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Coogee Stormwater Solution on the Horizon

By Bruce Notley-Smith on November 5, 2018 in Other

Cars floating down Dolphin Street, Coogee back in May 2009, by Iva Leak

In 1862, Richard Heany recollected fishing and shooting as a young man, 30 years earlier, in the bay and the hills of Coogee. He recalled “a waterfall bounded by the cliff ” cascading into a brook below, one of several that fed a creek on the valley floor that meandered its way to the beach.

I’m not sure where exactly the waterfall Heany referred to was; my guess is where Albert and Pitt Streets now intersect. Or it may have been the waterfall that tumbled into Albi Place, or the one that spilled from Marcel Avenue into Pauling Avenue below.

These waterfalls, brooks and creeks, their magical sight and sound, are lost to us now, hidden from view, buried, incarcerated in concrete. But flow they still do, even in the driest weather, joining as one to cross the northern end of Coogee Beach into the sea.

The water quality of the Coogee creek has received much attention in recent times, and rightly so, as laboratory testing has shown it can contain a cocktail of nasties, even when the water is visibly clear. This problem should be easy to solve by simply stopping the contamination and diverting the creek’s beach outlet to another location.

This can be done, but there is nothing simple about it, as a collaborative working group consisting of Sydney Water, Randwick Council, some dedicated residents and I have learnt over the past 18 months, committed to solving this problem once and for all. How to deal with the dry weather base flow and the first flush of stormwater that arrives minutes after rainfall, both of which contain the most contaminants, has been the highest priority.

Options under investigation include diversion of these flows into the old Randwick Sewage Outfall in the cliff face past Dolphins Point, which remains as a relief valve to prevent sewage backing up should the system be overwhelmed. The better option is directing these flows into the Coogee Diversion, a trunkline below Beach Street completed in 1936 to carry Coogee’s sewage to Malabar. This would solve most of the problem most of the time, but both pipes have finite capacity.

Residents will remember the downpours of 1999 and 2009, but some will never forget the biggest in living memory. In October 1959, a storm cell twice the intensity of a one in 100 year event dropped 265 millimetres in just four hours. Hundreds of homes in the valley flooded and Coogee Oval sat below three metres of water.

By comparison, 1999 and 2009 saw 74 millimetres and 77 millimetres fall respectively, discharging 30,000 litres of water per second on to the beach, but still the waters backed up and the valley flooded, again.

If such an enormous volume of stormwater was directed and con- fined to the sewage system, we’d probably see geysers of raw sewerage spurting skyward, and with the flow so constricted Coogee would still flood.

So what can be done with such a huge volume of water if it’s not to be discharged into the ocean and can’t be disposed of via the sewage network?

Coogee’s stormwater has been captured, stored and reused for irrigation for many years, but its current capacity can’t store huge volumes. For many years I’ve been exploring options for expanding this capacity and to reduce the volume of stormwater reaching the beach so suddenly in the first place. It’s a risky business, though.

Any proposal to change the hydrology of a catchment requires expert studies and modelling, including challenges posed by sea level rises, to ensure that in solving one problem we don’t inadvertently create a bigger one somewhere else. Very soon we’ll have finished collecting this data and finally, after decades of inaction, we’ll
be able to remove contaminated stormwater from Coogee Beach.

Governments have to take the lead on issues such as this, but we can all play our part by preventing contaminants from reaching the stormwater system in the first place.

Bruce Notley-Smith is the State Member for Coogee. The views expressed here are his own, although we generally agree with them as well.