Heavy rains mean traditional 100-year water line now breached

Leading risk and safety agency believes insurance companies will now rethink assessment and premiums

Unseasonably high rainfall in Gauteng in early February has led to a reassessment of what is called the 100-year flood line and houses built-in low-lying areas over the past thirty years have an increased risk of flooding.

This, says Volker von Widdern the South African head of Strategic Risk at Riskonet – a global safety and risk management consultancy - is now of major concern to insurance companies who are being forced to reappraise their approach and strategy to cover. Inevitably he says, this climate-change phenomenon which will only amplify in coming years, will have a serious impact on insurance premiums. His advice to businesses and homes who are potentially threatened is to undertake a full audit of potential water breaches and implement construction changes to mitigate risk.

Von Widdern says high rainfall over Gauteng in the first week of February caused serious flooding in low lying areas including Centurion in Tshwane and caused severe damage, even leading to the cancellation of a professional golf event at the Irene Golf Club. In addition, there were many reports of storm water flooding through housing complexes.

He says severe rainfall is no longer uncommon, with many international and local examples. The concentrated rain over 3 days in 2021 in Germany caused massive damage, storms in the Eastern Cape caused mudslides and damaged infrastructure and many homes.

This he says has led to an inevitable reassessment of the “100-year flood line”. based on now outdated assumptions including flooding only occurring from high rainfall and rising river water; flooding only being experienced in rural areas; and average, monthly and daily rainfall measured to inform the 100-year flood line.

But he says those assumptions no longer hold true. “South Africa has experienced a significant change in the development of its urban areas in the past 20-40 years. Concentrated housing developments have proliferated, commercial and industrial developments are widespread, informal housing has emerged both in low lying areas and across large areas of unserved areas where there are no stormwater drains. “These factors substantially limit the natural spread of rainwater and its absorption. Rainwater then accumulates quickly and flows in concentrated areas until it overcomes localised walls, drains and verges in addition to the banks of the rivers that carried normal levels of rainfall.”

Von Widdern says housing and industrial developments completed 20- 40 years ago could assume that the risk of flooding from neighbours was low, in view of the low density of developments at the time. “Little investment would have been made in the management of extreme levels of rainfall. The present situation is completely different – both the density and water accumulation factors are multiples higher.” He says the combined effects of sharply increased rainfall and concentrated accumulation of water in many developed areas means that floods are more likely to occur in the cities and suburbs and will then be experienced in the rural areas as the water from of the flash floods enters the related river systems.