13.2 The Wallis Lake Estuary Management Committee - Great Lakes ...

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Wallis Lake Estuary Management Plan E.3 Management Area A, B, C Management Objective Protect seagrass beds from being buried by shoaling sand bars or covered/shaded by sediment from stormwater and run-off Action No E.3.1 E.3.2 Action Consider dredging the sand bar encroaching on Posidonia australis beds between Wallis and Tonys Point Islands Assess and report impacts of sediment from stormwater and run-off on seagrass through the seagrass monitoring project Indicative Priority Responsibilities Progress Cost $250,000 High (D1) GLC, DPI $25,000 Medium (B5) GLC Comments The sand bar between Wallis and Tonys Point Islands moved south 300 m (5 m.yr -1 ) in the period 1937 to 1997 (Webb, McKeown & Associates 1999). This movement of sand threatens to bury beds of Posidonia australis, which does not appear to be recolonising the sand in its wake. Any possible impacts of dredging this sand bar should be adequately assessed to ensure that erosion and sediment transport is not exacerbated in other areas of the Lake. Sediment cover is a parameter measured for the seagrass-monitoring program, coordinated through the HLP. When sediment cover becomes too great the seagrass cannot receive light for photosynthesis. If the health of seagrass is being severely compromised, dredging should be considered. Early results from the SMP suggest the following seagrass beds are suffering from sediment and epiphyte cover from stormwater and run-off: • Pipers Creek • Coomba foreshore • Green Point • Pacific Palms recreation club Implementation of the Wallis Lake stormwater management plan (W.1.1) will also aid considerably in achieving this management objective. 42
Wallis Lake Estuary Management Plan Hellsgate Wallis Island Tonys Point Island Sand bar encroaching on Posidonia australis bed Dago Island [Plate 4.4: Location of sand bar encroaching on Posidonia australis bed between Wallis and Tonys Point Islands] 43
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13.2 The Wallis Lake Estuary Management Committee - Great Lakes ...

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