Residents reminded to comment on proposed modification of weirs at Zeekoevlei and Rondevlei

17 July 2024

The City of Cape Town wants to remind the public to comment on the proposal to redevelop and upgrade the weirs at Zeekoevlei and Rondevlei in the False Bay Nature Reserve. The proposed redevelopment is to supplement other medium-term interventions, amongst which the dredging of Zeekoevlei, to improve the overall water quality of this Ramsar site. The closing date for comments is 26 July 2024. 

The False Bay Nature Reserve is a site of international importance according to the Ramsar Convention on Wetlands.

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.

The redesign of the weir complex entails the following components:

• Modification of the existing Zeekoevlei weir to allow rapid lowering when needed. The redevelopment includes the lowering of the channel apron to facilitate the drawdown, expansion of the weir, new mechanical sluice gates, gatehouse for maintenance, and stabilisation gabions
• Construction of a new Rondevlei weir with sluice gates further downstream to allow improved management of Rondevlei's water levels. The work includes a gatehouse for maintenance, a timber pedestrian bridge, and retaining walls
• Construction of a fish swim way between the new Rondevlei weir and modified Zeekoevlei weir to facilitate the movement of fish into and from the vleis. The reintroduction of natural estuarine fish into the vleis will assist with the lowering of elevated nutrients, and benefit the overall fish stock in the inshore coastal environment
• Alterations to the existing Rondevlei weir, including the construction of new sluice gates and a gatehouse for maintenance
• Construction of a fish ladder at the Zeekoe culvert bridge to facilitate the movement of fish from the lower Zeekoe River upstream, towards the vleis

Benefits of proposed modification

• The proposed redevelopment and modification of the weirs will allow deeper and more flexible annual drawdowns of the Zeekoevlei and Rondevlei to facilitate sludge and reed clearing, and oxygenation of exposed sludge

• The new design will allow for a deeper drawdown level, which will assist significantly with the improvement of the water quality of the vleis
• The new Rondevlei weir will allow for a raised groundwater table in the southern portion of the nature reserve section

• It will allow for much more flexibility, and the movement of natural estuarine fish into the vleis

Call on residents and interested parties to register to comment on the proposal

The City has appointed an independent Environmental Practitioner to undertake the necessary Environmental Impact Assessment related to the proposed redevelopment of the weir complex located within the False Bay Nature Reserve.

The City is required to, in terms of the National Environmental Management Act (NEMA), obtain environmental authorisation from the National Department of Forestry, Fisheries and the Environment.

Part of this process is the opportunity for the public and interested parties to comment on the proposal:

• Interested parties are encouraged to register and comment on the draft basic assessment
• The relevant documents can be accessed at www.infinityenv.co.za/zeekoevleiweir
• Comments can be submitted electronically by sending an email to comments@infinityenv.co.za, remember to provide your name, contact details, and the interest you may have in this application
• For more information, send a WAPP message to 060 524 7676, or phone 021 834 1602
• The comment period closes on 26 July 2024

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. 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.

'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,' said the City's Deputy Mayor and Mayoral Committee Member for Spatial Planning and Environment, Alderman Eddie Andrews.

Caption: The proposed redevelopment of the weir complex at Rondevlei and Zeekoevlei, located in the False Bay Nature Reserve, is one of the City's interventions to improve the overall water quality and estuarine life.

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Published by:
City of Cape Town, Media Office