X                ' \        . x \       ' a vX Mi ' ' \
XX X
GOVERNMENT OF ETHIOPIA
MINISTRY OF WATER RESOURCES
UY ORO 1.0(1 1 CAl./HYDROMh’Th’ROLOG I CAL data/analysis
ANN NX - 2
AMIBARA DRAINAGE PROJECT PHASE-II
PREPARATION OF DETAILED DESIGNS, TENDER DOCUMENTS PROJECT PREPARATION REPORT AND
ENVIRONMENTAL IMPACT ASSESSMENT REPORT
WATER AND POWER CONSULTANCY SERVICES (INDIA) LTD
(lnlomiition.il Consulhints in Wutor Resouicns)
KAILASH', 26, KASTURBA GANDHI MARG., NEW DELHI - 110 001, INDIAhydrological/hydrometeorological data/analysis TABLE OF CONTENTS
Section
..
Description
Table of Contents List of Tables List of Figures 
Page No
1
1
1V
1.0 INTRODUCTION
2.0 DATA       AVAILABILITY
2.1     Hydrometeorological Data
2.2     Hydrological Data
3.0 HYDROMETEOROLOGICAL DATA
3.1     Climate
3.2     Rainfall
3.3     Depth-Duration-Frequency             Analysis 
3.4     Average Catchment Depth
3.5     Evaporation
4.0 FLOOD ESTIMATION OF THE PROJECT AREA
4.1     Previous Studies 
4.2     Present Study 
5.0 FLOOD ESTIMATION OF RIVER AWASH
5.1     Comparison of Discharges       at Gorge Gauge and Melka Warer Sites
5.2     Estimation of Peak Flow Rates 
5.3     Design Flood Hydrograph
1
2
2
2
5
5
7
8
9
10
11
11
11
14
14
19
ig
i6.0 ESTIMATION OF FLOOD LEVELS AT MAIN DRAIN OUTFALL SITES
6.1         Development of Rating curve at MD2 Outfall Site
6.2         Water Levels of River Awash at MD2 Outfall Site
6.3         Water Levels of River Awash at MD1 Outfall Site
6.4         Water Levels of River Awash at Alternate MD2 Pumped Outfall Site
6.5         Longitudinal Section of River Awash 
7.0 STUDY OF IRRIGATION WATER SUPPLIED & MAIN DRAIN 1 DISCHARGE RELATIONSHIP REFERENCES
21
23
24
26
27
27
30
33
11Fig No
1
2
3
4
5
6
7
8
9
10 1 1 12
13 14
LIST OF FIGURES
DESCRIPTION
General Map of Project Area
Rainfall        Depth        -        Duration        -        Frequency        curve        for        IAR, Melka Warer
Layout       of       the       Awash       River       Hydraulic       Mode       1 
1985)
'.(Hal       crow, V
Flood       -       Frequency       Curve       for       Melka       Warer       site       on       River Awash
Dimensionless Flood Hydrograph for Melka Warer Site
20, 50 and 100 years Design Flood Hydrographs for
Melka Warer Site
Gauge       &       Discharge       Curve       for       River       Awash       at       MD2       outfall Si te
Water        level        Plot        for        River        Awash        at        MD2        Outfall        Site for 20, 50 & 100 years Floods
Gauge       &       Discharge       Curve       for       River       Awash       at       MD1       Outfall Site
Water        Level        Plot        for        River        Awash        at        MD1        Outfall        Site for 20, 50 & 100 Years Floods
Gauge        &        Discharge        Curve        for        River        Awash        at        Alternate MD2 Outfal 1 Site
Water Level Plot for River Awash at Alternate MD2 
Outfall Site for 20, 50 & 100 Years Floods
Longitudinal Section of River Awash Showing Water
Levels for 20, 50 & 100 Years Floods
Plot          of          Irrigation          Water          Supplied,          Runoff          Volume          due to Rainfall and MD1 Discharge
Ml i •! Ill 111 III »■-HYDROLOG ICAL/HYDROMETEOROLOG1 CAL DATA/ANALYSIS
INTRODUCTION
Hydrological studies were undertaken  by  M/S Halcrow A Partners during  the preparation  of Master Drainage Plan  for Melka Sadi and  Amibara areas in  July,  1985.  The studies at that time were based  on  the limited  data available with Water Resources Development Authority  (WRDA) and  other
sources. 
Subsequently 
considerable
additional
climatological data for the area and  hydrological data of
river Awash  have been  collected  at the Project Control
Centre (PCC) ,  Institute of Agriculture Research  (IAR), 
Melka Warer and  Hydrology  Deptt.  of Ministry  of Water
Resources.             The             present
hydrological
studies
based             on 
updated  data were carried  out mainly  to  compute the surface drainage requirement from project area,  flood  studies- of river Awash  and  analysis of water level at the alternative outfalls of the main drains of the study area.2.0 DATA AVAILABILITY
The
principal
sour
ces
of
hydrometeoro
logical
data
for
tl»c
project
area
were
the
meteor
ological
stations
at
IAR. 
Melka
Warer
and 
PCC. 
The
hydrologi
cal
data
of
river
Awa6h 
were
collected         from         PCC         and         Hydrology         Deptt.,         Ministry         of         Water Resources.
2.1 Hydrometeorological Data
The hydrometeorological data like rainfall, temperature, 
relative humidity, evaporation, sunshine duration & wind 
speed were collected from IAR, Melka Warer and from PCC for
their weather station, PCD-3. The PCD-3 station had, 
however, worked only for the period 1983 - 1993 (June).
The         status         of         data         availability         for         both         PCD-3         and         IAR, Melka Warer is shown in Table 1.
In  addition  to  above,  the mean  monthly  values for rainfall, temperature,  relative humidity,  sunshine duration  & wind speed  for the period  65  - 94  were also  collected  from IAR, Melka warer.  The location  of meteorological stations at IAR, Melka warer PCD-3 is shown in Fig 1.
2.2 Hydrological Data
water        eye        observations,        three        times        a        day        (8.00,12.00        & t      UG      hit,.      were      collected      from      PCC      for      the      gorge      gauge
t      tt      about      aOOn      upstrean      of      headworks      of      Amibara      Irrigation
f-rcje.
t         Equation*         for         gauge         and         discharge         relationship
4   ur   ve   we«c   aiso   co   1   iar   ted   f   r   on.   PCC   to   that   water   levels   can I <   « «»i vci tcC into cur i cupor.d 1i »g discharges.
oauyc l-t yl t t oi.c flit.J.Biyt fur
Melka Wafer gauge &I
v*          «    1 •         • '• 
•
«kev»t
<<           I
♦    •     V>
• ’ 1K
>»
*
«
<<H < m*M. «
<1
• l.Aiwe c< 4
*U act •     *• w-W>
* rt» <■» . •» » • < '
* ' • • t 1 t 1
, •         •>><<>.          *•♦ ♦ •          • w              *»«•«
**w
•><«          0        • • •«
* • * ♦’7‘             v>          4k«»•* ■'
i
i
t
i
i L t
L
1
1 El
i
• *v»» ’. e •>< • :
Tl>< loftlion of it.« < < e>M>t
w
• d • ♦•
r «      ♦ * 1 »«         • w‘ •••♦*<
Mg ,
3TABLE 1 - STATUS OP HYDROMETEOROLOGICAL DATA AVAILABILITY
s.
No
Data
Type
IAR
MELKA WARER
PCD-3 Station
Daily 
or
Monthly
Avai
labi
lity
Missing
Period
Availabi
-li ty
Missing
Period
1
2
3
4
5
6
Rainfall
Temperature Relative
Humidity
Sunshine
Duration Wind Speed Evaporation
65-94
79-94
79-94
79-94
79-94
79-94
-
1980
1980
1980
1980
1980
83-91
83-92
83-92
83-92
83-92
Nil
10-11/85,10-12/86
3-5/87,10-12/87
6/83, 2/85,3-4/87
6/83,1-2/85,35/88, 9-12/86, 1-2/89 6/83, 2-3/87,5/90,
8/90
6/83, 1-2/85,11/88
N.A
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
TABLE 2 - STATUS OF DISCHARGE DATA AVAILABILITY FOR RIVER AWASH
Na&e of Site
Period of Availability
No
Gauge  Hieghts/ Water  Levels
Discharge
G&D Curve
Equation
1
2
Gorge Gauge
M< !ka Werer
1983- 85
1972- 95
Nil
1972-1989 1993-1995
Available
Available
L- . o HYbki mn *k> HXJG I < A i
3.1 C 1 i life t c
7hc Mh!<Hr Aufefeh %a)lr> lie* >»
*•          • 
••          ♦ .*
cliufete       will,       fe       bl-annuAl       »*u.f*H       |»*<<*tn       lAufw*'       •       r       •       *       *       *       »       •       *
A Feb-Apr 1 1 ) a t» *oc 1 At rd with
convrrtfrncr 7. one al thi* latitude
r.t < f I l»r i • • • • 
< * • I
Records of
tuo ttr t eo r o 1 <>< 1 <  A 1      • t A 1             I on• on* at
1 A* .                Well.
Warcr(upto
1 994 )
a nd o < ho r
A<
I li«
1|’
1 WW >
1 wet*
aval 1 a b1e.
S 1 nee
1993 only
one
thf t
rond of i t a 1
• 1 A t 1I Ull
A’
values          for climatic data from 1905-94 air alto
Temperatures exceeding  38'C have been  observed  nopm! i *r
r
in 
