46    9126    85 17  79.13  7304   66.78  60.14    52.6 71          123.9      110       106       102      99 2       96       93      90 1     87.2     84.2 7.2          116.5      102      95 7      889       82      74.9    67.3      59      49.3      37 a.1          121 8     110       104        99      93.6    67,9      82      75.6    68.2     59.1 6.2           120       108       103      97 6     92 7    87.6    62 4     76.9     708     63.5 91          108 5     97 9      921      86.1       80      73.4    66.3     584      489     36 1 9.2           73 7      58.7      52 5      462       40      33.6      27       199      12      2 37 10.1          41 8       292      24.9      208      168     128     877     4.68    0.38       0
10.2
11 1
11.2
19.7      13 l      11.1       9.3      7.54    5.83    4 16      2 5     0 82       0
11 8      4.15       2 92      1.83     0.85       0          0         0         0          0
6.1       2.02      1.21      0 46        0           0          0         0         0          0
12.1 66 0 83 0 0 0 0 0 0 0 0
12 2
1453
1353     7304     1253    1202     1148    1090     1025    950.5  853
Annual
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Taw» 5 7 Marf-Monlhly Rainfill Magnitudes m Percent nt Iht Mean Corresponding Io Different Reliability LiJmels
Month Avg
—
Reliability level
55%      W%       65%      70%    75%    80%     85%    90%     951.
1.1
100        59        46         33        21        9         0         0         0          0
1J
100
51
40
29
IS
9
0
0
0
0
2.1
IDO
25
16
5
u
0
0
0
0
0
22
100
58
44
31
1&
6
0
0
0
0
31
100
64
51
38
25
13
0
0
0
0
32
100
74
64
54
44
35
24
14
2
0
4,1
100
67
55
43
31
19
7
0
0
0
4.2
100
75
54
54
43
32
21
9
0
0
5.1
100
76
68
59
51
42
34
25
15
4
5.2
too
52
75
68
62
55
48
41
33
24
0.1
100
64
77
70
63
55
47
36
28
IS
6-2
100
86
80
74
68
61
55
46
40
30
7.1
100
85
60
75
70
65
60
55
49
43
7-2
100
89
66
82
80
77
75
73
70
68
51
100
&a
82
76
70
64
58
51
42
32
6.2
100
90
85
61
77
72
67
62
56
49
3.1
100
90
86
61
7?
73
69
64
59
53
9.2
100
90
85
79
74
68
61
54
45
33
10.1
100
80
71
63
54
46
37
27
16
3
10.2
100
70
&D
50
40
31
21
11
1
0
11.1
100
66
56
47
38
30
21
13
4
0
11.2
100
35
2$
16
7
0
0
0
0
0
12.1
100
33
20
£
0
0
0
0
0
0
12.2
100
13
0
0
0
0
0
0
0
0
Annual
100
93
90
86
83
79
75
71
65
59
Vj
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Me te o ro I a glc a I a od Hyd ru logical As pec ts Tabla 5.8          Max t mum Annual 24-hr Rainfall
____________ Hjy__gw£
Vear    (rnrn/dj
19B7      47 1
Vear    (mm/d)               YMf        (mmsd) 1980       45.6                 1993       50 1
196S      47 0               1981
1994        57 8
1969      640                1983       50,0                 1995        61 0
1970      57 0               1984       51 7                 ■■996     60 1
1971      70.0               1985      62 2                 1997       104 5 1
1972      45.2               1986      64 6                 1998        63.5
1973      35 9               1987       584                  1999        63 0
1974       Si 8                1988       53 2                2000        47 9
1975      36 4               1989      46.8                 2001        69 0
1976      47 1                1990      49 5                 2002         570
1978
1991       87 8                2003
1979      45 0               1992      51 6                 2004        39.1
Average 54.14
CV           0.306
Ske^r        2E-04
Table 5.9 Maximum Rainfall Magnitudes and Frequencies.
Return           Frequency                Rainfall Magnitude [rnm>
Pe«so (T)
Factor (Kj
24-hr
1-hr
s
-0.16
51
27
5
0.72
66
35
10
l 30
76
40
15
1 64
82
43
20
1 86
85
44
25
2 04
88
46
30
2 20
91
48
40
2 40
94
49
50
2 61
SB
51
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TAfita 5L10 Maximum Ramfalt Mag n irudv* for Hi?h«r Duration!
Majr 2007
Ftalurn
Way Awg. of Mu.
Penod,T
(Yiarsj
EVI Factor
K(T)
Max 2day
Rainfall immi
Max. 3day
Rainfall (mm)
3 day Rainfall
|mmj
2
-0.164
70S
92 7
29.6
5
0719
94.6
112 7
37 6
10
1.304
106 3
125 9
43.2
15
1 634
1129
133.4
46.2
20
1 865
1175
136 6
46.3
25
2 043
121 0
142.6
49 9
50
2591
132 0
155 a
549
L— -
3J»
142 0
167 3
59 9
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i" i-
„ .200
9000 1
.py,
rMKl iO65 19*0 W5 W ’’Wi 1^C'
Year
20W
Figure 5.1(1 ) Trend Analysis of Annual Ri infall at Jimrrtl Slaton
M
ri ri ri
i i
I
i
Figure 5 1(b] Trend An*ly*j» of Annual Rainfall «r 0rdell» Slation
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Figure 5.1(c) Trend Analysis qt Annual Rainfall at DeuEssa Station
Fiflura 5 24a) Single Meat Curve cl Jimma Ramfall
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Figure 5.2(b) Single Mass Curvt Q< Bedellc Rainfall
>BTO >575 ’WO TMS i99C-
1W5 2COC 2005
tears
Figure 5.2(c):           Singie Mass Curvv af Dedassi Riinfall
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6.    MONTHLY STREAMFLOW ANALYSIS
6.1  Hydrological Observation Stations
Hyorgmeinc  stations  on me Odessa river and the neighbouring nvers  within the Abbey  basin lhe Omo-Ghibe basin have also been identified The hydrological daia are obiamed from ir.c Hydrology Department of the Ministry of Waler Resources fMoWR]
There   are   two   hydrological   observation   stations   located   on   the   Dedessa   Rive*   These   are Dedessa  near  Ago  town  (Station  No  114001j  and  Dedessa  near  Dembi  town  (Station  No 114014).  Station  114001  with  catchmeni  area  of  9981  Km3   is  located  about  44  km  downstream of  the  proposed  dam  sue  ano  nas  become  operational  since  i960  where  as  Sial  on  114014 with a catchment area of 1806 km3  is located about 137 km upsiream o1 the proposed cam site and has become operations, since 1985
Besides  the two hydrological observation stations  located on the main Dedessa over several hydrological observation stations  are located on its  tributanes. In addition. nydro»ogicai Observation stations on the neighboring Daoana n ear A oasma ( Station N o 114Q05) < Giige; Ghibe near Assencabo (Station No Q91008j, ano Gojeb near Shebe (Station No C9iDi2i have been 1ound la be relevant to the study
The  list  of  hyaroiogical  ooservation  stations  for  which  data  have  been  collected  along  with other details like their location and catchment area is available m Table 6.1
6.2   Extension of records
Streamflow gauging stations have peen installed on the Dedessa River near Arjo town [Station 1-4-001 j since i960 ano near Demth town (Station 14Q14) since 1985 Before the streamflow
analysis, data obtained 'rom Station 114001 (Didessa near Arjo) ana Slation 114D14 (Didessa near Demoi) were checked for temporal and spatial homogeneity The investigation pl nomogeneiiy was concentrated mainly on the outliers of the monthly data senes o1 the recoro Extremely high or low values of each senes, that nas occurred at time T(i) m each month M[il.
was checked agamst the records of the mooih M(i-1) and
that has occurred at the same
year T() so as to judge, wneiher the relation i$ still more or less the same as that of the atner years. Whenever the outliers were rejected by this lest, agam another test was performed wth
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other  Gala  senes  ot  Station  114005  (Dabana  near  Abastrta),  Slaton  91006  {Giigei  Gnibe  near Assendabo} and Station 9i0i2 {Gojeb near Shebe) for the same penod TO)
The data were checked Tor ils  consistency  before use for different analysis, The investigation will concentrated mamfy  on the outliers  of the monthly  and daily  data senes. Extremely  high or low values  that occurred at a given lime were checked against records  of other near by  nve*s (such as  Dabana) If the outliers  are found to be inconsistent with others  then they  were replaced by  new values  tnat were generated regionally  from dais  set obtained irgm other stations.
6.3   Synthetic flows
In this  section. analysis  of monthly  flows  is  made with the intension of improving information requires  fro reservoir storage design. Reservoir siorage design on the basis  of generaiec (synthetic^ flows is preassumec
It was  realized that the specific  sequence of historic  events  was  a random pecyr-ence that would certainly  never occur again m the same way  To get some idea about other possible sequence wifhir the population, m order to improve reservoir design, generating a long streamflow senes  is  a highly  acceptea procedure by  hydrpiogisis  However, it has  oeen oointed out synthetic  (generated} flows  do not improve poor records  Dut merely  improve the quality  oi oesigns mane with whalever records are available.
Mean monthly discharges, coefficient of variation of monthly flows Summary of regional
monthly flow characteristics statistics ot monthly flows at Arjo Dedessa Dam Site are shown by 
aoles 6 2 6 3 6 4. 6.5 respectively The monthly stream flows at different reliability level are
available in Tame 6 6
In order to maintain the historical skewness  m the generated flows  the Aieibull distnbution has been fitted io me standardized residuals  or the monthly  senes  Accordingly  the estimated parameters  or the random generator that were usm in the Thomas-Fiemng model are presentee in Taoie 6 7.
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Mone   details   on   various   results   are   shown   ir   the   annexure   B   'Results   obtained   Iron hydrological analysis."
The (lows at the dam site at annual level are as beiow
Mearyear 75 % year 80 % year 90 % year 95 % year
2328 Mm! 1729 Mm1 1625 ' 1384 ■ 1224 ‘
Tish 6.1              Aviilability of Slr»*mfldw Data in the Region
Si hC
Si
he
Station name and Location             Let
North
Area         Flow
IMm’ryrj
R li noli
|mm)
1
114001
Dedessa near Arjo
8 41
36 25
9981
3826
383
2
114014
Upper Deaessa near Demoi
6 02
36.28
1806
1221
676
3
114005
Daoana near Aoasma
902
36.03
2281
1870
820
Gilgei Gibhe near
4
091008
AsenOabo
7 45
37 11
2966
1211
408
5
091012
Gpjeb near Shet>e
7.25
36.23
3494
1803
516
Table 6.2:          Mean Monthly Flow (in Mm’fseci
Si. No
Jan Fab Marc
h April May June July
A
ug
Sep
Oct
h
ov
D
ec
Annual
114001
114014
114005
41 9 26 7
26     33 5 63 6 216
646
1050
902
526
148
80.7
12.2 9.5
11.5  169       36 4 112.4
228 9
306.9
262.8
154
3
48.
4
20.5
35.4 19.8
16.3  17 Q      351 107 0
258 8
433.0
473 4
313.
9
103.
3
56 6
091008
901012
14 7 13 5
12.2  15.9      33 9 100.3
2l6 5
319.2
277.8
13
7
60.
2
24 5
31 3 22 1
22 1  31 3      86.4 169 2
323 7
415 6
400 9
202.
3
82.
8
465
3761
1221
1870
1211
1803
I
Table 6.3:         Coefficient of Variation of Monthly Discharges
SL ho Jan Fab Much April May
V40C1 0.51 0 57      0 66     068      0 62 114014 0.47 0.5        0.48     0.56     069 114005 0 28 0 42     0.33     0.43     0.60 091008 0 46 0 58      0 78     0.45     0 43
901012 079 0 36 L. J _
0.34      043     D63   0 44   0.31     0 26     034      0 49     054     0 70
June July Aug Sep Oct hov Dec
--------- 1 0 45   D35      0.3      0 33      0.67     0 62     0.59 0 53   0.29     0 27     0 30     0 56    0.81     0 53 0 47   0.20     0 16     0.25     0 44     0 30     0 34 0.36   0.22     0,28     0.27      061     0.79    0 58
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Table £ A Sum miry of Rug oral monthly flow G haritle rlstics
May £00?
Param   Year   Jan j Feb M»r Apfil May cv        194 i  0 51    0.68 0 595 0.5B Q61
Siifrbv    151    1 BO 1 66 i 503 0 B6 1 fiS R        194    0 3fi 0 57 0 527 045 049
fi        194    0 34     0 76 0 46 044 052
June July Au-i Sep Oct Nov Dec
0 47 'a.33 0.29 0 32 0 58 0 66 Ij 57
1 05 a 12 0.7 0.59 0.94 2 1.9 2 02
0 66 0 53 0.56 0.51 0.5 0.56 0 51
0.51 0 37 0.5 0 56 091 0.64 0 44
Table 6 5           Tibbe Statistics of monthly flows al. AfJo Dedessa dam srte
i in hliilioii m*i
Pi rim        Jan F*U Mar A;>r May__________ Jun Jul Aug Sep Oct
H ™ -=—
_____ ____
Dec        Annuli
3? dev
Skew
Max
*fln
25.00l6.97   17fifi24.2l   48.26157.2   4i2.fi   633   540-6   299   8   105   9   46.11
12 81 9 72 11.82 16 41 29.69 70 67 143.2 189 6 179.2 160 5 09 35 27 17
0 626 0.743 1 067 0.937 1 629 0-891 0 126 0.037 0.254 0 585 1 666 0 96
59.09 40 3 46.01 68.61 144 9 3fifi 1 751 5 1043 905 1 661 4Q0 fi 120 1
2328
619 3
0.498
4089
6.806 3 462 1 775 4 586 9.fifi5 3fi.7l 143 8 296 2 195 6 49 32 12 69 4 BOB    1124
R
0 446 0 828 0 889 0-59 0.296 0.765 0.45 0.529 0 436 0 431 0 796 0.704
fl
0.2l 0.62fi 1.081 0.819 D.54 1.6680.9120701 0 412 0 434 0.394 0.214
Title 6.&; Reliability Level Vl Monthly Streamflows al Qarti Site
[7n MmJ
Reliability
Level         Jan Feb Mar    Apr May    Jun     ■All     -Aug    Sep     Oct      Nov  Dec
-------------- 1
4
17. i
55         20-2 12 7 14 1 19 3 3? 5 T3i 4 371 1 56B 8 400.4 239  75.$ 35.5 2114
60             19.0 11 6 13 O 17 4 34 7 122.3 34fi.4 $4?   8 454 6 216 6 69.0 33 2   2019 65                 17.9 10.6 12 D 15.632.0 H3 5325.3 518  7 429 0 1 94 7 64 631.1    1924 70         16 9   9 6 H 0 13.6 29 5 104.9 301 3 490 S 403 3 173.1 S9.fi 29.2 1828
75 16 0
BO 15 0
0.7 10 1 11 927 1 96.4 276.Q 464 5 376.9 151.6 55 0 27 4 1729
7 0 9.2 10 124 9 87 8 240 5 437 3 349 4 129 7 5Q.9 25 7 1625
85           14.2   59     0.3     8 1 226 78.92l7.fi4Q&.3 3l9 $ 107 047.024 1               1512
90          133   Bl     7 4    6 0 20.4 69 5161,2 376 4 286 7 82 5 43.5 22.6             1384
95         12.5   5 2    6.5     3.518.2 59 0132.1 337.9 246 0 54440221 2                 1224 L_A¥fl_______ ______________
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Tabla 6.7 Characteristics of Random Numbers Used for Flow Generation
Ma? 2007
Param
Jan  Fib    Mar         Apr
Jun       Jul        Aug         Seft       Ctal          WOV        Dec
Average 0 00
CV 0.51
Skew 1 80
0O0
0 00      000     0 00     0 00     0 00     o.oo      000     0 00     0.00     0 00
060    0 60     0 58    0 51     0 47     0.33     0 29     0 32     0 58      066     0 57
1 66   1.50      086     1 65     1 05     0.12     0 70
0 59     0 94     2.19     2 02
088
1/a        0 933       7 0 834 0 620 0 883 0 683 0 373 0 567 0 530 0 647 1 063 1 007 0.05
y|aj 0 033              7 0 083 0 190 0 058 0 158 0 313 0.217 0.235 0 177-0 032-0 003
1.15
2(a)       1 081      6 1 262 1 978 1 162 1 713 3 543 2 241 2 444 1 860 0 948 0 993
Weibui Distribution 
X=E+
U - Xm +Cv'Xm"y(a)
_ E_= U^Cv'Xm'z'a}
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7 ESTIMATION OF FLOODS FOR UNGAUGED CATCHMENTS
in the hydrologic analysis for dams, weirs. bodges and drainage structures it must be
May 2007
recognized that Ibere are many vanable factors mat affect floods Some of the factors that
need be recognized and considered on an individual site by site basis are
o rainfall amount and storm distribution.
o catchment area size, shape and orientation
□ ground cover;
o type of soil.
o stopes of terrain and stream(S),
o antecedent moisture condition
o storage potential (overbank, ponds wetlands reservoirs, channel, etc ), and
o catchment area
tn g eneral t nree t ypes o f e stimation I foods magnitudes (namely i he R ationai M etbod, S CS method and Transferring Gauged Daia method) can be applied for the project area.
7.1 Rational Method
The  Rational  Method  can  be  applied  to  small  catchments  if  they  do  not  exceed  12.8  km‘  (or  5
square mile) at the most (Gray  1971) The consequences  of applying the Rational Method to larger catchments  is  to produce an over estimate of discharge ano a conservative design The method is  nevertheless  trequently  used in standard or modified form for much larger catchments. This  is  because of its  relatively  simplicity  The vast majority  of catchments producing flooos  imposed on tne command drainage system lie within the validity  o1 the Rational Method and it has  been used as  the principal methoa of estimating design discharges of dykes, culverts, drainage channels etc
The Rational Methoa is oasea on the following formula
Qm = 0.2778 C.IAFr
where
Qm = peak flow corresponding to return period of T years in m^sec C = a runoff coefficient expressing the ratio of rale ol runoff to rate of rainfall
(see Annex C1 ano C2).
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i = average maximjm intensity of rainfall in mm/hr. far a dural.on equal to the lime al concentration,
A = drainage area rn knr.
Fr = is the areal reduction factor (this factors improves the catchment limitations 
imposed on tne use ol rational melhod}.
Coefficient of runoff C lor lhe formula are given by many soil and water conservation texts (see Annex  C.lj. information on rainfall intensity  I in a time or concentration (time period required lor flow io reacn itie oullel from lhe most remote point in ine catchment} is  required and can he estimated by  me following formula The selection of the correct value of C ' presents  some difficulty  It represents  a parameter lhal can influence runoff including, soils  type, antecedent soil conditions, “and use, vegetation and seasonal growth Therefore, the value of C can vary from one moment to another according to changes especially soil moisture conditions
Tc = (1/30B0)xL*lSa
(Kirpich equabon)
(7 2)
where
Tc = lime pf concentration (in hours).
L = maximum length of main stream (in meters).
h = elevation difference of upper and outlet of catchment, (In meters).
The area reduction factor (Fr) is  introduced to account for the spahal variability  of po«nt rainfall over lhe catchment This  is  noi sigmlicant for small catchments  Out becomes  so as  catchment size increases. The relationship adopted for 'Fr is  based on that developed for the East African condition (Fidd&s, 1997) The relationship can oe expressed as.
where
Fr = l -0 02 djbA’m
D = duration in hours,
A = drainage area in xm .
(7 3)
2
This  equation  applies  for  storms  of  up  to  B  hours  duration.  For  longer  durations  on  large catchments the value of D can be taken as 8 for use in the above formula
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rological Aspects
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7.2    SCS Method
A  relationship  peiween
accumulated  rainf
all  and  ac
cu
mulated
ru
noff  was  derived  oy  SCS  (Soil
Conservation  Service;.
The  SCS  runoff
equation
is 
therefo
re
a  method  of  estimating  direct
runoff from 24-hour or 1-day storm rainfall. The equation t$.
Q = (P - La) flP-la) + S
?
(7 4j
where
Q - accumulated direct runoff mm
P = accumulated rainfall \potennai maximum runoff), mm
la = initial abstraction including surface storage, inception, ana infiltration prior to
runoff, mm
S = potential maximum retention, mm
The relationship Between ta ano S was  developed from expenmeniai catchment area data H removes  the necessity  for estimating ia ror common usage. The empirical relationship used m the SCS runoff equation is
la = 0.2xS
(7.5)
Substituting 0.2xS for la »rt equalion 7 4 me SCS rainfall-runoff equation becomes
Q = (P-0.2S) f(F*0.8S)
s
{7 6)
S is reiated to soil and cover conditions of the catchment area through CN CN has a range ot 0 to 100 (can oe obtamiM from Annex C3 and ERA 2002;, and S is reiated to CN by
S = 254x[(lQQfCN)-*]
(7 7)
Conversion 1 rpm a vetage a nteceaeni moisture conditions to wef conditions can be d one by multiplying the average CN values by Cf [where Cf = (CN/lOO) '3<j
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ay
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7.3     Tran
sferri
ng Gauged Data
Gaugeq  qaia
may 
be  Iransferred  to  an  ungaugco
site  o'
inte
rest
provided  such  dat
a
are  nearby 
(j   e   wilhjn
the   s
ame   hypnniDgic   region,   and
there
are
no
major   tributaries 
or
diversions 
between the gage ano tne site of interest? These procedures  make use of tne constants obtained in developing the regression equations  These procedures  are adopted from the work, of Aamasu 0989/ as fallows.
[7 Bf
where
Ou Qg^AufAgj11 rD
Qu = mean annual daily maximum flow ai ungaugea site
Og = mean annual daily maximum flow ai nearly gauged sire {m /sj,
a
Au =■ ungauged sile catchment area (km ).
2
Ag = gauged sue catchment area (km ),
2
The  estimate  daily  (or  the  24-hr)  annual  maximum  Hoot  could  be  converteq  into  a  momentary peak as,
Qp = Cf. Ol
(7.9)
Here, Cf is factor estimated as Cf - 1 * O.SfTc (where, Tc is lime of concentration).
7.4   Estimation of Weighted Average
In general, the Rational methoa SCS method ano Transferring Gauged Daia are recommended 1<x  rerahve^y  small, medium ano large catchments  respectively  However, ii is very  important io esiaotish a smooth pattern qt transition from small to medium and from medium io large catchments.
Accordingly (he recommended weighted average estimate of peak flood can oc given as
Qw = On + W  Q  + Wi.Ch
2?
(7 10)
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where.
Qi Qi and Q  are mean anhuai momentary 
Mi) 2OC7
3
eshrnal&d &y Rai ona- SCS anj
Transferring Gauged Oala method* reipectivtiy
W, W; ana W3 are weighing Tactor? cF mean momentary pea- eshmalK by Ral»na> SCS and Trah$(emng Gaugea Data methods respect, veiy
and
Wi - 12 5r(l2S^Au) Wi = (Au.'Aqf70 Wj =1-(Wi + W )
3
( 7 11) 0 t?i
if 13>
Where Ag and Ay are gauged and ungauged site catchment areas, respectively
7.5    Synder Method of Constructing Synthetic Hydrograph
The Synder memod has been usea extensively to provide a means o< generalmg a syndetic 
ymt hydrograph The i-ol lowing steos are used
Stea 1 Detemvne the lag time. T. ol the unit hydrograph Tne lag time is me time from me centroid Ol the excess raanlgll 1q the 1o the hydrpgrpph oeek Syndgr oerrvpd the Iqlkfwing empirical equation for lag time
Tl = Ci (L Lea)"
(7 44)
where
TL = lag lime (in hrs).
L = length akjng the mam channel h*m cmnei to Oiuiae (in kmi,
lea - length along the main channel from the outlet to th? point opposite th* catehmem area centroia m km. and
Cl = an empincai c&ellicent ranging lrcm 1.36 io 1 66. For Ethiopian condition. Ci can be estimated be. ct □ 4 + O.WfeS'111
S = slope of 1he main stream
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Ste p 2 Determination pf nydrograpn duration The relationship developer Dy Synder for " -■ durgiipn of me excess rainfall. Tr in 4 a function of Inc 1391™ canpuiec above
Tfl - T /5 S
l
(5.15)
This  results  m an initial, value for Tft ot TJ5 5 Hcwwer 3 retatrotiMp nas  bean de-eiope^ to adjusi the computed iag lime for other durations  Thu is  necessary  because the eQualux1 3tJQue results  in inconvenient values  Ol unit hydrograph duration The adjuSlrT4b! relationsnip 1$.
Tlfwfl) T * 0 25(1^ - Tr)
t
(7 18)
where T,; adj h js the adjusted lag time Far the new duration T .
fl H
The unit peak discharge can tie determines Irofn I he (ollowng equation Up ’ (1/2040>{0 B4 - li'PfcfS 08 - Jn Tc)Sl
wfiere.
Up ■ unit peak discharge [m
Tc - time o4 concentration (m hrs),
The peak discharge Qp 15 computed Irom
Op = up A (P - 0 2S]7 /(P+0 88)
and the time from rise Qt the hydrograph (p tno peak, Tp. is COmpured irpm Tp - 0 5 TRh * V(adp
(7 171
(7 1Q1
(5 19>
Finally the nyarograph can tw constructed using T^Tp and Q/Qp values iwesenteg m Table
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fable*  5  1  to  5  3  show  csiinuicd  m^n  flood  J  at  seven  relative  I)  la^t  caicHmcntt  crowng cwnnLand ires irwm ihc left and nghi bank directions
Tabic 5,1 l.ucalEon of Proposed Lroil Drainages and Calchment Chara ctrislir!
Cachm- *nt
Area Scream Max- Eiei
Length
Min.
Elev.
Stream
Slope
C :(for National Method!
CN scs
Method
(km' (km i im ash             im ash
(%)
1     CDR-16     27/5        15.50     2400        13 3f?     0.0725         U 24             71
2     CDR-19       4025    13 50     2360         1339      0 0756         0.24             71
3     CDR-28        3300    17.40     2480         1338       0 0t56         0 23             71
4      CDL-3       20j6O      9 00     17SQ        I34O      0.0489         0.22             71
5     CDL-25     300 00    44 00     2480         1335      0.0260         021              70
6    CD L-28       61 00    27 00     19OC        1335      0 0209         0.21              70
7     CDL-33       70 00    17.50     1990         1330      0 0377         0.22             71
Table 5.2 {'baraclcrisiicE of Flood Hydrographs
COThiffir- rur
Base ct Tc (time
How of cone.
T.
r
Tiiadji
Tp (peak
time)
Tp fatty
Th
(kmf
<m sj                     (hra)
(hrs>
(hrs)        (hrs?
(hn)           ■thfsi
1 CDR'lG 0 935 1 43 J.SO 0.27 632 6.15 b. 76 90 95
2     CDR-19      1387       1 43        133       0.24       5.K0         5 65           6.] 9           89.39
3     CDR-28    1 137      i 43        171        03i        6 81         n.62           7 32          92.43
4       CDE.-3       1.020       ] 45        1.15      0.21       4 63         4 49           4 97          85 88
3 CDL-25 10 34 ] 4B 4 98 0.90 12 62 12.06 14 09 109 87
b COL-28 2-102 1 49 3 72 0.68 9 48 9.06 10 58 100 44
7 CDL-33 2 412 1.46 2.12 0 j9 7.03 6 79 93 09
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Mar 3opz
(ichmenl
Qlh
Rational
Method
QUl
scs 
Method
bin
kdmaiu %
Q*vk
(Weighted
Method              A% era*>e 1
I 1 nil
R u no FT
iknu
(hr}
mm hrn
i II h'km" I
1       CF)R-H>          34 94            18 98            10 35      /9J0
2 CDH-19 5545 30.37 1232 29 74
3        CDR-2B           37.&             21 15            |U "'2              21.02
4          t [>t 3             43 25            23 30            9 93              23.11
5        CDI.-25          127 43           90 45            5" 25              79.28
6        CDL 28           35.ti 3            22.24             It 4?              21.93
7        CDL 33           62 3ft            37 56            18.14             15.94
7J3t
637
?Ji/
JriJ
359
5/3
______ _  53
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8 FLOOD FREQUENCY ANALYSIS
8.1 Introduction
MlJ 2007
In flood frequency  analysis, me objective is  to estimate a flood magnitude corresponding io any required return Denod of occurrence The resulting relationship tjeiwaen magn tude and return penw is  referred as  the Ci-T relationship Return period T, may  be delmeo as  the nme-inlervaf ion the average/ for which a particular flood having magnitude (also known as  qunablej is expected 10 De exceeded
A reliable estimate1 of the entire Q-T  relationship cannot be obtained from small samples  oi at- site data The benefits  of regionalczat»on in flood frequency  analysis  nave been recognized at ieasi since tne work  of Deirympie t1960) Nowadays, the regionalization approach io flood frequency analysis (particularly the moex-tiooa melnodl is becoming more popular
An essentiai prerequisite for the .ndex-flood method i$ the stanoardization erf t ne flood dala from sites  wilh different flood magnitudes. The most common practice, used also m ltns  siudy is to standardize data by division by an estimate of the at-sne mean, thus
Xj = OifQm
(0 U
Where  Xi  is   the  uh  standardized  flow  Qi  is  the  i"  annual  maximum  flow  Qm  is  me  average value of at-srte annual maximum flow senes.
Then the quantile QT is estimaieo as
Q- =
Qm X-r
Thus, the mean annual flood ts lhe inoex-flood The parameters of the distributor! or X are obtained from the combined set of regional dala
In  this  study  iwo  distnbutions  have  been  jsed  for  flood  frequency  analysis.  These  distributions are.
(3j Generalized Extreme value (GEV) distribution (Jenkinson I969j
(bj uog-Logistic (LcG) distribution (Ahmed et al,, 19&8)
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Meteorological and Hydrological Aspects
8.2 Estimation of Probability Weighted Moments
KlJ 2007
Probability  weighted  moments  (PWM)  are  useful  for  estimating  the  parameters  of  distributions whose inverse forms tan expridlly be defined such as GEV and LLG (Greenwood el Al
1979:  and  nosning,  1986).  Accordingly,  p  rofcabilily  w  eighted  moments  (PWMs)  for  unbiased sample estimates can be calculated as.
N
m
lDt = . lWX,.(l-F.f i=1
|8-3)
where
Xi = flocc navmg ranxeo order ol i
F = (i - 0.35 j/N = plotting position of the flh ranked flood
n = record length
The regionally averaged prooabdity weighted moments were computed as follows
1   The standardized °WMs were computet) tor each site as
Xi - Oi/Qm
where Xi is tne i* standardized flow Qi is the i**1 ranked ’low and Qm is the average or the date set
2      For eacn annual maximum flood record the first two prooatulity weighted moments. PWMs. .e mlOh. k = 1 ano 2) were computed using Equation (1)
3. For each k, weighted average values of PWMs aver M sites tncludeo in the region were calculated as follows
M
- X, N| [miQk|
Mi*= _15L ----------------------------- 1 M
£ X. Nj
1=1
( 84j
These Ml[a values were then Heated exactly as sample estimates ol PWMs for the regional standardized annual maximum flood population. LLG and GEV were fined to the standardized regional PWMs
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rological^ As peels
________ _________ Miyjwjff
PWMs
M10G - 1 QCKJO
Ml 01 = 0.411954 AHQ2SS 0.250375
8.3 Generalized Extreme Value Distribution
Jerikison (i969j introduced the Generalized Extreme Value (GEV) distribution for modeling floods  It has  oecome more important <n hydrology  since it was  recommended by  NERO (1975) tor modeling annual maximum streamflows o! Bntisn rivers
The GEV distribution is defined as
X= u + uVkj (1 - (-In Eft
The shape parameter k, can be estimated as
k= 7 859 C + 2.9554 C1
wnere
C — — Min,, - in 2
i2 M,w’6.M ui*3 Mict) In 3
(6 6) (a 7)
(S.6)
1
the scaie parameter
a = x (Mjjxj - 2 MituJ
(i-2*).r(l^kj
ana the location parameter u= m<w - lafcHi - m+K)}
GEV Parameters               C =      -0 00061
Gam* =       1 0023
u — 0.879428 a s 0.253011
(8.9)
|,8.l0j
k =       -o.ww
8.4 Log-Logistic Distribution
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Key 2W7
log’Loqistic  (LlGj  distribution  was  introduced  for  flood  frequency  analysis  by  Anmed  et  at (19B8J
The LLG distribution is defined as
X- a + 0.{F/(1-F)}‘
The parameters c. □ and a can be estimated as follows The snaps parameter
M
tne scaie parameter
(0.11)
(3.12)
d-
(6 13.1
c.G
ana the location parameter
a- h4
1(X
-c G
wnere
G= trcysifiKCj
LLG Paameters       G =        1 05tD33
a  =  -0.01767
t>  =  0.968257
C = 0.173014
8 5 Regionally averaged quantiles
(8 14)
48 15)
Generally  the differences  between estimates  ot standardized quantiles  by  GEV and lLG distnbultons  increases  with increase tn return penoos. In all cases  clear differences  are observed tor the >arge return periods where lLG distribution gives larger quantiles compared to GEV distnbui>on Estimated flood quantiles  based on GEV ana lLG distributions  are presentea in Tables 8.1 and 8.2. respectively
62
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May 2007
RoDustness  as  a cntena has  received widespread attention tor choice ol distribution tor an annual maximum flood (AMFJ. Robustness  is  assumed 10 test whether a distribution and metriM or parameter estimation, considered jointly  are insensitive 10 departures  from assumptions  maoe tn their use. In Ibis  regard. LLGfPWM has  teen lound to de more robust than GEV/PWM (Admasu 1989J.
Otten, a compromise has  to be reached between flexibility  and sensitivity  to outliers  One may need to compromise on some kind of mid-way  solution The compromise could be to use a three-parameter disinbution such as  GEV and llG However for this  purpose. LLG has  been found to be more attractive than GEV
in addition, llG is .ess  sensitive(compared to G EV} to c  hanges  1 n the small values  of the annual maximum IIddos Therefore, LLG/PWM is Getter than GEV/PWW lor modeling AM samples thai display a dogueg shape when plotted on probability paper
In general. ILGVPWM nas  been found to be more appropriate for modeling annua* maximum floods  (AMF] oomoareo to other distributions. Therefore, LLGJFWN nas  been applied for estimating design Poods required for trie project.
Thus, cased on probability  weighted moments  method and using Li,ift disinbution on a regional flood frequency  approach, the return period floods  have beer arrived at lor the proposed oam site The monetary  peaks  discharges  at various  levels  of probability  of exceeoance (return benoas; are summanzed beiow
10 yr return period flood = 575 m /sec
20 yr return period flood = 654 nrP.'sec
50 yr reiurn period 1 locus - 77lm^sec
100 yr return penod flood = a71nP/sec 500 yr reiurn penoa flood = 1155 m’rsec 100G yr return period tlooc = 1303 m^sec 1Q00D yr return period flood = i94flm Jsec
3
J
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Table 8 1 Estimated Flodd Quantiles Based on GEV Distribution
Hay 2007
T
Xt
Mean
Max. Da
ily Discharge
Moment
ary Peak
-----------------4
Return
Growth
Gauging
Gauging
‘“77TT. "' 
|m >5/
Wama it   Dtm
JUrtCtHjn  site
Gauging
Gauging
TVama at
period
factor
Site 111
Site '2i
Site tTi
Site 121
Junction i
?am sfle
. Jj-earsy
1 ratio i
IfTp/S.r
(m’rsj
im7s.J
im'/s'i
;m >S) (
2
0 95
670
214
238       354
768
272
264
392
5
i 23
669
2?8
309       460
1022
353
342
509
10
i<3
1DQ1
320
356       530
1178
406
395
586
20
1 50
1129
361
402       597
1329
458
445
651
50
i S3
1296
414
459       666
1526
526
509
759
IX
2D1
1422
455
505       752
1674
577
559
833
200
219
1549
495
550       619
1822
629
609
907
500
2 43
1716
549
610      SOB
2020
697
676
1005
100C
2.61
1644
589
655       975
2170
749
726
1080
2000
279
1972
631
700      1043
2321
801
776
1155
5000
3 03
2143
685
761       1134
2522
870
842
1255
1000C
3.22
2273
727
806      12C3
2875
923
895
1331
Avenge
7
707
226
2S^        374
632
287
278
414
The anafys/s js based on rp^pone/ flood /racpue-ncy analysis tiaseo cw? Genera/ Ejdrame Ublue (GEW dAirrtbi^iOfi iwtfi paranjerens estimated* £jy pro&aEirMy merginm? mcimwjte ^efnoo1
Table S.2 tltimaiaa Fiona Quantile?
on LLG Distribution
T            Xt             Mean I
Return        Growth    Gauging Site period         factor               hi_
(years J      ratio i        (mJ,sj
2           0 95           672
5           1 21           854
100          2 1           1488
200          2.38          1680
500          2 79          1972
1D0O        315           2225
fajr. Daily Discharge
iWomenrarv Peak
Gauging
S4e (2
Warns a;
junction
De/n
SJfr
Gauging  Gauging
Sue 1
Si1e I2i
Wama at Junction      ■**
(m'/sj        (mVsj    ■ m3/s i  <i——s—    m?s?  1 (m^s)             m rs; m is
215          238
------- n 356
791          273          264         394
w           1 39           982              314               349
S19
20           1 56          1118            357            397
50           1 86          1317          421            467
591
697
2?3            304         452       1D05        347           336          500
1156        399           386         575
1315        454           439         654
1550         535          57?        771
476            527
787
1751         604           5M        871
869
1043
2000 3.55 2511
50D0 4 17 2947
117
10000 4 71 3326
Average ___ T 707
803            891
942           1 4
1063
226
S3?            597                       1977        682           662         984
63C            700                       2320        800           776        1155
711               791               7      2619        903           876        1303
1329      2956        1020         987        1471
0                 9      3488       1196        1153        1726
7 1182 25J
155
175
374
0      3915        1350
832
?87
wrtfi jhomhiiu unmafaf ^Oa&hry 
»
momtrnJs metf
1309         1948 jfj
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1Ar Jo Deaessa Irngauon Project Meteorological and Hydrologicai Aspects 9, PROSABLE MAXIMUM FLOOO
May 2007
The   probable   maximum   flood   is   defined   as   the   most   severe   flood   considered   reasonably possrbfe to occur II ts customarily obtained by using unit nydrographs and rainfall information
