RAPID: Lidar and Sonar Surveys of a Dune Reinforced with Geotextile Sand Containers Impacted by Tropical Storm Hermine

University Of Rhode Island, Kingston RI

Investigators

Abstract

The devastating effects of Hurricane Sandy in 2012 on the northeast United States highlighted the need to improve the ability of coastal communities to quickly respond and rebound from natural hazards. There is a trend towards implementing "soft" engineering solutions such as dunes reinforced with Geotextile Sand Containers (GSC) to improve resiliency rather than traditional hardened structures like stone revetments. These have the potential to protect communities from smaller storm events (e.g. 25-year storms) while at the same time providing flexibility in design considering the uncertainty regarding rates of sea level rise and storm frequency. "Soft" engineering solutions may also be less disruptive to the natural morphology of barrier beach systems than hardened structures. However, there is still considerable uncertainty regarding the mechanisms that affect the stability of reinforced dunes under wave attack. The objective of this Rapid Response Research (RAPID) project is to collect perishable data to assess the stability and performance of a 1000 m section of a dune reinforced with GSCs in Montauk, NY that was impacted by Tropical Storm Hermine in September 2016. The reinforced dune was constructed in March 2016, and Tropical Storm Hermine resulted in complete erosion of the protective berm, exposure of the GSC core, and movement of the lower level of GSCs. A detailed 3-D digital elevation model of both the eroded beach (topography) as well as the near-shore bathymetry will be constructed. This will be accomplished through two surveys: an aerial LIDAR survey using an Unmanned Aerial System (UAS) and a combined ship-mounted LIDAR and interferometric sonar system. These data will provide a detailed case study of the effects of wave action on a dune reinforced with GSCs. This will allow for the application of findings from numerical and wave flume studies to an actual field case at a scale not reproducible in the laboratory. It is hypothesized that current stability equations are unconservative in that they underpredict the hydraulic stability of geotextile containers associated with reduced scale experiments. Analysis of this case study will also improve our understanding of whether reinforced dunes perform as "soft" coastal structures and do not significantly modify the natural morphology of the shoreline.