In February 2022, Umvoto was commissioned by the Department of Water and Sanitation (DWS) Chief Directorate: Water Ecosystems Management (CD: WEM) to conduct a High Confidence Groundwater Reserve Determination Study for the Berg Catchment. The study aimed to address the impacts associated with the increasing number of Water Use Licence Applications (WULAs) and the potential influences of already implemented and proposed groundwater developments on water resource quantity and quality. This project concluded in March 2024, culminating in an integrated Groundwater Reserve Determination Report.
The study area
The Berg Catchment, located in the Western Cape Province of South Africa, spans approximately 13 891 km2 and includes secondary drainage regions G1 and G2. The catchment is characterised by its Mediterranean climate, with winter rainfall varying from approximately 300 mm along the coastal plains to around 3 000 mm in the high mountain ranges. The mean annual temperature ranges from 10-14°C in the mountainous areas to 16-20°C in the coastal lowlands. The Berg River, the largest hydrological feature in the catchment, contains 22 estuaries and several significant wetlands, including the Berg River Estuary (a Ramsar Site) and Langebaan Lagoon (a UNESCO Biosphere Reserve), both of which receive contributions from groundwater. Other significant wetlands include Edith Stevens Wetland Park, Zeekoevlei, Rondevlei (part of the False Bay Nature Reserve Ramsar Site), Zoarvlei, and Rietvlei.
Geologically, the Berg Catchment is predominantly underlain by Klipheuwel and Malmesbury Group rocks, intruded by the Cape Granite Suite (CGS). These formations have undergone significant erosion and uplift, leading to the deposition of sandstones that form the Table Mountain Group (TMG). The aquifers arising from these formations include the Peninsula and Nardouw Aquifers, contributing to deep fractured rock aquifers. Sediment deposition in the western and coastal portions forms major primary sedimentary/intergranular aquifers such as the Cape Flats Aquifer (CFA) and the West Coast Aquifers (Atlantis, Yzerfontein, Adamboerskraal, Elandsfontein, and Langebaan Road Aquifers).
Reserve determination procedure
The Groundwater Reserve Determination (GRD) process followed an eight-step procedure outlined in the Resource Directed Measures (RDM) manuals. This comprehensive approach included data collection and collation, delineation of Groundwater Resource Units (GRUs), assessment of ecological reference conditions, determination of Basic Human Needs (BHN) and Ecological Water Requirements (EWR), evaluation of operational scenarios, and the implementation of a monitoring programme.
The Reserve, the water “set aside” to provide for BHN and sustain water ecosystems, is the only right to water in the National Water Act (NWA; No. 36 of 1998). It has priority over all other water uses and must be met before water resources can be allocated to other users. The NWA clearly includes groundwater in the definition of a “water resource,” but the characteristics of groundwater sometimes require an integrated management approach.
The Groundwater Reserve
The groundwater Reserve for the Berg Catchment was determined to be 72.33 million cubic metres per annum (Mm3/a), comprising 2.35 Mm3/a for Basic Human Needs and 69.98 Mm3/a for Ecological Water Requirements. The Middle-Lower Berg, Wellington, Adamboerskraal, Elandsfontein, Langebaan Road, and Eendekuil Basin GRUs accounted for the majority of this Reserve volume.
The project is now complete, having successfully achieved its objectives of providing high-confidence insights into the groundwater resource systems within the Berg Catchment. The findings and recommendations from this study will facilitate well-informed management decisions concerning stressed or over-utilised groundwater resources, aligning with the gazetted water requirements and ensuring the protection and sustainable use of these vital resources.
For more detailed information, you can access the full report here.
