Thesis Defense: Jessamin Straub

The Master’s Thesis Defense of UNC Marine Sciences graduate student, Jessie Straub. Presented by the UNC Institute of Marine Sciences (IMS) and the Department of Marine Sciences at UNC Chapel Hill.The location of this event will be in room 222 at IMS and streamed live to conference room 3204 on the third floor of Murray/Venable Hall on UNC-CH campus in Chapel Hill, NC. This event will be held on Friday, May 10th at 9:30 am. This event may be available for online viewing via Zoom.

Seminar Title: Predicting dune erosion at dissipative, intermediate, and reflective beaches

Abstract: Coastal communities commonly expend resources on the conservation and restoration of dunes, because dunes help protect infrastructure from storm waves and flooding. Predicting dune erosion is increasingly important for making management decisions related to flood-hazard mitigation as sandy beaches continue to erode, coastal populations increase, sea-level rises, and storms become more powerful. The information necessary to implement a dune erosion forecasting model includes the elevation of the dune toe, beach slope, and total water level (tide + storm surge + wave runup). Contemporary beach morphology data is important for predicting dune erosion because the elevation of the dune toe is the water level threshold for erosion, and the beach slope is needed for calculating wave runup. Beach morphology is commonly dynamic, limiting the duration over which these data are useful and forcing models to be parameterized with beach morphology data that does not reflect current conditions. We used hindcast water level and wave information from the coupled ADCIRC+SWAN (ADvanced CIRCulation + Simulating WAves Nearshore) model in combination with recent beach morphology data to predict collision events at three barrier island sites in North Carolina: Core Banks (dissipative), Shackleford Banks (intermediate), and Onslow Beach (reflective). Predictions were compared with continuous observations of water level and time-lapse beach photography to assess accuracy. Results show that when beach topography was 1-2 months old, the model accurately predicted collision at Core Banks and Shackleford Banks (75-80%). At Onslow Beach, lower prediction accuracy (25%) was due to low-elevation dunes where overwash occurred frequently during large storm events. As the age of the beach survey increases, the accuracy of predicting collision decreases at Shackleford Banks (intermediate) and Onslow Beach (reflective) due to high beach slope variance (0.016-0.133), while accuracy remained constant at Core Banks (dissipative) with minimal beach slope variance (0.020-0.041). Coastal communities with limited funding and resources to collect topographic surveys, should prioritize mapping at intermediate and reflective beach environments.