The next stage of the Washington Valley Infrastructure upgrade begins in August connecting the stormwater upgrade and mixing chamber completed in late 2023.

The $10 million project will require various closures of nearby roads spanning 12 months, including parts of St Vincent Street and the Haven roundabout.

Group Manager Infrastructure Alec Louverdis says Council staff have spent considerable time with local businesses developing a traffic management plan that minimises disruption.

“While we will try and make sure that road access is maintained, the road, at some point will need to close to enable certain works to be undertaken,” says Alec.

“We’re digging a massive 3m-deep hole in the road. The best way to protect our contractors and the public, while also completing the job efficiently, is with a closure. Having one side of the road open throughout the project would not be possible and would extend the project by months.

“The construction programme has been divided into several stages to balance the need for businesses to have access during the busiest trading time of the year and to allow the project to progress effectively.”

Nelson Mayor Nick Smith says this is essential underground work that, although disruptive, Council must invest in.

“The old box culvert’s concrete is badly deteriorating, compromising its structural integrity and it is currently being propped as a precautionary measure. There is a risk that if it is not replaced, at some time in the future, it will be at risk of collapse. Council’s Tenders Committee last week approved the contract being awarded to Tasman Civil.

“We ask for motorists’ tolerance over the next year as the intersection moves through different configurations to enable the existing culvert to be replaced by two large pipes. The benefit of this work is that it will increase the resilience of this area to flooding from a 1:50 to a 1:100-year event and provide improved security for this critical part of the city’s roading network.”

Alec says the renewal of the box culvert is also part of Council’s responsibilities as a good custodian of our city’s infrastructure.

“In this project, we will be replacing the box culvert with twin pipes that are 1800mm in diameter from the mixing chamber where stormwater from St Vincent Street joins stormwater from Washington Valley into Saltwater Creek.

“Investigations have found that the current culvert, which is 79 years old, is showing significant deterioration of the concrete and reinforcing. The time has come to replace this culvert to ensure it continues to protect the area from flooding as far as possible.”

The project will begin with the relocation of services including sewerage, water and power and construction of a temporary dam at Saltwater Creek to prevent tides from entering the worksite.

Contractors will then use a combination of pipes inserted into the existing culvert and road excavations to build an open trench. Sheet piling will maintain the integrity of the trench to keep the site safe for workers.

Once the new pipes have been laid, a new stormwater outlet will be built into Saltwater Creek. Finally, the temporary dam will be removed, trenches will be backfilled and the road reinstated.

The contractor, Tasman Civil, has undertaken extensive contingency planning for weather events that may affect the works to ensure any stormwater is managed.

While Council has contractors working in this area, it will take the opportunity to upgrade other surrounding infrastructure.

“There are 115-year-old cast iron water reticulation pipes and sewer pipes in need of an upgrade and both will be upgraded at the same time.” Alec says.

“The three waters upgrade in this area, along with other projects like Bridge to Better, beginning later this year, will increasingly future proof the city and allow for future development.”