Birete Dam Project Hydrological Study Summary

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PROVISIONAL MILITARY GOVERNMENT OF SOCIALIST ETHIOPIA
o A r a 'j i
ETHIOPIAN WATER     RESOURCES
AUTHORITY
BIRETE DAM PROJECT
HYDROLOGICAL STUDY
a4ft 1 ann > A. * f It f •
Addis A baba
Ethiopia
kThia report omri th*®
ABSTRACT
availability study for Bircte
Daa Project and Includes the derivation of an inflow design flood hydrograph* Flood, routing haft boon carried out to fix the spillway capacity* The atn-ly Is baaed on very ecantly data and ±a applicable to this particular case. Any reference to thia for use in the case
of other baainsp where enough data ie not availablOj, could only bo with caution*1
abstract
■Thia report cpvjrs the- wat^r availability study for Birote Dora Project and includes the derivation of an inflow design flood hydrograph, Flood routing has boon curried out to fix the spillway capacity.. The atply is based on very scantly data and is applicable to this particular case,. Any reference to this for ui^ in the case of other basins, where enough data is net available! could only
bo with caution»table of CONTENTS
abstract
TADIC of contents LIST OF FIGURES 1  INTRODUCTION
t
2, WATER REQUIREMENT
j, VATER AVAILABILITY
a} Ctttehm&nt area
b)    Hydrometeorological data
c)    Runs ff
d)    Kusa curve
4.       HEIGHT OP DAM
5.     DESIGN FLOOD
a)      Etaporical me the da
b)    Pook squat ions for a triangular hydrograph concept*
c)     Unit graph derivation
d)    Derivation of inflow design hydrograph from the unit hydrogreph*
6.     FLOOD ROUTING
7* CONCLUSIONS
8* ACKNOULEDGAMLWT 9. INFERENCES3
t
list of figures
l  Reservoir capacity and area curve
2  Mass curve of Inflow and Outflow-Draught
e
94 litres/Bec*
J, Mass curve of Inflow and Outflow-Praught 6& 11 tro/see.
4. Lay out and dam axis croae-aection 5* DincnslonleaB graph
6, Log relation curve
Birate River Butin
8* Unit hydrograph
9* Inflow design flood hydrograph 10# Spillway discharge elevation curve
11. Inflow and Outflow hydrograph- tfr -
SlftETE DAU PROJECT 
]rrDROLOGlCAL STUDY
1i INTRODUCTION
The Birete river basin is located in Shoa sdaini atrative region about 106 ko  North Vast of Addis Ababa* It ia planDOd to
t
j!
conserve the surface runoff of the basin to a»t the water roquirccie
of tbs proposed eynont factory* Bireto river ±5 a tributary of
Sodoble river which in turn draino into Mur^f river, A site for
a fiir-dara baa been selected on Birete- river which is about 10
kD, from the proposed ccroone factory# The location of ths dais
aits la approxicKhtoly at S^-Zg^N and J8 -2O *E
2, nTAT^a REQUIREMENT
Aeaardinji to the inforcation received ths present water
doiffimd of thu cement factory is Z,000 m^/day or 23*15 iitree/soc*
No projected doound is indicatedp however the provision for increase
need in future is cc-ntpizplated B To aeat the- water reQuircEcnt
the following water availability study is conducted.
3* WATER AVAILABILITY
a)           Catctocnt area
Upstrecra      of      the      Oereti      Dan      sitet         the      catchment      area      of the      dralnHEQ      biain      which      would      contribute      to      tbtj      aur-ftec      runoff la Kmp.5urt'd aa 37-&5 kn^<
b} E!yd rociLbt role gl e al do tn
No hydronotOQFQ Logic al station a
K etS
i    in the cotchraont.
Tha QIC»rt rainfall a tat loti, aT» lotted at Derha (O^-26'K, 3$°-39'E) □nd In hi.ni (<^1^, 
t
la o
ne
-voporition .tatloo at Hinn in the cat chi^t of
1b cloas tp Qiireta^
Easin which±) Rainfall data
Only four y^ars raiwW“
f  ., data Is cvailabl# rroro flarba
station* Annual flgursa ar# reproduced in table
TsMSImI- Annual Rainfall at Derba----------------------------------------
Year
Annual flainflll in nun
i?75
197^
1977
19?B
944.2
890*8
1,143.8
1,007.6
11) Evaporation data
Three yeori Annual ovqporntion data froo Hine atntion Is available £s given in table 2.
Table 2 - Evaporation data for Hine
Year
- -------------------------------------------- 1 Pan Annual Evaporation
on
Actual Annual Evaporation E          a 0*8 X E
act                            pan
no
1976
1977 1 1978
1,624*2
1,525.2
|                     1,499.1
1,299.4
1,220,2
1,199.3
The above value* have been adjusted for the jaisain^ date! for 1977-78* p^n coefficient, K, far working out the actual evaporation free the reservoir area is taken equal to O 6,
p
c) Runoff
A few diA-charge Eeaeuruiggnts were taken on Birute river fiflar Inchini uhich are reproduced in table 3*
Table
Date of moasuranient
20  Hatch       1979
12  Hay          ■
26     ti
II
16  Dec           iri
i?
H          ■It
Di a charge bf Bi re to riw
roar Inchin!
Litres/use
81!   ™          ip
1?      "          *
11      *         r-
vi) Ruinfall dati>
Only four y&ars rnlrtiaJA
„ 
a to Sion, Annual figure# afa reproduced in tabl
dite is available
froQ Dcrba
Table 1  J
-
Rainfall at Derbo.-----------------------------------
Yqar
Annual Hain full in. bq
1975
197«
1977
1978
$w.z
S9O.9
1(143,6
1,007.6
li) Evaporation data
Three years annual evaporation data, front Hine station is avallabia as given in table 2*
Table 2 - Eviparption data for Hine
Year
Pan Annual Evaporation
EE
Actual Annual Evaporation
“art - °-     P-»
ED
s1E
1976
1977
[^978
_
1,£24,2
1,499,1
1,399,4
1„220*2
1,199,3
The above valuee have been adjusted for the Dissing data
for 1977-78* Pun coefficient! for working out the actual
ev-ipcration free tbn reservoir area io taken equal to 0,8..
o) Runoff
A few discharge aeasumintE vara taken on 31 rot a river near Inchinl which arc reproduced in. table
Ta-blo 3 - Diech^riip of Birate river near Inchinl
Discharge of Qi re la river
noar Inchinl
Data of a&aBUTnoftnt-
2B March 1979
12 Hay  i*
2G •
16  Out w
17      f
2U Litres/aoa
81 11 11
19 M
11 *  11
23      "LEGEND
3KC nilMK A U.H fl
main volumes of WORKS
GCHOBH'JlE ObbEMbl PA60T
’4
bi it ?
'x - r
H
■
Description
HanMeHOMKHt
JvtrFlo^ dam
J>OAOCJinBHd* nncnHHd
Description Hawr-ie to&anne
Unil
Ej.-*
K3
■V
1
Excavation Bbiert^a
W-
Earth dam SeMDAnaa nnoiwHa
>
3
A b □ t merit
^ciow
1
2
A
backfill and fill , OSpaiHaji lacwnw h ncw
Pier
btin
3
Gravel r*ith pebble
rpaaMMHO ’ rjneHHUKOtbW rp-jHi
$
6
7
Enerq^ dissipator
ritHierib jutw
4
Riprap
HaopoCM h* HiopTHpDimorij kimh?
M>
M>
H*
Bridge
MOCT
Slide qdte .(bulkhead)
|
5
JdTSOp IlJlOtKMM CKWltiaiUHil I PiMCKlU
blu^
J
Filter (sand , qresell
06paTnbiii cpn.nbfp (necos. rpjB/w)
Radial qalt
.
Jerao^ ce‘M6HTHi>i w
&
Concrete and reinforced concrete &eiort ia MtMiweTotf
1 a Operatic t^ear
7
1,
i Tra’rtUin^ qantry crane
KpaHi KCiHQS&M.
Gantry crane rail track 
flvTrt *03 no torn       *p*Ha
4---- £ -- ----- —---——J------------ -
Reinforce me "it ApMaTjjpa
8
Metalwork,
M eTJJinQKOHCT?^ K J.HH
I   Site   For   storaae   of   gates 
9
‘ | r\namiAm am ipaneHWi wreop&l _
Mechanical         e^uip-tncnt MeMHbtaecxje         riq?yma*iAe
ma
•n
Ck
m
M a c uiipn
Sea1  1 ,        1 500
.
II    IS           -          ■ 1 ear.rrrrv - 5        fl
- —t*-—i        . n
<ii      ?a
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iinq             fin t'W
I
