Durban’s location is at once a blessing and a curse. While the city hugs world renowned beaches, it is also placed squarely in the way of rainwater on the way there.
As for any city, the route and impact of stormwater in Durban depends very much on where it is placed.
Welcome to the eThekwini municipality
The eThekwini Municipality, that Durban is part of, is located on the East coast of South Africa. It overlooks the balmy Indian Ocean. The municipality spans an area of about 2 555 km², rich in diverse biodiversity, spread over a steep and dissected landscape.
The municipality has 98 km of coastline, 18 major river catchments, 16 estuaries and 4 000 km of rivers. The city of Durban itself lies low in the catchment. It lies right at the bottom in fact, in the vicinity of the mouth of the Umgeni River.
Lying this low in a catchment full of steep slopes, Durban is familiar with ﬂoods. This creates a number of unique challenges, underlined by the rich mixture of people that call it home. It’s not for nothing that Durban is often called a ‘melting pot’ of cultures.
The people of Durban
Most (around 68%) of the municipal area is considered rural with pockets of dense settlement. Commercial farms and metropolitan open space make up about 10% of the rural areas. The rest is hilly, rugged terrain with scattered settlements.
The rest of the municipal area (about 32%) is urban. This is where you will find residential, commercial and industrial developments. There are also many informal settlements scattered across the city, especially towards the borders. These are also often located on steep terrain or ﬂood plains.
The hilly landscape, expanding city and growing informal areas together, have created living spaces ripe to all the possible dangerous impacts of stormwater. Floods, erosion and pollution are rife.
How Durban manages its stormwater
In order to try and keep people and infrastructure safe from stormwater, the municipality maintains an intricate system. This includes just over 3 600 km of stormwater pipes, over 171 300 manholes, 620 km of culverts and canals and 19 detention ponds. Then, a number of attenuation ponds slow down the ﬂow of water during ﬂoods.
The whole stormwater system mostly collects the rainwater and sends it directly to the rivers and the sea without treatment.
As with most cities, the system is designed to cater for the probability of ﬂoods. You can see this best in the size of the pipes that the water has to go through. The system is built according to the return period of ﬂoods (the estimated average time between ﬂoods). This statistical measure is typically based on historic data taken over a long period of time.
In Durban, this system is designed to deal with minor and major ﬂoods.
Balancing small floods and big floods
Inlets at the side of the road, for example, are designed for a one in three-year return period (a small storm). Major systems like canals are designed for one in 50-year return periods. These are much bigger storm events, says Randeer Kasserchun, Deputy Head of the municipality’s Coastal, Stormwater and Catchment Management Department. “When you get a storm that exceeds the design capacity, you expect ﬂooding,” he explains.
In this way, Durban has been maintaining a relatively acceptable balance with the stormwater that it generates. In general, the impact of rain is almost unnoticeable. Sometimes, however, more rain falls than what the system can handle. As Randeer says, this then, is when there is a flood.
Be that as it may, the balance is increasingly swinging out of hand. The system is feeling the pressure of a changing environment. More often, the balance is swaying in favour of those times that the system cannot achieve its primary purpose anymore. This is why…
Durban develops ahead of its stormwater system
For one, the eThekwini municipal population is growing rapidly. In 2001 it was 3.09 million. This number is growing at an average of 1.13% each year and reached 3.44 million in 2011. By 2016, the population was some 3.6 million people. Projections place numbers at 4.4 million by 2030. As people increase, so does houses. At the same time, the services that the municipality has to provide has to be cranked up.
As the developed area expands, more areas are covered with things like buildings and streets. Now, water that would have filtered into the soil, rushes down hard surfaces, downwards. The municipality has experienced a dramatic increase in the velocity of river ﬂows.
“People expect all of that extra water to go into a pipe, but it was designed to only cater for a speciﬁc proportion of water,” says Randeer.
The great headache of stormwater pollution
Except for the quantity of stormwater, the quality is a big headache. In particular, trash has become a forceful foe to reckon with.
“Our biggest problem is pollution,” says Randeer. We have both soluble and non-soluble contaminants in the water, so while water quality is a challenge we also get huge blockages caused by litter, which impacts negatively on the stormwater system capacity, he says.
Durban’s rivers and estuaries are feeling the punch.
