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Spawning grounds protected in a first for Opihi River works

Published: 18/06/2012 3:32 p.m. 
A method of stopbank protection work never before used in the Opihi River bed is under way near Pleasant Point.

The Environment Canterbury work is vital to protect a section of stopbank from eroding after the river at the Saleyards Bridge began to cut into a heavily vegetated area between the channel and the stopbank behind it.

Normally a protective barrier of railway iron and cables would have been constructed from the riverside but this section of the Opihi is also an important spawning area for salmon and trout.

Paul Eddy, Environment Canterbury’s Southern Area river works supervisor, said the work in progress involves stabilizing the bank from the land side rather than the more conventional approach of temporarily diverting river flow and working from the riverbed itself.

“We’ve done this successfully in other rivers but this is a first for the Opihi. We always try to avoid doing this kind of work during spawning but this time it was unavoidable as if the river reached the stopbank itself the resulting damage would be very expensive to repair.”

Environment Canterbury has liaised with Central South Island Fish and Game officer Hamish Stevens about the work.

“This approach, a first for the Opihi is a really good option, especially when it is spawning time or we want to avoid damaging the redds (the gravel nests where fish lay their eggs) We’re very happy with the work – it’s an excellent example of how the two organisations can work together.”

The river works cover about a 300 metre stretch downstream of the bridge and also involves stopbank restoration, along with the removal of old man’s beard (Clematis vitalba) which had strangled and killed many of the trees in the area.

The larger trees close to the river’s edge are felled and whole trees are relocated to the river’s edge and anchored, where they act as a first line of defence against river erosion.

“This method is also very useful in places like this where there are water intakes nearby, in this case for the Timaru District and the Levels irrigation scheme along with river flow metering sites as we don’t disturb river flow,” Mr Eddy said.

Mr Eddy says the newly cleared area, which was visible from the Saleyards Bridge and had attracted some queries from the public, would be further tidied up over winter.

“Then we are planning a re-vegetation project, using native species, possibly involving schools in the area.”
The work will take about three weeks to complete and is being done by Environment Canterbury staff and sub-contractors.

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