FIG.BjLftFGULA’nNG     RESERVOIR.     DAM     SITE,     CONTROLLED     SPILLWAY     (Altci p'jfcEikPEnMP'mAfl EMKOCTb. IWO^EH. EOiOC&PQC C 3A1WAMM ftBIflETE DAM PROJECT HYDROLOGICAL STUDY
1 * INTRODUCTION
The Bireta river basin 1b located in Shoa administrative region about 106 Jem. North Vest of Addis Ababa* It is planned to conserve the surface runoff of ths basin to oeot the water requircac? of tho proposed cement factory* Sirota river is a tributary of Sodobls river which in turn drains into Mugor river. A site for
a fill—dam has been selected cn Eircte river which is about 10 kiii. from the proposed cement factory* The location of the dam site is approxiraatoly at 9°-29"N and 3BO-2D E
P
2* VATER REQUIia.KENT
According to the information received tho present water demand of tho cement factory is 2 000 n^/day or 23*15 litroe/ooe.
f
No projected demand Is indicated! however the provision for increase need in future is contemplated.* To moot the water requirement
the following watar availability study is conducted*
J* WATER AVAILABILITY
a)    Catchment area
Upstream of the Beroti Dam site, the catchment area of the drainage basin which would contribute to th3 surface runoff
2
is measured as 37«8& km .
b)    HydrumcteoroloKical data
No hydrometeorological station exists' in tho catchment* The nearest rainfall stations are located at Uerbu {O9  -24S  Nt 3&%39'E) and Inchini (09°-l?'N  38°-23*E}, Thore is ano
,0           1
t
evaporation station at Hine in the catchment of jlwr.eb Basin which is close to Bircta*BIRETE DAM PROJECT HYDROLOGICAL STUDY
I « INTRODUCTION
The Birets river basin is located in Shoa adtiinis trativ e region about 10b km* North Uett of Addis Ababa, It ia planned to conserve the surface runoff of the basin to neet the water requircnic of the proposed cement factory* Birote river is a tributary of Sodoblo river which in turn drains into Mugar river, A site for
a fill-daa has been selected on Birete river which in about 10 kid. froa the proposed cement factory, Tho location of the daa Site is approximately at 9°-29 N and 38°-50 E
>
l
2 f WATLR REQUIREMENT
According to ths information received the present water dotaend of the cement factory it 2^000 m^/day or 23  15 litros/scc*
v
No projected dciEmnd i? indicated, however the provision for increase need in future is contocplatod, To moot the water requirement
the following water availability study is conducted,
3 # WATER AVAILABILITY
a) Catchment area
Upstream of the fieroti Dan site  the cutchnont area of
f
the drainage basin which would contribute to the surface runoff
2
is measured as 37-85 km
b ) Hyd romotworol cgi col ,da tn-
No hydrometeorological station uxiate in the catchment* Thcs nearest rainfall stations are located at Dor bo (O9°-26’h?p
3B°-3?’E) and Ihchlnl
5B°-2J'e), Thors IB onfi
evaporation station at Hino in the cfitchncnt of Ayub Basin which is close to Blreto.i) Rainfall data
Only four yoars raini-j-x >^-v-
_ .         . 
infall data is available fron Derba
station*
Annual fi ures arc reproduced in table 1.
e
Year
Annual Rainfall in Ora
1975
197*
1977
1978
9^4.2
890*8
1,143*8
1,007*8
At) Evaporation data
Three yo^rs annual evaporation data from Hine station Is QVQilablLi aa given in table 2,
Table 2 - Evaporation
far Kino
Year
Pan Annual Evaporation
rnn
Actual Annual Evaporation E          n 0.8 x E_
act                            pan
1976
1977 1 1978
1,624,2
1,525.2
|                    1,*99•1
1,299.4
1,220.2
1,199*3
Thn above valuaa have bean adjuatad ter the ai«aln£ data for 1977“78* Pan coefficient, K  for working out the actual
(
evaporation froc the reservoir area la taken
c)           Sujinff
to O*0#l
A few di a charge noa jur-viaenta were taken cn Si rote river near Inchinl vhich are reproduced in table 3,
Table 3 - &i3Chr,rft4i of Bi rote- rivgr near Lnchini
OiicliargQ of Birute river
Date of neasureaent
near IncMni
2S March 1979
12 H?y  ’•
2b «
16  Doc "
17  " "
2^ Litres/oec
01 *                 *
15     it
11 «                H
33     «station B
Ro-infall data
Only fouf yea« roi" Annual figure, nr® reduced
1,  (1-rtilDW*  f^D Derba
in tibXe 1*
Rainfall nt
__-------------------
Year
Annual Silnftll in on
_
9 44.2
19?5
197*
1977
1970
1,007.0
Li) Ev-ipu ration data
Thr^ ye=.rs annual t-vapoTation duta froo Hln* station 
la available as given in table 2*
Table 3 - Evaporation data for Kiria
Actual Annual z^vsporat ion
E . a o.a s E
—
Yeor
Pan Annual Evaporation
r~ir~i
act
pan
1976
197?
1978
1,624,2
1,525.2
1,453.1
1,299*4
1,230*2
1*199.3
The above value* have been adjusted for the Hissing data
Cor 1977-7&i
coefficientt Kg. far working out the actual
e-viporatlon frw the reserveir area i± taken equal to D fi»
B
c) Sunoff
A f*V dieebargt. zzwaauruonnts vero t~ken on 3irat& rjvW near Inchini which are reproduced in table 3»
 L "  JU
--■•■      , Data of nseaeurccient
x Dira^ rivar near Tnchint Discharge of Birute r±v&r
notr Incbini
2  fl  March  197$ I?      May      ”
26        ■         h
l6      D&c      “
1?        "         «
24 Lltr >/  e
fl     ae
Si ii i
T9 '■ «
11"  .
23 m6
As earlier within the catchment ao & not possible- To 
rainfall st Durba Eire to oatchmuat,
have an station
Bn;>tbd on 
direct rsimll «■''”»« •or*1“tl0“ “
idee or t». «*« 
la ocMlUMd to no t»« ““ ta r°r thia oasueplifa n11 attempt Paa
th “
baen       Bade       td       estimate
runoff" based on 
the
y.S, Soil Conservation Service
the method developed by
publiBhed in 1■
for
May
co.pl... doily r.lnr.11 «*» tor Oort. 1. evolloblo Four mr. tr™ 1975 to 1978. However 1. la avcllnW- r™
to Decoer tor 1979 
Iron January co October ror 1979
which has
aloe boon utilii&d fnr computing runoff- Baaed on the cbaracterlsties like> hydrolofiic sail
grcup|i laxnd use ft nd t rpatia&n t ciflaa   and hydrologic soil cover
8
complex, th© U*S< Sall’ Cun servo, tian Service ha? developed various turves far direct rungff ginornted by ro-in fall stern* Rijjicfi oaefflclGuit is calculated, by dividing direct runoff by th© corresponding rainfall fitcriBa To estimate the runoff coefficient
for ©vwry month, it would be important to first arrive it the roprcs-sjiitatlvu atom for the relevant month agp.lnsi; which the direct runoff value tould be read fnw thb curvg. Far this
purpose th© daily rainfall data has b«*n unalyaed. Far uvury uonth tho first ten values of dally rainfall stgr^a starting
frorj the maximum value in descending order have been considered as partial serleo* The values are listed is tables U and 5.
Averages of atom for eneh month and stonss for a return
period Of 3 
have boon oaU l ti<5. In t
u3
hv  bight of
rfipres-ntiitlvi utami,  tbs values of runoff colCricients
«&cb month have t>vOn calculated with ths use of curve DS
in tb» »» of
<Uv»lap*d by U.S. Soli ConBrfVutisn
th id a g for
given
Service
Oiroto        n „ 
v
eatthwnt        oh ve
5
the        dec        fl±to        baa        i»„n
to ffln vlthln thtI fQliowlna oh±ractliriatl£ai
l] Hydrological Soil Group
. f .toy 
clay aM la llkBlT t„ h
oon.1^, , 
" U l" th‘
lnriltaaaa.
~^r «»».!...
t  r=11 £„ 
D>
« la6
M(iy to 
