Threatened flora species
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In April 2010, a riparian vegetation survey was conducted by North Barker Ecosystem Services. Numerous threatened plants were located.
The exact location of the threatened flora species within the gorge was determined in relation to water level. The number of plants inundated during the 3 cumecs flow releases was recorded. Inundation at 2.5 cumecs was estimated.
The survey found a total of 13 threatened flora species, with six species (including one recently considered to be extinct) located between the current 1.5 cumecs flow level and a 3 cumecs flow. An increase in flow would potentially have a negative impact on these six species.
Fauna survey
Cataract Gorge snail, Beddomeia launcestonensis - full report.
During the 0.5, 1.5 and 3 cumecs trial releases, habitat availability (scour holes) in Cataract Gorge was assessed for the threatened snail, Beddomeia launcestonensis by Freshwater Systems. An analysis of the relationship between habitat availability and flow was conducted. This study concluded that a flow release of up to 3 cumecs would have no connection with, and no effect on, scour hole habitat for B. launcestonensis in Cataract Gorge.
Fish passage assessment
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A qualitative assessment of the gorge’s ability to accommodate fish passage at different sites was conducted at a flow of 3 cumecs. The gorge was surveyed for the presence of fish habitat and barriers to fish passage. Inundated zones and the substrates within the gorge were assessed for the potential to create suitable fish passage and habitat conditions. It was determined that increasing the environmental flow release up to 3 cumecs, or decreasing it to 0.5 cumecs, would be of marginal significance due to the presence of natural and artificial barriers (e.g. weirs) that already exist in the gorge and limit the passage of native non-climbing fish species.
Trial flow releases - videos
The videos show flows at four locations:
Trevallyn Dam, First Basin, Duck Reach and Deadmans Hollow.
The flows are filmed from different viewpoints at these sites and include 0.5, 1.5 2.5 and 3.0 cumecs.
These flows were considered because:
- the 2.5 and 3.0 cumecs were most supported by stakeholders for baseflows
- 0.5 cumec between Deadmans Hollow and Duck Reach if a mini hydro is installed at Duck Reach Power Station
- 1.5 cumecs is the current flow release.