Dredging under way at wetlands

Dredging work is under way at the Lower Silvermine Wetlands and is expected to be completed before winter.

Planned dredging of approximately 79 000 square metres on the Lower Silvermine Wetlands (LSW) is under way in an effort to reduce flood risks for residents in the surrounding areas, and boost biodiversity.

The City’s Catchment, Stormwater and River Management (CSRM) branch is investing approximately R7 million into the project, which will start from Main Road until the major wooden footbridge that runs between Hilton and Carlton roads.

Phase 1 started on Saturday April 1, and is expected to be completed by Friday June 30.

“The dredge of the LSW wetlands is critically needed to remove the expansive reed beds and create open water for the endangered western leopard as well as bird and fish species that prefer open water habitats,” mayoral committee member for water and sanitation, Zahid Badroodien, told the Echo.

He said the dredging will also remove excess silt and sludge from endless sewage spills, wildfire erosion and stormwater run-off which will then reset the water capacity of the ponds back to their original levels.

“Siltation causes can be natural (stormwater run-off) or man-made (disturbances of landscape caused by agriculture or urbanisation). If not mitigated properly, siltation negatively impacts ecosystems in many ways,” he said.

During the dredging process, excavators inside the river remove accumulated sediment and move the dredged material towards the river banks

The material is then lifted by a long boom excavator to stockpile it 10m away from the banks and allow for dewatering for three weeks or more before the material can be carted away to the relevant disposal site, explains Mr Badroodien.

According to him, there is no option to burn the reed beds to reduce their expansion along the river embankments since they are nearby residential properties and infrastructure such as electrical pipes, bridges, and board walks.

“A controlled burn would also not solve the problems caused by the siltation nor address the issue of the reduced water capacity of the ponds,” he said.

The LSW have been awarded conservation status with provincial conservation body CapeNature as the wetlands are essential for the breeding period of the western leopard toad.

According to Mr Badroodien, toads will travel 2.5km to LSW’s breeding ponds to lay their eggs.

“Once the toads leave the ponds after laying the eggs, the eggs in the pond hatch and the tadpoles feed on algae at the bottom. The pond must be fairly open so that light can reach the bottom of the pond so that the algae can photosynthesise,” he explained.

Currently, Mr Badroodien says, the extensive reed beds shade the water which negatively impacts the breeding habitat of the western leopard toads.

Friends of Silvermine Nature Area (FOSNA) chairman, Dave Balfour, says they welcome the commitment of the City to commence with the dredging of the LSW.

“The dredging serves as a practical way for the city to both reduce the impact of possible flooding on existing infrastructure such as roads and houses, while at the same time managing the wetland habitat for local biodiversity,” he said.

Mr Balfour added: “We are encouraged by the collaborative engagements between civil society and the authorities to achieve a better natural environment for all citizens and hope that it is a model that can be expanded to other areas.”