Integrated Water Resource Management And Planning
Through Basin Development For Sustainable Development
NATURE AND FEATURES OF THE ETHIOPIAN RIVER BASINS
ABSTRACT
A River basin is the portion of land drained by a river and its tributaries. It encompasses all area of the
land surface dissected and drained by many streams and creeks that flow downhill into one another,
and eventually into one river. The final destination is an estuary, a sea or an ocean. There are basins
which are closed and loss the totality of their water resources to evaporation and seepage. As a bathtub
catches all the water that falls within its sides, a river basin sends all the water falling on the
surrounding land into a central river and out to the sea.
Ethiopia have 12 Basins, 8 of which are River Basins, 1 Lakes Basin and the remaining 3 Dry, with no
or insignificant flow out of the drainage system. The dome shaped nature of the country, with high
raising mountains and a high tableland at the center that descends in all direction and the surrounding
lowlands that circumscribe the plateaus is a peculiar nature of Ethiopia. The Ethiopian Rift Valley that
dissected the highland plateau from North-east to Southwest which tilts from the center in the Northeasterly and South-westerly direction is also responsible for creation of the Lakes Basin and
determining the direction of flow of some rivers that terminate in the Rift-Valley System.
Due to the legacy of its proximity to the equator, and high altitude that rises above the surrounding
regions, the upper catchments of the Ethiopian River Basins is relatively endowed with a better rainfall
that is in excess of evaporation and seepage resulting in surface run-off that cascades to the
surrounding lowland in all directions. The historical settlement in the highlands associated with fast
growing population and total dependence on natural resources of the basins, resulted in the sever
degradation of these highland areas.
The complex interaction between the climate, biophysical and socio-economic characteristics of
Ethiopia resulted in important features of the basins such as high level of spatial and temporal
variability of flow, enormous turbidity, and tremendous potential for hydropower in the highlands and
of irrigation in the lowlands and sceneries along the major gorges.
1. INTRODUCTION
Ethiopia is a country of diversity. There is tremendous diversity of climatic, biophysical and socioeconomic settings. The climate ranges from equatorial rainforest type climate in the south and
southwest characterized by high rainfall and humidity to afro-alpine type on the summits of the Semien
and Bale mountains and desert like conditions of the Northeast, East and South east lowlands.
Altitudinal gradient ranges from 160mbsl at the Kobar sink in the Dallol Depression where the
temperature is in excess of 600c to about 4620masl at Ras Dajen in the Semien Mountains with
freezing temperature in most part of the year. The resulting rainfall also varies from about
3000mm/annum at Masha in the Baro-Akobo Basin to barely 200mm/annum along the Ethio-Jibouti
and Ethio-Somali Border in the Ogaden and Aysha Basins.
The diversity also extends to socio-economic conditions. Economic activities in the country ranges
from booming industrialization and modern agriculture in and around Metropolitans such as Addis,
Bahir Dar, Mekele and Nazareth to Hunters and Gatherers, Shifting cultivators and Nomadic
Pastoralists in the peripheries. The distribution of social and economic infrastructure and amenities is
also like wise very variable with some parts of the country relatively well served and others barely
reached.
2. WHAT IS A RIVER BASIN?
Definition
 A River Basin is a natural depression in the surface of the land often with lake at the bottom of it
 It is the entire geographical area drained by a river and its tributaries
 A drainage basin (also often: watershed, river basin, or catchment): is an area that topographically
appears to contribute all the water that passes through a given cross section of a stream
 A River basin is the portion of land drained by a river and its tributaries. It encompasses the entire
land surface dissected and drained by many streams and creeks that flow downhill into one another,
and eventually into one river. The final destination is an estuary or an ocean. As a bathtub catches all
the water that falls within its sides, a river basin sends all the water falling on the surrounding land
into a central river and out to the sea.
Generally a river basin with in a country is a hydro-geographical boundary of an area of land that feeds
the water it receives to a common river or lake or swamp before it crosses the international boundary
or terminates in sea or ocean. How this occurs is the product of the interactions between land and
water, particularly the watershed's underlying geology, rainfall patterns, slope, soils, vegetative cover
and use. It is a natural boundary that is permanent as opposed to Political or Administrative Boundary
that is liable to change with change in governance.
