Is sustainable stormwater management possible in Durban?

The promise and peril of stormwater management in Durban

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.

Durban city
Durban’s location is both a blessing and a curse

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.

Randeer Kasserchun talks about stormwater management in Durban
Randeer Kasserchun, Deputy Head of the eThekwini Municipality’s Coastal, Stormwater and Catchment Management Department

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.

Durban's polluted beaches
Durban’s famous beach front

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.

Green roof at Durban Municipality
Durban’s Green Roof Pilot Project

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.

Notes

Leave a Reply

Your email address will not be published. Required fields are marked *