Cowra Council has reviewed a major report into the long-running West Cowra stormwater project, acknowledging both the scale of the work and the challenges of managing water flow in a built-up area of the town.
The project, which has been under discussion since before 2008, involves creating a system of retention basins, underground pipelines and overground topography to direct stormwater safely through industrial and residential zones.
The latest progress report highlights the need for further modelling and investigation, with councillors agreeing that careful planning is critical to ensure flood risks are reduced without creating downstream impacts.
Councillor Tony Horton described the report as a major milestone.
“This is a significant report, a significant amount of work to get us to this stage,” he said.
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“We certainly commend the director and his team for the effort they’ve gone to thus far.
“Effectively, what we’re being asked for is the opportunity to continue investigation, do some more research, test some theories and hypotheses, and before arriving at a final decision.
“There’s a range of different implications, not the least of which is, we’re trying to do this in a built-up area, some of which is light industrial, some of which is residential.
“Then, of course, you’ve got roads and other infrastructure in the way as well,” he said.
The flat terrain of West Cowra has always been a major obstacle.
With little natural slope, water moves slowly, often pooling in streets and backyards.
Councillor Peter Wright said the issue had been under discussion for quite a number of years - even before he was elected to the council in 2008.
“The biggest problem is it’s flat, and water only moves slowly in a flat area," he said.
“A lot of the streets are kerb and gutter, and so they have no control of where the water goes, which comes to the other road or the street or anything.
“It’s a big project."
The report recommends further work on a range of technical measures.
These included a detention basin in Waratah Street, a low-flow pipeline leading from the basin to Grenfell Road, adjustments to pipe design to reduce surcharging and backflow, and swales and overland flow paths to guide water safely.
Updated flood modelling shows that all proposed options would reduce flood levels during common storm events, but the option known as “1C” provides the greatest benefits in major floods.
The optimal pipeline diameter has been identified at 900mm, with smaller pipes increasing inundation and larger ones offering no further gains.
Councillor Wright suggested that expanding the planned basin capacity may also help.
“It has opened my eyes about making the retention basin bigger between Lyall Street and Waratah Street to increase the capacity there,” he said.
“You’ve got more time then for the water to make its way where you want it to go, to the Grenfell Road.
“Unfortunately, today, under EPA regulations, we’ve got to be able to handle water in a managed situation that doesn’t do damage to anyone else, and this is what staff are working towards,” Councillor Wright said.
While much of the discussion has focused on engineering, councillors stressed the need to remember the human impact of flooding.
Councillor Nikki Kiss said the project wasn’t just about pipes and basins.
“It’s an extensive study that’s being done,” she said.
“I think we can be confident that the investigations are thorough and very well informed.
“It is a big job and there is no easy fix, and there are a lot of properties.
“It’s not just the properties, we also need to consider the value and the lives that are impacted.
“Sometimes quite traumatically as well, I just want to acknowledge that we do understand, that we do feel that,” Cr Kiss said.
Cr Horton also pointed out the importance of research in avoiding mistakes other councils have made.
“I think that’s why the research is so important, so we do have some understanding about where the water goes,” he said.
“There’s been any number of councils that have come under some fairly negative feedback, where they’ve happily taken on land release and allowed building in areas they should not have.”
The estimated cost of a full detention basin is around $3.5 million plus contingencies, which raises questions about funding.
With a benefit-cost ratio of just 1.16, it is unlikely the project would qualify for state floodplain management grants.
However, councillors noted that intangible costs, such as disruption to businesses and the emotional toll on residents, are not captured in the financial modelling.
The council’s long-term financial plan already includes $340,398 for drainage improvements, but further funding will be required if the full scheme is adopted.
Despite the scale of the task, councillors were united in supporting the continuation of investigations.
Cr Wright summed up the need for persistence, saying, “hopefully we have something that can happen, because there’s bits of development happening all the time, that can increase the runoff from different places, I wish them all the best.”
Cr Horton also endorsed the staged approach being taken, saying, “at the moment, what it looks like is we’ll end up with a combination of a retention basin and then a combination of some underground piping, as well as overground use of the topography to move water from point A to point B”.
“It’s a significant piece of work thus far, and happy to support the continued investigation.”
The project is set to undergo further modelling and surveys in the months ahead, with council staff refining designs and exploring staging options to balance effectiveness, compliance and cost.
