Karen Trebilcock

Trial sediment traps on farms in the Pomahaka catchment seem to be working with positive signs the water quality in the Otago river is slowly improving.

Pomahaka Water Care Group project co-ordinator Lloyd McCall said farmers were building different types of sediment traps and planting out riparian strips.

“We’re water testing in these areas regularly and the results are encouraging,” McCall said.

The catchment is crisscrossed with tile drains, put in last century and some of the current landowners have no idea where they are.

The tiles efficiently drain the rolling country but just as efficiently also transport E.coli, sediment, nitrogen and phosphorus into the creeks which flow into the Pomahaka.

So much so that in 2013 the Otago Regional Council identified the river as one of the most degraded in the province.

The following year, with input from New Zealand Landcare Trust and the council, the Pomahaka Water Care Group was formed and now 160 farmers, of the 350 in the area, are paid-up members.

The 2020sq km catchment has 3500km to 4500km of waterways, depending on what you class a waterway, McCall said.

A tributary of the Clutha River, it’s known for its fishing and is also home to the Pomahaka Galaxias, native fish which have the status of threatened – similar to the blue duck and kiwi.

Farms include sheep, beef, deer and cropping and about 110 are dairy farms.

Since the group started, regular water testing is showing the health of the river improving. McCall, who used to be chair of the group before he took on a paid role, is excited by what has been achieved so far but especially how the community has become engaged in their river.

“I’m really proud of the people living in the Pomahaka.

“Small changes will lead to big changes and that’s when we are really going to see results.”

Getting the community to feel the pride is important for McCall and the water group as well.

Signs on major roads show people they are entering the water group’s area and declare “Your water – your future”.

“It’s part of the whole community buy-in. This is just not about farmers, it’s about everyone.”

McCall, a former sheep farmer, banker and farm accountant has a son and daughter-in-law sharefarming in the catchment so his role in the group is more than an employee. Just like everyone else living there he has a stake in cleaning up the river and making sure it stays clean.

What has really got him buzzing is an experimental sediment trap by Waikoikoi Flat Road near Tapanui.

Set up 18 months ago, it cost about $1000 to create and takes up less than a quarter of hectare of land, encircled by a 100m coil of netting fencing it off.

Water from tile drains flows into a deep pool with the sediment falling to the bottom. After that the water meanders along a short open ditch through plantings of flax and carex.

“Putting in several wiggles into the open ditch has really made the difference,” McCall said.

“For me, this is a game-changer.”

The water entering the area had been “off the scale” for E.coli but now water testing every two weeks by the regional council is showing a 90% reduction.

“A digger has so far taken two cubic metres of sediment out of the pond and the nitrogen and sediment levels are 40% lower.

The farmer thinks the tile drains pick up a spring as the water never stops flowing, even in the summer dry.

Also impressive are a series of ponds a dairy farmer has built near Waipahi between Clinton and Gore.

A low spot in a paddock near the dairy has always been too wet to graze properly and now the water flows through two ponds and then trickles out into an area of ungrazed rushes.

“Four tile drains were opened up and that’s where the water is coming from and the two-pond system captures the sediment and then the rushes and long grass do the rest,” McCall said.

“When the farmer first opened up the tile drains and took water samples it wasn’t good.

“You can’t fix a problem on the farm if you don’t know it’s there.

“We certainly know there is a problem in the river but we need to know where that water is coming from and clean it up before it gets in the river and that’s why it’s important to test the tile drains.”

Just down the road is a major planting project on a dairy farm with thousands of carex, flaxes and native trees going in supported by the water care group which is seeking funding for the project.

Again the water has been controlled into ponds and what was once called Goose Flat by the farm owner will hopefully one day be a water-cleaning wetland.

The water from the paddock flows into Webb Creek which then goes into the Waipahi River before entering the Pomahaka.

Some of the plants come from the water care group’s own nursery.

About 15,000 plants this year will be ready for projects, grown from seed and cuttings collected locally and tended to with the help of volunteers including kindergarten and school children.

Also part of the catchment group is a best practice response team of about 15 farmers. People can ring a phone number on the website if they see worrying land management and the members of the response team will visit the farm.

“It’s not about telling farmers what to do but about talking with them about the different options,” McCall said.

The hotline, which has been in place since May, has so far had about six calls and was working well, he said.

“We have to give people time to change. We’ve been told to farm this way and we’ve done that for so long and now we’ve been told to do it a different way.

“Farmers have got to see the value in it and why it’s better for the rivers.”

  • This article was first published in NZ Dairy Exporter, October 2019