THE City of Cape Town proposes the redevelopment and upgrade of the weirs at Zeekoevlei and Rondevlei that are located within the False Bay Nature Reserve.
The proposed redevelopment of the ‘weir complex’ is to supplement other medium-term interventions, amongst which the dredging of Zeekoevlei, to improve the overall water quality of this Ramsar site.
The False Bay Nature Reserve is a site of international importance according to the Ramsar Convention on Wetlands.
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 weirs limit the depth of water which can be drawn down. The weir walls, built in the 1950s, prevent the movement of marine and estuarine fish into and from the vleis.
“Our intention is to lower the weirs at both Zeekoevlei and Rondevlei and to install mechanically-operated sluice gates, as opposed to the current systems where we remove the penstocks manually for the drawdown,” said the city’s deputy mayor and mayoral committee member for spatial planning and environment, alderman Eddie Andrew.
“Many residents and interest groups from the False Bay Nature Reserve join us for the annual drawdown and are well aware of what this task entails. With mechanically-operated sluice gates we will be able to do drawdowns quicker, and the lower weirs will allow for a lower level drawdown of the vlei water.”
Andrews said, “We intend to keep the existing penstocks, but will modify the Zeekoevlei weir with a new sluice channel with channel gates in addition to the wooden penstocks.”
The installation of fish swim ways will assist with the reintroduction of natural estuarine fish into the vleis, restore fish diversity and abundance, restore the nursery function of the two estuaries, and enhance the conservation status of estuarine dependent marine fish species.
“We are extremely excited about the prospect of having our indigenous fish back in the two vleis.”
The proposed redevelopment of the weir complex is in addition to the city’s medium-term interventions, amongst which is to dredge a large part of Zeekoevlei to get rid of the contaminated nutrient-rich sludge. Also, by limiting nutrient and pollutant inflow into the vlei, the overall condition and functioning of the system can be improved, and water quality can be enhanced.
Andrews encouraged residents and interested parties to participate in the process by registering, and to read the documents, and submit comments.
“I want to add that the proposed construction work will result in limited disturbance of existing dune vegetation, but we undertake to do specialist dune rehabilitation afterwards that will involve the rescuing of plants before the earthworks commence at the site. We will then keep these plants in a nursery and replant them after construction.”
