Quantifying Focused Groundwater Recharge Induced by Irrigation Surface Water Reservoirs in Crystalline Basement Areas for Complementary Irrigation

Through the practice of irrigation, surface water reservoirs (SWRs) contribute to the socio-economic development and food production activities of populations in Sub-Saharan Africa (SSA). However, they tend to dry up prematurely. One solution to circumvent these irrigation water shortages is to ensure their conjunctive use with groundwater. The objective of this study is to better understand the contribution of SWRs to groundwater recharge and to determine if groundwater may be considered as a complementary local resource for irrigation. The study was carried out on two watersheds in Burkina Faso, Kierma and Mogtedo. The spatiotemporal analysis of piezometric and SWRs level records coupled with physico-chemical analyses of water was used to characterize exchanges between SWRs and groundwater. The regional groundwater recharge at the scale of the watersheds was assessed. At the SWRs scale, a water balance methodology was developed and used to estimate focused recharge. The results show that SWRs interact almost continuously with groundwater and contribute focused recharge. The magnitude of this recharge is a function of the geological context and the sediment texture of the SWRs. It is estimated at 5 mm/day in Kierma and 4 mm/day in Mogtedo. These values are higher than the natural recharge estimated at 0.2 mm/day in Kierma and 0.1 mm/day in Mogtedo. Additionally, the values of hydraulic conductivity are between 0.01 and 2 m/day in Kierma and between 1 x 10(-4) and 0.2 m/day in Mogtedo. These conductivities could allow pumping in large-diameter hand-dug wells with a significant yield between 0.5 and 120 m(3)/day in Kierma and between 0 and 10 m(3)/day in Mogtedo to palliate the early drying up of the SWRs.