New Zealand

Testing of pipe to flush lake to start next month

Testing of a water pipeline, which will eventually be used to help flush out Arrowtown’s Lake Hayes, should begin next month.

The line is designed to pipe water from the existing Arrow River irrigation scheme, near Macetown, to augment the water volume of Mill Creek, at Millbrook Resort.

From there, the water will be piped into Lake Hayes, near Arrowtown.

Otago Regional Council (ORC) operations general manager Dr Gavin Palmer said once the $1.1 million pipeline was commissioned, the new system would be used to begin flushing the lake.

The pipeline would access the colder and denser Arrow River water to displace and help flush out the phosphorus-laden water at the bottom of Lake Hayes during the summer and autumn periods, Dr Palmer said.

The lake has been suffering for decades from the build-up of lake-bed sedimentation and declining water quality, prompting the Wai Whakaata Strategy Group — comprising representatives from the ORC, Kai Tahu, the Queenstown Lakes District Council, Department of Conservation and Friends of Lake Hayes — to implement several restoration programmes to reverse the impacts of 70 years’ increased sediment runoff, which had accumulated in Lake Hayes and its connected waterways.

“The lake is now nutrient rich, especially in phosphorus, and is stratified, meaning there’s a lack of oxygen at the bottom of the lake,” Dr Palmer said.

“Algal blooms have become regular during warm summer months, which are often toxic.

“The lake’s poor health also causes pollution further downstream in Hayes Creek.

“This work marks a significant step forward in an important and effective collaboration as part of the Wai Whakaata Strategy Group,” he said.

Hayes Creek was also being targeted in the wider project.

The group had further work planned to improve the health of the creek, which drains water from Lake Hayes into the Kawarau River.

Sediment loads coming into Lake Hayes were also in focus.

Friends of Lake Hayes chairman Mike Hanff said central to that had been the creation and maintenance of sediment traps in the catchment and riparian planting, work which had been led by the Mana Tahuna Charitable Trust, thanks to a $4.45 million Jobs for Nature grant.

Over the past two years, sediment loads had reduced to about 500 tonnes, from almost 2000 tonnes in 2020.

Mana Tahuna has also removed exotic vegetation from the existing natural wetland at the northern end of the lake, and plans to plant more than 130,000 natives in the catchment.

Mana Tahuna environmental projects manager Sarah Mukai said they hoped the restored regionally significant wetland would support endemic, rare and threatened fauna, including the koaro and longfin eel and birds such as shovellers, Australian coots, marsh crake, bittern and Australasian crested grebes.


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