lor 197^
Frotif Jsnmry to OcUbor For 1979
which h.i.t tlao tiban tatlllnd FO±L computing rmioif,
Eai&d on the characteriities like, hydrologic soil group] land use and tro^tfliont class, cvnd hydrologic soil covor complex, the ILS* Soil Conservation Servlati has deVolgpad various curves for direct runoff ganoratod by rainfall atom* Runoff
cooffi tiimt is cnlculatod by dividing direct runoff by the corresponding rainfall Bigrin* Tq sstiaate the runof f coefficient for every month  it would bo lrapgrtcnt to first arrive st the
p
rapr^nt-itive storm for the relevant month ngnlnat which the direct runoff value could be reed from ch  curve, For this
o
piurp-Dse the daily rainfall data, has b-en-n analysotl  For every
ft
month th© first ten valuta of daily rainfall storraa starting
i) Hydrological Soil Groupli) Land Use and
Lund uae or
-7-
Treatnent Claeo
cover is tcKcn o* Small Grair.
and tha
troatmotit or practice
j, elassifiod as Good for nyeroLofic
conditlon
for inflitera lion.
liil
Hydrologic Soil-Cover Complex
Storm rainfall related to antecedent nature condition.
AMC Up ha> bufrn considered.
For the. above characteristics curve number, Ct 85
has been adopted to  read th*  direct runoff corraspontllne to  the monthly  representative otorma  arrived at in tables 4  one.  5,  and the runoff codfficicnts have boen c^lxulaiod»
Tablu - Maximum daily rainfall storms, avcragts  2 years
f
return period storms and runoff cocfficitnts
JAN
3 year
data
75-79
FEB
5 year
du tu
73-79
MAZICH
5 year
data
75-79
APRIL
5 yoar
data
75-79
MAY
6 year
data
r -79
JUNE
6 ygar
data
7^-79
1
2
3
u
5
6
7
fl
9
io
X
S
X2
Runoff ICouff,
20.0
20.O
6.6
5.7
4.7
4.6
1 .6
1 .0
0.1+
0.1+
6.50
7,46
5.55
0,00
29.0
12.5
10.0
8.4
8.0
6*5
5.7
5.5
5*2
5>0
9.5a
7.23
8.66
0.03
17.2
13.6
12.5
12*0
9.2
7.5
7.4
7.4
6.9
6.8
10.05
3.5B
9*60
0.04
34.a
20.0
14,5
9.0
8.0
7*5
7*3
7.2
6,7
6.6
12.10
a. 89
1^*87
0.05
44.1
44.0
34.1
30.9
26.0
24.3
17*5
l4 ,0
13.3
15.0
26.08
12.03
24-5 5
O.JO
50.1
29.3
27.0
22.2
22.0
2 i ,7
1 -9
1 °. O
T '.O
1 ',5
2 *77
’ .63
2 *55
0,20
_________Table 5 - Ha^lciun doll
jU 11 ,tr
return period storm md run^
JULY
6 years
data
74-79
„iro.
6 years
data
7*-79
5LPT
year
dttn
7*-7
1
2
3
it
5
6
7
8
9
10
X
s
X2
Runoff
Coeff*
59.6
*0.5
*0.0
35,0
33.7
29,3
28*8
26.7
2U.6
2*,U
3**26
10.36
32.95
0.27
67,0
37.0
31*9
30**
29.1
29.1
28.9
28.0
27.7
2**3
33*3*
12.27
31.78
0.26
r fc
1 .7
21.5
18.6
18*5
18.3
23.53
5*31
22.86
o. ia
a.3
20.80
i*.53
18.96
0.12
1-3
0.6 7*00 7*20 0,03
3*05
3.50
2.61
0.00
1
1
To calculate the runoff, rainfall data for the year
>976,     which     happens     to     be     the     driest     year     in record, has been adopted.
d) Ha a a c urva
Kaaa curve study it carried out to establish vat^r availability. Other parameters to ccrry out the study are the bate Clow| evaporation from the reservoir, infiltration and
sc-cipatfc through the dam. Re^adlnti bas^ flow, tabl<. 3 fjvsiIb that thu Qiifiiuua flow rucanivd is T1 litrcs/scc. It hat boon learnt that a V notch’ w«ir is contemplated downstream of tho dam site* to record the base flow^ however no further data other than listed in table J i> aval lab lu so far. Ab suck it has
the f<u_- year*
l0
Table 5 - Masitmuii daily rainfall sterns, av«r3£5B|   years ruturn period jtorns and runoff covrficlj"^
2
JULY 6 yenrS
1  data
7 **-79
AUG*
6 ytara
data
7^-79
SEPT.
b years
data
74-79
OCT* 6 years
data
7^-79
| NOV s
ye "irs
datt
t OEC. j
j 5 years
! data
I  r 74-70
1
2
3
4
5
6
7
a
9
10
X
s
x*
Runoff CO4»ff*
59,6
40,5
40.0
35-0
33.7
29.3
20,8
26.7
24.6
24,4
34.26
10,36
32,95
0.27
67,0
37.0
31.9
30.4
29.1
29.1
28.9
28.0
27.7
24,3
33.34
12.27
31.78
0,26
S ■ ■!
34,5
30.4
24,8
24,0
23.0
21.7
21*5
13.6
18,5
10.3
23.53
5*31
22,86
0,18
45,6
45.4
30.0
17.6
18.0
14,2
11,0
9,4
8.5
8,3
20.80
14.53
18.96
0.12
23,0
12.0
12*0
11.0
10.9
4.t
4.0
2.0
1,3
0.6
8.09
7.00
7,20
0.03
__________
9,7
3-6
2.8
1.0
1,0
0.2
-
-
-
-
3.05
3.50
2.61
0*00
__________■
To calculate the runoff, rainfall data for the year 1976, which happens to bo the driest year in th« fcu_' years
record, has b^en adopted.
d) Mags curve
Mass curve study is carried cut to establish water avallability. Other parameters to ecriy out the study ar* the base flow, evaporation front the reservoir, infiltration and seepejo through the dam, R«fradln^ base flow, toblj 3 roVonls that the minimum flow rocordvd is 11 litroa/sec, It has boon learnt that a V notch  weir is contemplated downstream of the dart site to record the base flow, however no further data other than listed in table J is avcilshu so far. As such it has
f
1-9-
been ossumod that 10 litres per second vauld be a*--
in the driest oonth. Lt ha» further been aiaumvd tha
IQ litres per second base flow, 5 Litres per second vould be last duo to infiiteration and seepage through the dan. For evaporation from the reservoir  data for the year 1976 (tabla 2
"      ”
t
is adopted. Monthly figures of ovaporation are given in teblo 6 Table 6 - Monthly evaporation dots for Hine
Month
1
Pan Evaporation
EP
Actual Evaporation. E                    „        E
act a 0*8 x pan
cun
January
l February March
April
Kay
Jun*
July
Au^ub t Sopterabo Octeihur
Novernb^T
168
153
163
176
120
108
102
13?
106
129
125
139
122
130
ll+1
96
86
82
1 IO
85
1O3
100
data       is January and     for year*.
| De c ctibax                     138                                         110
For the wstiraation of the nonthly runoff, monthly rainfall ^alyaed In table 7. Rainfall ^ta for the months af
to April, NoY«b„ and Dacembur is available for 5 yu£ra the months from May to October it ±, available far 6
Average rcTnfcii t  calculated for
8
annual rainfall for the four years available and the total of
the lies column of
data is available,
annual rainfall of
totals. Out of
each north. Total
for which repute data is monthly rainfall la shown In
thv four yu3ra fcr uhlch ciITlplate
y*ar 1976 ha. boon tho dr^  with
st              a t6tal
890.8  tan, which is
Hgp.fi
7~“ * 100 = 87.78$
1014.8of tho total of average monthly rainfall. To reflect a dry y«sar within the scope of deta available, the monthly average rainfall
is reduced to the sane 87-7B#, Final figures of monthly rainfall
are shown In the last line.
The above approach of arriving at the representative monthly rainfall for a dry year has been adopted because the pattern of monthly rainfall is not regular* Perusal of the
monthly rainfall data would show that thcro is a large variation in the rainfall for the same month in various years and thia variation is much more in tha dry months. As such the figures of monthly rainfall adopted in further study are considered to give a bettor picture in which large variations within the scanty data are absorbed to a certain extent.Trib Io 7 - Monthly rainfall at D^rbn
1 Yenr
1ST*
1575
1 1976
1977
197s
1979
= M.B = bB«k K : TOTAL          1 Avcira^Q
Rwp, dry
year
1 Jan *   |K«b.
: 1 = BBB =
0.7              3 l .9
6*2               22.8
6.8               48.9
0.4             TO.9
52.3                 l4,0 — = ® =■:   3i ■ sbh a
66,4           126,3 13-3         25-7
