In an industry-first, the Marlborough Roads Recovery team has turned to nature for inspiration.
The initiative sees old mussel shells used in road works to filter harmful runoff from entering the pristine water of the Marlborough Sounds.
Marlborough District Council Transport Recovery Advisor, Steve Murrin, says the idea to use mussel shells for filtration, rather than man-made alternatives, came about after the July 2021 weather event.
“The release of sediment to Marlborough’s rivers and the Marlborough Sounds is a critical issue, and the subject of several studies recently carried out by Marlborough District Council.”
Standard measures to control erosion on earthworks are usually sediment fencing, sediment socks, settlement ponds and stabilising planting at the end of a job.
Mr Murrin says the Marlborough Roads Team, with Leslie Brothers Contracting, thought using crushed mussel shells would be a better and more environmentally friendly alternative.
“They’re a natural product, readily available, and we know the shell make-up enables sediments to collect and stick to them.”
“Using a locally sourced, natural, low impact by-product from one of Marlborough’s key industries which would otherwise go to waste has huge environmental benefits,” Mr Murrin says.
Following the system’s rollout, a site visit was done by Marlborough Roads in February 2022 to check how the new approach had worked.
Mr Murrin says results showed a discharge quality of pH7.0 after water had travelled through two mussel shell pits.
“That’s pretty much near neutral, and the turbidity and clarity of the water also showed the new filtration process had improved the quality of stormwater before it entered waterways.”
The team is now trialling mobile versions of the system by placing mussel shells inside control socks for use on a range of works near waterways.
In recognition of this initiative the team was awarded the HEB Environment Award for The Protection of Fresh Water.
The Marlborough Roads Network Outcomes Contract (NOC) is a joint venture between Heb Construction and Fulton Hogan. It maintains the state highway network for Waka Kotahi NZ Transport Agency, and local roads for the Marlborough District Council.