Mapping surface features with remote sensing to prdict the 10-year runoff in small basins in the Sahel and dry tropical zones ; Cartographie des états de surface par télédétection et prédétermination des crues des petits bassins versants en zone sahélienne et tropicale sèche

[Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiques ; In 1992, Jean Rodier published : "The rainfall simulator and representative basins in the Sahel". This paper presents the main relationships between the runoff potential, calculated for heavy daily rainfalls (50 and 70 mm) for small sahelian basins (1-20 km²), and the surface runoff depths observed at the outlets. The runoff potential is the weighted sum of the elementary surface runoff depths calculated from the relations given in the catalogue of basic surfaces in the sahelian zone (Cazenave & Valentin, 1989); First we develop in detail the use of remote sensing to map the surface states (soil, vegetation, land use and the superficial structure of the soils). This makes it possible to employ Rodier's relationships for small bains on the same satellite picture coupled with ground observations for a single reference basin. then we present how we define the loss functions on the map units and the basins. Finally we apply this methodology to determine the 10-year runoff from small basins in the dry areas of west Africa. With runoff potential as input, the Rodier's tables allow the determination of indices of permeability (PI, I, RI, P, TP) and/or the fitting of coefficients according to the area and permeability of the basin.The indices of permeability are significant input parameter for the Orstom method (Rodier & Auvray, 1965 used in predicting the 10-year outflows(FAO, in press). The adjustment coefficients include the transfer of runoff from upstream to the outlet in order to compute the surface runoff depths. We have tested this method on several small basins in sahelian and dry tropical zones. ; L'utilisation de la télédétection pour la cartographie des états de surface (sols, végétation, cultures et organisation superficielle du sol), permet d'envisager l'emploi, sur les petits bassins versants non jaugés, des relations proposées par Jean Rodier en 1992 dans l'ouvrage intitulé : "Du ...