Water stress is frequently experienced in many parts of South Africa. To ensure the longevity of the country’s water resources, particularly groundwater, accurate quantification of the resource and prediction of the responses of each water resource unit to natural and anthropogenic stresses are necessary. To this endeavour, Simbithi Eco-Estate, located at Shaka’s Rock, KwaZulu-Natal requires the implementation of a Water Management Plan that includes a hydrogeological investigation. A hydrogeological conceptual model was developed for the eco-estate, based on which a numerical groundwater flow model was calibrated to simulate the impacts of different rates of groundwater abstraction within the estate. Hydrometeorological information, subsurface geology, hydraulic head, hydraulic characteristics of the aquifer units and hydrochemical data were analysed to develop a two-layer hydrogeological conceptual model. The conceptual model was used as the main input to the numerical groundwater flow model. The calibrated steady-state numerical model, developed using the finite-difference groundwater modelling code, MODFLOW, was used to determine the sustainability of groundwater abstraction within the eco-estate. During calibration, the hydraulic conductivities of the hydrostratigraphic units, and recharge were varied. The Model calibrated recharge was 5.5 % of the mean annual precipitation (MAP). The five abstraction scenarios considered were: Scenario 1, which is the sustainable abstraction rate determined from the analysis of pumping test data, and Scenario 2 to 5 which are assigned progressively increasing abstraction rates of Scenario 1, by a factor of 20%, 50%, 100%, and 1000%, respectively. The numerical model simulations indicate that Scenario 1 is most sustainable in terms of groundwater level drawdown and saltwater intrusion. The simulated groundwater drawdown progressively increased throughout the succeeding four scenarios.
The simulation results of the 5th scenario indicate that part of the model domain within the vicinity of the northern boreholes becomes dry and subsequent application of forward particle tracking on the simulation results predicts saltwater intrusion from the Indian Ocean towards the south eastern boreholes. It is accordingly recommended that groundwater resource development should be limited to below the abstraction rates of Scenario 4. Additionally, continuous monitoring of all boreholes within the eco-estate is recommended to generate time-series groundwater level information, which would be used to improve the predictive capabilities of the current steady-state model through a transient numerical groundwater flow model. To that end, an immediate establishment of a groundwater level and specific electrical conductivity (EC) monitoring network, equipped with data loggers, is recommended.