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.