Morphodynamics of reflective and dissipative beach and inshore systems: Southeastern Australia

摘要: Abstract Field experiments involving direct measurement of surf and inshore current spectra, circulation patterns, depositional morphology have been replicated under different energy conditions in several environmentally contrasting beach localities on the high-energy coast New South Wales, Australia. The region exhibits compartmentalized systems is dominated by a highly variable wind-wave climate superimposed persistent swell (T = 10–14 sec). Two general types system occur: (1) predominantly reflective which much incidentwave reflected from face; (2) dissipative with wide zones high turbulent dissipation. Reflective are characterized steep, linear faces, well-developed berms cusps, surging breakers runup minimum setup; rip cells associated three-dimensional topography absent. Wave height spectra beaches consistently their dominant peaks at incident wave subharmonic frequencies, cross-spectra indicate existence low-mode edge waves those frequencies. Infra-gravity negligible. Under low-energy low relative to incident-wave peaks; however, increasing breaker tends be accompanied dominance. Analyses shore-normal currents near bed show that all strongest shoreward motions induced waves; seaward motion face subharmonic-dominated. Dissipative characterize exposed open fronted concaveupward nearshore (seaward break) profiles flat zones. Waves break 75–300 m dissipate before reaching beach, creating significant radiation-stress gradients setup. Topography more complex varied than case beaches; one or bars, scales normally present. commonly occurring time-and-environment-dependent morphologic states can classified into six types. greatest total dissipation Type 1 prevails regions most abundant sediments during immediately after severe storms. Setup highest lowest (relative height) this type surf-beat part (80–120 sec) spectrum. As bar migrates (Types 2 3) steepens deep trough develops within partially dissipated reform. Although outer zone remains dissipative, synchronous resonance occurs and, as beaches, form cusps. A conspicuous feature Types 3 occurrence pronounced resonant spectral 4T ( ⋍ 40–50 sec ) bar. Edge frequency may responsible for development crescentic forms (Type 3). Lower beat also remain present but secondary. peak attenuates 4 not 5 first (2T) becomes pronounced, particularly tide. 6 represents fully accreted state only prolonged periods swell. This steep very berm continuous long distances alongshore; rips always similar described beaches.