1
1L7          22,6
2J.4
43.4
74.6
30.6
23,7
197,7
39.5
34.7
| Apr,
76.3
51.0
19.9
17.7
29-5
194.4
36.9
34. T
May
165.0
36,3
14.3
62,6
0.7
132.9
413.6
69.0
60.6
June
'104,4
133.7
107.2
115.4
115.7
154.7
731.1
121.8
106.9
July
288.4
268.0
219,5
258.2
330.5
202.9
:          ■bw■ — 1 1567,5
261.2
229.3 1
Aug.
t68,1
202.3
285.7
199.7
296.8
232.8
= ■ B ■ ■= = 1387,4
231.2
202,9
Sjpt<
= cfl ■ at = = 128.7
164,2
97.2
146.7
139,3
207-2
= 3 S B BBS 3
883.3
147-2
129,2
Oct.
= »F = = =- 12.8
3,4
12*0
183.6
27.6
35,0
Nov. =  H1E= =
0.0
0.0
31.3
24.3
27.1
eBbBBBQI
274,8
45.8
40.2
82.7
16.5 14,5 ;
DOC .
■===■
0.0
0*0
0.2
8.9
14.3
B K K K 23.4
4.7
4* 1
Total sBBXBBBB
^44.2
890.8
1143.6
1007.8
= = B 9e s awB|
1014,8
890.8
_- 12 -
Tabic 8 sbov« the computations of monthly volume of
Inflow which is,
’ Vr * Vb
Where V  =" monthly volume of inflow
4
V = monthly volume of runoff
r
> Runoff coeff. x Catchjp*nt Area x monthly rainfall
i
depth
Vb « monthly volume of baav flow calculated nt the
rate of 5 lltres/sec*
Table B - Monthly Volune of Inflow
"th
Runoff
Co»rr«
Monthly
Rainfall Depth
Monthly           Vol, of Runoff
V
Monthly            Vol, of Base flov
Monthly Vol,
of Inflow
V, - V +v
1         «r b
©J
1
2
3
4
5
6
t.
▼.
a.
b.
irch pril
iy
Bly
«e. *pt»
0.12
0.03
40,2                                 182.590
14.5
D.00 4.1
0,00 11.7
O.03
0,04
22.6
16,460
-
-
25,660
34.7                                   52.540
0,05                       34,1
0.20                       60,6
0,20                     106.9
0.27 229.3
*4,530
458(t4O
609,230
2,343,330
0,z6
202*9                            1,994,740
Q.18                    129.2                                 880,240
13,390
12,94a
13,390
13,390
12,100
13,390
12,940
13,390
12,940
13,390
13,390
12,960
195,930
29,420
13,390
13,390
37,760
65,930
77,490
4/2,130
822,190
2,356,720
2,010,00
893,200
In tabla B* evaporation loaass from the reservoir hove not b^&n accounted far. For calculation of evaporation losses*
the reservoir surface area relevant to the reservoir level i
n
the particular month is estinmtad with tha help of roswrvair
• tags-volume and raurvoir ath&e^araa ourvao( capacity ±nd area13
la 2 million, cubic metres with one million cubic matron as dead
and th*a other for the condition when the live atorago ia 1*5
million cubic laetrea with the samo dead itorogo of one million
enable mgtr&a and a con»tnnt draught of 6B litrea/aec, Tables 9
and 1Q ihow the computation for the first case iwd tables 1 T
and 12 for the second, Tho basis for adopting the dead storage
as one million cubic metre is fuplnined below,
i) Sediment inflow
There is no sadinqont flow data available. No sediment sampling: has been done* In view of the topographic features, vegetation cover, rainfall intensity and other characteristics
of the catchment p it is assumed that 1 man depth of soil over the catchment area would flew as aedlmont annually. In view or the variation cover la the catchment it may ba an. assumption an the coMomtlve side, but in the absence of data it han been adopted* Further it has boen assumed that th* unit weight of the sediment trapp*d in the r*servOir and deposited would ba 00^ of the unit weight of thu loose soil including organic natter eroded from
thu catchft&nt,
Regarding trap efficiency of th* reservoir, th* live
storage and the drainage area ratio l.e, 2   m6
x
TMsxio6 ’15
Therefore, yearly sediJseDt volume  S^  eroded froia
rT
Cfttehnsjant and retained in the reservoir p
1                     3
S ■= A x h x iCr x 0,8 m.
y  ' 2
Where A ■ C St thine nt area in m
sediment bei^'it eroded In m,
Volume oT the deposited sediment in the reservoir,
s
3
 A i h  r IO  X 0.8 
ft
-
■ 37.x 1 x 1<3  ■ 37|05O a^/year
3
It is proposed to provide u d*td ptonifo toI.uhg of the reservoir which gives a raaaonablo life boToro th* jcidiifiunt
aneroachaa upon the live a tor age<, Eneroaebmont on Llvo storage ia alow becauae progrcsaivsly the asdiment pa a sing downstream increaaoa and ultimately a balanen it reached.
Considering a dead storage ■ 1 x 10^
Life of tho dead storage
6
■ 1 x 1Q- o 26 yeara-,
37i850Table 9 - Reservoir surface area relevant to each caonth^ Live storage, L ■ 2 x W* Dead Storage, D  . 1 * 10 m 1
b
Draught D ■ 9^ litr&fl/sec*
Accumulated
of Inflow
Acc,  Vol.  of
Inflow + live
Sturage
♦ L
AflC* vol. Draught
of
Availnblo
St ora fto
V +L +D
Reservoir
Surface Aron
195,980
225,400
238,790
252,1 BO 289,92*0
355,870
1*33,360
905,490
1,727,680
t*,oei*,uoo
6,094,530
6,967,730
2,195,980
2,225,400
2,238,790
2,252,180
2,209,91*0
2,355,870
2,1*33,360
2,905,490
3,727,680
6,084,4OO
8,094,530
8,987,730
251,770
1*95,1*20
747,190
998,960
1,226,360
1,478,130
1 ,721,780
1,973,550
2,217,200
2,468,970
2,720,740
2,964,390
592,000
570,000
535,000
506,000
1*00,000
2*52,000
2*2U,O0O
U60,000
51*2,000
600,000
600,000
600,000
The accumulated volmac of inflow (runoff) estlraatgd In table :? Is 6 987 73O n . According to Mr.. C»A,Munoz  a not* attached
I
tf
1
as Appendix A, th.a runoff baaed on the miniauiB flow per Kru^ of Koger rlvor nt Chancho for the driest year 1971 works out
6
= 0,3399938 X 10  x 37.85
« 12,B6B,76a n?
The 1 icrf calculated in table 9 la less and l, adopted for
further study.I- *
- 17 -
Table 10 * Wet accumulated Volume of Inflow + live storage (continued from tabla 9)
Monthly
act. ovep.
mm
Monthly
Vol. of Evap,
ACC*       Vol, of Evap.
n
3
3
4
592,000
570,000
538,000
506,000
480,000
452,000
4 24,000
I* 60,COO
542,000
600.000
600,000
600,000
103
iao
110
134
122
130
IM
96
86
62
no
85
60,980
571OOO
59,100
67,800
58,560
58,760
59,780
44,160
46,6io
49,200
66,000
51,000
60,980 117,980 177,160 264,960 30J,520 362,260
422,060
466,220
512,830
562,030
628,030
679,030
Net Ace. Vol. of Inflow +
Live atoree® (Col. 3 of table col, 5 Of tail* to)
■?
6
2,135,000
2.107.420
2,061,630
2,007,220
1.986.420
1,993390
2,011,300 2339.270 3,214,850
5,522,370
7,466,500
8,306,700
Mass curve la shown ln Fig. 3+ rt vould bfl flpQn frq>D th&
'^   curve and the tabla,, 9 and 10 that at the end
8i
of  April
(2.UII.300 - 1,721,780) * 289,520 cubic metres of live storage
■s left in the reservoir which would provide enough cushion for a very dry year or would add t  the life ef the project.
ot'fr“ MilTable 11 -
Reservoir surTaec area relevant t& each month
Live storage ■
= 1.5 x 10^
D = 68 litres/aec.
Dead storager = 1 K 1:0
Accumulated Vol. of Inflow
y±
w?
Acc. Vol. of Inflow ♦■ Live
storage
+ L
Acc. Vol
of
Avallabia
Draught
Storago
D
WDrD
Reservoir Surfaco Arco
2
to
_3
i
2
3
4
5
195,980
225,1*00
238,790
252,100
2B9,9l*o
355,870
433,360
905,490
1,727,600
4,084,400
6,094,530
6,987,730
1,695,980
1,725,**00
1,738,790
1,752,180
1,789,91*0
’,855,870
1,933,360
2,1*05,1*90
3,277,600
5,584,400
7,594,530
0,487,730
182,130
358,390
540,520
722,650
887,160
1,069,290
1,245,540
1,427,670
1,603,930
1,786,060
1.96B,190
2,144,450
2 500,OOO 2,3673OtO 2,190.-7°
2,029,530 1,902,780 1,786.580 1 667.020
:
(5
540,000
524,000
500,000
472,000
456,000
440,000
4* 
,000
1,977,820
2,SCO,000
464,000
2,500,000 2 :500,COG
2,5QQ.COO
540,000
540,000
540,000
540,00020
