Tharwa Fish Habitat Project

Tharwa fish habitat ELJ’s and rock groyne built into sand bar

Widespread erosion caused by land clearing in the late 1800's to 1900's has caused a build-up of sand in the Murrumbidgee River. In some areas, such as Tharwa, the sand build-up has caused the depth of water in the river channel to become very shallow which prevents fish moving up and down stream and provides little habitat as there are no in-stream rocks, or fallen trees. The impact of these areas on fish is even greater during droughts.

Studies of the Murray-Darling Basin have shown that native fish populations are currently at or below 10% of pre-Eurpoean settlement levels. The Tharwa region of the Murrumbidgee has been identified as one of the areas where fish habitat could be improved.

The Ecological Sediment Mitigation Study investigated options to improve fish habitat in the Tharwa region recommending the construction of engineered log jams (ELJ"S). The rationale for using ELJ structures includes the following:

  • it is a proven technique for river rehabilitation in Australia due to the positive effects on the physical and ecological functioning of streams
  • ELJ structures generally cost less than equivalent loose rock structures, providing a better cost-benefit ratio
  • the use of boulder structures has been shown to have a less consistent beneficial effect than woody debris.
Tharwa fish habitat View downstream from Tharwa bridge.

Further information about ELJ's and similar woody structures can be obtained from the document "Design guideline for the reintroduction of wood into Australian streams" below (entire document) or for individual chapters.

Funding obtained under Caring for Our Country (CFOC) will allow for the construction of two ELJ's and augmentation of some of the existing rock groynes in the Murrumbidgee River downstream of Tharwa bridge. In terms of the project time frame:

  • log and rock stockpiling is planned to begin April 2012 (weather dependant)
  • A community information session with Dr Andrew Brooks, Senior Research Fellow, Australian Rivers Institute, Griffith University will take place on 26 March 2012.
  • ELJ construction is planned to take place in early 2013 (weather and river flow conditions dependant).
  • Site restoration and riparian plantings are planned for Autumn 2013.

The map below shows the area of proposed works and a further report discusses results of Dynamic Cone Penetration testing carried out on the sand bar. A general information flyer about this project is also available.