the        month        of        May,        June        A        July        whereat*        minimum        temperature* of        about        12.5fiC        have        been        observed        in        the        month        of        berrmbri &        January.        Mean        maximum        temperature        of        38        C        is        observed        In the        month        of        June        and        mean        minimum        temperature        of        I4.2T        in observed          in          the          month          of          December.          Daily          mean          temperature is       in       the       range       of       23°C       to       31°C.       The       maximum       temperature       of 39.9°C           has           been           observed           in           June,           1981           and           minimum temperature          of          12.3&C          has          been          observed          in          January,          1984. Mean         monthly         value         of         relative         humidity         varies         iri         the         range of      38%      in      the      month      of      June      to      59%      in      the      month      of      August. The          maximum          &          minimum          values          of          relative          humidities          have
been       observed       as       70%       in       February       1990       and       29%       in       June       1986 
respectively.             Mean             daily             sunshine             duration             varies
in 
the
range         of         7.3         hrs/day         in         July         to         9.6         hrs/day         in         November with annual sunshine of the order of 3,037 hrs.
Mean  wind  speed  at 2  m above the ground  varies in  the range of 4.75  Km/hr in  November to  8.73  Km/hr in  July.  The maximum wind  speed  of 11.18  Km/hr has been  observed  in June, 1984.
5The mean values (65-94) of temperature, relative humidity^ sunshine duration and wind speed arc shown in Table 3.
TABLE 3.    - MEAN VALUES OF HYDROMETEORLOG!CAL DATA.
Month
l
Mean Temperature ( C)                 Kelat         Sun-               W i nd -ive           Shine             Speed 
Humi-       Durat            at 2m
d i ty          ion                 (km/hr)
(X)            Hrs/day
Max          Min           Mean
Evaporation
Daily
Mean
(mm)
Monthly
(mm)
66-94        65-94        65-94         65-94        69-94             69-94
69-94
Jan 31.4 15.4 24.2 52 8.6 4.78 6.10
Feb 32.2 17.3 25.2 54 8.4 5.02 6.57
Mar 34.3 19.0 27.1 51 8.4 5.14 7.18
Apr 35.1 20.2 28.0 51 8.2 4.93 7.33
May 35.6 20.7 29.3 44 9.0 5.61 8.32
J Uh
Jul
Aug
38.0 23.5 31.1 38 8.1 8.42 9.49
35.2 21.8 28.7 50 7.3 8.73 7.65
33.6 20.7 27.4 58 7.4 7.39 6.41
Sep                  35.0          20.7          27.9
f
7.9                5.49              7.00
189.10
183.96
222.58
219.90
257.92
284.70
237.15
198.71
210.00
Oct
Nov
bee
34.4          17.4          26.8                46                9.1                 4.85 32.4          15.2          24.9               48                9.0                4.75 31.3          14.2          23.5               51               9.2                4.49
r-----------
7.22 223.82
0.79 203.70
6.03 186.93
Annua 1 Meal.
34.04        18.84          26.99         49.67            8.46
5.8              7.17         2618.47
____________
1The mean values (65-94) of temperature, relative humidity, sunshine duration and wind speed are shown in Table 3.
TABLE 3. - MEAN VALUES OF HYDROMETEORLOGI CAL DATA.
Month
Mean Temperature (°C)
Relat
-ive
Humi
dity
(%)
Sun-
Shine
Durat
ion
Hrs/day
Wind
Speed 
at 2m
(km/hr)
Evaporation
Max
Min
Mean
Daily
Mean
(mm)
Monthly
(mm)
66-94
65-94
65-94
65-94
69-94
69-94
69-94
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
DeC
31.4 15.4 24.2
32.2 17.3 25.2
34.3 19.0 27.1
35.1 20.2 28.0
35.6 20.7 29.3
38.0 23.5 31.1
35.2 21.8 28.7
33.6 20.7 27.4
35.0 20.7 27.9
34.4 17.4 26.6
32.4 15.2 24.9
31.3 14.2 23.5
52
54
51
51
44
38
50
58
53
46
48
51
8.6
8.4
8.4
8.2
9.0
8.4
7.3
7.4
7.9
9.1
9.6
9.2
4.78
5.02
5.14
4.93
5.61
8.42
8.73
7.39
5.49
4.85
4.75
4.49
6.10
6.57
7.18
7.33
8.32
9.49
7.65
6.41
7.00
7.22
6.79
6.03
189.10
183.96
222.58
219.90
257.92
284.70
237.15
198.71
210.00
223.82
203.70
186.93
Annual
Mean
34.04        18.84          26.99
49.67
8.46
5.8
7.17
2618.47i • 2 II * , t J fc ] j
7 rtf *11
ltL.Gj.Ai . *
inter - tropical <
•( ( ut • 
|'*ht J *H )
•••        1 I e r a • 1 * f »
4u»        1 <     < I r
|
er<rr<•
< r. v «• I < r n« e t or.»
7 Lr mo* r mr • ’
7 one .           M • d . f » e         1)         t hr          a 1 e A        v | <   (1*|t)
if
’ *•*          < ♦ ♦
1 t h I O j     .A 1 r A< l.r t»
i t u hu | t he f t< 1 I » ♦ t i •> Joi* *••«!
*
Rec ord Cl A\ Cl . 1 abl e u j t h |*CC Lad I ».d I < a I e»l 1 hr r • k * t r • 16 Fa i f» gAUtf c Hint koh» il» and Atouiid t hr j f v J r < 1
• • r a
how      Ohl)      one      roln      i£4U<«*      fetation      flint*      At      3      Ah      .      Mr      1      I      •      ba*r« for         which         rrcord«i         Arc         n\nH«blr         from         IV<»&         oiiw*tilfe indicated   in   Table   1   ,   record*   of   da   i   1   >   i   *   Hil   *1   1   d   *   t   «   f   »   «■*
PCI)    -    3    fetation    da
i    nt    allied    by    l*CC    were    nl    a«>      mva
I    I    aide    f    r    «    *
1983  - 1993.  Rainfall data  of PC I) - 3  fetation w r i r ( o| In I »d
in tic form of daily  data  and monthly  utimmaf jen of 1  lie
climatic data.  On compariMon of the monthly  viilun
computed from daily  data  and thone available In monthly
summaries,          number          of          discrepant
k?m
were          noted.          Therefore,
it      was      considered      to      make      use      of      data      of      1      Al<,      Helkn      Water only which is available for 30 ycurs.
The mean annual rainfall for I AR, Melka Warcr ra I ngHuge
station (65-94 ) is of the order of 563 mm. The high*at
monthly rainfall is recorded as 262.4 mm in August 1988. 
The highest one day rainfall is recorded as 100 mm on 31l1
March, 1982. The monthly distribution of the rainfall at
this station is shown in Table 4.
From Table 4.  it is observed  that July  and  August account for about 40% and  February,  March  &.  April account for
about           32%           of           total           annual           rainfall.           This           indicates
that
the            project
area            has            two            fairly            distinct
periods            of
rainfall           during           February           -April           and           July           -           August.           :The second period is the main rainfall season.
73.3          Depth-Duration-Frequency Analysis
The daily  rainfall data of IAR,  Melka Warer were subjected to  frequency  analysis to  obtain  the depth  of rainfall for
various
return             periods.             The
frequency             analysis             was
carried 
out            for            both            annual            extreme            series
(ie.            maximum            rainfall
depth  in  a year) and  partial duration  series (ie,  rainfall depths above certain  threshould  value usually  minimum of the maximum series) for selected durations.
TABLE 4 - MONTHLY AND ANNUAL RAINFALL FOR IAR, MELKA WARER
(1965-94).
I tern
Max
(mm)
Min
(mm)
Mean
(mm)
% of Annual
Jan
135.6
0.0
14.6
2.59
Feb
264.1
0.0
53.8
9.56
Mar
199.2
0.0
64.0
11.37
Apr
166.4
1.2
63.9
11.35
May
80.5
0.0
28.4
5.04
Jun
73.5
0.0
24.5
4.35
Jul
186.0
41.0
107.1
19.03
Aug
262.4
28.8
117.8
20.93
Sep
114.6
10
48.7
8.65
Oct
131.2
0.0
20.2
3.59
Nov
94.9
0.0
17.2
3.06
Dec
14.6
0.0
2.7
0.48
Annual
818.1
390.1
562.9
—
100
8The frequency  analysis was carried  out for durations from
1-day  to  10-days for 5,20,50  and  100  year return  periods. 
Depth-Duration-Frequency            curve            for            rainfall
at            IAR,            Melka
