Water Resources Planning for the Senegal River Basin

Abstract

ABSTRACT The Senegal River Basin (SRB), located in the Sahel region of West Africa, is simultaneously undergoing fundamental environmental, hydrologic, and socioeconomic transitions. The trination (Senegal, Mauritania, and Mali) river basin development authority, the Organisation pour la Mise en Valeur du Fleuve Senegal (OMVS), is attempting to execute a shift to irrigated riceproduction for domestic consumption in the river basin in order to ease the severe foreign exchange shortfalls these riparian nations face. With the recent completion of the Manantali and Diama dams, year-round irrigated agriculture is now possible in the SRB. The full agricultural developmentpotential of the SRB is constrained, however, by the basin's limited water resources. Significantly, a time series analysis of Senegal River hydrology has provided powerful evidence that the prolonged Sahelian drought may be permanent. The negative impact of the state-imposed rice production policy compounds the severe effects of the drought on the river basin ecology. Rice production in the arid river valley has been a financial and social failure. Irrigated rice projects suffer a high rate of abandonment and have intensified the desertification process in the river valley. As an alternate use of the basin's scarce water resources, an agricultural development policy based on village-scale irrigation projects and intensive, irrigated agroforestry projects has been proposed. Village-scale irrigation is dedicated to low-water-consumption cereal grain crops and is managed by traditional sociopolitical structures. The agroforestry production system analyzed has the dual objectives of using irrigation to reestablish a protective biomass cover in the desertifying river valley and of reversing the drought-induced migration from rural to urban areas. A comparative river system simulation study was conducted to analyze the effects of both the rice production development policy (policy RP) and the natural resources management policy (policy NRM) on the SRB's full agricultural development potential. The simulation study compared three alternate hydrologic scenarios using, (I) the predrought era, (2) the 1970's level drought and (3) the 1980's level drought. Principles of dynamic programming were applied to Manantali reservoir management to optimize water allocation in each scenario. All the hydrologic scenarios generated showed that the lower overall water demand pattern exerted by policy NRM allows a higher full agricultural development potential than does policy RP.