3. RIVER BASINS OF ETHIOPIA
The overall land mass of the country is hydrologically divided into 12 Basins. eight of these are River
Basins, one Lake and three Dry Basins. Four of the River Basins, Abbay, Baro-Akobo, Mereb and
Tekeze are part of Nile River System, flowing generally in the Western direction toward Sudan
eventually terminating in the Mediterranean Sea. Five Basins namely, the Omo-Ghibe, Awash, Riftvalley Lakes, Denakil and Aysha can be safely categorized as the Rift-valley system as all of them
drain their water in the Great East African Rift-valley. The remaining three, Genale-Dawa,
Wabishebelle and Ogaden are part of the Eastern Ethiopian Basin that generally flow in the Southeasterly direction toward the Somali - Republic and then to the Indian Ocean.
4. MAJOR PHYSICAL FEATURES OF THE BASINS OF ETHIOPIA
4.1 Location and Size
Almost all of the basins radiate from the central ridges that separate the Rift Valley from the highlands
of Ethiopia to all directions out of the country. Basins drained by rivers originating from the mountains
west of the Rift Valley flow West into Sudan, and those originating from the Eastern highland flow
East into the Republic of Somalia. Rivers draining the Rift Valley Basins System originates from the
adjoining highlands and flow North and South of the uplift in the Center of the Ethiopian Rift Valley
North of Lake Ziway. Map 1 indicates the location of the River Basins of Ethiopia.
There is very big variation in the size of the Basins. The size of a basin in mainly the function of the
geological formation. The Wabishebelle Basin is the largest basin in Ethiopian with an area of 202,
220 km2 followed by the Abbay Basin covering an area of 199812km2. The smallest basin is the Aysha
Basin with an area of 2223 km2 followed by the Mereb that has an area with in Ethiopia of 5900km2.
Table4.1 below shows some physical characteristics of the Basins of Ethiopia.
Table 4.1. Important Physical Characteristics of the Ethiopian Basins
R.No. Basin Name
1
2
3
4
5
6
7
8
9
10
11
12
type Source
Location
Bale Highland 4045'N-9045'N
38045'E-45045'E
Abbay
R West,
7o45' N-12o45' N;
Southwest HL 34o05'E-39o05' E
Genale Dawa
R Bale Highland 3030'N-7020'N
37005'E-43020'E
Awash
R Central
8030'N-12000'N
Highland
38005'E-43025'E
Tekeze
R North Wollo11040'N-15012'N
Highland
36030'E-39050'E
Denakil
D North Wollo 12o0'N- 1500' N
Highland
3900' E- 4200'E.
Ogaden
D No flow
5030'N - 9044' N
42041'E-45000' E
Omo-Ghibe
R Central,
4030'N - 9030'N
Western HL
3500'E - 3800'E
Baro-Akobo
R Western
5031'N-10054'N
Highland
3300'E-360 17' E
Rift
Valley L Arsi
and 4020'N-8030'N
Lakes
Central HL
36030'E-39030'E
Mereb
R Adigirat HL 14003'N-14052'N
37051'E-39027'E
Aysha
D No flow
10000'N-11000'N
42000'E-43000'E
Wabishebelle
R
Area
(km2)
202220
Direction
of Flow
East
Terminal
199912
West
(Nile)
East
Mediterranean
Sea
Indian Ocean
64380
Northeast
West
(Nile)
NF
Terminal Lakes
(Internal)
Mediterranean
Sea
Internal
77120
NF
Internal
79000
South
75912
West
(Nile)
South
Rudolph Lake
(Internal)
Mediterranean
Sea
Chew Bahir
West
(Nile)
NF
Swamp
Sudan
Internal
172259
110000
82350
52000
5900
2223
Indian Ocean
in
Source: Respective Basin Master Plan Studies
HL Highland
D-Dry
R-River L- Lake
NF-No flow
4.2. Topography and Altitudinal Gradient
Ethiopia is often fabled as the country of high mountains, flat plateaus frequently cut by deep gorges
and wide valleys in the highland and plains in the lowlands. The highlands with very rough terrain are
impenetrable making accessibility as well as other development efforts a complex endeavor.
The Geophysical setting of the country is generally characterized by highland in the center
circumscribed by the lowlands. High raising mountains with flat top and steep sides are common
features of the Ethiopian Highland. The lowlands are flat with frequent incision by ravines and gullies.
The transition from highland to lowlands is very abrupt with sharp falls and cataracts.
