Johannesburg - A rise in extreme rainfall events in Ekurhuleni was likely to be accompanied by flash flooding and a range of “deleterious impacts” if planning and maintenance of the region's water services infrastructure were not improved urgently.
This result was likely to be valid for all large metropolitan municipalities, according to an October 2014 study by a team of local climate change researchers, who warned that Ekurhuleni bore the brunt of the destruction wrought by flash flooding this week. Six people were killed, vehicles swept away and homes and businesses damaged.
The paper, Climate Change and Urban Development in Southern Africa: the Case of Ekurhuleni Municipality (EMM) in South Africa, compiled by a team of researchers from North West University, University of Pretoria and Wits University, presented outcomes from an investigation of plausible climate futures over the next century, and the potential impacts on water services. This includes water resource management and disaster risk reduction, such as flooding in Ekurhuleni.
“Climate modelling conducted for this research indicates that it is plausible for an increase in the number of extreme rainfall events to occur over central and eastern southern Africa over the next century,” said the researchers.
In Ekurhuleni, as in other major cities, about 22 percent of the population lived in settlements with inadequate housing and low or no access to basic services.
“The natural hydrological systems in EMM that comprise six rivers or spruits have been significantly affected by pollution from sewage works, human settlements, mining and agricultural activities.
“The urban and infrastructure development has had a major impact on infiltration of water in EMM. It is estimated, using EMM development data, that urbanisation has resulted in an increase in surface water run-off by almost 300 percent above the natural catchment yield.
“There is an extremely high likelihood that more intense floods in the future pose a significant threat to informal settlements located on marginalised land which lies within the designated flood lines.”
The study noted that development pressure on land within the EMM was directly related to urbanisation, population growth and the prioritisation of the industrial economy.
“With many areas in the region needing further land and infrastructure development to facilitate socio-economic development, increased potential for flash floods developing into high-level hazards is expected as natural areas are urbanised. Poor communities usually live in the most hazardous and unhealthy environments in African cities.”
The study found that, despite the purpose and design of stormwater drains to reduce flood risk in urban and built-up areas, when these systems fail they can exacerbate flood risk.
In many urban areas within EMM, streams are routed underground into stormwater drains in Nigel, Alberton and Springs. In other urban areas, the outlet of stormwater into natural streams considerably increases stream flow. This practice has the potential to compound damage caused during periods of heavy rainfall, as the storm drains become overwhelmed, and roads and buildings are flooded. The knock-on effect of the channelled water being released into streams downstream of the urban area adversely impacts on the natural systems by increasing the risk of more serious flooding.”
If climate change and variability induces increased rainfall intensities over shorter time periods as anticipated, the affected region would experience increased stream flow.
“Preliminary hydrological analysis suggests that streams in the medium to large catchments will be most affected. Some of the anticipated stream flow consequences include: higher velocities and increased depths during storm flow; lower base flow due to a decrease in catchment infiltration during storm events; longer dry periods; and changes in geomorphology of the stream due to changing sediment loads.
“The anticipated changes in rainfall patterns therefore require that greater emphasis be placed on catchment-scale planning and solutions to urban drainage problems.”
The study noted that there were three primary components to manage extreme rainfall events at a local scale, which included identifying the risk of a flash flood event, developing prevention and mitigation strategies and developing a flood action plan with communities.
In EMM “the actions are being undertaken with various degrees of success”.
“A range of social factors, including allocation of budgets in the metropolitan municipality, political agendas and various other governance factors can either enhance or impede adaptive measures to environmental risks in cities...
“Significant risk management of flash floods by local governments usually occurs directly after a flooding event as an immediate crisis response. The response can be slow, with typically no action occurring beyond the normal daily activities in cities unless a major disaster threatens.”
The study noted how calls were being made for a more mainstreamed adaptation approach and sufficient planning to minimise loss of life and property from flash-flooding events.
“Careful management of water supply challenges and associated potential disaster risks that may arise with climate change will be essential.”
Saturday Star