Low river flows lead to Powlett closure

Low rainfall in 2018 has resulted in low river flows and natural river closures at estuary mouths across Victoria. The Powlett River is one of those that has recently closed its connection to the ocean.

West Gippsland Catchment Management Authority CEO, Martin Fuller, said closures provide critical habitat for many threatened species.

“Over the coming weeks, if the Powlett River mouth remains closed, we can expect to see water cover the wetlands,” explained Mr Fuller

“This helps maintain the health of the wetland that surrounds the estuary.”

Mr Fuller explained that it is very important to let this natural process occur, otherwise the integrity of the surrounding wetland and the species it supports maybe jeopardised.

“There is a flow on effect when the river mouth closes,” continued Mr Fuller. “Algae begins to grow which provides food for insects and fish.

“The calm waters then turn into a fish nursery and with the increase in fish and insects – birds flock to the wetlands to feed.

“The environmental benefits of the estuary mouth closing cannot be overstated and if the river mouth does open naturally, particularly as a result of increased water level height and freshwater river flows, it will trigger fish migration upstream and out to sea,” explained Mr Fuller.

When adjoining farmland is inundated for long periods of time, it can have a negative effect on farmland. Trying to find a balance between environmental needs and landowner needs is difficult.

If it is decided that an artificial opening is required, it will only take place if it is deemed safe to do so and can be sustained.

The decision to open the estuary mouth is informed by the Estuary Entrance Management Support System (EEMSS) and additional data and information collected through onsite monitoring and stakeholder consultation.

An artificial opening, if completed at the wrong time, can cause extensive fish kills.

To sustain an artificial estuary opening at the Powlett, a large volume of water is required to overcome the power of Bass Strait’s tides and swells, which involves waiting for an increase in water level height and river flow.

In 2016 an opening was attempted at a low to moderate water level height with moderate river flows and ocean swells. This opening was unsuccessful, as the volume of water wasn’t great enough to sustain an opening. Ocean swells and tides closed the mouth again the following day and water levels didn’t change.

To find long-term solutions and alleviate the need for artificial estuary openings, WGCMA is working with landholders and other agency staff to explore options for future management of the adjoining farmland.

For more information about the Powlett River Mouth, the estuary and the closure visit www.wgcma.vic.gov.au and follow the links from the homepage.

An eastern great egret at the mouth of the Powlett
Eastern Great Egret (Endangered) at the mouth of Powlett carpark