Table 12 - N&t accymulawd volume of Inflow +■ live storage
(continued from table 11)
Re jcrvoir
Surface
Aren
2
m
Monthly
Act. Evap.
Monthly
Vol of
Evaporation
3
Net Acc. Vol
of Inflow + Live
Ace.  Vol. 
Evapora tl on
of
storose
(eoi* 3 o
f table 11
- col. 5 
of tab.12)
540,000
3
1OJ
524,COO                 100
5ta,oco
110
472,CCO                134
456,000
440,000
420,000
122
130
141
464,ODO                   96
540,000
540,000
540,000
540,000
66
82
1 10
85
55,620
52.400
55»0C0
63,250
55,630
57,200
59,220
44,540
46,440
44,260
59.400
45,900
5
55,620
IG8,O2G
163,020
226,270
261,900
339*100
396,320
442,660
469,300
533,580
592,980
633,800
6
1,640,360
1,617*360
1.575.770
1,525,910
1,508,040
1.516.770
1,535,040
1,962,630
2,730,380
5,O5O,S2O
7,001,550
7,046,850
Maas curve l  shown In Fig, 3. it would be observed
s
from the mass curve and the tables 11 rmd 12 that at Che and of April I,1 ,535,040 - 1 ,245,54C} « 239,500 cubic metres of live
"torngc is left in the reservoir which would provide,   cushion r^r
a
a. vary dry year or add to the life <jf the project.
The present demand of the cement factory ia 23,15 litres per aec, Tha accumulated draught by tho end flf April at that rate starting from October would bo,
- 23.15 x 3600 x 24 x 
Th * h»t Acc. Inflow from tables 10 and 1i > 433,360 - 396,320 storage required = 424,034 - 35,040 = 388,994
. 424,034 H3
- 35,040 m322
Considering a margin for a very dry year* a minimum livs atOTBge of 5O0 OUC an® may ba nec»*snry.
p
4. HEIGHT OF DAN.
The dead storage for a rsisofiftblt life may bn =■ 1 ,□ z 10^ m^i For the aanse dead storage, the three cases of tGtc.1 storegu arc listod in table 13* Reservoir elevation against the total storage is read from the capacity curve  Fig. 1»
T
Cross-section of river at the dam Cl3e±s  FIg* shows that the
p
CD-mpoteOt bed rock may be at elevation 1G7.5 (with reference to
an assumed local beach mark)*
Tabla 13 - Alternative heights of dam
Draught
lit/sec
Total
Storage
-3
Rosarvoir
Elevation
Bed rock
EL  nt deepest
n
point
Maximum
Height of dam including  3  ra freeboard
m
68
23.15
i
3.0x10°
2.5x10°
y
1.5x10
125
124.2
122
107.5
107,5
107,5
20.5
19.7
17.5
1
The difference in the height of the dam for 0,5 x lO^m^ of live storage and for 2,0 x IO^b^ live ttbrsge is 3 metres, whereas tho draught (withdrawal) is four times. For etonomical utilisation of the available water and to provide for projected
demand p it is recommended to adopt a.20,5 metre high dam with Q
total storage of 3,0 x 10 n ,
5, DESIGN FLOOD
a) Lmpcrical methodsi
6 3
1) tir. C»AiMunoz in his not&  Appendix A  has computed the
#
p
flood peak by the two emperichl incthada  the values ore given
t
hQl&w,
By Fiddas method, flood peak =
a
111,2 m^/secB
1
By modified My«r a method, flopd peak = 104.6 m^/soe,Considering a 
2-2
for a very dry y*3r' Q lainimu
livfr
of 500,000 ns5 nay be n«C**Kliy<
It, E3EIGHT OF DAJf.
The dead atofigc for a  n*soncble life nmy t*
r
x               m\ Tor the spm d&acJ stc^fs, the three eases of
tetal stooge
tUfl total itarige i» road from the eapicity curve  Fig,   +
listed ±ti table 13- Hoserveir Novation ageinst
1
f
Crass-aecticn or river at the dam axis, Fig, shows chat the ccmpotent bod rock may be at elevation 107-5 (with reference to an assumed local btnch mark).
Table 13 - Alternative heights of dan
Draught
11t/sec
■■ ■
Total
Storage
Reservoir
Elevatian
Bed rock
El* at deepest
point
Maximum
Height of dam including  3  m freeboard
ns
6B
23.15
J.OxlO6
2.5x10
1.5*10
125
124.B
122
107.5
107.5
107.5
20.5
19.7
17,5
The difference in the height of the dam for 0*5 x lO^m^ of live storage and for 2*0 x IC^nP of live storage la 3 metres# wher&fis the draught (withdrawal) is four tinea* For economical utilization of the available water and to provide for projected
demand, it is recommended to adopt n20*5 autre high dnm with a total storage of J 0 x 1(Ah\
#
5. DESIGN FLOOD
a  ) ^mperical- method 5 a
i) Mr* C*A  Muno3; in his note. Appendix A  has computed the
fc
f
1 l&od peak by the two oraperlcal methods* ths vqIuob are given
By Fiddos method  flood peak =
t
By modified Myer's method  flood peak ■ lOU+6 n^/soc,
p
111,2 ra/see*- 23-22*
According to th* Bln* Mil* Bonin
.it.
3
?lcuro IT! - W, P*** rlocd **lu* for '™e> ln raad from th* curve • 8 J h /b»c,
Mr, Munoz hn» r&ccfflEun^- t^i
flood ■ 11fi rt“ /sac.
Li) Based on basin character!sites
[jluo Hi Xq Baeln for the Ribb and ^=zr_r-_ f- w£ - following formula has bean d«velape4 by 'tr. *--sgoJL
0                3         C'"’
%,x - 0- °7« »'‘  c A
_.
____ — 4 -»-i a ■•*■
nl^
/“"-I lX«
3^
whore H = Miiinifi IOC yans- =^i
C w Basin ch-rac t era* Tic =;•
A
According to the Blue Nile ksab Stpcrc tt 4 uaxazniB 100 year one day rainfall ■ 124 sn&
—7
Thcroforo 
* 0.OCJ76 x iX?*.1'*’ x i,7 x 37.f5“**'1
o 96,9
bj           foak           vguatlona           for           a           triangular           hydrograph           tengept
u? intr
thia gtntral peak equalIans fcr a trmn.-mlar
hydrograph .
O.3S5
(Rafi
Dvsifn qf Snail Dzlisb
by USHR)
Uharu
r c
■ Timo of concentrution - travel tin*.  cf vi t r
v
from most distant point
■■ Length af   ^tr^xin] in miles
to dam siro in
Haura
L
H
■ Elevation difference between th» uppur and the dnci sito of the atroaa in foot
paint
The
dirr
length          of          the          stroa.ni          11c91          km          find          iho          olovation
ererioo bvtwaon the upper point and th* dam site of the m  is (231.65 — 107 BJ) v 123,02 mei trot. (Ttii a 1 nf ora .a t i on
* trifln’ Length and elevation difference la supplied by
Dr - Tsog )
at25
1-1 ■ $( 1J.9» -x 0.62137V
123,62 K 3.2800 
]
2^59 hoxita diy = 2,6  °w*
b
4
T -
P
0*6 T
c
Where D
Rainfall excess period which
is
taken as 4 hours
rate
T
P
T         Time frii start of rise to peak
P
“ + (0,6 k. 2.6) = 3*5^ hours
T = 2 fi7 T = 2.6? x 3,56 =
bt
p
■ Time bfiflit of hydrograph,
G,?4  AQ
9
9*5 hours
F
* T
P
n
Where q ■ thu puak discharge in m^/sec
P
A ■ Drainage area in ra
Q ■ Depth runoff in mutroj, 
2
of the max# WO year
one day rainfall of 12k tutu is token as runoff*
T ■ Time from start of rise to  peak rate in seconds.
6
=  0.749 x 37.65 x 10  x a.O^g
p
3.56 i 3600
•■ 137.2 D^/asu,
e) Unitgraph derivation*
To develop unit hydrograph, far Birote ungaged area , the dimensionless, graph. Fig, 5 &nd lag relation curve Fig, 6 developed for Blue Nila Basin are used. Curves are taken from
Blue Nile Basin Report  Appendix. Ill - Hydrology prepared by
USER.
f
The paraiBC tara used aret
Log « time from contra of period of excess rdin to centre of vqIuejg of runoff in seconds.
L =■ Length of longest watercourses front dam site to watershed divide in metros.-> 2.3 -
TO
11.9(11.91 x 0,6a07)
123.82 X 3.28OB
2,59
hours day a 2.ti littnr-j
V- i
tc
J
'* iere D
=
Rainfall vxctM period which Timo frost ■tart of rise to peak
taken ae hours
rets.
T
P
TP
*‘
<0 6
-
- *.<)
3M
-  *■>».
’p
2,67 1  * 2,6? r 3.56 = 9-5 hours
p
a Titno base of" hydro graph,
TP
Where q
P
A3
; the peak discharge in nr/sec
2
Drainage area in m
Q - Depth runoff in eiotros#
J
