Wave-induced sediment transport in a coupled berm-dune system: a near prototype experiment.

Maria Pontiki1, Jack Anthony Puleo2, Rusty A Feagin3, Meagan E. Wengrove4, Tian-Jian Hsu1 and Daniel Thomas Cox5, (1)University of Delaware, Center for Applied Coastal Research, Newark, DE, United States, (2)University of Delaware, Department of Civil and Environmental Engineering, Newark, DE, United States, (3)Texas A&M University, Ecology and Conservation Biology, College Station, TX, United States, (4)Oregon State University, Department of Civil and Construction Engineering, Corvallis, United States, (5)Oregon State University, Civil and Construction Engineering, Corvallis, United States
Abstract:
A near-prototype laboratory experiment was conducted to quantify sediment transport rates in a coupled berm-dune system during extreme forcing conditions. The study was carried out in June-July 2019 in the Large Wave Flume at Oregon State University. A dune profile from Mantoloking, NJ, USA was constructed with a 0.265 mm median diameter sediment, after applying scaling laws. The profile was tested under surge and wave events from a segment of Hurricane Sandy recorded in October 29-30, 2012. The significant wave heights and wave periods were obtained from the random phase spectral model WAVEWATCH III wave at a grid cell 680 m offshore northern Mantoloking at (40.12 N, 74.00 W). The changes in water levels during the tests followed the hydrographic information obtained from the NOAA 8534720 buoy station near Atlantic City, NJ. The 18-hour storm duration was discretized in smaller test intervals and extensive measurements were collected from the berm to the lower dune face during and after each test. Optical backscatter sensors (OBSs) provided suspended sediment concentrations, while the sediment concentrations in the sheet flow layer were estimated with conductivity concentration profilers (CCPs). Sediment concentration measurements were collocated with the near bed cross-shore flow velocities obtained with acoustic Doppler profiling velocimeters (ADPVs). The contribution of wave-breaking-induced turbulence and bed shear stress to the sediment concentrations is discussed. The time-series of suspended sediment and bed load will be compared to determine the relative contribution of the two different transport modes to the total transport rates. Further analysis of the sediment concentration data near the bottom will evaluate the fluctuations of the sheet layer thickness and changes of the instantaneous bed levels. Visual observations during the tests revealed that the sediment erosion accelerated following berm lowering associated with offshore-directed net offshore sediment transport. The effects of bed level changes on sediment mobility and the critical Shields parameter are presented.
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