Water, Sewage & Effluent May-June 2017 - Page 20

Manda Hinsch, SRK partner and principal scientist. Murray Sim, SRK partner and principal civil engineering technologist. 18 Encroachment of rivers by formal and informal urban development reduces water quality through litter and nutrients; it also destabilises riverbanks and leads to siltation, raising the flood risk. instability of the river systems and the increase in peak flows have meant that these structures are now inadequate,” said Sim. The steady rise in flood levels inevitably leads to the flooding of houses and other developments close to the riverbanks, causing substantial damage to property and even loss of life. The flooding of river crossings like road bridges or weirs is particularly dangerous; high volumes of traffic in cities like Johannesburg raise the risk of vehicles in motion being washed off these crossings by a river in flood. “It is important to start reducing the flood peaks and minimising the energy potential in the outer catchment by promoting attenuation facilities,” he said. “This can be done through introducing strategically placed ponds, dams, and wetlands; these large permeable areas will encourage groundwater recharge and help reduce peak flows.” These mitigation measures can potentially minimise future impacts and counteract years of urban development. “Uncontrolled changes to the run-off levels in the catchment also lead to a general environmental degradation of the river ecosystem through the loss of soil cover and vegetation,” said Manda Hinsch, SRK partner and principal scientist. “Biodiversity in rivers is also undermined when water quality is affected by human settlements and related development, including sewage treatment plants that are not fully functional or are poorly maintained.” Hinsch said wastewater remains an issue in many parts of South Africa, where the Department of Water and Sanitation’s Green Drop certification programme Water Sewage & Effluent May/June 2017 has been trying to raise the standard of wastewater treatment by municipalities. “Data from the department indicates that in only one out of three municipalities is the quality of discharged water from wastewater treatment plants of an acceptable quality,” she said. She also warned that river system instability is not limited to urban environments. “In rural areas, the natural base flow of many rivers has been affected by other changes in their catchments, such as dam construction and water transfer schemes,” said Hinsch. “Water quality in rural rivers is also at risk of nutrient enrichment from chemical fertilisers on farmlands, or run-off from cattle feed-lots.” For current Department of Water and Sanitation (DWS) data on Green Drop compliance, visit https://www.dwa.gov. za/dir_ws/gds/GDS/Default.aspx The DWS uses a number of variables to award Green Drop status to wastewater treatment works, which include operational standards, maintenance, and level of staff training associated with the capacity of the plant. Sustainable technologies In response to intense urbanisation and its impacts on rivers, a multidisciplinary best management practices (BMPs) approach has been developed and successfully applied in the US, Australia and Europe, and it guides SRK’s strategy