Slowly But Steadily, Narrabeen Lagoon Is Going Bottom Up
Sydney Morning Herald
Thursday March 21, 1991
There were once three 16-foot yacht clubs which used Narrabeen Lagoon. It is now so shallow you can walk almost across its central basin.
The two-square-kilometre expanse of water lies just half an hour's drive north of the city - like a jewel between a strip of sandy coast and a reserve featuring sandstone cliffs and rugged vegetation.
But its surface hides an insidious illness which, left untreated, will surely kill it.
While other Sydney waterways have been fouled by sewage and industrial wastes, this lagoon is dying from the effects of an ever-expanding city.
As land in its vast catchment area has been cleared for housing in recent decades, sand and sediment have been filling up the lagoon, decreasing its depth by about 2 1/2 centimetres a year.
This has helped to wipe out much of the once-plentiful aquatic life and made some people predict that the lagoon will be dry within 10 years if nothing is done.
It has become hazardous for recreation too. The 16-footers have gone and last year a windsurfer broke his neck after his board hit a sandbank.
The problem is so serious that the Narrabeen Lagoon Committee, the largest environmental group in the area, is supporting a Warringah Shire Council proposal for radical environmental surgery - dredge the waterway's central basin.
While this appears at odds with environmental messages which urge us not to disturb natural ecosystems, Mr Phil Colman, a marine biologist and a founding member of the committee, stresses the urgency of the problem.
"Dredging might sound like drastic action but it's nowhere near as drastic as what will happen if it doesn't go ahead," he said.
In the lagoon's shallowest parts, wind-stirred sediment has turned the waters murky and inhibited the growth of grasses where aquatic life breed. The build-up of sandbars has also created intolerable conditions for many creatures. Sandbars inhibit tidal flushing, causing the salinity to vary wildly depending on the amount of rain.
Most aquatic animals can live in either seawater or freshwater but rarely in both.
Further, the shallow lagoon means that windsurfers who fall off their boards inevitably trample on worms and grasses that do exist, said Mr Colman.
The dredging would triple the depth of the central basin and the project could take as long as eight years. Included in the proposal is a $3.1 million processing plant where up to 200,000 tonnes of dredged sand a year would be mixed with other materials to make garden soil.
While an environmental impact statement has concluded that the plant will not significantly affect flora and fauna, Warringah Council is awaiting advice from the State Government.
The proposal is opposed by some residents who worry about increased truck traffic and noise and visual pollution.
While the debate continues, the lagoon gets shallower.
Mr Colman and many others feel the problem will become worse now that bushland near Beacon Hill has been cleared for a 34-hectare housing development.
Warringah Shire Council had rejected the development application but later approved it, despite vigorous local opposition, when it failed to get the Minister for Planning, Mr Hay, to support it in quashing the scheme.
The residents are not convinced that sediment basins to be installed as part of the development will prevent further siltation of the lagoon.
The Minister for the Environment, Mr Moore, has promised that total catchment management plans will be prepared for all lagoons on the northern peninsula, with Narrabeen to be "first cab off the rank".
© 1991 Sydney Morning Herald
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