A comprehensive economic flood risk assessment for Prospecton

The challenge: Identifying flood risks and economic impacts across a major industrial zone

In April 2022, a catastrophic flood event occurred in Durban, South Africa. The flood destroyed homes, caused loss of life as well as a huge economic impact. The national government mobilised teams to assess the damage. However, no comprehensive assessment was done for the South Durban Basin (SDB).

The Prospecton area, a major industrial zone in SDB, was one of the worst affected areas. As a low-lying area and a former wetland, it’s highly susceptible to flooding. Between this and the suburb’s critical infrastructure assets, Prospecton has a large economic exposure – making effective risk management vital.

As the actual flood risk in the area was unknown, there was no clear sense of urgency for government to invest in adaptation measures. This made it difficult to select and prioritise cost-effective flood risk reduction measures.

The solution: A complete flood hazard and risk assessment to quantify economic risk

Royal HaskoningDHV performed a flood hazard and risk assessment to quantify the damage during the 2022 event, as well as the existing economic risk in the area.

The methodology included a system analysis to better understand the area of interest, relevant stakeholders, and root causes for flooding. A flood hazard assessment was also conducted, focusing on pluvial and river flooding, which required simulation of multiple flood scenarios.

Flood hazard modelling was conducted in HEC-RAS and PCSWMM and the results were combined with exposure and vulnerability datasets that were verified during in-depth interviews with affected parties. These

insights were fed into Royal HaskoningDHV’s in-house Global Flood Risk Tool to quantify economic damages and flood risks.

The result: A comprehensive guide for cost-effective flood resilience

With an extensive analysis across multiple areas, South Africa’s government can now see the primary and underlying causes of flooding for Prospecton, future flood risks, and the impacts and effectiveness of proposed flood reduction measures.

The study estimated that the total damage of the April 2022 flood event was US$4.1 billion, while the economic flood risk is estimated to be almost US$29 million per year. These results show the urgent need for a comprehensive flood resilience strategy.

Crucially, the study showed that the benefit-cost ratio of proposed measures that reduce the risk of the fluvial (river) flood risk are very positive. This creates an urgent call for immediate investment.

Meanwhile, the benefits of in-progress flood relief projects across Prospecton that focus on reducing the pluvial (rain) flood risk were shown to likely not outweigh the investment costs.