Estimation of Groundwater Recharge Response from Rainfall Events in a Semi-Arid Fractured Aquifer: Case Study of Quaternary Catchment A91h, Limpopo Province, South Africa

This study was focused on estimating groundwater recharge response from rainfall events in a semi-arid fractured aquifer. Determination of response of the groundwater recharge from rainfall is important as it directly affects the available groundwater in an aquifer. Groundwater level data was used to evaluate the response of groundwater recharge from rainfall events using Extended model for Aquifer Recharge and soil moisture Transport through unsaturated Hard rock (EARTH) model. Chloride Mass Balance (CMB) method was also used to estimate groundwater recharge in quaternary catchment A91H. Chloride concentration from groundwater and precipitation in the catchment were collected and analysed. Calculated local recharge using CMB method was interpolated in ARCGIS to generate groundwater recharge distribution maps of the quaternary catchment. The estimated local recharge rates using CMB method ranged from 0.24-8.75 mm/a (0.04-1.3% MAP) using rainfall chloride concentrations of 0.1 mg/L. Regional recharge of 30.1 mm/a (4.6% MAP) were calculated using groundwater chloride concentration of 0.1 mg/L. The estimated recharge rates from EARTH model ranged from 3 to 10.3% of mean annual precipitation(MAP). The average estimated recharge rate was calculated as 6.12% of the MAP which is equivalent to 40.1 mm/a. Both EARTH model and CMB method yielded comparable results and were found to be similar to those obtained from other studies. High recharge was estimated in high elevation area while low recharge was estimated in low elevation area. The results obtained from this study have confirmed and expanded existing knowledge on the nature of groundwater recharge response from rainfall in fractured aquifers in semi-arid areas and the applicability of EARTH model and CMB method in recharge estimation in the same environment.