Rapid recovery: The benefits of restoring natural flow regimes (Baan)

by Harry Eason

Pretty Valley

Pretty Valley. Credit: Harry Eason and Claudette Kellar.

Artificial structures such as weirs, sewerage and stormwater drainage systems, and hydroelectric dams are all necessary parts of our modern society. However, they commonly result in changes to the amount of water that flows through a river system and the frequency with which these flows occur. Altering the patterns of flow within a stream can negatively impact the health of a river system by disrupting or even eliminating the animals that live in it, such as macroinvertebrates. As part of a study aiming to investigate the effects of modified flows on macroinvertebrates conducted by CAPIM in 2012-2014 we undertook an assessment of the Pretty Valley river system, located in the Victorian Alps near Falls Creek.

Altering the patterns of flow within a stream can negatively impact the health of a river system.

The study focused on the Mt. McKay Power Station, part of the Kiewa Valley Hydro Scheme, which for decades had discharged large volumes of water into the river system when active. In 2010 however, AGL diverted the station's outflow through a newly constructed tunnel, resulting in Pretty Valley Creek returning to its original flow regime. The study looked at five sites across six years from 2008-2013. This allowed for a comparison between the health of the river before and after a return to more natural flows. Using a combination of kick, sweep and rock-picking methods, the study found a strong resurgence of macroinvertebrate populations across nearly all groups when a more natural flow regime was restored. Coleopterans (beetles), Trichopterans (caddisflies) and Chironomids (non-biting midges) showed the strongest recoveries. In addition, the study found that macroinvertebrate community structure and complexity also improved as a result of modified flow cessation.

The study found a strong resurgence of macroinvertebrate populations when a more natural flow regime was restored.

Overall, we saw a strong and swift recovery of macroinvertebrate groups, which is exciting because it appears that there are direct and immediate benefits to restoring the natural flow regime to a river. This provides a strong incentive for other organisations like AGL to consider making similar efforts to reduce the impact of their own hydro stations on rivers.

This study was funded by AGL and Ecology Australia,

For more information contact Dr. Claudette Kellar: ckellar@unimelb.edu.au.