Managing releases from small upland reservoirs for downstream recharge in semi-arid basins (Northeast of Tunisia)

This paper describes the methodology used to estimate the efficiency of a small upland reservoir that is aimed at artificial groundwater recharge. A conceptual rainfall-runoff model was used to estimate the surface runoff of the ungauged catchment associated with the reservoir. Then, the water balance of the reservoir was computed. The model was calibrated and tested by comparing the simulated water volume of the reservoir to the observed one. The simulated reservoir water balance indicated high losses by evaporation. Another conceptual model was used to estimate the recharge rate during artificial recharge operations. These operations consisted of releasing water from the reservoir to the natural downstream bed of the wadi channel. The model was calibrated by comparing the simulated streamflow and the simulated water table level to the observed ones. The water balance of the artificial recharge operations indicated a high recharge rate. Simulations of artificial recharge were carried out to analyze the effect of the small upland reservoir on the water table. The simulation of an additional water release of 51% of the volume actually released over a decade indicated an additional rise of the water table of about 7.5 m.