Geological control of beach morphodynamic state |
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| Institution: | 1. Water Research Laboratory, School of Civil and Environmental Engineering, University of New South Wales, 110 King St. Manly Vale, NSW 2093, Australia;2. Griffith Centre for Coastal Management, Griffith University, Southport, QLD 4222, Australia;1. School of Geosciences, University of Sydney, Sydney NSW 2006 Australia;2. Institute of Geoscience and Natural Resources, University of Copenhagen, Copenhagen Denmark;3. School of Civil Engineering, University of Queensland, Brisbane QLD Australia;4. School of Environmental and Life Sciences, University of Newcastle, Callaghan NSW Australia;1. Geocoastal Research Group, School of Geosciences F09, The University of Sydney, Sydney, NSW, Australia;2. School of Science & Environmental Research Institute, University of Waikato, Hamilton & Tauranga, New Zealand;3. Coastal & Marine Sciences Institute, University of California Davis, Bodega Bay, CA, United States;4. Department of Environmental Science & Policy, University of California Davis, Davis, CA, United States |
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| Abstract: | The concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid-1980s and expansion in the 1990s. Much of the pioneering work was undertaken in Australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3-dimensional morphology and the Dean's parameter (Hb/WsT) was established. Subsequently, the Relative Tidal Range parameter (Hb/TR) was extended to beaches of all tidal ranges.In this paper, observations are presented from 25 beaches around the north coast of Ireland. These beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability (micro to macrotidal and low to high wave energy). Each beach was visually categorised into one of several established beach states described in the literature, on the basis of field observations. For each beach, the RTR and Dean's parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships. Observed and predicted beach states were then compared.Comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria, most other beach states did not. Lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the RTR and Dean's parameter. In addition, this study identifies geological factors as important constraints on actual beach state. In the majority of beaches studied, inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics. |
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