Prepared by:- Tefera Gebeyehu Werku
Ethiopian Catholic University
Addis Ababa
2022
CHAPTER FOUR
DRAINAGE SYSTEMS AND
WATER RESOURCES OF
ETHIOPIA AND THE HORN
Drainage
pattern Vs.
Drainage
system
Drainage
 The flow of water through well-defined channels is known as drainage.
Drainage System
 The term system refers to the direction and destination of the rivers.
 the network of river channels is known as drainage system.
 Consists of the main river-tributaries-sub-tributaries (Origin to destination)
Drainage pattern
 The term pattern refers to the fabric/underlying structure/framework or
surface arrangement of the main rivers and their tributaries.
 River patterns, the spatial arrangements of channels.
 In the landscape, are determined by slope and structure.
 The drainage pattern of an area is the result of the geological time period, nature,
and structure of rocks, topography, slope, etc.
 There are different types of drainage patterns – dendritic, parallel, etc.
Dendritic drainage pattern
 Dendritic drainage systems (from Greek dendrites, "of or like a tree") are not
straight and are the most common form of the drainage system.
 In this, there are many sub-tributaries (analogous to the twigs of a tree), which
merge into tributaries of the main river (the branches and the trunk of the tree,
respectively).
 It
develops
in
regions
underlain
by
homogeneous
material. That is, the subsurface geology has a similar resistance to weathering
so there is no apparent control over the direction the tributaries take. Tributaries
joining larger streams at acute angle (less than 90 degrees).
Rectangular Drainage Pattern
The rectangular drainage pattern is found in regions that have
undergone faulting.
Streams follow the path of least resistance and thus are
concentrated in places were exposed rock is the weakest.
Movement of the surface due to faulting off-sets the direction of
the stream.
As a result the tributary streams make sharp bends and enter the
main stream at high angles.
Radial Drainage Pattern
 The radial drainage pattern develops around a central elevated
point.
 This pattern is common to such conically shaped features as
volcanoes.
Ethiopia’s Drainage systems & Water resources
Ethiopia has huge
potential water
resources. i.e.
“water tower of
Northeastern
Africa”
Characteristics of
Ethiopian Rivers
• run through steepsided river valleys
and gorges.
• rapids and
waterfalls
• seasonal fluctuation
• serve as boundaries
Some of the Ethiopian rivers
are given new names after
they cross the country’s
borders.
River Abbay
becomes -
River Baro becomes
River Ghenalle
becomes –
Baro-Pibor
Ghenalle-Dawa
Drainage Systems of Ethiopia
• The drainage systems of Ethiopia are
basically divided into three major groups:
• The Western (Mediterranean) drainage
system
• The Southeastern (Indian Ocean) drainage
system
• The Inland (Rift Valley) drainage system
1.The Western
(Mediterranean)
Drainage
System
The largest of all,
both in aerial
extent and volume
of water outflow
• River Tekezze
• River Abbay
• River Baro-Akobo
2.The Southeastern Drainage System
• It consists of the Ghenalle and Wabishebelle.
• collect waters from the highlands of Hararghe, Sidamo, Bale and
Arsi.
• Wabishebelle at Benadir coast & Genalle+Dawa= Juba
Ocean
Indian
3. The Inland (Rift Valley) Drainage System
The smallest of the three systems
Number smaller streams like:
Bilate and Gedabo, flows into Lake Abbaya;
Segan, flows into Chew Bahir;
Meki and the Katar, which flows into Lake Ziway.
The major rivers in this drainage system are the Awash and the
Omo- Ghibe.
 Awash – Lake Abe
Origin &
Destination
of some
rivers of
Ethiopia
• The Awash rises south of Mount Warqe, west of Addis
Ababa in the woreda of Dandi, close to the town of
Ginchi, West Shewa Zone, Oromia.
• River Abay orginated from Choke Mountain in Sekela
woreda, Western Gojjam. At this place, it is known by
Gil- gel Abay and sometimes Gish Abay, next 70 miles
flowing north-ward to Lake Tana.
• River Wabi Shabele - the Shebelle River’s name is
derived from the Somali term Webi Shabeelle, meaning
"Leopard River". Rising between the Arsi and Bale
mountains, it curves round the Bale massif and flows
south-east to Somalia.
• River Ghenalle - Rising in the mountains east of Aleta
Wendo, the Ganale flows south and east to join with the
Dawa at the border with Somalia to become the Jubba.
Major rivers of Ethiopia and their tributaries
Length in km
Rivers
Catchment
area (km2)
Major Tributaries
Inside
Outside
Total
Ramis,
Wabishebelle
205,407
1,340
660
Erer,
Dakata,
Fafen,
2,000 Yerer, Gobelle, Galleti, Mojo
Dabus, Didessa Fincha, Guder,
Muger, Jemma, Beshillo, Shinta,
Abbay
198,508
800
560
1,360 Dinder
Ghenalle
168,141
480
570
1,050 Dawa, Weyb, Welmel, Mena
Awash
113,709
1200
-
Tekeze
87,733
608
560
1,168
Tirari, Anghereb, Ghiba, Guang
Ghibe/Omo
77,205
760
-
760
Gojeb, Gelgel Ghibe
Baro
75,718
227
280
507
Akobo, Gilo
1,200 Akaki, Kessem, Borkena, Mille
Lakes of Ethiopia
• Compared to other countries, Ethiopia is rich in lakes.
• The natural lakes found in Ethiopia can be classified into highland
and Rift Valley lakes.
Highland Lakes
• Found dispersed on the plateaus, either as crater or watershed
lakes.
• explosive volcano breaks a mountain open… (Crater Lake)
• A sheet of lava dams up a shallow surface depression (Watershed
Lake)
Bishoftu, Kuruftu, Babbo Gaya, and Arsedi (Bishoftu)
 Wonchi, Dendi (Ambo), Hashenghe (Tigray), Tana (Amhara)
Rift Valley Lakes
• Unlike the highland lakes, the Rift Valley lakes are clustered.
• found in a linear pattern along the floor of the Rift Valley.
• Abaya, Chamo, Shalla, Abjata, Ziway, Langano..
• The largest…
• The Smallest..
• The deepest..
• The shallowest
Significance of Ethiopian Lakes and Rivers
 As source of hydroelectric power (H.E.P.)
 As source of Fish (Abaya, Chamo, Baro…)
 As a sources for irrigation (Awash)
 As a tourist attractions
 As source of transportation