Border dyke system improving soil health at Masterton waste water plant

Grass crops are grown on the border strip paddocks.
PIERS FULLER/FAIRFAX NZ

Grass crops are grown on the border strip paddocks.

Branded as "dinosaur technology", fears about the effectiveness of Masterton's $50 million waste water scheme's irrigation system have  been proven unfounded.

Before the installation of  the border dyke scheme there was heated debate as to whether the method would destroy the soil quality.

Now fully functional, monitoring has shown that the 72 hectares of ground is doing a good job at absorbing the waste water and the soil quality is improving, after it was extensively excavated for border dykes.

Large valves open to flood the strips.
PIERS FULLER/FAIRFAX NZ

Large valves open to flood the strips.

In the years leading up to the commissioning of the scheme,  different methods of irrigation were considered by Masterton District Council to dispose of its waste water, and the border dyke was chosen because it has the capacity to take the greatest volumes.

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In 2010 before the works began neighbouring farmers, Sustainable Wairarapa and local iwi questioned the council's choice.

Masterton Waste Water Treatment Plant from the air.
supplied

Masterton Waste Water Treatment Plant from the air.

 Stuart Forbes, a  farmer who sold some land to council for the scheme,  said border dykes could be a costly mistake with "disastrous consequences" for the soil.

Despite those concerns the border dyke method was chosen ahead of more modern methods such as centre pivot irrigators that are a favourite distribution mechanism for dairy and crop farmers. 

Creating border dykes involved dividing the land into strips and grading them until they were level. Large valves open at one end releasing thousands of litres of water onto the land and flooding each strip one by one. Grass crops are planted on these strips which are harvested for baleage.

Border dyke irrigation system at work at Homebush.
supplied

Border dyke irrigation system at work at Homebush.

Disposal to land is a key feature of the scheme which allows the council to conform to its resource consent to only discharge treated waste water to the river at times of high flow when it has the least effect of the ecosystem.

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MDC assets and operations manager David Hopman said the commissioning of the scheme had not been without its challenges but they were pleased with the way it was  functioning.

Environmental monitoring of key indicators by Landcare New Zealand show that soil bulk density and the carbon-nitrogen ratio are steadily improving

The operators are concentrating on improving soil health by re-establishing the organic structure so that it can do the best possible job of filtering the waste water and absorbing nutrients.

The council now has a live update on its website so that people can find out when it is discharging to the river.

 - Stuff

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