one day rainfall of 12 -i
V
Time from start of rise
0.7*19 t 37.85 x TO6 x 0.065
3,56 x 3600
137,2 ra^/seo.
50$  st the tnnje*  100  yqur
ram is taken aa ninafC.
to peak rate In seconds
V
p
dovelopo-d for Blue Nile Basin
e ) Dn 3- tern ph de rd vfl ti a n t
To develop unit hydrograph for Birote ungnged areap the dini&nflionless graph  Fig* 5 and lag relation curve Fig*
used* Curves are taken frarn
blue Nile Rusin Rupert  Appendix III - Hydrology prepared by
f
VSBR#
The parameters used area
Lag « time from centre- of period of excess rain to centra of volume of runoff in seconds,
L = Length of longest watercourse from dara si t-c to watershed divide in metres.BUfE Hla-L.MSIM IC**L KTMiOERAPH‘I
Z1BIAETE river BftSIN- 30 -
Tnblo 1U - Ordinates of unit hydrograph
Time
% of
D
Lag   2
|
+
- 44.4
2.25
Ordinate
(From Fig, 5 )
Unit <-
cfo
Ord, x 393
2.25
Unit q
m^/acc.
col* 4
35*314
1
2
3
4
5
0*5 
1.0
1,5
a,0
2,5
3.0
3.5
4.0
4.5
5,0
5,5
6.0
6*5
7.0
7.5
o>
9.0
'                   22.2
44.4
66.7
as* 9
n i. i
135.3
155.6
177.8
200
222.2
244,4
S66.7
288.9
311*9
333.3
355.6
400
3
12
19
20.8
16,2
12.3
7.0
4.7
3*1
a,13
1*52
0.97
0*65
0.45
0.31
0.21
0.1
525
2095
3320
3635
2S30
2150
1225
820
540
370
265
170
114
79
54
37
18
14.86
59,32
94,0i
102.93
80. 14
6o. as
34.69
23.22
15.29
10.48
7.50
4,81
3,23
2.24
1 . 53
1,05
0.51
Tho unit hydrograph 1* plotted
in Figure C-IB-
■
nt- *334
- 3S
D&rlyA-Mon Qf ^nflow^dosi^Ti hydrograph from thu unit hydrograph Since there is no recording ruin^iujy# vlthin tho catchment
fl rfl Q*
the
1 day 1OO yoar probable precipitation of 124 mm 1b
□■■a
for
the
fflO*- °r 11
i>S3
in
for
.tor.. The storThmu rataio n 1. arranged in a syniutrical tins distribution Fig* 9,
th# middlii of tho storm to give the flooding. Tho rainfall excels ir«
with the grcitpat worst possible
assumed in the
eo
rtdi-tion
r DLiov±ne
manner*
lot
2nd
4th
hour
41
net
1D%
qf
rainfall
■i          4&#     ■i
41          75#
ti
■i
ip
ii
!■
The unit hydrograph, of | Hr. duration are d.rivsd for rainfall oxce.a of Itnm, lnm, 6W, i2.ua, 22.5'oni, 
and S.4mm, Using the principle of unit hydrograph superposition tho design inflow flood hydrograph 1, obtained both graphically (Fig, 9) and analytically in table 15,
The unit hydrpgrQph is computed for 1 inch rainfall which in metric units irf for 25*U nun or w 25,t4mm.
The rainfall excess, from one diy 1OO year probable precipitation is distributed into -J- hour unit rainfall durations and is termed by i2
Therefore f
Ordinate for each 4- hour unit s Pxdiftatq of unit
15^
s- 33-TDbl* 1 5 " Computation of inflow flood hydrogr^ph
OrclinsitB for
Q
Tiff*
3-5
1-0
1.5
1 2a1
0.0
0.58
2.3*
5*7°
<4,05
3.15
2.39
i.?6
D.?2 D.6O
0.4l
0.30 0.19 0. 12 G,08
o.o6
0,04 0*02
‘a-1
i 2-6
l .12
a
1 ?"22.5
l -15
±2-2.4
z
"3
nr J flee
a
,0
J
Lc
.5
.0
5
<0
5
0
•’
,0
■ 5
.0n
■5
i.0*
1.5
!.O
0.0
0.5&
2.3*
3-70
*.05
3.15
2.39
1.36
0.92
0.60
0.*1
0.30
0.19
0*12
0.0B
0.06
0,0*
0*02
0.0
3.*8
14.04
22.20
2*.30
IB.90
l*-3*
6.16
5.52
3.6o
2.*6
1.60
1.14
O.?2
0,48
O.36
0.2*
0.12
0.0
6.96
28.08
**.*0
*8,60
37-80
28,68
16,32
11,0*
7.20
*,92
3.6
2,26
1.4*
0.96
0.72
0.48
0.2*
0|0
13.05
52.65
83.25
91,12
70.0?
53.7?
30.6
20.7
13.50
9.22
6.75
4.2?
2.7
1.8
K33
0.9
0.45
0.0
8.7
35.1
55.5
60.75
*7.25
35.85 20. *0
13,80
9.00
6.15
S50
2,85
1.8
1.2
0,9
0.6
0.3
0.0
1.74
7.02
11-1
12.15
9.*3
7.17
4.OB
2.76
1.80
1,23
0.90
0.57
0.36
0,2*
0.18
0,12
0.06
L
0,0
1.39
5.62
8.88
9*72
7.56
5-74
3.26
2,20
1.44
0.98
0.72
0.45
O.29
0.1?
0.14
_
0.096
0.048
0.0
0,5a
2.92
9.52
28.75
70.53
135.59
191.34
209,45
106,70
144.90
100.97
65.98
44,15
29.18
20.04
13.46
8.81
5.87
3-96
2.57
1.42
0.56
0,156
0,048
flow design flood hydrograph ia plotted £n Fig. 9. The
^Ith L " >h°* that th* peak Of tht* infl0W flood Lb 289,45^/^©
'druw J thj mQ3tirailin Computed compared to all the tflithada ho It la ar"! 4! Q fO ’F
Ca P*city routi^$ It through the roaarvolr to fix the spillway6#
of
to
the
flOOD ROUTING
209*^5 m /9aC
For flood routing inflow flood hydrogrnph with a peak boon computed* The outflow hydrograph ha*
be       computed       for       which       a       spillway       width       is       assumed       limiting
of tbo
economic
keeping o
20 astroa,
computing the rating
crest 1* taken aa 31
ie given by formula,
head above the crest to 1*5 metree dnni above the full coniorvation
reasons the crest is provided straight width of ZO metros*
the semicircle length would
so that the total height
level is ruaeonable. For
in the shape of r* somicircle
So, for a diameter of
be 31*4 metres* For
curve of the
nifttrbD. The
a C B H1
spillway#
the length of the
where
■i
Q
discharge over the spillway
spillway dischargo in
■
Table 16 ahova the
values of head# H» Spillway
C      V  coefficient      of      Ct      is      charge      which
la taken aa 2
Crest         length         of         spillway         width# which is taken ai 31 metros
R          Head      of      water      abpvo      crest      in
setrea*
values of discharge for various rating curve la plotted in Fig, 10- 37
Tat?le 16 - Spillway rating ourvp computationv
H
0
Q - C B H1
0
*
0.2
O.fl |
o.«
0.8
1 <0
1.2
1.U
1.5
1-6
1.8
2.0
5.54
15.68
28,Bl
44,36
62.00
81.50
102.70
113.90
125*48
149.70
175.36
With the help of spillway rating- curvo fig* 10p jsierrolr capacity curve Fig* 1 „ and the inflow flood hydrograph Fig. 9jflood rovting computations are carried out by trial and error method as shown in tables 17 and 18, Ths crest level of
the spillway for th© full conservation level is taken as 125( iiE-litr indicated in table 1J,Flood routing computations
Ini'll* at
time t
J/sec
Average rite
J1n| Croit lavai ■ 125
Trial RanflFviiir Storage alavation
Out flow at tine T
tn^/iec
0.0
1800
1000 I SOO
522
3150
11232
34443
89352
1855CS
125.01
>25.01
6,24
19.35
1000
1000
0.58
2.92
9-52
26.75
70.53
135*59
191-34
209-45
186.70
144.90
100.97
65.98
44.15
29.18
20.04
0.29
1.75
49.64
103.06
125.01
125.08
125.20
1 000
1000
(SOD
163.46
200,395
294220
360711
1 BOO
198.075
356535
I BOO
1000
1600
>000
1000
t&OO
1800
taoo
1800
1800
1000
1800
1000
■atm
1E00
>3-46
8.81
5*07
3.96
2.57
1.42
0,56
0.156
0.048
>65,8
122.935
83.475
55.065
36.665
24.61
16.75
11.135
7.3b
4.915
3.265
1 .995
0.99
0.358
0.102
290440
221283
150255
99117
65997
44298
30150
20043
13212
B8U7
5077
3591
1782
644
18b
125.46
125.85
126.22
126.45
136.57
126.58
126.5
126.38
136.23
126.09
135.98
125.86
125.75
125.65
135.59
125.52
125.45
125.39
125.35
0.5
0.5
0.5
2.0
6.0
20.0
48.5
84,0
107.5
121.5
122.5
113
too
8?
70
60
48
40
32.5
28.5
24.0
20,0
16.5
14.036 -
Flood routing computation*  h ■ JTm| Cro?t level a 125
r
L bl* 17
goof'dri
dt
Tlnflo* *t
tlpm *
Average z-ate of Inflow q for dt m^/s&c
Inflow
Trial Reservoir Storage elevation
tn
Out flew
at tine T
n>2/ see
3
4
2
1000 Ifioo ratio 1000 ifiDO FflOO 1000 lSOO P300
1 BOO 1800 1800 1800 3800
TflOO 1800 raoo
1800
Ifloo
1 BOO l&OO 1B00 1800 1900 1800
5
6
7
0,0
0.58
2.92
9.52
28.75
70.53
135.39
191.34
209*45
186.70
194,90
100.97
65.98
44.15
29. 18
20,09
13.46
8.8i
5.87
3.96
2.37
1.42
O.56
0.156
0,09a
0,29
1,75
6,29
19.35
99.69
103.06
163.96
200,395
198.075
