On Wednesday 14 September 2022, the Murray Lower-Darling Environmental Water Advisory Group (EWAG) met in the Ramsar-listed Millewa Forest near Mathoura to discuss the use of water for the environment for the 2022-2023 water year.
Blackwater
The risk of hypoxic blackwater events occurring over late spring or summer is anticipated due to continued floodplain inundation with wet catchments and full Hume and Dartmouth storages.
The response to potential hypoxic blackwater events requires good collaboration among agencies (including the Department of Climate Change, Energy, the Environment and Water, Commonwealth Environmental Water Office and NSW Department of Primary Industries [Fisheries]), community groups (such as the Edward-Wakool Angling Association) and Murray Irrigation. The Environmental Water Advisory Group discussed how community expectations could be managed around the NSW Government's preparedness to act on potential hypoxic blackwater events.
Water for the environment has been delivered in previous years to help create areas of freshwater refuge for a diversity of aquatic fauna (predominantly large-bodied native fish such as Murray cod).
Field trip
Little Edwards regulator
A series of regulators were installed in the Barmah-Millewa Forest from the 1940s to manage unseasonal flooding of the forest and reduce pressure on the river banks during periods of high flow. Unfortunately, these structures also act as barriers to native fish accessing floodplain habitat and trying to return to the river.
Earlier this year, the department's environmental water managers, in partnership with National Parks and Wildlife Service and the Arthur Rylah Institute (the Victorian government's research agency), instigated a sequential, temporary closure of these regulators. The project aimed to provide exit cues for native fish and allow water to flow more naturally through the forest. Murray cod and golden perch were tagged with electronic tracking devices and monitored by fish researchers.
The data collected shows that native fish become stranded behind regulators under normal operations. Work is now underway to design fishways that allow fish passage through regulators and to modify the regulator operations to improve native fish passage and avoid stranding if possible.
Picnic Point
Picnic Point is between two sections of the Murray River that are naturally constricted. The Tocumwal Choke is located on the upstream side of Picnic Point, and the Barmah Choke (known locally as 'The Narrows') is on the downstream side. These natural flow constrictions cause flows from the rivers to spill into the Barmah and Millewa forest floodplains and sustain these important Ramsar-listed ecosystems.
Overbank flows are naturally diverted around the chokes via a series of forest anabranch creeks. These are the Edward River, Gulpa Creek, and the Bullatale, Native Dog and Tuppal creek systems located upstream from the Tocumwal Choke. These waterways take enormous volumes of water away from the river and ensure a constant bankfull level is maintained at Picnic Point. Whenever flows exceed the capacity of the Murray River. The natural levee is rarely overtopped, even during large floods.
This is a remarkable natural and cultural feature of the Murray River that is under constant pressure from a highly regulated river system and needs to be protected.
