Water

Pulses can limit harm

By Country News

Goulburn Broken Catchment Management Authority is recommending that planned summer water transfers are delivered as a series of pulses through the lower Goulburn River, rather than a steady flow, to help minimise damage to the river bank.

From December 14 flow in the lower Goulburn River (below Goulburn Weir) is expected to increase from the recommended 800Ml/day to up to 3000Ml/day to meet downstream (Murray River) water demands from towns, irrigators and the environment. Higher flows of between 2000Ml/day and 3000Ml/day could continue well in to 2019 if conditions remain dry and demand remains high.

‘‘We share the community’s concern that high unseasonal flows could damage the bank-stabilising vegetation that had started to re-establish and spread thanks to previous environmental flows,’’ Goulburn Broken CMA chief executive officer Chris Norman said.

Since river regulation, winter and spring flows have been captured and stored in dams such as Eildon and then released during peak demand periods in the warmer months.

This means rivers now generally flow higher in summer than they would have under natural conditions.

Water for the environment is generally delivered at variable rates between autumn and spring to mimic the more natural flows that would have occurred before flows were captured, stored and diverted via dams, weirs and channels.

Modelling shows that this year, if the water hadn’t been stored and diverted, Goulburn River flows of more than 20000Ml/day would have occurred in August and September after rain in parts of the upper catchment.

‘‘After seeing the impacts of the high unseasonal flows delivered in summer and early autumn this year, we have worked closely with river operators to ensure that whenever possible, future water transfers in summer and early autumn are delivered as a series of pulses, as this is better for river bank health than a steady flow,’’ Mr Norman said.

He said Goulburn Broken CMA would continue to monitor bank vegetation at various sites along the lower Goulburn River to measure the impacts of high unseasonal flows.