Harer is shown  in  Fig  2.  The one-day  and  two-days observed rainfall depths were adjusted  to  24-hour and  48-hour values using  the standard  factors of 1.13  and  1.04  respectively. Rainfall depths of durations 1-day  to  10-days for various return periods are shown is Table 5.
TABLE 5 - RAINFALL DEPTHS OF SELECTED RETURN PERIOD FOR DURATIONS 1-DAY
TO 10-DAYS FOR IAR, MELKA WARER
Duration
(Days)
Rainfall Depths (mm) for Return Period of
5 Yr
20 Yr
50 Yr
100 Yr
1
2
3
4
5
6
7
8
9
10
70.8
83.7
95.3
103.4
111.1
117.8
124.3
129.6
133.2
136.8
92.0
109.7
127.2
138.2
148.5
157.9
166.4
171.4
175.1
177.6
105.4
126.6
147.4
160.2
172.8
184.0
193.0
197.8
201.6
203.5
115.4
139.5
162.6
177.0
191.2
203.7
213.0
217.6
221.5
222.9
3.4        Average Catchment Depth
From       the       records       of       PCC,       the       mean       rainfall       based       on       the       16 
stations        located        in        and        around        the        study        area        was        collected for        the        period        from        1985        to        1991.        Ratio        of        mean        annual rainfall       (       1985       to       91)       of       project       area       and       IAR,       Melka       Wurer has       been       computed       as       0.7       and       same       has       been       considered       to convert         rainfall         at         IAR,         Melka         Warer         raingauge         station         to study area catchment rainfall.convert rainfall at IAR, Melka Warer raingauge station io study area catchment rainfall.
3.5        Evaporation
From the analysis of the climatic data of the IAR, Melka Warer it is observed that mean daily evaporation varies from 6.03 mm in December to 9.49 mm in June. The mean daily evaporation on annual basis is 7.17 mm. Total annual evaporation is of the order of 2,618 mm.
F rom that
the available
data        from 1979 to daily          evaporation
1994
» it
maximum mean
is 13.57
1985       and minimum               mean
February, 1990. evaporation values Warer
The are
daily evaporation is
mean daily, monthly
shown in Table 3 for IAR, Melka
is observed
mm in June,
5.38 mm in
and annual
104.0            FLOOD ESTIMATION OF THE PROJECT AREA
4.1 Previous Studies
NADECO           (1982),while           carrying           out           the           reappraisal           study           of
Anglele-Bolhamo               &.               Amibara
Irrigation               Expansion               Project, 
used  the series of ’maximum’ rainfall depths of different durations to  work  out the runoff from the storm rainfall within  the irrigated  area.  The 2- hr.  rainfall of 40  mm was considered  to  be drained  in  a period  of 24-hr. Drainage duty was worked out as 1.05 1/s/ha considering
runoff coefficient
of 0.4.
In 
the
feasibility 
study 
of              Anglele              &.              Bolhamo 
Projects,Halcrow(1975) assumed  10  mm of runoff from the 24-hr,  5  year rainfall depth.  Drainage duty  of 1.16  1/s/ha was obtained,  if the area is considered  to  be drained  in 24-hr.
While preparing  the Master Drainage Plan  Halcrow,1985  (Ref 1) considered  the duration  of rainfall equal to  the time of concentration  of each  catchment area along  with  runoff
coefficient
of
0.2            and            constructed            the            storm            hydrographs
using  time-area diagrams.  Peak  discharge of 10.65  a?/sec
for the area of 8,353  ha was estimated  for that by  them. This gave a drainage duty  of 1.27  1/s/ha and  they considered  this figure atleast 20% high  because of the
inherent approximate
underestimation 
of
attenuation 
provided 
by 
the
routing             procedure             adopted             by             them.             Therefore, 
drainage        duty        of        1.0        1/s/ha        was        finally        adopted        by        them        fos. preparing the master plan.
4.2 Present Study
l’he method developed by Soil Conservation Service, U.S 1 1Department        of        Agriculture        was        used        to        work        out        runoff        from
Project         area.         The         method         takes         into         account         the         type         of
textures hydrologic condition.
of condition 
the
soil, 
land 
use
pattern,treatment, 
of
area
and 
antecedent              moisture
The type of soil have been  divided  into  four categories depending  on  the infiltration  rates which  in  turn  affect the runoff potential of soil.
Land            use            patterns            have            been            divided            into            9            major
categories, 
e.g.             fallow,             row             crops,             small            grain             crop, 
pasture,           woods,           roads           etc.           Fallow           land           &           roads           have
highest
runoff
potential
and             for
other
types
runoff
potential varies with the type of crops.
Land  treatment is considered  into  3  different categories like straight row (highest runoff),  contoured  and  contoured &. terraced (lowest runoff).
Hydrologic           condition           has           been           considered           as           good           rotation (lower runoff) and poor rotation (higher runoff).
Antecedent moisture condition  (AMC) has been  divided  into three conditions as AMC-I,  AMC-II & AMC- III based  on  the
previous            5-day            antecedent            rainfall.            Runoff
is
lowest           for
AMC-I         condition         and         highest         for         AMC-III         condition         for         the same rainfall depths.
Based  on  the above factors and  AMC condition,  curve number (CN) is found  out and  runoff corresponding  to  the selected curve number and  rainfall depth  is computed  from the figu're given in SCS hand book (Ref.2).
The average catchment rainfall depths have been  computed  by multiplying  rainfall depth  as given  in  Table 5  by  a factor of 0.7. The 24-hr and 48-hr rainfall depths have been
12computed  by  multiplying  the 1-day  & 2-day  rainfall by  a standard  factor of 1.13  & 1.04  respectively.  The runoff from the project area for the rainfall depths of various return periods is given in Table 6.
Table 6 - RUNOFF FROM 24 HOUR RAINFALL FROM PROJECT AREA FOR VARIOUS RETURN PERIODS
s.
No
Return
Period
(years)
Average
Catchment
Rainfall
( mm)
Runof f
( mm )
Runoff
(1/s/ha)
1
5
56.00
8.89
1.03
2
20
72.77
17.78
2.06
3
50
83.37
23.62
2.73
4
100
91.28
28.96
3.35
From        Table        6        it        is        observed        that        runoff        from        24-hr,        5        year
return         period         rainfall         to         be         drained         in         a         period         of         24-hr
is         about         1.0         1/s/ha.         which         is         in         agreement         with         the         value
adopted           by           Halcrow,           1985           (Ref.l)           in           the           Master           Drainage
Plan.          Adding          the          value          of          0.35          1/s/ha          (0.2          1/s/ha          from
sub-surface
drinage
flow             and             0.15 
1/s/ha
from             canal
rejection  flow) the total rate works out to  1.35  1/s/ha and the same has been  adopted  for the design  of surface drainage system.
13M               VT1MAT1OK CH 1 \ I AVAS*5
n<r •   ' rm ♦
t er”
1 hr      f I ow rtat ft of r
V e 1       V d ♦ l fi 1 hr V’
rr.iwr t a r-r »•                 » Ahfir        a       f r « *  ft i 1 ft)» 1 r f r’ »            1 wr
*  1 1 C »               <            Go r'lr •       (»ftuf <        » ' 1 •           fthd Mr             k • V ftrr r • I t r .
M. 1 hr hfirr •  ft 1 « * d r*Wr»ft 1 * raw of t hr rnttf i ttrm r
The
of
1 • ) I H t 1 i ft •     « ♦     1 rbrnr-
W k.ft * ftrfr .        hr hr r
1 hr r oh!tihu1 1nh» of
a \ ft . 1 a ♦          <     * or       or.
\rri 1 k» i 1 rd
fM» r I r»d        wr rr       no t
made uar