Annex  C-4 gives  the recommended reservoir Mood standards  for three mam catego 'es  o reservoirs  Category  A nas  me mosl stnngent standards, since for suet* a reservoir a breach m the oam would enoanger the fives  of people congregated m a town or village downsiream The worst conditions  are envisaged the spillway  aireaay  taking ihe average daily  inflow wnen the probate maximum Ikxw (PMF) amves  ano the wave surcharge allowance must be tor heights greater than 0.6 m Categories Bano C have decreasing standard requirements
In Ethiopia, the study of design flooos on the basis of PMF requires further investigation The challenging proDlem is particularly that of storm rainfall and the varying temporal pattern of
intensities throughout a storm's duration, ihe occurrence ol the peak intensity is a variable to
oe considered for further study at national level The initial stale of Ihe catchment is also of
great significance in trie generanon or an exireme flood A thorough Knowledge of a caicnmEni
ano of ns varying responses during adverse conditions 1$ essential far an engineering
hydrologist to evaluate design floods and such situation need to be investigated at an institute
level.
However in sucn a situation where Uwe 1$ maximum rainfall data, hersfieid (1961) suggests the use cl following equation to estimate 2*nr PMP in region so as  to superimpose H on design unit Hydrograph to give the PMF
PMPj, = Pm +K.Sn = Pm (1*K.CV)
Where
PMiPs*            = 24-nr probable maximum precipitation
Pm = mean of the 24-hr annual maximum over the penod of record
Sn = standard deviation of the 24-nr annual maximum
CV = Pm/Sn = coefficient of vanation
K = a constant equal to 15
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Tihe mean annual maximum 24 hr ramlaM lor Bedele and Jimma are 55 5 mm and 5 3
Mar 2tKr;
respectively, ana also the coefficient of variation for Bedete ano Jimma are 0 198 and 0 20i
respecuveiy For the Arjo Oedessa dam calchmeni
Pm = (55 5+51 3)/2 = 53 4 mm
CV = (0 198+0.2011 2 = 0 20
Sn = 0.20* 53 4 - 10 68
K -15
Then
PMPj, = Pm +K Sn
= Fmil+K.CV)
-1 01■fffl
= 4 01*53.4 = 214 nvTvday
Total volume of daily rainfall
Vp= A PMP^ = 5310*214 = 1129 5 Mm1
Assuming  runoff  coefficient  C  that  corresponds  io  the  occurrence  of  continuous  rainfall  to  be C.68 ihe estimated rainfall depin mai produces pcobatue maximum Ifood becomes
tfpe= C Vp = 0 W'1120.5 = 768 5 Mm’
Using 1he calcnmeni charactensiics given m Table 12 1 and applying ine dimensionless 
hydrograph given oy Tatue C4 the Pood pea* component due to the probable maximum
rainfall becomes 3502 m’rs Assuming the a base flow of 188 m /s me toiai peak flood
Becomes
Qp = base flow + peak due ro storm - 188 * 3502 = 3690 m\s
Cumuiaiive volumes  of Probable Maximum Floods  (PMF) derived from probable maximum 24-
J
hr ramlalt is given by  abie g,i
T
design flow? hydrpgrapn derived from estimaied PMF i$
given by 9.2
fWj
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Taole & 1 Table Cumulative Volume qI Prooao:fr Maximum Flood
Time
(hrsj
Cum. Volume     Time     Cum. Volume     Time       Cum. Volume
{Mm3;       (%)          (hrs)      (Mm3i
(Mm3)       (%,)
0 00        0000        000       103 50     687 8       89.5       207 00      765 3         99 6
4.M        0 440        0.06       108 00     698 7        909       211 50      765 8         99 6
900        2.936        0 38       112 50     708.3       92 2       216 00      766 1         99 7
13 50      9 389        1 22       117 00     7164        03 2       220 50      756 6         99 7
1800      21 87        2 85       121 50     723 2       94 1       225 00      766 8         99 8
2? 50      42 15        5.48       126.00     729 i        04 9       229 50      767 1           99.fi
27 00     71 51        9 31       130 50     734 4        95 6       234 00      767 3         99 8
31 50        1105        14 4       135 00     739.0        S&2       238 50      767 5         99 9
36 00      157.6        20.5       139 50     743.0        96 7      243 00      767 7         99 9
40 50      21D4        27 4       144 00     746 5       97 1       247 50      767 9         99 9
4500     266 4        34 7       148 50     749 3       97 5      252 00      768 1         99 9
49 50      322 6        42 0       153 00     751 7        978       256 50       76B2         700 0
MOO     376 4        49 0       157 50     7536        98 7       261 00      768 3        100 0
58 50     426 4        55 5       162.00     7555        98 3       265 50      768 4        IDOO
83 00      471 6        6’ 4       166 50     757 2        98 5       270 00      768 5        100 0
67.50        5li 8        66 6       171.00     758 6       98 7      274 50      768 5        100 0
72 00
546 4
711
175 50
759 9
98 9
76.50
575.0
75.0
180 00
761 0
99 0
81 OG
601 7
78.3
184 50
762 0
99 2
85 50
623 9
81 2
189 00
762 9
99 3
90 00
6434
83 7
193 50
763 6
S94
94 50
660 4
85 9
198 00
764.3
994
99 00
675.1
87 9
202 50
764.8
99 5
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Table 9.2 Design Flood Hydrograph Derived from Estimated PMF
Maj 2007
n          Or            Ti
-----D-j----- 1   77    . Qr
Qj
oQ
r—
1 rnl'5,1
— ■ Xhr■ j » -X.
fhr.'
1
000         188      45 00     3690     90 00     1309    135 00     451       180 00      251 2 25        216      4? .25    3655     92 25     1239    137.25     433      182 25      248
4.50        241       49 50     3620     94.50     1169    139 50     419       184 50      244
6 75        339       51 75     3515     96.75     1099    141 75     402      186 75      241
9 00        451       54 00     3410     99 00     1028    144.00     384      189 00      237
11 25       573       5525     3270    101 25     958     146 25     367       19125       234 13.50       748       58.50     3130    103 50     923     148.50     349      193 50      230
15 75       958      60 75     2990    105 76     853     150 75     332      195 75      230 18 00      1169      6300     2815    108.00     818     153.00     314       198 00      227
20 25      $449     65 25     2674    110 25     783     155 25     297      200 25      223 22 50      1694     67.50     2499    112 50     748     157.50     314      202 50      220 24 75      2009     69.75     2324    114 75     678     159 75     307      204 75      220 27 00      2289     72 00     2149    117 00     643     162 00     300      207 00      216 29 25      2604      74 25     2009    119 25     608     164 25     290      209 25      216     i 31 50      2885     76 50     1904    121 50     573     166 50     283      211 50      213 33 75      3095     78.75     1764    123 75     552     168 75     279      213 75      213
36 00      3305     81 DO    1659    126 00     531     171 00     272      216 DD      209
38 25      3445     63 25     1554    128 25     514     173 25     269      218.25      209
40 50      3585      85 50     1404    130 50     496     175 50     262      220.50      209
42 75      3655     87 75     1379    132 75     472     177 75     258      222 75      206 1
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10 SEDIMENT ANALYSIS
10.1 Estimation of Sediment yield
Suspended sediment data from Stations 14001
14014 and 14005 *ere obiamed These
d.scna/ges are gwen m Annex E5 Suspended concentration rates varying between 45 mcj/lt to
1670 mg-'li were observed from Odessa over
Refanonsnips  Detween water discharge and sediment loads  al various  sues  in the region are presented in Table 10 1 Al site and regional approacn has  been useo to to estimate sediment rates  from the estimated streamflows  at the dam site Accordingly, the following relationship nas oeen denved
Gs = 0 078 0’5
(10 1)
Where
Gs = sedimeni load (in gm)
Q = monlhiy mean discharge (in It/s/km')
Caretui  assessment  regarding  reservoir  sedimentation  will  De  required  in  the  site  as  the  life  of the   storage   created   Dy   a   cam   is   dependant   of   the   sedimentation   situation   Accordingly reservoir  p.annmg  will  include  assessment  of  ine  probabie  rate  of  sedimentation  in  order  to predict tne useful fife of the proposed reservoir
in esiimalng reservoir sedimentation maienais  originating as  oed load will De assumed to have a density  of 1 4 gm/cc  and matenai cameo m suspension will be assumed to have a density or 1.2 gm/cc. Tne Dec load at the dam sites shall De assumed to be 15 percent of the suspended load
Monthly  toiai  sediment  load  (suspenoed  and  bed  toad)  and  accumulated  total  sedimeni  load  ai the reservoir site are given o> Table 10.2 and 10 3 respectively
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Meteorological and Hydrological Aspects 10.2 Distribution of sediment in the reservoir
May 20(17
So far rhe sediment load likely  io o&posjt in me reservoir rias  been esiimated Bui e&iima. ng me sediment inflow to lhe reservoir is  ndt enough as  now high the sediment *i1 accumulai? in the reservoir is  31 w important Accordingly  Area-increment method has  been used i&r this purpose The method is expressed as
lW2f
Where
Vs = AO(h-MP)+V0
Vs = sediment volume to be distributee
Vo = sedimem t>eiow me new zero elevation
ti = original reservoir depth from the stream oeo level
ho neighi iq winch me reservoir is completely fitleo with sediment ■ e
■ heigni of rhe new zero elevation
Ao surface areas of the reservoir at the naw zero elevation ana 15 tne = area correction factor
The results nONathad Prom the analysis of distribution of sediment in me Ago-Dedessa Reservoir are g iven in T able 10 4
Titole 10.1 Relationships between water discharge ana sediment load
r—— r Mo
Station
Area
ifasii
Mooule
J
10 Vyr
Loss
t/km’iy
Vales oF C in.
Qa =C iQwi1
1
3005
Guder at Guder
524
77
oc
C025
■ '1
4007
Little Angar near Gubn
1975
176
69’
0 096
4005
□anana near Abasma
2881
453
157
0 059
4002
Anagar near Meqantta
4574
702
150
6002
Aiitj-a, al Sudan ElQfoer
0 061
172254
335170
1946
0 165
Arjo De&ttssa Dam srfe
5278
776
147
0.078
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Meteorological and Hydrological Aspects
May aw
Tjoia ID.2: Moniflly Total Sediment Load at (tie Reservoir Srle
i in 1000m3J
Jan Feb March April May June July
Aug S»p Oct Nov 0#c Annual
—I
Avg
2 46 1 33
1 14
1 11
1 71 4 57 27 2 131 1
1 72 42 17 6 62 72
243.5 2TT 5
120 J T& 29 6 87
SttMcv 1 71 101
93  19  92  6
99  01  14  7  4  95
CV
Sittw
3.63 4 01
7 36 6 29
515    5 31 4 91  3 42 2 526  2.086 2 311
3 83   7 54 11 4  7 48 3 696
0678 3509
4 349 4.024 3 8 7051 1C 92 8.77
Tab I* 10 3      Accumulated Total Sediment Load ac the Reservoir Site
1■1
|7'n
Jan Feb March April May Jun* Juiy Aug S ap
Oct N ov           Dec
---------- 1 Annual
V«4fB
25 0 06 0 03 0 03 0.04 0.11 0 6B 3 28 6-2 5.29 3 00 0 43 0.17 19.39
50 012 0 07 0.06 0.09 0.23 1 36 5 6 <2 4 10 6 6 0 0.96 0.34 38.78
75      0 19 0 10 009 0 13 0.34 2 04 96
10 6     15 9     9 0     1 45 0.52        58.17
100    0.25 013 011017 045 272 131                    24 6     21 1     120 1.93 0.69             77.56
125    0.31 0.17 D 14 0 21 0 56 3 40 16.4 31 t 26 4 ISO     0.37 0 20 0 17 D.26O66 4 08 19 7 37 3
15 0 2 41 0.66            96.95 31 7     16 0 2.69 1.03            116.3
175     0 43 0.23 0.20 0 30 0 79 4 76 22 9 43 5                 37 0 21 0 3 36 120                 135.7
200     0 50 0 2 7 0 2 3 0.34 0 9 0 5 4 4 26.2 4 9 7 42.3 24 0 3 36 t 37 1J
155.1
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Meteorological and Hydrological Aspects
Tjdio 10.4: Distribution of Sediment in the Arjo Dedessa Reservoir
Mj> W
50 yean smAment /Old
Ho - 2 .03 m
Ao ‘ 1.52 Mmpw1rri
c r. J4
1—          11 h
|
100 /*,rs *«*'*"*«»/o^
Ho-3 42 m
Ao = 3 15 Mffl
j
Oftp/Ui
S«fWv>«
Origzn>l *r<>
CJpJCAl
n>r
*,
Mm
Dujarn
rOhJfTM
71j
Mm
MM cjpwiV
W
vwinve
W
ftfWgpd
CjptCrty
II*.
Mm
[■rwi
,1_.
J
,Mm .
i fMmJ
.■ in
1
2
3
4
5
6
■y
1
2
3
■1
5
J
7__
1346 56 76 629 6 27 38 7 5524 591 i 1346 56 76 629 8 27 77 4 53 61 552 4
1343 48 13 466 4 24 34 2 46 61 432 2 1343 48 13 466 4 24 es 44 98 398 4
1340 39 92 331 S 21 29 6 36 41 302 2 1340 39 92 331 8 21 58 6 36 78 273 3
1337
32 17   224
18
25 1
30.66
198 9  1337 32 17 224
10
49.1
29 03
174 6
1334
24 93  140 7
15
205
23 41
120 2  1334 24 93 140 7
15
39 7
21 78
101
1331
t&?4   79 64
12
16
16 72
63 67  1331 18 24 79 64
12
302
1509
49 4
132$
12.19 3B 24
9
11 4
1066
26 82  1328 12 19 38.24
9
20 8
9 046
17 44
1325
6.911   13.6
6
6.86
5 395
6 724  1325 6 911 13.6
6
11 4
3 765
2 239
1322
2 619  2 322
3
2 33
1322 2 619 2 322
3
1.92
150 years sediment load
Ho = 4 69 m
200 years sediment load
Ho ~ 5.89 m
Ao-
4 90
Mm2
A
o ~ 6.
73 Mm
1
Onflrfiii #W
CJJMCif
■ir
Ptvr5« £M>*c r
■Mm
iffl.i
_r
£rrv «rw
ctptcKy*
Setiimt VOIU/T!«
JtfVJ
Hm'
.
ifflj
r*frnJ
.
1                 2         3        4        5         6            7H          12             3         4           5         6             7
1345  56 76 629.8     27     115    51 86  513 3 1346 56 76 629 8       27      155   50 02       474 7 1343 48 13 466 4     24      102    43 24  364 6 1343 4 8 13 466 4      24      135    41 4        331 5
1340  39 92  33* 8    21     87.1    35 03   244 7 1340 39 92 331 8       21      115   1319       217 1
1337  32 17   224     18     72.4   27 28  151 5 1337 32.17    224      IB      94.5  25 44       129 4
1334  24 93  140 7    15     57 7   20 03   82 96 1334 24.93   140 7     15     74 3   18 19      66 37
1331  18 24  79 64    12      43     13.34    36 6  1331 18.24  79 64     12    54 1     n 5        25 52
1328  12 19  38.24     9      28 4   7 297   9 887 1328 12 19 38 24        9       33 9  5 457       4 326
1325  6.911   136      6      13 7
1325 6 911    13 6      5       13.7
1
72
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Meteorological and Hydrological Aspects
May 2007
11. WATER QUALITY
Tha  watsr  quality  status  oi  ihe  Dedessa
nve
r  j$  evaluated
using  th
e  dat
a  collected  from  Mo/
vR
database  At>t>ay  River  Basin  Master  Pl
an
Study  Report
(1S98).
The
samples  were  laker
as 
pan of i he supporting measurement for tne aqu3t'c Study and appear i o r epreser u he o niy available data an water quality  within Jhc  catcnmeni. . able 11 ■ shows  water quality measurements  taken lex  Dedessa at two sites  The samples  were taken as  Dart of the supporting measurement for tne aquatic  sludy  and appear to represent ihe only  available data on water quality  within the catchment The samples  snown in Table 11 1 were taken after me sian af Ihe ramy  season and presumably  ail tributaries  of the over exhibited adequate waief quality at me time oi sampling
Total Dissolved So/jos fTDS) and E/ecfrieaJ Conduchv/fy (EC)
Total dissolved solids  characterized mamiy  by  major amons  ano cakons  are directly  related io tne electncai conductivity  of the water The tow Electrical Conductivity  (EC, and TDS value m general shows  mai the water is  soli m nature and has  low salinity  Moreover the low conductivity  is  sign of low fertility  of ine water wim regard to aquatic  life, Electrical conductivity (EC} measurements  wore very  low ai all the sampled sites  EC is  the ability  of 1he water io conduct electric current and directly related td the amount of canons ano anions in the water
pH
The pH vasue is the measure of me concentration of hydrogen (H+) ano hydroxyl tOH-J ions in ihe waier n is to determine ine acidity or alkalinity of the suostance.
Sodrum and Potassium
The Na'  ana K'  reading expressed m terms  of Sodium Adsorption Ratio (SAR) is  the useful parameter for the evaluation of the water body  for irrigation purpose For irrigation water it is important to measure me sodium adsorption ratio as follows
sar = —------—--------- (9 1)
[(Ca” * Mg”VJa 5
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The higher she SAR vaiueof the waler the I ess  suiiab e will be t<x  irrigation purposes  The maximum computeo value among the readings  is  0 29 which <$ l#ss  ihan 0 Tins  •  lustrates that rhe waler is ^ery much suitable for irrigation purpose.
Chio/rtfe
The cmonae cemcanirat^n of the riv«s stipulated in T soles 11.1 is very iw (1.01c 2 0 mg/H at times  ol sampling Hence the paramew was  m conformity  with the standard set by  EP A (ZSOmg/l for aquatic species>.
Table 11.1 Water quality results for sites on lhe Dedessa river
Sampling
Sample date
at Btdtle bridge at G-mbi ondtje Comment
13foa.'96             14/00/96
Elevation (m a si)                        1300                    1200
TDS igrpj'l)
20
20
N
EC i sfcrTi)
60
50
N
pH
6 74
6 97
N
Na"
3.3
3.0
N
«’
1.9
2.5
N
Ca" (mgrt)
64
96
N
Mg" {iTig/l)
2 43
1.4
N
Cl imgJl)
10
20
N
SAR
0 29
0.25
N
WQ Result for Major Rn/ers rSCEOM TS96. Citea By BCEOM flbbay Rjrtr MS** ituer/, 19S8J
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12. DESIGN FLOOD
12 J Synthetic Hydrograph
May wr
Among several known methods  of unit hyarograpns, lhe one developed by  Syndor ■1935) 'S most commonly  used The method is  derived from drainage basins  in the Appalachian Mountain regions  in the united 5lalos  ranging m areas  from 25 km io 25.000 km The relations  of unit hydrograph characteristics  ana catchment characteristics  are expressed as follows
Tp = Ct((LLC)”
(12.1)
Where
Tp a lag time from the mid point of the rainfall-excess duranon Tr 1O the
pea* of a unit nycrograph (hr).
Ct = coefficient depending on oasm charactenstics
lc = nver distance from the slation to tne point of interest nearest :he
centroid of the drainage area (km)
L = river distance from the station 1d the uostream limits of lhe drainage
area (km)
The  catchment  characteristics  (seen  as  L.  Lc  Area  Slope)  of  Desessa  at  tne  Arjo-Dedessa Dam Site is given by Table 12 1
The U.S Soil Conservation Service (SCS) developed a dimensionless hydrograph that has its 
ordinate values expressed as the dimensionless ratio, TVTp Qi is the disenarge at any lime Ti
The snape ol the unit hydrograph dimensionless hydrograph, and Tp is me period
corresponding to peak as shown m Annex Table C5. For a gwen caTChmeni. once me value a1
Tp is defined jsmg Equations 12.1, rhe unit nydrograpn can tie constructed
12.2 Flood Routing Through the Reservoir
The dam is located where failure may probably be confined to the irngalion command ano the
dam use I No excessive 1055 of human life would de expected For such condition, a design
flood corresponding 10 aiO,OOO-year return period has been proposed The volume of flow in
1000-year return period flood hydrograph is about 4OOMm3
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___ MaY j
00
.'-
Trie daia useu io corriplele surcharge storage due to the destfln flood and raubnp cukaABUons were inflow hyoxograpn tor all selected design storms, ejevation-sioragt refal<or>£ for propose .■ storage facility and suge-di&tiharge relations ‘or all outlet control suudurea
The Kiep-by-stap method of reservoir rouung method has  teen used The da-a required for the fneihad to construct the outflow hydrograph is  (a) the inflow hydrograph, (b) lha cieval.on- capaciiy  relation curve of the reservoir and (c? the outflow-elevation curve or the oufftow equation
Using these data a design procedure is  used 10 route the irifluw hydrograph through the storage facility  with different surcharge storage and spillway  crest ioutlet) pwmetry  until the desired duiiiuw hydrograph pas been achieved
A  spillway  with  ogee  shaped  crestsd  war  has  bean  assumed  The  equation  gansraffy  used  for such t}roaO“Cfcs;ed weir is
□ s CLH15
(12 2)
where
□“
d'Ectiarge in m’/sBC
c -
bro&d-cresiw weir coefficient
L=
Omad’Cresled weir length, m
H=
head over w&r crest, m
it the upstream edge of a wcu ■$ so rpunaeo as to prevent conrenirgtion and if the slope of ihe eras: is  as  great as  me loss  of need due to fnclion. flow will pass  inrougn criiic&i depth ai ms weir crest: lhus gives an average C value of 2.2
The following procedures were used IO perform roulirlg through the reservoir
5reP   1     Developing   art   inflow   hydrograph,   stage-discharge   curve   for   the   proposed   storage l&ciSty
2   Selecting  a  railing  Irrhe  period.  Ol.  Io  provide  at  least  five  points  on  lhe  rising  limb  Of tne inflow hydrograph
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Meteorological and Hydrological Aspects
Miy aWr
w  3.  using  the  storage-discharge  data  from  Step
1  to  develop  e(praHe  characterises  curves 
that prawne value S (*/■) lOttJ-Df versus stage
stop 4 Fur a given time mtervai 11 and I2 are Known Give ine oepin of storage or stage H1 at the boning of that ttflto mtervai Si - iQl -^.Dt can oe aeiermmcd frtxn the appropnato storage cnaractenslics curve
Srep 6 Determining toe value of S3 + (Q2 2) Oi from tne following equation
S2 + (Q2/2).Dt = [Si -(O1 2j Dt] * I
when
1
J                   11 + Dt]
Sz = storage volume at time 2 m . sec Q2 = outopw rate at time 2 n^fSK
Di = touting lime period sec
S1 - storage volume st time 2. m" Ql ■ outflow rare at time 1 m^sec |1 = inflow rale ai lifHt 1 m’/tec 12 ■ mflaw rale al lime 2. m'.'SCC
(12 3)
grad   6   Enter   me   storage   charactensnra   curve   al   the   calculated   value   of   32   +   (02/2;.0t determined m Step 5 and read off a new tiepui of water. rl2
Step 7 Oeiermine the value of Q2 whicn corresponds  io a stage of H2 aetormmed in Step 6
□sing the siege-discharge curve
Stax? & Repeat Stop 1 torougn 7 Dy sailing values oi <1 Q1 Si, and H1 «>uaf to the previous l2. 02. S2 and H2, ana us ng a new 32 value This process  is  continued until the enure mflow nydFograpn has MW rauBed chrougn the storage basin
Since  Equation  i12-3ji  contains  cwo  unknowns,  sBepw^se  Inal  and  error  procedure  is  used Results   Of   routed   oes»gn   floods   cased   on   LLG   distribulion,   half-PMF   and   fulf-PMF   are pressmen  py  Tatjie  12.2,  12  3  and  12  4.  respectively  Tne  elevation  -  area  capacity  curves  of lh&  reservoir  are  snowr  tn  Figure  12  1  The  lOOOOyr  reium  penod  design  inflow  and  outflow tiydrograpns are shown in Figure 12.2 Such inflow ana ourflpw nyarograpris lor smaller return
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al and Hydrological Aspects
-  Hay  rW>. —
periods  fake
10  20  50  and  100  year  return
Mfiods  are  slWffi  m  Figure  12  3.  Tne  average
hydrograph of mammiim flow at the dam sue ra available m Figure 13.4
12.3 Routed Design Flood at the Coffer Dam
Velocity Formula
The velocity equation inrough the pi&e outiei s gi^efl by
V=(2gHl,) ’
where
A = cross-secnonal area of barret tor cnpey, V = velocity lhrpugh the barret
Hi = toLai ri&M toss inrough ihe barrel,
fs
H  =(1.5 + fUCtj VV2g
l
U2.&J
L =? length of me barrevpipe
D/4 = R = hydraulic mean radius of lire barret
D - diameter of oanebpipe
7 = velocity througn me oarrel/prpe
f = coefficient of fndion
Manning's Formula
it is one ol the most common formula, which 13 commonly used lor me analysis of problems o1
fow  through  channels  Put  often  used  for  the  analysts  ol  pipe  Itow  problems  loo  According  10
this formula tne discharge  through pipes is given oy
V S (F^j.OOT Ssa
V = velocity through the pipe.
(12 6)
Where
n - Manning 5 roognn&$$ coefficient (3 value of 0 065 has been selected for old concrete pipe i
0 = diameler of the pipe
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S = slope of me hydraulic gradient or energy slope =• Fu L
F - is constartt equal to 0 39635
L = length of the pipe (m),
n, = n*ad toss through the p*pe '.no
Equalrwi 12 5 can be arranged to express me relations for head loss ihrough a pipe
May 2007
hL = L
( 127>
Combined Formula
Corntiijirng Equal ion 12.5 and 12 7 the above two expressions for velocity reduced io
Ht =11 ST2g*L Itn/FjD^}] } V
V = (HJ{1 5/2g + L [(n/F; D 2Of})c'5 Q - A               5.'2g * L [(nffJD ^lV1
22
ano
also
= <nD'/4i (H /(1 5/2g * L. ((n/F) D" ^®})
L
2
05
(12.8l (12.9)
(12 10)
Where A is cross-sectional area ot pi tie in m '
J
Substituting <t = 0 0165. g - 9 81 m Equation 12 8 can be expressed as hl = (0 076453* L (0 041577
V = (Hj{0.076453* L [0 041577 D   V))”
J1
Q = t0 7857 D:) (H^{0.076453* L [0.041577 D'2
*] })’*
2
Results of routed design flood at Cotter Dam al Ago Didassa Reservoir are presented in Table
12.5.  These results are available for 10 20 50  and 100 year return period Floods. According to We criteria, the appropriate results could oe adopted tor designs
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Table 12.1 Catchment Characteristics
Arjo Dedcssa Catchment
Characteristics
Dimension
Area (km2;
5278
Langin (km)
199
Centr<wd distance (km)
141
Max elevation (m aslj
3012
Minimum elevation im asij
1315
Elevation difference {mi
1697
S icnrrn/
0 0085
Ct
1.53
Tc (hrsj
24 00
Tl (hrs)
33 00
T  (hrs)
s
4.40
Tuidj) (  5)
hr
38-00
Tp :hrsi
45.00
Table   12.2   Routed   Design   Flow   at   FRL   Corresponding   to   1352   m
(a J     Based on LLG distribution
Max Surface              Sore barge
L.m
Qdut im'/S'
H -m
Area (Km )
7
Storage (Mm
50
871
397
87.06
1340 1
75
1031
3 39
85 20                       1288.C
100
1154
3 02
84 01                        1255 0
125
1253
2 75
83 14                       1231 4
150
1333
2 54
82 47                        1213 t
175
1399
2 36 _____ |
81.91
11933
Peak inflow - 1850 m3/s
(b) Based on Hatf-PMF
1
L < JL_
□out m
-
bumj
Max Surface
1 r——- Areaj-(-K.—irf£1—' i j
Surcharge
Storage VM”m" 1! '   4
50
798
3 75
as 34
75
941
13198
3 19
100
84.56
1051
1270 3
2 84
83 43
125
1239 1
1 140
2 58
8261
150
1212
1216 9
2.38
175
81.97
1273
1199 7
2 22
81 45
1186.0
Peak i
nflow = 1780 m&s
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fcj Based or? PMF
Mav 2007
L
Oout
H im)
Max Surface Surcharge
Area . Km‘. Storage Mm:
50
1668
6 13
93 95
1539.8
75
2008
5 29
91.28
1461 3
100
2265
4 73
89.50
1409.5
125
2466
4 32
86 16
1371 3
150
2625
3 99
87 10
1341 2
175
______2756
3 71
86 24
13168
Pea* inflow = 3590 mJ/s
Table 12,3 Rautea Design Flood at FRL Corresponding to 1555 m (a.j Based on LLG
1--------------
I— L ("V                   Qout m3/$i               h , m
1
Max Surface Area i km:
———■ *———1
50
012
3 79
96.26
75
964
3 24
94 57
100
1083
2.89
93 48
125
1180
264
150
92 70
1261
244
92 09
175
1329
2.28
91.59
Surcharge
Storage 'Mm1)
1601.8
1546 7
1511 9
1487 1
1468.0
1452 6
Peak inflow = 1950 mis
(b) Based on Hal/-PMF=
L Im
Qoui rrr’/s,
n m.
Max Surface
Surcharge
Area Knr
Storaoe f Mm3 i
n ir—  ■------tt-
50
746
3.58
75
881
3 os
95.61
1580 6
93 98
100
988
2.72
1527 9
125
1075
2 48
92.95
92.20
1495 0
150
1148
j.jg
1471 6
175
1208
214
91 63
1453 7
91 16
1439 2
Pean inflow = 1780 mj/s
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nD
B
B
B
B
■
B
B
B
B
Bl
II B
B
B
B
Arjo Bedesia IrripiUcE Project
MpicorcHugical and tfydrologlca.1 Aspects ________ (Cj SasetfpnPMF
l (m               Qout imJ-5'
H rml
5 81
5 04
Surcharge Storage* (Mm
50
1540
75                     1867
100                    2nB                       4 63
125 2320
150 2483
4 14
384
Meat Surface
Area ■ Km21
102-52
IDO 13
08 S4
97 36
96 41
175                   2618                      3 59                    9$ 64 Peak mflQVf = 36?0 mJ/s
1611 9
1730 7
1677 1
1637.8
1606.8
1581 3
TatrtB 12 4 Routed Design Flood at FRL Corresponding to 1356m
faj Based on LLG distribution
Max Surface
Surcnarge
L(m)
Qout m^s
rl mJ
Area (Km )
a
Storage (MTn )
s
50
BDD
3 75
99 11
1693 0
76
951
3.21
97 49
1637 1
100
1069
2.87
96 45
1602.0
125
T165
2 62
95 71
1577 0
150                   1246
2.42
T75                   1314                      2 27
Pean inflow = 1950m3/s (by Based On HaifPMF
1
95 12
94.65
1557 7
1542 0
_ llmj 50
Goul im /sj
J
735
75 869
100 975
126
1061
150 1134
ITS 1195
3 56
303
2.70
2 46
2 28
2 i3
Max Surface
Area (Km*)
98 49
96 93
95.94
95.23
94.68
94.23
Surer arge
Storage (Mm1)
1671 5
1618 2
1584 9
1561 2
1543 1
1520 5
1---------------- --------------- —------- Poak inflow = 1760 mis
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(Cj SasecfonPMF
Mav 2007
Max Surface           Surcharge
Ljm
Ooul inv/s.i
Him-
Area 'Km*/
Storage (Mm .!
3
50
1515
5 75
1D5 09
1905.2
75
1535
4 99
102.81
1823.3
100
2086
4 48
101 30
1769.3
125
2289
4n
100 17
1729 8
15C
2453
3 81
99.28
16955
175
2555
3 56
98 53
1672 9
Pea* j'nRowf = 3690 mJ/s
Taele 12.5. Routed Design Flood ST Coffer Dam of Arjo Dides5a Reservoir
T-Wrs Peak   = 654m].s
T = 20 yrs,           Peak    = 654 m5Zs
D               O                  Etev                                 D
Q                    Etev
tw 1        m3/5.             [m as?
(P/
imSrs.i                7nasri
L
5.0            210               1337.98                             5.0
211               1338 22
55            223              1333 01
5.5
225               1333.29
6.0            239              1330 00                             6 0
243               1330,32
6.5            258              1325.05
6.5
263               1328 40
2x4 0            220               1334 18
2x4. D
222                1334 45
,5          243              1329-88___                     2x4 5
247                1330 19
T - 50 yrs, Pea* - 771 m’/s
7= 700 yrs, Pea*    = 871 m\s
D                0                   Etev
D
m as?
o                     Ete*
1W.
A™'
im3/sJ               m as/J
5.0            213              1338 59
5.0
215               1338.89
5.5            229              1333.70
5.5
232               1334 05
60            248              1330 79
6.0
253                1331 19
6.5            271              1328 90
6.5
277                1329.32
2x4 0          225              1334.86
2x4 0
228               1335.20
2x4.5          253              1330 69
2x4 5
257             1331 10
Note Length of prpe, L = 400 m
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Eiavaltcn-Arw«-2C-jn* for Aqo
Anti |!Jn
Awrrair
Flflur# 12.1         6l*v*tio-ffc-A/<n-Capacrty Curv«« cf AfjO Ded&isa Reservoir
Inflow iM Ourftaw rtjrirograpte <i Ajjq DMaisa ft**»r>Qir
22 Inflo* *nd Outflow f looa Hywag njpn, Jt Arto D-dM a R<»»rvOlr
,
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E^vkIdh i,mJArja Dedcssa Im^auon Project Meteorological and Hydrological Aspects
Muy 2007
nub.
• m. t*4~i crfw a*- r
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irfld-dr >MH
bfrl inig idiQFrF »l * rjn ti>f»BlB
C«rr»i
»»■ - - .
t ■•
__________
v n -k i> >ib ■>
n-F (bril
Flflurt 12.3 Inflow ina Outflow Flood tiydrojjriphi at Ar|o Dtdn» Reservoir
MM
"*         >10      '15 ps
■•■RB a<¥"*Ha
S5
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Arjo Cedflssa Imgalicji k*rcjecL Meteorological and Hydrological Aspects
May 3007
'
I
—
Hrdroflnph ur
flew! V Arjo DMMM P*" *,r*
Fiqurfl 12 4 Average- Hydrograph of Maximum flaws al Arjo Dedmi Cam Sile
8&
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Meteorological and Hydrological Asp
ects
May 2007
13. RESERVOIR SIMULATION
Determining  oesign  capacity  of  Arjo
Dedessa
reservoir
req
uire
d
reservoir
simulation  study  The
factors  that  has  been  considered  in
the  anal
ysis  inclu
de
the
f
ollowing  T
his  particular  section
deals with the dam/ reservoir simulation for establishing the viability of contemplated irngat*on c Useabie flow between reservoir and diversion,
o Spill past diversion weir
o Flow into (he reservoir
o Evaporation from the eservoir
r
o Rainfall on the reservoir
o Total irrigation demand and
o Irrigation water release from inc reservoir
The  simulation  sample  is  provided  in  annexure  6  *  S  me  description  of  vanous  column, referred to there in are as oe«>w
S'
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Column       Abbrev       Unit
Kay 2007
Ovscripffort
Corp/ tear
Cat ]2] Month
Year Month
Cat fl]        inflow        Mm4          Natural inflow to toe reservoir  as simuialed Dy Tboma$- Feirmg model ■ monthly flows for 1QOO years)
Cor /4J        OF          Mm3          Natural  flow  icorresponding  to  75%  reliability  'evei)
between the dam site and diversion site
CoJ/5/
Eo-Rf
Mm
Evaporation minus rainfall over the reservoir Eo is 
evaporation at 75% exceedance level as estimated from
ETo and Rf is montniy rainfall at 75% reliability level
Cor 16]
IWD
Mm5
irrigation water requirement (given by Table 13 ■’)
Cq({7]
(Eo-Rf)
Mm’
Coi |5[ converted to volume covering the entire
zommand area
Cot {8]
SL
Mm3
Seepage loss \ assumed to be 1% percent of the
exislmg storage tn Che reservoir)
Cat ]9]
IWR
Mm’
Irrigation water release from the reservoir tCoi(6]-CoH4]J
Cot /ID]
CS
Mm3
Change in storage between 1he ends of the previous
and current months
Cai {11]
Storage
Mm3
Reservott storage at the end of month
Cot {12]
Area
Km2
Reservoir  average  surface  area  oetween  beginning
and
end of monto
Cot {13]
Lewei
m asi
Reservoir storage at ths end of month
Cat ,14]
Spill
Mm’
Spill from the reservcur between beginning and end of
month
Cai {15]
STRQ
Mm4
Toiai annual storage requirement
Cai ]16]
T Spill
Mn?
Annual spill from the reservoir (sum of Col114] from
month 1 to 12)
The d etails o f s imutalion < np ts 
u     3 re p rovioeo 1 n t ne T aDies 1 3 1 a nd 1 3.2. The a Dstract o f 1 he
detailed imgalior targeted simutaiion runs are provided in Tabie 13 3 With these parameters the contemplated irrigation 'Table 13 1j are successful al various rehabiklies shown in Table 13 3
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*I
I
I
I
I
I
I
I
I
I
i
i
I
I
I
I
i
J
Arjo Dedsssa Im fulon Project
MctCOrolnrif aS anri Kvrirnljipiriil A smurfs
Trtte 111: (mg al ion Water ftequJreme nts tor Various scenario 5
3
{for 13700 ft J in Mm )
May 2007
Phase J
Phase II
Month
Rod            Rol2            RmI              Rut?
Sep 8.38 8 43 12 43 12.45
Oct 10.41 10 69 13 19 13.72
NOV 2 89 2 90 316 3.39
Dec          11 04          12 49          14 02          16 07
Jan          19 00          22 18          24 64           28.61
Feb         23 25          27 87          29 98          34 92
Mar t8 49 22 15 22 99 26 41
Apr 4 98 5 21 5 09 5 30
May          2.01            7 01             201             2 01
Jun          21 64          21 64          32 42          32 42
JU!              5 97            5.97             895             8 96
Aug 6.89 6 89 10 33 10 33
Total 134.93 148 43 179 22 134.49
Taoie13.2 Reservoir Characteristics at Dead
Description
Minimum orawaown level Minimum river bee level Area ai deaa storage level Dead storage
ma.s.i
m a.s.i
kni2
Mm3
Level QtSJiaJtl.
' 350.0 1320 0 67 aa 074 7
I
N.J
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jrteteorotogicat and Hydrological Aspects
Table 13,3 Storage Reservoir Characteristics and Reliability Levels
May SWT
Description
--------------------lj
Unjf
Ra/iabiWy fev&/
|................ ....................................
80
75%
%         55%        90%
95%
Phase I, Rot 1
Dam heighfyat spillway
c.l)
m
30.89
30.98      31.00      31,24
31.42
Spillway crest level
mast       1350.69 1350.90 1351 03 1351.24 1351 42
Area at normal waler level           km?
70 797 71094 71424 71 952 72 546
uive storage
Total storage
Mrr? 67 3 74 4 02.3 95 1 109 4
MmJ 942 0 949 1 957 0 969 7 904.1
Spill over the spillway                  Mm1 Spill to Live storage 'ano
Phase l Rot 2
1000 0 1799.0 1754 0 1703 0 1640 0
26 74 24,17 21 30 17.92 *4 90
Dam Aerghtfar spillway c.11          m            31,05      31.14      31.24      31 41      31.59
Spillway crest level
m.a.s.t      1351 05 1351 14 1351 24 135* 41 1351.59
Area at normal water level           kmz
71.325 71.622 71 952 72 513 73 107
Live storage
Total storage
Mm2 30.0 07 1 95.1 108.6 123-1
MitT 954 6 9618 969 7 903.3 997 0
Spill over me spillway                  Mm1 Spill to live storage ratio
Phase II. Rot 1
Dam hejghtfat spillway
1706 0 1705 0 1740 0 1 689 0 1626 0
22.34 20 49 10 31 15.55 13 21
c.l)
m           31,14      31.22      31.33       31.5       31 66
Spillway cresl tovei
Area at normal water level km?
-351 14 1351.22 1351.33 1351 50 1351 68 71.622 71.806 72 249 72 010 73 404
