RAISING THE DASSIESHOEK DAM WALL TO STRENGTHEN ROBERTSON’S WATER SECURITY

Langeberg Municipality is investigating options to increase Dassieshoek Dam’s storage capacity and strengthen Robertson’s long-term water-supply resilience.

Robertson receives bulk raw water from several sources, including the Robertson (Brandvlei) Irrigation Canal, the De Hoops River Irrigation Scheme, the Vrekhoek mountain stream and mountain dams such as Dassieshoek and Koos Kok, which capture rainfall from the surrounding catchment.

Dassieshoek and Koos Kok primarily provide storage and water-supply resilience. Water from Dassieshoek is not normally used for Robertson’s day-to-day raw-water supply, except when the dam is overflowing.

The stored water provides an important reserve that can be drawn on when the available water from the canal, De Hoops and Vrekhoek sources is insufficient to meet demand. This includes periods of peak demand, particularly during December, January and February, and when the canal is unavailable due to scheduled maintenance, typically during July and August.

Increasing the storage capacity of Dassieshoek Dam could therefore provide a greater buffer for Robertson’s water supply during periods when other sources cannot meet demand, particularly during peak demand, canal maintenance and periods of low rainfall. This forms part of the Municipality’s long-term strategy to strengthen Robertson’s water security and resilience.

Investigating the potential to raise Dassieshoek Dam
In October 2025, Langeberg Municipality appointed a consulting engineering team to investigate the feasibility of raising the existing Dassieshoek Dam wall and developing boreholes in the Dassieshoek Dam area.

The Municipality has followed an inclusive approach from the outset, with participation by key interested and affected parties. Since the start of the project, numerous engagements have taken place between the Municipality, technical specialists, the local water users’ association, catchment management representatives and relevant government departments.

Groundwater investigation
As part of the investigation, a hydrogeological assessment and borehole-siting investigation were undertaken in December 2025.

The hydro-census identified seven existing boreholes in the area. These boreholes have an average depth of approximately 93.8 metres below ground level, an average electrical conductivity of 53.05 mS/m, and an average yield of 2.14 litres per second.

The average borehole yields identified through the investigation were higher than those indicated on regional groundwater mapping, providing useful information for assessing the potential contribution of groundwater to the area’s future water-supply options.

The development of new boreholes is, however, subject to funding. The current approved budget does not include the drilling and equipping of new boreholes. The Municipality is engaging with the Western Cape Department of Water and Sanitation (DWS) regarding potential funding for boreholes as part of water-resilience initiatives for towns within Langeberg Municipality.

The number of boreholes that could ultimately be developed will depend on available funding and the outcomes of the necessary investigations.

Two options investigated for raising the dam
In February 2026, specialist hydrological consultants were appointed to investigate the potential upstream and downstream impacts of raising the existing Dassieshoek dam structure.

Two alternatives were assessed:

• Option 1: A 1.85-metre raising of the existing weir, together with the associated infrastructure modifications.
• Option 2: Raising the existing weir by 2.26 metres, using a labyrinth spillway configuration, together with the associated infrastructure modifications.

The hydrological assessment considered the implications of both alternatives, and the final hydrological report was completed in June 2026.

Conceptual designs for both options have now been completed. The project is currently in the design development and cost-estimation phase.

What happens next?
The next step is to complete a cost-benefit analysis of the two alternatives. This analysis is expected to be completed by December 2026 and will assist the Municipality in determining the preferred option.

Once a preferred alternative has been identified, it will be presented to interested and affected parties as part of the environmental authorisation process.

The environmental process is anticipated to commence in early 2027 and is expected to take approximately 10 to 12 months to complete. During this process, stakeholders will have opportunities to participate, provide input and raise concerns.

This process will help ensure that the preferred water-security solution is developed responsibly, with due consideration for the environment, water users and other affected parties.

Subject to the necessary approvals, completion of the required technical and environmental processes, and procurement of a contractor, construction activities could potentially commence during the second quarter of 2028.

Strengthening Robertson’s long-term water security
The Dassieshoek Dam investigation forms part of Langeberg Municipality’s broader approach to strengthening Robertson’s water security.

By assessing additional storage capacity and groundwater opportunities, the Municipality is planning for the town’s growing water needs while preparing for periods of lower rainfall and greater uncertainty in future water availability.

The project is currently in the investigation, design development and cost-estimation phase and is not yet at the construction stage. The preferred option, construction cost and final implementation arrangements will only be determined as the remaining technical, financial, environmental and approval processes progress.

The Municipality will continue to provide updates as the project progresses through these stages.