Modelling exchanges between surface water reservoirs and groundwater in basement areas: Case of Kierma (Burkina Faso)

Small-scale surface water reservoirs are essential for water storage in arid and semi-arid areas worldwide and particularly in sub-Saharan Africa (Cecchi et al., 2020; Saruchera and Lautze, 2019). These infrastructures provide water for a wide range of activities, in particular irrigation (Forkuor et al., 2019). Besides their essential functions, surface water reservoirs can induce local groundwater recharge (Bambara et al., 2020; Mushtaha et al., 2019). In a context of increasing and pressing water needs of populations and the implementation of a sustainable and integrated water resources management policy, a more complete understanding of the hydrological processes in the watersheds with surface water reservoirs is essential (Ala-aho et al., 2015). It is mainly important to characterize the interactions between surface and groundwater (Boubacar et al., 2020) which remain very complex in general and particularly difficult in semi-arid watersheds where few accurate data are available. The objective of this study is to characterize and assess the interactions between surface water reservoirs and groundwater for water supply to the population. The study was carried out in the Kierma basin in Burkina Faso, which contains surface water reservoirs for irrigation. The physically-based hydrological model, HydroGeoSphere, integrating surface and subsurface flow processes was used for the study. A fully integrated hydrologic model of the Kierma watershed hydrologic was built and calibrated with a three-stage temporal resolution approach. This ranges from steady-state average conditions to dynamic equilibrium with repeating monthly normal forcing data and, fully transient conditions. Simulations results show that the model reproduces seasonal surface water flows and the dynamic of the groundwater levels fairly well. The model allowed to qualitatively and quantitatively evaluate the interactions between surface water and groundwater. The water reservoirs constitute privileged zones of focused recharge estimated on average at 504 mm/year. Direct groundwater recharge also occurs during the rainy season and is estimated on average at 144 mm/year. Groundwater in the Kierma watershed can therefore be exploited for water supply to the population and complementary irrigation