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How plan for Cape Flats Aquifer to store stormwater will work - research study

24 November 2021 12:02 PM
Tags:
Cape Flats Aquifer
Dr Kevin Winter
Cape Town water supply

Dr Kevin Winter from the Future Water Institute at the University of Cape Town speaks to Zain Johnson.
  • The underground 'sand dam' stretches over 400km
  • It's depth varies from 40 metres deep in some parts to 15 metres deep in others
  • All open spaces in the city act as recharge zones allowing natural rainwater to flow underground int the sand aquifer below

Contractors extract groundwater from the Cape Flats aquifer. Picture: Cindy Archillies/EWN

Capetonians will remember the dark days of Day Zero where we were on the brink of running out of water. Well, a new scientific study suggests that the solution is not in the skies but underground.

The massive Cape Flats Aquifer could be used as an underground storage facility for treated sewage water and stormwater that normally runs off into the sea.

UCT's Environmental & Geographical science Depts' Kevin Winter is the co-author of the study and chats to Zain Johnson about the findings.

How big are Cape Town's aquifers?

They stretch over an area of about 400 square km - but the depth varies quite a bit and in parts is as much as 40 metres deep and in other parts 15 metres.

Dr Kevin Winter, Future Water Institute - UCT

In essence, it is a very large underground sand dam.

Dr Kevin Winter, Future Water Institute - UCT

He likens an aquifer to digging in the sand on a beach and finding water underneath the sand.

It is called 'recharge' which refers to the replenishing of groundwater through natural elements such as rainfall.

It is water that is literally running underground. Water falls from the sky and finds its way into the sand or soil and it gets down to the bottom of a layer which is usually as in our case a shelf of shale rock that runs through most of the bottom of this aquifer.

Dr Kevin Winter, Future Water Institute - UCT

It is like filling up a bucket that has sand in it and the water falls below the level of the sand.

Dr Kevin Winter, Future Water Institute - UCT

But the water flows very slowly through this large sand aquifer, almost like a filter system, he explains. The water can then be removed at various places but it would also find its way into the sea as well.

This is not a new project by any means. This is something the City has been examining for many years and if you look at some of the papers it goes back almost 40 years.

Dr Kevin Winter, Future Water Institute - UCT

He recounts a good example of one aquifer that has been 'recharged' or replenished 'unnaturally by treated stormwater and wastewater in the Atlantis area that has been going on for a long time.

Now what the City is trying to do is explore how to recharge it [the Cape Flats Aquifer] artificially - in other words to allow water to be injected from a treated wastewater plant and that could include stormwater at some stage too.

Dr Kevin Winter, Future Water Institute - UCT

But at a natural scale, any open spaces such as Table Mountain are also recharge zones as water flows off the mountains and goes underground, and travels through the aquifer. This can happen very slowly.

The more and more open ground we have in our city, the more those act as recharge zones where water can filter from the surface into the sand aquifer below.

Dr Kevin Winter, Future Water Institute - UCT



24 November 2021 12:02 PM
Tags:
Cape Flats Aquifer
Dr Kevin Winter
Cape Town water supply

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