Friday 10 November 2023
Numerous work programmes are underway cleaning up Lake Hayes in Central Otago, which has been suffering for decades from the build-up of lake-bed sedimentation and declining water quality.
The partners in the Wai Whakaata Strategy Group are Otago Regional Council, Kāi Tahu representatives, Queenstown Lakes District Council, Department of Conservation, and Friends of Lake Hayes.
ORC's General Manager Operations Dr Gavin Palmer says the Wai Whakaata Strategy group is implementing several water restoration programmes to improve the The partners in the Wai Whakaata Strategy Group are Otago Regional Council, Kāi Tahu representatives, Queenstown Lakes District Council, Department of Conservation, and Friends of Lake Hayes.
ORC's General Manager Operations Dr Gavin Palmer says the Wai Whakaata Strategy group is implementing several water restoration programmes to improve the Lake Hayes catchment ecosystem, water quality overall, and native biodiversity.
"Together, the Wai Whakaata/Lake Hayes Strategy group has a series of programmes and policies aimed at reducing the impact of 70 years' of increased sediment run off which has 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," says Dr Palmer.
"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."
Wai Whakaata Chair Prof Brian Boyle says bringing together the Strategy Group has allowed government/local government organisations, iwi, and community groups to come together to share knowledge and discuss solutions in a constructive and positive environment.
"It is wonderful to see the effective coordination of programmes made possible by ORC targeted rates, the New Zealand government's Jobs for Nature fund and local philanthropists towards improving the health of the lake" Professor Boyle said.
Months of work constructing a water pipeline which aims to help improve the water quality in Lake Hayes is coming to fruition, with testing of the works planned to begin in the next month.
The works are 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 irrigation water will be piped into Lake Hayes.
Dr Gavin Palmer says the pipeline connection to the Arrow River irrigation is located about 4 kilometres upstream from where Mill Creek enters Lake Hayes, on Millbrook Resort.
"When ORC commissions these works, it is really the first step of testing and ensuring everything is working as it should," he says.
Dr Palmer says the pipeline will work by accessing the colder and denser Arrow River water to displace and help flush out the phosphorus-laden water in the bottom of Lake Hayes during summer and autumn periods.
In recent months the last of the pipe and manholes have been constructed and buried underground/ A flowmeter and valve actuator will shortly be installed.
"This work marks a significant step forward in an important and effective collaboration as part of the Wai Whakaata Strategy Group. We are hugely grateful for the work these groups have put into this project over many years – we could not have got this far without them."
The budget for the Mill Creek pipeline project is $1.1 million, partly funded by targeted rates. The next phase of the project, planned to commence one commissioning is complete, will involve using the new system to begin flushing the lake, with monitoring at each step of the process to ensure the flushing goes to plan.
Another aspect is improving the health of out-flowing Hayes Creek from the lake to remove the overgrowth of vegetation and silt, and to widen and deepen the creek in specific places. This will assist with the function of the existing culvert which is located under State Highway 6 and will allow for more efficient water flow between Lake Hayes and Hayes Creek.
Hayes Creek will also receive some slope stabilisation and planting as required.
There is further work planned to improve the health of Hayes Creek, which drains water from Lake Hayes into the Kawarau River. This involves earthworks to remove overgrown vegetation and silt, widen and deepen the creek in specific places and also undertake slope stabilisation measures and planting.
A proposal to upgrade the existing out-flow culvert which empties Lake Hayes is on hold because the works on Hayes Creek is most likely to be more effective and cost much less.
The Chair of Friends of Lake Hayes group, Mike Hanff, says the work ultimately targets sediment and nutrient loads coming into the lake to improve the quality of the lake.
"Central to this has been the creation and maintenance of sediment traps in the catchment, as well as riparian planting," he says.
Sediment traps are a dug out hollow or a built-up bund, ideally in non-flowing sections of a watercourse, which collects sediment-laden water and slows the water long enough for the sediment to settle; to be removed later.
Sediment loads around Lake Hayes during the past two years have reduced to about 500 tonnes, from a high of almost 2000 tonnes in 2020, Mr Hanff says.
Additionally, the Mana Tāhuna Charitable Trust has undertaken extensive work, having been granted $4.45 million from the Government's Jobs for Nature programme.
The trust recently removed exotic vegetation, mainly crack willow trees, from the existing natural wetland at the lake's northern end and plans to plant more than 130,000 native plants within the catchment, says Mana Tāhuna Charitable Trust Environmental Projects Manager Sarah Mukai.
"Willow trees channel the water and restrict its flow through the narrow outlet of Mill Creek, into the lake. Their removal will improve the native biodiversity and support water flow within Mill Creek and into the lake."
"The lake and its wetlands also provide habitat for indigenous species, including fish, birds, and invertebrates. A vegetated margin surrounds most of the lake, with this restored regionally significant wetland hoping to support endemic, rare, or threatened fauna including the koaro and longfin eel, and birds such as shovelers, Australian coots, marsh crake, bittern and Australasian crested grebes," she says.
Environmental monitoring and data are the key to measuring the success of this work in the long term, says Dr Palmer.
"To track the state of the lake, ORC is collecting data from an environmental monitoring buoy, which is about 30m below the lake surface in the north-east section of the lake. This data includes temperature, oxygen levels, and the current stratification state."
Lake Hayes is also part of the ORC's summer recreational monitoring programme where staff test the water every week to check that it is safe for recreational use, Dr Palmer says.
Over time there have been changes to landuse practices within the catchment which have contributed to the current state of Lake Hayes. The water quality in Lake Hayes has been impacted historically by erosion and sediment discharges, application of fertiliser to the surrounding catchment which has run into the waterways and industrial discharges
There has also been historical clearance and drainage of wetland areas and artificial channelisation of the waterways. and increasingly there have been warmers summers and severe weather events due to climate change, says Dr Palmer.
"ORC's remediation work programme is part of its long-term plan to support the enhancement of Lake Hayes and the ecosystems it supports, as well as providing enhanced recreation opportunities for lake users," says Dr Palmer.
Lake Hayes catchment ecosystem, water quality overall, and native biodiversity.
"Together, the Wai Whakaata/Lake Hayes Strategy group has a series of programmes and policies aimed at reducing the impact of 70 years' of increased sediment run off which has 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," says Dr Palmer.
"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."
Wai Whakaata Chair Prof Brian Boyle says bringing together the Strategy Group has allowed government/local government organisations, iwi, and community groups to come together to share knowledge and discuss solutions in a constructive and positive environment.
"It is wonderful to see the effective coordination of programmes made possible by ORC targeted rates, the New Zealand government's Jobs for Nature fund and local philanthropists towards improving the health of the lake" Professor Boyle said.