Atlantis Managed aquifer recharge_

Pushed aside, Atlantis once took the lead for water wise cities

In fiction, Atlantis is a city that fell out of favour with the deities and sank to the bottom of the ocean. In South Africa, the town of Atlantis had similarly volatile dealings with the powers that be. But, it will go down in history books as a place that rose above one of its biggest challenges.

Placed far away from water, Atlantis has become an example of a water wise city long before its time.

Atlantis was established as a ‘growth point’ according to the apartheid-based development plans of the then-government. Located 50 km north of Cape Town along the west coast, it was to be a coloured-only town with incentives to attract industries.

Judging by sight alone, the area displays an almost complete lack of water. Yet, in part due to its unpractical location, it has become an award-winning example of a water resilient city long before many others caught onto the concept.

At Atlantis, stormwater and treated effluent, traditionally seen as waste-water, were used as major resources of water to create a water secure settlement. Only around 25 years after it was founded was more water piped into the town from further away.

Water out of sight, but not out of bounds

The development of Atlantis started in 1976, planned to grow to up to 500 000 residents. Government also provided incentives to industries to move there. Water was initially supplied from a local spring (the Silwerstroom) and boreholes, but it was always understood that these sources would not be enough over the long term.

The challenge was that Atlantis was located far away from most other possible sources. The closest was the Berg River 70 km away, where the Misverstand Dam was commissioned to accommodate water demand from Atlantis. This was, however, far too far in the future to ease the already-existing concerns of water supply.

Thinking out of the box, and under the ground

Town planners and engineers had to make another plan. For a solution, they turned their eyes underground. Atlantis is located in a semi-arid type climate. Most of the 450 mm rain that falls there, does so between April and September. Up to 30% of this water drains into the aquifers. This is where the town has drawn its water from since its establishment.

The town actually rests on the Atlantis aquifer, a groundwater system that covers an area of about 130 km² inland from the Atlantic Ocean to the town itself. The groundwater enters the aquifers through the sandy surface, in particular, at the bare sand dunes, and then flows towards the coast down a relatively steep gradient.

The aquifer originally drew the attention of town planners because of changing laws. In South Africa, it used to be common to get rid of waste water by pouring it in the sea, but by the 1970s the public really started complaining about this.

At the same time, government started seeing the practice as a waste of valuable water. This eventually led to a change in laws. Suddenly, municipalities needed to make alternative plans with their dirty water.

From finding new water, to re-using used water

At Atlantis, the recharging of stormwater and treated wastewater into the aquifers through the sandy soils started in 1979. Unusual at the time, it was also to here that town planners and engineers turned their attention when they had to make new plans to ensure a secure water supply for the town. They decided to shift their focus to recharging and recycling water in order to increase the yield of the aquifer enough to meet the long-term water needs of the town.

New choices, big changes

This decision resulted in major developments. First, stormwater was used to top up the aquifer and eventually, domestic and industrial waste water were separated to allow for only the best quality water in the areas of greatest importance.

The Atlantis Water Resource Management Scheme

As a result, the Atlantis Water Resource Management Scheme (AWRMS) could make use of treated domestic effluent (wastewater), all of the domestic stormwater, and most of the industrial stormwater for recharging the aquifer. Throughout, the undertaking was also that no water of a lesser quality should be put back into the aquifer. As a result, the town was supplied totally from groundwater for over two decades, while enhancing the local environment in the process.

The Atlantis Water Recharge Management Scheme (AWRMS)

In a nutshell, the AWRMS is a great example of managed aquifer recharge, or MAR, in practice. MAR is an indirect water recycling method through the transfer of surface water underground. The water is then stored in an aquifer either via infiltration from basins, dams or ponds or through injection boreholes.

In this way water can be stored during wet periods or when there is more than enough, to be abstracted during dry periods. In the process, water and the environment is conserved. As a result, dams aren’t necessary and because the water is stored underground, the minimum is lost to evaporation. In addition the water is relatively safe from pollution and the porous medium (in this instance, sand) through which it infiltrates acts as a filter to improve water quality.

Why Atlantis, and not everywhere else?

