Crushed mussel shells are being used in the Marlborough Sounds to prevent the material from landslides and construction polluting the pristine environment.
And the industry-first innovation was thought up by some locals in a very Kiwi way.
Leslie Brothers Contracting’s Phil Leslie said he heard from another local they were being used in the mines to manage pH levels.
“We were all sitting around having a beer one night and we said why don’t we give it a go. We’ve got nothing to lose.”
The Marlborough Sounds was hit by a large storm in 2021 and an even bigger one last year with devastating impacts on the roading network.
It’s estimated up to 1600 slips have come down and 200,000 cubic metres worth of material like dirt and rock have been disposed of – that’s about 80 Olympic sized swimming pools.
One of the challenges has been figuring out how and where to dispose of the material from the landslides and ongoing construction work.
Marlborough District Council’s transport recovery advisor Steve Murrin said they knew they had to be sensitive about how they disposed of the material. There are a handful of sites around the Marlborough Sounds that are being used.
“The way we’re doing it here is we’re marrying it in to the natural landscape…it’ll will be reverted to a nice pasture that the farmer will be able to use.”
“We’re only 300, 400 metres away from the sea here so we don’t have much room to work in. But we need to make sure that the water we’re discharging from the Sounds is the best water we can make it.”
When it rains some runoff from the sites could wash into the sea if it isn’t treated. While they usually use plastic sediment fences, the crushed mussel shells are working just as well.
There’s a series of four ponds downhill from the site with the shells filtering the water before it reaches the ocean.
Marlborough Roads’ Simon Smith said testing has shown good results but it’s also clear to the naked eye.
“When you hold two samples from the first catch pond and then the discharge next to each other it’s like looking at you know a chocolate milkshake and drinking water. It’s completely different.”
The project is the joint work of Marlborough Roads, Heb Construction and Leslie Brothers Contracting. They’ve also come up with a mobile version which will soon be rolled out at construction sites across the Marlborough Sounds.