Weir Pool Manipulation (In-channel and wetland effects) - Report on Pre-drawdown Monitoring: Weir Pools & Wetlands

"March 2008".

Project Number: Monitoring of wetlands disconnection in New South Wales: Locks 8 and 9 weir pool manipulation - M/BUS/252.

MDFRC item.

1 of 2 reports associated with project see (Monitoring of selected wetlands associated with Lock 8 and 9 weir pools on the Murray River).

Weir pool drawdowns are one of the ten interventions identified as part of the TLM Intervention Monitoring Assessment Framework. The major impacts of weir pool draw down identified by the IMAF process were effects on aquatic vegetation that were thought to then provide additional habitat and food for invertebrates fish and potentially birds. The weir pool drawdowns provide an opportunity to see if weir pool manipulation can achieve vegetation benefits. If this is found to be the case then future monitoring may be extended to examine the effect on invertebrates, fish or birds. The major risks associated with a weir pool manipulation are in the area of water quality where changes in current speed within the weir pool will lead to the entrainment of sediment and organic matter and lower water levels may lead to inflow of salty groundwater. There is also some risk of acid-sulphate sediments developing as water levels are drawn down. Locks 8 and 9 are under consideration for drawdown and will be monitored for changes to vegetation understorey, water quality, blue-green algae (BGA), and groundwater. Lock 11 is the control weir pool for this project and will have the same parameters measured throughout the duration of the project. The wetlands which are monitored are those associated with Locks 8 and 9. There are four wetlands being monitored for Lock 8 and five for Lock 9. The Great Darling Anabranch is the largest of the wetlands being monitored.