Les études analytiques de l'infiltration, du mouvement de l'eau dans le sol et de l'alimentation de la nappe phréatique sur quelques bassins représentatifs de l'O.R.S.T.O.M.

Directeur de Recherches à l'O.R.S.T.O.M

Résumé

For nearly twenty years O.R.S.T.O.M. hydrologists have been investigating runoff in 80-odd groups of representative basins in intertropical and arid regions. Due to difficulties experienced in establishing a rainfall/runoff transformation model they are now concentrating their efforts on the analysis of the remaining terms of a storm shower water balance, i.e. infiltration, storage and movement of the water in an unsaturated ground zone, and aquifer recharge. This new line of research started in about 1996 and is now developing. The accuracy and quality of gravimetric and neutron probe measurements are discussed. What is most important is that the likely measurement error can be established by variance analysis. Reference is also made to systematic standardised measurements of the hydrodynamic characteristics of ferruginous tropical soils in 25 groups of basins, the purpose of which was to obtain a basis of comparison between basins with a view to analogue processing of the information. Detailed studies are in progress on elementary basins of 3.6 sq.kms. and 5 sq.kms., the former on granitic sandstone in the North Ivory Coast region (Korhogo) and the latter on shale and granite in the Malagasy uplands (Tafaina). The first concrete results obtained are presented, concerning variations in the water profile under the effect of storm rainfall causing a flood, estimated true dry season evapotranspiration, the process whereby an initially dry soil becomes saturated and then dries out again.