Abstract
Within the international AMMA project (African Monsoon Multidisciplinary Analysis), the Upper Oueme catchment has been selected as the southermost site of the AMMA-Catch Observatory in Environment. Raingauge, limnigraph and piezometric networks have been gradually set-up since 1997 over the catchment (10 000 km2) and particularly on the Donga sub-catchment (586 km2).<br />The purposes of this work are (i) to identify the prominent hydrological processes on the Donga catchment by comparison of precipitation, streamflow, water table and potential evapotranspiration data and (ii) to determine and quantify the streamflow components by geochemical field surveys. A coherent hydrological scheme has been deduced from hydrodynamic and hydrogeochemical information. The seasonal character of surface water, the lag between the river drying up and the low groundwater level, the low streamflow mineralization lead to consider a poor connection between the deep groundwater and the hydrological network.<br />Based on this result, a two components (effective runoff and subsurface flow) hydrograph separation has been implemented for two hydrological-contrasted years (2003 and 2004). In each case, a major contribution of superficial groundwater to streamflow has been found.