. f              Th< 1.1ft
« ft 1 • hfftr » ’ ft r r A o 1 f river
ft% kw
Aw m ft h      Hpt               Mr 1 k a
U ft • « ♦
♦         1<               ♦
f « »«tf «
of            l> . ft«'har » a<
<*•» rgp«
Gaugr*
AH«1
Mr I k m
Karri
’! h<     Vft 1 « 4         « S <       Oft 1 ft     ft A              Will ♦ • 1
*«*»   <t« |fWMp
k ft t 4-4 ♦ i 4
t «4l      * 1
<  * diwrlargi
ft 1 4          ft r *           * • * k 1 al 1 * f r
*»ft t <4           , < % <
aftktf 41 i ft• i»ft i |«
« t.jt • u r v r f^ual  A♦           for
1 •• 3 •? and r »> • M«     1 ka
•1a (a al 0»m w i t It i a i i »»>
4 4*4
ft t 4           ft
ft . 4 at> a « f r . -a 1 >15       >• A» the
da t a       t »j i
i l>
♦ . «<♦      • ♦
t»Af fr.M I >1)3
*4
table
• 4.4 4 < txpoin!
. 4«t   *5 . a* l«ft. >4                 *        Mi   4 kft     Wft x • 1     > 1  I < ai*d v            A • r            * r r a a
f l *»*            ! ><•              : . A
I * *»» ’IftLli
0a*40« a * 4 r jmm M* w. fta* < j a li .ft a •.<••!
. at>.» - :»4 aoxj ii.. *
• I 4-444 I * . l<u lai . k x A.aLi i«4. x fcaaaa*
fiww4t 4 4 I m4mi4»4- 4
. I .4
4.:.Af J . Al!
!•■*< I igl<« ftl I ‘<4 ft I * . I » .
..
...
.!• . 4w *.f
* -m i a t*9
.*
a • t • i is* . i i t Uu l i w. e
iI*
. a..> • • a L * >
al. 4....................................... 1*4-4
• «          . I I , . 4*
.
Aftaal. i • ' « 4 A la*. wl. - * 4 *iu .. - w...................................................................................................................................................«li. I »
■            ’          .4 I l»I Mm*. I » i h* ft . 4«4»ft » I . ft4
ft a - 4 . •
w I.*
• t 44 4           . J . a-. U«4 * ft 4
ft » 4 ft » ft 4- Mft »
♦- • I » ftft»rant r *                 F u r • 4 Mifl'*.s <- gt/KG? ;a G~ '• -«F' z > o-.ggR
GAt/GF a
T. i $< II <»GK
>**-;m 4 £
-:u
,
; Ma^GE * < ~ i^'
?w
YFAR
•;» ii ,e
ga-gs
t
^RRS’SPGMG
‘ MG
QP
riM«
D/t ric
..b
4 A • MW 4
"
(hr* )
»44 m
TG
>A *>7
M
1 91 1          J 14      j;
i.oo
is/ r
14 'HI
4 Ml
' 3 '*
t ■•
JI''
4'f ’
JU                  ■> 5 .   ' >
r •♦
<F
4U      4 4
45 *
jo
M
>
10
4 ’.
• ,
i:
<•4
'* .
<
44
*
•i
j ■;
1
: •:
9. 0
4*
>4
I 911
1 4 1     • '• 
14 OU
l4/3
14 Ml
4 >U
«, *•
A•
kt)
14 3
*'1,3
1
•J .
**»
SO, *
-n
4
I *43
<04
4 OU
4/1
4 JU
4 JU
«. 3
JK
43
3
9
•
iJ
'. >9
L 94C          40 I      4 :          14 OU
I 0 4 in )U : 3 9U
94
0, 1
1
‘4       .j
1           : tiri
1J     4 >
>2      IU
. 94 1               3 1 0
4 OU               13/1
I 4 JU                     4 AU
J . 1                 ic      jy
- 3, 3 34 i j
1<     1
i O, >
; :3
94 4 94 ' 49 l 3 OU 4 9 4 4 AU I 4 Ml
1, *1 1 >
3
u  .XJ
k ■1 »
:oj      ' <J
iua        1 L>
>u
9 1t 1Q
94 1          •<l *
4 OU
40, 4            13 OU                 U Ml                                    4            9         >u
13. -i
3*      4
la
. 4 ll 9U
•a
44
4l4
1»4 4
.J
1U
* 1 IW
9*
4 9U
41      4
k4 JU
i* AU
4
■A
A AO
4 4* < 4
4 3 /     4 r
-     4*
lu. 4
A1TABLE
SHEET 2 OF 3 7 - PEAK DISCHARGE AT GORGEGAUGE^MELKA^WARER
GAUGE K
DISCHARGE
SITES ON RIVER AWASH (DISCHARGE IN Cumecs)
YEAR
GORGE        GAUGE
QP                  TIME           DATE
SITE
FLOOD
(hrs.)
1991 516.09  16.00 16/9
FROM 16.00
8/9
CORRESPONDING Q AT MW SITE
TO DATE  Q
8.00
23/9
16/9  216.30 17  201.35
z 18  218.23
19 220.16
20/9 
159.25
27/4
16.00 12.00
26/4 
26/4
9.58
1992 
677.90
8.00
28/4
27
20.25
28
16.34
29
18.00
30
26.14
1/5
38.51
2
45.74
3/5
23.31
8.00 
3/9
8.00 12.00
28/8 
3/9
193.60
1993 
484.74
10/9
4
192.60
5
193.60
6
193.60
7
193.80
8
193.80
9/9
193.60
16.00
13/8
16.00
12/8
8.00
14/8
13/8
174.60
1 994 
524.07
14
179.80
15
183.60
16/8
178.90
ILSHEET 3 OF 3
TABLE 7 - PEAK DISCHARGE AT GORGE GAUGE 4 MELKA WARER GAUGE & DISCHARGE SITES ON RIVER AWASH
(DISCHARGE IN Cuaiecs )
YEAR
QP
MELKA TIME (hrs.)
WARER
DATE
GAUGE SITE FLOOD
CORRESPONDING
Q AT GG SITE
FROM           TO         DATE                 Q -
1983
214 .25
29/8
22/8
9/9
12.00
160.94
28/8
1984
125 .62
8/8
6/8
11/8
16.00
49.84
1985
260 .00
11/8
8/8
13/8
7/8
16.00
156.46
10/8
1986
174 .60
17/8
13/8
22/8
16.00
31.90
1987
181 .10
29/5
27/5
1/6
16/8
28/5
8.00
230.17
16.00
174.33
1988
221 ., 90
14/8
12/8
19/8
13/8
8.00
222.73
12.00
222.73
16.00
222.73
1989
204 . 60
5/9
3/9
9/9
4/9
16.00
335.75
1990
245 . 33
11/9
6/9
16/9
10/9
8.00
422.96
12.00
422.96
16.00
422.96
1991
259. 17
23/8
20/8
24/8
22/8
8.00
249.42
1992
242. 21
24/8
23/8
28/8
23/8
8.00
573.59
1 993
263. 0 4
16/9
14/9
28/9
15/9
8.00
445.70
12.00
445.70
16.00
445 . 70
1994
195.60
1/8
30/7
11/8
31/7
16.00
467.93
17high discharge at Mojka Waver
t hr re
if
be
Fit* M VC 1 i ni i ng
d j s c h a i • K • v , t he r<? is
compAird,gr nrra1y het urrn 1 hr
A t       gorge
a]
t
tr
hr
a rou rid
prak o hot wr« h
t
11 A I
The r < of
if 5 to
me reemmt
j . e . when ho peak a
1 I n»r F in
int
t hr r < M < k A
At 1 r nil a 1 mon t
rI
of
1*
k a re r •• i
ion of t
t hr* < A v r >
(
hr
hr
I wo
Rite
I   I lll<* . o rdr r
gorge
gang* And M< 1 k a Ur re !
IF < X (C > > ] \ »
] n     some htld             cou
< a Hr R t hr nt
the consequence of
1 r nun t
ion
When         peak         flood         at         M<         ]         ka         Usrrr         site         if            compared         with         t         hr
correspondj
ng              discharge              at
gorge              gauge
site,
the              discharge
at gorge g aug< f * t <
. > loo or just equal to 1 k n Wa re r
Fite in the years 1983,84 86,86 88.A 91 indicating that
(
t
1 he re            n«a >         be
cont ri  butlone
1 M F fr> < fl      a t         Mr ;   ka         ka re- r        site.
f roi t r I but a r 1 ea n o t he r yea r >
Ka be ria      A d J  acha rge               at
Mr 1 k a         k a r<           r f  4 t<
i f at1 1 enua t e-d
b) n bo u t 1.3                1 o                 2.4 t i me* s
1 he d i          F< Lx.    » g<       fct         gorge         gauge ft 1
te.
BarJ< rov . f
1 lie Master Dr ft.nage Plan
study 1
[ 1 985
) have
< ai i t< • d out
Lydraulie sedr1 f t uc> t c
eomput r
the
rout rd
f J ooO Lv <3t <4 l
npl a t a.e. . t d i «*. i. 2 MD2 )
out f a 11
site
The
rr suit of t l.<
e’ufl) is giver .1 lai it 8
The           map Hai< row ,
1* I oft. t he
pO J t 1 Oh o
fr liOk . tif
1 04 I      f 1 4>l         of          r hftififtgr ft
J 98 t      1 1.    1 he 4 1        hyd J aui 1< ftudr
l t> t udj
at          adopt rd
b>
1ft at big 3 .
?at > j e        8      l4l.C        8 . g 3
it          4ft f At  1enua t         4 Oh     of f.ggC peal 1
4. f      J 1 X C 1        |-.4»b<  ll<4     A 4 t   1    Aft • a a i 1 . v e J 
■ I.      / 4 9     0 i
knJ rJ (ch
(ley oi«d M<
1 e F F ft ft
! kt
oha j               Wil 4 4  L 1ft of the u/dri uf about y ( 1ftr&
k a Fr i          <4 I t 4  h u a I .uh j t (he
It but
observed that major be f Heel. 4 Ofi f 1 ueht e
ft* ) aliit Mr 1 k a I iia t 1ft C r>
< ompaFcd              t &          the            a U*_. v i          j  e a* 1. The
ratio
uf
at 1 c? h u a t j i       Qh he I wee 1.
goj g< gauge. ahd Hr
1 k a k a J        Cl ft i t r 1 If 5
to 3 II me ft j 1 j There f uTc
k a J e 1 it
be-1 wee 1. Mejia
t      J h 4       J OAK     ag J eemt I. !              » . 1 J
. i 1        £ ah       be        4 4-»l»t J uded ! ha ( I he        a I I e h ua1 r d               d . a . i 4 a J r a 14 d
tills al            I ud)
d j a k ha I gc at Nrlka
t ul 1 1.. 4
kftlrl     44 | «d
Mb. Ou ( f a j | a ,.It          All,
♦‘I I LJ i U ft { JWIi hr l4..ft i na 1and       part       of       it       may       h<       comp~r.wa*       *d       by       inflow       from       the I n t e r v*' n i n £ < «t < hn* n t .
Table H - FLOOD PEAK DISCHARGE AT SKLKCTKD CHA I WAGKS OH RIVER AWASH (AS OBTAINED BY HYDRAULIC MODRLtIHG STUDY BY HALCROW,I985)
Rr  t  urn Perlod (years )
F I ood   Peak«       ( Cu®*»‘- a ) at
haing-       ' a a
—
748 . H
U---
10
1------------------ 1
725.7
j
757.0
376 . 1
1
70 1 . 0            681.0                 666.0                  650.0
!N«ar 9D2 out fall )
338.9                3 3 4.3             3 2 4.0                 315.0
20
1012.0
505.5
4 38.6
419.3
4 09.7
J ii 3
L
|
50
14 66.0
766.3
683.0
6 46.1
1
8 2 12
608 2
- . ,1
5.3 fctfttlBatLon of Peak Elow Rataa
