INDUSTRY INSIGHT
Increasing dam storage capacity through the NatSilt Programme
South Africa has a history of building dams to address water security needs and to provide essential bulk water supply to its population. Several large dams are steadily losing storage capacity each year due to soil erosion and land clearance, with many smaller farm dams now full to the brim with silt.
D
ams disrupt normal surface water and sediment flow, leading to sediment being trapped and unavailable for essential downstream ecosystem functioning. This can lead to erosion and ultimately reduce a dam’s water storage capacity over time. Sedimentation rates in South Africa are extremely high. One of the country’s worst-hit large reservoirs is the Welbedacht Dam on the Caledon River in the Free State – which has lost more than 90% of its storage capacity due to siltation. In 2016, the CSIR estimated that South African national dam storage capacity loss due to siltation was 10%. This reduction threatens water security, which threatens food security,
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JUL /AUG 2021
ABOVE A pilot plan will potentially be rolled out at the Hazelmere Dam in KwaZulu-Natal
ecosystems, and economic progress in the country.
National Siltation Management Strategy
In response to this, the Department of Water and Sanitation (DWS) has appointed the Water Research Commission (WRC) to develop the National Siltation Management Strategy for Large Dams (NatSilt Programme). This will represent a collaborative, transdisciplinary approach to tackle the wide spectrum of dam sedimentation and storage capacity challenges in South Africa.
The NatSilt Programme is initiated and funded by the DWS through its Infrastructure Build, Operate and Maintenance (IBOM) branch, which is responsible for the asset management and infrastructure maintenance of 276 government water schemes across the country, including 320 large state dams that make up more than 90% of the country’s total storage capacity. Occurring in three phases over three years, the NatSilt Programme is expected to be concluded in 2023. The WRC will be developing a package of siltation management solutions that include relevant tools, models, frameworks, protocols, guides and plans in order to assist with the implementation and monitoring of the strategy. This will help the DWS in ensuring sustained supply to domestic, industrial and agricultural bulk water users, as well as save scarce financial resources by extending the life cycle of existing dams. Among the vital insights that have been gleaned so far include the role municipalities play in the maintenance
