DOI: 10.17603/ds2-nf3k-fe18
title: Dune Subsurface Hydrodynamics During an Extreme Event
title: in Physics of Dune Erosion During Extreme Surge and Wave Events

description: Experiments were conducted in the LWF (Linear Wave Flume) at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. A scaled model of a dune from Mantoloking, New Jersey, was constructed in the wave flume and tested under wave conditions scaled from observations of Hurricane Sandy in 2012. The dune was tested in two model configurations: vegetated, which included Panicum Amarum beach grass grown for 4 months prior to testing, and bare, which had no vegetation.
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.