Retired geologist Andy Killick has again called for the dredging of Zandvlei, warning of an ecological disaster if this doesn’t happen.
The City of Cape Town concedes the vlei needs dredging but says it doesn’t have the money to do so after battling the drought.
The City also rejects claims made by Mr Killick that the area’s sewage system is in serious need of repair due to its age.
Zandvlei is the only breeding estuary in the False Bay and is home to a wide variety of fish including white steenbras, carp, leervis/garrick, tilapa, Cape stumpnose as well as mullets, elf, klipfish, goby and blaasop.
The white steenbras, Cape stumpnose and garrick are all on the International Union for Conservation of Nature (ICUN) red list as endangered species.
According to Mr Killick, the accumulation of unnatural amounts of sediment in Zandvlei is a serious threat to it’s functioning, both as a recreational attraction and a healthy fish nursery, particularly near the “the Narrows”, the mouth of the vlei.
A sewage line protected by a rubble weir at the mouth, he said, hampered the removal of sediment; the mouth itself was constrained and couldn’t meander to deposit or erode sediment naturally, and accumulating rubbish was tightening the chokehold.
Felicity Purchase, mayoral committee member for transport and urban development, said dredging had been done before, but it needed a budget and specialised equipment.
“The amount of sediment which can be flushed out of the vlei is, however, limited by the rubble weir at the estuary mouth. This rubble weir is in place to protect a sewer pipeline which crosses the estuary mouth underwater. While this sewer line crosses the estuary mouth, natural estuary functioning is not possible,” Ms Purchase said.
However, she said the need to dredge Zandvlei was part of the estuary-management plan and the City recognised the vlei’s importance.
“The City’s budget and staff allocation to the estuary and surrounding recreational area is a reflection of this,” Ms Purchase said.
Mr Killick said pesticides in run-off from Constantia vineyards could also be contaminating the vlei.
Ms Purchase said the Department of Agriculture, Forestry and Fisheries (DAFF) regulated the use of pesticides on Constantia farmland.
“The City supports the initiatives of some wine farms to reduce the use of pesticides and use ‘green’ farming methods. Where pesticides have known to be a problem, the City refers the matter to DAFF as the competent authority,” she said.
Litter entered Zandvlei not only from four river sources but was also blown in by the wind, Ms Purchase said. Catch nets in the canals, clean-ups in the streets and canals and at picnic spots and public anti-litter drives, were just some of the ways the City tackled the problem, she said.
Xanthea Limberg, mayoral committee member for informal settlements, water and waste services and energy, said most sewer pipes surrounding Zandvlei did not need repair or replacement.
“Only some sections are in need of attention, and these are being replaced,”she said.
An incident earlier this year, (“Collapsed main contaminates stormwater system,” False Bay Echo, April 26) when effluent streamed into the estuary after an underground bulk sewage line in Overcome Heights collapsed, had been due to a corroded concrete pipe, she said.
“This corrosion is unique to concrete pipes, which are not in mainstream use in the Zandvlei area,” she said.