INDUSTRY INSIGHT
National siltation programme to preserve SA’s large dams A three-year programme managed by the Water Research Commission and funded by the Department of Water and Sanitation, the National Dam Siltation Management Programme sets out to develop the Siltation Management Strategy. This will ensure the effective and sustainable management of the nation’s bulk water resource infrastructure.
A
s a water-scarce country with extremely variable rainfall, South Africa is highly dependent on the storage of water in large dams for its water supply. Nationally, the total storage capacity of the country’s major reservoirs amounts to an estimated 33 900 million m3 – or about 70% of the mean annual run-off. Most of South Africa’s dam infrastructure was constructed before 1980, and thus many of these engineering structures are decades old. In addition, seven of South Africa’s nine provinces rely on interbasin transfers – where water is transferred from one catchment to another through sophisticated water infrastructure – which provide more than half of their water requirements. However, these large dams experience various threats to their sustainability, not least of which is siltation. South African rivers, in general, carry large loads of suspended silt, as a result of both natural processes and humaninduced activities, such as deforestation, industry activities, improper farming techniques and overgrazing. Silt ends up in the country’s dams, where it reduces the storage capacity. The problem is exacerbated by an increase in high-intensity rainfall events coupled
14
IMIESA June 2021
extending the storage life of its existing large dams. There are several options for preventing and managing siltation in South Africa’s dams. Siltation management should not be a blanket approach and should be site-specific.
NatSilt initiative
with longer periods of aridity as a result of climate change. All of South Africa’s dams are affected by siltation to a greater or lesser degree. The most well-known example is the Welbedacht Dam on the Caledon River in the Free State. The dam was originally constructed in 1973 with the purpose of supplying water to the city of Bloemfontein. By 1988, merely 15 years after construction, the dam had already lost 73% of its original storage capacity. Another example is Hazelmere Dam, located on the Mdloti River in KwaZulu-Natal. This dam, completed in 1975, has lost more than 25% of its original design capacity through siltation.
Countering annual losses It is estimated that South Africa is losing about 1% of storage capacity in its dams to siltation every year. The limits to the development of surface water sources have almost been reached and the opportunities for the spatial economic placement of new dams are few. Dam construction is costly, and it is not costeffective to replace the lost capacity in existing water infrastructure by building more bulk water infrastructure. It is therefore imperative that the country manages its existing bulk water infrastructure as effectively as possible,
There is thus a requirement for a toolbox of solutions to address the siltation challenge. To this end, the Department of Water and Sanitation (DWS) appointed the Water Research Commission (WRC) to develop the National Siltation Management Strategy for Large Dams in South Africa, more commonly known as the NatSilt Programme. The programme represents a collaborative, transdisciplinary approach to tackle the wide spectrum of dam siltation and storage capacity challenges in South Africa. The programme was officially launched in May 2021 at the NatSilt Virtual Symposium on Protecting Our Source Water Systems. Key outcomes included the role municipalities play in the maintenance of the catchment areas and how crucial it is that there is cooperation between the various government departments in ensuring the success of the programme. Leonardo Manus, acting deputy directorgeneral: Regulations, Compliance, and Enforcement at the DWS, said, “We have established our whole economy and livelihoods around these majestic dam structures, but we can so easily lose them if we don’t apply proper management procedures to keep them in that state. “The NatSilt Programme will provide the department with the tools and intelligence to make appropriate, site-specific decisions regarding each dam instead of having a blanket