Live storage
Total stooge
Mm’ 87 1 93.5 1022 115.9 130 4
Mm3 961 0 968.1 976 9 990.5 1005 0
Spill Over the spillway                 Mm5              1755.0 1 754 0 1 709.0 1658.D 1595 0
Spill co live storage ratio Phase II Rot 2
Dam he/ghtfat spillway
c.l)
30 15      18 77      16.72       14 31      12 24 m           31.32      31.39      31.52       31,69      31.87
Spillway crest level
Area at normal waler level
Live storage
Totai storage
Spill over the spillway                  Mm3 Spill to live storage ratio
m.a.s.;      1351.32 1351.39 1351 52 1351 69 1351 87 km3                         72.215 72 447 72.B76 73 43? 74.031 Mm3               101 4      107.0      117 5      131.2      145 7 Mm3              976 1      901.7      992 1      1005 0 1020 4
1739 0 1738.0 1693.0 >642 0 1579 0
17 14      16 24      1441       12 52      1004 L
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Meteorological and Hydrological Aspects 14. DEDESSA SUB-BASIN MODELING
May 2007
14.1. Modeling for Arjo Dedessa dam for Irrigation
The simmialions  discussed in previous  secnons  is  lor a comprehensive analysis  or Dedessa dam. which 15 the mam focus  of the TOR A detailed Ms-Excei based model. using 1000 years of monthly  data o1 inflows  generatM synthetically  were incorporated in (he vano-js  runs  to obtain the results  as  indicated in the Table 13 3 As  can be seen from the water requirement available at Table 13 I. for the ultimate development phase II of the Dedessa dam, the optimal water abstraction is  (or RoT  2. scenario cropping pattern Based on various  combinations  of the simulation runs  which are ^ery  exhaustive it could be stated that there could be two net phases of development The designs however need to be made for the phase II devetopmeni
The fimneo up geometry of lhe reservoir at Dedessa dam for these two phases could as below This is lor lhe success or irrigation at B0% reliability The following abstracts are based on the results oi simulator considering only contemplated imgabon.
phase 1 development of Deoessa dam
Irrigation command
Full reservoir tevei
Storage at full reservoir
□eaa storage level
w Olume al Dead sLage iev& Live storage
River bed ieve>
Area al Dead storage tevet Area at full reservoirs level irrigation Demand
13.700 na 1351 14 m 961.8 Mm3 1350.00 m
874 67 Mm 07 lOMm’ 1320.00m 67 88 kmz 71 14km2
148 43Mm3
□ pot phase II dewelopmem of Dcoessa oam
■ irrigation command;
13 700 na
■ Full reservoir levei
1351 39 m
■ Storage aL full reservoir leve.
981 7 Mm1
* Dead storage level
1350 00m
■ Volumes at deao storage icvei
874 67 Mm
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•    Lt-ve storage
•    River bea level
*    Area at dead storage level
■ Area al full reservoir level *    Imgalion Demand
May 2007
137 OD Mm’ 1320.00 m 67 8S Km’ 72.07 kmz 194 49Mm3
Thus  boln ine above pnases  satisfy  contemplated irrigation with 60% reliability  in me phase I and phase II. me cropping palierns  envisageo are different However, for the linai design pi Deooesa dam. i| nps 1o oe based on phase if oevelgpmeni wiin ine above oam features  il the development is for imgalwi only
14.2 The sub basin modeling
When the aspect pf the development of Dedessa Sue oasm as  a whote. including ihe present proposal of Dedessa dam. is  laken for considerations, the need for the simuialion of the sub basm peoomes  relevant The del ails  end components  of sucn sub basin simulation modeling could t>c for me following objectives
■     To  explore  the  possibility  of  power  generation  at  Deoessa  aam  Since  only  a  small (ractior  of  the  total  inflow  is  io  be  jsea  for  irrigation,  looking  at  power  development options at the siie by raising the nam height rs an important consiaeranon
■    In  such  a  scenano  as  above,  thai  is.  full  scale  upper  optimal  development  gi  Dedessa dam,  it  becomes  a  necessity  to  check  that  this  optimal  water  abstraction  does  not jeopardize  future  developments  in  the  whoie  ol  the  Deoessa  sub-basin  This  requires basin  modelling  at  a  larger  scale  considering  contemplated  developments  upstream  ana downstream
in this report simulation exercise has been carried out to aadress the first objective A tailor made sub basin modeling was cameo out by developing a Fortran source code named
Aijosim to quicxty undertake simulation exercise ol vanous components with alternatives
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_
_________ ________________ —
14.2.1 Power Generation in Dedessa Dam
The  Oedessa  aam  with  its  please  II  configur
atio
n.
cou
ld
irrigate
I3
700ha  ar
80  n
r c<iabiilF
Since,  left  and  ngnl  bank  mam  canals  take
off
fr
om
me
dam.,
no
incidental
power
can  d^
generaced as such. Hence, power tJe^efopmenc options are sought by raising ihe da nr height .□ nave additional storage for separate power releases. The FRL for optimal phase II irrigation development is  1351 39 m. Two scenarios  for Higher FRL values  are considered with FRL ol 1353 m. and 1356 m For each FRL consiaered lour different power release options  are taken up for the simulation as  depicted tn Table 14 1 ft should be noted mat the given releases  are total monthly  releases  for irrigation and hydropower That i-s, the given tola! releases  less  the monthty i rngarion requirement shall b e used 1 or p ower g enerauon I here will o e a s epara le outlet for power al the same level as thai of irrigation outlet, that •$. ai 1350 00m
The reservoir charactensiics at the two FRLs considered for the simulation are Full Reservoir Level = 1353 m
* Storage al lull reservoir level
•    Live storage
•    Deac storage level
■   Volume at aeao storage level
■   Area at full reservoir ievei
Full Reservoir Level = 1356 m
■ Storage al full reservoir level
■   Live storage
■   Deaq storage .evei
« Volume al deao storage ieve:
■   Area al full reservoir level
1093 51 Mrr3 217.33 Mm3
1350.00m 074 67 Mrr’
77.83 krr.J
1341 16 Mm3
46B 49 Mm1 1350.00m
874 67 Mrr’ 87.85 km2
93
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Miy 2W7
The effective turbine center was fixed ai 1322 00 m elevation This or course. needs to oe toahzed 99 per ground wnditan ano dam head jot otherwise, omer kicaton based powerhouse aiw. me plant factor adopted in the bufc  simulation runs  te onfcy  and with unrestricted instated c apacdy B ssed on a ctuai D Jdg&t ano power requirement a nalyvs o y Hydropower and Dam design engineer lhese msiaiied capacities could be changed or power generator, could ^e *esincted The results presented m the Hydrcnngic-ai simulator, are witn lhese assumptions on turbine center level and plant lacier However, ai deta led design singe with Lhese *irmed up Figures, die Sub ba&m models wuio be re-run in shon lime
The power duration curves lor the vantius runs are shown m Figures '4 1 (al) 10 14 1 (b4| These iigures  are useful io reckon the monthly  power generation al venous  exceeoanee prcoapiiily  -evcls  at proposed FRls of 1353 and 1356 With respect to annual energy production the resuiLs are prasented in (he Tahte 14 2 for Dedesse dam. This pfture of energy generation is after satisfying irrigation needs fully al B<]% reliability However the quanmm oF energy and power are of nol very detractive type.
14.2.2 Optimal Power Generation
With FRl upto 1956, as seen above, ihougn imgalum h successful, the power generation scenario is no* atdadtvi i-ience thE Simula ton moaei Aniosim' was slightly recoded lor
maxing simulators (or -ncreasea FRL considerations eno expionng inc possib'hly or power generation at a higher ievCi Though the exerc.ses are oeyond the scope of Che present TOR A Large numoer of runs ot Aqasim were undertaken under 3 different domains of preposilion These are
Domain 1 seeping the power outlet at a lower lev&o! 1346 m and increasing tne FRL in stages, with rdnout monthly power release patterns
Dmmd   2  keeping  lhe  power  oullel  at  1346  tn  and  increasing  the  FRu  in  Stages  as  aoovt  Pul with model in bui'l decision support based power releases
_______  D4
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Maj 3007
Domain 3; Keep.nS lhe power outlet * the «nw bevel » tnai of irrigation outlet [Q( course a separate power ouUei) and increasing (he FRL m stages. with decision support Jasttd powo releases b> ihe model
Domain 1 Simulations
a sei at 12 afferent runs were atunipted within th* FF?L ranges from 137G to 1376 m. and with drived menihiy power release pattern. Borneol the optical ones are
i. With FRL 1370, the 97% power is 11.22 MW
■ Witn FRl 1372, the 97% power is 13.3QMW
lii With FRL 1374 me 97% power :s B62MW
Beyond FRL 1374 mere were no encouraging improvements m power generation
Domain 2 Simulations
These runs ipLaimg in 10 were made wtin decision suppon cased power releases in built in rhe model This obviously increases me power generation tor me sei or FRLs The opiifnai runs inpicaieo me following situation
i Mh FRl 31 1372. ihe 97% pgwer is 1B.49MW
ti Wuh FRL at i3?4 rhe firm power is *7 2QMW
iii With FRL Ht 1376, me firm power is 17 90MW
,¥ With FRL at 13170, me firm power is T9.50 MW
Domain 3 Simulations
Here in aodiLcon to decision support power releases, the outlet was best ai 13S0W instead of 1346M aeopled in the previous domains This improved the Situalron Same ol the SBiieni model runs yielded the fo'.owing scenarios.
3 At FRL 1373 the iim-power at 97% 15 17MW li At FRl 1372m, the 97% cower is IB 1MW iu At FRl. t374-n, ine97% poweris IS &5MW n AL FRL 1376m, the 97% power is 20MW
•>5
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14.2,3 Reduction Ln flows at Dedessa Sub’basin
in «ilhar oi lhe cases  covering 8 oms  of simulation, that u no netrimer-tai effect on foe downstream f Lows ol Dedessa sub basm The maximum consumptive utilization is only for
irrigation winch is only 104 49Mm  annualty, as tne additional
3
releases made 1o* power are no:
J
for consumptive uses  The power releases  flows  downsiream Thus  a net reduction >r the
subbasin Hows will be up La a datum ol *95mm . even wilhout accounting for any regeneration
irom irngaiion The sub basin ol Deoessa contributes al its end annually to Atobay a auualum
Pi i4,033t™r3  (6CEDM Master Plan study) This will gel:
reduced to 13,838mm  because ol me
1
proposed ago Deacssa project, whtfih is only a negligible reduction of ' 39% As such ine Ajjo Deoessa Dam proposal is not going fojjaOpfifdljK tne overall developments of the sub basin cons dwing vancms .deniiKec projects of me sub oasm
14.2.4 Conclusions
The simulation runs cau.d be made tor runner difforem scenario. A1 1*hs stage, it coutc de satd that me optimal power generation would de wnh FF?l at 1378 m and with power ouifoi al 1350 m. The tail race rs assumed to pe at 1322 m in an the runs. With a plam factor pt 0 6. me installed capacity coula b e arouno 33MW H ybTDipgtcally. 1 ne simulations c an be porformeo lunner without any constraints, provided met there are no geoiogitai. gepthechniGsi, design environmental social arm tuber cansiramis  The power generation at different reliaaifity paroemagas are shown tn the Figure 14.2 tor tne last run
However io lorm jp power generation even at higher FRLs. a prefeasibilrty sluoy ifi required 1pr expionng the poss-bitiiies ot increasing the height ol aam and establishing tne technical feasibility ana economic viability tex generaltor ot hydro-power
%
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Hay 2W7
Table 14.1:      Total Monthly Release (Irrigation plus Power} options for various FRL values considered
Options
FRL = 1353 m
FRL = 1356 m
Optwrn         75 Mm' lor all months           Twice ol monitiLy irrigation releases
Ooitor 11
75 Mm  - May to
3
September 6 50 Mm  -
3
Ocl loAoril
Opton Lil
75 Mm -May to September £ 40 Mm} -
3
Three limes monthly irrigation Feieases
100 Mn?for all months
Oci toApnl
Option IV      150 Mm ' May lo August £ 40 Mm’ - Oct. Io Marcn 75 Mm  m Sepi £
__Aprt        __  __ _____
1
75 Mm - September to Apnl £ 100MCM - May. to August
Table 14.2: Annual Energy generations at Oedessa dam for the various options
FRL              Release
Annual Energy Production (GWti) at Exceedance
Prohabilily Levels of
Scenario       Options
Mean
50%
75%
90%
95%          97%
-evei
1353 m              1
32 0
32 3
29 .B
27 3
25 2          220
II
260
28.9
26.5
24.3
22.7         20.5
111
253
25.9
25.5
22 9
21 3          196
IV
43 6
44 7
43 3
40 1
36 3         26 3
1356m               1
11-fi
12.0
11.9
n.a
II
24 5
11.7          117
24.5
24.3
ill
24 0
540
23 8          23 6
55.2
50 6
SV
45 9
47 6
48 5
42 9         39 2
47 5
43.0
.
40 9 38 1
_____ -J
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(0 1) Power duration curve for FRL = 1353m - Option I
\3.2) Power duration curve for FRL = 1353m - Option H
{a.3) Power duration curve for FRL = T353m - Option III
Water Works Design & Supervision Enterprise
In Association with tnismuiinemal Consultants and Technocrats Pvt LidIkdessa Irrigation Project Meteorological and Hydrological Aspects
M^y 2007
p 4j Power duration curve For FRL - 1353m - Option IV
(b.1) Power duration curve for FRL = 1356m - Opt*o,n i
fb.2j Power duration curve for FRL = 1356m - Option H
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liar
(b.3}       Power duration Curve for FRL = 1356m - Option 111
(b.4) Power duration curve for FRL ” 1356m - Option /V
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kArjoDeihtok IrrUJUhtt Project
Meteorologic al and Hydrological Aspects
15. RECOMMENDATIONS ON TRAINING NEEDS
Vir W
11  is  very  neartenmg  development  thM  the  water  resources  exploitation  to*  opitrna  ’  ia towards  economic  stabihly  is  getting  me  major  thru  si  m  En^op**  i/Vrfh  pnase  o<  ac  * soon  me  ncfi  wer  basins  will  be  impounded  in  deferent  storages  associated  wff  -  a  r   w  >_ runoff  the  over  schemes  eilher  tor  irrigation  or  power  or  in  a  multi  objective  sens*  As  suet
the  present  scenario  the  hydralog  ica-i  planning  and  design  are  in  me  usage  Howeve  w  * me  basins,  in  the  near  future,  become  stuffed  with  mar-y  projects  then  Che  real  r  me  operated oi  most  projects  will  be  me  dire  necessity  JuCkc^al  operation  of  a  mum  reservoir  project system  has  a  lol  oi  benefits  in  combating  floods;  tiding  over  drought  reduction  w  waiwr  osses and   others   However   such   real   nme   operation   would   require   a   complete   Knowledge   ih® hydrological  sense)  of  the  basin  system,  and  hydrology  and  simulation  techniques  S'mylatKXi coupled  wim  optimization  mooeis)  Such  a  scenario  oi  real  lime  operation  wiu  nave  to  oe oacKeo  up  by  flood  forecasting  networks,  aovance  prediction  oi  seasonal  i-amta^  adequate telemetry  (lor  transfer  oi  data),  oeoicated  computers.  telecommunication  soft  ware  m  addition to  subject  matter  <  hydrology,'simulation)  software  The  personnel  heading  sue*"  operations  r   a easin and those workrng in suer- a team need io be trained in the above mentioned asoect se as 10 u nderWte o peration which has i mmerse a du enrages h ence it is r eoommenoed t *a' expens   on   Hydrology   and   Hydrological   modeling   snoukl   be   identified   for   undergoing   such trainings  in  InsiituUon&'unrversities  m  appropriate  countries  Though  there  could  be  many  such institutes.  the  consultant  leete  for  such  multi  system  operation  adequate  expertise  is  available in  countries  like  U  SA  and  India,  where  many  institutions,  Jniversilies.  River  oasm  authorities, and  research  stations  could  be  identified  for  offering  such  trainings  Such  ironed  personne' with  expertise  in  hydrology  will  be  able  to  hea<j  luture  nver  basin  authorities  optimal  "ea time operation of (he systems
IN
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Meieorologlcal and Hydrohitlral H’^rii
references
*•»
Admass      Gebfjyehu      19&6      Region      a-      Ar      ..tlys't      ■»      StF*      A&Cw*♦      1 m Ethiopia lUnpubbsned Oran Report August 1 -J
Admasu GeMyertu 19S9 Regional dood Ffogue*-1- . Ana *’■ ■ ' ' ■ Technology. Bulletin Nd TRlTA VB' 1J|d J *'
‘ ** . *- m ***'■''
BCEOM 1999 Abbay River Pam Intonated Oi^'-JP",nr'' Matter p:an Pro.................................. " m -           - ■ *> Colled-on  Site  Investigation  Survey  ar.g  Aral/S-S  Section  h  ><cl'y.»  Si  x'  <J    > Volume in Water Resources Pan I Cl.matoingy and Part H ■ Hydr >iog.- B_t JV
French Engineering Consultants in associjl nr with 1S4 i BRGM ERA (Ethiopian Reads Authonlyt. 2002 Drainage Design Martu.r Hnlrotoc*
FrtMes D. 19?7 Flood ealimglipn 1or small East African n a calcnmen-t^ Pr&- - ? ■■ .■
JftgWu6wi nf Civii Engtneors, Pari 2 63 21 i 11 r
1
1
Gray. DM Editor in Chie< 1971 HadtTboo* on fho Punrjpw, ■.■» tw * Haar. CT 1977 Statistical Methods in Hydrology The (owa »«• Unewsity 
Aw
HersfieW   DM   1961   Estimating   the   probable   maximum   precip   tai-or   ASCE   i-tydi   D»v   f No HyS 99 116
MataiHS  N.C  196-J  Probability  OiSlrtthJ  I  K)n  ot  Low  F  tows  Stalahcal  Studies  •  Hvdm*xj- Geai Survey Prof Paper 4 34-A
Snaw Eluabeth M igea Hydrology in Practice Iniemationat Van Nosttend Re*oho*C USSR (Ifnilen Slates Department oi the Inferior Bureau ol Reclamation 1. tgfrt i and aod
Waiir Studies or the Blue Nile Basu- Ethiopia Appemjn lit ■ wydranjgy WAPCOS (Waler and Power Consultancy Services (India) Lid '■ 1990 Preliminary VS ate*
Resources Development Masi er Plan lor Ethiopia Fmai Report V C4ume ill Anne- A H^njiuyv & Hydrogeology Acktis Ababa
Waterworks Design & Supervise tnterprisp
In Asiofiaiion Wilh InEtrtvnUneatal CtMvkutt urf TKhnocrw PvtV
V
M
M
N
I M
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M
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Arjo Deflessa Irrigation Project
M^eorological and Hydrological Aspects
ANNEXES
Annex A Results obtained from the Meteorological Analysis
Al Eslimateg Mean Temperature al Arjo Dedcssa Project Area ■ in Cj
/ear     Jan      Feb    Marcn    April    Ma     JuW       Ju.     l. y    AA ... dy    Sept     Oct_
-____ my 4Cir_
fclAi
4
IMO*     Dec
1961    222        2i a      24 7     24 Q     23 2     71 4     20 7    20 2     21 6     22 0    21 9     19 7
1962     200      21 8      24 9      22 5     23 2    21 0    EC 0    200      21 3     22 1    20 2     190
1963     21 7      23 2      24 3       163      159     21 &     2i i      20 6     21 4     2i 7      24 6    21 3
1964     21 7       229     25 4      24 6     23 7     21 5    26 4     20 4     21 4     22 0     2i 5      20 b
1965     21 5           8       24 8     24 8     23 5    21 6     2i 3     20 8     21 5     22 4     23 2     20.5
1966     22 7      23 6     25 3      24 fl      24 i     21 7     21 J     20 8     21 5     22 3     22 0     16 6
1967      195      22.5      25 i      24 a     23 7    21* 2   20 7    20 5    21 3     21 1     23 0     ia r
1968     19.9       224      23 6       245     24 1     21 6     21 6    21 i      2i 2      21 4     2i 2      196
1969     22 4       23 2      25 1      24 6     24.0    22 0     20 7    20 7      21 5     21 7     21 2     ’6 9
1970     21 5       229     25 0      24 9     24 3    Z2O     21 4    20 8     21 6     22 8     19?     10.2
1971      2i 8      20 4      23 9     24 7     23 7    21 a     21 0     19 9      2i i      22 4     2- r      IB.2 i
1972     21 8      23 1       24.2      24 5     23 2    2i 0      21 &    21 3     2i 6      Z2 3    22 8     20 2
1973     22 7      22 6     25 8      26 8     24 1     2i B     21 3    £0 0      21 5     21 7     21 7     174
1974     21 2      23 3     25 3      23 9     23 9    21 B    20 8     21 3     21 3     21,2     19 1     19 0
1975     21 O      23 B      25.9      24 8     23 7    21 7     20 5     20 2    2i 3      21 9    20 4     10 9
1976     20 6      23 0     24 8      24 3     231     21 0     21 0    20 8     2i 6      22 4     22 5    197
1977     23 0      23 5     24.9      25 3     24 4     2 ■ 4    21 0    2i 3      2i 9      23 5     23 0    209
197B 21 1 22 6 26 1 25.6 23 8 219 20 9 21 2 21 1 22 3 20 9 20 4 1979 22.2 235 24 7 24 2 24 2 21 9 21.3 21 6 22 0 22 3 23 6 20 9 i960 22 3 24 ■ 26 1 25 H 24 4 22 3 2i 1 20 8 22.0 22 0 22 0 19 5 1981 22 * 22 6 262 25 1 24 7 22 3 20 6 21 1 2i 5 22 0 2i 6 192 19B2 227 223 23 8 24 9 23.5 21 9 21 2 20 7 2i 6 2i 8 23 0 20 6 1963 20 3 23 6 26 1 25 6 250 228 223 21 8 21 7 22 4 22 3 166 1984 2C6 20 6 25.4 20 2 24 5 2i 9 20 9 20 7 2i i 20 2 23 4 20 6 19B5 21.5 22 9 25 7 25 1 24 0 21 7 20 5 20 4 21 5 21 5 22 1 19 7 1966 21 5 24 7 23 9 24 5 24 6 22 0 2i 3 21 1 21.2 21 7 22 0 20 4 1907 2i a 23 0 25 4 25 1 24 2 22 6 22 2 21 6 21.9 231 22 7 202
19BS    22 4      24 5     25 1      25 8     25 3     22 5     21 3    21 6     21 9     22 5     20 6     10 0
1989     21 3       22 3      24 5      24 5     23.3    21-9    21 3    2i 6      21 7     22.0     71 9    21 5
1990     21 0       2’ 9      24 8     25 1       iaa     224      21 4    21 4     21 9     22 1     22 4     20 9
1991     23 0      23 6     25 1      25 1      24 6    226      21 3    20 8     22 0     21 4     21 d     16 2
1992     22 1       24 1       25 2       25?     24 6    22 3    21 1     21 3     21 8     22 7     21 8    21 3
1993     22 6      23 5     24 3      25 6     24 4     22 7     21 4     21 4     21 8     22 9      2t 7     196
1994      2 <       24 2      26.8      24 9     24 3    22.3    21.1     21 5      2i 8     22 0     23 3    2Q.0 1995      ??3       24 5     28 4      26 5       M3     33 i      215     22 1     22 3     23 0      233    222 1996      226        24 t       26 3      25.9     24 7    21 9     21 7    21 8     22 4     22 4     22 0    20 2
1997     23 4      22 4      26 9       255     24 4    23 i      22 3      223    23 2     24 0    25 i      22 9
1998     24 6      24 9     27 4      27 7     26 2     23 4     22 4     22 3       23 ’      24 2     22 0      ’9 i 1999     21 9      22 A      26.2      26 3     24 9    22 B     2i 6     21 3     22 9     23 5      2i 0     19 8 2000     21 6       22 9       26 5      26 6      25 5      226    31 9    21 B     23.0    24        23 5    20 0
2001     23 0      24 3     26 0      26 4      255     23 0    22 0     22 2     230     24 2
2002     23 2      23 6      269      25 9     25 8     22 8    22 7     22 2     22 S    23 3    £3 T     22 7
23 6    21 6
2003      2i 9       24 5      284       25 7     25 8     23 2     22 0    22 2     22 7    23 0     23 5    20 6 2004     24 2      24 2      262      26 5     25 6     22.8     21 5    22 1     22 5    22 5      232    21 8
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May 2007
A2:      Estimaleti Minimum Temperature at Arjo Dedessa Project Area .in Cl
Year Jan Fen Match A. nl MP. June July Aug Sepi Oc i NOV Dec iSfii 97 10 5 13 6 14 7 14 9 14 6 14 7 14 3 14 5 13 0 103 8 0
1962       08       W 5      13 9      130      15 0     14 3     14 2     14 2     14 4       130       9 S         7 7
1963      9 5       11 2      13 6       99       10 3     14 7     15 0     14 7     14 4      12 0       116        8 6
1964       95       11 1      142       150       153      *4 6     14 5     14 4     14 4         13        10 i         0 5
1965       94       106       *39       15 1      15 t      14 7    15 1      14 7     14 5      132       10 9        6 3
1966      9 9       11 4      14 2      151       15 5     14 0     15 2     14 7       4 5       132        to 3         76
1967       85       109      14 1      15 1       153      U 4     ■4 7     14 5     14 3      12 b       108        7 6
1966      a t      ’08        13?       150       155     14 7     15 3     14 <4       14 3      12 6       100        8 0
1969      9 0       n 2        140       150       155     14 9     14 7     14 C     14 5      12 8       10 0        6 9 1570       94       11 1      14 0      152       t5 ?      149     15 2     14 7     14 5      13 5        9 3         7 4
1971       9 5       9 9        134      15 1      15 3     14 3     ■4 9     14 1     14 2      13 2       102        7 4
1972       94       n 2       13 5      15 2     14 9     14 3       ii 4     15 1     14 6      13 2       108        8 2
1973
99
10 9
14 4
16 3
15 5
14 8
51
14 7
14 5
;2 a
10 2
71
1974
93
113
14 2
14 6
15 4
14 B
14 8
15 1
’4 3
’2 6
90
77
1975
92
31 4
14 5
15 1
153
14 6
14 6
14 3
14 4
12 9
96
77
1976
90
11 6
13 3
14 8
14 9
14 3
‘4 9
14 7
14 5
13 2
106
80
1977
W1
It 4
14 0
154
158
14 6
14 &
15 1
14 6
13 9
108
85
1978
92
11 Q
14 6
156
15 3
14 9
14 fl
150
14 2
13 2
9 fl
03
1979
97
11 4
13 fl
148
156
14 9
15 1
15 3
14 B
13 2
10 2
a5
i960
90
T1 7
14 6
15 7
150
ii 1
15.0
14 7
14 8
’30
ID 3
79
mi
90
10 9
14 7
153
16 0
15 1
’4 6
14 ft
145
130
102
ra
1982
99
10 6
13 3
15 2
15 1
14 9
15 1
14 7
14 5
12 9
10.8
84
19B3
fl 9
11 4
14 6
156
16 1
15.5
156
15 5
14 6
13 2
10 5
76
19&4
90
10 0
142
16 0
ISO
14 9
14 8
14 6
14 2
ii 9
11 0
84
1965
94
11 1
14 4
153
15 5
14 0
?46
144
14 S
12 7
10 4
80
1956
94
120
134
150
15 0
150
15 1
14 9
14 3
12 8
10 3
6.3
1987
95
11 1
t4?
15 3
156
154
is.a
15 3
14 a
136
107
82
198S
9B
11 9
14 0
157
T0 3
153
15 1
153
14 0
13 3
97
76
1959
93
to a
138
149
iso
14 9
15 1
15 3
14 fl
13 0
10.3
8 fl
1990
97
106
13 9
15 3
12 0
152
152
152
14 8
13 Q
10 6
85
1991
10 I
11 4
14 0
153
159
15 4
15 1
14 7
148
12 6
10 l
74
1992
97
T1 5
14 1
104
i5 8
15 i
150
15 i
14 7
134
10 3
1993
99
11 4
136
H5
156
157
15 4
15 2
15.2
14 7
1994
13 S
102
79
9.5
11 7
ISO
152
15.7
152
ISO
152
147
13 0
HQ
1995
B1
9B
11 9
140
16 2
16 3
15 7
15 5
1996       99      11 6      14 7      156      160     14 9    15 4     15.4     15 1      13 3       104        82
1997     10 2      108      15 1      156       »58     15 7      158     is a       155      142       11 0        93
1998      lOB     12 1      15 3      169      169      159      159     158     15 6      14 3          10 3       7 R ’999      9 6      11 0      14 7      16.0      16 i      IS 5      154     15 1      154      13 9        99         B 0
2000       95      11 1      14 9      16 2      16 4     154      156     15 4      155      14 2      11 1        0 d 2001     10 1        ii fl      146      16 1      165     15 6    15 6     157      15 5      14 3      11 1       0 8
2002       io?      11 4      15 0      15 fl      16 6     15.5    16 1     15 7     154       138       109        9 2
2003       96      11 0      14 0      15 7     16 7     156     15 6     15 7     15 3      136       11 0       fl 4
2004      106      117      14 7      162      165     • 5 5    15 3     1ST     15 2      13 4   _HL?          88
Water Works Design & Supervision Enterprise
Ln A^cciadcn wna Inicrrcntlnenul Consultants arm TKhnocniU pvi Ltd
15 6
150
13.6
11 0
90<Jj<* DfStwa Jrn;a LI on Project
MetEprolaRicaJ anil Hydrological Aspects
A3:       Estimated Nanmurn Temperature st Arjo Drdessa                Project Area (in QC}
tear      Jlari     '*■ ''I    Match    ApflF    Ma ■    June     July     Au9      serf        (Jd         NOt               Uec
1961 34 7 33 0 35 6 33 6 31 7 26 6 26 7 - 26 1
1962 3T 2 33 0 35 8 3i 6 31 B 27 9 25 8 25 8
24 4 30 9 33 5 31 4
24 2 31 1 30 9 JU 4
7963 33 *j 35 2 34 0 22 8 2' 7 76 a 27 2
1964 33 <# 34 7 36 6 34 4 324 2B6 75 3
26 9 24 2 10 6 37 6 34 n
76 4 24 2 31 0 32 9 33 3
1965     33 6     33 1      35 7      34 7     32 1     28 8     ?7 5     26 9
24 3      31 5      35 5      3? 3
1967     304      34 1      362       34 7     32 4     282     26 7    26 5
"966      IS *      35 B     36 5      34 7     32 9     28 9     27 6    26 9     2J 4      31 4       33 6       30 i
24 1      29 5      35 1       29 9
1968     3i ■      33 9      34 0        14 3     32 9    2B 8     ?? a    27 3     24 0     30 H      32 4       31 3
1970     33 6     34 6     36 0      34 0     33 3     29 2     27 6     26 9    21 4     32 11      30 2      29 1
1971     33 7      3i a      34 5       346      32 4     28 0     27 o    25 7     23 9      31 5      33 1       29 1
1972      336      35 0      ■U8      348      31 7     27 9    28 1      if 5      24 5      31 4       349       32 3
1973     35 4     34 7     37 1      37 5     32 9    7S II    27 5     26 9     24 4      30 5      32 1       27 8
19?4 33 1 35 3 36 5 33 5 32 7 28 9 26 fl 27 6 24 1 29 » 29 2 30 3
1975 32 8 35 7 37 3 34 B 32 4 28 9 26 5 26 1 24 2 30 0 31 2 30 2
1969     35 0     35 2     36 1      34 4         32 8     29 2     26 7     26 7     24 1     3C 6      32 4        2^0
1976
32 2
362
35 7
34 1
3* 5     27 9     27 0    26 9
24 4
31 5
34 6
3i 5
1977
15 3
35 6
35 9
35 4
33 4    2B S    27 1     276
24 8
33 0
352
33 4
t$?e
32 9
34 5
37 5
35 9
32 5     29 2    27 0     27 4
23 9
Ji 4
3t 9
32 6
1979
34 7
35 5
35 6
33 9
33 i     29 1     27 5     27 9
24 9
31 4
33 i
33 4
™
34 6
36 5
37.5
36 i
33 4     29 6     77 3     26 9
24 9
309
33.6
31 2
1961
35 0
34 2
37 8
35.1
33 8    29 6     26 6     27 2
24 4
30 9
331
30 6
1962
35 4
33 7
34 3
34 8
32 i     29 2     27 4     26 8
24 4
30 7
35 2
32 9
1963
31 7
35 7
37 0
35 B
342     30 4     28 8     28 2
74 5
31 5
34 1
29 8
1984
32 2
31 2
36 5
36 7
335     29 1     27 0     26 7
23 9
28 4
35 6
33 0
1985
33 6
34 0
37 0
35 2
328     28 9    26 5     264
24 3
30 3
33 8
31 4
1986
33 6
37 5
34 5
34 .1
33 6     29 3    27 5     27 3
24 0
00.5
33 6
32.6
'987
340
54 B
365
35 i
33 1     30 i     28 6     27 9
24 8
32 5
34 7
32 3
1986
35.0
37 2
36 i
36 1
34 8     299     27 5     279
24 8
31 7
31 5
30 1
1909
33 2
33 8
35 4
342
31 9     29 1    27 5     27 9
24 6
30 9
33 5
34 5
1990
32 8
33 2
35 7
35 2
25 4     29 8    27 6     27 7
24 8
31 1
34 J
33 4
1991
35 9
350
36 1
35 2
33 7     30 1    27 5     26 9
24 9
30 1
32 7
29 i
1992
34 5
36 5
36 3
35 3
33 6     29 6    27 2     27 5
24 7
32 0
33 3
34.0
1993
35 3
35 5
35 0
35 9
33 4    30 1     27 6     27 7
24 7
32 2
33 2
31 3
T994
33 7
36 7
38 6
34 8
33 3     297      27 3     27a
24 7
31 0
36 7
31 9
1995
340
37 2
38 0
37 2
346     30 8    28 2     28 5
25 3
32 3
86 6
35 5
1996
35 3
36 5
37 9
36 3
33 8     292     28 0     28.2
254
31 5
33 7
32 3
199?
365
33 9
368
35 7
33 4     30 8    28 7     28 9
26 3
33 8
M3
36 6
1998
38 4
37 7
39 4
38 B
35 8    31 1     28 9     28 9
26 i
34 i
33 6
30 5
1999
34 2
345
37 8
36 B
34 i     30 4     27 9     276
25 9
33 0
32 1
31 6
2000
33 7
34 J
38 2
37 3
34 B    30 1     28 3     28 2
26 0
13 7
36 0
33 2
2001
35 9
368
37 4
37 0
349     305     28 4     26 7
26 0
34 l
36 2
34 5
2002
36 2
35 7
38 7
36 2
35 2     30 3     29 3     28 7
25 8
32 8
35 3
36 2
2003
34 2
37 i
38 0
36 0
35 3     30 8    28 4     28 7
25 7
32 3
35 3
33 0
2004
37 9
36 6
37 H
37 2
35 0     304     27 8     28 6
25 5
3? 8
35 5
34 n
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Water Works Design & Supervision Enterprise
In Association wtui LniErcontmtnial CoiisuJianu and Technocrats Prt. Ltd5Dflflrtu lirMLUjn Fir-|. J
Meteorological and Kydralogtcal A'ipwte
Ad
EMimited
Rtlitiwe
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^ ji Arp
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Year
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pci .
1961
67
52
46
70
71
71
0/
07
62
AJ
Neu
60
O'
rT■j.
1962
77
69
64
73
fl6
05
94
94
96
95
1963
45
72
6J
a?
64
05
69
91
AJ
71
66
57
63
75
6?
83
BH
92
04
1965
67
53
50
68
69
76
63
65
84
02
*966
65
66
SO
71
73
76
M
>:
05
04
1967
65
M
57
56
76
91
9-t
0M
92
05
00        M 07        as 73        75 B6        ‘4 60       6 J
r
09       73
1966
55
66
54
66
75
Bi
00
85
69
BT
76
ft
1969
73
66
64
69
75
82
iW
3j
K**l
Bl-
1970
71
42
64
69
74
79
66
92
69
06
77
72
«
66
1971
SO
46
SO
64
76
01
67
07
07
197?
M
65
56
70
74
79
69
65
06
50
1972
&5
59
57
66
76
01
62
flq
62
1974
49
53
SB
70
di
90
yfl
93
M
6?
S3
77
72
75
63
63
1975
52
5m
Si
70
74
»3
06
93
90
04
1976
55
55
57
79
Si
92
9t
91
91
73
93
■6-6
62
1977
ft
6f.
56
57
66
11
0M
18
07
0fi
as
74
1970
56
ST
56
64
75
77
67
06
A4
04
1979
SH
65
61
64
70
77
64
05
Bn
79
75
69
55
07
196(|
SA
55
53
08
76
6i
86
B7
65
79
iBfil
M
46
56
63
72
76
B6
06
63
a?
t982
67
62
55
65
75
30
IB
90
90
07
75
77
06
65
79
1963
66
S3
Si
70
79
76
65
09
60
T9&4
W
49
47
61
76
SO
86
08
a-ti
74
tBB5
60
SO
Si
67
76
SO
90
as
67
61
62
62
77
72
75
TO
1986
sa
60
57
60
73
65
67
B7
M
82
1907
SA
56
63
60
79
Bl
63
09
86
65
73
79
72
75
1966
73
64
«
62
75
82
90
91
93
67
1969
S3
61
60
75
73
79
9i
66
9i
84
73
82
66
55
1990
67
70
62
66
77
6i
90
90
91
80
1991
68
65
60
M
74
63
90
91
»
62
ao
75
71
75
1992
66
57
54
69
79
34
90
94
88
in
04
79
1993
65
63
56
75
eo
65
09
09
90
»
1994
SF
53
55
67
71
fi-6
06
98
0A
75
82
BO
69
72
1995
iXi
sa
$7
73
79
90
96
90
92
04
61
79
1996
73
43
63
?3
ftD
63
69
07
01
1997
73
53
53
72
76
01
66
M
67
66
69
B9
70
80
1996
74
66
62
64
79
66
74
74
93
92
1999
61
48
53
65
76
60
90
69
92
2060
55
46
45
67
77
61
69
72
69
93
70
73
84
2001
67
57
5fl
69
67
M
61
90
91
92
69
06
2002
71
56
«2
64
71
61
d5
08
67
a-i
62
76
71
60
60
66
75
79
2003
65
ft
90
B9
90
@4
T
ZUCM
46
59
55
70
?3
76
31
07
09
69
91
76
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Water Works Design & Supernal on Enterprise In AalocliUnn wlUl Ijiierromlnrolii CansultEnu ,lnd TxtmKnK P\i LtdArjo IMessi IrTiEn'foa rtnj^l
Meteoroiogkai and llydrolot l
f r *sPPf fi:
.
-—
A5 EtUmaiM M*»n DiUy Sumion* OsMjtro<‘ it AJjo D*d»*w f r'Jlr ■1 *'•'
yin hrVfliy.i
tear Jan Feb Mar ch April
1961 83 ? 3 7 1 6.B
1962 6 7 b 9 82 7.8
1963 72 62 84 69
■964 96 fl 3 J 7 60
1965 91 fl 3 86 55
M.bJ __Ju__n_e___■_J,_J7__
L                     p’
A kJ
CM
5  90 4      66?5      4J. 93      6JO7      fi 1       6 5       7 6       7 5
9 1        92
X fl 9       7 4
73      44
38       5 8       6 0      9 T       fl 3
1966      7 8        fl 2       7 1        fl 5       7 9      5 ?       4 K       j a      tfi         9 2
8 7 58 30 3 0 6 8 9 1
fl J 34 -1 5. S 1 9 7 4
1971      9 2         76        7 5        7 3       7 5      6 I'       3 ’       4 1       67        7 9
1967 79 96 8 4 72
196B a r flO T 7 9 1
1969 fl. i 76 75 73
19?O 10 0 9 5 9 7 7 B
9 i 8 + 4 9 Sr 63 H 5
69 66 2 -1 J 2 5 7 6 5
7 fl 6 1 J? 4 1 62 7 «
94 SO 4 - J. 7 7 5 7 9
1972      92        8 B       7 4        94
90 IOC
fl 4 fl T
98 <3
76       1-0
10 t      8 3
a3       03
a3       83
B3      03
99 77
1973      9 5        fl 5        85        fl 4       10 1      7 3       32       4 1
8 3       64          4      a a       80         A?
T Tl
■ 'SI
95       9 5       90
1974        7 9        fl 1        7 3       6 7       9 1       59       4 B      4 fl       5 fl        56
1975      94         A3        75        64
1976      90         a 7        7fl        fl 7
1977      62         S3        66         72 1976      94         5B        75         7 6 1979      S3         65        60         70
i960 6 1 53 1901 95 es 1962 74 60
1963      80         76
1984     B 1        9 9
D t       83
84 92
67 J 1
7 4       5 fl       3 7      4 1       6 3       6 9       82       8 3
71 5D 3 1 i 6 4 1 7 5
69 7 1 3 7 4 1 5 2 6 ti
89       7 1
6 7       5 1      24        3 8      4 2       5 fl       7 8       r 5
7 8      6 1       23        J a       55       6 El
5 fl
65
74
58       36        3 9      59
79
78
aa
46
59
79
58       3 7       4 5      26
65
96
ra
83
65
71
68       39       3 7       6 7
75
66
73
71
80
66
78       54        3 8       56
66
84
82
ai
89
66
60       4 7       4 3       70
10 1
86
8i
1985
B6
?fi
75
68
64
59       28       3 1       5 8
76
67
78
1986
89
62
65
53
72
37       33       40      41
74
94
82
1987
ai
78
6 2        8 3        SB       56       4 9       4 2       7 4       7 8      B 3      H 0
1968
B4
76
9 5        04
a 3       70       2 7       4 9       55        a 5
102      9 i
1989
98
B4
73
72
96
73
37
5 1       S3
a3
B2
68
1990
92
49
63
33
54
46
37
39       59
96
B9
92
1991
B3
73
71
6B
54
85
43
62       9 1
92
09
74
1992
