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Dredging implemented to enhance biodiversity at Lower Silvermine wetlands

Posted on April 10, 2023

A dredging project at the Lower Silvermine wetlands is set to have immense benefits for biodiversity.

The project, which is expected to commence this week, will include manual reed clearing, mechanical clearing and opening of the river channel and Leopard Toad pond.

Alex Lansdowne, deputy chair of the mayoral advisory committee on water quality in wetlands and waterways, says natural processes and nutrient inflow from various run-off sources has resulted in excessive reed growth and the siltation of the wetlands over a 20 year period.

“I visited Fish Hoek with City of Cape Town officials, water quality advisory committee members, as well as local community stakeholders as we prepare to dredge the Lower Silvermine wetlands.

“City of Cape Town officials from Parks, Environment and Catchment have collaborated to develop a method statement to guide this operation with ecological sensitivities in mind.”

He further explained that natural siltation, run-off from a golf course upstream and minor sewage spills have resulted in the “eutrophication of the water” which has encouraged reed growth.

“The endangered Western Leopard Toad occurs here and the opening of the ponds and channels will create more breeding habitat for this threatened species.

“A variety of threatened fynbos plant species occur here including the Cape Flats Conebush (Leucadendron levisanus) which is classified as critically endangered on the red list of South African plants.”

The dredging project will be conducted under the exemptions granted through the stormwater maintenance management plan for the City of Cape Town with larger dredging projects planned for Milnerton Lagoon and Zeekoevlei.

“The clearing of the reed overgrowth will increase line of sight which will improve security and use for the local community and user groups.”

He added that all dredging work is expected to be completed by the end of the financial year and before the onset of winter rains.

According to the City, the area to be dredged is approximately 79 000 square metres, starting from Main Road until the major wooden footbridge that runs between Hilton Road and Carlton Road.

The City’s Catchment, Stormwater & River Management (CSRM) branch is investing approximately R7 million into the project.

Acting Mayco member for water and sanitation Siseko Mbandezi says over time, the area had become concentrated with both pollution and alien invasive vegetation.

As such it is crucial for dredging to take place.

“The Lower Silvermine wetlands has been used as a reference location as to what urban waterways should look like – an interface between the environment, people and well-being.

“Dredging work starts on the first week of April to reduce the risk of flooding for residents of the surrounding areas. This work is being done as part of ongoing river maintenance and programmes to improve inland water quality.

“The dredge will remove the excess silt and sludge from any sewage spills, wildfire erosion and stormwater runoff. This will then reset the water capacity of the ponds back to their original levels.

“The polluted top layer of sediment is being removed, leaving cleaner sand underneath.”

Phase one of the dredging process is expected to be completed by Friday 30 June.


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