The discharge data of
Melka Warer Site from
ware u a a d t dlscharget
carried out
4idk 1 Mutti annual
o
c a r r y     out
. 4 ’2 to 1 144
>Bpu a >da4
o r   * a r i om »
f r«4u<ih y analysis Lj latum po r l ud a
Fha
IH4 « i
-• k <
fo  r
the two « a r l a a valuer and other «or
I hreL d
t he     aa \    i auia
L
oau•ur
3 a Ulla lu i g
- a a urn
•R
»U
I
Lhu
value* above certain
umiiiiua * a L ue of
•a
**
nu
4d r l 34
hd UW4A
« ».
rata»
ubt (i i n«d t
4 ‘
■Aii.k L
yai»
t annual -
au* auu aariaa
4.a
i 1 v a n
in I able
9
I* * 4
♦
a Hu ••
t h t3 L uuU
.'C<|UUUu
y
VUk•V
loi X a I a a Ware
«ite
IT L« U C
% •• a uh
Uvuigu Huud HydiugLu^h
lv 
4w4lgU         I  Loud  tl  d  -  u  4  .  «a  p  U  u
I MV     / w a 1 a            iWkulU
pML1Ud
t . 4 u d
.............................
* -> t 4 L .»U It kl-l.lLaaihydrograph       was       developed       for       Melka       Warer       site.       For       this purpose       discharge       data       of       the       site       was       examined       and       six independent       flood       events       given       in       Table       10       were       selected. The        ordinates        of        each        hydrograph        were        expressed        as        a proportion        of        their        peak        discharge        and        results        superimposed with        their        peaks        coinciding.        An        envelope        curve        was        then drawn       through       the       plotted       points       with       weightage       being       given to        the        event        having        the        largest        peak.        The        dimensionless flood       hydrograph       of       river       Awash       at       Melka       Warer       site       is shown     in     Fig     5.     The     20     ,50     and     100     year     flood     hydrographs were       then       obtained       by       multiplying       the       (Q/QP)       ratio       of       the dimensionless      hydrograph      in      Fig      5      by      the      flood      peak      values for        respective        flood        events.        Table        11        gives        the        (Q/QP) ratio        of        dimensionless        flood        hydrograph        and        design        flood hydrographs      of      20,50      &.      100      years      return      period      flood.      Fig 6 shows the 20,50 &. 100 years design flood hydrographs.
20Table 9 - RETURN PERIOD ANALYSIS OF FLOOD AT MELKA WARER SITE
Return Period 
(year)
Peak Flood 
(Cumecs)
3
235
4
247
5
256
10
282
15
296
20
306
50
339
100
363
Table 10 - SELECTED FLOOD EVENTS FOR DEVELOPING DIMENSIONLESS
FLOOD 1IDROGRAPH OF MELKA WARER SITE
S.
No
Period
From
To
Peak Discharge
(Cumecs)
1
25/10/77
18/11/77
294.4
2
13/2/90
18/3/90
234.0
3
4/4/90
20/4/90
185.4
4
4/4/89
16/4/89
170.6
5
24/1/93
4/2/93
163.9
6
26/4/93
7/5/93
139.4
21TABLE    11-
20,50    &    100    YEARS    RETURN FOR MELKA WARER SITE ON
PERIOD FLOOD HYDROGRAPHS AWASH RIVER
DAYS
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Q/QP
RATIO
0.207 
0.221
0.247 
0.266
0.293 
0.321 
0.372 
0.448 
0.528 
0.617
0.721 
0.833
0.921 
0.976
1
0.979 
0.931 
0.852 
0.745 
0.634 
0.534 
0.452 
0.376 
0.328 
0.293 
0.272
0.255 
0.241
0.228 
0.214
0.201
0.198
20 YR
63.42
67.71
75.68
81.50
89.78
98.35
113.98 
137.27
161  .78 
189.05 
220.91
255.23
282.19 
299.05
306.40
299.97
285.26
261.05
228.27
194.26
163.62
138.49 
115.21
100.50
89.78
83.34
78.13
73.84
69.86
65.57
61.59
60.67
DISCHARGE IN CUMECS
50 YR
100 YR
70.07
74.81
75.06
83.61
80.13
90.04
89.56
99.18
9 6.45
108.66
106.24
125.92
116.39
151.65
134.89
178.73
162.44
208.85
191.45
244.06
223.72
281.97
261.43
311.76
302.05
330.38
333.95
338.50
353.90
331.39
362.60
315.14
354.99
288.40
337.58
252.18
308.94
214.61
270.14
180.76
229.89
153.00
193.63
127.28
163.90
111.03
136.34
99.18
118.93
92.07
106.24
86.32
98.63
81.58
92.46
77.18
87.39
72.44
82.67
68.04
7 7.60
67.02
72.88
71.79
226.0 ESTIMATION OF FLOOD LEVELS AT MAIN DRAIN OUTFALL
SITES
To  study  the flood  blockage period  of MD2  at its outfall when  river Awash  is in  flood,  it is essential to  develop  the rating  curve of river Awash  at the MD2 outfall location.  The rating  curve at the MD2  outfall site can  be developed  either by  carrying  out hydro dynamic modelling  study  of the entire reach  from Melka Warer site to  some location  d/s of outfall site or by developing  a site specific rating  curve from the cross-section  (c/s) of site and  using  Manning’s equation.
For carrying  out hydrodynamic modelling  study,  the cross-sections of the river Awash  at suitable interval and  at locations wherever river topography  changes are required  along  with  details of Manning’s roughness coefficient along  the reach  and  its variation  with height for the cross-sections.  For the second  case c/s of the river at outfall site,  slope of water surface and  estimate of Manning’s coefficient are required.Consultant wanted  to  carry  out the later of the two  studies,  but no  survey  could  be carried  out at site due to the Afar problem.
6.1            Development of Rating curve
at MD2 Outfall Site
In  the Master Drainage Plan  study,(Halcrow,  1985),the hydraulic model study  was carried  out and  the water levels for various discharges were computed  which  are given below in Table 12.
Using  these water level and  discharge data,  a gauge and  discharge curve for River Awash  at MD2  outfall site has been developed (Fig 7), the equation of
23rating curve is given below.
Q = 0.4096 (H-713.2 )1,2666
Where
H = Water level in m
Q = Discharge in cumecs
Table 12 - WATER LEVELS AND CORRESPONDING DISCHARGE  OF RIVER AWASH AT  MD2  OUTFALL  SITE  (AS PER HARLCROW, 1985)
Water Level
(m)
Discharge
(Cumecs)
Remark
719.60
175
0.65 m below bankfull
level
720.25
260
bankfull level
721.00
315
1 in 10 years flood 
of Master Plan
721.5
399
1 in 20 years flood 
of Master Plan
722.5
608
1 in 50 years flood 
of Master Plan
725.4
1465
6.2           Water Levels of River Awash at MD2 Outfall Site
Using  the rating  curve equations developed  in  section 6.1  above,  water levels of river Awash  at MD2  outfall site have been  worked  out for the design  flood hydrographs of 20,  50  & 100  years return  periods.  The water levels so  worked  out are given  in  Table 13  and the plot of water level v/s time for three flood hydrographs is shown in Fig. 8.
24TABLE 13- WATER LEVELS OF RIVER AWASH AT MD-2 OUTFALL SITE FOR 20,50 & 100 YEARS RETURN PERIOD FLOOD
RATING CURVE Q=0.4096(H-713.2)"3.2666
DAYS         RP=20 YR
Q                    WL (CUMECS) (M)
RP = 50 YR
Q                    WL (CUMECS) (M)
RP=100 YR
Q                    WL (CUMECS) (M)
0 1 2 3 4 5 6 7 8 9 
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
63.42 67.71 75.68 81.50 89.78 98.35 
113.98 137.27 161.78 189.05 220.91 255.23 282.19 
299.05 
306.40
299.97
285.26 261.05 228.27 194.26 163.62 138.49
115.21
100.50
89.78
83.34
78.13
73.84
69.86
65.57
61.59
60.67
717.881
717.976
718.141
718.255
718.407
718.554
718.801
719.129
719.435
719.740
720.059
720.369
720.593
720.726
720.782 
720.733
720.618
720.419
720.128
719.794
719.457
719.145
718.820
718.590
718.407
718.289
718.190
718.104 718.022 717.929 717.839 717.818
70.07 74.81 83.61
90.04
99.18 
108.66
125.92
151.65 
178.73
208.85 
244.06 281.97
311.76 330.38
338.50 331.39
315.14 288.40
252.18
214.61
180.76
153.00 127.28 111.03
99.18
92.07
86.32
81.58
77.18 72.44 68.04 67.02
718.026
718.124
718.294
718.411
718.568
718.720
718.975
719.313
719.628
719.942
720.272 
720.591
720.822
720.959 
721.017 720.966 720.847 720.642 720.343 719.999 719.651 719.330 718.994 718.756 718.568 718.447 718.344 718.256 718.171 718.075 717.983 717.961
75.06
80.13
89.56
96.45
106.24 
116.39
134.89
162.44
191.45
223.72 
261.43 302.05 333.95 353.90 362.60 354.99 337.58 308.94 270.14 229.89 193.63 163.90 136.34 118.93 106.24
98.63 92.46 87.39 82.67 77.60 72.88 71.79
718.129
718.229
718.403
718.522
718.682
718.837 
719.098
719.443
719.765
720.086
720.422
720.749
720.984
721.124
721.183
721.131 
721.010
720.801
