The City of Cape Town reminds residents to comment on the proposed redevelopment and upgrading of the weirs at Zeekoevlei and Rondevlei in the False Bay Nature Reserve.
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The proposed redevelopment is to supplement other medium-term interventions, such as the dredging of Zeekoevlei, to improve the overall water quality of the Ramsar Convention site.
‘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,’ says the City.
The redesign of the weir complex entails the following:
- Modifying the existing Zeekoevlei weir to allow rapid lowering when needed. This includes lowering the channel apron to allow the drawdown, expansion of the weir, new mechanical sluice gates, and a gatehouse for maintenance and stabilisation gabions.
- Construction of a new Rondevlei weir with sluice gates further downstream to allow for improved management of Rondevlei’s water levels. Work includes a gatehouse for maintenance, a timber pedestrian bridge and retaining walls.
- Construction of a fish swimway between the new Rondevlei weir and modified Zeekoevlei weir to allow for the movement of fish into and from the vleis. Reintroducing native estuary fish into the lakes will help reduce excessive nutrients and improve the overall fish population along the nearby coastline.
- Alterations to the existing Rondevlei weir as well as building new sluice gates and a gatehouse for maintenance.
- Building a fish ladder at the Zeekoe culvert bridge to facilitate the movement of fish from the lower Zeekoe River upstream towards the vleis.
The benefits of these alterations and upgrades include deeper and more flexible lowering of water levels in Zeekoevlei and Rondevlei, which will help clear sludge and reeds, improve water quality, and encourage natural estuary fish to inhabit the lakes.
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Zeekoevlei and Rondevlei currently use penstock sluice gates to lower water levels, called the annual ‘drawdown’, typically done after the summer sailing season. This helps flush out nutrients and sediment and prepares the lakes to hold more water before winter to prevent nearby flooding.
However, manually operated weirs limit the depth of water which can be drawn down. The weir walls were built in the 1950s to 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,’ says Alderman Eddie Andrews, Cape Town’s Mayco member for spatial planning and environment.
‘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,’ he adds.
‘The installation of fish swimways 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.’
An independent environmental practitioner has been appointed to undertake the environmental impact assessment for the proposed projects.
- Interested parties are invited to register and comment on the draft basic assessment.
- To access the relevant documents, visit www.infinityenv.co.za.
- Comments can be submitted electronically or emailed to [email protected]. 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 will close on 26 July 2024.
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Picture: City of Cape Town