A groundwater-planning toolkit for the main Karoo basin: Identifying and quantifying groundwater-development options incorporating the concept of wellfield yields and aquifer firm yields

Abstract

This paper provides an overview of groundwater-planning tools that were developed during a Water Research Commission project that was initiated due to the need to place the significant knowledge on groundwater of the Karoo Basin within the realms of water resource planning. In essence, the project aimed to identify favourable areas of groundwater potential for bulk municipal water supplies, to provide a method to quantify them, and to package the information so that it is assessable for planning purposes. In identifying favourable groundwater areas, the focus turned to developing a detailed transmissivity map of the Main Karoo Basin. In order to present yields in an accessible manner to water-supply planners, the same concept used in surface-water resource assessments and dam or reservoir design were adapted and applied to groundwater. Two methods were developed, namely the Aquifer Assured Yield Model and the Aquifer Firm Yield Model (the latter of which was developed into a software package together with the other products). The Aquifer Firm Yield Model provides the historical firm yield and uses historical monthly rainfall data together with recharge, evapotranspiration and baseflow to determine aquifer storage in any given month. The firm yield can be considered to define the upper limit of the groundwater resource. In order to establish possible wellfield yields, the C-J Wellfield Model (based on the Cooper-Jacob approximation of the Theis groundwater-flow equation) was developed whereby borehole spacing can be optimised after inputting estimated transmissivity values from the transmissivity map. To aid the planning process, groundwater-quality maps were produced together with the Wellfield Cost Model which provides an easy way to obtain first-order cost estimates of the wellfield options. This paper briefly describes these 'tools' that were produced and provides slightly more detail on how the transmissivity maps were developed

Towards defining a baseline status of scarce groundwater resources in anticipation of hydraulic fracturing in the Eastern Cape Karoo, South Africa: salinity, aquifer yields and groundwater levels

“…6a). Similar results have been reported for the Eastern Cape Karoo (Department of Water Affairs and Forestry 2010; Murray et al 2012;SRK Consulting 2012). However, this research has also identified increased areas where water exhibits a considerably lower quality (poor to unacceptable).…”

“…Similar groundwater depths have been observed for the Eastern Cape Karoo (Department of Water Affairs and Forestry 2010; Murray et al 2012;SRK Consulting 2012).…”

“…The potential overabstraction of groundwater is seen throughout the region, where isolated areas exhibit a groundwater level deeper than 30 mbgl. The possible overabstraction is highlighted by the increasing size of areas exhibiting a groundwater level below 20 mbgl when compared to previous observations (Department of Water Affairs and Forestry 2010; Murray et al 2012;SRK Consulting 2012). Aquifer yield has been interpolated from the calculated yield of individual boreholes (Fig.…”

“…Woodford & Chevallier 2002;Usher et al 2006;Murray et al 2012). However, these results are outdated when keeping in mind the goal of this baseline research, which is to determine the current state of groundwater conditions.…”

“…Woodford & Chevallier 2002; Usher et al 2006;Murray et al 2012), only limited studies have attempted to characterize these groundwater sources based on hydrochemistry.…”