Utilisation of the analytical element method in a groundwater reserve determination

Abstract

The most important factors of South African water resources are the quantity and quality thereof. Therefore, as prescribed in the Water Services Act (108 of 1997) the Reserve needs to be protected, used, developed, conserved, managed and controlled through various guidance principles. To achieve these goals, the principles of sustainability, equity and efficiency should be used according to the National Water Act (NWA) (36 of 1998). Regional datasets are mostly available on quaternary catchment scale, as this is the boundary that the Department of Water and Sanitation (DWS) uses for reporting purposes. This has led to the quaternary catchments being used as the basis for GRDM calculations, even though the surface water boundaries and groundwater aquifers are rarely the same. On a regional scale assessment, some of the problem areas are lost to the process of averaging and therefore local scale or well field scale analysis is important. Recent studies in the Vaal and Crocodile catchments has brought the issue of scale to light where Resource Quality Objectives (RQOs) for groundwater systems were set on well field scale for effective protection of the water resource. This dissertation sets out to improve the current groundwater Reserve methodology by addressing identified limitations of the current water balance approach through the implementation of an Analytic Element Method (AEM) model. Rather than a predefined mesh, which allows for a highly scalable solution, the AEM model domain is described by various analytical elements. The AEM supports elements that represent different recharge zones and aquifer parameters to model an inhomogeneous aquifer system. This study demonstrates that Visual AEM can be applied to study regional groundwater flow and provide solutions for the existing scale issues by adopting model calibration parameters to obtain a satisfactory representation of the groundwater system. Thus, the overall conclusion is that the model is proficient in representing catchment scale processes that South Africa generally experience.