The City of Cape Town has commenced with the modification and upgrade of the weir at Zeekoevlei in the False Bay Nature Reserve. This project will strengthen other medium-term interventions to improve the overall water quality of this Ramsar site.
According to the Ramsar Convention on Wetlands, the False Bay Nature Reserve is a site of international importance. The modification of the weir will support the City’s medium-term interventions, amongst which the current dredging of Home Bay and Storm Bay will remove the nutrient-rich sediment in Zeekoevlei.
Also, by improving the water level management and facilitating more effective flushing of nutrients and pollutants, the overall condition and functioning of the system can be improved, and water quality will be enhanced. The contractor is currently setting up the site camp and is busy in preparing for the works that will commence in all earnest by May 2026. If all goes as planned, the project is expected to be completed by mid-2027.
Considering this, Deputy Mayor and Member of the Mayoral Committee for Spatial Planning and Environment – Alderman Eddie Andrews stated that by improving the water quality of the vleis remains one of the top-priorities and the weir project is key to achieving this outcome. The project entails the lowering of the weir at Zeekoevlei and to install mechanically operated sluice gates, as opposed to the current systems where they remove the penstocks manually for the drawdown.
With mechanically operated sluice gates, the operations will be streamlined, and the lowered weir crest will allow for a deeper drawdown of the vlei water. The deeper drawdown will enable them to better manage the organic sediment and reeds, and they will be able to more fully flush the vlei of nutrient-rich water and sediment.
According to Andrews, they will also be installing fishways to make it possible for natural estuarine fish to enter the vleis. In doing so, they aim to support the restoration of fish diversity and abundance when water quality improvements within the entire system allows for it. They are extremely excited about the possibility of having locally indigenous fish back in the vlei for the long-term.
Both Zeekoevlei and Rondevlei are managed by a system of penstock sluice gates to allow for the water level to be dropped to a minimum depth, which is known as the annual ‘drawdown’, usually at the end of the summer sailing season. The intention of the drawdown is to remove nutrient-rich water and sediment from the system, and to increase the capacity of the vleis prior to the winter rainfall season to reduce the risk of flooding of surrounding areas.
The current manually operated weir limit the depth of water which can be drawn down. The weir walls, built in the 1950s, also prevent the movement of marine and estuarine fish into and from the vleis.