Wildlife flourishing after first phase of dredging

There is new life in the Lower Silvermine Wetlands following the first phase of a City dredging project there, says Friends of Silvermine Nature Area (FOSNA) committee member Martin Scholtz.

“From an ecological point of view, we have, in recent weeks, seen the African spoonbill, grey heron, and yellow-billed duck, as well as a pair of black-winged lapwings, with fledglings, and in this past week, the western leopard toad has started to be vocal at night and into the morning,” said Mr Scholtz.

Mayoral committee member for water and sanitation Zahid Badroodien said the first phase of dredging had started on Saturday April 1 and teams of workers had cleared reeds and invasive plants on the boundary of the waterway and the boundary of a coffer dam to expose gabions, headwalls and other stormwater infrastructure.

“They have also found and exposed pipes in the wetland which seem to be an irrigation system,” Mr Badroodien said.

Machines had then been used to dredge the area, removing silt, alien vegetation and reeds from 10m below the cable bridge and down towards the first pond, known as the Western Leopard Toad Pond, he said.

Clearing around infrastructure and the dredging had been finished by Friday June 23, which had left a week for clearing material that had been cut or dredged.

However, the following week, it had been found that the coffer dam was damaged, there was “extensive erosion” on one bank and cut reeds had floated into the Western Leopard Toad Pond, he said.

It had taken a further two weeks to attend to those issues with work ending on Monday July 31.

“The dredging activity has been done in such a way that all reeds within the deeper section of the waterways will drown and not sprout. The reeds that are growing back now are those on the banks and will be dealt with systematically, during non-breeding seasons,” he said.

The coffer dam wall had been temporarily reinforced with an earthen berm and sandbags, he said.

"Depending on how this structure performs, a more permanent structure will have to be put up in the future.“

The coffer dam is needed to stop raw sewage entering the wetland if load shedding knocks out the pump station.

“During load-shedding, when the pump station fails, sewage is discharged into the coffer dam. The coffer dam is meant to trap the sewage from flowing further out into the wetland. This gives the sewer department enough time to be alerted of the situation and bring a honey sucker to the site to suck out the sewage from the coffer dam.

“The coffer dam also has an overflow channel, which allows water to flow over and out into the wetland instead of damming up and flooding the walkways.”

Mr Badroodien urged residents to stick to the pathways provided.

“During the rainy periods, the department noticed the stepping-stone pathway at the Western Leopard Toad Pond becomes covered with water, so we would advise not to use that path until the stepping stones are above water again and dry to minimise the risk of slipping.

“Residents have been canoeing and children playing on the coffer dam walls, using the overflow channel as a slide. We urge residents to not use the wetland for these types of activities. It damages property and puts their safety at risk.”

Mr Scholtz said FOSNA had posted signs asking the public to refrain from walking on the coffer dam walls as they were narrow, temporary structures and downward pressure could destabilise them.

“We need to keep sewage out of the river system at all costs. We also ask the public to make sure their dogs don't bound into the water and onto the island structures, as these are ecologically fragile and habitats for various organisms - both plants and animals, including birds.”

Mr Scholtz said the second phase was expected to start early in 2024 - at the end of the western leopard toad breeding season.

“We have a responsibility to be active custodians of this remarkable resource in the heart of the city,” Mr Scholtz said.