Spatio-temporal variations of hydrochemical and isotopic patterns of groundwater in hand-dug wells: the Cuvelai-Etosha Basin, Namibia

The rural population in parts of the Cuvelai-Etosha Basin (CEB) in Namibia depends on groundwater as a source for drinking and livestock watering. The aim of this study is to investigate spatial-temporal patterns for understanding water origins and recharge processes of perched aquifers in the CEB. The study uses hydrochemical data and water stable isotope signatures (18O and 2H) of samples collected during (10) ten field campaigns over a three-year period (from 2014 to 2016) originating from two regions within the basin (Ohangwena and Omusati). A clear distinction between the shallow groundwater in the Omusati and Ohangwena regions documented by TDS values, hydrochemical water types as well as the isotopic compositions of water. These differences are influenced mainly by their location in the landscape, depth to water table, the type of well infrastructure and aquifer material. Spatial and temporal variations indicate that even though these perched aquifers are both within the same basin, they are chemically different because of the rock materials in which their flow. Therefore, these differences in the water hydrochemical composition as well as the processes governing perched aquifers must be taken into account when planning groundwater management in the basin.