Background
Cape Town is the second-most populous city in South Africa and the largest city in the Western Cape province. Sitting at the feet of the iconic Table Mountain, this port town is the legislative capital of South Africa. Established in 1652 with the arrival of the Dutch settlers as a supply station for their ships, Cape Town is known as Africa’s ‘Mother City’.
Population Demographics: According to the 2011 Census, the population of the city is 3,740,026 which represents an annual growth rate of 2.6% compared to the previous census. The households in the municipality are 1,068,573. Of those households, 78.4% are formal structures (houses/flats), where s 20.5% are informal structures (shacks).
Climate: Cape Town has a warm Mediterranean climate, with mild, rainy winters and dry, warm summers. The region is characterized by mountain ranges, inland valleys, extensive coastline and coastal plains.
Political History: Like other African cities, Cape Town has a complex colonial history. Prior to the mid-twentieth century Cape Town was fraught with racial inequality and disputes since 17th century over its limited water supply. The National Party won the election in 1948 and apartheid (racial segregation) legislation was implemented forcing the hands of colored and black Capetonians to areas with inferior access to water and sanitation. In 1990, Nelson Mandela’s speech after his release from prison marked the beginning of a new era for the country. The first democratic elections were held in 1994. Since democracy, there have been ambitious goals to improve conditions for the disadvantaged however, municipalities have struggled to support adequately, especially the rapidly growing informal settlements.
Water Resources
The city sits on top of three aquifers, Atlantis aquifer, the Table Mountain aquifer (the largest aquifer running under Cape Town extending under the mountain ranges) and the Cape Flats aquifer (acts as a source of irrigation). The city has 14 dams, with a collective capacity of 900 000 MI approximately. Out of which major water capacity is provided by 6 large dams – Berg River dam, Steenbras Lower, Steenbras Upper, Theewaterskloof dam, Voelvlei dam and Wemmershoek dam. Cape Town’s surface water supplies are stored in six major reservoirs, recharged by precipitation, as well as a small portion from groundwater sources. The Western Cape Water Supply System (WCWSS) supplies water from these reservoirs via its distribution networks.
The Great Water Crisis
Physical Water Scarcity: The Cape Town water crisis was a period of severe water shortage in the Western Cape region. Decline in the dam water levels was evident since 2015, with dry, hot summer and extremely low winter rains followed by a moderately dry 2016 giving little chance to recover. The crisis hit its peak during mid-2017 to mid-2018. The water levels in the dams drifted between 15-30 % of the total dam capacities. During 2017, the term ‘Day Zero’ was first mentioned, a reference for the day when the water levels of the six major dams supplying the City fell below 13.5 %. ‘Day Zero’ was a culmination of three consecutive years of meager rainfall. April 22, 2018 was projected to be ‘Day Zero’ based on the dwindling water in the dams.
Institutional Mismanagement: The crisis was further exacerbated by Department of Water and Sanitation (DWS) failure to maintain Western Cape Water Supply System (WCWSS) adequately, letting alien vegetation spread and leaving pumps and canals out of operation which were used for augmented water harvesting. Across the continent of Africa, more water is being used for irrigation, increasing pressure on the limited water available. Agricultural practices follow age-old methods for crop production such as inefficient intensive irrigation, growing long-term crops for exports adding pressure to water supply system. The unprecedented dramatic changing climatic conditions (El Nino effect) lead to the peak mismanagement and pushed the underlying problems to the forefront.
Water Restrictions as a response to the Crisis
Cape Town supplied on an average 87 liters/person/day to approximately one million people in formal households (about one in every four persons in the city). In practice, many households used more water than allocated which was additionally billed. The rest of Cape Town previously used more water – about 220 liters/person/day on average. Informal settlements were supplied 50 liters/person/day which is less than the basic-need amount constituting only 5% of total usage.
During the drought, water allocation for all household was brought below 70 liters/person/day. The City of Cape Town introduced increasingly rigid restrictions during the crisis period, which expanded and developed as the water shortage became more acute. Water restrictions defined limits on how water could be used, in what quantities and for which purposes. At the most extreme level of restriction implemented, Level 6B, residents were restricted to a maximum of 50 liters (13.2 gallons) of water per person per day.
Overview of Water Problems
Low Hanging Fruit: Groundwater recharge and How?
Existing Groundwater Scenario
Following severe water restrictions in the city, people sought to other means of water supply which majorly constituted of privately tapping into groundwater. However, the levels of groundwater remains questionable due lack of data.
The city proposes to utilize 100mld of groundwater from the Cape Flats Aquifer and Table Mountain Group to augment the water supply. There is an increased concern of reduced water quality from these aquifers as well in places with lower yields. Although the solution can be an effective response to the ongoing water crisis, it is imperative to implement recharge measures for sustainable yield.
