The promise and peril of stormwater management in Cape Town

Cape Town is a place like no other. That’s why millions of local and international visitors stream to the city’s famous shores each year. A large part of the attraction is the natural environment that it’s built on – not only the famous Table Mountain, the endless beaches and the icy sea, but also a vast array of rivers and wetlands.

In Cape Town, life happens in close collaboration with nature, and the city is intimately dependent on the services it supplies (also known as ecological services).

“Cape Town is very unique,” says Richard Nell, Head of Strategy Specialist Support for the City of Cape Town’s Catchment, Stormwater and River Management Division. He explains that Cape Town actually sits on 21 catchments, which are the mainstay of its stormwater system.

A city with a natural stormwater system

Though the city mostly depends on rainfall for its water supply, this is imported via a supply system of six dams outside the municipal boundaries. The rain that falls on the city itself mostly drain as stormwater into the mentioned rivers to the sea.

The system that keeps the city safe from flooding is actually a combination of built stormwater infrastructure and natural systems. The backbone of the stormwater system is about 1 920 km of rivers and 7 800 man-made and natural wetlands. Built infrastructure includes 5 100 km of pipes, 500 km of channels and canals, 10 stormwater dams, 892 detention ponds, 35 pump stations and 64 rainfall and flow monitoring stations.

The challenges of stormwater management

The challenges that the city faces regarding stormwater management, are similar to the problems experienced by cities across the globe. Richard lists some of these to include old infrastructure, failure of small pump stations and “development that gets ahead of itself”.

Urban growth is outpacing the capacity of the stormwater infrastructure, he says. In Cape Town, challenges like these are made worse during the winter rainfall season, when water from stormwater system can overflow into the sewage treatment works and overload the infrastructure.

Pollution is another problem. Litter, garden waste, dog poop and industrial pollution are but some of the endless list of things that contribute to contamination.

Richard says that they also often encounter some forms of sabotage. People put things like mattresses and lawnmowers down the system which causes blockages and overflows, he says. “Throughout the city there are huge pollution problems.”

Though the bulk of the city’s stormwater management to date has focused on managing runoff quantity and quality, the municipality was one of the earliest in South Africa to embrace the principles of Sustainable Drainage Systems, or SuDS, towards becoming a water sensitive city.

Cape Town embraces sustainable stormwater management systems

They started around 2005, says Richard, and this work resulted in the promulgation of two policies in 2009. Both took their lead from the water sensitive cities concept in Australia.

The Management of Urban Stormwater Impacts Policy aims to “minimise the undesirable impacts of stormwater runoff from developed areas by introducing Water Sensitive Urban Design principles and SuDS to urban planning and stormwater management in the Cape Town metropolitan area.”

The second, The Floodplain and River Corridor Management policy recognises the importance of watercourses and wetlands to the stormwater management system, the city’s biodiversity network, and recreational and economic opportunities.

The objectives of this policy are to reduce the impact of flooding on communities and the economy, keep us healthy, protect the natural aquatic environments, and improve and maintain water quality for recreational purposes.

Richard says that the concept of SuDS was initially a tough sell, and the uptake slow, especially from technical experts. “Roads engineers traditionally look at stormwater as the enemy, and that’s a difficult mindset to change.”

Still, since then the municipality has forged ahead. The concept has progressively been incorporated into development plans.

Big plans start with small steps

For one, the management of catchments and stormwater was moved from the previous Roads and Stormwater Department, to fall under the jurisdiction of Water and Sanitation.

“In the past we use to issue directives against the sewage department, but now we collaborate with them,” says Richard.

While the city’s stormwater bylaw and the two policies are under review, a green infrastructure plan is in process to help sustainable management of valuable natural infrastructure (this is stuff like wetlands and rivers). A comprehensive water resilience strategy is also being written. This will identify challenges and opportunities for the city.

Though the municipality has been working away at more sustainable stormwater management for years, the topic was thrust in the spotlight during the recent water crisis. At that time, stormwater was punted as an untapped water resource going to “waste” seeing as very small amounts of stormwater is currently put to use. In fact, Richard puts a rough estimate at less than 10%!

However, he points out that changing this is not as simple as it may seem.

Tapping into the potential of stormwater in Cape Town

The biggest problem of stormwater harvesting in a winter rainfall region is that you’re receiving the water when you don’t need it, he says. The water thus needs to be stored somewhere until necessary, usually in a dam or reservoir, large infrastructure for which very limited space is left in Cape Town.

Storing the water is not the only challenge. First, it has to be captured. Some of the municipal rivers are short, with small catchments, leading to quick runoff during rain.

Should you try to capture the water upstream, time to do so is even more limited, while attempts to capture the water close to the outfall leaves the upstream system vulnerable to floods.

Furthermore, the infrastructure underlying the city has been built to accommodate water pumped from outside, limiting its capacity to transport a sudden increase of water supply from sources within.

The challenges continue

While storage and transport are issues, so is water quality. Seeing as Cape Town’s main water supply is from outside the city, this is also where the potable water treatment plants are located.

Should water be harvested in the city, it would call for construction of suitable treatment facilities too.

There are small stormwater harvesting schemes currently active in the city for purposes of irrigation as one example. But, says Richard, the challenges particular to Cape Town has led to the general idea that stormwater harvested here would not be stored, but rather be treated to a good enough quality to be returned to the rivers. In this way, less water needs to be abstracted from dams.

Taking this is mind, (at the time of the interview) the city is in the process of writing a stormwater harvesting strategy.

Bringing Capetonians back to the rivers

One of the biggest thing we have to get right is to attract people back to the rivers, says Richard. “The minute people see rivers as an asset they will care for them better.” Richard mentions places like the Kruger National Park and Singapore as examples. Though these are vastly different, they are both places where rivers are loved, and favourite destinations for visitors to relax and enjoy. As a result, there is strong public sentiment for their conservation.

“In Cape Town many of the rivers and wetlands have become places where people don’t want to be.” Instead, the rivers are used as dumping grounds, rather than public spaces to enjoy and conserve.

This will be addressed in the strategies under development. “We are working towards livable urban waterways,” says Richard. This includes creating places where people can grow gardens and spend their leisure time. “We want to open up canalised rivers to create blue green corridors throughout the city,” he says. These will create pleasing spaces for people to enjoy, while serving practical purposes like water quantity and quality management.

The difficult thing is to change people’s mindsets, he says. Should the municipality be able to do this, both within the public domain and governmental spheres, Cape Town too can become a place where the rain is embraced once again.

Notes

• This blog is part of an ongoing series tackling the problem of how we will live with less water (and this is why we will have to). The first article looked at how cities developed, and what went wrong. The second, looked at how a new direction in how we develop the places we live can help solve our water problems (it’s an overview of Water Sensitive Urban Design and the concept of a ‘livable’ place). The third dug into the details of South Africa’s water crisis (it’s not a pretty picture). Then, we looked at the one thing that cities that need water MUST do.
• The whole movement of so-called water resilient cities started with stormwater. To be more precise, it started with sustainable drainage systems or, SuDS. Still, long before it became a bit of a buzz word, a small development in South Africa set the trend – though the reason that they did has to do with politics, and location. It’s called Atlantis (just up the road from Cape Town).
• None of this would have been possible without the support of the Water Research Commission (WRC) in South Africa. The series of blogs are excerpts from the book I write for them on Water Resilient Cities. If you don’t have a copy yet, get in touch, or leave a comment below. I’ll send you one (for free!).