Hydrogeological Assessments of Impacts of Irrigation on Alluvial Water Table of Delta of Senegal River

摘要

Building dams on the Senegal River has facilitated the development of irrigated farming in Delta of Senegal River. However, this practice is threatened by the increasing degradation of soils mainly caused by salinization. The main cause of this problem is the presence of a salty aquifer at a low depth. Nevertheless, the characteristics and functioning of this aquifer are not well known. The main objective of this study, funded by Wallonie-Brussels International, is a contribution to the characterization of the hydrodynamic functioning, the hydro geochemistry of the aquifer and to identify the impact on agricultural waters. A two-step methodology has been developed: Firstly, a regional survey has been performed in the whole delta; secondly an irrigation plot has been monitored to have a detailed description of the groundwater dynamic and of the transport of salt under irrigation. Results of the regional survey show (1) the main factors that explain the fluctuation of the groundwater level are the artificial high water levels in the River, rice growing and to a lesser extent precipitation and (2) the high salt concentration in the upper aquifer. The monitoring of the Ndelle rice growing area (30 km to the North-East of Saint-Louis) has allowed calculating water and salt budgets at the scale of the irrigation plot. The influence of the irrigation on the groundwater levels has also been studied.