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Cataract Gorge – Relationship between environmental flow releases and habitat for the Beddomeid snail, Beddomeia launcestonensis [Report to Hydro Tasmania]


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Davies, PE ORCID: 0000-0003-2651-4061, Cook, LSJ and Smith, B 2010 , Cataract Gorge – Relationship between environmental flow releases and habitat for the Beddomeid snail, Beddomeia launcestonensis [Report to Hydro Tasmania].

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A survey was required to assess the potential for proposed environmental flow releases from Trevallyn Dam to connect with or enhance habitat for the aquatic snail Beddomeia launcestonensis, a species endemic to Cataract Gorge.
Habitats occupied by B. launcestonensis within Cataract Gorge are described by Davies and Cook (2002) and Spiers (2003). B. launcestonensis is known to occupy a restricted range of habitats within Cataract Gorge. The two principle habitat types occupied by the species are:
• Boulder fields within the First Basin – particularly at shallow to intermediate depths along the north-eastern shore of the main Basin pool. This restricted range is believed to be a result of the location of higher flow velocities within the First Basin during flood events, combined with the distribution of fine sediment deposits which accumulate during prolonged periods of flow;
• Scour holes within the Gorge, particularly between Deadman’s Hollow and the Second Basin. These holes are formed by local erosive action of cobbles on the main bedrock within the Gorge channel. B. launcestonensis occupies scour holes occurring within a limited range of elevations above the centreline (thalweg) of the Gorge channel. This restricted range of occupied locations is believed to be due to the interacting effects of flood frequency and the magnitude of shear stress during flood.
The magnitude of minimum environmental flows in the Gorge is being evaluated by Hydro Tasmania, as releases from Trevallyn Dam. These flows are aimed at providing a range of environmental services. This report describes an assessment of the degree to which releases of various magnitude may interact with known scour hole habitats for B. launcestonensis. A flows of 3.0 cumec was scheduled for release from the Dam on 27 April 2010. Field observations were made of the relationship between water levels associated with these releases, and water levels associated with known habitat locations within the Gorge

Item Type: Report (Project Report)
Authors/Creators:Davies, PE and Cook, LSJ and Smith, B
Publisher: Freshwater Systems
Copyright Information:

© Hydro Tasmania 2009, © Freshwater Systems 2009

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