Nearshore and Surfzone Morphodynamics of a Storm Wave Environment: Eastern Bass Strait, Australia

摘要

A field investigation of inner shelf, surf-zone, and beach processes and associated morphodynamic changes was carried out on and seaward of Eastern Beach, on the Gippsland Coast, in Eastern Bass Strait, Australia. The beach is part of a long straight beach system fronted by a wide continental shelf. Frequent passage of gales through Bass Strait results in relatively high energy but variable and rapidly changing deepwater wave conditions. Time series of benthic currents (u and v) were recorded at depths of 20m and 10m over the nearshore profile and from different regions of the surf zone. Over the nearshore profile, wave-induced oscillatory flows dominate to depths of 20m and are responsible for agitating and suspending sediments. Despite the microtidal range, reversing shore-parallel currents and superimposed wind driven currents are second in importance and determine the fate of sediments suspended by waves. Frictional dissipation of the obliquely incident waves over the rough, rippled and low-gradient nearshore profile is particularly pronounced and, as a result, bottom orbital velocities measured at 10m depth were slightly weaker than those measured at 20m. Of fundamental importance to surf zone processes, nearshore energy dissipation by bed friction causes not only a reduction in average breaker height but also significantly reduces the temporal range of breaker conditions.