Environment Southland staff have come up with a cunning plan to remove a troublesome gravel island in the Mataura River bed.
The island, which is about 220m long and 107m wide, is not far downstream from the bridge which crosses the river in Mataura.
Environment Southland catchment operation manager Randal Beal said the regional council did not have the resources to deal with the shingle.
‘‘We don’t have targeted rate funding to solve the problem.’’
Usually the shingle build-up in river beds was sold to contractors, but in this case after a contractor took some of the gravel it was not up to the standard required.
However, when drawing up plans to replace a Gore stop bank, staff realised they could use the gravel as fill.
‘‘We’re intending to take 30,000 cubic metres over two years.’’ Central Government would fund the project.
‘‘Without it we wouldn’t be able to do it.’’
While most of the island would be removed, 300mm above water level at normal river flow would need to remain.
The council had a two-year resource consent to remove the gravel.
The island had always been there but had grown ‘‘substantially’’ larger after the 2020 February flood.
It was upto 5m deep at some parts.
Large boulders which were the first to sink out of the river flow had settled at the upstream end of the island.
‘‘The smaller gravel builds up behind them.’’
The boulders also forced the river to flow sideways which led to erosion of the river bank alongside River St, Mr Beal said.
Once the boulders were removed or dearmoured ‘‘it would encourage the river to take more of the material away’’, he said.
It was intended the work would start in April.
Mataura Community Board chairwoman Nicky Coats said it was ‘‘about time’’ something was done about the shingle.
‘‘It’s fantastic that they are actually making progress towards getting it shifted.’’
The river had been slowly eroding the bank near River St, Mrs Coats said.
‘‘All those residents along the bank side — it’s got to be a relief for them as well.’’
Mataura Ward councillor Neville Phillips congratulated Environment Southland on its plans to remove the shingle.
A major source of concern for many Mataura residents had been the build up of shingle under the bridge, which they believed was holding up the flow of the river, Cr Phillips said.
When the shingle was gone it should increase the flow of the river, he said.
‘‘It’s a win-win not just for the local ratepayer but also for the downstream ones as well or upstream.
‘‘If you can speed the water out that’s what it’s all about.’’
It would be interesting to see what path the river would take when the shingle was removed, he said.