Nearshore and Surf-Zone Morphodynamics: A Global Environmental Model for Predicting Hazards and Changes. Appendix 4. Morphodynamic Responses of an Energetic Beach to Temporal Variations in Wave Steepness, Tide Range, and Incident

摘要

Previous empirical analyses of short-term beach and surf zone morphodynamic response to changing breaker conditions are extended to examine the additional roles played by daily tide range and incident wave groupiness. Complex demodulation of original tide and wave time series from the moderate energy Narrabeen Beach, Australia, resulted in new time series of daily tide range and a daily grouping factor which expresses the relative amplitude of the alternation between groups of high and low waves. Using these new time series together with time series of daily beach state and of the parameter Omega = (H sub b)/(w sub s)T, statistical analyses were performed to determine the contributions made by each factor in explaining time-varying beach state. Eigenvector analyses of monthly surveyed beach and surf zone profiles provided a set of time series on modes of profile configuration change which were also analyzed to determine the relative effects of Omega and tide range on profile shape. Both tide range and groupiness are significant determinants of beach state. The six beach states are: reflective, low-tide terrace, transverse bar and rip, rhythmic bar and beach, longshore bar trough, and dissipative.