Three multimillion-dollar projects in the Shotover River delta are dovetailing neatly.
All resource consent applications have now been made for the projects, with the Otago Regional Council's three for flood mitigation work on the river now filed with Lakes Environmental, the regulatory arm of the Queenstown Lakes District Council.
The work will be done in conjunction with the Queenstown council's upgrading of the town's sewage-treatment ponds and the Queenstown Airport Corporation's runway extension safety area (resa) - all in the same area.
The co-operation between the three bodies was "unusual" but ultimately mutually beneficial through cost savings, QLDC chief executive Duncan Field said.
The flood mitigation work is expected to cost $1 million-$2 million, probably raised through a targeted rate in the ORC's long-term community council plan, ORC environmental engineering and natural hazards director Gavin Palmer said.
QLDC's Project Shotover is a $40 million move to more environmentally sound disposal of treated wastewater to land rather than into the river.
The $10 million resa is needed to ensure the airport remains viable as an international facility under Civil Aviation Authority rules.
The regional council plans to construct a temporary bailey bridge across the river for trucks to carry equipment and rocks while it extracts the shingle to build the training line on the eastern side of the Shotover-Kawarau confluence.
Dr Palmer described the 700m arm as a "floodbank" made of gravel with rock armouring.
It is predicted the wall will prevent floodwater from pushing a "slug" of silt into the Kawarau River on the eastern side which could intensify flood events in Queenstown by not allowing water to drain.
Dr Palmer said the measure would not prevent 1999 flood levels but would make sure they were not worse.
The gravel extraction will lower the river bed about 1.5m and also "encourage the river to return to its natural braided state" in the delta.
The three main willow-covered river islands in the delta are to be removed - records show the islands have expanded since the 1950s due to the invasive tree species and they could add to the flood problem if left.
"In the 1950s, the delta was much more open," Dr Palmer said.
Having all three projects done at the same time also means the gravel extracted by the regional council can be used in the resa and Project Shotover, which require about 900,000cu m and 350,000cu m respectively.
Because of past shingle build-up in the delta, the regional council was confident the large "one-off" extraction was ecologically sound.
Additionally, the work would secure a corridor for the New Zealand Transport Agency's long-term plans for a state highway route behind Frankton, Mr Field said.
