How City can counter water shortage
Urban farming allotments should be created as rainfall catchment areas over Cape Flats
URBAN sprawl due to historical legacies and perpetuation of apartheid spatial planning has resulted in city bulk water and sewerage distribution being 20 000km. The ability to maintain this infrastructure and services in the city’s 2 461km² geographical area is difficult and costly, while increasingly hardened surfaces are fingered as a contributor to droughts and climate change.
Dr Kevin Winter’s (UCT: Geological and Environmental scientist) presentation to the Greater Cape Town Civic Alliance’s 2017 AGM revealed that a “more compact city will certainly lead to a more efficient city, with more water than we need being only one of the benefits”.
The 2017 Philippi Horticultural Area (PHA) Summit heard the Cape Flats receives twice the amount of water Cape Town needs, but the CFA is depleting, as it’s not being sufficiently recharged from rainwater infiltration, which can be traced to the sprawling Cape Flats where Mitchells Plain, Khayelitsha, Manenberg and surrounds formed part of an important rainwater catchment area. Managed Aquifer Recharge (MAR), using both slow infiltration and injection rails to force water from different areas at great speed to where you want it, is advised.
Recharging is important as abstraction from the aquifer could cause the hollowing of the subterranean area, leading to the ground level sinking or even sinkholes forming, while ocean propinquity could result in salt water ingress.
For MAR purposes, land use of the Cape Flats had to be analysed, which found 42% was residential, but growing; natural vegetation 20% and shrinking; agriculture 16% and shrinking; informal settlements 5%; and urban open space 3%.
It was found that Cape Town receives four times the water we need, but this flows into the sea via our bulk stormwater infrastructure designed to direct water away from our roads.
Managed stormwater can prevent groundwater flooding and flooding of informal settlements in low-lying areas by removing water at the right time. But if you could remove the water just after winter rainfalls to areas where you could hold the water (in 480 retention ponds), to be used during summer months or released for slow infiltration and injection, it would increase volumes from 2 million m³ to 10 million m³.
Winter states that we shouldn’t get rid of stormwater: it should form part of bulk water and be brought to the surface, with a traditional gutter – turned into a wetland, filtering stormwater through canals filled with stones and plants – running along the side of the road. Housing developments should be shifted into apartments overlooking parks and canals.
From the presentations, it is clear that we need fit-for-purpose water that does not have a risk to it, where “using expensive water coming out of our dams to flush our toilets makes no sense”.
Researcher Lizette Rabie said: “The groundwater recharge of this (CFA) aquifer varies between 15 and 37% due to annual precipitation. This will be reduced if precipitation is further prevented from reaching the aquifer, with the advent of extensive housing developments.”
If the City wants to counter water shortages, agriculture should be protected from unscrupulous mass housing developments, with urban farming allotments rather created as rainfall catchments all over the Cape Flats and outlying sub-economic areas, which will also reduce poverty and inequality.
While the PHA should be declared an agricultural conservancy to protect the CFA, recycling of water is also needed.
The development of Mitchells Plain, Khayelitsha and Philippi is considered poor and extremely unfortunate planning, as the greatest storage space for our water is beneath these areas.
Plans to perpetuate the apartheid city via inverse or inward densification, manifested in the sprawling Cape Flats (sprawling Khayelitsha, Mitchells Plain, and Delft etc) is irresponsible and unreasonable considering how Mitchells Plain has caused less recharge.
Winter revealed that, theoretically, Philippi and Mitchells Plain/Khayelitsha are most suitable to undertake abstraction from the CFA.
However, if not properly managed and monitored, large-scale flooding is possible, as drainage is insufficient, thus creating danger to property and possibly life.
Thus a disaster risk management plan is needed, which should include monitoring, reducing population density over time and an evacuation plan as a worst-case scenario. The volume yield a year from the CFA theoretically could be 10 million m³ in Philippi and 7.8 million m³ p.a. in Mitchells Plain, with the total sustainable yield a year about 18 million m³ (ie, 18 billion litres p.a.).
MAR lessens the risk of unsustainable and inequitable water use.
With current water demand at 320 million m³ and the city needing 100 million m³, “we will need an incredibly intense monitoring” of managed aquifer abstraction.
The City’s Inverse densification proposal that places a huge cement slab over an infiltration area, is extremely irresponsible. A better solution is, first, promotion of multi-storey, mixed income and use developments in the inner city (Cape Town CBD and 10km radius around the CBD) and inner suburbs that run along the M4 (main road that runs from central Cape Town through the southern suburbs); and second, urban farming zones on the Cape Flats and outlying areas.
Greening urban areas is very important, but due to Cape Town’s increasingly arid climate, you need “water- wise trees, which have flat or round crowns to give extra shade”. Trees and urban farming improve biodiversity, water and soil conservation, and provide control and regulation of spiking temperatures. While the drought decimates agriculture because of the CFA, urban farming on the Cape Flats is viable, where trees can reduce water evaporation by 30%, leaving soil moist for longer.
CapeNature botanist Rupert Koopman bemoans large lawns, but advocates indigenous urban farming and gardens that don’t require lots of watering.
Winter adds: “The problem is that our reaction to water now is to pave over everything. We have to avoid stances of no vegetation. We need to cool down our cities and trees and shrubbery play an incredible part in doing that. Let’s avoid the idea that we should give up on water and gardens, which are incredibly important in reducing temperatures. “The temperatures are rising from around the 1960s by 1% on average and we could have another increase of 1.5ºC by 2025.”
Cape Flats topography resulted in numerous permanent and seasonal wetlands.
Where urban development reduced or removed many of these wetlands, resulting in a drier climate, the creation of housing in the inner city, where stormwater from a more compact city can be injected into the CFA, will allow for a biodiverse and liveable Cape Flats, and sustainable water management.