STORMWATER MANAGEMENT
Stormwater management should be firmly on the urban agenda Urbanisation increases the coverage of impervious surfaces, preventing water from infiltrating the ground and increasing the volume of run-off.
T
he impervious surfaces (such as roads) are spaced closely together and have their own stormwater drains. This means that the whole system responds rapidly to a high-intensity storm – causing frequent flash flooding. Compounding the issue is the fact that run-off often carries debris, chemicals, bacteria, eroded soil and other pollutants, and transports these into streams, rivers, lakes or wetlands,” explains Chris Brooker, a consulting engineer specialising in water management. Urban stream syndrome Flash flooding can damage road infrastructure, stormwater drains and bridges, and degrades the morphology of water courses. Run-off increases the occurrence of flowing water courses – tearing up vegetation and causing soil erosion. Due to the high frequency of this run-off, the vegetation does not have an opportunity to repair itself or grow back. Stream banks become more vulnerable
to erosion, as they are not protected by vegetation, creating more run-off and more erosion. “The regular, rapid flow of water in water courses – where the rate of flow changes quickly – creates a negative ecological impact. There is increased shear stress on the beds and banks of a water course, and the living organisms do not have the time to find a place to hide before they are washed away. The movement of sediment affects the ecology, as organisms either have no place to live (as sediment has been washed away) or they are swamped by too much sediment (where it has been deposited),” says Brooker. Pollution – ranging from shopping trolleys and mattresses to chemicals and microplastics – is carried to water courses via the run-off. “Urbanisation has a major impact on water courses. Groundwater resources are reduced, as much less water is absorbed into the soil. There is the drying up of small springs that previously provided a
Chris Brooker, a consulting engineer specialising in water management
ABOUT CHRIS BROOKER Chris Brooker is a professional engineer working as a specialist consulting engineer in the field of environmental water management. He enjoys river and wetland rehabilitation and renaturalisation, and actively promotes stormwater management and modelling. With many years of experience in the computer modelling of stormwater management systems, Chris teaches numerous workshops and occasional courses, such as PCSWMM Workshops for the Computational Hydraulics International and the SA Roads Federation Urban Drainage Course. He is an external examiner and honorar y senior lecturer in the Depar tment of Civil and Environmental Engineering at Wits University, where he teaches par t of the postgraduate ‘Design for the Environment’ course. He gives advice and acts as an exper t witness in High Cour t hearings and arbitrations.
perennial water source to flowing streams. Streams are becoming ephemeral in urban areas, unless they are fed by water leaking from municipal sewers and water supply pipes,” Brooker adds. Stormwater infrastructure Stormwater management can mitigate the negative effects urbanisation has on the receiving system and the reduction of usable water. “It is a multidisciplinary aesthetic and technical engineering design process – first to find the right mix of interventions suited to a particular location and then requiring careful mathematical calculations, meticulous specifications and properly supervised implementation,” maintains Brooker. A number of technologies and infrastructure (grey and green) are
