Meridian has taken the opportunity to improve the fish habitat during relining work in the Mararoa River channel in Southland.
The work was necessary to address issues which have evolved in the 20 years since the Mararoa Channel was cut, to take water to the Manapouri Lake Control structure, explains James Holloway, Natural Resources Advisor for Meridian.
“Over those years, the channel has naturally widened and eroded its sides,” he says. “This meant the speed of the river flow had fallen, so shingle was not moving through the channel. The work we’ve done now has narrowed the channel and placed rip-rap – rock rubble used as armour – along the new banks to prevent erosion.”
Large boulders have been placed about every 50 metres along the rip-rap on both sides of the channel. On the left bank, the boulders are mainly still on dry land in the lower half of the channel and in shallow water in the upper half. On the right bank, they are in the river flow. The current will move gravel and create pockets of deeper water behind the boulders so fish can shelter there.
“In the two days after the work was completed, we could already see fish habitat holding pockets beginning to form,” says Mr Holloway.
“As the gravel moves, we expect the holding pockets to become more pronounced.
“There is still a lot of naturally deposited gravel in the lower channel. At the moment, we have an increased flow which will be moving some gravel, but I expect significant bed changes in the first significant flow.”
The channel work has taken about two months to complete, under the watchful eye of staff from DamWatch, an independent company specialising in dam safety advice and surveillance services.
Grassing, fencing and some native habitat development will also be undertaken along the Mararoa River channel next summer.
For more information contact:
Claire Shaw
Meridian External Relations Manager
021 370 677.