River managers: Health mission far from over

Annual and regular fresh water flows remain the critical ingredient for nursing sick northern reaches of the Wimmera River back to health. Despite a significant flow reaching Jeparit and having an immediate impact on water quality, vast stretches of the waterway remain incapable of supporting complex aquatic eco-systems.

That’s the general assessment of Wimmera catchment leaders studying the impact of the flow on the river environment.

By early October, more than 6500 megalitres of water from the river’s south-east origins had made their way along more than 320 kilometres. Along the way, the water had an immediate impact, filling dry riverbeds and in some circumstances leading to 12-fold reductions in salinity.

Monitors recorded some of the most dramatic change in readings at Ellis Crossing upstream of Dimboola. Here saline pools, some previously measuring more than 34,500 µS/cm or almost two thirds the salinity of seawater, dropped to 672 µS/cm. The new readings were well within state environmental water-quality objectives for the river.

Boards went back in at Jeparit weir, where salinity levels have at the height of summer reached more than 20,000 µS/cm, on Tuesday (October 13) after the flow flushed a significant amount of poor-quality water into Lake Hindmarsh.
At a Jeparit museum site salinity levels fell from 61,500 µS/cm to 9050 µS/cm and are likely to decrease further as flows continue for the next fortnight.

Figures on this Wimmera River map show salt levels in the river before and after the spring flow.

But Wimmera Catchment Management Authority leaders have warned that any suggestions the winter-spring flow had provided a quick-fix to river-health issues were wrong.

They said data suggested the river at Jeparit needed to regularly receive ‘new’ water to have any chance to recover from years of degradation. Previous experience had shown salinity levels in the river steadily rose without follow-up flows.
The also warned that salinity levels threatened to rise again in response to hot summer weather.

Wimmera CMA chief executive Marc Thompson said this year’s flow had provided only a glimpse of the river’s potential to respond to fresh water.

“It represents the first tentative step on a long road to establishing a healthy river from its source to its end,” he said. “A major message from this experience is that if we want a healthy and vibrant river that supports people, towns, communities and the environment, we need to consider it in its entirety. What’s important at one end of the river is no less or more important than the other.”

Mr Thompson said the environmental and socio-economic impact of drought during the last 10 years had provided clear reasons why the entire length of the river needed to receive an appropriate share of available water resources. “The Wimmera River system is a unique living asset. If a lack of water during the last decade has taught us anything, it’s that the condition of the river has an enormous influence on life across a large portion of western Victoria,” he said.

Water flows through weir gates at Dimboola Weir. Photos by David Fletcher