165.8
122.935
83,975
55.065
36.665
24.61
16.75
11.135
7.34
4.915
3.265
1.995
0.99
0.358
O. 102
522
3150
11232
39993
89352 185503 299223
360711
356535 298990 221283 150255
99117
65997
99298
30150
20093
13212
8897
5877
3591
1782
694
184
125.01
125.01
125,01
125.08
125.20
125.46
125.85
126.22
126.95
126.57
126.58
126.5
126.38
126.25
126.09
125,95
125.86
>25.75
125.65
125.59
125.52
125.45
125.39
125.35
0.5
0.5
0.5
2,0
6,0
20,0
98.5
84.0
IO7.5
121.5
122.5
113
100
87
70
60
48
IkG
32.5
28,5
24,0
20,0
16.5
14.0d fpjiulxiK computations, b « 
Croi t l«vel s 125
l8 - P^
n."
Incremental
Storage
da fli-J
T--------------- - --- Total
5tora^
nir
| JteBorvoir
elevation
and of dtp H
Robbrk
r i*
-
' 9
450
900
900
2250
7200
2 3 boo
61650
119250
H735O
506100
219600
211950
191700
168300
141300
11925O
97200
79200
65250
54900
47250
40950
32850
27450
10
11
13
13
72
2250
10332
32193
02152
162108
232578
241461
184105
92340
1683
61695
92583
102303
97002
89100
77157
659B8
56403
4 9023
43659
396OO
32206
27266
3000072 3Q02322
3012654 304484? 3125999 3288107 3520685 3762146 3946331 4038671 4040354 397E659 3886075 3783772 3686770 3597670 3520513 3454525 3398122 3349099 3305440 3265840 3233634
3206368
125.01
125.01
125.015
125.075
125*21
125.47
125,86
126,21
126.45
126,57
126.5B
126,5
126.36
126.25
126.09
23 99
125.86
125.75
.125.66
125,59
125.51
125,44
125.39
125.35
o*qo
0,00
0,00s
0.005
0.01
0,01
0*01
0,01
0,00
0,00
0,00
0,00
0,00
o.oo
0.00
0.00
0,00
0,00
0,01
0.00
0,01
0.01
0.00
0.00TM *
fig ntlfi -
HtPtftE^ES
*)
p.*ign of Small Dgujb
by  United States Bureau Of H«©laaatloil j^nd and Water nMourc„ or tJw Appendix III - Hydrology by 
United States Bureau of Rocimtlon
e 3aln  Ethiopia
p-
APPENDIX A
Mr. C.A. Munoz's Note44
tiovembfir 5th, 197?
Ref:         Hydremoteorologicul data
for 31 re to giver.
for the design of a small dam on Dirote River which will far the water supply of the cement factory. I
No hydrometeorological stations exist in the catchment -.■ coly published maps at a scale of f:250 D00 which are not
f
:ftquatsf the tributary area has been determined by Dr, Tsego from iiziJabU aerial photographs at scale 1;5G,000 and has found to
uv» □ value of 37*^5 3*1* knits*
The area was visited with Mr, X. Ahood and Dr* Tsega fl lYidiy November 2nd, 1979 &nd fl vid data were collected for
;tj  pojjible peak flood design* It appears that the catchment
bwn proj'orly located on the aerial photographs and the
■Jcalatitas have been based on the value of the area *s computed T for. Taagu*
Tho nearest evaporation station is located at Hine with ,JiU'l Tcluae in mm of 1624.2, 1525*2 and 1499.1 observed in
Oh.------------- «...
_ 
_ 
r-_O ^.*.1 
--- ^_.hl|le-
Values of runoff hQVe
-«     *.r Rive, 
K<1
a trJbotilry
fr °" d»t“ available
Hivor is a tributary O
f Mu^e , 
r
** + 3q* JrB,ta I Biroto
Enclosed herewith please r<
mfornwtioD, 
n tho datailod avanable
c»c>
Dr- Taefjo, EWRa,- 46
> n 11on o f peak flood for Biroto River at possible daro site p.,sfid on c tributary ar&a or 37*85 Bq. kmts* calculated by
p  Tsaffs from available aerial photographs lt50 0O0)
r
#
J P^ddwg,Method
fitld datat Length of stream 11 <91 kmt»<
Elevation at upper part:
”              " dem site:
Difference of elevation:
Slope of moin strain:
(information supplied by
231.65
127-rj
123.fiz
123.32 =r O.OIO3963
11310
Dr. Tsefja)
Standard         contribution         area         coefficient         Os         for         a         rollin*         catchment slope and soil type with impeded drainage Cfl w O.J
Catchment       watnoss       factor       Cw       for
Cv = 1-00
L=fld u=o factor Cl (Internee cultivation) * 1.50
CA ■ Cs x Cw x Cl = 0.5 x 1.00 x 1.50 = 0*75
Catchment lag time K ■ 3,00 (cultivated land) Volume of runoff RO = (P - Y) A X 10^
“ 0.75 (60-0) 37*^5 x
= 1703.25 X 10  (m )
wet zone and perennial
stream
33
«v
mg   Q
. 
 . ^2g-seTo . M2 Q ,
103
T TB ' T-
^38 Time;
? 
■ T + 2.3K + T
Bp
A
T . Ox.OZS L w 0,028 x 11.SI w
s* 
T  = 0,96 + 2.3 x 3 + ?
0
Q1* x 0.0103963^
A  e 7.86 +
0*33348
0.1019622q£
3.270623fl
3.2706tria l and error?
J.
3.2706233             7.86   + 3.27Q623B
440
Q
Q*
Q*
Q
>0.0
2.659147
1.229952
9-089952
a.Bo
48.4
2.6J7614
1.239993
9.099993
9.0909
46.35
2.636933
1.2403135
9.100313
9.10031
OX
-
from Blue Pfilw
2.3 Q -             2.3 * *B.35
- 111 .20 m^/soc
Studies, Appendix III  Figure
2)
ff
Fr*£uency
Once in x years
Peak value in nr/soc
111-46:
*5
5
40
10
49
25
64
50
75
JOO
83
j) Uy the modified Myer's method for a C coefficient of 17
Q = 17 x A  =x 17 x 37-85^ - 10^.6 n^/sec.
r
From the above values and to satisfy the results of th? Fiddes method it is advisable to design the spillway with
o capacity of 75 m^/aoc with a freeboard of 28 iP/sec and an emargency spillway of 15 ni^/eec* The total capacity for evacuation of thtf peak flood would be:
Q = 75 + 28 + 15 = 1 18 gP/^e<
—~*Xjn fa 11 cjjfl ta,
The station installed at Derba (09° 26’N and 38°39*E) Pril I97h gives the following values;
Y Qa/r
’975
1976
1977
1978
Annual Precipitation mn
944.2
890.8
1143.9
1007.8Th» station located at Incbino (O9°19 N and 3B°23’E)
r
ln dicQttS
. ai loW®
rv
higher values due to higher altitude but th* data
are questionably Details are available in the office
o
f th*          Land and Water Studies Agency of Ei.TlA
for those two
st& tions.
Observations haV* boon ruadir at Hino
slneo June            22,    1975
in ci evaporation
catchment of the
closf to Diroto,
pan class A; howuvor Hine is located on the
Awash       basin       and       not       on       the       Nile       basin,       but       r*latevily The adjusted values would bo;
Year
1976
1977
1976
Annual Evaporation in
1624.2 1525.2 1499*1
Daily and monthly values are available in the Lt.nd and Ifatur Studies Agency of EVRA.
Runoff values;
Xo hydrological station is existing on Birete River, Continuous data of runoff are available for Huger River at CJiancho for the period 1971 -1976; tho tributary area is 484 sq*
krats. The values of runoff are as follows;
Year
3 
Runoff nr x 10
6
3 
Runoff par sq ■ kmt4 in nv x IO
b1
1971
164.557
0.3399938
1972
206.00
0.4257S51
1973
275.033
0.5682500
197^
208.907
0.431626
1975
JO3.99T
0.6280005
J 976
207.195
0.4280888
Average              227.627
0.470304- 4?
APPENDIX B
Area and Volume Computation
for platting Area and Capacity Curvesf----------------
Wo
z
rfl
A
2
rzi
* 50 -
Area * Volmnq computation
(Ai} + Ui * 1} a„ 2
2 m
’
V
1
2
3
4
5
6
1
no
1360
906,6
9O6^(;i
906t£
2
111
7160
4260
4260
5166,6
5
112
1668O
11920
11920
17036
4
5
6
1 13      | 3368O
7
8
9 I 10
11 12
114
115
116
117
118
119
120
121
122
13
i4     123
50600 68040
87O8O 118000
159O8O 200680 256400 321880
392480
465440
25180 42140 59320 77560
102540 138540 179880 228540 289140 357180
428960
25 l 80 42140 59330 77560
102540 138540
17988O 228540 20914C
3571 BO
428960
42266 84406
143726 221286 323026 462366 642246 870786
1159926 1517106
1946066
15
124
533200
499320
499320
2445386
Tfi
125
6036OO
568400
568400
3013786
17
126
669400
6365OO
636500
3650286
18
127
740600
705000
705000
4355206
19 |
128
312200
776400
776400
51316B6I
f
K