Except the Ogaden and Aysha Basins which are totally located in the lowlands, the other basins of
Ethiopia exhibit a large altitudinal gradient the highest being in the Denakil Basin. Table 4.2 below
lists some topographical features of the Ethiopian Basins.
Table 4.2 Important Topographical Characteristics of the Ethiopian Basins
R.No. Basin Name
1
Wabishebelle
2
Abbay
3
4
Genale
Dawa
Awash
5
Source
Locality
Mt Bale
Altitude
(masl)
4000
Sekela, West 2000
Gojam
Mt. Bale
4300
Highest point
Locality
Altitude
(masl)
Galama & 4000
Ahmar
Mt Choke
4100
Mt. Batu
4307
Ginchi
3000
-
-
Tekeze
Lalibela
3500
Ras Dejen
4620
6
Denakil
-
-
4170
7
Ogaden
-
-
8
Omo-Ghibe
Ambo
2800
Abuna
Yoseph
Divide-line
with Awash
Mt. Guge
9
Baro-Akobo
Illubabor
3000
-
3900
10
-
Arsi Mt.
4193
11
Rift Valley Lakes
Mereb
Zalanbessa
2500
-
3242
12
Aysha
-
-
1200
-
Source: Respective Basin Master Plan Studies
Mt- Mount
1900
4200
Lowest Point
Locality
Altitude
(masl)
Somali
200
Border
Sudan
500
Border
Somali
180
Border
Terminal
250
Lakes
Sudanese
550
Border
Kobar Sink 160mbsl
Somali
Border
Rudolph
Lake
Sudan
Border
Chew Bahir
400
Eritrean
Border
Djibouti
Border
900
350
395
300
400
Topography and altitudinal settings of a basin are the main functions of geological formations and can
clearly reflect the potential for and constraints to the development of the given basin.
4.3 Climate and Hydrology
Climate is the function of the location (latitudinal), altitude, angle of the sun, distance from oceans or
other water bodies, terrain and the like. The different combination of these factors resulted in the
prevalence of diverse climatic conditions in Ethiopia. The major climatic conditions in Ethiopia can be
categorized as tropical in the south and southwest, climatic in the highlands and arid and semi-arid in
the Northeastern and Southeastern lowlands. Climate has a direct implication on the development of
the basin with particular influence on the availability and use of water and pattern of settlement.
Hydrology of an area is a direct reflection of the climate, the terrain and other physical characteristics
such as porosity, permeability and vegetation cover. Water travels on the surface, underground and in
the atmosphere in a well-known cycle. Here emphasis is given to part of the water that run on the
surface in the form of streams and rivers or stored in the form of lakes.
The very high variability exhibited by the climatic components of the country over time and space is
the main reason behind the spatial and temporal variability in the availability of water. The shape, size
and other physical features of the River Basin does also contribute to the same. The nature of the river
channel, which is a direct function of the relationship between the flow and formation of the channel,
governs accessibility to and pattern of use of the waters flowing in the rivers or stored in natural
depressions. Table 4.3 indicates important climatic components and water resource potential of Basins
in Ethiopia in terms of mean annual run-off, storages in major lakes and impoundments and
underground.
Table 4.3 Important Climatic Features and Water Resource Potential of the Ethiopian Basins
R.No. Basin Name
Temperature
Rainfall(mm)
Evaporation
Water resource
(oc)
(mm)
potential(Bm3)
Min. Max. Max. Min. Average Average Surface Ground Stored
1 Wabishebelle 6
27
1563 223
425
1500
3.4
2.3
1.1
2
Abbay
11.4 25.5 2220 800
1420
1300
54.4
na
30
3
Genale Dawa <15 >25 1200 200
528
1450
6.0
na
4
Awash
20.8 29
1600 160
557
1800
4.9
0.8
2.2
5
Tekeze
<10 >22 1200 600
1300
1400
8.2
na
6
Denakil
5.7
57.3 1500 100
na
na
0.86
na
na
7
Ogaden
25
39
800
200
400
na
0
na
8
Omo-Ghibe 17
29
1900 400
1140
1600
16.6
1.0
na
9
Baro-Akobo <17 >28 3000 600
1419
1800
23.23
1
na
10 Rift Valley <10 >27 1800 300
na
1607
5.64
na
56.55
Lakes
11 Mereb
18
27
2000 680
na
1500
0.72
0.11
12 Aysha
26
40
500
120
na
na
0
na
Source: Respective Basin Master Plan Studies
.na: data not available
5. SOCIO-ECONOMIC FEATURES OF THE BASIN OF ETHIOPIA
The socio-economic features of most of the basins of Ethiopia can be characterized by a simple but
strategic terminology of Poverty and Isolation. Poverty expressed both in terms of absolute poverty or
through some socio-economic indicators is one of the lowest in the world. The different parts of the
basins are physically and psychologically isolated from each other and from other parts of the country.
