Stability of artificial beaches in port Phillip Bay, Victoria, Australia

Abstract

This study investigates the drivers of beach morphodynamics on the highly modified fetch-limited beaches of the urbanised north-eastern coast of Port Phillip Bay in south-eastern Australia. Repetitive beach profiling, sediment characterization, and aerial photo analysis were conducted to quantify morphodynamic change across six distinct beach systems on a seasonal to annual-decadal scale. The observed morphologies contained features similar to those found on open-ocean wave-dominated and tide-dominated beaches, and included reflective unbarred beaches and intermediate beaches with low-tide terraces or transverse bar-rip systems. Sediment typically ranged from medium to coarse or very coarse in size. The consistency of wave energy across the study sites suggests that sediment size is the primary determinant of beach morphodynamic state, and the relatively low energy of Port Phillip Bay suggests that only storm conditions are energetic enough to mobilise sediment and alter beach morphology. On a seasonal scale, alongshore sediment transport is a major driver of beach change, and groynes and other coastal modifications have considerable influence on planform beach morphology. Over the medium term it appears that these beaches are eroding towards a landward position of equilibrium. With current projections of sea level rise it is expected that rates of beach erosion and sediment loss will accelerate over the coming decades, leading to an increased necessity for beach renourishment or other management interventions if wide beach profiles are to be maintained.