Part of the relative ease with which the practice has been applied at Atlantis is due to town planning. The layout of the town allows for the separation of stormwater from the industrial and residential areas as well as separate treatment of domestic and industrial wastewater. Stormwater and industrial wastewater are channeled into separated systems to each undergo sufficient treatment.

Domestic wastewater undergoes full treatment and is sent towards a series of maturation ponds. Stormwater from the residential areas is collected in a system of detention and retention basins and blended with the treated domestic wastewater. This is then sent into the main recharge basins for artificial recharge of the Witzand wellfield.

The stormwater from the industrial area is more saline, and is discharged into different recharge basins along the coast. From here it seeps into the ocean through the subsurface. This also helps prevent that seawater flows back into the aquifer.

Water for the town’s people and industries is then abstracted from the Witzand and Silwerstroom wellfields. The first contains a blend of natural and recharged water, and the second contains natural groundwater. It is estimated that the groundwater abstracted as part of the AWRMS represents a blend of 30% water derived from recycling and 70% natural groundwater.

The performance of the water recycling system at Atlantis has proven to be relatively good. Based on what we know, the recycling of the water does not threaten the drinking water supply.

A complex system that needs expert management

The AWRMS is a complex, large-scale system that depends on specialised management. Long-term sustainability of the system depends on proper maintenance of all components, requiring a multidisciplinary approach. The challenges are many.

The challenges to run the system

New pollutants and varying quality of groundwater throughout the system are some of these challenges. The erratic quality of urban run-off and wastewater add to this. As fine sediments and organic material settle on the bottom of recharge basins over time, it gets clogged.

If too much water is extracted from the aquifer the water levels drop, allowing air into the system. This disrupts the balance of the natural ecology at the borehole site and can lead to fouling of the water.

Uncontrolled abstraction by illegal users, and invasive alien plants affects predictions of how much water exactly can be taken out. The natural characteristics of the aquifer material, such as calcrete and calcareous sands affect the groundwater quality. As a result the water tastes a little hard.

Furthermore, the Atlantis aquifer is unconfined and thus vulnerable to pollution from several other sources.

Looking beyond Atlantis

The planned water supply to Atlantis from the Berg River system was never realised. Since 2000 the town’s water supply has been linked to the Cape Town distribution system. Some water also come from a reservoir at Melkbosstrand.

The town also never reached the potential that was originally envisioned. It was later joined with the metropolitan area of Cape Town. A 2011 census reported a population of just over 67 000 residents.

Still, the town stands as a good demonstration of stormwater harvesting and treated sewage effluent reuse at scale. Ultimately, the Atlantis Water Resource Management Scheme has proven to be an innovative scheme to supply bulk water for drinking and industry. It has proven that these types of recharge schemes can work.

It set an example that others now follow

A pioneering innovation at the time, it resulted in new thinking about stormwater and wastewater in the Cape and beyond. For one, the concept of ‘natural groundwater recharge’ was included in the City of Cape Town draft stormwater by-laws.

Furthermore, lessons from Atlantis contributed to the development of the then Departments of Water Affairs and Forestry’s National Artificial Recharge Strategy in 2007.

The city of Atlantis has a checkered past. Yet, it has shown that bulk reuse of stormwater and wastewater is possible, and sustainable.

As such, the legacy of Atlantis has not become one of the failures of the past. Rather it’s an example of how to meet the future.

Notes

  • This blog was included in the book, Water Resilient Cities, I wrote for the Water Research Commission. Atlantis really is a fascinating example. It shows us what we can do if we practice sustainable stormwater management. Its one of the key concepts of a water resilient city which, again, is a key concept for cities that will face dryer futures.
  • The lead photo is of one of the AWRMS’s coastal infiltration basins
  • The lead photo and graphic is from the publication, The Atlantis Water Resource Management Scheme: 30 years of Artificial Groundwater Recharge, published by the Department of Water Affairs in August 2010.

Sources

  • The Atlantis Water Resource Management Scheme: 30 years of Artificial Groundwater Recharge, published by the Department of Water Affairs in August 2010.
  • Water Management in Atlantis, by N Armitage, PB King and ATP Bishop

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