Artificial log jams were constructed on the Cotter River as part of the Tharwa Fish Habitat Project. Photo: ACT Government
Climate change is likely to cause decreased flows in the Murrumbidgee River, which will reduce the availability of, and access to, good river habitat for fish. The Tharwa Fish Habitat Project has installed structures that will help fish survive stressful climatic conditions by increasing the depth of the river channel and providing habitat. These structures have been placed in a degraded stretch of river that is the corridor between two good river sections.
Engineered log jams near Tharwa are a rehabilitation activity undertaken as part of the Upper Murrumbidgee Demonstration Reach (UMDR) initiative. The UMDR is a 100-kilometre stretch of river from Bredbo to Casuarina Sands. The log jams, which are made of interlocking hardwood logs and rock, will benefit native aquatic species including threatened Murray Cod, Trout Cod, Macquarie Perch and Murray Crayfish. Water flowing past the log jams is scouring away a century of sand build-up from human-induced erosion, deepening the channel to help fish move between good habitat and breeding zones.
The Tharwa Fish Habitat Project has received funding of approximately $300 000 and is supported by organisations including the Australian Government, the ACT Government, ACTEW and the Southern ACT Catchment Group.
The river corridor will be further improved and stabilised with tree planting, weed control and site rehabilitation under the ACT Million Trees Program. This revegetation will improve bank stability, thus reducing the risk of erosion and further deposition of sediment into the river.
Despite the short amount of time since completion, channel deepening in the UMDR has already been observed.
Completed log jams in the Cotter RiverPhoto: ACT Government