Summery

Project: Birete Dam Project, Ethiopia

Location: Shoa administrative region, 106 km NW of Addis Ababa (9°29'N, 38°20'E)

Purpose: Water supply for proposed cement factory (current demand: 2,000 m³/day)

Key Findings

1. Catchment Characteristics

Catchment area: 37.85 km²
River: Birete (tributary of Sodoble → Muger river)
Hydrological soil group: D (clay with slow infiltration)
Land use: Small grain with good hydrologic condition

2. Hydrometeorological Data

Parameter

Details

Rainfall (Derba station)

Year	Rainfall (mm)
1975	944.2
1976	890.8 (driest year)
1977	1,143.8
1978	1,007.8

Evaporation (Hine station)

Actual evaporation = 0.8 × pan evaporation
Annual averages: ~1,200-1,300 mm

Runoff

Estimated using U.S. Soil Conservation Service method (CN 85)

3. Water Availability & Storage

Component	Value
Base flow	10 litres/sec (minimum recorded: 11 litres/sec)
Dead storage	1.0 × 10⁶ m³ (26-year sediment life)
Recommended live storage	2.0 × 10⁶ m³ (total storage: 3.0 × 10⁶ m³)
Dam height	20.5 m (including 3m freeboard)

4. Flood Analysis

Method	Peak Flood (m³/sec)
Fiddes method	111.2
Modified Myers method	104.6
Blue Nile Basin (100-year)	83
Triangular hydrograph	137.2
Unit hydrograph method	209.45 (design value adopted)

5. Spillway Design

Crest length: 31m (semicircular shape)
Discharge coefficient: 2
Maximum head: 1.5m
Peak outflow after routing: 122.5 m³/sec

Conclusions

The study recommends:

Construction of a 20.5m high dam with 3.0 × 10⁶ m³ total storage (1.0 × 10⁶ m³ dead storage)
Spillway designed for peak flood of 209.45 m³/sec
Water supply capacity of 94 litres/sec (current demand: 23.15 litres/sec)
Note: Study based on limited data (4 years rainfall, 3 years evaporation)