Year 2: An update on the NatSilt Programme

YEAR 2: AN UPDATE ON THE

NATSILT PROGRAMME

Executed by the Water Research

Commission and funded by the Department of Water and Sanitation, the National Dam Siltation (NatSilt)

Programme aims to reduce the risk of siltation in dams.

By Lesego Gaegane, senior project manager, NatSilt Programme

The programme addresses siltation at the source (catchment area) and identifies pragmatic interventions in minimising the transportation and transfer of siltation into the river system, and managing siltation in the sink zone (dam). The NatSilt Programme is implemented over three phases, with the first phase completed in March this year. Phase 1 developed a Dam Operations Model that can be used for the planning and designing of new dams where siltation management interventions are incorporated into the design phase of dams. This will allow funds that are made available to design and construct a dam to be utilised further to implement catchment management interventions and thus extend the lifespan of the dam. The focus of the model is on improved and sustainable storage capacity of dams, through catchment and engineering interventions with a focus on maximising the yield of water resources and their economic benefits.

This Dam Operations Model is also used to prioritise siltation management activities and interventions on existing dams through a cost-benefit analysis. It identifies interventions in the three zones – the catchment, the river system and the dam – where users of the model can see which interventions are more feasible for implementation. Upstream interventions can be more easily justified by making the socio-economic benefits associated with a longer life of a dam quantifiable.

The uMkhomazi River

Smithfield Dam

Currently, the Dam Operations Model is implemented at three existing dams to improve their storage capacities and enhance their sustainability. It will also be used for a dam earmarked for construction – the Smithfield Dam.

Located in the upper uMkhomazi river catchment in the southern part of

KwaZulu-Natal, the proposed Smithfield Dam project will have both built and ecological infrastructure. Ecological infrastructure and its conditions in the area will be mapped and used as a baseline for the development of a catchment and ecological infrastructure management plan for interventions. The

The release of large volumes of muddy water can inundate riverbeds and drastically affect downstream ecosystems if not properly planned

goal is to create a healthy catchment that will limit siltation. The integration of ecological infrastructure into the Smithfield Dam design will operationalise siltation management at a catchment scale and will enable the improvement of water security through improved water storage capacity of the proposed dam, but will also improve livelihoods and increase the climate resilience of communities in the catchment.

The uMkhomazi catchment area forms part of the Southern Drakensberg Strategic Water Source Area, with a number of industries and farmers. It is therefore important to ensure that ecosystems within this catchment are functioning well to maintain the sustainable water requirements of all users.

One of the components of this project will entail the co-development of certain aspects of the catchment and ecological infrastructure management plans with the communities and stakeholders within the catchment to ensure the long-term sustainability of siltation management interventions. The stakeholders will include traditional authorities, subsistence farmers, working groups and catchment management forums. Knowledge transfer to the communities is crucial to enable capacity development and the maintenance of ecological infrastructure interventions.

A primary goal of the NatSilt Programme is to see the incorporation of siltation management in the operations of dam activities to ensure that siltation management is embedded in every aspect of dam management. Through this project, proactive mitigatory measures against soil erosion, sediment transfer to the reservoir, and siltation of the reservoir will be incorporated into the dam design, catchment and ecological infrastructure management plan, as well as the dam operations and maintenance manual. We hope this will inform enhanced dam planning operations and new ways of dam design going forward.

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