Maintaining a water flow through Cataract Gorge in Launceston is important for many reasons: social, economic and ecological. However, determining the most appropriate level of flow to best meet these diverse needs is a complex balancing act.

Balancing the flow through Cataract Gorge

Over many years we’ve developed an understanding of the full range of issues and the different views of our many stakeholders.

In 2003, we increased the flow from the legal requirement of 0.43 cumecs to 1.5 cumecs to provide additional habitat for important species and to better cater for recreational uses. At that time we also committed to review the flow after 5 years.

As part of that 5-year review, stakeholders raised concerns including: reduced visual amenity, poor water quality, algal blooms and poor ecological health.

In response to these concerns, we conducted studies on the threatened Cataract Gorge snail (Beddomeia launcestonensis), looked at implications for native fish passage, surveyed threatened flora and conducted flow assessments at different flow levels, using video.

Ecological and social needs within the gorge

• For example, fifteen threatened flora species were found within the gorge, seven of which were located near the water’s edge. Inundation and loss of some of these plants if the flow was permanently increased needed to be considered as part of the final decision on flow level. See Cataract Gorge Flow report.

•  The study assessing habitat availability for the Cataract Gorge snail showed that flows up to 3 cumecs provided suitable habitat for the threatened snail. See Cataract Gorge Snail report.

•  The fish passage assessment determined that higher flows would impede fish passage for some native species due to water velocity, but lower flows would also impede fish passage due to a greater number of obstacles.

•  Videos of trial flow releases of 0.5, 1.5, 2.5 and 3 cumecs were recorded at a number of locations (Trevallyn Dam, First Basin, Duck Reach and  Deadmans Hollow)  through the gorge to provide a visual assessment of flows.
  
  

Hydro Tasmania's response

In 2011, after the conclusion of the review, we voluntarily increased the flow level again, based on our stakeholders’ concerns and the assessments conducted.

To balance social, economic and ecological needs, we increased the environmental flow to 2.5 cumecs. This level provides sufficient water through Cataract Gorge to provide visual amenity for visitors, acceptable water quality, and provide sufficient habitat for the threatened species present in the area.

In 2016 we undertook work to replace three large dewatering valves built into Trevallyn Dam. The valves were installed in Trevallyn Dam when it was built in the 1950s and had reached the end of life. The $6 million project was vital to the dam’s future operation and safety, and has improved the reliability of water releases for the environment and for a range of stakeholders.

In 2017 we committed to providing two recreational releases for kayaking each year for the next five years. This has been made possible because of the new valves.