RST Environmental Solutions Ltd

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Bio-Engineering

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Strong roots: Jason Read-Jones, of RST Environment Solutions, works on a willow brush wall on Masterton Castlepoint Road.

An ancient technique for shoring up unstable hillsides is being revived with the help of modern technology to save Wairarapa roads from landslides. This winter, willow brush walls have been popping up again around five locations on Masterton Castlepoint Road, thanks to RST Environmental Solutions and the Masterton District Council. Willow branches arranged in rows make brush walls to keep eroded dirt in place and
 

were commonly found across New Zealand in the 1940s to 1960s, but disappeared as wood and concrete retaining walls became popular.

RST Environmental Solutions managing director Robert Coulson said willow brush walls are cost effective and work just as well as other modern methods.

"Basically it's a reinforced earth wall. Firstly the damaged soil is removed, followed by willow branches placed into the land in a way so they cross over. Once in spring, their leaves come out and the branches grow roots which help to keep the land in place.

RST Environmental Solutions use plants and trees grown in their nursery to repair and improve land. They are likely to be the only company in New Zealand making willow brush walls, which they started in 2003, and have adapted the old technique using new technology.

"It looks straightforward but it's not that straightforward to design. There are certain plant arrangements and plant species. We've taken soil bio-engineering courses and use shrub willows to make sure they will not grow too tall."

Masterton District Council rural roading engineer Alec Birch said there were many reasons why the council decided to use willow brush walls.

"It's not only cost-effective, it's easy to maintain, it's not intrusive, and it becomes part of the landscape. It's a more environmentally friendly solution than concrete or metal. We saw it as a good win all-round."

The council plans on putting up more willow brush walls across Wairarapa over the coming years.

July 2009