Improving Groundwater Recharge Estimates And Groundwater Management For The Cuvelai-Etosha Basin

Abstract

Various studies have shown that the use of tracer techniques such as the chloride mass balance (CMB) and stable isotopes’ methods are suitable and good practical approaches to estimate groundwater recharge. Estimating groundwater recharge improves the understanding of groundwater availability in making informed strategies for groundwater resources management. Using secondary data, this study estimated groundwater recharge within the Cuvelai-Etosha Basin (CEB) via the CMB and stable isotopes’ methods along six flow paths. Chloride content in groundwater at the flow path’s endpoint was treated as an integral value of what has been happening from the starting point up to that endpoint. The stable isotopes’ method has used the hydro-calculator to compute fractional losses along transects which determined evaporation losses assuming the rest of water retained along flow paths forms part of groundwater recharge. From the CMB method, endpoint recharge rates range between 0.21% and 38.46% of mean annual precipitation. Based on stable isotopes’ method, about 50% of the initial recharge reaches the discharge zones in comparison to only 11% that of the CMB method. From the obtained results, there is much significance between the two methods with the stable isotopes’ method estimating much higher values whilst the CMB method seems to underestimate, however, the notion of using CMB method to calculate integral recharge instead of point recharge seems more usable. Groundwater recharge rates determined by both methods agree well with the range of values found in previous studies. Study outlined the protection of recharge zones such as the southern rim of the basin for great groundwater management strategies. The calculated recharge to aquifer systems has indicated that there is a need for sustainable groundwater use as demands may exceed the current potential in the near future.