Traps helping lake to turn a corner
by Guy Williams · Otago Daily Times Online NewsThe installation and regular clearing of sediment traps in Lake Hayes’ catchment is making a major contribution to restoring its health, the Friends of Lake Hayes say.
Among the dozen or so traps or ponds helping to reduce the amount of sediment flowing into the lake — especially during heavy rain — two are on the Dagg family’s farm.
Friends chairman Mike Hanff says the traps, which capture run-off into Mill Creek — the lake’s main tributary — from above the farm, including Mt Dewar, Coronet Peak and new cycle trails, are performing outstandingly.
Despite last year’s exceptionally wet spring, they captured record volumes of sediment during their third year of operation.
More than 1000 tonnes was removed in the past 12 months — two and a-half times more than the first year.
Hanff says that played a major role in helping keep total sediment inflows to the lake below 400 tonnes last year — compared to 2300 tonnes in 2020 — signifying a major milestone in the long-term recovery of the lake’s ecosystem.
That has been reflected, quite literally, in the "amazing" clarity of the lake this year, with no significant algal bloom occurring.
The improvement has prompted a lot of positive feedback from people who get out regularly on the lake, particularly rowers.
The gains made are the result of a collaborative effort by an alliance of organisations, the Wai Whakaata strategy group, in which "everyone’s singing off the same song sheet", he says.
Along with the Friends — which will mark its 20th anniversary later this year — it comprises Kai Tahu, Queenstown’s council, the Otago Regional Council and the Department of Conservation.
The group’s into its sixth year of implementing the Lake Hayes Vision study, a science-based plan of action for reversing the impacts of many decades of sediment runoff that has accumulated in the lake.
Hanff says thanks to systematic monitoring by the regional council, the group is capturing a "huge amount of data", which is giving its members a very good understanding of the impacts of a series of interventions since 2020.
The data is coming from the regional council’s data-collecting buoy in the lake, as well as its monthly sampling of Mill Creek and the lake’s outlet, Hayes Creek.
"So we’re able to calculate how much nutrient we lose out of the system every year.
"We’ve never been able to do that before — now we know what goes in, what goes out, and what’s going round and round in the lake."
Along with the installation and regular clearing of sediment traps — including by private landowners Millbrook and Ayrburn — the interventions overseen by Wai Whakaata include restoring the wetland at the lake’s northern end and large-scale riparian planting.
Vegetation’s also been cleared from Hayes Creek to alleviate flooding at its southern end.
Hanff says continuing improvement will come down to how well landowners manage the 12 to 20 million cubic metres of water that runs off the lake’s 42sq km catchment each year.