DOI: 10.17603/ds2-csmw-8x65
title: Sediment Transport Processes Across a Rapidly Eroding Bare Dune
title: in Physics of Dune Erosion During Extreme Surge and Wave Events

description: A scaled bare dune profile from Mantoloking, N.J. was constructed in the large wave flume at the NSF NHERI O.H. Hinsdale Wave Research Laboratory, Corvallis, OR., United States. Waves and water levels driven by Hurricane Sandy off the coast of Mantoloking were simulated to examine morphodynamic and hydrodynamic processes across the bare dune profile during an extreme storm. 

Sediment transport in the water column (suspended load), and in the sheet flow layer (bedload) were investigated. Acoustic Doppler profiling velocimeters (ADPVs) were used to measure near-bed flow velocities, conductivity concentration profilers (CCPs), and near-bed suspended sediment concentrations were obtained with optical backscatter sensors (OBSs). Offshore water surface elevations were measured by wave gauges (WGs) and non-intrusive ultrasonic distance meters quantified swash depths, instantaneous bed level progression, and free wave surface elevation shoreward the inner-surf zone. 

The collected data can be used to estimate sediment fluxes from the seaward berm slope to the dune front and associate them with the wave characteristics and the flow shape, the turbulence induced by the wave breaking in the nearshore, and the instantaneous bed elevation changes. The contribution of two different transport modes to the total sediment transport can be examined by comparing the suspended to the sheet flow layer fluxes. This is a unique dataset consisting of data in the swash zone during near-prototype storm conditions.
description: Sand dunes are often the primary and only "line of defense" for coastal infrastructure. Coastal managers require knowledge of how dunes respond to extreme events so assets can be pre-positioned. However, there is a limited understanding of how dunes sediments and vegetation can modify hydrodynamic forces and alter beach-dune profile evolution. This project focuses on dune response to a range of water levels and forcing conditions that mimic the passage of an extreme storm event. A near prototype-scale laboratory study was conducted over a mobile bed in the large wave flume at Oregon State University. Experiments occurred over a bare dune and a dune with live vegetation. Data related to processes ranging from short-term (turbulence) to longer time scales (individual events) were collected and analyzed to develop a fundamental understanding of the fluid-sediment-vegetation dynamics affecting dune stability, as well as damage mitigation strategies for extreme events. 

The collected data are used to validate numerical models and further inform the creation of improved parameterizations of turbulence- and wave-scale processes in event-scale morphodynamic models. The collected data provide the required input parameters for the fragility analysis. Moreover, the experimental data are used to (i) identify the fundamental processes (including waves, turbulence, and sediment transport) that drive dune evolution during extreme events; (ii) define the conditions by which dune vulnerability increases as a function of berm erosion; (iii) investigate the interaction between the different processes and identify the threshold forcing conditions and time scales beyond which vegetation no longer enhances dune resilience; and (iv) examine the extent a fragility modeling framework can be used to improve risk-based decision for dune erosion during the extreme surge and wave events.

This project will publish six datasets/experiments consisting of data collected with different sensors across the bare and vegetated dune profiles. Near-bed flow velocity profiles, sheet flow layer concentrations, suspended sediment concentrations, swash depths, and free surface elevations will be published by the University of Delaware. Line laser scanner data, offshore flow velocities, pressures, and moisture content in the dune profile, are published by Oregon State University. Plant characteristics (e.g., stem density, height, plant architecture) and drag forces (strain gauge data, elasticity) are provided by Texas A&M University.