Water released towards Barwon River

WATER has been released from Lake Colac in a controlled fashion along nearby waterways and towards the Barwon River as part of a pre-existing scheme.

The Corangamite Catchment Management Authority (CMA) is the statutory manager of the Lough Calvert Drainage Scheme (LCDS), and says it started releases on July 21 at a conservative 6ML/day to enable the wetting of the channel, infrastructure to be tested and the gauges to be calibrated.

Outlet flows were gradually increased across the week, and kept below the levels that would trigger any concerns with salinity at Winchelsea.

Rain during the first week of operations of the LCDS caused inflows into Lake Colac to increase, so the Corangamite CMA increased releases to maintain lake levels while avoiding downstream impacts.

As a result, the level of the lake was successfully maintained across the weekend.

Corangamite CMA says it has a water quality monitoring plan in place, with several water quality gauges that measure salinity, flow, and water level at Lake Colac, along the drainage channel, and downstream along Birregurra Creek and the Barwon River.

“Earlier this month, gauges along the Barwon River at Kildean Lane and Winchelsea showed salinity was increasing, and the outlet flows were decreased accordingly,” the authority stated.

“The Corangamite CMA further reduced releases to mitigate this increase in salinity at Winchelsea, while managing for downstream erosion that could result from sudden changes in flows.”

Wormbete Creek and other waterways that flow into the Barwon River are contributing to high levels at Winchelsea.

Corangamite CMA noted site monitoring over the course of a week at Wormbete Creek showed levels above 5300 EC (electrical conductivity; a measure of salinity).

“Corangamite CMA is now continuing to monitor salinity in Wormbete Creek and other nearby waterways to understand how these streams contribute to salinity changes in the Barwon River at Winchelsea.

“The salinity level at 9am on Monday last week had reduced to 2269 EC at the Barwon River at Winchelsea.

“Corangamite CMA has been advised that this recent salinity spike should not be a concern for native fish species or domestic stock.

“The Corangamite CMA will continue to operate the scheme flexibly in response to changing conditions.

“The health of the Barwon River remains a priority in how the CMA manages the scheme.”