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The Senegal River basin

The Senegal River basin, located in West Africa, covers 1.6% of the continent and spreads over four countries (Map 1 and Table 10).

TABLE 10: Senegal River basin: areas and rainfall by country

Rivers and discharges

The sources of the Senegal River are located in Guinea and in the wetter south-western part of Mali. Total annual discharge leaving Guinea is estimated at about 8 km³, but during the dry season the rivers frequently run dry. The Falémé River forms the border between Senegal and Mali over most of its distance. By the time they reach the border point between Mali, Mauritania and Senegal, the different tributaries have become one river, the Senegal River, which then continues to form the border between Senegal and Mauritania. The Karakoro River, flowing into the Senegal River at more or less the same point, originates in Mauritania. The annual discharge of the Senegal River at Bakel is 20 km . The Gorgol River, originating in Mauritania, joins it about 200 km downstream. Further downstream there are no other important tributaries.

Irrigation potential and water requirements

The irrigation potential in Guinea is rather limited by the topography. It has been estimated at 5000 ha [*]

The irrigation potential in Mali is also limited by the topography. Once the Manantali dam (on the Bafing tributary in Mali) is operational, it is estimated that about 10000 ha can be irrigated [182a].

The Senegal River valley in Mauritania is rather narrow, with the exception of two depressions in the downstream part. It is expected that with the Manantali dam about 125000 ha can be irrigated [182a]. In the present transitional period, with the dam not yet fully operational, an artificial flood is created through the dam in order to practice flood recession cropping on an area of 50000 ha at maximum. In the Gorgol and Karakoro tributary areas the irrigation potential is estimated at a maximum of 40000 ha, mainly through flood recession cropping with the construction of small earth dams [144]. This brings the total to 165000 ha. In addition there are some 2000 ha of oases in the Senegal basin area [145].

For Senegal, the prospects for irrigation development in the Falémé basin are very limited: a few hundred hectares. However, with the Manantali dam and the Diama dam (near the mouth of the Senegal River), it is expected that 240000 ha in the Senegal River valley will be irrigated [181]. During the transitional period the flood created through the Manantali dam allows flood recession cropping on 50000 ha, as is the case in Mauritania. The Diama dam, essentially designed to prevent intrusion of salt water, was completed in 1985.

Table 11: Senegal River basin: irrigation potential, water requirements and areas under irrigation

If double rice cropping is practiced in the Senegal River valley, the water requirements are estimated at 37000 m³/ha per year in this study. In the delta, gross water requirements of 18000 m/ha have been measured for rice in the rainy period and well over 20000 m/ha in the dry period [182]. Some literature even gives estimates up to 50000 m³/ha per year for double rice cropping [181].

In Guinea and Mali the annual river discharges largely exceed the water requirements for irrigation. However, if double rice cropping is to be considered on the whole potential area in the Senegal River valley and delta in Mauritania and Senegal, the total quantity of water in the basin might not be sufficient to meet the demand for irrigation. Therefore, the figure of 420000 ha for the basin should be considered as an upper limit.

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