Video of the Murray River flowing ‘backwards’ at Barmah on social media certainly generated a flurry of interest last week.
And while much of what is posted on social media can be taken with a grain of salt, the Murray is known to run backwards in sections during high flows and floods where it meets major tributaries, such as the Goulburn River.
“Water flowing down the River Murray has been backing up at the junction where the Goulburn River meets the River Murray at Barmah,” Goulburn-Murray Water emergency controller Sam Green said.
“This is due to the Goulburn River flows being higher than those reaching the junction from the River Murray.”
The Murray is constrained by the Barmah Choke upstream of the confluence with the Goulburn.
The high flows from the Goulburn use the capacity of the Murray downstream of the choke and raise the river level, which backs up the flows at the choke.
On October 20, Goulburn River flows at the McCoys Bridge gauge were 81,794 Ml/day and 32,633 Ml/day along the Murray River at Barmah.
On October 24, they were 57, 017 Ml/day and 37,943 Ml/day respectively.
“The higher Goulburn River flows come in over the top of the Murray flows, with the River Murray being ‘pushed back’ when it reaches the Goulburn River flows,” Mr Green said.
“Flows from the Goulburn are starting to recede and water arriving at the choke has contributed to flows over-topping into the forests on both sides of the river.”
A similar phenomenon happens at the junction of the Darling River and the Murray River, when the Murray backs up into the Darling.