Seawalls and acceptable beach width for public amenity

Dry beach width is one straightforward measure of public beach amenity. The area of dry beach available to beach-users varies with the dynamic nature of the shoreline and its proximity to landward truncations in the beach profile such as cliffs, rock outcrops, sand dunes, dune vegetation, dune fencing or seawalls. Even natural, unmodified beaches are not suitable for walking or sitting 100% of the time. Determining an optimum or acceptable beach width is important for coastal management, particularly coastal erosion hazards as well as public beach amenity. This project has completed an updated literature review on beach width amenity to determine what is an acceptable dry beach width to local beach-users at various beaches. The construction of a seawall can often be publicly perceived as having detrimental implications on dry beach width and beach-user amenity. Collaroy-Narrabeen beach is characterised as having the most highly capitalised shoreline in Sydney's Northern Beaches, is also classified as the most at risk from coastal processes in NSW and the third most at risk nationally. The 3.6 kilometre-long embayment comprises sections of beach backed by vegetated dunes and existing ad-hoc (mostly non-engineered) seawall structures including rock rubble, vertical and composite designs. Using a 40-year dataset at Collaroy-Narrabeen beach, an hourly timeseries of dry beach width fronting a range of seawall structures has been modelled to examine the impacts of seawall structures on public beach amenity. The results provide a valuable assessment of beach amenity implications of coastal management options and are useful for informing public perceptions around the impacts of coastal management practices.