Morphological Modelling of Intermediate Beach State Transitions

Abstract

Temporal and spatial changes in nearshore bathymetry result from sediment transport interactions with the hydrodynamic processes and provide a highly variable and rapidly changing environment. Rip currents are one example of a morphody- namic system presenting a significant hazard to swimmers unfamiliar with their behaviour. Rip currents pose a particular threat as they can develop suddenly and quickly transport water offshore. The widely accepted beach state model of Wright & Short (1984) uses param- eters which are functions of breaking wave height, wave period and sediment (Dean 1973, Gourlay 1968, Guza & Inman 1975) to classify the beach environment into distinct morphological states. These states range from reflective through inter- mediate to dissipative. Breaking wave type is influenced by the bathymetry as the wave approaches breaking point within the surf-zone and can be classified by the the Iribarren num- ber or surf-similarity parameter (Battjes 1974). Intermediate beach states can be more difficult to assess with these parameters and may even consist of a combination of outer dissipative and inner locally reflective zones.