720.495
720.143
719.788
719.460
719.117
718.875
718.682
718.559
718.454
718.364
718.277
718.179 
718.085
718.062
256.3 Water Levels of River Awash nt Mill Outfall Site
Io  study  the f lood  blockage period  of MDl out fal I due to  high  water levels in  river Awash,  gauge A discharge curve of river Awash  was developed  for this site. Halcrow (1985) carried  out hydraulic model study  of river Awash  during  Master Drainage Plan,  the water hovels of river Awash  cor respond  i rig  to  various discharges at MD1  outfall site ( ch  .  681  .  0  urn  ) arc given 
in Table 14.
Table 14 - WATER LEVELS AND CORRESPONDING DISCHARGES OP RIVER AWASH AT CH 681.0 k 666.0 KM (AS PER HALCROW. 1985)
R
R
R
R
•a
MDl OUTFALL S1TF                                ALTERNATF MD2 PUMPED
(CH 681.0 KM)
OUTFAl L SITE
(CHG6 6.0KM)
REMARKS
water levels     DISCHARGE        WATER LEVELS       DISCHARGE
(CH 681.OEM)              (CUMECS)
|
723.8 227.0
(Ml (CIJMECS)
1
727.00                         227.0
727.90
304.0                       724.2                       304.0
728.06                              234.3                      724.4
324.0
728.40                         419.3                     724.8                       409.7
729.26                     C4< . 1                      725.6
624.2
1 in 10             ars flood of Manter Plan
1 in 20 yearn flood of Mauler Plan
1 iii 50 years flood of Maut er P1 an
731.60
1465.0
728.2
1465.0
I »■ i ng 1 h<
gaug< a i,d
tit- ve 1 oped g j vt r> la low.
ahow water JeveJb and discharge
d;M ha r
rum of i i ver Awauh
'I
■ 1    9 i a fad f h» equal ion of fat i fig
d ata, a
haw been
curve lbThis rating  curve was used  to  compute water levels of river Awash  at MD1  outfall site for the design  flood hydrographs of 20,50  and  100  years return  period.  The water levels worked  out are given  in  Table 15  and  Pig 
10.
6.4 Water Levels of River Ou t f a11 Site
Awash at Alternate MD2 Pumped
To  carryout study  for alternative pumped  outfall site
for MD2  ,  a tentative site near pumping  station  for
pumped            irrigation            area
in            Ar.gelele            has            been 
identified.  In  order to  developed  GAD rating  cur/e for this site,  water levels corresponding  to  various discharges computed  by  Harlcrow(1985) during  hydraulic model study  of river Awash,  near ch  666  km,  were
taken  from Master Drainage Plan  as given  in  Table 14. G&D curve was developed  using  the water levels and corresponding  discharges for this 3ite (Fig  11; and the equation of rating curve is given below.
The water levels corresponding  to  20,50  £  100  years return  period  flood  hydrograph  were computed  using this equation.  The water Levels so  worked  out are given in Table 16 £ Fig 12.
6.5 Longitudinal Section of River Awash
The water levels for 20,  50  £  100  years floods are plotted  on  the longitudinal section  of river Awash  aa show n in Fig 13.
)7I
I ABLE 15- WATER LEVELS OF RIVER AWASH AT MD-1 OUTFALL SITE FOR 20,50 A 100 YEARS RETURN PERIOD FLOOD
Rating curve q=o
days RP=20 YR
Q                     V<L (CUMECS) (M)
114(H-720)*3.86 RP=50 YR
Q                     WL (CUMECS) (M)
RP=100 YR
Q                     WL (CUMECS)       (M)
0            63.42   725.140              70.07       725.275
1             67.7]    725.228              74.81
2            75.68   725.381              83.61
3          81 . 50   725.485              90.04
4            89.78   725.625              99.18
5            98.35   725.759               108.66
6          113.98   725.983               125.92
8          161.78   726.551               178.73
137.27   726.279
15].65
1 0 220.91 727.102
1 1 255.23 727.373
9          189.05   726.821               208.85
12
244.06
281.97
1 3 299.05 727.682
1 4 306.4 0 "2" 730
727.567           311 . * ()
1 5          299.97   "2" .688             33 1 .39
330.38
338.50
1 C         285.2(    727.588
1 7          261.05   727.4      (           288 40
o a ,.i . j1 z s
1 
1 8        2 2 8 2r      " 2 "     63           202.18
21 138.49 "2l . 293 153.06
2 2 116.21 726 OOC -27.28
23 106.50 725 "9. 111 .03
24 89.71- 7 2*  12 f 99 j ►
1 9          194.26   726 869 2(           163.62   7 21 : '
2.4.61
180.76
21            83.34      z
2t             78.13   721 .42t             8<   3 2
91   (/
2fe         69.8 <    7 2! .2 ' : 29           65.5 7    7 21    8 * 30          6 1 .59
3 J           66 6 7    725.082
27           7 3.84    ' 2 t 3 4 r                   8 . 58
]► 7 7  4 4 69  0 4 t ( 2
725.365
725.522
725.629
725.772
725.910
726.140
726.443
726.723
727.000
727.288
727.565
727.765
727.882
727.932
727.889 727.787 727.610 727.360 "27.049 726.742 726.458
726.167 725 943 725.772
"25 662 725.568
25.487
"25    409
' 21 .321
' 2 t 2 3 t '2!      214
75.06 725 . 370
80.13 725.461
89.56 725.621
96.45 725.730
106.24 725.875
11 6.39 726.01 6
134.89 726.250
162.44 726.558
191.45 726.844
223.72 727.125
261 .4 3 727.4 1 9
302.05 727.701
333.95 727.904
353.90 728.024 362.60 728.075 354.99 728.030 337.58 727.927
308.94 727.74 7 270.14 727.482
229.89 727. 1 76 193.63 726.864 163.90 726.574 136.34 726.267 118.93 726.050 106.24 725.875
98.63 725.763
92.46 725.668
87.39 725.585 82.67 725.506
80 725.416 7 2.88 725.329
71.79 725.308TABLE  I fl-
WATER LEVELS OF RIVER AWASH AT ALTERNATE MD-2 SITE FOR 20,50 ft 100 YEARS RETURN PERIOD FLOOD
OUTFALL
RATING CURVE Q = 0.39(H-717.5)* 3.49
DAYS        RP=20 YR
Q                   WL (CUMECS) (M)
RP = 50 YR
Q                    WL (CUMECS) (M)
RP=100 YR
Q                    WL (CUMECS) (M)
0 1 2 3 4 5 6 7 8 9 
10 1 1 
12 13 I I 1 5 16
1 7 I 8
1 20
2 1
2 2
2 3
2 4
25 2 6
27 28
2 9 30
3 1
63.42 67.71 75.68 81.50 89.78 98.35 
113.98 137.27 161.78 189.05
220.91 255.23
282 . 1 9 
299.05 
306 . 10 
299.97
285.26 261.05
228.27 194.26      9 
16 3. 6 2 
138.4  9 
115.21
100.50
89.78
8 3 . 34
7 8.13
7 3.84
69.86
65.57
6 1 .59
60.67
721.800 721.881
722.023
722.120
722.250
722.376
722.586
722.865
723.123
723.380
723.648
723.908 
724.095
724.205
724.252
724.211 724.115 723.949 723.706 723.426 723.141 722.878 722.602 722.406 722.250 722.    I 50 722.065 
7 2 1 .99 1 721.921 721.841 72 1. Z64 721     ?45 
70.07 74.81 83.61
90.04
99.18 
108.66
125.92
151.65
178.73
208.85 
244.06 281.97 311.76
330.38 338.50 331.39 315.14
288.40 
2 5 2. 1 8 
214.61
180.76 
153.00 127.28
111.03
99    18 
92.07 8 6 3 2 
8 1.58 77.18
7 2 4 1 88.04
721.924 
722.008
722.154
722.254
722.388
722.517
722.734 
"23.020
723.286
723.550 
723.826 
724.093 724.286 
724.40G 724.448 724.406 724.307 724.136 723.886 723.597 723.305 723.034 722.750 722.548 722.388 722     285 ? 2 '*    4 1
’ -- 121 722 J49 
72 1 96 ’ 721 88’
'2' 868
75.06
80.13
89.56
96.45
106.24
116.39
134.89
162.44
191.45
223   .72 
261.43 302.05 333.35 353.30 352.50 354.39 3 3 7 . $ g 308.34 270.1> 229.99
1 93 53 133.90 136.34 119   93 138 2 4
98 53 9 2 15 
i 1 j 4 92 5’
71 .60 '1 58 ’ 1  ?9
722.012
722.098
722.247
722.349
722.485
722.617
722.838
723.130
723.401
723.670 
723.952
724.225
724.421
724 . 537 
”24.586
724.543 724.442 ”24.263 ”24.013 723.719 ”23.420 723.   144 
'22     854 
'22     649 
'22     183
'22     180 
'22.    290 
'22.213 '22.>39 
'2  2  Jid 
’2.     975
’2: 955*7.0 STUDY OF IRRIGATION WATER SUPPLIED & MDl DISCHARGE RELATIONSHIP
There are 13 canal offtakes which supply irrigation water to various entities like IAR, Melka warer, MAAE, Melka Sadi Banana unit,State farms etc. The data of monthly irrigation water supplied from each offtake
for a period from July, 83 to September, 1994 were collected from PCC. The total monthly water supplied through all the offtakes for the above period is shown in Table 17. From the table 17, it is seen that total quantity of irrigation water supplied has reduced considerably since 1991 onwards.
Discharge of Main Drain 1 (MDl) is being observed at Parshal flume. The available discharge data of MDl at Parshal flame were collected from 1989 to 1992.
Presently  MDl is catering  mainly  to  the surface and 
subsurface drainage of Melka Sadi area.  It was decided 
to           find           out           relationship           between           total