fi 7
69
62
7B
90
83
29
20      63
65
7 fl
75
1993
72
62
64
60
73
44
28
38       58
50
91
83
1994
96
fl 3
77
80
87
56
30
30      68
91
90
too
1995
91
S3
86
65
83
34
43
55       79
74
H4
8i
1996
?a
62
71
85
76
53
42
38      60
9?
98
83
1997
79
96
B4
72
91
fl 1
49
5?       83
a5
7 fl
90
1998
fl 1
60
r?
ai
88
80
23
37       57
65
W1
03
1999
«2
76
75
73
7 fl
6l
37
4 1       82
79
93
63
2000
100
96
97
7B
94
80
48
4 7       25
79
93
83
2001
92
7fl
75
73
76
61
37
4 1       62
79
83
93
2002
92
Bfl
74
94
a3
U
54
4 0       60
09
99
77
2003
05
B9
as
a<
10 1
73
32
4 1       72
95
95
90
2004
79
fl 1
73
6?
91
59
4H
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01
83
Water Works Design & Supervision Enterprise
In Asswi.nU on wiLh Intercontinental ConsurtAnls itnd Twhtiomta Kt ltdAxji> [#■ -di JrzlxAil' d I'rnj' l
M?U«rulo<kal and H»drolQrfi< al A-s^’1T
A6 t5Um*|Crt Mean Dally ETo of Ar o DfUlisj Projad
m*j 'tr
(
i m innu'da,
Year        Jan       Feb    Macrt     April      Mb, 1M1       an        3*1      4 4 I      4 26     J 73
1962 J 23 3 "5 4 btl 4 32 4 4 ■
1963 348 3 72 4 3 44 J ll'i
1964     3 95      4 18      4 65      4 66      4 .
•         J J j
3 49 . t»3 2 5 3 72 .1 €3 3 48 3 Sfr
1 f ; is 1 1 f>3 J 98 4 2* J 56
1
A.jg    Sept     (Xi        Nov    Ue*- j J           1     J 4 i     427      i tie.        24
J 4f        2 \
1966      364       4 22     4 47      4 73     4 35      34        ill/         3        J 7      4 31     J G9    3 15
1965     3HJ      4 J J     4 83      4 25     4 4 1     Z97      31
2 79     J 67     4          386      382 43    4 13     3 M      3 92     3 44
1967     3 45      4 44       4 77     4 45      4 6      3 95      3 i'j          32     4 22     4 .M     J 72     1 46
I960     3 53      4 06       4 5      4 64      J 1
1969      3 7i      4 D6      4 S      4 43
1970     401       4 *5      5 08     4 56     J 76
T971 J 86 39 4 49 4 49 4 74
3 7i 2 Oj 2 9 3 Mr 159 4 06 3 4
3 W- ; 91 306 3 72 ■ 94 3 7 A 19
4 >i-     4 1 4    1 54     3 28
1972 3 66 4 34 45 5 03 4 34 3 55 J 39 31* 4 ’ ‘ 4 23 4 2 3 34
1973 301 4 3 4 87 4 42 491 3*4 2 81 j it. 4 5 tf.7 4 4 01 3 M
j 49     2 93      3'Jt     J r-U       4        J 75     3 29
j fr       321
1974 358 4 18 4 S3 4 24 46>
1975 3 82 4 27 4 66 4 34 4 09
3 51      3 3      3 29     J 62     4 07     1 95
3 35
3 3     2 73     ■ M      3 7      3 87     3 64     3 49
1976     3 73      4 38     4 65      4 75     4 02     36B    2 93                  3 5      j ft ?
1          3 48      3 «
1977 34 3 85 4 34 4 40 4 24
t97B 3 65 362 4 64 4 7 4 39
3 46 2 9 3 1 3 H
+
3 67     3 06     3 52
1979     3 36      3 S9     4 18      4 37     4 08     3 3fi     2 64      JP7      3 3       3 5      3 64     3 34
3 57     2 56      3 W      3 M      3 74     3 *9     3 23
1900 329 383 4 21 4 39i 4 32
1901 3 78 4 2$ 3.W 4 U 4 42
356 2 93 3 05 3 7 3 96 366 J 44
3 53 291 32 2 W 364 401 33
1982       36        3 74      4 53     4 32     4 13     3 77     2M       ?98     3.67     3 86        4 •     3 a
1903 3.54
1984 3 58
4 14 4 55:
4 31 4 73
4 76
502
4 15
4 08
4 08
3 55
3 43 3 03 361
3 14 3 11 3 67
37
43
182
J 96
332
34*
1965     3 73
4 04     4 59
4 36
3 03
3 53
2 M      281     3 63
386
3M
337
1986     3 43
V04      4 31
4 03
4 22
304
2 85     1 oe     3 22
3 82
4 0*
346
1907     3 67
4 M      4 31
4 ?4
3 83
35
3 27     3 18    4 Dfl
4
3 83
3 96
1988     3 76
4 2       504
462
4 5M
3 78
2 71     3 34     3 59
4 17
4 02
3 48
1989     3 72
4 18     4 42
4 39
4 64
3 ft!
2 97    3 36      3 rr
4 06
3 74
3 24
1990     3 82
3 38      431
3 57
3 35
325
2 92     3 07     3 69
4 37
3 92
3 6?
1991      179
4 05     4 43
4 31
3 82
3
306     3 59    4 49
4 22
:i m
3M
1992     3 4?
3 94     4 71
4 82
4 85
3 63
2 73     2 59     3 78
37
3 81
J 38
1993     3 M
3 75     4 68
4 29
4 25
321
2 72      304     367
4 OT
3 »i
14
1994     3 B4
4 3       4 79
4 65
4 55
35
2 75     2 63     391
4 26
4 06
3 75
1995     392
4 34     4 9b
4 34
4 53
2 98
3 11      352     4 21
3 94
3 92
J »
1996      M4
429      4 57
4 88
4 37
3 35
3W     3 03     3 77
4 31
4 00
3*6
1997     3 77
4 43     4 85
4 46
4 65
40/
323     3 46     4 41
4 32
39
3 85
1998     391
4 33      46
4 03
4 24
3 85
266      296     3 74
383
4 12
3 36
1999     3 68
4 t)J      4 67
4 57
4 36
3 63
2 96     3 M     3 63
4 11
37
3 42
2000     4 03
4 45      5 24
4 Jfl
4 86
4 15
3 31     3 35     4 19
4 16
3 92
35
2001      1 78
4 21      466
4 64
4 42
3 65
2 96     3 16     3 84
4 19
3 92
3 57
2002       4
4 39      4 75
5U
4 59
3 71
3 46      3 4       *29
4 34
4 24
3M
2003     3 75
4 49     4 92
4 62
506
JBB
2 85     3 16     4 08
4 47
4 If
363
2004     1 84
4 28      4 5B
4 51
4 83
36
3 22     3 35     3 72
4J1
2 06
3 6i
:A
Water Works Design 4 Supervision Enterprise
In A^nrlatlon with Intareor tinentaj CotuuJtvUa ind Tecbhocral* pst LidArjcDedcssa IrrlcatlOQ Project
MfiEeonologicaJ and Hydrological Aspects
A7:     EXllmufldi Mtin Ma ntMy ETo pf ArJO DedesSff PrOJect Area (in mmJmonth?
------- — J __________ — -   -—■ r ■ * Cafli Nov Dec I AnOiJsl
Year Jan I
May 2007
116
IDO
108
no
105
104       99
104    145       103      104    93 2     64     92 °
139      128       nS
144 130 137 105 01 6 ?7 4
133
H2
109
112
124    127
85 6       ns     132
no
11&
122 117 144
119 110 150
140       140     104    84 3
116
124     120    118     107
114      110    H8       142      135     132   95  1  93 i     111     134    123     104
128      137      89     95 2    106
107 in
ns
■124 It3
«2O 118 ail H8 116 105 ii9 104 102 li7 112 HO 111 116
124     148       133     143      110    97 7    103    127     125    111     107
114     140      139     127     111     814    69 9     108
114    140      133      133
107    90 i    94 8
124      157      137      14&      120    90 4   99 7
112
122
111 122
122 1-11
125 10?
IDS
99
102
109 172 120 117 :20 123 106 igi 109 119 105 116 121
139      135      132     105    90 8   93 2
111     124      113     102
140       151       135     106     105    102     125     131    126     104
151      148      152     115    87 2   95 9    119     134      120     104
140       127     143     105    102    102      m
125   56 6    104
144       130-      127     99     84 7   75 7     95      120      109     108
135
144
143 125 111 90 8 94 8 105 115 104 105
135 132 104 90 98 113 120 116 109
141      136     107
942      106    116      114     100
130 131 126 -01
130 132 134 107
00
gi 9
909
90 9
1T1
124
14’ 140
123     122
95 3
94 5
99 2
925
94
m         109
123
124       137     106     90 i
86 5    113
HO
120
104
1D7
102
Ida         129       128      113   92 3
116    120    105     102
143
108     115    ns
151      127     107
tO6
97 4
966      116    133    120
103
107
n3      142
122     106     84 1    07 1     109    120    116     103
106 110 134
114 116 134
131
121
U2
131    91 3   382    95.6    95 5    118    120
119     105    101     98      122    124
ilb
107
123
117       110    156      145       142      113 115      117    137      132      144      n5
842       103     108    129
121     108
92
105      113    126     112     100
116     94 0    133
:37
107
129
104     97 4
906      95       111
117       113 106       no
118     112    94 6    in
135
146      139      144     109    84 5   80 3      113
136 117 114
131 115 964
115 108 105
110       105      145      129      132    964
94 3     1T0    127    117     105
122      120      149      139      141
117    132    122     116
122
1,14
117
121
121    154        530
120 '24 ijl
142
153
149
”47
140
135
84 4
65 2
96 4
95 8
100
126
113
122 110 111
134 123 107
134       144
IDS
29 4
1Q1 122
87 0
109
&4
107
132    134    117     119
146       132    115    07 6   91 9    112
119    124
■ ’4     114 ’24
117       ns 124      123
145 137 135 1.09 924 963 H5
162 144 151 125 103 104 126
127
129
111
US
144       139
137     110    92  4     98      115    130    ns 
147
l-§4
I 4?      111    107      106      129    135
116
Ti9
- 26
153      145       157      117    00 2       98      122
T39
127
126
120    142        135     150      108     100    104    112
130 61 7
1Q4 106 109
in no
112 112
i
1300
1303
1420
1410 1408 1444
1353
1369 1466 1366 14 66 1464 1346 1332 1375 1362 1359 1299
1343
1338 1 358 1401 1432 1349 1320 1412 1443 1408 1318 1411 1160 1355 1437 1439 1425 1505
1419
1402 1518
1429
1515
1498 1393
Water Works Design & Supervision Enterprise ’
In Association with iTicercoililniEntai Coasultanu and TBchnocrats Prt Ltd.k^Tjottedessi Irrigation Project
Meteorological and Hydrological Aspects
A8;: Estimated Mean Monthly Rainfall at Arjo D&dessa project Area
May ZOQj
J*n               March       April      May    June      July        Au^     Sept      Oct       Nov    Dec       Annual
196?    156    0      96 3     21 7     172     172     140     ?20     ?20   111 5    151    D 12       1320
1968     □    57 6   0 75     36 4    93 0     169     186     207      192    90 9?    21 7    145        1070
>969   37 7 35 9   53 7      140     121      144        159     212      IBS    56 39    7 39      0          1132
1970   2SJ   30     51 3     21 2     149      154        249     162     256    107 2   4 44   4 CM      1217
1971 T1 3 0 32 20 7 30 8 142 193 180 135 262 *88 2 32 3 14 1 1210
1972 156 11 1 15 89 T 53 166 106 157 170 49 48 69 9 24
1973 0 9 97 5 66 294 236 155 166 233 -43 50 82 12 2 5 77
l9?4 3B 7 798 31 0 5 14 2fl7 205 242 166 212 72 7£ 4 02 16 7
1975 23.5 55 1 21 1 60 4 116 124 189 159 -41 131 3 11 5 12 5
930.6
1075
1292
1045
1976   23 7 16 2   90 3     55 B    154     154     192     215     273    aa 6b      36     5 37        1303 T37B     3     3 5    66 5      103     122     154     206     206      1BI    122 6    0 50    12 5       11B1 1979    15 6 8 E9     17      25 6    97 5    202     235      159     154   64 94    312    12 5        1024 19BD   15 6 178    57.3     110     164     100     136     176      246    49 87    20 7      0          1 no *961    156  8 23   27 6     35.6     149     213     296      270      177    1139     57 2      0          1362
1964      156    0      31 6     69 a     234     249     4-43        19B     230    0 716    26 e    5 77       1514
iws     2 79    0       123       ros     257      341        242     212     315    48.2     32 5    37 7        1607
1966     □    39 2   46 9     56 4    37 5    3T5     274     244      191    iwa       359    0 46        1345
1967   2 89 172     886     79 9     123     2B2     488      328      183    1164     42 3    34 3        1785
1988   14 1 42 7    74 3     15 3     335     325     177     297      343    259.9     154    3.87        1903
’989    26 5 26 7    76 3     106     245     284     316     332     297     109.3   61 3    47 1       20DB
1990   6 77 37 B   50 4     B3.3    906     436     228     319     241    73 69    33 4   3 12        1607
1991   26 4  7 9:     682     74 4     139     106     364      309     222    98 59      35      13         1464
1992   24 8 32 8    106      105     222     225     267     291      250    104 7    53 5    156         1697 199 J   1 04  31      695      100     213      313        217     347      166    149 4    2.03      0          1649
112   i 15    20 i      539     127     227     255     228     279    8 467    13 7      0          1223
1995      a    22 9   75.5     103     222     195     229     3T0     2?o    85 45    11 2   22 3        1563
1996   45 5 19 1    162     71 7     330     225     245      197     215    74 57    44 6    7 56        1645
1997   39 6 0 97    566      139     293     814     205     291      234      213      40 4      2 54        1830
199B 13 84 01 1 15.2 162 280 264 272 239 2359 67 2 1 04 1638 1999 31 7 291 15 92 3 393 427 257 239 309 197 3 8.89 42 1 2014 2000 0 0 3 69 105 195 345 222 260 274 255 344 7 39 1702 200’ 0 32 65 5 50 3 327 346 298 292 312 206 3 19 3 24 1 1903
2002    177  2 19    39 7     42 2     106     252     2?4      153     224    59 11    1 8*    531         1226
2W3    5W   63 5    117      121     58 9     358     232      300      155    51 S3    11 5   t 86         1466
ZOC-a  4 96   2 '     61 2      5! 5     1.50    353     325      243     249    193 9    40 7    13 i         1689
Av*f>Q4      15 3 Tfi 4    53 6     69 5   T80 8  243.0  245 9  238.3  228 6   715,5    31 4    127       1452 9 cv      0.85 3 96    0 68     0 55    fl. 49   0 37    0 31     0 25     0.24    0.591     0.9     1 13       0.203
SMW        0 62 0.78    0 74      0 1     062     0 38     7 44       o.a?    Q.17   0 635    2.31    1 48        0 26
Mu       45 5 576    161 7   TJ9 9  392 7  437 6  487 6   345 6   34J1    259 9   150 7  53 1      2014.5
Mln        GO   0.0      08        5 1     37 5   100 3  336.2  135.3   14* 3     J-5       0 6     00.        990.6
Water Works Design & Supervision Enterprise
In Association with Intercontinental Consultants and Technocrats Pvt. Ltd
I ioAijo Dedessa IrriRitloti Project
Meteorological anfl Hydrological Aspects
II1H
Mnt too?Arjo Odessa Irrigatloa Project
MeteoroloEica^ndHytlrolDg'Ica^spects
A9: Estimated Mean HaN-Monthly Ralnfal at the Project Area (in mm/hrl
May 2007
1.1  1 1 * 21       22     3 1       JZ     4 1       42      5 1       52       81       02       7 1       7 2     8 1     fl 2    9 1      92      JO      10    ff 7         I?     T2 I      *2     Fof#/ Year
1967    79   7 79    □       0    22 4   739    0    21 7   752  9697    112  60 8   68 4   71 7   110   110   132  07 7   11D   1 92  75 7    75    0 12     0      1320
1966
I0
0     57 3  0 29    0    0 75  1 27  35 i    31      02 8   81 4  67 4   82 5    104   12 ■ 86 1   76 5   115   76 6  14 2    0     71 7   in 3   4 25   1070
1969  ?B 1  11 6  14 7  21 2  376  16 1   6 75  133    18    103 1 72 3  71 9   55 2    103   106
106   83 6  81 7    38   20 4  3 46  3 92     0       0      1132
1970   2 1   27 1  7 27  227  23 6  27 7  1 73  195  34 3  114 3  49 4   104   127 4   122  81 7  79 8  94 4   162    5U   57 3  4 44     0       0    4 04   1217
1971 ' H      0 2?  0 32    0    4 62   16    304  0 46  42 1   99 06  62 2   131    63 4    116  81 4  73 9  125   137   104  64 3  26 6  5 48  3 17    11     1210
1972    78    7 79  4 31  6 04    0      15   36 5 52 6  25 5  27 53 70 1   07 9    872     99   89 7  67 2  94 2   758  25 7  23 6  61 3  7 69    0    9 74   990 6
1973     0       0     9 97    0       0    5 65  25 4 4 04   140  96 39   962  58 9   91 0   94 7   108  125  70 8  64 1  57 1  1 73  17?      0       0     5 77   1075
1974  30 6  0 12  2 26  5 72   199  11 9  0 29  4 05   168   98 87   102   103   119 5  123   101  67 5   102   110  44 4  28 3     0     4 62  4 62  12 1   1292
1975     o    23 5  47 7   7 4   0 69  20 4  5 14 55 2  67 5  40 89  80 8  43 3   75 2    113  62 1  96 9  92 5 48 R  86 9  444   11 5    0     6 06  6 46   1045
1976  23 7    0     103   5 69  57 9 32 4  32 2  23 5  76 8  74 81   7?   01 6   102 9 89 1   51 9  163    t9B   74 2  40 1  46 6    32    398   2 89  2 48   1303 1976     3       0      35      0     564  10 1   124   909  49 1   73 14  87 8   60     79 7    12?   71 2  134   84 8   965   72    505   058      0     6 06  6 46    1181
1979    78   7 79  6 89    0    0 46  16 5   11 6   14    572  40 35  99 6   102    145     903  85 5  73 6  97 2    57    404   24 5  156   15 6  6U6  6 46   1024
1®W    76    7 79  0 69  6 69  27 7  29 6  28 6  69 8  64 2   100 3  41 6  58 7   65 6   70 6   99   78 5   130   109  26 3  23 5  11 9  16 9    0       0      1110
1963   7 0   7 79  7 90  0 25  16 7  0 89  20 7  14 9  54 3  94 53  69 7   123   168 1   128   134  136   89 9 8 b 7   78 7  35 2  44 2    13      0       0      1362
1904   78    7 79    0       0    4 73  76 9   17 3 52 5  53 9   160 3  138   111   232 6   211   51 A  147   66 7   163   7 16  1 56  15 2  11 6  4 96  081    1514
raes   0 3   2 49     0       0      1 5   10 8  57 5  47 8   121   136 6  16B    173   94 1    146  62 6  130   160   155  37 2    11    24 9  7 58  36 9  0 81   1607
1966    0       0     2 75  36 4  15 2  31 7  28 1  28 3   124   36 22   195   119   147 6   127    110  134   114  77 1    as    18 9  20?   7 60  0 23  0 23   1345
1967    0    2 69     0     17 2  49 1  40 5  6 93   729   192   104 3  158   124   224 5   263   215   112   116   66 0  01 4    35    31 2    11     343    D     1785
i960    94    4 73  2 66    40     57     173  098   14 3  145   190 2  172   154    75 i     102   175  122    179   164   155   tO4   154     0       0     3 87   1903
1989  16 6  7 03   26     0 7   43 9  32 5  65 3  42 7   148   96 74   182    102  208 4   107   186   145   194    t(]4   915   97 8  29 5  31 6   190  27 3   2O0B 1990    0    8 77  13 1  24 7  21 6  28 8     0     83 3  60 3    303    253   185   123 1   105    IO8  211   98 1   143   53 4  20 4  32 4  1 03  3 12     0     1607 1991  14?   12 2     0     7 91  37 6   306  1 27   732  89 9  49 04   133  93 1   195 1   169    1?9  131    144   77 9  97 3  1 27  IOS  24 5   12 7  0 20   1464 ’992     0    24 6   177   152   252   606   3 34   102   152   70 12  82 1   143   161 3   106   159  131    102   148  81 4  23 3    79    24 6   1 15  14 7   1697
:
_____________ 111
Water Works Design & Supervision Enterprise
Id Association wlLh Intercontinental Caasultaals and Technocrats Pvt Ltd.I I I I MArjo D«d*»a lrriEUlJon Project
Meteorological and Hydrological Aspects
mi 2007
| —r  5 1   1 2   2 1 2.2 3 1 3 2 4 1             4 2      5 f      52      *7        fi 2     7 1     7.2    f.T     02       9 .1    9 2      10
M | ■ ■< ” —I ■ |
10 JI 1 TJ 12 1 12
Year
ms
0    1 CM 6 64 24 4 3 06 66 4 63 6        36 6   93 7   119 7  06 2    227    797     137   149   197    RM     61 9   03 9    65 5 1 39 0 65 0 D
Tott)
1609
11 2   0             0 1 15 1 3 IBS 29 2  24 7     55    71 64   105    122   109 7   145   116   111     106    112    7 24    1 23 9 52 4 16 0            0      1223
0      0               56 17 3 0 75 5052   109    116   105 9  63 4    131   123 9   105   177   133    125    154   40 0    45 7 5 95 5 3 1 96 20 4         1563 1995
92   36 3 4 09 15 Z8 0 62 9 26 6       45 1    146  192 4   159   66 1   34 7     160   '00   966    932     122    582    16 4 fl 40 36 1 0 69 6 07       1645 1996
2 1  37 5   0   0 97 20 1 28 5 72 0   66 6   71 7  2?1 5   15?    161    70 6    127   165   126    140   05 0    119        94 2 25 3 15 1 0 06 7 40|  1830
199 7
1990   11 2 1 B4   1 94 6 46 24 6 56 5 6 89  6 33   69 7  92 10   142    130   141 7   122   131   142    110      121    92 9     143 62 3 4 92      0 IM          1638
1999   2fl 3 3 36    0 291       0     15    19    733    227     166    209    217    99 2    150   141  902     146      162    140             48 9 B 89 0 26 6 15 5   2014
2030     0      0      0      0 2 31 1 39 28 4      76 2   76 9  118 6   215     129   994     123   149   112    139    135    160    87 1 25 2 9 15 2 89 4 5         1702 2001      0      0        23 7 0 3 1 24 64 3 36 9  23 3             230 6   122    224   1163    100   126   155    187    124    96 4     110 7 27 12 7 14 4 9 75       1903
2002    12 5 5 19   0    2 19 0 37 31 3 37 7   4 49    19 6  06 64   139    114   156 4   110  51 7   102   95 4    129    35 3   23 8     0 1 84 3 29 49 8        1226
2003      2    3 64   17 8 35 7 39 ? ?7 6 68 8  52 3   20 3  38 67   165    193   127 5   105   133    Iflft     059    60 1   23 7          27 9 6 64 4 91 1 4 0 46   1466
2004    02   4 76              1 4 07 106 506 97   41 fl    28 5  121 9   146    204   256 7  69 6  91 1    152    132    117     inn       25 T 11 3 29 4 9 24 3 88   1689
Avtr«g«     >5    7#    0 0 9 0 21? 0 33 fl 22 7     46 7    78 2    1028   1F90   12J 2 122 0 123 9  117  121 fi  1200   roa 5  73 7   41 fl 19 7 1 r 8 6 f 66           14529
GV        F ftf J 23 14$ f 21 1 03 0 74 0 95        0 72   068   G5f F   0 46   041   0 425   031   0 J6   0 29    0 3      0 32   0.50          0 tfb 0 94 1 76 f 57 15    0 209
ShtfMa    1 27 1 82 2 47 1 27 0 95 0 83 0 95 0 63       0 94   0 64    041    057   1 039   f 64  0 36  0 4Z   0 72    0 1    0 63           TIT 1 4? 261 2 15 29    0 20
Mftk      30 6 3 7 5 57 3 40 0 78 8 82 9 72 8 133 1 226 7 230 8 252 9 226 0 256 7 263              216 210 9  198 4 164        T&8 3 143 0 75 7 75 0 36 9 49 8 2Q14 5
M.n       GO   00                   00 00 00 08 00     05       f 2    27 5    i J 3   43 3   55 2   69 6    51 7 67 2   66 7    48 6      72
12 0.0 0 0 0 0 0 0 990 6
A
Water Works Design & Supervision Enterprise
la Association wilb Intercontinental Consultants and Tech nor rats Pvt LtrttatuilrriEaEJM fayed
Meteorological and Hydrological Aspects Annex S Results obtained from 1 he Hydrological Analysis
01
Eshmaied Monthly Flows 41 Arjo Dodessa Dam Site
I'm? mHqta- of) __________ . ------------------------------------------------ _ ____ u-__
Ytir .
luar ~Ia<X May Jun Jul A**fl S*p __lpcl 30 ”4 26 02 25 73 63 61 49 78 207 7 7515 972 5 KX)
Nov -D,c
2914 101*
’962   34       ‘8 SB 1947 5 073 21.39 157? 397 6 540 6 7DO 8 512 2 64 92 31.95
AnOU»l
I
2*25
22 72 12 3 12 26 30 S6 111 6 235 3 429 5 626 3 622 6 223 9 mS 97.23
2736
1%4   7 542 24 32 17 86 2*21 4169 lfi-7 670                       784 4 705 4 621 4          307    42 03
3413
1965  33 05 16 1       11 24 34 56 21 07 12? 1 532? 633 6 410 3 573 5 194 6 90 12
| 2»M
1966
42 41 40.3 39 6' 5361 <7 41 134 3 M7 5 6S4 6 ?26 3 49 32 25 34 >1 62
2372
'967
5 656 5 354 15.57 14 73 1924 82 14 452 6 764 7 719 5 634.6 40<14 '-20.1
3236
1
1965 30 4 29 71 46.01 2U.M 55 55 252 9 607 657 565 3 74.2 53 41 24 41
2726
WO
20 38 5351 9 245 24 2’ 34 36 209 3 593 4 635 7 673 2 121 1 110 2 35*6
2472
l*7i     221     10 44 7 454 9Q19 40 6 175 5 525.6 704 6 566 4 450 3 ’44 3 60 15
2763
1972
313 16 92 1343 25 78 42.79 BSfii 512.9 746 2 430 7 125 4 7109 29 96
2134
1973  T5 44 7121 3 221 4 586 8Z.W 181 5 156 2                533    539 1 354 5 90 45           37
246*
1974
?1 79 10 31 9 487 6 56 1 71 15 19C 409.5 7706 195 6 43 73 72 32 27 9
1069
19T9  10 27 7 8(H 5 815 15 56 35 18 $4 19 340 6 497 5 37i                      157 1 5707 25.13
1619
i960   10 73 9 737 6 439 45 56 144 9 364 1 544 3               777      74 5   235.5 6 2 7 1     52 8
3W5
1961
4775 27 57 28 73 25 54 40.74 36 7i 412.6 633 540 6 315 2 19 85 7 ’38
2139
*902  36 71   1J2    1963 13.95 34 68 180 3 451 6 57i 2 414.6 455 6 107* 53 96
2156
1993  25 9 2013 23 4          ’6 68 39 8 ■ 1 i 5 36i 4            687 668 2 6i7 6 242 5 69 26
2924
i9B4
23 01 ’Ofii a I4« 8 954 2i 59 134 7 449 2 4012 311 8 78 36 12 69 4 808
1463
190-5  7'52 3 46? 1 775 3.54 47.33 523 1                 240      559    504 1 155 7 46 31 25.72
1?64
19M
104J 6-352 11 02 9 W3 9 685 86 35 254 9 2W 2 43B4 132 9 50 52 28 15
1369
1907   7 756 3 775 8 501 12.5 27 62 157 2 412 8 633                    402 9 23 1 4 97 4 7 38 7
2034
1W
2*16 17 49 14 79 5 553 28 06 203 6 35*5 689 1 905.1 315 2 ’14 9 46 11
Z71»
19*9
25 u B4 '357 24 24 2058 4763 174 3 30 H 851 3 3152 66 16 7031
17M
19®
J'93 19’I 23i 9 44.03 3'9i 114 4 219 3 1043 669 7 280.5 46 23 23 01
2546
199 *    16 3 12 32 ’0 51 18 94 44 17 113 4 517.4 954 2 456 9 3109 29 61 2i 7
2547
"992   1462    5 23 9435 14 95 4? 55 116 8 2351 497 2 336 1 482.9 99 78 4'9
1905
TM3   254 ’7 72 16 74 3956 79 B6 226.9 383 1 698 7 377 8 243 8 107 6 36 17
2253
199*
23 32 12 45 1062 11 34 45.32 160 1 3413 736 3 514 93 66 4135 31139
san
1995   12 15 7 787 1015 14 M 29 04 6C 34 1438 343 1                  391    9356 38 44 82 8
1124
1990   2925 16 4* 26 36 ?1M 1G7’ 271 3 462 2 515.2                     358    22S 1 7187 49 76
2157
2003    50 5 37 M 45 32 41 35 97 36 29i 4 4731 830 3 M2 2 403 8 130 5 63 78
796*
2W2  5909 36 35 37 91 4585 35 1               127   292 1 356 4      348     1     2 7004 47 88
ISSG
2003
33 56 2305 3»53 53 75 36 41 87 39 347.2 393.2 540 6 3i5 2 M 27 46 :1
203*    312 25 55 20 78 20 73 49 47 1468 336 3 385 2 384 9 322 3 85 26 *6'1
1055
WatEr Works Design & Supervision Enterprise
Is 43Sficiluqii iiiih lniKt€£nl! []£3i:3j Cdiu-uIiaqes n.n3 fec&uscfm Pvt Ltd■Arjfl DrJtsta ImeauoB Project
Meteorological and Hydro logteal Aspects
B? Regional monthly coefficient o( variation* (C V]
■ SWw? roar Jar? Feb Mur April May June- July: Aug
May
—
1140Q1 35 0 51 0.57 O6£
114014    20     0 47     0 46    0 *8
114005    23     0 26     041     033
114004   22       on      0 42     045
1T4O03  21     0 51     0 63    0 57
91000 30 D.66 13 D7
0 6-3  052     0 45    0 35       0 3
0 56 0 69 0 53 0 27 0 33
Dec
0 33 0 67 0 62 0 59
0 26 0 56 0 31 0.53
043     D.6    0 47      0.2        0 16       0 25     0 44     0.3      0 34
0 55 0 56 D 43 0 57 0 36
o n     066     0 56    0 35      0.25
0 43 0.64 0 35 033
0 35 0 56 0 46 0 55
9 1012      35      0 6i      0 49    0 76    0 49    0 57    0 42      03        0 29      0 32       0 52     03       0 56
06      0 61    0 4€    3 29-     0 32      O2S       OM      1        0.86
Hl           OimnHJkl mnotnlu t&efflCiftflt
SkC^neSS
Srawi- t«ar jsn FcO Mar April Ma/ June Joly
114001 35        5 63      0 74      1 07    0.94 1 63 0 B9 0.13 114014 20        1 35      0 31      0.47 O.Bi 0 65 103
So/j
Dsr
0 04        0 25     0 99 1 37         096 0 5      0.93        0 69     067      26        1 96
114005 23        0 33      1 4G     0 59     -0 1 2 IB 1 54           0 0?      □ 45       0 B'      0 42 0 52          i 09
91006    30      2 73       029      3.26    0 77 1 14 0 Bl 0 17
1 14       1 13     0 77 3 14         2 65
91012 35         3 17       4 9*      1 22     1 5 2 34 1 15 0 <3                 0 94       DOS          1 6 286        2 79
B4 1$ Regional monthly coefficient of correlations (Rj Slafw? rear Jan F®0 Mar M?y Junto- Jufy Ajy Sey. Oct a/om- l>\j
1 ’.4001  35      .0 1       0 63      0 09    C 59     0.3
114014     2C       036       0.5       0 77     D56   0 62
114005  23      0S«        0 5       0 35      0.3    064
t14QQ4 22 Ofl 0 52 0 2i 0 52 06
’14003 21 u 3a 03 0 18 0 52 0<5
91006 38 o:? 0 33 037 027 0 53
0.76 0 45 0 53 0 44 0 45 0 74 0 78
0 BI D*S 054 0 28 >0 04 0 65 0 7B
0 3B 048 0 60 OB 0 B3 0.25 01E
9.68 0 56 0 69 0 6‘ 077 037 014
Q 73    0 66      0 56       0 5B       082   056        0 1
0.59 0 54 0.55 046 0*5 0 77 0 62
91012   35     012       0&3      0 72  ■2 48   041     0 72    0 53       041         0 48        03i   0 44      0 65 1
j 1.4
Water Works Design & Supervision Enterprise
Id Association with TncertoDtinunal CoMiiluteis and Technocrats Pvt. Ltd.
1
81
I I I I I I I I
I
VMo Dsdeua Irdzidcn Pjojch
jteteorotogical and Hydrological Aspects
May L:LMT7
85 Standardized probability weighted moments
Station           Name of Station         ------L-o--cja-—  tion ——Area Record ________ PWMs
Deg N. Deg E |km2l Lwnflh.N Wim _! fflm_______________ 1    114001    Dedessa near Arjo               B41    3G 25   9981        29         0 40739    0 243171
2   114014
Upper Dedessa near
Demoi 6 02
36 28    1806        15       0 420504    0.262951
3   1140Q5   Qabana near Abasina         9 02    36.03   2881         16
0 414042    0 253945
4    91008     Gilge< Ghibe                        7 45     37 11   2966        37       0 400025    0 240847
5    91012     Gojeo near She De Angar Cutin near
7 25
36 2 3
3494
34
0.408619
0240091
6 114007
7 1140Q4
Neqemte
Wanna near Neqemte
1975
20
0421145
0.254033
e S3
36 47
844
21
0 419805
0.254029
i 8   114003    Sitfa near Neqemle
9   115008    Aleltu al Nejo
10 101001    Sor at Meiu
11 91013 Ghlbe-Limu near Limu
12  91001     Great Grube near Abell WetgJlteo Average
B 52
35.45
951
20
0 416527
0.251324
930
35 3
155
7
0 400261
0 2475B2
a 19
35.36
1622
17
0 401323
0 244655
a 35
37 13
663
TO
0 425296
0 261749
a 14
37 15
15460
19
0.424754
0 250656
—
255
JZ471964
0 250375
Water Works Design & Supervision Enterprise
Id Association with Intercontinental ConsulUnis anti Technocrats Pre LtdAJJ* Qttftssi Ijflpncn Project
Meteorological and Hydro logical Aspects
B6 Mcjq Monthly Total (Suspended and Bed) Sediment Loa d
1
at Arp Deduct Dam Site (In 1000 m }
Hay
Mar     Jin     Frb      Mirth       Apr>l   May      JuAff     July    Aug      5#p     Otl        Hoy      Dec       Annuli >9fil     2 11     1 75      1.2?     T?3~      3 IT       33*        ji5     S23    4 76     372     32.3     15 3        1781
2H    0&4       051        1 C7    3 18      224     114     216     319     189     6.92    2 41        878.9
1 3    047       0 39        1 6      11 3     40 8      129     403     264      504      i$5     14 3       932.5
1964    17a    1 32     0 71        1 07     2 34     236      262     3?0     322     387     i& 7    3 74
1 397
2 3?
0 72
D 34
1.91
0 79
14 3
162
263
135
22?
40 1
12 7
880.5
1966
354
313
2 54
3 56
2 98
22 4
190
277
338
102
40 8
9 14
995.4
1967
064
0 57
057
0 45
3 18
22 4
140
358
333
352
71 4
20 1
1300
1966
5 73
2 22
0 52
0 22
2 26
2.27
123
265
290
102
104
2.9?
815 6
19B9
?£7
1 92
3.22
1 42
023
3 71
1 72
46 1
338
224
216
427
246
205
205
102
102
5 13
16 1
1 78
285
10Z4
1970
1 09
0 75
04
82fl.7
I9?i
1 25
0 36
0 18
0 22
2 25
25.5
176
315
220
154
36 9
«&4
MB 3
W
2.17
ow
045
12
2 44
B.09
171
342
146
199
6
2 IS
704 9
1973
07
02
0 05
0 08
7 04
269
123
246
425
105
11 8
3 05
9*9$
197*
i 22
0
D28
0 13
5.51
29
119
360
MS
102
6 23
i 94
(39 J
1979
i 9i
i 29
0 65
0 59
1 79
9 43
88 9
179
115
2B S
5 63
1 64
434.5
19M
0.39
03
D 15
3 41
172
82 8
2H
365
352
54 6
6 55
5 39
1098
1982
2.69
096
0.83
0 45
1 74
26 7
140
223
138
157
15.5
5 58
711.7
1983
1 61
1 03
1 09
06t
2W
12.3
97 7
300
296
3 39
29$
8 32
1089
1964
i 33
0 3S
02
0.14
0 82
15 7
138
127
67.3
9 39
15 5
524
402.1
1945
52
0 05
0 02
02
2 6?
14.5
65
216
100
28 2
4 31
1 71
520.8
1966
0.35
a 15
0 33
026
0 23
8 21
68 3
76
151
21 9
155
5 24
34^
IM?
0 23
007
0 22
0.38
1.23
22.4
91 7
301
132
S3 l
13.3
3.28
615.6
isse
144
a 7B
0 52
QI
1 24
32 4
948
246
2OS
102
17 3
l 3’
703.4
1989
2 36
a 63
G4B
1,08
0 76
8.4
30 4
80.1
28*
'D2
696
8.52
US.4
1990
Z24
095
1 36
2 82
1 53
12 9
44
246
205
102
15 5
5 24
619 8
*962 &S4 062 026 0.5 2.48 133 49 1 i?9 M 4 172 13.0 3 72 534 7
1993 ■ 1 56 OB* 084 2 37 6 63 36 5 107 308 119 57 ? 155 2 94 66D.6
199*
1 34
0 48
031
0 32
268
22
89 2
335
194
12 5
337
1.24
562.4
19M
046
0 23
029
045
i 31
4.63
22 4
98 7
78 2
12 5
275
5.24
227
1996
1 70
0 6?
0 71
0 93
10 7
51 2
MS
189
109
102
155
49
631 5
200-
4 72
2 83
3 15
2 55
9i
57 5
ISO
26’
250
129
21 1
7 29
899 3
2002
6 01
2.56
2 37
301
i 78
152
105
103
20 1
7 62
4 61
3*1 1
2003
2 44
1 26
2 43
3 88
1 69
8 37
123
123
205
102
15 5
5 24
594.5
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1 43
09
084
3 08
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MEieorologtcal and ihdrological Aspects
2007
.
Bfr Situation■ AreaOpatrt). Pelatlonships E.'eirefjon Area Volurrw g/evetton
(mwfl             (km*)         (Mm*) _
132C 0 54
1321 09?
1322 2 39
1323 3 73
1324 5.11
1325 6 64
1326            8 03
1327            9 46
"328            10 87
1329 12 6?
1330 14 40
1331 15 89
1332 17 74
1333            19 46
1334           23 59
1335           26 66
1336 29 05
1337 31 73
1336 34.24
1339 36.62
134C 39 45
1341 41.97
1342 44 25
0 0              1356
0 8              1357
25              1358
5 5              1359
10 0             1360
159             1361
23 2             1362
31 9             1363
42 1             1364
53.9             1365
67 4             1366
82.5            1367
99 4             1366
1180            1369
139 5            1370
164 6           1371
192.5            1372
222?            1375
255 0            1374
291 3            1375
329 3            1376
370 0            1377
4131 137B
,_     ■---------- —'
of Afjo Dfrdetaa Resurvoir
Area Voium*
B? 05           1^41 2
90.75           1430 5
94 18            1522 9
97 23            1618 6
100 54           1717.5
103 64           1019 6
106 39           1924 6
109 00           2032 3 111 91           2142.B 11505            2256 3
117 58           2372.6
120.20           2491 6
122 76           2613 0
125 28           2737 1
127 69           2063 5
130 25           2992 5
133 03           3124 2 135 45           3250 4
138 oe           3395 2
142 36           3535 4
145 27            36792
148 00           3825 8
150 75           3975 2
1343
47.05
458.8
1379
153 73
4127 5
1344
49.96
507 3
1300
156 02
4282 3
1345
53 11
558.8
1381
159.05
4439.9
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56 31
613.5
1382
162 13
4600.5
1347
59 15
671 2
1383
166 96
4765 0
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51 56
738 8
1384
173 01
4935 D
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63 97
800.7
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183 38
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1351
70.62
943.9
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188 10
5477 5
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10164
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5668.2
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77 68
1092.5
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197 36
5863 6
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81 28
1172.1
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201 95
6063 2
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84 51
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Meteorological and Hydrological Aspects
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576 4
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333 3
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1 ti
00
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10
00
3?4 I
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74 1
1351 9
124 1
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Nov
102 7
00
143
46 2
10 6
10
46 2
44 9
11106 3
74 1
1351 9
44 9
404
Dec
47 7
DO
135
60 0
100
10
600
23 4
982 9
73 1
1351 5
DO
404
Jan
J? 5
00
146
74 0
10 7
10
/4 0
63 7
919 7
70 4
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00
404
i eb
72 J
00
147
85 0
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09
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Meteorological and Hydrological Aspects
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Meteorological and Hydrelugical Aspects 
k*}' 2007
__
'
Annex C: Standards
Cl. Commonly used values of runoff coefficisn
Runoff
Class
Description of catchment
A
Fiat, cultiyaieo and Dick cotton soils
percentage 10
B
Flat, partly cullivawd stiff sails
C
Average catchment
15
20
D
Hills and plains witn little cuHivabon
E
1
ve . hilly and steep with little q* no cultivation.
35
45
C2:          Runoff Coefficient for pervious surfaces by selected hydrologic sori
grouprngs aria
Terrain Type
/
i slope ranges
Soil Type           ____________ ___
B
c
D
Flat <2%
Rolling, 2 ■ 6%           G 09 - 0 14          012 - 017          0 16-0 21          0.20 - 0.25
Mountain. fr-15%          013-0.1A          0 10 - 0.24         0 23 - 0 31         0 29 - 0.30
Escarpment >15%        0 IB -0 22          0.24 - 030         0 30 - 0 40        0.38 - 0 4B
0.04 - 0 09          0 07 0 12          0.11 - 0 16         015 - 0.20
NrjLt Whm A. B C and D are defined as shown in C3
121
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■4rjo DetfEssi imgauM Project
Meteorological and Hydrological Aspects
■far 2007
Cl: SCS Curve Numbers for Various Conditions
Cover Descr/pf/on
J
Curve numbers for
hvdrolooic soil qroup
Cover type
Hydrologr
c
condition
A
8CD I
Fallow flare soil                                                          77           86          91
---- XT.- 1
94
Crop residue cover ,CR)
Pasture grassrand. ex range-
conlmuDus forage for grazing'            Fair                 49          69           79          Ba Good              39          61          74          8u
Meaoow-conlinuous grass.                                         35          59          72          79 protCCled from grazing
Brush-weed-grass mixture with           Poor               48          67          77          83
Poor 75 65 90 93 Good 74 83 88 90