The physical isolation is mainly due to the terrain which is very rugged and impenetrable making
accessibility and the development of infrastructure very challenging and the sever shortage of
communication infrastructures and systems. The psychological isolation is the reflection of physical
isolation in which case citizens have the perception of total isolation from the central government.
More than 90% of the inhabitants of the basin are rural and subsistent farmers. The ever increasing
population of the basin coupled with absence of alternative source of livelihood resulted in high level
of land fragmentation and total dependence on the natural resources of the basin. Land holding size per
household barely exceeds 0.5 ha. Most peasants are subsistent farmers with little product to put on the
market.
Except in some dry basins such as the Ogaden and Aysha, where the dominant mode of agriculture is
totally pastoralism, mixed farming in the highland and dominantly livestock production in the lowlands
is common feature. Urbanization is very low averaging 10% in most basins. Industrialization and the
service sector are not well developed. Settlement pattern is very variable. The general trend is that
settlement is very dense in the highlands and sparse in the lowland. Some important socio-economic
features of the basins are detailed in the table 5.1 below.
Table 5.1 Important Socio-economic features of the Ethiopian Basin
R.No. Basin Name
1
Wabishebelle
Population
'000 '000
1995 2010
5880 9489
Urbanizati
Other Social
Administration
on
Indicators
GR % Density
%
Productive Illiteracy Regions Woreda
p/km2
Force
%
3.9
29
7
49.7
80
O,SN, 76
H,S
2.6
72
7.9
na
74
O,A,BG 162
31.9
9.8
46.7
81.5
O,SN,S 43
2.9
100
10
na
na
O, SN, 80
A, Af, S,
DD, AA
3.7
57.3
10
51.7
84.4
T, A
54
3.9
na
na
na
na
A, Af, na
T
3.9
na
na
na
na
S
na
2.9
81.5
7.5-11.7 43.6
na
Or, SN 81
2.2
26.7
8.3
49.6
na
O,BG,S 72
N,Gm
3
153
7.3
na
79
Or, SN 60
2
3
4
Abbay
14231 22000
Genale Dawa 5100 5100
Awash
11000 14000
5
6
Tekeze
Denakil
4720
2068
7
8
9
Ogaden
Omo-Ghibe
Baro-Akobo
1464 na
6500 10000
2211 3077
10
Rift Valley 7964 12407
Lakes
Mereb
437.5 671.8 2.84
11
7550
na
74
5.54
51.4
82
T
11
12 Aysha
56.6 na
3.9
26
na
na
na
S
1
Source- respective Basin Master Plan Studies
A-Amhara, AA.Addis Ababa- Af-Afar,
BG-Benshangul Gumz, DD-Dire Dawa G- Gambella
H-Harari O-Oromia
S-Somalia, SN-Southern Nations and Nationalities and Peoples, T-Tigray
The most populous basin in Ethiopia is the Abbay Basin. The Abbay Basin is the most important Basin
in Ethiopia by most criteria as it contributes about 45% of the countries surface water resources, 25%
of the population, 20% of the landmass, 40 % of the nations agricultural product and most of the
hydropower and irrigation potential of the country. Population density is highest in Rift Valley Lakes
Basin indicating the immense pressure on the resource base. The basin with the lowest population size
and density is the Aysha Dry Basin mainly due to its remoteness, inaccessibility, harsh environmental
condition and low resource potential and shortage of socio-economic infrastructures and services.
Despite the huge productive force in the basins (Age group 15-64), the high rate of illiteracy could be
an obstacle to their development.
Administratively, most basins drain more than one Regional States. Awash Basin drains seven
Regional States and / or City Councils where as the Oromia Regional State is drained by seven
different basins. Three of the basins; Ogaden, Aysha and Mereb fall with in one Regional State,
Somali and Tigray respectively and the Gambella Regional State falls within one basin ie the BaroAkobo Basin. The discrepancy between the basin boundary which is considered as an appropriate unit
for planning and management of water resources and the administrative boundary, within which most
decisions of development are made, will be one of the challenges forthcoming with the progress of
basin based water resources management approach under implementation.
