Baseflow as a Proxy for Groundwater Recharge Variation Following Environmental Disturbances, Jonkershoek Valley, Western Cape, South Africa

Groundwater recharge is of strategic importance in groundwater research both globally and locally in South Africa as it ensures that the development of groundwater does not exceed the systems rate of renewal, protecting the integrity of these resources. The Table Mountain Group (TMG) system is considered to a potential source of future bulk water supply with a recharge potential ranging from 7 to 23% of Mean Annual Precipitation (MAP). However, estimation of true groundwater recharge is challenging as groundwater recharge is affected by many factors which influence the ability of water to reach the water table. Various studies have been carried out within the Jonkershoek Nature Reserve which investigated the response of a catchment’s hydrological functioning and biodiversity to land use management and disturbance regimes such as fires. Previous studies assessed the effect of fire on the hydrology of the catchment, highlighting the associated increase in streamflow components and hydrological response of catchments due to the development of soil water repellency which generated rapid runoff but do not discuss the possible effects on the recharge potential to the groundwater system. The present study investigated the possible effects of wildfire disturbances on local groundwater recharge system of the TMG aquifer system in Jonkershoek Valley, Western Cape Province of South Africa using baseflow as a proxy for groundwater recharge. The possible effects of wildfire disturbance on groundwater recharge processes were determined through review of literature, lithological logs and geological maps. Baseflow separation of hydrographs was conducted using the Recursive Digital Filter Method. It was found that the baseflow response to rainfall events following the March 2015 fire remained unchanged for the Tierkloof sub-catchment of Jonkershoek whereas Langrivier experienced a decline in baseflow response following the winter rainfall period later that 2015. The findings suggest that wildfire to some extent influences groundwater recharge but not all times thereby providing insight on the extent of influence of a vegetation cover on groundwater recharge and confirming findings from previous studies. The present study recommends long term studies on the influence of wildfire on groundwater recharge and the use of both direct and indirect methods for investigating groundwater response to fires.