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Sedimentation and irrigation schemes in the Niger river basin

Author(s): Bioeconomic simulations at the watershed level
Congress: 2008
Author(s): Adam Mamadou , Bruno Barbier, Michel Benoît-Cattin
Adam Mamadou , phD student university of Montpellier, Lycée Agricole, Route de Mendes, Montpellier, France zadam111@yahoo.com Bruno Barbier, Center for International Cooperation in Agricultural Research for Development (CIRAD), UMR Geau, 34 270 Montpellier, France, bbarbier@cirad.fr, 00 226 76 47 77 16 Michel Benoît-Cattin, Center for International Cooperation in Agricultural Research for Development (CIRAD), 34 270 Montpellier, France, michel.benoit-cattin@cirad.fr,

Keyword(s): erosion, sédimentation, simulation, irrigation, bassin versant, économie
AbstractSedimentation is becoming a major issue in the Niger river basin because erosion has increased tremendously along the river. Many irrigation schemes have been damaged by floods and sediment coming from lateral intermittent streams that are changing courses every rainy season. The massive removal of the vegetative cover is the main cause of erosion which is itself due to crop expansion, increasing grazing pressure and fuelwood recollection in a typical population pressure / resource scenario. Stakeholders are conscious of this situation and accept that there is a need to change the current management especially when their expensive and productive irrigation schemes located downstream are under risk. Subwatershed management options are various. One is to reduce the cropping area in the subwatershed. Under typical Sahelian climate yields are so low that rainfed cropping has become very hazardous. Grazing and fuelwood has a much milder effect on vegetation cover in this area. Many conservation practices have been tested in the area. Few have been adopted. Some success stories are recorder but little systematic analysis has been carried out. A recursive optimisation model of a representative subwatershed has been developed and validated to simulate the impact of various management options on the subwatershed and on its irrigation scheme located at its outskirt. Data has been collected to assess the farming systems and erosion was simulated using an erosion model. The results suggest that reducing rainfed cropping is the least expensive option to reduce risk downstream. The gain in increased irrigated cropping offsets the reduction of the rainfed area. The return of land conservation practices is relatively low because rainfed yields are not likely to increase sufficiently. When climatic risk is factored in the solution is not very different because rainfed cropping is not a sufficient risk coping strategy in the Sahel. We predict that farmers will progressively reduce rainfed production to focus on irrigation production and off farm activities.
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