Hydrology: Current Research

Investigation of Groundwater Recharge and Stable Isotopic Characteristics of an Alluvial Channel

Abstract

Modreck Gomo, Steyl G and van Tonder G

An investigation was conducted to assess the recharge of an alluvial channel aquifer that is located in Southern Africa. The investigation utilized stable isotopes, groundwater levels response to rainfall and infiltration tests as complimentary tools to identify and understand groundwater recharge processes of the alluvial channel aquifer. The alluvial channel aquifer is characterized by shallow water table conditions (<3 meters below ground level) and quick groundwater level response to rainfall events thereby justifying the application of the water level fluctuation (WLF) method to estimate recharges rates of the aquifer system. The recharging of the alluvial channel aquifers occurs through high preferential infiltration rates as enhanced by pathways created by tree rooting systems. Cavities and holes created by the burrowing animals also contribute to high infiltrations rates along the riparian zone. Saturated infiltrations rates in excess of 1 m/d were determined on the riparian zone of the alluvial channel aquifer. A groundwater recharge rate of 53 mm/year was determined for the alluvial channel aquifer. The groundwater Oxygen-18 (δ18O) and
deuterium (δ2H) compositions plot below the local meteoric water line (LMWL) indicating that the groundwater in the aquifer was exposed to evaporation prior or during the recharging process. The study shows that groundwater levels response to rainfall events can be used as a qualitative tool to distinguish between piston and preferential recharge mechanisms. In general, the study findings suggest that application of complementary tools to assess groundwater recharge can enhance understanding of the process.