Impacts of Irrigation Water on the Hydrodynamics and Saline Behavior of the Shallow Alluvial Aquifer in the Senegal River Delta

The Senegal River Delta located in north-western Senegal is a strategic region for the development of irrigated rice cultivation for achieving rice self-sufficiency. The presence of a shallow salty water table is often considered as a brake to the development of irrigation, by causing salinization of the soil, although the mechanisms of operation are not well known. An experimental study was carried out in a rice paddy located in the village of Ndiaye, 35 km north from Saint Louis, to characterize the water and solute flux processes below the irrigated plots. The objective was to better understand the irrigation-driven dynamics of soil salinization processes. An experimental monitoring network was installed for monitoring the transit of water at the plot level, in the unsaturated zone and in the aquifer. The results show that the supply of water by irrigation contributes to significantly recharging the water table, as shown by the rise in piezometric level, with a concomitant dilution of the water salinity in the soil zone and in the shallow groundwater. However, when irrigation is stopped, the groundwater level and salinity return within a month to their initial level and salinity status because of the evaporative recovery, which strongly governs these processes. Thus, water flow and solute transfers operate in the delta following a recharge-discharge and dilution-concentration cycle controlled by the water balance, and we do not expect to observe in the short- to middle-term any significant reduction in soil salinization processes by drainage.

Automated summary

An experimental study in the Senegal River Delta showed that irrigation significantly recharges the water table and dilutes soil and shallow groundwater salinity, but when irrigation is stopped, water level and salinity return to their initial levels within a month due to evaporative recovery.