Benefits of sediment traps explained

Maitland farmer Craig McIntyre hosted a field day on his property on Monday last week....
Maitland farmer Craig McIntyre hosted a field day on his property on Monday last week. Environment Southland staff talked about the benefits of sediment traps. Karl Erikson (right) talks to those attending. PHOTO: SUPPLIED
When it comes to improving water quality on farm, no one size fits all situations, Maitland farmer Craig McIntyre says.

"Sediment traps are a useful alternative to establishing wetlands," he said.

Environment Southland land sustainability officers Karl Erikson and David Moate discussed the advantages of installing sediment traps compared with wetlands at a field day on Mr McIntyre’s property last week.

They also provided construction tips and discussed design features that Mr McIntyre has adopted on his farm.

About 35 people attended the day.

In addition to being the fifth generation of his family to farm the 266ha sheep and beef property he is also co-chairman of the Waikaka Stream Catchment Group (which includes Pukerau), which organised the event.

He runs about 2300 stock units, including 50 Friesian-Hereford calves.

The country is quite steep in places and has three streams running through gullies.

"I don’t have a lot of flat land, more just a series of ridges with quite steep faces. That provides a lot of challenges."

He feeds out baleage and swedes to his Romdale sheep and houses his calves in a wintering barn for four months.

He buys in the calves at 4 days old, and takes them through one winter before they are sent to slaughter at about 250kg.

Following advice from the Environment Southland land sustainability officers, he used a digger to create three sediment traps in a row, and a bund, in one stream, about six weeks ago.

The traps were designed to capture sediment, nitrates, phosphorous and E. coli and improve water quality.

They encourage the water to slow, pool and divert around the bund, giving the sediment the chance to settle.

"It is too early to measure what was captured, although I can see a bit of sediment build-up already.

"Once the grass is re-established, it will act as a filtering system, like a wetland."

He had intended to plant a wetland but was advised to use traps as they did not encroach on pasture, which he could not afford to lose.

"I want to emphasis the importance of using Environment Southland’s staff as they come out to the property and give free advice.

"What I have done may not suit everybody but the field day gave them a chance to think about what they can do on their place."

He wants to establish further traps on the other creeks on his property.

"It is not a problem we can fix overnight — it is a work in progress."

Mr Moate said sediment traps could be designed to fit into a specific site such as a drain, critical source area, or gullies.

"Niwa estimates a sediment trap size of 3% of the catchment area can capture 50% of sediment from water run-off.

"A number of well-positioned and designed sediment traps can be better than one larger one, as they can be cheaper and easier to maintain.

"The harvested sediment is often rich in nutrients and is valuable fertiliser that can be put back on to paddocks."

The land sustainability team could help with farm plans, and if sediment traps were recommended, they could also help to design them, he said.

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