Hybrid cross shore and longshore shoreline evolution modeling for probabilistic assessment of beach erosion

Winds, waves and tides associated with storms are capable of causing severe damage to coastal property and infrastructure. Locations that are prone to erosion and inundation first require an accurate assessment of risk before deciding the most cost effective mitigation option. This research aims to produce probabilistic assessments of the coastal erosion and inundation risks associated with storms, particularly for coincident or clustered events, thereby helping to strengthen the resilience of coastal communities. Coastal erosion and inundation hazard is modeled in this study by simulations of realistic sequences of storm condition forcing (waves and tides) through a morphodynamic model to calculate return periods for maximum extent of shoreline retreat and storm demand. This approach of estimating erosion return periods is superior to the assumption that the single most energetic storm causes maximum erosion. The methodology is demonstrated at Old Bar, NSW and the metropolitan Adelaide beaches, SA, which are both currently erosion hotspots in Australia. These sites were selected to test the methodology for a span of geographic conditions in terms of storm climate and deep-water wave exposure, working towards developing this method into a transportable framework applicable to other coastal areas. Desktop and field assessments of each site were conducted to document geomorphic and sediment characteristics to inform shoreline modeling. Having established the historical framework at each location, multivariate statistical analysis of wave (buoy or hindcast models) and tides for peak storm events has allowed for the synthesis of realistic future conditions. This complex sequencing of cycling between accretion and erosion incorporating cross-shore and alongshore sediment transport has been estimated using a probabilistic shoreline evolution model. Here, model outputs for both sites are illustrated and used to access risk to infrastructure based on the most probable envelope of the shoreline. This study was undertaken for the Bushfire and Natural Hazards CRC project ‘Resilience to clustered disaster events on the coast - storm surge’. Presented at the 5th Young Coastal Scientists and Engineers Conference 2018