Coastal flooding from wave overtopping and sea level rise adaptation in the northeastern USA

In the northeastern United States, flooding arising from wave overtopping poses a constant threat to coastal communities during storm events. The purpose of this study is to construct a novel integrated atmosphere-ocean coast and overtopping-drainage modeling framework based on the coupled tide, surge and wave model, SWAN+ADCIRC, to assess risk and facilitate coastal adaptation and resilience to flooding in a changing climate in this region. The integrated modeling system was validated against the field observations of water level, wave height and period during the January 2015 North American blizzard. The water level collected by a sensor in the Avenues Basin behind the seawall in Scituate, Massachusetts were combined with the basin relationship between basin area and water level given by the USGS LIDAR data to obtain the field measurements of wave overtopping water volume in order to verify the model predictions. At the storm peak, the significant wave height was increased by 0.7 m at the coast by tide and surge. The wave setup along the coast varied from 0.1 m to 0.25 m depending on the coastline geometry. The interaction between tide-surge and waves increased the wave overtopping rate by five folds mainly due to the increased wave height at the toe of the seawall. The wave overtopping discharge would approximately double in an intermediate sea level rise scenario of 0.36 m by 2050 for a storm like the January 2015 North American blizzard. The wave overtopping discharge would increase by 1.5 times if the seawall crest elevation was raised by the same amount as sea level rise as an adaptation strategy. An increase of 0.9 m in the seawall crest elevation instead of 0.6 m currently planned by the town is required to bring the wave overtopping discharge to the current level under a 0.36 m sea level rise scenario. This result is primarily due to larger waves arriving at the seawall without breaking in the presence of larger water depth.