In 2010, an estimated 40% of rivers were considered to be in a poor condition and only six (or just over 3%) were classiﬁed as near natural. Only about 10% of the total municipal estuarine areas were classiﬁed to be in good condition. The results are due to impacts from multiple sources. Still, the quality of stormwater is said to be a big contributor.
The consequences ripple out far and wide. The rivers become highways that transport litter and pollution to Durban’s famous beaches, a huge drawcard for the tourism-dependent city. And, says Randeer, the poorest of the poor is often the most harshly affected. Often, they still directly depend on the services oﬀered by the rivers and streams that they live next to.
The municipality has been driving various initiatives to try and improve the situation.
The responsibility of home owners
Fore one, building regulations ensure that stormwater runoﬀ from individual properties is reduced, says Randeer. For Durbs, the stipulations are provided in the municipal Guidelines and Policy for the Design of Stormwater Drainage and Stormwater Management Systems. This policy places the responsibility of managing and reducing runoﬀ in the hands of the property owner. This is because they are increasing the impermeable surface area of the city when they build. As a result, they are creating more stormwater runoff.
This is a problem because, back in the day, the municipality designed the piped stormwater systems on the basis that not more than 40% of the area of the residential properties would be hardened. This is no longer the case. Now, many properties have hardened their sites with extra patios, canopies, entertainment areas and pool surrounds.
Commonly, there are now more driveway and parking areas and larger garages. All of these improvements increase the stormwater generated from the sites. This now calls for onsite management, harvesting and retention of rainwater.
As a result, the owner of any development connected to the eThekwini municipal stormwater system, of which more than 40% of the surface is hardened, must manage the excess runoﬀ generated from his site.
“We would not approve your development if you do not adhere to this stipulation,” says Randeer.
How you can manage your stormwater
The policy also stipulates preferred options to manage stormwater runoﬀ. These include options to keep it on site (retain it) or catch it to make use of it (harvesting).
Soakpits (which allow rainwater to inﬁltrate into the groundwater table, or to tanks for reuse) are suggested as the better, responsible and preferred option. Guidance for a range of other controls is also supplied, such as attenuation ponds and stormwater harvesting tanks.
In this way the municipality is actively promoting rainwater harvesting. People can then use it in gardens, to ﬂush toilets and wash cars, for example. The guidelines also stipulate that paving, surfaced driveways, pool surrounds and the likes should mostly drain to buried tanks unless the topography allows otherwise.
Green roofs are another option seen to hold great potential in Durban. The municipality’s Environmental Planning and Climate Protection Department initiated a Green Roof Pilot Project (GRPP) in 2008. The project investigated the eﬀectiveness of green roofs in Durban, in particular to reduce temperatures and stormwater runoﬀ. Results proved to be very promising in Durban. (In Toronto, green roofs have proven to be an extremely efficient, and budget friendly, stormwater management approach.)
As part of the initiative in Durban, guidelines for the design of green roof habitats were developed.
Why stormwater is not harvested in Durban
However, large-scale harvesting of rainwater across the city is hampered by its location. “We are right at the end of the catchment, so for us to catch and use large-scale stormwater runoﬀ we’d probably have to pump it upwards again for storage somewhere,” says Randeer.
Not only would this result in more costs and infrastructure, but it’s also not practical to create a dam in Durban.
How they are managing the stormwater quality in Durban
Ongoing campaigns are run to improve the quality of stormwater runoﬀ across the municipality. For one, nets have been constructed at some of the main catchments of the area to capture the vast amounts of litter before it washes downstream.
Here, Randeer sees one of their biggest challenges to change people’s mindsets about their contribution to the problems the municipality has to manage.
To try and change that, the municipality now runs regular clean-up and awareness campaigns. “Our catchment management education work is extremely important.” Randeer says they also focus heavily on schools. “We aim for the messages to be taken home by the children from school,” he says. “When a parent wants to throw their cigarette butt out of the window, the hope is that the child will tell them not to do that.”
Different city, different stormwater management issues
This then, is how Durban is trying to work more sustainably with its stormwater. In this city’s case, the bigger challenge is not how to use the water that is ‘going to waste’, but rather how to keep people and the environment safe from the impact of the water. The journey ahead is a long and arduous one.
Now, compare this to the journey that Cape Town is on. This city’s location is resulting a vastly different perils, and promises a completely new opportunity for development.
- 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, every city’s journey to SuDS is unique. This interview with Dr Debra Roberts explains why.
- 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 wrote 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!).