For the first time in more than 100 years, variable base flows will be introduced to the Goulburn River, downstream of the Goulburn Weir.
Base flow releases have remained steady since the weir, Australia’s first major diversion structure built for irrigation, was constructed in the late 1800s.
Environmental water coordinator with the Goulburn Broken Catchment Management Authority, Daniel Lovell, said the aim of the change was to mimic the natural rise and fall of the river.
“We’re wanting to introduce some variability into the base flow,” Mr Lovell said.
“Traditionally we deliver our environmental water over winter at a constant flow from Goulburn Weir. But for the first time this year we want to see the level of the river to go up and down as it would under natural conditions in response to rainfall.”
Mr Lovell said it was impossible to precisely replicate natural winter flows but under the plan the lower Goulburn River would change by about 80 centimeters during the period.
“River regulation means that most of the natural inflows in the Goulburn River upstream of the Goulburn Weir are diverted off for irrigation purposes.
“But by varying the release from the weir we can try to copy what would have happened naturally.”
The introduction of variable flows follows the release of scientific studies which revealed that varying the river level promoted the growth of native vegetation and helped limit the risk of bank erosion.
“A couple of years ago we got really good vegetation growth down at the bottom of the bank and we’re hoping by varying the flow, we’ll encourage that growth to come back,” Mr Lovell said.
He said the most noticeable variation in river height would be found between Shepparton and Nagambie as downstream of Shepparton Broken River and Seven Creeks inflow change river levels after rain.
“It will be pretty hard to see the daily river changes but it’s noticeable between the highest and lowest flows.
“Goulburn Murray Water has an obligation to pass a minimum flow, so the river would run at about 250 megalitres per day throughout the winter period without additional water for the environment.
But under the variable plan the flow would increase to between 500 and 1500 megalitres per day.
“Rather than keeping the river at a steady level, we’re just raising the height up and down a little bit.”