Work to remediate an old landfill by the Ashburton River, and add flood protection, is making good progress.

The landfill was capped after it was closed in the 1990s and is now strictly managed to conditions set by Environment Canterbury.

The remediation work involves laying a special liner 600 metres along the southern slope of the landfill then securing it in place with the help of 14,000 cubic metres of shingle taken from the river about 10km upstream.

Concrete waste, recycled from the CBD renovation, will then be used to create 11 groynes at the base of the slope to act as flood protection.

Infrastructure Services and Open Spaces Group Manager Neil McCann said the shingle and groynes would then be covered with topsoil and the whole area beautified.

“It will look like a natural slope, planted with natives, and the groynes will act to deter floodwater if there is another major event in the Ashburton River. Even if the topsoil is washed away, the concrete groynes will redirect floodwater and protect the landfill from being exposed.”

In 2021, floodwaters came to the foot of the landfill.

“We know that floodwaters can reach that far, so that’s why this important project is under way. We’re working with Environment Canterbury, who look after the river and river banks, and with the contractor Fulton Hogan to get the job done and generally clean up the area.”

Some old poplars near the southern slope of the landfill have been removed and the river track used by mountainbikers and walkers relocated. The track previously went up over the landfill, known as Mt Ash.

The top of the landfill was also previously used as an informal dog exercise area, but this is now closed to the public.

Mr McCann said the whole project could cost close to $1 million but it was important the landfill was securely capped and protected for the future.

“Plus we have these other environmental wins. We are taking shingle from the north branch of the river, which will help better control floodwaters at vulnerable points, and we are also recycling concrete waste from the CBD revitalisation project to make the 11 groynes.

“Once the area is finally planted, it will be a very pleasant spot, and the biking and walking track can be relocated back to its original position.”

The project is expected to be carried out in phases over several years, depending on funds available.