Behavior Analysis of the Upper Cretaceous Aquifer Reservoir at the Athieme Outlet, in the Benin Portion of the Mono River Basin

In recent years, water levels in some of the most heavily tapped aquifers (Upper Cretaceous) in the Beninese Mono River basin have fallen to the point where some boreholes, which used to have a permanent regime, now have a temporary regime, raising questions among the population. This study attempts to answer these questions by analyzing the behavior of the Upper Cretaceous aquifer reservoir at the Athiémé outlet, in the Benin portion of the Mono River watershed. It was based on statistical tests. To this end, the Students’ t-test at 95% confidence for linear trend analysis was applied to static data collected from 5 piezometric stations around the Cretaceous aquifer recharge zone, covering the period from 2007 to 2020. Next, Pettitt break detection tests and the Bayesian method of LEE and HEGHINIAN were used to study the homogeneity of the various static levels of the aquifer’s wells and boreholes around its recharge zone on these data. The results showed that four (04) of the five (05) piezometric stations used are representative of the hydrodynamic functioning of the aquifer, with the exception of the Volly-Latadji piezometer in Aplahoué. These piezometric stations showed a significant downward trend in static levels until 2020, with a clear break in 2013. Compared with the 2007-2013 sub-period, water levels in the aquifer’s catchment structures (wells and boreholes) rose by 23% in the center of the aquifer, 10% in the northeast and south, and 11% in the southwest, between 2014 and 2020. This increase in the aquifer’s water resources, which today contrasts with the realities on the ground, raises concerns about the future of the area’s groundwater resources, and calls for in-depth reflection on the part of all concerned (decision-makers, craftsmen, scientists...).