Starting near Murtho, the Lock 6 Reach crosses the border into New South Wales and Victoria and supplies water to the iconic Chowilla Creek and floodplain; is home to many iconic and endangered native species; and is the traditional home of the First Peoples of the River Murray and Mallee region.
Changing the operation of locks and associated weir pools has been identified as a way to help restore more natural river patterns in the River Murray. This is known as weir pool manipulation and can include weir pool raising or weir pool lowering.
Weir pool raising of the six weirs in South Australian River Murray has the ability to introduce intermittent wetting of up to 5000 hectares of above pool wetlands and floodplains, improving vegetation health and mobilising organic material back to the main river channel.
Weir pool lowering has the ability to dry up to 2000 hectares of channel edge, creeks and wetlands offering enhanced water level variability, drawing of nutrients and salt from backwaters and increasing lotic (faster flowing water) environments.
Weir pool lowering, when undertaken in concert with the commencement of wetland drying phases also has the potential to provide a natural cue for native fish to move out of the wetlands and back into the river. In addition, the wetland water that enters the river becomes a net gain for the environment as this water would traditionally be evaporated off as part of a wetland drying cycle.
The South Australian Riverland Floodplains Integrated Infrastructure Program (SARFIIP) has been able to undertake weir pool lowering planning, trials and investigations for Locks 5 and 6 and is in the process of finalising the optimal weir pool lowering depth that best balances the benefits and costs.
Building on from SARFIIP, the Sustaining Riverland Environments Program will focus on the Lock 6 Reach for the assessment and implementation of third-party risk mitigation works (primarily pump modifications). These works will assist in enabling irrigators to manage lower water levels in the river during weir pool lowering and also drought.
The weir pool manipulation project aims to deliver the following outputs in Lock 6:
- Infrastructure upgrades, on farm, to enable business continuity during increased variability of water levels.
- Off-farm infrastructure upgrades to ensure ongoing enjoyment of the river during periods of weir pool lowering.
- Increased resilience of irrigators and community to periods of low flow or weir pool lowering in the river.
This will enhance environmental outcomes by:
- increasing the extent of fringing vegetation (aquatic and terrestrial) that is exposed to variable water levels as a result of weir pool manipulation in lock 6
- increasing faster flowing habitats within the River Murray channel and creeks to benefit key fish species
- returning valuable nutrients and water to the river from pool connected wetlands.
The Sustaining Riverland Environments Program is a $37.6 million program funded by the Australian Government through the Murray-Darling Basin Authority and delivered by the Government of South Australia through the Department for Environment and Water.