River deepened as dredging project winds-up

A $4.3 million project to remove 800,000 cubic metres of silt from the Mahurangi River will draw to a close later this month.

An estimated 15 barge loads are still to be removed from an area near the boat ramp in Baxter Street and then the fill site in Hepburn Creek Road will be levelled and covered with topsoil, ready to be re-planted with grass.

In total, an 8.2 kilometre stretch of the river has been dredged to a low tide depth of 1.5-metres.

Mahurangi River Restoration Trust trustee Hugh Gladwell says prior to dredging there were parts of the river that were ankle deep at low tide.

“While the river will never be sparkling blue, the objective has always been to make it swimmable again,” he says.

“This should be achievable when the sewerage works closes.”

Watercare is promising that when a new $123 million wastewater treatment plant at Snells Beach opens in 2024, the existing Warkworth wastewater treatment plant on the river will be decommissioned. It says this will put an end to the treated discharges into the river, as well as far fewer wet-weather overflows.

The dredging project has been carried out in stages over three years, as funds permitted. The biggest boost came when the Ministry for the Environment awarded the project $4.06 million under its Jobs for Nature initiative. At the same time, it gave Auckland Council $5 million for riparian planting and fencing to prevent sediment building up in the river again.

The Rodney Local Board contributed $250,000 specifically to dredge the town basin and the trust raised a similar amount through grants and donations. A large component of the support came in the form of in-kind help from local businesses, service clubs and individuals.

“The fill site alone saved us millions of dollars,” Gladwell says. “If we’d had to dump at sea it would have been a $15 million project. We have landowners Mac and Tania Cookson to thank for that. Hutchinson Engineering has also contributed hugely in time and expertise, as well as many other professionals.”
Gladwell says the Warkworth-based scow Jane Gifford will be able to sail across almost all tides in future.

While the trust accepts that there will be a need for maintenance dredging, it may be focused on keeping the town basin clear of silt.

“Hopefully, if we can do this, along with the benefits of the riparian planting, silt loading along the rest of the river will be minimised.”