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The Shebelli - Juba basin

This basin occupies about one-third of Ethiopia, one-third of Kenya and one-third of Somalia and covers about 2.7 % of the continent (Map 6 and Table 33).

Table 33: Shebelli - Juba basin: areas and rainfall by country

Rivers and discharges

The Shebelli and Juba Rivers originate in Ethiopia and flow together just before the mouth in Somalia.

Over 90% of the discharge of the Shebelli River originates from runoff in the Ethiopian highlands and there are large inter-annual variations in discharge. The surface water resources in Ethiopia are estimated at 3.2 km³/year. Within Somalia the discharge decreases rapidly as it flows to its confluence with the Juba River, as a result of losses by seepage, evaporation and overbank spillage due to a low channel capacity [186]. Often the river ceases to flow in the lower reaches during the early part of the year.

The water resources of the Juba River in Ethiopia are estimated at 5.9 km³/year. The river crosses Somalia for a distance of 875 km and is one of the important rivers of east Africa. Within Somalia its discharge decreases significantly for the same reasons as the Shebelli River. This river can also cease to flow in the early part of the year. While the basin area of the Juba River at the border with Ethiopia is smaller than that of the Shebelli River, its discharge is almost three times as much due to geological conditions.

The part of the basin in Kenya collects drainage from the northern side of Mount Kenya and the Aberdares, and from smaller mountains or uplands in the north and north-east. Except for the Ewaso Ng'iro River itself, streams flow only in direct response to rainfall. The water reaches the border with Somalia only in very wet years.

Irrigation potential and water requirements

The irrigation potential in the Shebelli basin in Ethiopia has been estimated at 204000 ha [106]. Considering an irrigation water requirement in this region of 14000 m³/ha per year in the present study, this would lead to a total annual irrigation water requirement of over 2.8 km³, which is already more than the water resources available for agriculture, estimated at 2.5 km³/year [103]. The irrigation potential in the Juba basin has been estimated at 423300 ha [106], requiring nearly 6 km³/year of water, which is also more than the 4 km³/year estimated to be available for agriculture [103].

In Kenya sufficient water is available in the upper basin, but no significant storage sites can be located to control the natural flow. In the lower part some suitable sites are available. According to the national water master plan 9460 ha could be irrigated, based on 80% dependable flow [125].

In Somalia it is estimated that, if the flow could be regulated, 60000 ha could be irrigated in the Shebelli basin [188]. In the Juba basin, the planned, but up to now never constructed Baardhere dam was designed to irrigate up to 170000 ha, but the size of the dam already seems to have been reduced to irrigate 50000 ha, in view of the sharing of water with Ethiopia [103].

Table 34: Shebelli - Juba basin: irrigation potential, water requirements and areas under irrigation

In view of the total available water resources, it will not be possible to irrigate all the areas proposed by Ethiopia and Somalia. If 5 km³/year of water is available for agricultural purposes, the total irrigation potential has to be reduced by 60% to about 350000 ha.

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