1 Poor 68 79 86 89
brush me major element3
Fair Good
Woons-grass combination’                 Poor
35 56 70 77
30* 48 65 73
57 73 82 86
Fair                 43          65           76          82
Woods*
Good Poor Fair Good
32 58 72 79
45 66 77 83
36 60 73 79
30* 55 70 77
Farms—CuiWings ranes driveways.   -                      59          74          82          86 and surroundme 101$
>Vrd and semr-awo1 range/antfse Hyd
cond'
48C
etemsni
Mixture of grass, vreeos. and iow-      Poor                —           80          87           93
growing brusn, with crush the minor    Fair                 —          71           01           89
Good               —r         63           74          85
Mountain orusn mixture of small          Poor                              66           74          79
trees ano orusn
Small frees with grass unoerslory Poor — 75 65 89 Fair — 58 73 80 Good — - 41 61 71
Fair 48 57 63
Good — 30 41 46
Brusn witn grass jndersiory
Poor                —          67           60           65
Fair
-- -          51           63           70
Desert snrub Drusn
Good               —           35          47           55
Poor                63           77           05           86
Fair                 55           72          81           86
Good 49 68 79 84
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Meteorological and Hydrological Aspects
C3;           (... confrnueW
Average runoff condtfion. and I. ■ 0.2'S
" °0€i * 5u% ground cover or heavily grazes wim no muren
Fan 50 io  5% ground cover ana nut heavily grazed-
Good ' "5% ground cover anc iigmiiy or only occasionally gr<uec 3 Poor < 50% ground cover
Far SC io 75% ground cover Sdod * 75% ground covet
May 2007
7
.
‘  Aciuai  curve  nufnoer  is  less  than  3d  use  GN  =  30  tex  runoff  compuia  ors  r-^miwkalion*  of
: CHs M»wn rt<e cwipulod For areas 50%
(pa*Jure> cover . e
conSfliDris ma >■ oe KKnpuled Troffi CN s ror *ooJS and pa s iui e
’ P«r Fiwrt MW smal wrts, and
are a«uoy«J &y heavy graz.rtg or regular
nr r»muiar
Far
Gd<k _______ _______
Outniftg
.
Woods grazed Oui riert burned, and some forcs-i litter covers c e 501 Woods protected from grazing, litter ano bruin adequately cove* sc
p-:xx < M % grcHMMJ cover filter grass and crush overstory ■■
Fa>r 30 la 70 % ground covet               Goaa * 70 % ground cover
Sort Groups
grpup jCi Sana , loamy  sa-no or sanoy  ioam Soils  having a low runoff potential due to high mhltraiion rales  These sorts  primarily  consrst of deep well-d rained sancis  and1 graven
Group fi Silt oam or 10am Sorts  having a mooerateiy  low runoff potential due to moderate infiltration rates  These sorts  primarily  consist of moderately  oeep to deep, moderate^ well co well drained sails with moderately fine to moderately coarse textures
Group C Sanoy  ciay  loam Soils  having a moderately  high runoff potential due to slow iiMiHralion rates  Tne&e sods  primarily  consist of soils  in which a layer exists  near the surface Inal impedes  the downward movement 04 water or soils  with moderately  fine [0 fine texture
Group 0 Clay  loarr, salty  clay  loam, sandy  day, silly  clay  or oay  Sorts  having a ntgh runoff potfrniiac  due to very  slow infiltration rates  These soils  pnmarily  consist of ciays wtr n»gn swelling potential, soils  with perman-en!ly-ri»gr water Cables  soils  with a day pan or ciay  layer ai or near the surface, and shallow sorts  over nearly  impervious  parent material
r
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Meteorological and Hydrological Aspects
C4:     Reservoir FIftfld Standards
Dam design flood (inflow
Min Standard,
Mi)
Category 0/reservoir          Initial
condition
Spilling long term av
A Breach endangers in      Daily
Gerrera/
lives m commentary     inflow        PMF
S Breacn may endanger li^es nd in a community
Larner ol
0 5 PMF ar
Rare overtopping
Largtf of 0.5 PMF or '0.000 yea' flood
Larger of 0 3
10 000 year      PMF Of 1,000
extensive drainage        Full            flood
year flood
C Breach win negligible risk iq hie and causing limited aamage
Full
Larger of 0 3 PMF or 1.000 year
flood
Larger ql D 2 PMF or 150 year I loot?
A(ofe Pcx r/v purpose of PMF tne (riintfti uf ffre jompufpd are                  Dy fhe proportion indicated
bV/nd speed,
M/rt    wave
surcharge
Average annual max Hourly wind Wave surcharge allowance >06 m
Av Annua* max houhy wind Wave surcharge allowance >04 m
KF nytJrcgratfh
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Meteorological and Hydrological Aspects
CS; Ratios of the basic dimensionless hydrograph of the SCS
TJTp           Cii.'Qp           TiTTp           QnQp            Ti/Tp            QuQp 6                 0               1.05           0 99               26               0 13
0 05            0008             1 1              0 98               27               0.11 0 1             0015             1 15            0 95               2 6              0.098 0 15           0 043             1.2              0 92               29              0 088
0?            0 075            1.25             0 68                3               0 075 □ 25             o.n               1 3             G S4              3 2              0 056 0,3             0 16             1 35             0 60               35              0.036 0 35            0.22              1 4              0 75               37              0 027 0.4             0 28             1 45             0 71                4                0.018 0 45            0 36             1,50             066               4 2              0 014 OS             0 43             1 55             061               4 5              0.009 0.55            0 52              1 6              0 56               4.7              0 007
0 6               06               1 7              0 49                5               0 004
m*j ajc?
0 65
0 69
ia
0 42
07
0-77
19
0 37
0 75
0 83
2.0
0 32
0.8
0 89
21
0 25
0 85
0.93
2.2
0.24
0.9
0.97
2.3
0.21
095
0 99
24
0 10
1
1
25
0 16       B
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Meteorological and Hydrologica
l Aspects
_________ ____
C6:
CuIMl™, tor .rue,prelates of
Water Ooality for
irrjga|ion
Waler parameter
Symbol U
SALINITY
Sall Contani
__
—
Eieciricai Conouctfrly
ECw
dS;rr.
0-3
dS/m
(Of)
Teiai Diswi^ea Solids
70S
mgl
0 - 2000
mgi'l
Gallons and Anions
Calcium
CaT
me/i
0-20
me/l
Magnesium
Mg"
me/l
0-5
me'l
Sodium
Na"
me/l
0-40
me.'l
Chioripe
Cl
mefl
0-30
mert
NUTRIENTS"
Potassium
mg;E
0-2
mgfl
MISCELLANEOUS Aci<j;Bs&icJly
pH
1-14
6.0-8 5
Sodium AdMMplipn rtatio3
SAR
(me/l)1 2
0-15
Source fACt ’99* Urjjarr Quaftfy for/ipnGurfunj.
and Drainirge Paper Na Hiir 1 RttmnieU. ’99*
126
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Meteorological and Elydrolcglcai Aspects
Ann ex D;             M eteo rologic a I Da ra
Pl: Dtiails of Meteorological □bserwalJon Slatians
Miy 2DO7
Station Name
S.No.
1            Agaro 2            Arjt
Latitude
North
Longitude
East              Altitude
1
crass
D(*g.     Mtn.        Deg      Min -•
(mj
Period
OB        45        30        30           2565        1972-2004           3
or      Si        36        36           2030        198U-20O4          1
3            Bedehe                   08         27        36        20          203D        1967-2004           1
4             Deaessa                  59        23        36        06           1200        1971-2004           1
5            □emtx                      08        04        36        27           1950        1954-2004           3
6            GimD«                    09        10        35        47           1970        1978-2004           1
7            Jimma                    07        40        36         50           1726        1952-2004
a            KOfte
9             Meno                      oe     41        36         oe           2000         1980-1989           4
10          Ne*emie                  09        05        36         28           2080         1971-2004          1
08        41        36        47          2U0O        1979-2004          4
11
w_-___ -
Wama
0B        59        36        40           1450         1980-1987           3
Types of Climatic Data available at the various Meteorological
D2:
S.Na    Station Name            W      ’Yrs       RF           TM        RH    ws     SD 1        AgSrO                        2030         25           X              X           X           X             X 2       Ai>j                                    2565         33          X               X
3       Beoelle                       2030         38          X               X            X                           X
4       □eoessa                   1200         34          X               X             X          X
Altitude
EP
5       Demoi
i960         51           X               X
6       GimDf                         1970         27          X               X            X            X             X
7       Jimma                         1725         53          X               X            X            X              X
a       Kone                       2DDD        26           X
X
X
X
X
9        Meko                        2000         10          X
10 Nexemte 2080 34 X X X X X
Wama
>450          3           X               X
RF
monthly rainfall
SD
sunshine duration
Tm
average lemperature
reler co rainfall series 
relative tiumtdity wind speed
1 nr
maximum 1-n.our rainfall
RH
WS
1 day maximum 1-day rainfall Rday number or rain days_____
" Dara itfrXNfi /efers re ftarfifarr and rcrapBratare owe
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MjieoroId^JcaI and Hydrological Aspects
M»J EOC7_
03:        Mean Monthly Ramfafl al Settle Station
Jan      Feb    March    April  Miy
June
July
Aug
Sept   'Ocl
1967 IMS 1969 1970 Wi 1972 1973 1974 1975 1976 1978 1979 1950 1983 1984 1994 1995 1996 1997 1998 1999 2000 200'. 2002 2003 2004
0        0       152     33     1B1     ?Sl     212     J$1     360     167
0 iW i 55 163 0 323 380 324 137
67 59 Bl i90 710 250 275 36$ ies 9B
54 50 69 258 258 266 432 200 444 186
253        0
null 1980
35        22       1539
20       1       41       53     246     334     311     234
455     326
0 20 42 178 TIB 263 337 267 207
0 19 10 51 337 zee 322 403 248
110
102
66      13       55       9      497     355     351     292    368      126
44      :0l      37      105    202      JIS     337     276     245     22B
41       29      15$     97       0       267     333     373     472     154
5        7        I’S     179    204     J67     J3t>    303    201      ZtM
0        0        W       44      169     350     4M     276    267      113
0        0        0      20$    285      174      236    304     363      SB
Q       B       48      62     237     369      4^      466     306     197
0        0       45      66      291      275     46$     2H     242       9
2       34       80     141    243     222     218     357     200     103
1? 2 33 100 225 2B1 250 25B 276 21
0       17      102     130    257     292     257    310     353      77
4B 34 208 83 317 232 290 203 120 70
53       2       50     142    340     307     221     304     232     309
13      15      07      57     203     332     314    327    291      245
20       3        13     147    431     441     319    242     324     329
0        0        4        133    256     420      ’86     273     286     242 0       33       07      72     322     390     297    329     370     211
16        4       03      30     1B9    29B     290    202     253      S3
7       66      B4     131      37      320     270     256    197      52
6        3       46      01      343     447      299     268     273     160
70
07
56        25
i22 26
21        iQ
0         29
20         0
62         9
4T T2
00 50 0
1897
2322
2101
1788
1790
2171
1796
1993
1926
1655
1706
99         0       2293
26 5
i0
17 0
ID 24
1637
1580
1484
1837
45        13       1670
aa 4
59 1
2001
1942
8         39       2321
29 B
29 14
3 46
13 3
1827
2155
1450
1446
62        15       1917
23 ’ 25     * 28 3 J5    1 8
W     101 0Q
65      Jt35    239     291     310     303     302     IJnB      *1         12
0.77
F u9
20B
0
0 58  0 454    0 312 0 2<2  02?   0266   0.563 1236      1 114
0.68  0 090
■0.91 0 837   0 56  0 345  0-375 2 913     i 172
255      497      447     499     468     472     32B     253       46
90
0       ?86    202     T29       9         0          0
1864
0 14
0 18
2322
144$
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Water Works Design & Supervision Enterprise
In ASHKtidM With Inurconunental OnnttUHi and Technocrats Pn LidAt]q Deiesii ImgauoD Project
Meteorological and Hydrological Aspects
04:      Mean Monthly Rainfall at Jimma Station ___  (inmmi____________________ ______ _______ -
T«r Jin               Feb     March April
Ma)' ZOO"
Aw
Sept Oct
1953
1954
1955
1956 19S7 1958 1959 1980 1961 1963 1564 1955 I960 1967 1966 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 i960 1951 1942 1963
33        49        88       T33                 283     399      211       255        116
0         49        00       T33                 210
214       152
33 49 85 135
91 25 100 109
29 4 83 250
0 52 117 215
43 06 53 13&
Bi 140 06 138
11 3<* 104 i<5
0 86 98 225
40 57 131 110
43 4 39 203
21 73 100 153
79fi
194
235
244
169
183     288       254       215
226      169       195
270
292
170
2T9
237
185
203
272
135
iB9
215
’30
249
S2
285
151
210       212
272      262       243
206     221       206       225
249     205       191
58
161     307      172       139
4         15       19B       02                  273     207       233       250
3         74        63       105 55       81       199       91 78       135       91       100
18        3         50        81
12        74       127      115
20        11         7         149
5        56        TO       ’03
4         65       100      ’71
36        65       107      112
n       56        54        10 5        71        42       130
32       110      111       23
233 173 240 210
165 189 105 104
288 197 263 148
153 205 204 20'
161     159      193
167
150 297 160 101
165 221 265 240
198 252 194 151
124      211      233
190
27
TO3 50 110 80 57 130 35 97 154 107 55 132 31 S5 149
55 57 25 95 93
197     203      265       191       229
1
88
36
16
3
25
15
68
68
22*
24
ng
215
59
35
68
107
103
10
1 7
110 61
222 104 215 203
232 153 164 115
134       57
23        42        100        30i                  189
1          7        130       62
105      43        61        136
20        40        97       161
114      193
'64
250
141
154
223     141       192       157
70
109
31
94
9
27
127
212
3
36
23
96
3
11
42
3?
28
73
109
25
13
2
$5
5
36
44
0
10
1
55
25
15
35
22
2ft 1
37
Annual 1743
1270 1507 1523 150B 1446 1604
1509
1494 2012 1606 1341 1333 1819 1400 1253 1743 1465 1350 1237 1479 1414 1723 1491 1442 1169
1326
1337 1611
19B4     24       11        32        83
1985
1966
1987
1938
19B9
1990
199’
1J3Z
25        20        77        14J
0         48        02        H5
26        89        :5B       60
01        59        31        67
28        47       138      179
25        40       133       56
79       81        62       169 28        58        56       162
168
183
136
256
204
174      229       299       141        S4          7         1614
211 166 187
260 160 120
233 134 163
12
63
09
188      100       136       116
165 185 294 220
179 232 213 204
320 280 280 245
*7?
107
23
50
12
47
52
0
1208
1297
1331
1440
1477
170       1627
223
2B7
200 246 140 51
212 344 175 150
138
50
14
46
2
28
93
S
70
19
76
36
1712
1445
1749
129
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Meteorological and Hydrological Aspects
Q4; continued^
^ar       Jan        Fro         March April    May       June  July      Aug         Sept    Oct
Dec
Annual
1993
1994
1995
1996
1997
1994
1999
2000
2001
200?
2003
2M4
I—
9        01         110       237      237     225     1tt?t     263       164        17          3           0
?3       20        07        153     213-    274     255      155       177       11         16         11
a        2?        74        193      H5      -63     101      216        I4t         54         30         95
35       22       135      203      175     183     231       91        245        24         93         40 65         49         69       170     274     237     122      276       140       31?       24 3       36
103      22        97        93        174     223     243      307       200      201        47          1
30        1         64         72      214     575     136      102      131       196         1           2
0         1         39        194     210      ’54     266       ise       255      244        47         25
16         13        06       117     341     299     312      161       183      ">63       76          4
69          5         11         90        137     242     150      235       165       00          a         110
29       61        87         HI        12       272     187      151       239       92         30         15 51       24        46       131      162     126     216      219       210       133        67         89
1534
1415
1298
1476
203*
1713
1540
1622
1772
1330
12B6
1402
CV
5*flw
Max
JWji*i
33 49 W JJ3 172 219 2tW 2T0 702 103 60 36
O.fffi     0 7j        0 4t      0 43     039     034    0 24     0 26      0 26      0 67      0 96      T.05
0 95     9 60     0 55     0.41      041     2 53    0 3 r       0 f2      0 04      1 TO       T 32      T 74
;os      r4C      ?99     30?      34T      575     312      344       299       337       243       170
0          t             7         16         12      114      9F        9f         50        TT          1           0
15C2
0 13
0 0J
2034
T769
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In Association with InttKontlneiittLl Consultants and T&cliiHMniis Pn. ltdII4rjo Maia ImgaOnn Project
Wteoro logical and Hydrological Aspects
OS- Mean Monthly Rainfall at Dedessa Station
V«r     Jan       F»U      Warth April          May    June July     Aug
Sgpl O c<
mqV d«c_                     —
40
1971
1972
1973
1976
1977
197A
1979
19B0
19B1.
1M3
ifta.
1985
:«g
1987
1M8
1989
^990
1M1
1992
1993
"Km
1995
-986
1W7
1998
1999
2WJ
2«H
2042
2<W3
ZC-IM
11 6 5 90 1&7 2B3 497 21 (i
0 0 3 41 266 273 203 289
iSI 146
152
123
0
B5 14 1579
1222
00
217      196
0          0          □         S3       80
0         0          0          0         0       191     245      197
0         0          2         13      228     285     272      240
104       121 49
289 193
139
0        48        39        88       i&0
0 0 35 11 244 207
205
96
39
00
334     625      401
196       107
5
0
3
4
0
0
7M
1128
1278
1695
0           0          9         20      221      306     25?      309 1         0         47        89      219     318     373      295
0         5         12        73       50      184     339      259
4           3         25        29      141     399     425      296
1           5         32         8       275     341     370      442
0         0         :60       38      24 3     269     337      289 4          10        39         2       11      250     402      245
7         J7        33        74      101     215     355      104
4           0          0          0        84      197     153      207
0         6         26        95      14T     224     307      264
0         0          1         79
0         0         34        19       Bl      112     285      241
21         4         71        60      239     311     3B0      380
13        0         13       154     184     203     277      24? 0         0         13        14      251      395     196      371
IB         0          0         47       178     306      iSi       274
0         0          a        -.54     241      448       136      347 0        11        27        3i       143     214     196      224
6         IS        30        3i        77      203     252      126
0        35        50         0        73      366     417      302
0          5          6         35      105     252     427      310
123
158
221
215
□
140
94
97
1306
1695
1284
380 241
305 120
152 53
1691
2101
1880
1216
132
5
171 163
170 132
17?
370
147
254
351
89
0
0
191
141
300 192
254 128
17
67
147
1LM
0 64
-0 04
241 0
60
20
14
7
68
32
8
27
5
54
3
22
19
1
55
15
10
12
6D
29
17
22
40
0
38
36
■■1 23
1
1
□
76
0
10
6
0
1251
1069
1382
CV
Shew
Ma.
Wtan
3         6         26        49       156     274     312      277
1. 91    T 87     1 28     oea     0.5T    0 29    0 37     0 25
2 IB     2?8     2 75     0.94    ’0 25    0 25    0 54     0 36
21         48       160      154     275     44B     625      442
0          0          0          0         0       112     138      126
102
193
140
299
0.3&
0 87
3S0
102
5
Q
0
0
11
0
29
6
6
0
8
2 D5
3 66
76
0
1032
1856
1299
1717
1494
1842
1296
065
1544
1470
1426
0.23
005
2101
764
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in tottditiu with Imerconunentu Consultants ar d Ttchnacrais hm Ltd.
HII
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toArjo Dedessa Irrigation Pnojtst Meteorological and Hydrological Aspects
06; Mean Temperature at Bedele Station
(moC>
May 2007
——
jin        Feb      Mar      Apr
May     Jun          jul_
Aug      Sep      Oct       Nov      Pec
1971      17 9     19 S      2i 2     2G 8    2i 3       20.4        132        167       i® 6       15 5        154       17 2 158       159
1972                  T9 5     209      10 4     17 9     19.6      18 3       1&4         180       17 3      17 4      24 9
1973      179          7      21 5     21 5     19 4     179       14 3
1974     17 7     19 8     T9 3     20 2     ie 7      18 2       ’6 9       15.7      17.2      17 1       17 9      17 9
1975 17.3 19 3 19 7 i9fl 19 4 17 7 1® 7
1976 17 9 1® 1 “9 i 18 8 17 8 1 7 6
1977      1B2     19.0
1976      173                   193     18 9     186      17 5
’979
’98C
ji 0       20 5     19 7     19.5      79         166 19 2     19 t      17 5      17 2
1901      171     17 5     17 1                  17 0
21 J      2i 2     22 0     19 7     100        169
ms       20.5     205     21 4          5     18®      180      17.2
1986     19 9     20 6     20®     20.9     21 4     10 1      17 4
IM 7       194      20 8     204
1988      19?     203     2O.B     21 5     19.6     10 1      17 0
19W      178      IB 7      19 i      19 3     190      17 0       150
iSrSO     18 1      1®7     19 5     20 2     193      18 5       174
1991      193      20®      20 7     21 0     204      18 3
1992 19 i 20 1 21 3 20 6 207 19 5 184
1982
1W3
7 5      19 1     20 1     17®     174         17®       1B 3      18 7       i90       19 4     20 0
16.2       17?       18 1      17 2
17 2      17 1       177         17      1® 7 168        160       16 1       :9 ?
*60       18 5
1? 3      17 3      17 5
16 9      17 4      17 0        176      17 4
T® 9     19 6
1   17 7.31     11 77 43       177       18 8       189
17 6      17 7       ia 2       18 7        184 IS 1       1B2       18 3       190
17 3      1? 5      18 3       182       17 9 1  1 7 743      117787      1178.25      1100.09      1197 B1 17 4      18.2      1B4       18 7       20 0 IB 0       19®      19 1        IBB        20.8
1993
1994      209     20 9    22 D     21 3     19 5                  17 8       17 7        182      19 £■      198       19®
1995     20 5     20 0      2i 3     21 4     tSJB   19 4      17 6       18 1      18 5      18 8       189       19.5
1996      19 2      21 0     ?□ &     20 7     19 1     IB 4      17 8
18(1      18 3      18 3        IBS       18 7
1997 192 15 9 21 5 155 19 3 18® 17,® ISO i® 8
1998      139     21 2     21 2      232     21 0     19.3     18 1
1999      196     21 7     21 7     21 &     19 1     18 7      17 3
1® 3
17 7
IB 9
16 6
1&2 186 192
17 9 184 19 2
2W0
2001     19 1
2002      19 2
2003     20 0 2MM     20 &
?8 7
17 7
17.9
16 5
169       18 ®       109
209 20 7 21 2 19 9 100 175
21 T 21 6 21 6 21 2 18 5 18 3
177
17.5
10.6
18 1
19 4 18 7 192
18 1 18 6 189
21 5 21 1 21 2 21 5 10 7 1?&
2i o 22 i 21 5 208 18 3 17.8
1® 1
18 1
106
186
19 0 19 ® 19.®
18 7 19 1 19.6
T9 7
206
20 8
T9.6     ISO
17 3
174
T79
18.0
?8.3     T8 9
CV
i? M     0.13     0 05     005      0®      0 12      0 05      0 [)4      0(J5      0 05      0 06      0 09
Sxe*
-T 21    -3 96   -T IS    -0.08    3.00     ^.24       -2 06     -0 86     -0 58    -42.54    -1 35     T 44
Jtfin
T3 9      75      17 1     18.4     17®       79        ?4.3       15 7      160      15.5       15.4        15 9
JO.P    2? 7     2? 1     23 2     21 9     20 4       18.4       IS. 3     T9.®      1.9 4      F& 7         20
Water Works Besign 4 Supenrisltm Enterprise
In tssociauirn nitb IntertontlneniaJ CctisultMta aod Technntnts Pm. Ltd.IlArjolieDtisalnitratHH] Project
Meteorological and Jlvdrctugica I Aspects
D7 R eutivo Humidity at B g go le St at fo" ■,r % 1
•it Jtn FsC Mtr Apr .Way -Ju" jLfl
_ _ _ _ _ . ___
9007
■ ■-
198?
19BB 80 56 52 70 75 60 84 83 76 63 SO
1990        59         62          56         BO         70          rd-           82            60          80           70           60          60
i9aa         51          S3         67         &2          M          Hi'
Sop Pel ■ No¥ -D**
00         ■HO          60           50 63            8$          H4           72           64           75
1991         55         «         55         67         76         BC           62            04
77           71            65          65
199?       •58         65          50         62         SS          75 1993
1994        53         4 5         46          57         76           Bl
1995        46          M       51          59         72          ?□           85            63           70           69           6A           67
7? 61 74 72 69 «
65 72 81 61 66 61
1996        59          M          63          62         75         82 1997        55
L99S        55          55
64
1S»         59         50         49          55         76          7b 2000        58
S3 04 6b 72 68 w
64 aa 80 76 64 63
82 84 82 60 74 70
2W1         62         62          65          65         73           Bj           84            84           83           00           74           87
KW 62 55 63 60 57 61 86 06 94 73 69 61 20W 61 54 56 62 66 fill 85 84 82 7.1 70 69
Arfr..^        60          57         58                       70          78          84            83           87           89            63   —
59         60          66         65         67          61
65           86           83
135
Water Works Design & Supervision Enterprise
In touctoion wUi lnttrconHnsntai Gansultanu aad Tfchnoenis pn Ltd.Dtfessa Irrigation Project
MeteoroloRical  and  Hydrological  Aspects w                          ----------------- ii i ■
D8:     Wind Speed at Jimrna Station
pn m/sj
freer
.an Feb March April May Jwrw July
Oct
1973
1974 09
1975 09
1976 oa
11 12 09
1 2 00 1 3
07 1 0 1 0
1 1       09
14
3*
C9
09
1977 Wfl
□ ?        08           09           09
10        09
1979      C 9        0 8         OS          09       06         0 9       67          00           08
07
08          1 2          i 1        09         09
08
09
□a
08
08
07
□8
08
03
J  9 09
00
09 09 09 09 09 08
1980      07
06          0.9         0.9       0 0       0 7       0 7         07           0 7
1961
07
00          09           07        a a        □ y        3 6         0 7
1902      0 7         OH         06           08       o h
07
06
06
06
07
03
11
OB
09
aa
oa
o7
o&
06
06
0B
09
00
08
07
10
0&
oe
o5
05
09
09
06
07
oe
07
07
0.6
06
05
1963      0.6 1964
06          0 0         0 7
o7
0 ?        0 6         0 6          06           06            0 6           0 6
1985
06
□ 6        06
05
06
Ob
0&
05
06
1900 1907 198B
I 1989 1 1990
1991
1992
1993
1994
1995 fc996 1997 1998 1999 20OC 2001 2002 2001 2004
OS 0 8 07 0 6 06 0.5 0.5 0 6 05 04 0.3 0 3 05 05 06 0.6 0 5 05 05 04 04 0 3 02 0 3
0 1        0 i          0?          0.2        02         0 1        0 1         0 i           0 1           0 1           0 1          U 1
01        01         ai          01        0i         01        01         o1          01          □ 1           01          01
05        06          0 6         06         □ 6       05         06          06           0 6           06           0 6           05
0 i 0 1 0 1 0 * 0 1 0.2 0 1 0 1 j i 0 1 0 1 0 i 06 06 07 0 7 07 06 05 0 5 fl 6 0 5 0 5 05 05 0 5 0.6 06 0.5 0 5 05 0.5 0 5 0 5 0.6 05
0 1        01          04          02         03         0 l         0 1         0 1          0 2           0 1          C t              0 1
04        06          0 6         0 5        0 5        04         04          0 4          04            04           0 4          05 04         D 5        0 6         05         04         0 4        04           0 4          04           04            04           04 04         0 5        □ 6         0 5        05         0 4        0 4         04          □ 4        0 4           0 3           04 04         04         05          0 5        04         0 5        03          0 3           04           0 4           0 3
03        03          0 3        03         03         0.3        03          0 2         0.2           02           0.2           02
02        0 3          03         03         0 3        03         02           0 3           03           02           0 2          02
02         0 3         0.3        03          0 3       0 3         02          02           03           02           02           02
6 i         □ 2         02         0 2        0.3       0 2        0.1          02          02           0 1          0 1          0 1
0 1        0 1          02         0 2        0 1        0 3      0 10       0 11        0 09        0 tfl          0 15         0 10
0 52      □ 62       0 72      0 73      0 75     0 74       071        0 76       0 82         082        0 83        0.8'-
Cv
0 52
05
o«
0 44
0 42
0 36
0 36
0 35
0.33
0 34
0.32
□ 29
Sin
0 04
0 16
0i
0 29
0 63
-0
-0 1
-0
0 02
03
□ 31
OOH
Mai
09
■2
t2
13
14
0.9
0&
0.9
09
11
10
09
Ifai
01
ai
01
01
01
01
01
01
01
01
01
01
Water Works Design & Supervision Enterprise
In Association wills Intercontinental Consultants and Technocrats Pvt Ltd.IAf}d Ltdes.,4 Imgatmn Project
Meteorological and Hydro topical Aspects
09- Sunshine Duration at Bedel e Station
Jin hrsj<lay>
_________
. ---------- — --— —
tear            Jan     Fcd           Ma^       Apr        Maj        Jun          Jul          Aug         Sep         oct          Nov
F
Dec
1MT 7 2 6 9 a 5 5 6 6 6 3 5 7 8 4 8 8 3 8 3 «W8 7 1 6 5 8 2 7 9 6 4 2 6 4 2 5 1 9 7 9 5
8 5         0 2         79         7 9         7 4          6         3H           5 1           65           7 9          6 6          6 4
’990        8 9         56         7 7         54          82         6 4          3 8          4 8            6            9.6          H 7           9
1991         79        B 1         58         6 3        7 1        •4 5         2 7           3 4          5.9           e            ti 4            7
194?                      5 7        7 7        7 1         8 3        6 1          3 4           2 2          6 7           62          6 2          8 3 19U        76         66          75         55
19&4                      7 7         7 5         77         7 6          ■           2 4          3 4         SB          9 5           94          9 3 1995       6 8       66         7 7         66           r           •B            ■             ■             ■             ■             n             •
Wj            ■           ■          79
•B         ■B         ■■          3?            4 3          6 7            9            7 9          78
-997        7.2         92         7 5         ca           7           6 i           4 1           4 6          e 4          7 ft          fi 7           83
1998 7 5 7 7 54 6 7 6 4 6 7 29 3 3 4 7 5 4 84 92
1999       8 1        9 1       88          76         76         6 6       3 5           4 6           66           58           9B
2000 9 B8 9 6 1 7 8 e ■ • 5 5 b 4 ■■ •
2001
■
2002        ■■         82         7 5        91         84         6 1          5 6           3 1          6 9          98           8 3          7 5
2005        79         86         7 3        8 0         96        5 7          2 9           36           6 i           9.5          0 7          8 6
200 -        7 5         79          6          5 7        7 -5        4 3          4 2           4 5          3 5          8 2          8 3          7 7
tJj         76         75         73         70         6 1          3 7          4 F           62           7 9          8 3          8 7
|-5
ta
wt
L[ir
I t
I IIAl)(>Dedsssa Irrigation PrOjtct
Meteorological and Hydrological Aspects
Annex E. Hydrological Data
M*y zoo?
El
S
No
Lisi Pf Sciectta Hydrological Observation Stations 
J
--------=-
____ Latitude. N           Lonflitude. t
Staliun No.
Slatton Name                Dag      Min-       D#g.     Min.
Catch.
Area
1
(km )
1     114001     OttdhKtSB near Aqd
OB       41          36        25          9961
2     114002     Angar near Nekemi                  1 09          30         36         35        3742 3     114006     Osoana near Abas ma                 09         02    I 36            03        2BB1
J----=—
1--------Za.
Period
4i yhruairzu.fjf1ir-vi 4
i n1fiyAgf.f■l'siUnUri*d.
■4 rhfi 'Ti i DR.4
iyoz ij”4
■4 rtfin "ann^
lyyy-^uuj
«
1140G7     Angar near Gutin
2S
5    114DOB       Yetou al Yaou p-----
1
07’        43          36 1*-- -
42
—_■—
47                 1y79-d£UU4
6    114009      Urgessa near Genroe                  07         50         38
3S           19
4 r=iT-fi TiFIAlI
19 ry-Zu'jM
7    114013      DaDana near Bunno BedeHe      CM       24         36         17
47              1904-2003
a     1140'4          Dedessa near Dembi (ToDa)      08        03 —1
27
.---    1606
4 r-i*£
19E5-2UDJ
J lJT.rTi'"3
s     114016     LOKO near Nekernt                     09        22         36        36
-
375
__—------
10 114019 Temssa near Agarc 07 51
..
36
—
35         47 5
1997-20O4
1989-2004
ii   113004     Melke near Guder                        08        51           37        44           38              1998.2004
12    1:3038      meins near Guder                        OB       56           37
45         111
—JL
1966-2004
IS    101006     Jka ai Uh a
□8        10        35
22         52 5            1980-2004
14    Q9100B    Gilgeignibe near Asendabc         07        45
37
11        2966            1967-2004
' 15 09’312 Gojeb near Sne&e 25
d
36
23 3677 1970-2004
L
Water Works Design & Supervision Enterprise
In AMMilttoa with ]niereonilneni>L Coniuliants and Technocrat Pvt LtdArjo Dedessa irrigation Project
Meteorological and Hydrological Aspects
Annex E2 Mean Monthly Streamflow at Dedwan near Arjo Station
i Million m3)
May 2007
Tear       Jan
Feb j Mar ] Apr j M*y 1.
Se£
Nov Oec
■
1054
1124-
-
■
s
51 5
44 0
37 5      94 9    65 6
286
1176
1613
1503
1304
280
581
3*1
29 B
28 4-
622
930
1170
855
107
19 3
179      42 7  147 1
324
672
1370
1040
374
184
38 2 ‘
54 9
230
1049
1301
1178
1337
205
55 4
253
164      47 8    27 8
168
834
1051
665
957
320
71 0
63 4
57 7     74 1     62 5-
857
1086
1212-
•
-
22 7     20 4
708
1.2*8
1201
1260
459
96 0
52 9
21 4
a
-
W
"IB
50 9
46 7
67 1      39 7    732
349
956
T421
944
291
89
34 l -
45 3       288            929-
-
-
181
177 5 55 9
170 3 73 e.
157-5 210 4i
88 T 4*2 62 1
37 0     16 4     10 9     12 5    53 5       241           *23        1175           949         752        304         105 3
52 4 29*
25 9 112
196     35 7    56 4       118          003        1237           719         209        117
4 7        63  109 3       250-