6. POTENTIAL OF THE BASINS FOR FUTURE WATER RESOURCE DEVELOPMENT
Table 6.1. Simple Parameters Indicating the Potential of the Basin
R.No. Basin Name
Water Resources
Irrigation
Specific
Per-Capital
Potential
Per capital ha.
yield
availability ' 000ha
(l/s/km2)
M3/person
1 Wabishebelle
0.53
578
209.3
0.04
2
Abbay
8.63
3823
1800
0.13
3
Genale Dawa
1.10
1176
1070
0.21
4
Awash
1.41
445
206
0.02
5
Tekeze
3.16
1737
186.9
0.04
6
Denakil
0.42
416
0.00
7
Ogaden
0.00
0
0.00
8
Omo-Ghibe
6.66
2554
90.4
0.01
9
Baro-Akobo
9.70
10507
631
0.29
10 Rift Valley
Lakes
3.44
708
131
0.02
11 Mereb
3.87
1646
5
0.01
12 Aysha
0.00
0
0
0.00
Source: Derived from Respective Basin Master Plan Studies
Hydropower
Firm Energy Per capital
GWH
KWH/person
7457
55000
9270
5589
8384
26026
19826
1268
3865
1818
508
1776
4004
8967
12240
-
1537
-
By virtue of its high potential and less inhabitants, the Baro-Akobo basin has the highest value in most
of these indicators. The efficiency of the basin to generate run-off is also the highest when compared to
other basins. On the other side of the picture come the Aysha, Denakil, Mereb and Ogaden Basins with
less prospect for future development of their water resources.
7. GENERAL FEATURES OF THE BASINS AND THE IMPLICATION ON THEIR
DEVELOPMENT








High rate of population growth and their total dependence on the basins' resources for their
survival and the age-old agricultural practices that is not conservation oriented has resulted in
serious watershed degradation which manifested itself in the form of severe erosion and
sedimentation. In addition to reducing the productivity of the system, this watershed
degradation and the resultant soil erosion has other consequences such as changing the
morphology of rivers leading to flooding and change of course, deterioration of water quality,
siltation of hydraulic infrastructures thereby reducing the lifespan and capacity of dams and the
efficiency of hydropower plants. Remedial measures for this problem can escalate the overall
cost required for the development of the basin.
Social and economic infrastructures and services are not well developed in rural parts of the
basins. This problem is more pronounced in the lowlands of the country. Added to this is the
harsh and inhospitable climate of these areas. Contrary to this, most of the land and water
resources of the basins are abundant and accessible in this part. More effort is needed to
promote development under such circumstances.
Major rivers of the country are characterized by big fluctuation in their flow. Optimum use of
these rivers requires large impoundments and efficient regulation. The large dams and
associated infrastructures that should be erected for this purpose are so costly as to reduce the
pace of development of the basins.
The terrain of the country is characterized by mountainous highlands circumscribed by flat
lowlands. The highlands are sources of major rivers. The transition from the highland to the
lowland is sharp and abrupt. The head difference resulting from this steep slope is an
opportunity for generation of tremendous hydropower.
The lowlands are flat and sparsely populated. Most of the rivers cascading from the highlands
merge before reaching or within the lowlands boosting the volume of the overall flow. The
potential of these lowland areas for irrigation is enormous. These irrigation potential areas can
also benefit from the regulated flow of hydropower schemes upstream.
Most of the major rivers of the country cut deep into the protective basalt layer creating
awesome and amazing gorges that can attract visitors to the basin.
Though the fluctuation of flow and the rugged terrain of the basins do not allow wide use of the
rivers for transportation, the few rivers and lakes that are currently serving for this purpose will
be reinforced and others also benefit from the regulation effect of planned storage dams.
Most of the rivers and lakes of the basins are rich in their fisheries potential. Future
development interventions in the basins can boost this potential if planned in a manner that can
consider their integration.
CONCLUSION
The different basins of the country have a diverse and varied resource base. A planned approach to the
utilization of these resources in a holistic and integrated manner can change the existing grim picture.
These plans should take the specific socio-economic, ecological and resource bases into consideration.
The interaction between the different components of the basin and the impact of one on another should
also be given due emphasis. In this respect, the proper implementation of the existing Integrated Basins
Development Master Plans can help reverse the prevalent watershed degradation on top of improving
the socio-economic status of basins.