SRK Consulting's Xanthe Adams, Principal Engineer, discusses the importance of floodline measures and why they should be enforced by municipalities.
The question of floodlines is in the spotlight after the serious flooding in parts of South Africa earlier this year were declared a national disaster by the National Disaster Management Centre (NDMC).
The heavy summer rains – mainly in the Eastern Cape and KwaZulu-Natal but also in the Free State and North West provinces – destroyed property and infrastructure, and led to many lives being lost. While the declaration allowed more direct intervention in recovery efforts by national government and organs of state, the NDMC noted that “these threatening conditions call for an all-of-society and government approach to promote risk reduction”.
Among the standard measures in place to protect communities, businesses and infrastructure from flooding is the regulated floodline alongside rivers in urban areas – below which any building or development is not permitted.
What’s a floodline?
“A floodline is an imaginary line on the ground that denotes the edge of the water during a flood,” said Xanthe Adams, principal engineer at SRK Consulting. “ The floodplain is the area alongside a river that will be expected to be under water
during a flood, with the upper edge of this floodplain being designated as the floodline.”
The National Water Act requires these floodlines to be shown on plans for housing and other developments, which show the highest level that a flood could reach every 100 years – the most commonly stipulated timeframe. All buildings then need to be above this floodline, to avoid the danger of flooding.
Who needs one?
Adams highlighted that municipalities are responsible for enforcing compliance with floodlines as part of reducing flood risk to communities and infrastructure.
Their planning must mitigate and manage the effect of urbanisation, which generally means more rainfall run-off and greater risk of flooding.
“Urbanisation is certainly a significant factor increasing the size of floodplains and the velocity of floods,” she said. “We see its effect frequently as we determine
floodlines, especially in older urban areas, where we often find that some of the infrastructure is actually already within the floodline.”
Among the efforts by local government to address rising run-off levels is to ensure that developments design water attenuation facilities into new projects. These dams, ponds and wetlands will act to slow down the flow of water and allow more of it to percolate into the ground.
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