irrigation 
water       supplied       in       Melka       Sadi       area       through       offtakes       1 
to  4  and  MDl discharge.  Runoff from the Melka Sadi area due to  rainfall observed  at PCD-3  station  of PCC was also  computed  to  study  the effect of rainfall on variation of MDl discharge.
Table 18  shows the details of monthly  total water supplied  through  offtakes 1  to  4  and,  volume of MDl runoff and  runoff volume due to  rainfall observed  at PCD-3  station  from 1  989-1  992.  The three data were plotted  on  some plot as shown  in  Fig  14.  It is observed  from Fig  14,  that no  definite relationship exists between  quantity  of irrigation  water supplied and MDl discharge.
30table month
JAN FEB
MAR ; APR MAY
JUN JUL
AUG SEP
OCT NOV DEC
TOTAL
17- YEARWISE MONTHLY IRRIGATION WATER SUPPLIED THROUGH OFFTAKES 1 TO 13
1983
MONTHLY CANAL WATER SUPPLIED (1000 Cu.M.
1984                  1985                  1986                  1987  )
1988
16972.26 29837.86 18044.54 19256.80 15625.70 10032.00
109769.16
1794.00
1560.60
1811.60
2596.22 14932.37 21804.15
26439.10
23419.75
19768.88
21510.02 13115.60
148752.29
1478.40 1101.90 1206.60
5726.14
18283.28
18633.84
13674.40
12337.40
19405.62
17143.20 6709.10 5909.40
121609.28
3002.40
5037.00
483.30
10014.90
19757.30
16969.60
18232.80 
23701.00 18646.70 13102.30
7649.80 136597.10
6064.80 4479.40
3013.00 
6178.00
25073.10
17118.30
27456.20 46544.80 48845.20 17196.40
25189.00
9288.00
236446.20
2587.70 3215.70 2798.10
10742.90 17155.80 14862.60 18719.90
3054.10
16343.70
14448.80
8089.14
6835.34
118853.78
MONTH
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
TOTAL
1989
5779.40
2798.80
1563.84
4615.58 15179.29
15375.71
14291.57
19321.80
18850.89
16456.22
10717.26
4724.64
129675.00
MONTHLY CANAL WATER
1990 1305.80
502.92 7781.00
12510.34 15330.01 11709.85 13893.62
18416.18 8748.68 3507.39 3190.36
96896.15 
1991
1500.84
1097.28
2191.32
10171.58
15592.19 15940.36
14870.16 12703.70 
7350.06 12380.59
9606.52 10899.99
114304.59
SUPPLIED 1992
2086.56
680.40
2003.40
5318.65 
13417.01 13158.31 13964.06
8033.88 11221.04 14332.66
5884.27
5155.74
95255.98
(1000 Cu.M. )
1993 2246.70
2678.40 3733.88
5682.16 8691.59
7840.48
8839.62 
3292.78 
5169.06 
2241.72
2268.96
52685.35
1994
2551.32 1742.10
930.96 7275.82
12705.35 12700.35
6605.33 16240.71 15972.68
76724.62
31TABLE 18
details of monthly irrigation
& RUNOFF FROM MELKA SADI AREA
nup ^
E  SU   PLlED FR°M OFFTAKES 1 TO 4 , MAIN DRAIN DISCHARGE n
10 RAINFALL OBSERVED AT PCD-3 RAINGAUGE STAION
YEAR  MONTH
MONTHLY
OFFTAKE-1
CANAL WATER SUPPLIED (1000 Cu.M.) OFFTAKE-2 OFFTAKE-3 OFFTAKE-4 TOTAL
DRAIN Q & VOL
MELKA SADI RUNOFF FROM RAIN
RELEASE
Q                VOLUME                          RAINFALL         RUNOFF        RUNOFF
cumecs     (Th.Cu.M)
1989     JAN89 FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC 1990     JAN90 
115.20
825.83
1292.94
1152.78 1456.56 1469.38
1339.20
598.59
227.88
320.76
1681.50
1390.60
1563.84 
154.08
478.50
704.52
500.40
467.68
1209.24
2163.96
2235.60
1434.96
1305.80
274.68 
1469.09
970.96
1208.70 1731.42 1371.06
849.58
257.04
142.20
304.68
1225.22
610.48
962.21 1088.64 
1107.00
629.64
136.98
126.00
1681.50
1505.80 
1563.84 
1559.27 
4465.75 
3438.74 
4127.87 
4757.12
5026.50 
4241.77
2857.50 
2023.92
1305.80
mm mm Th.Cu.m
0.00               0.00                  0.00
0.286
741.31
20.80 89.60
101.90
0.00               0.00 15.49           894.93 21.59         1247.04
0.255
682.99
0.00                0.00               0.00
0.290
751.68
0.341
913.33
0.359
961.55
0.148
383.62
0.288
771.38
29.10
85.10
42.60
35.70
24.80
0.00               0.00
13.46 777.57
0.51 29.34 0.25 ? 14.67
0.00              0.00
0.426
1104.19
0.00                 0.00              0.00
0.496
1328.49
FEB
28.10 0.70
0.00 0.00
0.00 0.00
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
1991 JAN91
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC 1992     JAN'92 
FEE
541.08
1541.81
1177.02
1189.17
1087.92
1001.88
388.70
227.70
12.06
1014.84
941.40
941.40
1565.34
861.80
406.08
186.76
104.40
105.48
502.92
1599.12
750.84
1446.84
927.40
980.88
1361.34 
1002.06
783.36
1787.76
1500.84
1097.28
2191.32
1010.88
820.98
1037.10
933.50
676.50
609.12
1433.88
2387.52
3481.92
2086.56
680.40
2003.40
86.44 
1249.20 
1542.60 
1829.70 
1094.04
354.24
889.84 
2152.44
2221.92
568.18
985.96
1239.84
858.69
1446.35
1590.58
452.81
127.80
17.82
609.34 
968.09 
930.50 
847.58 
835.92 
2154.24 
405.81
502.92 
3317.72
4246.70 
4794.20
3822.84 
4351.07 
6108.04 
2249.38 
1251.00 
1872.00
1500.84 
1097.28
2191.32
3981.62
3596.78
3689.58
5301.71
3319.40
1720.92
3704.42
2656.94 
3739.14
2740.32
1929.60
2734.10
2580.80
4027.18
2977.32
4270.68
2012.04
2097.76
3544.80
2679.66
2594.16
198.40             86.61            5002.82
0.234
606.53
0.270
723.17
32.90
54.00
20.30
0.260
0.00 0.00
3.05 176.05
0.00 0.00
673.92
0.260
696.38
0.00 0.00 0.00
105.30 23.11 1335.06
0.191
511.57
83.90
12.70
733.55
117.20             30.23            1745.85
20.60
112.14
54.36
0.00                  0.00
0.191
495.07
0.00                 0.00                  0.00
1.60               0.00                  0.00
0.00                  0.00                  0.00
685.20 
877.50
833.76
1653.12
1032.50
424.20 
936.36
80.26 
49. 14
1270.70
956.90 
877.32
1149.75
748.60
281.52
1147.42
84.76
102.60 
653.76
1249.20
730.70
1050.76
610.78 
864.00 
552.96
86.40
0.194
519.61
16.60
36.50
31.70
42.70
0.00 0.00
0.25 14.67
0.00 0.00
0.76 44.01
0.138
357.70
0.00                  0.00                 0.00
0.095
254.45
49.50
2.54             146.71
0.532
1424.91
107.10             24.13            1393.75
0.550
1425.60
30.20
0.00                 0.00
0.233
624.07
0.280
725.76
0.00 0.00 0.00
0.00 0.00 0.00
0.286
766.02
MAR
APR
MAY
JUN
JUL
0.223
597.28
AUG
SEP
0.132
353.55
10.60 31.35 68.25
0.00
87.00
5.12
36.33
46.11 73.55
0.00                 0.00
0.00                0.00
7.37            425.46
0.00              0.00 15.24          880.26
0.00              0.00 0.25            14.67 2.03          117.37 8.89          513.49
0.224
580.61
OCT • 
NOV
1273.68
72.48
1101.06
364.14
937.12 
2215.20
250.38
77.76
1443.60
893.52
498.24
786.96 
553.86 
720.00 
439.76
276.84
294.48
0.268
717.81
0.142
368.06
0. 147
393.72
0.268
694.66
DEC
32REFERENCES
1.   Master Drainage Plan for Melka Sadi &. Amibara Areas, Final Report, Vol 6, Annexe C - Hydrology, Sir William Halcrow &. Partners, London, July 1985.
2.   SCS National Engineering Handbook, Section 4 - Hydrology, Soil Conservation Service, U.S Department of Agriculture.
3.   Applied Hydrology, Ven Te chow & others, MC GrawFIGURESGENERAL MAP. OF STUDY AREADURATIC>N(days)
DEPTH (mm)
"H
□
in <r;
1
i
7J
V
4-
'<
o
r>
X
X
X
o
*<
X
m
X
o
*<ASSUMED LiV:T Or FiC’OD'VS
0 EOLHAMO FARM
RA UNIT I
ALGETA
SETTLEMENT AREA
A'ZIpAhA
UMTS
U 6 EL AI/.6ASHI
MELKA V.ARER SEARCH STATION'
(SUDLELEJ
A’CGELElE UNIT I
A-.'EARA     IRT-jGATON project
A'.'GELELE
UNIT 3
f.'.ELKA SAD; STATE TARM
0
CADA BlCU S-V-MP
Scc.’e - I.’ SO COOf-DLFXMO FASV
ELOPMENT
SETTLEMENT AsEA
AMIPARA UNTS
E 6H AM&4SHI
EH<ILU POUTAiq
(SU3LELE)
AVSELElE UW'T I
ASSUMED LIMIT
ANSElELE
f.'ELKA SAD; STATE TAAM
END OF EXISTING
DYKE
$c:'e- > 50 COO
LAYOUT OF THE WASH FIVER
HYCRAULlC IML
( h’o.’crcw. tS65)Q(cumecs).
FIG.4- FLOOD-FREQUENCY CURVE FOR MELKAQ/QP RATIO
FIG.5-DIMENSIONLESS FLOOD HYDROGRAPH
DAY S
+     -294.4
<>       234.02
A 185.4
X 170.6QCcumecs),
FIG.6-20,506: I 00 YEARS DESIGN FLOOD
380
20 YR
DAYS
50 YR
O          100 YRW.L.(m)
FIG.7-GAUGE & DISCHARGE CURVE FOR RIVERWater Level(m)
FIG.8- W.L.PIot for River Awash at MD2
20yr
DAYS
■+• 50yr
<>       100yrWATER LEVEL(m)
FIG.9-GAUGE & DISCHARGE CURVE FOR Er.-RWater Level(rn)
L.PLOT FOR RIVER AWASH a!
OUTFALL SITE FOR 2O.5O&1OO YEARS FLOOD
i
W
/z
727.6 727.4
727.2
726.8 726.6
726.2 726
725.8 725.6 725.4
725.2
/•/ B
A *
DAYS
50yr
1 OOyrW.L.(m)
DISCHARGE(c umecs)Water Level(m)
FIG. 12- W.L.PIot tor River A^'ash at MD2
724.6 724.4
724.2
724 723.8 723.6 723.4
723.2
723 722.8 722.6 722.4
722.2
722 721.8
721.6VOLUME (Cu.m;
(Thousands)
F IG I 4--PLOT OF RELEASE FROM OFFTAKE 1
IJ        RELEASE
MONTH & TEAR + MD1-Q
RUNOFF

