Cape Town is a rapidly urbanizing coastal city of over 4 million people in the Western Cape region of the Republic of South Africa. The city receives about 98.5 percent of its water supply from surface water resources. Most of the rainfall in the Western Cape falls during the winter months (May to September), thus the runoff generated during this period needs to be stored to meet the water demands of the city for the whole year, in particular during peak demand during the hot dry summer. A network of major and minor dams that form the Western Cape Water Supply System are used to store winter runoff.

A Cape Flats Aquifer project was initiated in 1966 by the Cape Provincial Administration, triggered by foreseen water shortages for the Cape Town metropolitan area and environs. The Cape Flats Aquifer is made up of fluvial, marine, and aeolian sedimentary deposits, is predominantly unconfined and reaches thicknesses up to 55 m as shown on Figure 48. From 1973 to 1979, the Water Research Commission financed the project and extended its scope to accommodate various multi-disciplinary aspects (e.g., the feasibility of storing water from the Eerste River in the sand deposits adjacent to the False Bay coast and, in particular, the role the aquifer could play in terms of reclamation, infiltration, storage and abstraction of purified sewage effluents). For this, either infiltration basins or injection wells would be feasible. By 1980, a numerical model of the aquifer had been developed which could be used to delimit the potential of the Cape Flats and investigate scenarios of groundwater development. Concern was expressed that areas most suitable for recharge and abstraction were increasingly being used for high-density housing projects (Tredoux et al., 1980).

Figure 48 – The Cape Metropolitan Area with major catchments and settlements over Cape Flats sands (Adelana et al., 2014).

The Working Group for the above project proposed that groundwater development should begin in 1981. However, the City Council of Cape Town, the local authority responsible for the metropolitan water supply, decided not to develop the Cape Flats Aquifer. The City Council was known to prefer high quality surface water from the mountain catchments of the Western Cape above their own, poorer quality, groundwater resources. A further scheme, a major dam in the Berg River, was finally approved by the South African Cabinet in 2002, following considerable opposition from the environment sector and interested and affected parties, who all prioritized water demand and supply reconciliation options.

In 1996, the national Department of Water Affairs and Forestry, by way of its Western Cape Systems Analysis, provided a new target to have the Cape Flats scheme operational by 2005. It found that the Cape Flats Aquifer remained a viable resource because on the order of 15 to 20 Mm³ could be abstracted annually at a very favorable unit cost of US$ 0.03/m³ (Wright and Conrad, 1995). Again, there was no response from the City of Cape Town. By 2005, further studies found that the Cape Flats groundwater resource had deteriorated over the past decades and was now non-potable in certain areas, with varying degrees of contamination. The deterioration was due to a combination of pesticides and fertilizers from agricultural practices, wastewater treatment plants, numerous waste disposal sites, informal settlements, unlined or leaking canals and leaking sewer pipes. Removal of sand dunes and encroachment of urban development, in particular informal settlements, into low-lying wetland areas had resulted in flooding every winter, now enhanced by the urban recharge and elevated groundwater levels. Also, periodic phytoplankton blooms along the False Bay coastline had been worsening, impacting the marine and beach ecosystems (Adelana and Xu, 2006; Hay, et al., 2015; Mauck, 2017).

A follow-on study commissioned by the Department of Water Affairs to develop an urban aquifer management approach for the City of Cape Town recommended a set of multiple solutions that could run simultaneously. In the short term, non-potable groundwater should be supplied to small scale users for irrigation such as schools, sports fields, parks and community gardens. While this would provide some benefit from the aquifer, the immediate solution was to systematically reduce and limit contamination to the aquifer. Bioremediation was seen as a potential method to remediate the aquifer by using natural or man-made wetlands and vleis (marshes) for this purpose. Large-scale bulk supply in the medium term could be accomplished by combining artificial recharge and abstraction. An additional benefit of artificial recharge and abstraction would be the remediation of the aquifer. By recharging the aquifer with good quality water, it would be circulated, ultimately diluting and cleaning the contaminated groundwater in the aquifer (Hay et al., 2015).

Practical steps from the City of Cape Town only resulted after Cape Town experienced an especially severe drought from 2017 to 2018 (the worst in over 100 years) after several years of low rainfall. To manage the drought, the city prioritized reducing demand for water and then rationed the remaining water stored in the supply system. It introduced increasingly strict water restrictions as the water shortage became progressively more acute. At the same time, water supply augmentation contingencies were assessed – a combination of groundwater abstraction, water reuse and desalination. Particular mention was made of the need to recharge the Cape Flats Aquifer with treated wastewater and stormwater. The city’s recent Water Strategy aims to take a more holistic approach to water management and sets out five commitments, namely (City of Cape Town, 2019):

1. safe access to water and sanitation;
2. wise use;
3. sufficient, reliable water from diverse sources;
4. shared benefits from regional water resources; and,
5. a water sensitive city.

Under Strategy item 3, the city is committed to increasing the available supply by approximately 300 million liters/day over the next ten years from groundwater, water reuse and desalinated water, all aimed to cost-effectively and timeously increase resilience and substantially reduce the likelihood of severe water restrictions in future (City of Cape Town, 2019). This will require diversification of water sources and a much better understanding of the system, including environmental, physical, social, financial, economic and political aspects, and a new approach to managing the system beyond focusing on infrastructure (Parks et al., 2019; Ziervogel, 2019).

MAR and Increasing Urbanization

In terms of Strategy item 5, the City of Cape Town (2019) stated that:

“it will actively facilitate the transformation of Cape Town over time into a water sensitive city that makes optimal use of stormwater and urban waterways for the purposes of flood control, aquifer recharge, water reuse and recreation, and is based on sound ecological principles. This will be done through new incentives and regulatory mechanisms as well as through the way the city invests in new infrastructure.”

With intensification of land-use and increasing urbanization, the knowledge and institutional requirements for MAR have again increased significantly. It is timely that the Water Research Commission in South Africa, champion for groundwater resources and for artificial recharge for so many years, has taken up the challenge with a very relevant new project – Urban Groundwater Development and Management – allowing groundwater processes to be better understood in this environment and to fully feature in ‘Water Sensitive Urban Design’ (Seyler et al., 2019).

In terms of implementation, the city is currently in possession of licenses in terms of the National Water Act of 1998 for both the abstraction of groundwater and the practice of MAR. A monitoring protocol for a MAR system is currently being reviewed. During 2018, 159 boreholes were drilled into the Cape Flats Aquifer with a total yield of 41 million liters/day. Infrastructure for the treatment of water from the MAR scheme is already being constructed in the form of two reverse osmosis plants, as well as pipelines to the injection sites. The city has also explored implementation of MAR within the predominantly fractured rock setting of the Table Mountain Group Aquifer (Lasher-Scheepers, 2020).

While the Water Research Commission had actively pursued MAR knowledge and technology development for the Cape Flats Aquifer more than 40 years ago, it is the broader issue of sustainable groundwater resource development that still has not been fully addressed by the national government in South Africa. Had there been systematic development of regulations in terms of its National Water Act of 1998 to manage the unique aspects of groundwater resources, then important and vulnerable aquifer systems such as the Cape Flats would have been identified at an early stage. At that time, proactive measures could have been taken for their protection and development and adequate institutions could have been created for their local development and management.