School of Geography - Theses
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ItemThe morphodynamics of shore platform beaches( 2006)The morphodynamics of shore platform beaches near Apollo Bay, Victoria, were examined, to determine their response to changing wave energy conditions and influence on shore platform development. Three specific research questions were posed. 1. What is the morphological form of platform beaches in relation to different offshore wave energy conditions? 2. What influence does shore platform morphology have on how much offshore wave energy reaches the beach? 3. Do the models of Trenhaile (2004) and Wright and Short (1984) accurately represent the morphodynamics of shore platform beaches? Beach morphological change was determined by surveying of cross-shore beach profiles at two study sites over a four month period (22 March-19 July 2006), profiles were then compared to offshore wave data for this period. The modification of waves by the shore platform was measured by recording of waves across the platforms. Results showed that changes in beach profile form, width and gradient were minimal throughout the study. Beach morphology did vary to a degree during high-energy offshore wave conditions via erosion and accretion of the beachface. Recorded wave energy dissipation from offshore to the beach toe was high, and depth of water on the platform found to be a major controller of platform wave height. Depth of water on the platform was, in turn, controlled by platform elevation, offshore waves, and tides. The shore platform beach model of Trenhaile (2004) was shown to not accurately predict platform beach morphodynamics in microtidal environments. Wright and Short's (1984) model, specifically the dimensionless parameter, fl (Eq. 1.1) was found to correctly predict beach state, when data of waves already on the platform was used, and was incorrect when offshore wave data was used in its calculation. Beach morphodynamics were found to be largely controlled by platform morphology, specifically the elevation. Relating to this, platform beach morphodynamics are controlled by highmagnitude low-frequency wave conditions, low-energy conditions have little impact on these beaches. These beaches are characterized by low variability due to low sediment availability and the dissipation of offshore waves by the platform. To determine the relative susceptibility of these beaches to offshore waves, a shore platform energy window index, `lisp (Eq. 4.2), was developed by modifying the reef energy window index, 'I/ (Eq. 1.3) of Kench and Brander (2005). Further to this, a conceptual model of platform beach morphodynamics was created (Fig. 4.6), which demonstrates the main factors influencing beach morphology.