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Summery

Amibara Drainage Project Phase-II - Summary

Amibara Drainage Project Phase-II - Hydrological/Hydrometeorological Data Analysis

Project Overview

The document presents hydrological and hydrometeorological data analysis for the Amibara Drainage Project Phase-II in Ethiopia, prepared by Water and Power Consultancy Services (India) Ltd. The study focuses on flood estimation, drainage requirements, and water level analysis for the Awash River basin.

        Key Objectives:
        Preparation of detailed designs and tender documents
Project preparation report
Environmental impact assessment
Flood estimation and water level analysis

    

Data Availability

Hydrometeorological Data

Data collected from two stations:

IAR, Melka Warer (1965-1994)
PCD-3 Station (1983-1993)

Hydrological Data

River Awash data from two sites:

Gorge Gauge site (1983-1996)
Melka Warer site (1972-1995)

Climate Characteristics

Parameter	Value
Mean Annual Temperature	26.99°C
Mean Annual Rainfall	563 mm
Mean Daily Evaporation	7.17 mm
Annual Sunshine Duration	3,037 hours

Rainfall Analysis

Two distinct rainfall periods:

February-April (32% of annual rainfall)
July-August (40% of annual rainfall)

Depth-Duration-Frequency Analysis

Return Period	1-day Rainfall (mm)	2-day Rainfall (mm)	10-day Rainfall (mm)
5 years	70.8	83.7	136.8
20 years	92.0	109.7	177.6
50 years	105.4	126.6	203.5
100 years	115.4	139.5	222.9

Flood Estimation

River Awash Flood Peaks

Return Period (years)	Peak Flood (Cumecs)
20	306
50	339
100	363

Drainage Requirements

Total drainage rate adopted: 1.35 l/s/ha (including 0.35 l/s/ha for sub-surface drainage and canal rejection flow)

Water Level Analysis

Rating curves developed for three sites:

MD2 Outfall Site: Q = 0.4096(H-713.2)^3.2666
MD1 Outfall Site: Q = 0.114(H-720)^2.81
Alternate MD2 Pumped Outfall Site: Q = 0.39(H-717.5)^1.43

Conclusions

The study provides comprehensive hydrological data for the Amibara Drainage Project area
Flood frequency analysis was conducted for various return periods
Design flood hydrographs were developed for 20, 50, and 100-year return periods
Water level analysis was performed for critical outfall locations
The drainage system was designed to handle surface runoff from extreme rainfall events