Suspended sediment load and mechanical erosion in the Senegal Basin. Estimation of the surface runoff concentration and relative contributions of channel and slope erosion

The main purpose of this paper is to propose a method to better understand the suspended sediment dynamics in the Senegal Basin, and the behaviour of the river particulate load at Bakel gauging station (218,000 km2) during the period 1979–1984. The method is based on the estimation of surface discharge using a simple hydrological model which allows separation of the different flow components of the annual hydrograph. Then the suspended sediment loads can be correlated with the surface discharge. During the study period, the mean annual flow (330 m3s−1) represented only 46% of the mean long-term flow (1903–1984), and the mean yearly particulate load carried by the Senegal River was about 1.9 million tons. Two approaches are used to estimate the different contributions to the river's suspended sediment transport. The main contribution originates from slope erosion, which supplies 50–80% of the total sediment transport and the second originates from channel erosion. The suspended sediment concentration in the surface runoff, primarily calculated by a global annual method, ranges from 0.9 to 1.6 gl−1 and averages 1.3 gl−1. After correction for channel erosion input, this concentration is reduced to 1.1 gl−1