*                      1401          592        149
52 5
64 8
36 5     16 2     14 4       9 1    93 7        261          641        *278                                          119           48 9
24 5
21 9      11 5-
-
-
•48 3    37 8     24  7*
b
»
25 9 55 5     20 1
l* 1
12 7 -
12 4 80 1-
-
-
-
-
151 *w
324
89  5 128 7
-
-
1979
19&C
190'
1982
22 9    46 4       130          513          625          819         262          94 180      153       mo      6*6   1909        504         914       1288         1244         393        103
80 0     43 4      433     35 4    53 7          53-
-
*
-
-
59 8      ID 2     26 6     19 3    45 7       248          707          947          692         761         177          94
1%3         43 4     31 7     34 1     23 3     524        151         566       1119         1116       1231         265        121 3 i9fM         38 5      167      119        95    26 6       185          703          665          521           131-
1905
1986
1W7
19BB
1981?
1990
1991
1992
1993
120        54       2 5       n 8    62 4        169         438          927           842         260          79          45 0 176        9 5    16 1     13 8    12 B        H9          452          494                 732           222-
no          59      124     17 3     36 7-
-
673         388        160
era
5
4D5     27 5     21 6       7 7    37 a       2BC         555 •               *■
-
189
233     20 4     33 5    27 1       121          273          439        1QB7-                     107        123 1
53 5      300      338     60.9    42 0       157          343-
*
-■
--■
543       1143-                 ■             *
24 5     23 9       i3B     20 7     565       161          368         824          564         806        164
38 1
73 4
42 5     27 9     24 4     54 7   1052        3l2          600       1159           631         4Q7        177          63 3
19.1      196     15.5    ■ 57     59 7       220          534       1221           056         156          58
36 A
Water Works Design &. Supervision Enterprise
In ASSCtiaiion with IniertontmentaJ Consultants and Technocrats Pvt. Ltd.Mn a«k« [mfj-jui hujen
Mei&ortj Irinin nd Hydrolpgicai Aspects
UJUl l
£2;     /.... Continued)
L^ Jin Ftb 'Mar Aof JU tv Jun Jul
r
' ;a uq Sep JOgI
k&u |C    tec
1995
l^T
ltefl
1999
2000
2001
2002
2003
200
MM     122    MjB   t9 4    38 3        as        225         569         466          iW      gQ ■
*-
41 4 ■g o-
304 14? 8        373        723        654         598                                      87 2
-
f
-*                    >-
_ ■■
*■ T
-
*
-
-
■                           -                                 242      1357
B5 i    59 5      «■    57 2  126 3      401         740       1W5       1005       6?4
215        mi ?
99 0    57 2    55 3   63 4    46 2      >75        457       55?         575       211      115
__ Jr
83 *
362      552    74 3                 120-
«2-
--
521    40 2    30 3     26?    65 2      202         Sffi         639         543        536      140-
<nr
CV
S>#w
462 217 260 33.2 66.5 223 654 1007 389 581 177 909
0.4? 0.52 0 66 0 71 0 59 0 46 0 34 0 30 0.32 0 68 □ 51 0 50
0 66 0.6$ 1 14 0.54 1 M 0 74 0.22 -0 16 0 43 073 1_2fi 1,00
Mi-
990    63 4   67 1    94 9 190 9 503 5 1176 1        1612 8    15025   1337 4  459 2      210 4
W.in          12 0       54       2 6      63    12.6     53.2     225 0     49? 1     <a$.g    130 8      599 Mean annual flow « 1821 Mm3)
Water Warks Beslpi i Supervision Enterprise
Id AnomUMl Witt IblEKDQttltDOt CCBSultajiu ind TectkuDtnu Pvt Lui.<n-n Dedttta Irrljratnin Project
Meteorological and Hydrologies Ms pects
Efc 41 Mtan Monthly Stream Ilaw *t Oedcssafi near tMmbl Station
2O0"
(
Million mji
____ —.———i——------------------
fear
Jan
Feb      Mar i Aof Mnw
■■ —T"
Jun Jul Aug
s-e
Oct 1   Nair        pec
19B6
1967
i960
1909
1900
1991
199?
1993
199a
1995
1996
1997
1990
1939
2000
2OOi
2M2
2003
2004
fid 3 7 ■i 2 7 0 25 0 92 @3 1W 302 2T2 ?02 21 9 85 5.5 9 7 04 9> 4 50 262 2M 299 67 22 9 11 5
5 9       4 5       9 7       9 2     10 6       105          243          342           218           ’04      44 1          27 1
17.9      157     12 5        64     23 9       153          217          392          4B9          147       52 0          18 0 11 9        76       4 5     11 5         Bi         31          1&7          253           272          142      24 0          13 E 10 3        58        56     22 r        90          52         252      5454           362        126     20 9            9 4
72       6 3       56     12 5     29 5         76          305          622           263          14Q       13 4            6 ? 7fi      153     12 0       8 8      366         70          136          269           103         71£i      45.?          17 1
11 2     17 2     156     3? 6      80S       252          334          370           204         11D      40 7          nd 7
1.2 3     13.5      160     22 5      37B       n2            274          361           202          S9     30 5          16 4
129    12 1     15 5     23 B     48 7         07          >90          272          331          101       32 5          33 7
129        94     15 5     23B     48 5         07            IM          272          331          101       32 S          33 7
2i 2     13 8     23 2      30 i      552       >42          219         34 J         2CM        262                   55 1 2B 1       136    ?D 3     12 7    3T 1       no           ?72        415           595           329       880          21 l
130        55       6 3       9 5     54 9       14B          242          245           214           302      40 4          10 3
10 2        56       4 5       9 7     41 2       119          290          309           242         209       92 0          21 3
12 7       9 6     11 2     14 5     55 5      22B          330          322           295          212       59 fi          22 5
6 5       6 9        66        90        65         63          t’92          255           195           60       27 7         14.19
7 4       4 a       92     24 0        57         59         241          223           324           62       20 3         10 01
13 O    1.3 0     13 7     33 0     95 5       19*           206          208           145            39        IB a          10 0
Avrrjgc
icv
$*aw
WAX
Slftn
122      £47     TT 5      16.9    36 4    T»2 4       232 4      3569             273        ?54S       404          20 5
0-17    0 4£    <?48     0 56    G 69    0.526         0.27     □ 326           0 20     0 561      0 81          0.53
s 35    0 3F      G47    OUT     0 85    1 020        -0 47     0 927            0.89      0 658        26          1 96
2fi T      172     23 2    37 6     98.5       252          334          554           403        329    107 9          56 1 5.9       3.7        42       64       6 5         31           93        165          F45           39     13 4            89
Me»n annuls flow = 1l5S_Mm3i
Water Works Design k Supervision Enterprise
H9
to unnu)u wti mt,„„„„„„ CoK<ll,„H
rXoema
Ltd.irjft&Nltsui i motion Projeci Meteorological and Hydrologic*!^ P
May 2W"
S   PC1
-
E4:      Annual Maximum Floods linnOsi
rat J J SMI&e
r'**r
nrQe^rirr
4,n jr HToJr GuM
?
Fear
DWHl
flpjr -J ».-U
PtM-JESJ I n-r1-i oe*r
JltJf Of-m-liir
.giensMrao _________
1
2
151
198
3
4
5
6
7
a
244
271
300
370
267
467
130
330
132
272
173
127
159
25fl
2^1
217
15’
167
205
231
1?fl
ne
9
633
1173
m
789
BSC
951
814
1165
78'
335 3fil 2M
247 25fl 157 27i 252
10
11
12
13-
14
15
IB
17
634
536
721
49U
645
554
1063
360
480
502
574
771
750
646
804
353
525
525
744
213
206
21?
243
354
226
20D
151
109
262
i&4
175
226
175
211
264
434
440
247
196
257
297
■50
314
<56
129
■4B
151
223
135
339
105
136
284
214
140
249
177
288
138
143
341
236
202
248
119
92
9C
127
143
85
121
247
56
105
314
184
150
203
226
132
245
366
104
12a 14’ 73 S& 124
137
134
105 125 142 135 T 42 149 1 70 172
109 106 79
iai
120
312
EOi
192
237
153
255
100
174
16*
261
1134
150
282
132
193
199
439
236
Witer Works design Supervision Enterorlse
In A^dittaD WLLT1 iDtWWmiifflt!] Cnn^luncs and TKhMtntt Frt. Ufl.I I I 1
I
iE5 MeJisurod 5edim«M Conretilialien At Gufflira Gauging Station
No
Field
stirr.ple
Nn
I ab No Rivnr Stream Sl.il ion Dale 4 Time
of Sampling
1 uric
i.Secj
CV heigh
irrt‘i
Flow
imVt]
Depth
mi
W*dlh
Irtlj
Sediment Concen
mg/ll
Hrrn.iifcs AV
4H4 J 495 2
4Afi         3
604          1
66$          2
666          3
1057        1
1056        2
1059         3
1190        1
1m         2
1192         3
I 1223          1
| 1724           2
1225         3
Dertess-a
Toba
15 Mai 90
0 43
4 16
0 26
Dcctess-J
T oba
15-Mai 90
0 43
4 10
0 70
B 9ti          51 56
13 rl              40 00
Dedessa
Tuba
15 Mai -90
0 43
4 16
0 36
Dride&sa
1 oba
21 Mar-90
0 50
5 41
0 54
Dedessa
Toba
21 Mar-90
0 50
541
0 60
Dedes$a
1 oba
21 Moi-90
0 50
541
0 39
Oednssa
Toba
2-JUI-90
1 fll
9 14
fl 40
D*(tassa
Toba
? Jul-90
t ai
9 14
fl 00
Dedessa
lota              2-Jul-9D
1 61
Decfossa           1 oba            22 Dec 90          50          0 40
Dedcss a            Toba            72-Dec. 90          50           0 40
Dedessa           Toha            22 Dac-9<1         50           0 40
Dudessa           Toba             18 Sep-90
Dndessa            Toba             IB-Sep 90
Oedesss           Toba             18 Sep-90
2 46
2 46
2 46
9 14             7 no 4 37           0 43 4 37             0 74
4 37             0 46
98 50
90 50
96 50
20 ? 70
14 0 61 66
13 3
19 9
70 14 0 21 0
1 2696          1
1 2699         2
1 2700          3
I 2704          1
J 2?05          2
2706          3
Dedessa              7btja         16-May-93          45            0 46
Dedessa              Toba           16-May 93            45            0 46
Dedessa               Toba       16 May 93            40            046
2 59 0 66
2 89 061
2 69 0 71
19 5
65
13 0
42 fll 59 69
173 13 90 63
215 31 135 G?
190 00 90 94 99 37 63 13
141 56
187 B2
124 69
87 90
108 63
81 40
Dedessa
Toba
1?-Apr-93
0 64
8 01
73 05
64 61
Dedessa
Toba
l2Apr-93
064
a oi
______ Dqdessa
Toba
12 Apr 93
-
61 59
0 64
a oi
59 20
Water Works Design & Supervision Enterprise
In JssoclaUan with Inwreontinenfa] Consultanti and Technocrats, Pvt LidI
TMeleorological and Hydrological Aspects
ikjij CiiniJ'
F5
No
cortf/fluedl
Field
sample
No
Lab No
R>vor 1
SlicAffl
Station    Diilc A lime of Sampling
lime
iSec}
G/beight
iml
Frow
im>l
Depth
tm)
Width
.w
Scdimeiil
Concen Remarks
(mgi)             AV
541           1      179/04     Dedes&a         Arp        10 Aug U4      30       2 45
54? 2
M3 3
De-dessa Arjo tO Aug-04 26 245
Dedessa Arjci 10 Aug 04 20 2 45
544        1       ian.'O4     Dedessa         Arjn        11-Aug 04      32       2 56
545        2                      Dedassa         AijO       11-Aug-04      20        2 56
546        3                       Dedessa          Arjo         11 Aug 04      27        2 56
559        1       185/04     Dedessa         Afjo         1 Sep 04       29        361
143 12     9 05fl       17 5
143 12 9 111 35 0
143 12 956 52 5
196 11 11ft 1BO
196 11       9 6fl        36 0
196 11 9 6f1 54 D
611 23 13711 18 0
1417 50
1739 74
1740 74
1652 06
1718 12
1639 31
1360.22
560
2
Dedessa
Arjo
1-Sep-04
26
3 61
611 23
14 3R
37 0
1326 Bl
561
3
Dedessa
Arjo
1-Sep-04
29
361
611 23
1 460
55
1438 44
142
Water Works Design & Supervision Enterprise
In Asfioclatlon wilb Intercontinental Consultants and Technocrats Pvt. LtdAnnexure - 8
HYDROGEOLOGICAL
STUDIESI I I I I 111 !■■■■■.. ■HjdrpgeptogjcsJ LnvestigatKui^
TABLE OF CONTENTS
I*faLL OF CONTENTS_________ ______ LISTOF FABLES------------ -------
LIST OF FIGURES
1 ISTKODICTIOA __________
l 1 GJhl^al
T J LOCiH£»
TJ Pmyshkhapxv
1 .* Ml TXCrtXjL W AND 1fJ**CuUME5
1 PHI MGU HYDROGEOLOGY                     —...
2.1 HtaftOG4flH.i>&CJU-SETUP
2.2 Hrra»«6<X0CiC IMH
2 2 i FfKfurfliP anchor MfltfMratf ygtolM
2 ? J Affvrt?/
2 2.3 Df R/■‘*3* ■Zfltfi'i'TNlinfS
2 J INVEnTMt and AEll DATA
2.4 HI*DRDDTMAifrC FaRAMETTHB <X aQuifERS
.   ..
I !■■
.«... „ - J. M. I I II I! ff—T—T
B . -         . . . . Mi a U. fi I I ■ rrc - ■           '
T-GROl'WMb aTEK POTENTIAL-..—.™™—........................
3.1 GROuhDWaTEB RECHARGE ESTIMATION
J. 1 T Sfl'ia iTo* arttfJ/JrS
3.t 2 WBrar ftatoME
■A- W Al 4R Qj! L A L.l FY —aai—u I.aa-J,1 M ua,i,aj —TTTwrrn-rrrBT—1 U-Jx"*
r?—Tr—“u“u “11
4.ii Water samples
4_2 SaWPUNG TECHNIQUES *NS ANALYSIS
4 J PHI TOfflAi. REPRESCNT*no«s Off WATER QUALITY ANAL^S-S
■I 3 i P^wf diaflfBm 4 3 2 SOwWflf (fraffTTiny
■f J J ST'fl tfrapra.TT
_______________-_________ ._____ ....a.................................
4.4 AflftlCVLTufeAlJWBiiGATlON WATER QUALITY
5. PIEZOMETERS OBSERVATION WELLS AND W ELL FILED . .J1.11Ja.a_ .. _
5.1 Eh 5 TRI ft im on DP PiEZOMETERS-’ObSEHY ATIOH WELLS
S_2 Future we ll held
4, WaTER LOGGING AND DRAINAGE_________ _____
6 1 TCPOGRAP MC FEATURES AND SOIL CHARACTERISTICS
■B J Existing wQuHCnwiTg r table
4.3 Future grguhcnvatea table and rechabge prom irwgatiom
J. SaLIN IT1 AND SO Diccn —------------------™—____________________________ __ L EXStTING AND FLT1RE PROSPECT OF GROUNDW ATER__________
I i Existing grgundwateh development
3.2 Future grouncw ater Psosf’tcT
Witcr Works Design L Supennsinn Enterprise
la AiBHkaEkii m iHCerMDUMnat MMkQQ ABd TecUBocrtu Pvt Lid.I I I I
■
■4r)o Oedun lnrtc*tJ« Project Hydrogeological investigations
Blay 2007
LIST OF TABLES
Tatxe 2 J      Details of boreholes m tne study area............... ........... ........
Table 3.1      Monthly local flow and Minrmum fk>w of Dedessa over near Arjo
Table < 1      SAR and EC values in terms of irrigation water suability
Table 4 2      SAR and EC values for surface and groundwater in Arjo-Dedessa area ... . Tab*e 5. i Locations of the Proposed Piezometers
Table 6 t Annual gross crop waler requirement at primary canal head Table 6 2 Estimation of wetted area for Arjo- Dedessa irrigation canal Table 6 3 Seepage ios$ from unhned Arjo- Oedessa irrigation canal
LIST OF FIGURES
c igure i 1 Location map of Arjo- DeOessa irrigation project
Figure 1.2 A map showing J- D view of Decessa over Catcnmenl....................................... .......... Figure 2 i A map showing nyorogeotogic units of Deaessa river cathmeru
Figure 4 1 Location of water sample points 
Figure 4 2            Piper Trthnear Diagram tor Water Samples Figure 4 3 Scnoeiier diagram for water samples ..
IIIRI I I 41 I I lit Bl IB IBBI I B■BB 11 IIIIH * IBM ■ HBM I •
Figure 4 4 Stiff diagram for water samples............................................................ Figure 4 5 Electncai conductivity (EC) in psrcm ano Total Dissolved Solids (TDS, in
htg/L for............................................................................................................ Figure 4 6a Map Showing Contour for TDS
Figure 5 1 Proposed Piezometers/Ooservation wells
Figure  6  4   Profiles  along  different  lines  in  the  command  ar',er“ a Figure 6.2 A map snowing lines of profiles in the command area Figure 8 1 A map showing groundwater potential areas 
............. ■--••• Miuri 11 i .
... . .... .
. _ _ _ ...................... ......... |
Water Works Design & Supervision Enterprise la UMcfcttoo nth (MertohUMataJ ComuUmu a d T^bnocrau, Pvt Ltd
CI I
■
I
II*no dmbu* rmr«j»n Project
BytlrogeoJogtcai Investigations
1 INTRODUCTION
1.1 General:
Hyarogeoiogy refers io me occurrence, movement. chetrialry (qualify), etc of grou m general it nas a diversified apprication in developing, utilizing and ma ' g 9
Half 2007
3
study and design of the pr^ct According th.s sttrij at Feas.bility Stody lecel has been undertaken
Water Works Design & Supervision Enterprise
tn A>«euaoti with loT.rHnflBwixl Cwiultaata d Tec tnotrvu Pn Ltd
groundwater Furthermore, different aspects of groundwater such as recharge drscna g
condition. aquifer type and set up, its interaction rmlh surface waler, elc are treated
(his discipline The nature of groundwaler and now il behaves, when subjected to natu
man-maoe activities r$ studied for different purposes such as for water supply ido
agnculture and industry j and construction of surface and sub surface engmeenng structures 
teg., dam, tunnels, drainages, etc). In order Io develop and manage groundwaiei one has 
1c know its potential, qualify and movement
Etnioptff  nas  diversified  nyorogeoiogical  icatures  mat  are  attributed  to  ils  geocogy  structure hydrometeorology,  topography,  eic  The  hydrogeology  of  me  country  has  noi  been  studied rhorougn.y so rar With the exception of few areas such as Rift valfey mai has oeen mapped al  scaw  of  1.25C  000,  the  country  rias  only  small  scate  (1.2,000.000)  hydrogeological  map Mydrogeckogy   >5   usually   applied   for   locating   borehole   sites   in   light   of   water   supply Groundwater  has  been  usee  without  oecail  understanding  of  the  resource  In  spate  of  ample groundwater  resources  01  the  country  very  little  been  studied  and  used  so  far  Currently however  ncrt  only  grounowsTer  development  anaror  utilization  but  also  rts  management  es gertma an attention
Smce any  development relies  generally  on proper utilization of natural resources, the gavemmeni has  also given locus  on water resource development both for domestic  water supply  and irrigation As  part of this  water resource development. Integrated Master Plan Study  ot various  Rrver basms  nas  been undertaken in Ihe country  since some years  The Abay  Rwer basin is  one of them Arp-Detfessa irrigation project has  been identified as  one of the projects during "he Aoay River Basin Master Plan study 
rtydrogeok^l mvestigaHon and study that mainly focuses on groundwater occurrence mo^manl, ChMtofy. etc ha Men incluow as one of the components of the feasibtlHy J•Arjfl Dedttii LrTtfiUcn ^reject
Hydrogeological investigations
12 Location
Mty 2007
The project area is  located within Dedessa River suobasm vrbich ifr in turn located m Abay River Dasm. it is  within the Western Oromia National Regional State, particularly  at m
junction of East woUega. Iluoabor and Jimg zones. Toe sub oasm of the irrigation' project is bodBreu oyQmo-Gibe River basin on eastern side and Sara Akobo River ba»n on SW 3MJe The total area of the catchment al the proposed dam is  about 5,632.Mk*t The project location is shown in Fig l 1
The project arBa can be reached from Addis  Ababa through two alternative hign ways  that take either to Sedeie or Nek&mt. The all- weather gravel road lhat lanes  from Nekemt to Bedeie passes  through 1he project area. Hence, in general the project area is  about 480km from Aodis Aoaoa through Jima and Bedeie
211 H I II1111F5uof^Auti
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Hydrogeological investigations
May 2007
GerJessa river caicnment rs shown in Fig 1 2
1 4 Methodology and approaches 
in order to unoenake it* hydrogeoigoicai. etvesugeiiDn of A/jo-Dedessa imgabon profect
area, (he tolldwing meffwtWtogy and approaches have Deen used:
•     Reviewing  of  tntr  previous  works  and  oats  available  with  different  institutions  such  as MoWR,   institute   of   Geological   Survey,   Regional   Water   Resources   Bureau   and Offices Regional Water Works Construction Enterpnses.
•        Feld     survey     to     collect     primary     information     on     georogy..     hydrogeology, geomorphology, ano other physical features of the area
•      Preparations  rn  inventory  for  water  supply  schemes  and  fixing  their  location  with GPS   measurement   oi   water   level   for   wells,   estimation   of   discharge   for   spnngs. water sampling Horn spnngs. wells and streams/rivers for physicochemical analysis
•     merpretaiion of aenai pnotos. satellite images and Topo maps (1 50.000 a 1
250,000); appucanons of various GlS and remote sensing software to identify and oel neale uthoiOgy and geological structures, and finally to analyze, ana compile the 5patia> cats, and tc incorporate them as maps Tor various themes.
*    m-situ measurement of pnysicai parameters of water quality indicators Uy using field water quality lesl kits (Ph. EC. TDS and Temperature meter)
*    F.ngly, preparations of hyoroqeoiocical marw umi-h based -an all che collected ana a^aiyzea data
____ _..________.
4I
I
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■Fig. 1-2 4 map s/ioidng 3-D rfew of Dedessa rivtf catchmenttlAllllIIIliiiiii**Arjo Uedtut JrrlfuJon Project
M»y w;
Hydrogeological investigations
2. PHYSICAL HYDROGEOLOGY
2 1 Hydrogeological setup
Ike    .n           w.oanc ».» flows ™.nry ».*»»> V—«’
MS     Mm(mes
s
“ ’"''’‘““7
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on    Jo.    ».    „
We
r     as    on    LuOnoo-    and    «o«ga    Sa>.o.    W    <*"=">>    •    "*"*    ca“,,'c
lava row e.ew wilPm ta Oeoossa River »*» ^erB OU,C",,, "
MseTO„,
or  vanoaa  9,annas.  sasses  ano  pogmawe  The  veloan.e  rooks  on  Jima  s.de  »»
r.1.oM    ,o   as   Lovv.r   pan   or   Jim.   WHoWe.   comping   Pood   Oasalr   with   ana   sakes   on the  wesiem,  soaihwestem.  eastern  and  sooiheasrem  pan  or  me  over  carciimeol.  vspe  > on  the  nigh  land  However  at  Iho  lowland  pan  or  the  calorene  nt  along  the  Oedessa  River, lhe  outcrop  <s  referred  Id   as  Alghe  group  comprising  biotite  and  horn  blende  gne  sses. granulite ana migmatite w>1h minor Meta-sedimentary gneisses
The  '/oicarucs  are*  05   Laie  Eocene1*  Lat&  Ohgoccne  ag&,  whsre  as  the  gneisses  are  of Arcnean  age  Tne  volcanic  rocks  (bawfoc  lava  flow)  m  Bedeie  area  is  referred  to  as Mflkonnen  basalt  cumpnsing  flood  basalts  di  directly  owftrltes  Lhe  orystaUina  oasamem  that snows   me   jncontormatite   relation   for   the   two   outcrops.   Il   is   Ohgocene-Miocene   age ^mitarly. Aro area is compnsed By such flood basalts ol 1he so-called Mawonnen basah
BasEd on tne investigations made m the area, variduS aquifer set up exist The main aquifers are weainered and /or fractured basaltic lava flows and other acidic volcanic rocxs such as rhyolite and ignimbrite The aquifers of volcanic origin have ooth confined and jnconf«ned character; for example the volcanic rocks in Agaro area shew both characters The confining layer in this particular area is highly weathered volcanic ash of clay size as reveaeo from existing well drillrig data There are aquifers that are attributed to sediments especially alluvial sediments along river valley and streams, and colluvial sediments near mounwms and escarpment in addition to these, there are also minor aquifers attributed to wealheren Dasemonl rocks tgranrtes and granitic pegmatatiles) This iast aquifer types nave hl*le significance m the area due to their limited areal extern and limited aquifer productivity T hc presBras of thermal springs, cold groundwater ana ratine springs m the area shows the o^rsrficalion o' the hydrogeotogitai set up of the nver catchment The aquifers of sediment
ano wwinerea basement rem origin are un confined. In
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Hydrog ec i HjficaJ Lei .mtig auons
,
Wrthift Dedessa River valley, deep £*nerra1ro<n of grou - underlying massive basement crystalline FOCfcB e*c*P geixogHLal structures as revealed by ttw presence -•■ ?r,Hr 1|
ma if W hinder ’*"*
.^ro th*v are contfOiBa E-'j
1   , r r -*
--
The volcanic ash a nd clay fonn th* confining taysr W w at^-Ewarmg
Aqurfer m Agaroarea can be menliofied as art exampte p'* *-' ■'l"lt'
wearherea i fractured) enhanciMg me mfiliwion of preopiialxr
grwuna^aiir recharge Groundwater recnirye m the area >5 «ry mammal due Io t r> ■
reasons, among them are the NQtl precipitation dense vegeialior co* J 
■ve^lherec and or fractured volcanic lava IIomvs
The  fin  am  groundwaler  r  echarge  of  (he  area  r$  the  SE  SW  and  the  M  E  par  a  r
*
he  n «
r
r
However tne presences ot thermal springs with in the Dedessa fiver valley ire atTntvuted
■ma n v i geological structures, faults The physicochemical characteristics of (he frwma
sprint;- mgniy vary from upsueam to uriwri stream along Dedessa River wrfhun (he proper
are* Allhough it needs Further investigation to verify the physico-chemical vacation me
long*- *e»xfence twne 0? rock-wilier interaction while groundwater hows trom upstream to
□own \nt-am could be one possibk? reason
The  topography  ol  Che  area  along  with  lhe  prevailing;  hydro-metecroiogical  conditions  favors the  tAisience  of  well  demarcated  grounowaier  recharge  and  discharge  area
2 2 Hydrogeotogic units
Graundwalm occurrence mom and quality  v» mamly  governed 6y  trre e^t.ng hyd^D^.c  units  The phrase hytogeotogte unit relers  to the nscks  (cwwoeoatw o unconsolHtaledi forming Lhe 1ran,B «,* for grouretwHwr Occurrence movement *r>i
calchmnni The pyroclastic  flits  of mannly  voicamc  ash uomposivon ts  found al most pads  o* the riYtr catchment such a-s  m Setema and Aina-gv  area The intercalations  of (he votaanjc asft with fractured and/or weathered volcanic lava flows- GBuM the emergency o imart *
5E T.j5 in me river catchment of the area
Wuer Works Desltn & Supervision Ltiifrprise
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Hydrogeological investigations
The hydrogeoicgic units m Dedessa nver catchment have Dfis^ catago
following unds They have Deen shown on map available at Fig 2 1
discussed nere under m brief.
2.2.1  Fractured andfor weathered volcanrc rocks
TM comprises basalbc lava ftows. acidic lava Kows and falls such as ig
pyrociMbc falls In this category of hydrogeofogrc unit, secondary porosrt
fractures produced due to weathenng and geological structures play immeasurao e
comparea to the primary porasityrpermeaoilrty The areal coverage of »h«s hydrogeo°g
unit r. Odessa nwr catcnmeni is 8.189 35 Kirf (79 56%).
2.2.2 Alluvial sediments
As  the name impba* these are c  oncentraied along rivers  and streams, and it comprises vancus  sediments  ranging in size Irom day  through sand and gravel to pouid&rs  The areal coverage of inis hydrogeologic unit in Dedessa river catchment is 1651 D5 Km (16.04% J
2,2.3 Delluvial sediments
Tnese sediments  bkisi at I ne t rendition zone irom the mountams/or piateaus 10 I he river valley  They  are aenved worn dawn siape moving earth materials  Irom mountains  mainly due to gravitational force From hydrogeological point of view. there are no as  such demarcated properties  between alluvial sediments  and delluvials  However, for Itie convenience Qi description, this  hydrugeologic  unit has  Oeen described separately  Delluvial sediments with m 1he project area have coverage of 452.91 Km (4 40 %).
2.3 Inventory and well data
in order io undertake detailed investigation pl the groundwater of the area, waler supply schemes  nave wen inventoried and their geographical locations  have been identified using GPS Borehole data have been oolleaed for detailed analysis  of hydrodynamic  parameters thougr complete well date are not available m the area Same of the measurements  that have been undertaken for water supply  sources  during the field Survey  are physical parameters ot water quality by using field test tots such as TDS, PH and temperature meter
Water Works Design & Supervision En terprlse
10 AlUCMti.. wtti taieretwtaeiteJ Consults tz  d TwfcaotrW Pvt Ltd.
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Hydrogeolog-jcat investigations
1,s * 2007
ln add-iion 10 thes* primary  data. secondary  data have atoo been collected on both water Qvaiily  and other Well data. Satellite images  and aerial photos  nave been interpreted to
•deniily   geological   struaures   and  other  ithological  boundary  demarcation  that  have  been venfieo py feia
2.4 Hycfrooynamjc parameters of aquifers
As  * nas  oeen mentioned previously, the mam aquifers  in Arjo-Dedessa project area are Irjctured a nd. or wealhered volcanic  lava flows  [basaltic  and acidic  lava flows  I ano sediments  alluvial and colluvial) The boreholes  in the fractured volcanic  rocks  ano sedJnenLs  are either with partial well data o< totally  without well data Table 2 1 snows the Dorenotes drilled previously in lhe study area and their depths.
Taoie 2. i            Details or ooreho*es in the study area ho         Weil ho           PAi*village            OopIFi              SWL
1               wei t               Metta                    55 75               te
2           Wd2               Metta                    43 4                 12
3           We«3             Metta                    43.5                  17
4               HT-2              Oollc Sin               27
5          HT-6               Chdaio Bddima     72                  "— ---------- •
6           HT-7              Chafe Anani         57
7          WCl T            Chuli                     62                    1.3
a Wen 2 Chuli 41
—
17
5                 Well 3            Chuli
’26
21
10            Well e            ChuH                    30
2.1
11            Wall 5            Chuli
25.5                 1.5
"2          WellS
—'■■■         ~ —i iJi
Cnuli
42.5
22
13         Maea Talila    SaKa«cna Brfiu    52 —
14            Iftu Brftu         Baxaieha Bdtu      35 55
Water Works Design & Supervision Enterprise
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Hydrogeo logical Investigation*
3 GROUNDWATER POTENTIAL
J t Groujiewater recharge estlmtrtioh
May art?
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-w.      «      usu^      nW      »      pc        gra—a®-      «*«*      "al         10          “      1'n°“n         G,!>“
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approaches is through waler balance metnod In eroer to employ 
groenonate, WK1> estimation, the necessary Oslo n»»e been acquire for analysis In
SU «»m.nta, to tlw msthot. Ms. flow analysis to. R.eer.'s«eam flow (DedWM R~W>
nm. c™ tod.he.eh to det,™ some coefficnmts >or water ba.ance Hence. - ■>»
ground water pQtenrtiai osiimston oi Oedessa River catchment ticin meintxi*
e<*iO*Oytd m order to come up with concreie result as much as possible
3.1.1 Base flow analysis
in onaer to employ  case lbw analysis  approach f<M groundwater recharge estimation. the rawMhi} discharge or Dedessa River from 1961 - 2002 for a total of 15 years  have been jsed. The nver flow aala -s  not consecutive aue la some missing dale tew some years AccDrWigly  the mean monthly  minimum flow of Arjo-Dedessa on annual base is  shown m TalMe 3 i
The diHerence between 1he total flew and the Minimum monthly  flow is  supposed to be lhe surface runoh Accordingly  The surface runoff For Dedessa nver catchment at the gauged statin is  1.105,7 96. 874 m’ Where as  the icnal minimum monthly  flow of lhe river is 1,5ra.W2,93B m3 as  shown in the TatJte 3 1 The basic  assumption in deriving groundwater recharge from oase how analysis r? that She monthly minimum stream discharge ■§ equal io ine base tow This  approach has  Uefln menUpncg fay  Wundt (197«) 1bSl the monthly rr nimum WMffi discnarg* Bost appreciates W base flow, especially Tor tipimd Climate
Tnaralom the base flow that l3 supposed to Correia tQ 1 b» gr^Mwater ™arqe.S round IP be i9t 6mm. This  value is  oMamK by  dividing I.SGZ.Q^.asBm3 py  the area erf (he gauged CBChnwnU, wt^ ta SjftW Th.s arnpunl of gropnd water ,echl3rge ,s
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BydnogeoJogical Invtstigadons
minima. as it amounts to only aooui 13 oj% oi *hnzh is ■452.9mm
Miy SOOT 11 53% of tne total 0Anual pfecjprtaiioo of me a
Furms.mo.e oases on the same method (he surface runoff ol me Rtve
m
teen
„ toe strferenee Oetzen toe .«.( ™=-
1(0. on annua, ease ano woras out to
Thft ■■aive <5 used to derive the run off coefficient surface r un o111 Of She e nlire D edessa c atchment t
o- D—» * .n—
m> ma> * a.tr.bated to so
w -n. the river catchrrisnl to asses tne i  ce
ha an
11     usftd in the water c glance
approach al 1he groundwater recharge estimation m the next section.
Tabtt 3 1 Monthly total now and Mmimtxn flow c4 Deoessa nver near Aqo Parameters
a,,
_________
Difference
—T-r-r—--- .aIj *—ak
Months
M'Tm
c
MJ?month           Mbiec             Mf month
M vse
c
Pfl ^niUHILM
_____ 1
J
- ■ IM                47238046
4 473                 11SBW8.3            13 16                 352575<i5
"F                           12 4
^934209
2^
owe
5443200             13 is.  i            24 551Q0P ]
M                       1Q44                279’3SZ4
2$87»4             9 48 _
253^3-89
A
M
J
’ 5 54
4052730?                      4 557
118117*4          11 OH                 25 715556
7SJ52326
10 3fr*
Z77sesM            IB 76
50293386 J
47             2SS23&5J2                    45.433                 11775233$           53 04                 137424496
J
75J 3?
7Q54O8&5B
137 385
367&1B416
126
A
423
i’3406W26
220 Gdz
590394317
202 74
33?*9O5*2
5*3G447Cft
s
6?
H-9’ l&igei
217 777
5454477954
126.C6
326713997]
0
2ifl.67
5sStii7513
58 377
156356957
150.3
429340555
------- B
66.32
177074554
.26 258
58004736
42 06
10901 i&iO
0
35 65
954E-5139
13 7W
369*0*93.
31 4*
58544646
□ad
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2,105,796,874
Q, = tulji rfior-lhiy d^charpe |nv), MiH Q = Mtnimum mgnihly tfi^ch^rge | M' ‘S) Ditf * difle^ence MTWeen
I he MUl rngnlhlv diS£Harge
3.1 2 Water balance method
By  *uier Balance it <s  meant equating or balancing the amount □( water inflowing ano out flowing 1or a given sysiem. such as  hydrogeoiogic  system, over a given duration for a given area hence i s  a a ynamic  s  ystem, ( Detay  1997) The nydrogeologic  s  y^tem c  an be a dra.nage oasm/oc  catch mem. groundwater basin* soil layer, or any  surface water reservoir
naLurai or artificial)
waler oaionce « a vaiuaoie too. tn tne 7tn y
al  S s 0  water
,|
in a reglOn The mol hoc
on oe employed for different purposes compulation of groundwater recharge, evapo-
Water Works Design & Supervision Enterprise
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Hydrogeological investigations
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The basic equation of waler balance is
trrllow = outflow +£bS
Where aS i$ cnange m storage
For ihv  siuOy  area, the mam rrfftaw component is  precipitation, but the outflow components are evapotranspiration ana surface runoff assuming all other components  such as  water aostracl»an Dy  human for other purposes  to be negligible Besides  this, the change in storage can be ccnsidereo to be zero if the water Balance rs made by taking waler year .'or hydrologic  year Hence. 1he ■/slue of AS will be negligible^ zero smoe the calculation is  lo be maoe on annual basis
Since ramiail record can be obtained from meteorological stations in the area the mam 135k left is  to e&iimaie /or calculate me potential ewapo-iranspLralion from which lhe Actual Evapotranspiration 1AET1 can be derived tor the catchment. In addition 10 this. the surface runoh has  aiw to oe esUmaled-'or caicuialeo since there is  no actual measurement of this component in the stuay area.
P*e surface rundl rcr Aip- Dedessa nver cawbrTrenl has been denvad (estimaied) as tallows
over land flo* from which 'he runoff coefficeni, Re. is caicuialeoaiiiiiiiiin mila
D = ovenana ftow = 2.105,796iB74 m
P = annual precipdatiDri -1452.9 rnm 1 452m
A = fl/ainage area = t.M, ™ 000 rflOOMW
alalron Bui this hoes not nwn lhai Ina total drainage area o1 The studied t>.
rfencs Rc = 2.105 796.B74 m’fl 4529 m * 9.9B1.000.000 m' "
This   Runoff   poeffioeni   is   used   w   estimate   the   surface   runoff   ’<x   th*   nv*r    bas'n    |OedeSSa Rrvwi under study 
in order io eswnate the surface runoff of Odessa area, the mean annual precipitation
1452 Sown nas bean used
rience w surface ^unott lor the entire Ded&ssa River catchment becomes  0 1452 X 1 452<n X 10.293,303.358 QB m2 = 2 170,141.254 31 ma Thus  the surface runoff wcxKs 
r
