The erosion was believed to have occurred during a heavy rainfall event just before Covid Level 4 lockdown in the middle of last month.
Three authorities — the Otago Regional Council, the Queenstown Lakes District Council and the Department of Conservation — are working on the case, following a stormwater and sediment discharge through the Hikuwai Conservation Area into the Clutha River on August 16-17.
Two landowners are involved: Northlake developer Winton Property Ltd, which owns the land where the discharges originated; and Exclusive Developments Ltd, which owns the neighbouring Hikuwai subdivision.
The Queenstown Lakes District Council owns the stormwater discharge assets.
The system is a permitted activity under local authority rules.
The Northlake discharge travelled through Exclusive Developments land, into the reserve, down the Rockabilly Gully and into the river.
Residents used social media to report the erosion and warn about its potential dangers to people recreating in the reserve during lockdown.
Don McKinlay, Alan Cutler and Anna Simmonds complained to the councils. Mr McKinlay also complained the regional council did not physically inspect the site during lockdown.
Department of Conservation senior community ranger Nicole Sutton said Doc was working with the councils regarding track damage and erosion.
Doc’s letter of complaint to the ORC was a formal requirement, enabling the two local authorities to work with the landowners on the investigation.
‘‘We are not having a go at them,’’ she said.
Ms Sutton confirmed the Rockabilly Gully was not a public track, so no warnings were in place and no repairs were planned in the gully.
The mid-August washout had crossed two other public tracks — the Hikuwai Loop Track and the Outlet Track.
Orange cones have been placed on the Outlet Track, but there are none on the Hikuwai Loop Track.
ORC regulatory manager Richard Saunders said the discharge did not meet the threshold needed to ask staff to attend in person during Covid level 4. However, staff had called the developer’s earthworks contractor and given instructions about appropriate controls.
The contractor had repaired the sediment control assets and there would more follow-up, he said.
Queenstown Lakes District Council communications spokesman Sam White said two district council teams were working on the case.
A monitoring, enforcement and environmental team was doing compliance work at the Northlake site regarding the erosion and sediment controls.
A property and infrastructure team was working with Northlake to find a stormwater storage solution, Mr White said.
QLDC chief engineer Ulrich Glasner is leading the investigation over the next four to six weeks.
He will address options to improve discharge quantity and velocity throughout the network, review the suitability of the original stormwater system and look at how future connections to the network are managed.
Other actions would include talking with Doc about managing and mitigating the effects of the discharge, and an on-site meeting with ORC staff.
Ms Simmonds said she was heartened Mr Glasner was on the case but said she felt sceptical.
‘‘From the outside, these are the same words our community has heard on this topic for three years running, and yet the damage worsens every rain event,’’ she said.
Ms Simmonds said she would share any images and footage of future discharges with the council.
