The recent heavy rainfalls which have caused widespread flooding throughout parts of Victoria will benefit the environment enormously according to a leading Charles Sturt University (CSU) researcher.“The high flows in many of our river systems will provide great benefits for our river ecosystems,” said aquatic scientist Associate Professor Robyn Watts. “They will ‘spring clean’ the whole system and ‘reset’ it. These so-called ‘pulse events’ are fantastic for the ecosystem.”
Professor Watts, a researcher with CSU’s Institute for Land, Water and Society in Albury Wodonga, said the event was particularly important for regulated river systems which have major dams built on them, especially after a long drought.
“We haven’t had an event like this that can reset the river system in Victoria since 1993,” she said. “The small to medium rainfall events we have had since then have been ’buffered‘ by the dams and have not been large enough to cause high water flows. The current situation is different.”
Unregulated rivers such as the Ovens and the King have brought flood waters to the Murray River. The region has experienced good winter rainfall so the ground is wet and there is plenty of run-off from the smaller creeks and streams, with many farm dams already full and now over-flowing.
Professor Watts said the high flows will scour out or flush through sediments in the rivers.
“Because we have had such low flows for so long, the holes and crevices in the river beds and banks, which provide homes for various organisms, have silted up,” she said. “This will clean them all out. It will also flush out other nuisances like build-ups of salts and algae.”
The high flows will also ‘wet up’ the river banks, wetlands, and in some cases, the flood plains.
“This revitalises the food web,” Professor Watts said. “It brings in a whole lot of leaves and twigs that triggers a big increase of carbon in the water which little bacteria instantly use, and then small organisms eat the bacteria, and then insects eat these small organisms … it kicks along the whole food chain.”
Some river systems have been reduced to a series of waterholes and haven’t flowed for some time, so the high flows will link those waterholes again. “This means fish and other organisms can move between areas and connect again,” she said.
The event will also help bird and frog breeding in spring. “For some species it may be a bit early but it means they will be in good condition for the coming breeding season.”
However Professor Watts was quick to point out that the current flooding does not mean that the environment doesn’t need releases of ‘environmental water’ down rivers later this year.
“This is a major flushing of the system,” she said. “We don’t want to go back to a constant low flow river system for the rest of the year. Under unregulated conditions, the river systems in this region would have received several pulses: some in August, some in September, some in October.
“Even if we don’t get any more natural high flows this year, putting some water in to top up the wetlands for bird or fish breeding will still be needed. These water releases provided through the Federal government water buyback scheme will now be more beneficial than if they had just been releases without this flood.”
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