Identification and prioritisation of type areas for detailed research in terms of the regional variability of the groundwater and ecological characteristics of the Table Mountain group aquifer systems
Report No 1332/1/04
The TMG Aquifer System is a regional fractured aquifer system with the potential to be a major source for future water supply in the Western and Eastern Cape. In 1999, the Coordinating Committee for Geohydrological Research, an advisory body for the Water Research Commission (WRC), recommended that attention be given to investigating the TMG Aquifer System for water supply purposes. A workshop was subsequently held in Cape Town in 1999 with key role players. It was agreed that the preparation of a synthesis of current hydrogeological knowledge and understanding of the TMG Aquifer was a prerequisite to forming a logical and coherent research programme for this aquifer systems.
A workshop was also held in Gordon's Bay on 3 April 2001 to discuss issues arising and to agree on ranking of research fields. In January 2002, WRC Report TT158/01 was published entitled, "A Synthesis of the Hydrogeology of the Table Mountain Group - Formation of a Research Strategy." One of the key areas identified requiring research was the "Ecological and environmental impact of large-scale groundwater development in the Table Mountain Group (TMG) Aquifer Systems".
Prior to embarking on such detailed research, it is important to determine key 'type' areas. This is required because of the variability in key aquifer and ecological parameters over the TMG outcrop and sub-outcrop area.
The research project therefore aims to identify suitable 'type areas' for detailed research into the impacts of large-scale groundwater abstraction from TMG Aquifer Systems on the ecology and the regional hydrogeological characteristics, taking into account regional and variations within the TMG Aquifer Systems.
The TMG Aquifer system occurs within the Western and Eastern Cape provinces, extending from just north of Nieuwoudtville to Cape Agulhas and then eastwards to Algoa Bay, a linear outcrop distance of over 900km. Recharge estimates to these aquifer systems vary from 10 to 50 % of mean annual precipitation (MAP). Research work carried out to date indicates that there may be billions of cubic metres of groundwater stored in the Table Mountain Group (TMG) Aquifer Systems.
The winter rainfall area of the Intermontane Domain of the TMG Aquifer offers a unique opportunity to maximise/optimise groundwater yield from this aquifer (Rosewarne, 2001). This area is characterised by reliable precipitation often in excess of 1000 mm/a, which is mainly concentrated during the period June to September. However, to unlock the true potential of the TMG Aquifer, quantitative studies need to be initiated, especially in terms of the New Water Act, to ensure that the nature and extent of potentially negative environmental impacts are quantified. A focal challenge in this respect is that the natural harmony of water and vegetation in the Cape mountain ecosystem is preserved.
Extensive use has been made of the advances in GIS technology and spatial modelling techniques, as well as the availability of a large number of GIS datasets (recharge, vegetation, aquifer systems, groundwater abstraction, rainfall, digital terrain models, nature reserves, ecologically sensitive zones etc.). This has made it possible to cost effectively develop a regional perspective of the variability of key parameters and therefore to optimise the selection of type areas required to address this variability. The GIS database developed for this study will also provide valuable information for input into more detailed research projects.