DUNE PERFORMANCE IN 2050 AND 2100 SUBJECTED TO EXTREME AND NUISANCE EROSION EVENTS

A physically informed, yet computationally efficient, fragility model is used to quantify dune vulnerability under current and future sea level scenarios. The model is applied to mean sea levels of 1997, 2050 and 2100 to quantify the increase in vulnerability attributed to sea level rise on an existing dune design template. Two separate storm intensities are considered; categorically defined as ‘Nuisance’ and ‘Extreme’ events. Both storms are modeled for sea level rise projections based on IPCC SSP1-1.9, 2-4.5 and 5-8.5 scenarios in 2050 and 2100 including ground subsidence. The results show the vulnerability of dune failure during Nuisance events will nearly double by 2050; from 3.3percent to 5.9percent under SSP2-4.5. By 2100, the vulnerability increases further to 12percent. Under Extreme events the vulnerability increases from 26percent to 37percent in 2050 and further to 56percent under SSP2-4.5. Next, the model is used to estimate the modifications to the design template to maintain the current vulnerability. Increases to the berm width and dune volume are considered independently under various constraints. The findings indicate vulnerability could be offset through 2050 by increasing the berm width by 27-m (61percent increase). By 2100, increases in the berm width would require 70-m (142percent increase). Alternative dune volumes are calculated assuming different design constraints (e.g., maintaining existing dune crests for viewshed concerns). Notably, by 2100, the required dune volumes result in a geometrically untenable configuration. It is concluded under near term time horizons, modifications to the dune volume alone or berm width are sufficient to maintain existing vulnerabilities. However, under longer term time horizons, beach nourishment templates must increase the project’s effective width or accept higher vulnerabilities to Nuisance and Extreme events alike.