Since December last year, flow into the lower Goulburn river has increased from the recommended 800 megalitres per day to up to 3,000ML per day to meet water demands from towns, irrigators and the environment.
The Goulburn Broken Catchment Management Authority (GBCMA) said recent dry conditions across large parts of south-eastern Australia have increased demand for water downstream along the Murray River.
More water is being delivered out of the lower Goulburn River to meet those needs.
But at what cost?
Congupna farmer David Miles said in previous years high summer flows had caused significant damage to the riverbank.
“Several years ago, [we] had some massive high summer flows ruin the banks,” he said.
“[There were] massive erosion problems and trees falling in and they were softening the bank and then letting it dry out a little bit, then letting the river rise.”
Mr Miles said the current high flows he had observed looked similar to those he witnessed about five years ago.
“There was a lot of damage done … and it takes years to repair that,” he said.
“In places where the banks ripped into the clay, nothing can grow on that, so we’ve just got to put up with that being bad for a long time,” he said.
“Let’s hope we don’t have [the] devastation we had back then.”
He worried that current high flows would undermine the positive impact environmental flows had on the bank-stabilising vegetation during last spring.
“Let’s hope that doesn’t kill all the growth they’ve put along the lower parts of the bank,” he said.
Mr Miles is not alone in his concerns.
Last month, the GBCMA recommended that planned summer water transfers to meet downstream demand be delivered as a series of pulses through the lower Goulburn River, rather than a steady flow, to help minimise damage to the riverbank.
Delivering water at a steady level means the bank plants are underwater for too long and effectively drown.
“We prefer that water be delivered as pulses because it reduces the likelihood of bank erosion and loss of important bank vegetation, which can be a consequence of more consistent high flows,” Environmental Water and Wetlands manager Simon Casanelia said.
Pulsing not always an option, says Goulburn Murray Water
Goulburn Murray Water (GMW) acknowledged community concerns about the health of the riverbank but said ‘pulsing’ was not always a viable option.
Acting head of Water Resources, Andrew Shields, said GMW was expecting to deliver higher flows for at least the next six weeks.
“We’re trying to implement a pulsed recommendation from the GBCMA but there’s not a lot more that we can do given the requirements for us to transfer the water downstream to meet those water demands,” he said.
“We’re hoping there’s an opportunity to bring the water levels down a little bit as some of those demands decrease … If we get a cooler spell we might have the opportunity to do that.”
Mr Casanelia said he was disappointed the GMW had not fully implemented the GBCMA’s recommendation.
“Our preference would be obviously to have flows averaging around the 1,000ML a day in accordance with our best scientific understanding, which supports the bank vegetation,” he said.
Damage to the environment recorded last summer
Mr Casanelia said high flows caused significant damage to the riverbank last summer.
“Our observations and some of the monitoring we’ve undertaken indicated the high flows did result in loss of bank vegetation and did cause erosion and bank slumping in some parts of the river,” he said.
“It was most prominent last year when we had lots of demand for water downstream.
“The vegetation below the water level drowns and dies, given it’s flowing for long periods of time.
“It’s certainly reducing the extent and cover of the vegetation over time unfortunately.”
Mr Casanelia said the GBCMA had observed similar conditions this summer.
“We certainly have seen some good positive responses from the bank vegetation over that spring [to] early summer period,” he said.
GMW’s Andrew Shields said it was delivering similar rates of water downstream as it did last year, despite the warnings and concerns raised by the GBCMA and community members.
“The demands are quite similar to this time last year on the Murray system so we’re delivering similar rates down the Goulburn River to what we did this time last year,” he said.
High flows could result in a decline in recreational users of the river
Environmental Water and Wetlands manager Simon Casanelia said there were concerns that a loss of environment life could result in a decline in people visiting the river for recreational activities such as fishing, boating and swimming.
“It’s certainly a potential impact,” he said.
“I understand the high-water levels obviously reduce access and amenity for campers and community users.
“Success of fishing is obviously reduced with these higher flows over the summer period.”
Source: ABC Rural 2019-01