Characterisation of the Rietvlei wetland: Implications for spatial distribution of groundwater recharge

Abstract

Abstract The current study aimed to determine the factors affecting groundwater recharge and its spatial distribution in the Rietvlei wetland located near Cape Town. To achieve this, the subsurface material was logged during the construction of eight shallow wells, complimented with field observations, and surveying the dug wells. The water stemming from these wells was sampled and analysed for Oxygen 18 and Deuterium to determine the source of groundwater in Rietvlei wetland. Downhole salinity logs of the wells were also undertaken, and rainfall samples were analysed for the stable isotopes. Isotopic results indicate that groundwater stems from rainfall, with the exception of Well 8 which has been influenced by the river due to its proximity to the surface water body. Additionally, results obtained indicate a distinct relationship between elevation and soil structure. Shallow profiles were mainly dominated by medium to fine sands, silty sand, and clay. Using the water table fluctuation method, this was found to have a direct impact on the spatial distribution of groundwater recharge on an event basis. It was therefore concluded that both lithology and topography have a direct effect on recharge rates and water quality.