Morphodynamics of a Macrotidal Beach: Broome, Western Australia

摘要

An intensive field investigation of hydrodynamic processes, processes of sediment entrainment and suspension, and morphologic change was carried out on an unprotected macrotidal beach near Broome in Northwestern Australia. The spring tide range was 9.5 metres; waves had heights of 0.5 to 1.2 metres and periods of 9 to 13 seconds. The beach had an overall concave upward profile with low gradient and dissipative subtidal and low-tidal zones, and steeper more reflective mid-tidal and high-tidal zones. Direct measurement of energy flux dissipation over the intertidal profile showed dissipation rates on the order of 2 to 5 watts per square metre of bed and indicated an approximate balance between shoaling and dissipation of unbroken waves so as to maintain a constant wave height. Time-averaged predictive estimates of wave work over the lunar half cycle for different points on the intertidal profile show similar dissipation rates and reveal a relatively uniform distribution of work over most of the profile but with maxima in the middle of the low-tidal zone and over the lower part of the high-tidal zone. Most of the work over the low-tidal and mid-tidal zones was performed by unbroken shoaling waves rather than by surf zone processes; surf zone processes only dominate over the high-tidal zone. The nature of the surf zone processes varied across the profile as local gradient and degree of reflectivity changed with changing tide level.