SuDS needed for protection of environmental, infrastructure

Video

GEORGE NEWS & VIDEO - Sustainable drainage systems (SuDS) can significantly reduce the destruction that storm water and floods cause to aquatic ecosystems (such as rivers, estuaries and wetlands) as well as to infrastructure and people's lives.

Therefore, it has become paramount that SuDS should form part of development planning in every city.

This was the message at a seminar last week at Protea King George Hotel hosted by Confluent Environmental in collaboration with the University of Cape Town (UCT) and the South African Institute of Civil Engineers (Saice).

In her presentation, Confluent managing director Jackie Dabrowski said conventional storm water management has produced predictable text book examples of degraded aquatic ecosystems.

"There is always one end result, which is that ecosystems are severely degraded and our own infrastructure is put at risk."

Vulnerable

Conventional storm water systems not only channel runoff containing pollutants and litter to wetlands and rivers, but the volume and velocity of the runoff also leads to erosion sediments which are deposited downstream in natural water bodies.

"High flow velocities cause channel incision or 'down-cutting' of river and wetland channels. This alters the hydrology of the ecosystems, impacting on aquatic life and reducing biodiversity. Most importantly for us humans, it compromises the ability of aquatic ecosystems to buffer us and our infrastructure from high velocity flood flows."

Dabrowski said the aquatic ecosystems in the Southern Cape are more vulnerable as their source-to-sea distance is short and there are steep gradients. This means that if they are degraded, they do not have a chance to recover by the time they reach the sea.

"Our water chemistry in rivers is also naturally low in nutrients, which reflects the fynbos through which it flows. It has a low pH and low dissolved salts and low turbidity, although tannin-stained. We have very sensitive endemic fish and amphibians that are completely unique to the Southern Cape, including the Knysna leaf-folding frog of which we have recently discovered a large population in the middle of George."

She said George was and is "a bit of a sponge city" with lots of wetlands, many of which are vulnerable to hydrology changes and flow velocities.

Rainfall and erosion

In this context it is important to consider introducing SuDS, also because George (like Knysna and Plettenberg Bay) falls in the highest rainfall intensity category in South Africa. We are mapped as a strategic water source area, which means the area produces disproportionately larger volumes of water per unit area than other regions.

"This presents challenges in terms of managing storm water."

The Southern Cape's erodibility is also mapped as very high because of its soil type. The area's characteristic steep slopes and location at the base of mountains add to the risk of erosion.

Integral

Dabrowski concluded that SuDS should not be an afterthought, but an integral consideration in the planning process. "If that has not happened, town planning is the regulator or gatekeeper so it is up to them to be vigilant and to look at catchment-wide developments and consider SuDS in terms of storm water management.

"Development should be guided by best practice and should be considered in terms of how sustainable it is."