oui 1c  2*O.B3mm Thu ^aiue ■$ only about 14 51% of the icrtai annual precipitation m I he area Note that the total arsa of me studied rwer catchment at the out Jet of (he command area U 10.293.303 358 0S m®
By  assuming the coincidence ol groundwater oasm with that of surface waler divide and ano by  assuming that mere rs  no artificial or natural mcra-oasin subsurface or surface flow, the grourawater recnarge of Dedessa nver catchment can tw estimated as follows
GWr = P - '.Sr * AET;
rotate Gro-= Groundwater reenarge
P = Annual prBcrprta1ron= 1452.9mm
AET ■' Actual E ^apo-trartsp*nation
Sr = Surface runoff = 21O.B3mm
Tnfl  Actual  Evapotranspiration.  {AET)  can  tie  estimated  based  on  different  melhods  one  ol *   » me emp.rlCfl( Turc method TurC method ,s represent by me foiling formula
am
Dtdrssa Lrrigiuirt Project
HydrogeoJ ogical investigations
Rc = OTP A Where
Rc  Runoff coefficienl
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Hydrogeological Investigations
AET = Pa|09 * ipVL)*']
Where p = grwsuai mean preCip^lation in mm - 1452.9mm
■>J 3007
1 - annual mean air Wftiperalur# in  C
n
3 20
L 3 300 * 25T + 0 06T* |mm] = tiOOrrim
Hence, far (Jedcssa nver calGHmtni.. AET - 94d.57mm
Therefore. n DrtEf n esLimale groundwaHT recnarge for DOClessa R^r catChmern, lhe
vWue lAET = BM 57mm j ootarned by Tyre metnMl is uM* in the groundwater recharge eslmslon
balance melhca dI
Hence  groundwater  recnange  m  the  Dedessa  wer  catchment  oecomes  as  follows 
GWr ■ P - Sr * AET) = 1452.9mm - <944 57+ 210 S3j mm - 297.5mm
This  yafot is  awui ZC 40% oi lhe total annual precipitation m lhe ana This  mgn recnarge
rare  na>  m   attributed  possibly  10  Lhe  r
0a
i frvBly  Petter  vegetation  cover  and  tp  the  highly 
fractured r«r prevailing in the area
F'-ally an average vafua from lhe two melhotis the tWM flow analysis method (196 6mm) and the waler oalance method (2&7 5mm). wmeh is 2*7,05 mm, has to Oe used as annual, flKMfowatar Hcrerga o( 1he area This value IB about 17% at the qocai annual precipitation
•n me area**irjt Dtdcua IrngaUon Prcjoa
Hydrogeological investigations
4 WATER QUALITY
4.1 Water samples
teiurai wier mtrtds wtih env.cormeni, an also rt -5 affected by ant^pogemc process 
M*T W
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changing <ts chem»cai. physical and Biological constituents The utilization o
reawres an understanding of such constituents. Hence, the water should mee
quaMy sianaard that «5 set ma«n>y cased on its purpose iff order IO use t Some po _
physical anc chemical parameters have teen determined for the water ol the study 
compare its quality with certain standards set by different Organization such as WHO
specific A-aler uses
Water samples  rrom drffereni sources  nave oeen taken for physicochemical and microDKMogoi analysis  oased on the actuabexisting geology  hydrogeology  and geomgroAoiogy  of the area Accordingly, a total oi thirteen samples  have Deen taken Irom springs  anc  Wells  Fig 4 1 snows  the location of the water sample points  All the samples haw* seen suomiiceo io the laboratory  or WWDSE ror analysis  In addition to these water s^mpes  collected during the field work, previously  analyzed water quality  Dy  drffereni institutions nave seen jsed for nydrogeologicai interpretation of the area.
Among the collected water samples, four samples  were taken from springs  and nrne were from oorenoies  The numbers  of samples  have Been oetermineo based on various conditions  such as  geoiog^cai and hydrogeological setup of the area and availability  of previously analyzed pnysico-chemfccai and* mHcrobioiogical data in the area
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Hydrogeological Investigations
4 2 Sampling techfiiqucs and analyst
a total of thirteen samples have b«n ofled
sampte » collected from spring m order <0 see lhe reproduobHrty of lhe Naiurai waler is sampled ift view of carrying out various y 
.     - h»wn nollected for physicochemica. analysis me waler quality analysis water sampttS- have been co
covert water samples were from ground water <E(W and Well.) sources The samples 
nave peen taken with one lifer capacity plastic Dollies Irt order to compare
phySiMcnemiqal parameters, some physical parameters such as TDS
Solids, Temperature and PH nave been measured at fiard m order to compare with mat nt Laboratory
4,3   Pictorial repftsentalions of water quality analysis
4,3   1 Piper diagram
The Piper diagram plots the major ions as percentages of milh-equivahenls m two base triangles The Piper irilinear diagram far water samples m Arjo- Dedesaa is available at Fig 4.2 Tne total cations and Lhe total anions are set equal to 100% and th* data points m the hwj mangles are profeci^d onto an adjacent grid This plot reveals useful properties and relationship? for targe sample groups The main purpose of the Piper diagram is to show clustering oi data points lo indicate samples that have similar compositions
2007
One duplies laboratory result?
_ ar^iucM nn ii In order Ko undertake an^iwsifi The
Dissolved
the result
Tne P^per diagram can be used to plot all samples  in the open database or selectea sample groups  m addition, the symbols  representing lhe sample values  can De Customised according Id shape and color Other options  include individual multiplication factors  for each selecctd ion 10 prevenl data point accumulation along a case line The highlighted sample points  indicate samples  that are selected in th# database ano are also highlighted on all other open graprnical displays  According to the water samples  ptotted in Piper Irilinear dag,ar, to, A,».0eo.saa area. samples  dan fie calegonzea baaed on (hei, claslenng aa Ad-01 iO-'O AD.12 ano M>« as  one category  AD 02. AD-03, AD-04 AD-OS AD-OS ano A0-11 as  saeana ca^on,. AD-07 ana AD-OS aa u™a ca.egar, and f.na»y  AD-OS aa fcWto c.l.gcy  rtowwr. d « reline (unbar the waler type baaed aa ,he cbem.de! composition, (hey can be categ&ri^Bd in to five categories
Wator Works Design iSuperrlsion Enterprise 1.                 ™ ...a™^ C M1UDU „a
.
18■
M
■■Arjo-Deftssa IrrtgiUsn Project
Hydrogeological investigations
■   Na- NCOS w.isam(« AD.01 ■ AC-07. AO-OO *0-10. AD-,2 AAd AO-.3)
•    Ca-rtCO3 type (Samples AD-02 end AD-111
Miy aw?
• 
■
• 
Ca- Mg- HCO3 lypc (AD-03 AD- 06 and AD- O9j Ca- Mg- Na- HCO3 type i Sample AD ■ 04 J
Ca
- Na- HCO3 type ]Sample
AD-0
6?
Th,
,□
aruor.
™ 
«.he    d.He-.
h.    aa.np.os    ^ea..ng    «r»ua    eonmuona    o'
rucn-water interection.
4 3 2 Schoe-ller diagrams
These   seoii-iDgaritlunit   diagrams   were   developed   io   represent   major   ion   analyses   in   meq baa   kj   aemonstrate   different   hydrocnemicai   water   types   on   me   same   diagram.   es   typ graphical   representation   nas   the   advantage   that   unlike   the   trihnear   diagrams,   actual   sampe concentrations   are  displayed   and   compared   The   Scnoelter   diagram   in   AquaChem   can   be
used  >c  p»i  all  samples  in  the  open  database  o*  selected  sample  groups  only  Up  to  10
different caramelers  can ce included along the K-axts  and the symbols  representing the samnie points  can oe customized according to snape and color The Highlighted lines ir-dcate specific  samples  that are selected m the database and ere also highlighted on all other open graphical displays  The Schoeller diagram for the water samples  of Ago Deocssa area is  available n Fig 4^3. Water of similar source (type! shows  a similarly snaptc  curve where as  water of different types  snow differently  shaped curves Accordmgty  two major types  erf water can oe .oentified from the graph Calcium Drcarbonate Lypes  Samo*es  AD-02. AD- 03. AO- 04. AD- OS AD- 06 AD- 09 and AD- 11) ana the sodium bicarbonate types ■;Samples AD- 01 AD- 07, Ad- 08, AD- 10, AD- 11 ana AD- 13)
4.3 3 Stiff diagram
The   Stiff   diagram   method   of   water   quality   representation   jses   a   scale   (or   concentration   of JO n& in             along me r3l« The tons are arranges along y-axis in such a way mat Ite
aeons Na' Ca*“. are w the iett of the cemw □! m  ^tnng scale ana me amans are
e
10  lhe  right  Dl  11  It  rs  snown  Im  some  the  analyze  samples  .n  F»g  4  4  Acoonj.pg  [D   this 
ngure   water   S.mpfe   of   the   project
r can oe calegonzed m io ;hwe majOf groLjps  Na.
9 SB
HCO3 type .samples  AD-Ol ADO?. AD-08 AD-10, AO,12 and AD-13), Ca-HCO3 type * a"pwS AD-02. AD-03, AD-09 and AD-11>. and Ca-Na-HCO3 type (samples  AD-D4. AD- 05 and AD-06).
Watw Work, ntsijtn 4 supervision E^rprise------------------- '------ -
In
V.U,
^  “ B
C „„||1OU <M r   M
19■ ■ ■ ■ 111 mil*4
»
SO4
•0
0 AW’
H    AtM#
♦    ATM3J
-    AiXM
X    AD-CS
*    .4^
■0    ac-;‘ A    mmm V    ACWB
>- AD-14?
X
*
A£>M
ACtiJ
AD-TJ
'K'
Ftg. 4-2 A map showing Piper trifinear diagram for water samples in Arjo- Deaessa area♦irwpf]
a
:±z
ACMJi
AD-02
—< ... AC-03
_ „ - AC-I>
s    -■■A —        AC-Ofi
A£j-O6
AD<F
aDZ#
- 3 -            AC-09
- ■ -    A&10
0       AD-11
A0-12
*
S'
Ca
Cl
SO*
NCQ3
fig. 4-3 A map showing SchoeHer diagram far wafer Mmptas in Ago-Dedessa areaci
C-
-
rtcca
so-
it
—
CQ3
»c
■ at?-
i
c:
I
c:
I
r>CC3
50-
C!3
I
I
Kl
Ci Mg K
Cl
w
d
i
1
I
&•
Mf
=- ■>
1LX
hCC3
hQO3
SO*
I
_L
EC3
I-
1
SO-
COS
3
3
I
* *A>OS’ *
1
I
I
V
fc nup sh*mfi San diagram wr watt, »mpirt in Arjo- TteaesM Prtyta ar«a rOonceriL maq?_j
0
1111111 I ._
ill
K
A
CJ
HC3J
50- COS
AD- P9
«1                                          3* AD- 11
c;
■fc                       Si
*a
K
1f
X
** HCQ3
SO4
CO3
<■
«K13
I
**
0Aflfrhdtni ]rri[id&D JTpJ wt
Hydrogeological knvestigatLom 4.4 AgriC'dlEurai/krigaiicrt wafer quality
.
AgncuttlMi EuiLaoihly of wafer depenas cn flop type. ClnmalB. M>il typ®. <ind l, TI<!u"i
fflflaban waLer use ■Dbvij 196Sj The mam pawrteW* Io be analyzed tD *vP'uaie
imgabort wafer quality ate Boran Sodium hazard. ang Sal mil j These parameters a e
pienU e^her di.-^dly (B.g by causing an aduerse pfiySKlfookSl effects ) or indirectly (BQ by 
Tiling pian[ j.M[ ftetntflt Or mpislure uptake) Sahndy is best eslrrnjled based OO ElacLnua
Co.idudiYily [EC} value OttWf Jirecl indicator □* salinity is Tolal Dissolves Sohns (TDSy 
Th* iwc parameten TOS 4 EC are twisted by the Following M nation
TDS  imgfL|=  E40  k   EC  fdSfm)  wtiar*  m^L  =  milligram  per  hire.  dS?m  -  deci  Siemens  per FMfer
Accc.'dmg   to   u   S   Daparlmenl   of   Aflflqrilure,   waler   witl   an   EC   greater   than   4dS/m   ft considered as salrne
Sodium ihasardi >5 dsfr&s&eti Dy 1he s&>callecl Sodium Adsorption Ratio (SAR?. 11 «s caused by  sotfc  water Sodic  water is  water Uhat mas  high sodium canraniration relative to the cDFizenLraliofi o1 caicjum and magnesium Water is said la oe sadic if rts SAR is greater than 12 SAR is calculated as foltows
SAR= tM*T^5[C» * * Mg**|
a
1
Where   Lht   concentration   of   each   calton   is   expressed   in   imt-q/L   If   the   concentration   is expressed m mmoi/litrt SAR = (Na‘p >' [Ca** + Mg ’]
According  to  Todd  (IMQ  and  reference?  there  in),  the  water  quality  evaluation  for  irrigation baseo gfl SAR an<j EC are shown in Table 4 i
Ta&ifr 4.1 SAR and EC valuer in terms nr irrigation waler sutedility
Ww :im
fjMiir-H
Gootj
Fair
< id
Poor
5-hP
i0- i&
’8-35
WJlrCW                      Easafttere
EC
«.]S IT ■ -iln
■■25u
250- T5Q
P-WmtiLfU>oi            Doucil lb
KMK              2000-M0Q
u™ Jirabe
-3000
„     Mtr     B     ™i.     »,l.r     ,     uailty       (w       lmga,iwi       (rom        3,,^     anfl       Sod|(]m W *, ltD.d.5S. we Mr.™.,,, Men mwula()
sno^fi in Table 4-2.
i. 
lister Works DesigniSupervision Enterprise —
CtD!Llunii iM T[
£«'
a
3**Fjd DEdnu Imf >uon Piajin
jy«ln)gBpn»gieaf iiiYisnganons
iBDlc i.2 SAR and £C values(cx swrtace and grounff-^aier in
at a ” *£ •■
3007
a area
n.1 lx         ■Q-J L___
r—-1
11^ ,     3JM 21 £
Acci-cnq k 5AR values owned IflT the MB»f »"'(*«■ AD-Ol . AD-07, AD 10. AD
AC-13 M all «#c -to. >« AD-OS.............................. ..         “A”'' m a,a al. non MO.O f-vr imganor ooisr flUPMy t*"* »' «*» IM’ ,3"9a ' ° excellent quality “□ poor ctuaiity
Buifromwlinifr pint Of the qurty «r«4 frtm
”• 'ne ,e,T!ainin9 "
fm
id unsuitable. i.e from 41B
Ii5.cn-.1o4450^cm ftothef worts  itMbtsaid fte salinity  ranges  from medium sahnny 1C vtry  Hh^i saliruiy  F<g i 5 snows  values  of TDS and EC far cftfcriwl walat samples  ft the ptoteci area
Fifing 4“5 Etecsncai condueimty (EC) <n us/cm ano Total Dissolved Solods (TDS) in mg/L lo< *aiar samples in A^o-Deoesse area
™ g.aon ca.ly mdKa.E, TO eTOn. o> SMnlly lor
„ ate,
a.   in,   TO   EC   and   TO   TOS   Contour   map   a   TO   TDS   ..   a.a.TO.e   al     F,o     4   6    the     „0]ic-
'« MKnp„w M me
“““ on to., Eiednc ^WM, „ TDS .„
-, MIag0IIZBa lmj
fr '
.,
us
lo ABSGtLul«  wm InrsttoBClnMol ..... ............. •
Water Works Oosigu 4 Supervision Enternrlsf
'
a
IflnjBitua M(1 TtclflQtrita
,ns e
24I
I
I
I
■
■
■Arjo Dedessa tmjatlnc PtoJbcI
Hydrogeological Lnvesttgadons
bUf 20(17
AD-OS  AD-Q4.  aD-05  and  AD  06)  nave  low  »i*»rty.  four  samptes  <*0   07■ and AD-13  have h^h salinity . and two samples (AD-01 and AD-10) are extreme y
?
Th,s qu3lltallve desertion doesn't lolfow standard procedure of water qu y 
classil.cation based on TDS and/or EC. but H * s^ply for the sake ot descnption sampes cooed as AD-01. AD-10, AD-12 and AD-13 are all from springs, all other waler samp^s are Irom bomholes (drilled shallow Wells) Hence, it is possible to conclude evan if they are all from groundwaler, they art from different aauilers The more sail water               high TDS values! are mainly from weathered casement rocks (granite granitic ^egmalde.i, and oeep-seaieC volcanic aquifers especially along fau I
Ihermai springs).
,9
1
Water Works Design t Supervision Enterprise
In ASMcUUM with lotencnilooat*] CoanKuu ud Techaocraxs Pn. Lid.
25□□2
ftg 44 4 mip stow/ng IM contour tor Totof DiMofred 4i>o - Detfesu Pro/rcf ar**
sobd* fros/ns^ *>'
4I
I
I
I
nt
M A imp sftors* contour tot Total Dni&Mrf SoMtfJ fTOS ‘ Arjo - Dedeiu Prttf«r <f*»>r w
Bl*rjn Qi'Otss* irrigation Project
Hydrogeological investigations
5. PIEZOMETERS OBSERVATION WELLS AND WELL FILED
51 Distribution of Piezometers/Observation Wells
In order to monitor groundwaler qufllily and quantity o! the afC3 bu1Tl bef°ra‘ a
Jiij 2007
constructicu", ot the oam under investigation, a total o1 f ourteen ppez&meiers Obse wells hire been proposed and their sites have been located. The geograph
config.jrabQn.'disirit>ution of the piezometersrObservation wells is selected base
gecH&gy nytvogeotagy. topography grwjntfwater flow direction, etc of the area Since the deplf c! the ptezometers io be construcied rarely exceeds 100 rneters, PVC casing rerem mendable tn soma cases the exSting well oeolh al the immed.ate down stream o' the proposed flam axis are 50 - 70 melers depth
Title 5 1 ihow$ <he geographical coordinates or the proposed piezometers
Tacie 5.1 Locations nt the Proposed Piezometers
u*Dgrrphic*l eoerdknatf E (UTM]
I
3*r Ko Pitigmirtir
codti
1                    p^l
2                 P-er2
Eitting
2*1243
23957B
Marthmg
945073
942443
AIMudW |m}
.. .............1
1332
134B
3                  P-orl
235229                           948568
1354
*
R*E.“4                             232364
9*5622
1345
5                  P.p-i
237407
Ml 746
1391
6                   P«-6                         22MS2                           944575
1374
7
p «r?
230 IM
952670
13B6
6             P-n-B
225779
947133
1324
9                  f\B-S                         220 ns
■»——------------
954111
1341
10              P-4S-W                           21767?
951707
1319
11
317135
M1437
1332
i 12                      P-^12
21271*
■
95244*
1354
13              Par-il
Lu
2l«S4
21333#
95508?
961320
The consLfuction o4 ihese piezometers shall iolfcow the standard
1323
1320
procedures although some
s.te-specihc   cdOdiHons   such   as   hydrogeology)   Mi   up   will   a.so   matter   Tho     ,
QCal1o n
'
o1 th8
’
proposed Piezometers >s available &n the map srm^n ,n Fig 5->
Water Works Design k Supervision &ternnsl - - - - - - - - - - - - - - - - - -
27I
>r
»(
*
*
w
wAijq D’Edem LrrlgjlUcib pjojecK
Hydngeclogical investigations
May 2*£T7
5 -2 Future well field
The  Poteniiai  aqurier$  for  groundwater  storage  in  the  area  are  basaltic  lava  flows  with  minor sai'Ci  including  rhyoliie  and  ignimbnte.  ano  alluvial  deposits  in  the  river  valley  of  Dedessa Thi$ can tie verified by existing boreholes data in the area For example, Borehole data m
Agarc area snow this situation.
Well field sites  on which detail geopnysioal investigation shall be undertaken have been ideniiliec  nasea on geotogtcaL hydrogeological and geomorphologicai seltmg/or approaches  Tesi wells  drilling and construction shall follow the detail geophysical invesiigaUon
Waterworks Design & Supervision Enterprise
In R-sshIiUoh with teuwiMttMMai Cvumtluia Mi Twhentcrats Pn Lulu
N
M
*
I*
*
*
*5-1 a nrap snowfng proposed ^Momettrs, water pomes arxf waf*r sampling pomts
L
—_
’VCW u#r**>
■h?u
Si£>u Str*
>uzo
AW |9orr#y4
Goto
Sex* Cfleif fi
M
M
0
*
0
&
*Arjo BfOrssa Irnftidca Frnject
Hydrogeological investigations
6. WATER LOGGING AND DRAINAGE
6 1 Topographic features and soil characteristics
The jnauiasing and rolling topography »n upper pari o1 the project area g a > gentle nope pl flat land m Hie txXIom valley of Deflessa. especially [he icwe pa . cormnand area necomtJ almost flat This Hat land is covered wifi sediments a y callu. .il aelluvial and alluvial angin This sediment is underlain mainly Dy Las
li*y 3XT
1
The topography and iand chaiacrenSUGS af 1he command area can t>e sa>d ■ o level > 1%). nearly level (1- 2% slope,1. very gentle (2- 4% slope , and gentle (4 6 slope categories as about 35% ot Ife command area (alls under firsl two categories and about 23% o1 the command area falls under lhe last two categories Though the command area IS sttin, d rtas a rolling topography ano there are several small hills dispersed m the coiTimarifl There are nftng hills also an the outer boundaries of the command area on Dot bank? ol river Dedessa
maior part of lhe area is comprised of vertisol (47% ol lhe command area) thal has vfrry low  LW^n^aciility  Nex:  w  vertisots  arc  cambisois  ano  luvtsols  covering  15%  ana  B  60%  of the  are  m  respectively  Hence  this  sb«l  type  hinders  lhe  in  fibration  of  lhe  most  incoming racial  during  rainy  season  On  one  hand  thia  neips  lo  restrain  the  rise  erf  (he  groundwater table  through  reducrig  infibration.  on  the  othe<  hand  lhe  plain  nature  of  the  land  wouldn't aito* t"<& surface run off to How out easily 
6 2 Existing groundwater table
Grou-Ml water teval m lhe projeci area varies from 2 lo 20m h g I In lhe command area the groundwater taoifi is  2 meters  baiow surface during rainy  season except in few exceptional cases  ,J  surface water logging During dry  season lhe groundwater table was  1ound deeper lhar 5 raters  below natural ground surface The nse of the groundwater table can happen oue JiHereni rwtoral condilans  anq man made activities. The appl,cation of irngaicn praence is  toe maior human mterfereftces  foe nse of groundwater table Th® method of xngaton (orip furrow ete) that is  practiced and the crops  proposed to be grown *,li deiemwva the extent to which if may affect lhe nse m groundwaler level of tr>e aoa
“ kmctali. |Bi™oUbmw
Water Works Design t Supervision Enierartse----------------
hl
u<
imIArjo DedesSa tm£itfo6 PTuJ-ctc
Bytlrogtologtcal investigation
MV 2OC7
6.3   Future groundwater table and recharge frorrt irrlgsrilon
f
Whenever mere is a mapr mgatpri project wilti continued BrHJ intensive irng
there IS always an apprehens.on of n$e of groundwater table * nse of ihe groundwa e
labie is significant, and n continues unabated, it may cause serious adverse p
lertiicy or (h® land Some of the -adors that aflect the nse of groundwater are
■ Topographic features
*    Lane cftaraaenul«
*    Naturae drainage system
*    intensity and amount of rainfall
*    ExisUng grounawater taole
*    Son characteristics
*   Crops ana «ls water requirement
*    Seepage and other losses from cana< system
*    Surface drainage system implemented ano its effectiveness
T*» esiimaiM  annual  crop  waier  requirement al pnmary canai neao. for venous crops Io be
cuflwBlrt m the command area of lhe pnjposea Arjo- Deoessa project composes lour set of
vaurt-s  categonaed  under  two  phases  each  phase  having  two  rotations.  This  rias  been
snowh in Taoie 6 1
Tania 6 1 Annual gross crop water requirartwrrt » primary canal head
Str ho             Phase                 Rotation
GCWR (mm)
1
1 -J
1
987 40
2
1
'
3
__ i
II
1
1086 14
bl
1
1311 47
4
II
II
1423.234
-
In  order  to  assess  groundwater  recharge  from  imgalwi  water  the  maximum  value  of  lhe Gross Crop Wwef Requirement l.GCWR? in the s*conn p base o f $ «ond rotaLon that
1423  234  ™vyr  has  been  used  Therefore,  the  groundwater  recharge  from  the  appl.cal.on or irngatoOH nas been eslimalec under two main situations as follows
Water Works Design t Supervision Eritmrtse--------------- — In ^scctttioa wim liLttxoclineat*) CoBsuluata nd Tech noerxe Lld♦
0
0
0
0
0Dedeisilmgidcn Project
Hydrogeological investigations
1   According to groundwater recharge estimation made •
M>y 2OT7
. ihni rjSTifjrt fiul Cjf ttlU' l‘Dl-tl'1
annual precipitation in the area, only 1T% is gcwng fo* recharging the grou
if Ihe same scenario is corwdaracJ. annual ground water recharge
application or irngaleon in the command area becomes 241 95 mm. T
crude estimation since various factors among which the irrigation method can affects 
the groundwater recnarge
2     Along  with  other  crops  cultivation  o(  paddy  rias  bMH  proposed  in  the  command area  Paddy  is  the  only  crop  mat  requires  constant  standing  water  in  the  field  for  rts growth  and  d  evelopmenl.  Thus  paddy  cultivation  results  into  percolation  loss,  and only  that  quantrty  of  water  which  fS  lost  through  percolation  has  lhe  cihancu  and tendency  of  reaching  groundwater  H  may  be  noted  that  about  330  mm  of  water  is eslimaifrd  to  de  ins!  through  percolation,  and  onty  this  quantity  of  water  has  tne scope  of  reaching  groundwater  which  may  add  to  the  rise  of  the  ground  water  The intensity  of  paddy  is  only  30%  in  phase-  K  which  will  increase  finally  XO  45%  m pnase-  ii.  Consfcdcnng  the  entire  command  on  average,  the  annual  contributions  Qi imgauon   wsner   tc   She   groundwater   would   be  99mm   in  the  Phase-   I,  which  will increase to 140 5 mm under phase- II.
Regarding other crops, they  are all qty  irrigated i e.. no standing water 15 required The imgauon waler applied to the field in case of all other crops  except paatfy  will be contained as  sol moisture- within the rooi zone. Very  smalt amount 01 water which will be lost below the root zone, will reach the ground water Other losses  will be in form of surface runoff wnicn will pe lanen care Dy  sunace oramage system As  HUCh (he afldihDn IO grQu(ldwa1er 3 ue to imgation of all other crops  except patty  may  be considered negligible and fherelcre. may oe neglected
Seepage ma » the graunawara, I™ the Mna5 (mair,
secOTd3ry
cans!J, TOs also peen aalrmalu According ro unmo Slates Bureau ot Reclamation
tU S6R r. seepage IM, Iron, anlinad lmgstlDrl ci na.r.a area tor «„ an0 ,oa„ !oite. Basm Qn
,s, 5
tan Ago- Dertessa rmgar.orr canal rs shown In Tattle 6.2 ano 6 3
8
32ir
■
0
0
0trTl(*dflU PrtjtCt
aydrogeologicaJ iLTtsUpdons_____  _ _—-
Tjbla 6.1 Estimation of wetted area for Arjo- DaOostJ irrigation canal
^OD?
■
Snr
to
Cmai
tit* gory
Av trig*
witttd
p*rrm*i*r
Tout length M
Art> (m )
1
1
.ft
_
Rtahl
—         —I
Left
. ----------------------- 1
Rignt
■ -------- ------ ——1
Ltlt
IN^I«1
1 Warn CrBnai
2
■zaniii
3          Tertiary
utill
Totai
a 7iis           Mill
42.800 00 .
eojflO 00 1
”279 639 00 .
"*60 873 00
131,896 05
2 795 2 795 49.370 00 47'9D 00 137 989 00
1 02        1.02        199,4M 00          Z39 100.00          203.453 00
Total
Am*
[m’f
7*0.312-00
269*85 05
----- —  f--------- 3—
1------ ""--------- ”1
243.882 30 *47.33 5.. 00
11_*4■737r 317• OS
&
621,061 00             836.651 05
U nt w ™ W*'
irx “>        ™>*
Table 6 5 Seepage iwb from jnllned Arjo- Pedessa Irrigation canal
Nt?
Cwnmarfl area l*nng]
Riqni Bank
Wetted area 0« Csnai (mi1)
M»n canal          Seconoa^
canal
Tertiary
oana<
Total wetted
3
area (m )
Total
seepage loss (mmj
?     LHttBawr
■3    Tout
rT Tfful Swp»4" t<nTl
279.639 00 137 959 00 203 *53 00 621.081 00
460 873 00 131,896.05 243,882 00 036.651 05
7*0 512 00
23,320.796,31
2M MS.D5- 447.335.00
10,605,35*73
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In (he seepage Isis  MHmlation 1ram the Main canal, Wly  75%. of (ha tOlai area has  tlMr considered TTifi duratran ol LTie seepage toss  13 cornered io tie eight months  {October - htayl ano twenty F&jr hours a day for the mam canal, where as for six ninths 01 twenty four hours  for secondary  and tertiary  tana, The oommanq area an which the seepage loss  has Man averaged duI is the gross  commanD area, i.e 17,625 hemares  (T7fJ  25G 000 m ’)
t   the  total  seepage  tass  uf  *0,33(1,350.60  m1    is  spread  io  the  grass  command  area rthich ge^e an average seepage loss of2Z6.36mm irom the wngai^n cangi
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Therefore. the Laiai annual g<Du nd'^ier recharge bom the application d imgatio me SUm of« s.epag. loss f,«n th. «™!. W 26 and both th. pa.Oy .m9®«l
(1 40 5 mm) ihat is 374.76 mmP
Aflhaujn aeiaii aourfer and- soil sampling and analysis is required io come up
May 2007
result of the p&r&stty. ils value has been estimated to b« 35% -nine command area >
considering a range from cLay to sand soils This parameter will &e used to
graondwaier leyei nse due co the application of irrigation.
Finally by knowing ttw grounowafer reenact from the appticaUofi of imgatiWk and the
pwwty Cl the anuiler and the SOlI maienals 3M>ve it. the extant ol IOe groundwater
nse du» to uh* aopticainjci d! rriQBilan has seen esiimateti under different scenarios as 
follows:
Scunano I: No grnundw»t»r ftow* out of the calcnment (stagnant condition)
Annual groundwater recharge from SpplicatKrfi of irrigation, GR = 241.95mm
Effectwe paroiity of aquifer <sand] in commanS area. - 0 35 <35%.
Grcundwaler level rise due 1Q application of imgaticn,
GlNLr = GRrn, =241 95mm?Q.3S = 0.691 m.
Howevr- H anquio be noteo fhal grrxinrlwacEr is  arways  in a dynamic  condition, nence. the siagnam groundwater condilton never prevails  in lhe area Therefore, the Stated value of gpourmwater fevei nse (0 will never nappen
Scenario Hr Groundwater flows cnjlof the catcfimem ^ynjmiC system)
Annuel gmunawarer 'echarge rrqm application of imgalion GR = 24i 95mm
Effective porosity o! aquifer;sandl in tOTimana aw, rk, = 0 35 (35%}
Awarding  Io  M«  flow  separation  methoa.  the  ratio  Ol  grounpwarer  outflow  from  the  ent.fe n.e<  ratcnmeot  to  the  groundwater  lecheigt  of  the  talchmenl  from  preciprtatLon  is  79  53% nance,  lhe  remaining  20  42%  of  in*  gibunqwater  recharge  contribute.  to  gr0unaw3[oMevB. n«.   Simtoflr   »   »e   apply   W     dynarmorty   to   ihe   gr^n^ier   recharge   from   .mgahon   wrter
■ppfcMW. lhe groundwaier purii™ from lhe imgabon  ppi,
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Hence it we reduce this amount Irwn the recharge ■' u
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Scenario III According io lhe paddy culbvation 3no seepage loss irom canals, ,h® annua
ground*™, recharge from the apphcabon ol .rngabon * 374 76 mm as mentioned before
ir |hi$ ts ihe case, me groundwBier level rise due to the application of irngalio
stagnant groundwater condition becomes
Groundwaier level nW oue to appltoabon of irngabon. GWLr = GR/ri, =374 74 mntfC 35 -
lQ70T4nwn* l.OTm
Scenario IV < Scenario III unoer dynamic  condition): This  Scenario assumes  that groundwater ls coiMinijousiy  I towing out of the catchment Hence only  20 42% (76 53 mm I of the groundwater recnarge from irrigation water w4l contribute to Ifre groundwater level nse There1cx«. the groundwater level nse under this Scenario becomes. GWLr =■ GRyn =
v
76 S3 rnrttfO 35 - 218.66mm = 0-2l9m
In conclusion. the assumption of stagnant groundwater condition Scenarios  (scenario I ano IIIH over esbmaies  me groundwater level rise due lo th* application of irrigation Because it assjntes- stati&or stagnant groundwater condrton that ts  not the case in reality  since grounawaier is  usually  in a dynamic  condition The second Scenario (Scenario II) relies  on ground water recharge estimator! from irrigation water application equals  that 1rom preopitatort However grourttwaw recharge from irrigation waler application, particularly from paooy  imgaiion and canal toss  should be higher than from precipitation Hence, this scenano underestimates  the ground water recharge Therefore, according to this ,n vocation. the Scenarw ihai works  Ms' is  Scenario IV Hence, the annual groundwater mb-vcI nse due to the application of irrigation water will oe 0.219 m
Hoover " has to be noted ma' the tk.sMg soil in lhe command area lS mainly clay and
.oam as 
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The soil has an average hydraulic condudrvdy of 0 CO00056 i .# C 402 mrd&y MJue s very small chibrting lhe miration of any water (precipnaJion or irngationj to GwidwaiBr Hence, the coninbution of ground-water recharge from me app..catmr
*Tgabor; should be less than the amount stated here Therefore the groundwater ■e,.ei ise one to ihe application oi ungation cannot exceed 0 219rrVyear
Another factor tnat tan reduce the contribution d imgatcn application io groundwater tecnarge is tne presence c* number of creeps ihai are transversal to the trena oi me commano ta and Dedessa River Soma titrated water from the miganon application will cwne cut as regeneration through lhe crMks belore reaching the groundwaler table Profile across some creeks ano Oedessa over m the command area *5 available m Fig 6 1 la. b c, d afflt ej The wies aeog winch me "ruPJes nave been 1aken are also shown in the map Fig. 6.2
Wfi-ougr there fi r» we^ documemeo well completion data in Ibe corr-mand area, [he depth 1c grrwrdw.r.er in ihe area u oeiow 5 melers Curing dry seasons except in some creeks such as Chub area I,eastern part ot command area I where the water table is about 2 meters beraw groyne surlace Onty lew ooretiales ano iheir data exist if. Ute Dedessa River vatley d  project  area  since  d  H  inhabited  manly  ihrough  resettlements  cmy  2-  4  years  ago hence. axi6lmc1ion pl wroix map depicting depth to grawawater is hardly posstble under SvC-i cala ItmiLanon wee vwy are enlvtiy constructed 1or emergency purposes
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7 SALINITY AND SODIOTY
Salinity    at    soilsfwaier    can    be    defined    ki     terms    ofelectrical    conductivity    Paflicu    3    y 
rt   is   the   electrical   conductivity   of   the   saturation   extract   However.   sod   icily   >5   Ine^
of   6   xtTiangeaDle   SQflium   percentage   Salinity   may   be   C   stegcrized   ■   n   to   two   b   a&fid   0 sources     primary     {inherent!     salinity     and     secondary     salmty     Primary     (inheromj     salinity     IS denvaij    bum    the    weafhermgi'tJegracJation    cl    primary    rocxs/mi    nera    is    It    usually    occurs    when evaporation    exceeds    precipitation,    Where    as    secondary    wlkirty    >s    derived    from    the    upward rnortmertl    dI    salts    from    saline    groundwater    through    capillary    size    ihXler    the    situation    of    ir adequate    leaching    Thu    situation    happens    mainly    under    shallow    groundwater    Mass    flow    Io
the   soil   surface   through   capillary   r»   fl   known   to   cease   when   the   water   table   ta   below   2
meLers m p oay and srlty nay; where as the seme value i& T 6 meters in coarse te flu red
Waler ana so-i salinity  occur aue Io differnm reasons. Among Inem are over irrigation that causes  groundwater level nse due 10 in appropriate provision of drainage and/or crop water
■nefluiremertt    calculaKm.    poor    method    of    irrigation,    capillary    ITM    of    grouhOwatbr    due    to natural!)   nigh   groundwater   tavel   below   surface,   etc   When   such   raised   grau   newsier   level   is SuOtedtrS   W   ewpontion   loss,   the   chemical   constituents   of   the   water   will   be   left   Over   ana
□eccmes   concentrated   on   IhE   surrare   leading   io   soil   and/or   water   salinity   The   leaching   of some   exiting   nwlnenls   m   soit   is   also   lhe   potential   source   oi   salinity   ol   water   and   soil   m ttygation   m   order   to   MWH   the   possibility   of   salinity   for   the   project   area   m   the   future.   data haue    dmr     collected    and    have    been    ovjlualeo    Among    them    are    the    existing    groundwater quaky       (physicochemical       characteristics       of       groundwater},       ano       soil       chemistry       Other Parameters    that    have    been    given    emphasis    here    te    the    meteorological    parameters    that cause    high    evapotranspiration    However,    the    high    rate    of    pncWnuon    (rainfall)    m    me    ares an   coufliarac   the   prat^m   by   leaching   the   hignly   soiuWe   saHS   such   as   chlorides,   au[pnares and arbowe sails
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Hence, !he roszorcj soiMwaiar salinity  during ine des«gn penod o» toe project can be controlled naturally  {through h»gh precipitation and topography  of ine areaj or artificially througn appropriate irrigate water management.
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8. EXSITING AND FUTURE PROSPECT OF GROUNOWATER
8 1 Existing groundwater development
Presently  the- majority  of the Woredas' caprisi lawn, and the rural community  m the n^er catchment are supplied potable water from groundwater, eilher through bor&hole OTnstmcttOfi or from sprmg development with the exception of Bedels  town that get water from Dating River Ihrougn lhe Treatment of raw water The yp&id of groundwater from some volcanic  .ava tlcw shows  very  promising result bofn for cuirent and future water supply  from groundwaler lor different purposes  Can be mentioned &5 examples  are boreholes  for Aga re Lown wnare The yield ■£ about SOliUsec  from a srngle borehole Furthermore, the aquifer in Ibis parbejiaf area has multilayer system attribulmg to a confinea aquifer
Here, il is  vital to discuss  Aggro town as  an example The town is  entirely  supplied water Srgm grouneweter through boreholes  There are three new Boreholes  and Two old boreno*es  Among these Ouratrc*es, four boreholes  are currently  functional, one from the okl anb imee of the new borehoies
m  addition  ip  ihis.  the  Quaternary  sediments  in  the  nver  valley  are  the  potential  aqurfers  for groundwater development, particularly shallow grounowaler
Other  Wgreoa  towns  ih^t  are  supplied  potable  water  from  ground  w-uur  are  Ajjg,  Atnago Gaura ano Atnago
8.2 Future groufi£twaler prospect
The sKisung gedog^BL meteOrofcogwai, hydrogeological and geomorphoiogicai conditions in ine fiver catchment indicate There are areas -Jhai can be aeveioped in tight of gfounowater lDTvariwS WMTftjpply  purposes  Acnnfotfy. potenuai well field sites  hm been loentified in order to de^Etap ^ovntfwMtf Th™  MwiMtad well fie« sues  hav« to be vnrifled based an g«pty»Cal mveshgalrann and Hit wM arifllLng bei<x& being wffiraty  Pe^eloped The
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Summery

