Hydrological process and origins of the runoff in a granitic basement: the case of the Kolondieba watershed in the south of Mali

The Kolondieba Watershed covering an area of 3,050 km2 takes place in the southern granitic basement of Mali. It's used as part of the international program RIPIECSA (Interdisciplinary and Participatory Researches on Interactions between Ecosystems and Climate in Africa) to study the hydrological process occurring in order to determine the origin of the runoff at the outlet. The method used is based on rainfall, hydrometric, piezometric and geochemical monitoring over three hydrological cycles (2009 to 2012). The results show that the runoff starts at the outlet when groundwater rises to a high level and stops when it's lower. Water resource mineralization monitoring based on the electrical conductivity showed that the superficial Runoff is very close to precipitations with EC=18.54 plus or minus 9.56. The groundwater provided by the wells (shallow aquifers) and the drillings (deep aquifers) are more mineralized than precipitations. Their EC values are respectively: 126.10 plus or minus 95.60 in the wells and 134.40 plus or minus 84.91 in the drillings.