Presentation on determination of water
potential
of the Legedadi Catchment
INTRODUCTION
Legedadi catchment was located to the east of Addis Ababa and part
of the drainage system that forms the northwest corner of the Awash
river basin.
The catchment area of Legedadi watershed is estimated at 205 km2.
It is drained by five of small streams. These are:-
• lege beri, lege sekoru, lege bolo, lege sendafa & south tributary
The elevations of the catchment range from 2400 m.a.s.l. to 3228
m.a.s.l.
OBJECTIVES
GENERAL OBJECTIVE
The main objective of this project is to determine the
water potential of the Legedadi catchment by using the
HEC- HMS model.
SPECIFIC OBJECTIVES
To study the HEC- HMS model
To compare the water potential of the catchment with the
demand of the town.
To determine the water potential of the catchment at two
points.
BACKGROUND OF THE CATCHMENT
The study area is located about 25 km from Addis Ababa
in the east direction.
The catchment is bounded by latitude 9o01' N – 9o13' N
and longitude 38o60' E - 39o07' E.
The mean monthly temperature is between 16oC and 26oC
throughout the year.
There are four types of soils in the catchment area on
which crops grows annually. Theses soils are Koticha
(Black vertisol soil), Dalecha (Grey soil), Gembore (Light
soil) and Key (Red soil),
DETERMINATION OF WATER DEMAND
Design period and population forecasting
For our case, the design period of 21 year is selected.
The population of the town at the end of the design
period is determined by using the Ethiopian Statistical
Authority (CSA) method.
The initial data that we got from the Addis Ababa town
water supply design report and other literature for the
projection of future population and demand are:-
Initial population @ 2007 = 2,738,248
Composition of per capita domestic water demand of year
2009 by demand category(i.e HC 80l/l/d, YC 40l/c/d and
PTU 30 l/c/d)
Percentage of population to be served by each demand
category
Annual growth rate
Forecasted population(
Year Growth Rate Forecasted Population
(%)
2007 3.7 2738248
2015 3.5 3623058
2020 3.3 4273009
2025 3.1 4989413
2030 3.0 5796871
2035 2.9 6701412
Projected per capita water demand by demand category
(l/c/d)(Qn = Qo*e^kn)
Demand 2009 2015 2020 2025 2030 2035
Category
HTU 80 90.20 99.69 119.35 135.24 153.24
YTU 40 49.05 59.30 53.35 58.37 63.87
PTU 30 31.86 33.49 34.65 36.24 37.91
Adjustments
Since the mean annual RF of Addis Ababa is 1257, the
adjustment factor for the climatic effect 0.9.
Addis Ababa town is also classified as the town under the
normal Ethiopian condition at present, therefore, the
socio- economic factor for the Addis Ababa is 1.00.
Adjusted average per capita domestic water demand (l/c/d)
Adjustme 2009 2015 2020 2025 2030 2035
nt factor
CF SEF
0.9 1.0
HTU 80.0 90.2 99.7 119.3 135.2 153.2
YTU 40.0 49.1 59.3 53.4 58.4 63.9
PTU 30.0 31.9 33.5 34.6 36.2 37.9
HTU 6% 9% 11% 12% 13% 14%
YTU 28% 41% 49% 55% 60% 65%
PTU 66% 50% 40% 33% 27% 21%
32.22 39.74 48.08 49.59 56.15 63.84
Adjusted average daily domestic water demand (m3/d)
Year 2009 2015 2020 2025 2030 2035
Adjusted average
per capita
domestic demand
(l/c/d) 32.22 39.74 48.08 49.59 56.15 63.84
Projected 579687 670141
Population 2948564 3623058 4273009 4989413 1 2
Daily domestic 325503 427808
demand (m3/d) 95002.7 143984.1 205428.5 247413.9 .1 .6
NON DOMESTIC DEMAND
Public demand is assumed to be 25% of the domestic
demand since the town has many public centers
Industrial demand is assumed to be 20% of the domestic
demand
Fire fighting demand is assumed to be 10% of the
domestic demand
Water loss is assumed to be 39.5% of the domestic
demand
Average daily water demand
Year Domestic Public(m3/d) Industrial(m3 Fire(m3/d Loss(m3/d Non Total average Total average
demand(m3/d /d) domestic(m3/ day day
d) demand(m3/d demand(l/s)
2009
95002.73 23750.68 19000.55 9500.27 37526.08 89777.58 184780.32 2138.66
2015
143984.08 35996.02 28796.82 14398.41 56873.71 136064.96 280049.04 3241.31
2020
205428.53 51357.13 41085.71 20542.85 81144.27 194129.96 399558.49 4624.52
2025
247413.91 61853.48 49482.78 24741.39 97728.49 233806.14 481220.05 5569.68
2030
325503.31 81375.83 65100.66 32550.33 128573.8 307600.63 633103.94 7327.59
2035
427808.61 106952.15 85561.72 42780.86 168984.4 404279.14 832087.75 9630.65
Therefore, the total required demand at the end of the
design period is 9630.65 l/s (9.631 m3/s)
As we get information from the AAWSA, 60% of the
Addis Ababa water supply is from the Legedadi.
Therefore, the total required demand at the end of the
design period is 5778.39 l/s (5.8 m3/s)
HEC - HMS INPUT DATA AND RESULTS
Legedadi Catchment Delination
Extracted channel network of the Legedadi Catchment
Shape file of the Legedadi catchment
Sub basin initial and constant loss method and Snyder Transform method data
Sub Loss Loss Loss Transfor Transfor
basin Paramet Paramet Paramet m m
er er er Paramet Paramet
er er
Initial Constant Impervio tp (hr) Cp
(in) (in/hr) us
Lege 0.02 0.14 9 0.20 0.16
(beri,
sekoru,
fule)
Lege 0.02 0.14 10 0.28 0.16
(bolo,
seudafa)
South 0.02 0.14 8 0.20 0.16
Sub basin area and base flow data
Sub basin Area(m2) Initial Threshold Recession
flow(cfs/m2 ratio to constant
) peak
1. 45.6 0.54 0.1 0.79
Lege(berin,
sekoru,fule)
2. 55 0.54 0.1 0.79
Lege(bolo,
seudafa)
3. South - 13.75 0.54 0.1 0.79
east
Precipitation gage weights
Sub basin Sendafa Addis Ababa
1. Lege (beri, 1 0
sekoru, fule)
2. Lege (bolo, 0.2 0.8
seudafa)
3. South east 0 0.8
Routing criteria for reaches
From To Method Sub Parame
reach trs
1. Reach Lege Jun 1 Muskin 5 K =0.6,
2 (beri, gum x = 0.2
sekoru,
fule)
2. Reach Lege Jun 2 Modifie 3 Table
1 (bolo, d plus below
seudafa)
Storage Discharge Function
Storage (1000m3) Discharge (m3/s)
0 0
200 37
450 38
750 39
1,100 40
1,600 240
2,100 610
2,104 930
2,700 1,400
RESULT AND DICUSION
Result of (HEC-HMS)
Hydrologic Drainage area(ml2) Peak
element discharge(cfs)
Lege(balo,sendafa) 55 52.2
Lege 45.6 41.0
(bari,sekoru,fule)
Junction 1 100.6 93.3
South East 13.75 5.5
Junction 2 13.75 5.5
Junction 3 114.35 98.8
Average discharge 296.30
