Residents to remain flood safe as contract awarded for key outlet

Houn Contractors was this week awarded a $261,080 contract to Huon Contractors to fill in a large sinkhole and repair flood gate 15A, at the pump station located beside the ARCC centre on Tarcutta Street.

Council's director of strategy and projects Phil McMurray said council identified damage to the pump station at that location around December 2022, in the wake of ongoing floods.

That damage led to the formation of a considerably-sized sinkhole adjacent to the Wiradjuri Walking Track, and while the pump has not been in use, that cavity has continued to grow, with Mr McMurray unsure exactly how far the damage extends.

"We noticed a problem and had major landfall situations open up around our pumping station and from that point on we barricaded it off to make it safe for the public," he said.

"We've been investigating what went wrong and have worked out what that was.

"We now have a solution to that and have engaged contractors to ensure it's rectified, won't happen again and the levee is secured back up the way it needs to be."

Mr McMurray said the issue arose after the grouting on the pipe at the bottom of a pumping well, located eight metres below the surface, failed.

"The pump above that goes eight litres per second and when the gates close and the river is up, this is the only solution for pumping all the storm water at the lower parts of Wagga so we don't have over floor flooding," he said.

Mr McMurray said the powerful force of the water "caused damage to the structural integrity of the pipes."

The council then engaged Stantec to develop a solution to the problem.

"It's a two-part solution. The first part is how do we stop it happening again," Mr McMurray said.

That will be done with the installation of a plate with a spigot or plug.

"The [spigot] goes inside [the plate] and stops the water hitting the grout area," he said.

That "ultimate solution" has been ordered at a cost of approximately $20,000.

Mr McMurray said council has now reached the second part of its solution, which will involve digging down below the pump station to identify the extent of the void created after the faulty seal saw earth sucked into the river.

He said after going out to tender, the council received just one quote to undertake the "quite... complex" task.

The works will involve digging up the existing site and carting in more earth to fill the sinkhole.

Mr McMurray said traffic controls will need to be put in place as the works are constructed on the embankment and hopes the project could be completed in two months time.

However, he said until workers open up the hole, it remains unknown just how big the cavity is beneath the surface.

He said as such, it is unknown whether the issue has affected the integrity of the levee too, but that will become clear as works get underway.

Mr McMurray said the decision to approve the tender had to go to councillors as it sat over the tender threshold of $250,000.

But he is confident Huon Contractors will do a good job and said it is important to get the project out of the way now, especially with the potential for a return to flood-prone conditions if a La Nina is forecast later this year.

"We have the perfect opportunity now to get in and do the work before the potential flood risk later on in the year," he said.