Emergency Response To Drought - The City Of Cape Town's Groundwater Abstraction And MAR Scheme (South Africa)

The Western Cape region in South Africa is currently experiencing its worst drought since 1904. As a result, the City of Cape Town (CoCT) implemented emergency response projects to augment water supply through desalination, re-use of treated effluent and groundwater abstraction from several groundwater systems. Amongst the targeted aquifers, the Cape Flats Aquifer (CFA) presents unique challenges and opportunities for abstraction and managed aquifer recharge (MAR). The CFA is a coastal unconfined primary aquifer within the urban and peri-urban environment. As such it is well situated to take advantage of enhanced recharge from treated effluent and urban stormwater. MAR is currently being tested and implemented with a three-fold purpose: (1) create hydraulic barriers against seawater intrusion and other contamination sources, (2) protect groundwater dependent wetlands and RAMSAR sites and (3) increase storage to enhance resilience to drought. Due to local hydrogeological characteristics and a high demand for open land, in the short term, high quality treated effluent will be injected directly through boreholes. Numerical modelling has supported siting and quantifying necessary injection rates. Current estimates indicate that available treated effluent will increase sustainable yields from the aquifer two-fold, as well as providing an additional storage volume equivalent to 2 to 3 years abstraction. In the future this is expected to be complemented with the re-design of urban water drainage to further enhance the recharge of stormwater. Given the time-constraints of an emergency response project, long-term testing and study of the system to support design and implementation have been significantly reduced and had to be replaced by a 'learn by doing' approach. We aim to present the on-going challenges of implementing MAR to complement an emergency response, as well as an overview of the scheme, new data and insights gained through the process.