Summary: Arjo-Dedessa Irrigation Project Feasibility Study

Arjo-Dedessa Irrigation Project Feasibility Study Summary

Project Overview

The Arjo-Dedessa Irrigation Project is a major development initiative in Ethiopia's Abbay Basin (Blue Nile Basin), focusing on water resources development for irrigation purposes. The feasibility study was conducted by the Ministry of Water Resources in association with Water Works Design & Supervision Enterprise and Intercontinental Consultants and Technocrats India Pvt. Ltd.

        Key Project Details:
        Location: Dedessa River sub-basin (largest tributary of Abbay River)
Catchment area at dam site: 9,981 km²
Mean annual flow: 3,761 million m³ (at Arjo gauging station)
Mean annual rainfall: 1,453 mm (project area)

    

Hydrological Characteristics

Climate and Rainfall

The Dedessa catchment has a uni-modal rainfall pattern with:

Main rainy season (Kiremt): June-September (70-90% of annual rainfall)
Dry season (Bega): October-January
Minor rainy season (Belg): February-May

Mean Monthly Rainfall (mm)
Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Annual
3	6	26	49	158	274	312	277	209	104	28	8	1,454

Streamflow

The Dedessa River shows significant seasonal variation:

Peak flows: August-September (52% of annual flow)
Minimum flows: February-March (<1.5% of annual flow)

Mean Monthly Flows at Dam Site (million m³)
Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Annual
25.0	17.0	17.9	24.2	48.3	157.2	412.8	633.0	540.6	299.8	105.9	46.1	2,328

Flood Analysis

Flood frequency analysis was conducted using Log-Logistic distribution:

Design Flood Peaks
Return Period	Peak Discharge (m³/s)
10-year	575
20-year	654
50-year	771
100-year	871
500-year	1,155
1,000-year	1,303
10,000-year	1,948
Probable Maximum Flood (PMF)	3,690

Water Resources Assessment

Evapotranspiration

Reference evapotranspiration (ET₀) was calculated using the FAO Penman-Monteith method:

Mean annual ET₀: 1,397 mm
Monthly ET₀ ranges from 91.8 mm (July) to 143 mm (March)

Sediment Analysis

Sediment yield was estimated using the relationship:

Gs = 0.078 Q^1.5 (where Gs is sediment load in gm and Q is monthly mean discharge in lt/s/km²)

Suspended sediment concentration: 45-1,670 mg/l
Bed load assumed to be 15% of suspended load

Key Findings and Recommendations

The Dedessa sub-basin has significant water resources potential for irrigation development
Strong seasonal variation in flows requires storage to support dry season irrigation
Sediment management will be crucial for reservoir sustainability
The study recommends further investigation into flood estimation methods for Ethiopian conditions
Training needs were identified for local water resources professionals

Note: This summary covers the meteorological and hydrological aspects from Volume III of the feasibility study report. The complete report includes additional volumes covering topography, geology, irrigation design, agriculture, and socio-economic aspects.