Drainage systems refer to the flow direction and destination of the rivers.
The drainage patterns and systems of Ethiopia are the results of various structural events that took place in the Cenozoic era.
Ethiopia drainage systems classified into three :
Western (Mediterranean) sea drainage system
Southeastern (Indian Ocean) drainage system
The Inland (Rift Valley) drainage system

1. The Western (Mediterranean Sea) Drainage System

largest in terms of catchment area and volume of water.
It contributes 60% of the country’s total annual water discharge.
It is made up of major rivers and their tributaries namely:
1. River Tekezze
Drains the Massif of western Lasta, northern Gondar/ Semein and southwestern, western and central Tigray.
2. River Abbay
origin in the Gojjam plateau.
A large number of streams join the river from the plateaus of western Shewa, southwestern Wollo, northern Wollega, and northern Illubabor.
It has a semicircular course from Lake Tana, separating southeastern Gondar from Gojjam and separating Gojjam from Shewa.
3. River BaroAkobo
drains the wettest highlands of the southwest and crosses the border to join the Nile.
These rivers joining the Nile in the Sudan and finally end up in the Mediterranean Sea.

2.indian ocean Drainage System

Second largest drainage system.
It consists of the Genalle and Wabe Shebelle.
These rivers collect waters from the highlands of Hararghe, Sidamo, Bale and Arsi.
This drainage system flows southeast, across the Somali arid and semiarid areas.
It contributes about 32% of the country’s total annual water flow.
The Wabe Shebelle, the longest river in the country, does not reach the Indian Ocean.
It ends at the Benadir coast of Somalia.
The Genale, on the other hand, reaches the Indian Ocean.
It joins the Dawa River at the EthioSomalia border, where it acquires the name Juba.

3. The Inland (Rift Valley) Drainage System

The Rift Valley drainage system is the smallest in terms of catchment area, discharge, and volume of water.
It consists of three main rivers: Awash and OmoGibe, with the Awash River basin covering 110,000 km2.
The basin originates from the Shewan plateau near Ginchi town and flows along the Rift Valley.
It ends in Abbe, a salty lake on the Djibouti border.
The middle and lower courses are part of the Great Rift Valley system, while the lower Awash River basin includes deltaic alluvial plains and terminal lakes.