Getting into the Solution
In lieu of recharging groundwater, the city can benefit from directing treated wastewater into the aquifers. And hence we look into the plight of waste water treatment plants in Cape Town.
Lost Opportunities – Targeting Wastewater Management
In case you missed the video, KfW Development Bank on behalf of the German Federal Government is providing the City with a loan of EUR 80 Million and additional EUR 2 billion as part of the Clean Ocean Initiative alongside two other partners. Currently, the City of Cape town plans on utilizing major chunk of these funds in increasing the present capacity of the wastewater treatment plants.
On investigating the dilapidated state of the waste-water treatment works, it is appalling that they are mostly running at overcapacity, due to limited investment in expansion. The technologies used to remove wastes are also below ecological standards. Due to high elevation of the abstracted raw water, most treated water is not returned to hydrological systems on land or reused, representing a large waste of fresh-water resource and pollution of marine systems.
Our suggestion is to use this funding more strategically to gain optimum profit. Using part of the funding for wastewater treatment through GSI (green infrastructure) and channel the treated water into aquifers using injection wells or infiltration systems.
Constructed Wetland Systems for Groundwater Replenishment – proven to be an effective alternative to conventional methods of wastewater treatment.
Constructed Wetlands System (CWS) is an artificial wetland designed and built similar to natural wetlands to treat wastewater. CWS uses natural processes involving vegetation, aquatic plants, and organisms, to treat storm/wastewater. The treatment process removes organic and inorganic pollutants to improve water quality. They tend to be located adjacent to natural water bodies to remove and minimize pollutants entering the receiving waters.
There are various types of CW systems such as Horizontal Surface flow constructed Wetland, Vertical Flow Constructed Wetlands, Horizontal Subsurface flow constructed Wetlands and Hybrid system. We propose a Hybrid system, a combination of HF and SF constructed wetlands used to ensure maximum BOD removal efficiencies. Aerobic and anaerobic conditions can both be achieved that can help with nitrification-denitrification, thereby helping with efficient Nitrogen removal efficiencies as well. Since it is a multi-step process, there is a significant reduction in sludge production. As the system is tolerance to low pH it, prevents the corrosion of pipes and concrete reservoirs.
Cost Benefits
Plausible Locations of CWS
Conclusion
In general, among the myriad water problems of Cape Town, our solution offers to contribute to some crucial infrastructure needs (Constructed Wetland System) necessary for the city to diversify their water resources through sustainable and cost effective means. Managing Aquifers and improving wastewater treatment is a high impact low effort solution to alleviate stress on water resources. Both these strategies are addressed through constructed wetlands in addition to their environmental benefits.
References
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“Cape Town’s Water Crisis: How Did It Happen? | Article | EESI.” n.d. Accessed March 31, 2020. https://www.eesi.org/articles/view/cape-towns-water-crisis-how-did-it-happen.
“Capetown Rainfall – Climate Trends.” n.d. Accessed March 30, 2020. https://briangunterblog.wordpress.com/2018/02/14/capetown-rainfall/.
“Dam Level – Capacity | Datasets | Cape Town | South Africa (Countries) | Metabolism of Cities.” n.d. Accessed March 30, 2020. https://metabolismofcities.org/cities/cape-town/datasets/104/.
“Effluent Use Exceeds City of Cape Town’s Expectations | Fin24.” n.d. Accessed March 31, 2020. https://www.fin24.com/Economy/Effluent-use-exceeds-City-of-Cape-Towns-expectations-20151101.
Enqvist, Johan P., and Gina Ziervogel. 2019. “Water Governance and Justice in Cape Town: An Overview.” Wiley Interdisciplinary Reviews: Water, May, e1354. https://doi.org/10.1002/wat2.1354.
“Managed Aquifer Recharge and Mine Water Management.” 2017. AusIMM Bulletin. October 10, 2017. https://www.ausimmbulletin.com/feature/managed-aquifer-recharge-mine-water-management/.
Parks, Robbie, Megan Mclaren, Professor Ralf Toumi, and Professor Ulrike Rivett. n.d. “Experiences and Lessons in Managing Water from Cape Town,” 18.
“Wastewater Treatment Plants | Cape Town | South Africa (Countries) | Metabolism of Cities.” n.d. Accessed March 30, 2020. https://metabolismofcities.org/cities/cape-town/infrastructure/wastewater-treatment-plants/.
Ziervogel, Gina. n.d. “UNPACKING THE CAPE TOWN DROUGHT:LESSONS LEARNED,” 29.