Analysis of Overwash Sediment Transport in an Experimental Laboratory Setting: Channel Dimension Influence on Washover Deposits

Abstract

Artificial dunes and other human-made solutions in coastal areas often result in changes to coastal hydraulics and sediment transport, which can lead to changes in long-term evolution of coastal landforms and places communities and other coastal infrastructure at risk from coastal hazards. Recent large-scale restoration projects have shown some success in restoring dynamic coastal processes while increasing habitat in built-dune environments. While there are initial successes, further research is required to: understand the dimensions of change needed to sustain the necessary coastal dynamics; determine the types of approaches to attain a resilient and functioning system and generate reproducible results that will support various coastal management approaches. In this thesis study, throat-dimensions (referred to also as channel dimensions) that induce washover formation are varied in a physical laboratory environment to examine overwash sediment transport and deposition. Uniform initial channels (multiple channel dimensions tested throughout experiment) are emplaced in an artificial sand barrier that serves as a physical representation of a barrier island within an experimental table. The experimental set-up comprises of an ocean-side that is filled at a constant infill rate to overtop the sand barrier, which induces overwash and resulting observed washover features. This experimental set-up was inspired and compared to a similar study observing overwash in an experimental setting. In this study, the methods from previous works were expanded to analyze different channel dimensions. The different channel dimensions mark different experimental runs, hereby referred to as scenarios. Each various channel scenario is repeated over five replicated trials to ensure that the observed results are not due to chance. Each trial is captured with a nadir-view camera, where the trials are video recorded and images from the video are extracted and resulting features are measured within ImageJ. Narrow, deep channels generally produced shorter washover deposits with smaller areas. Shallow, wider channels, or no channels incised, produced washover deposits with generally longer lengths and larger areas. The study results can aid in understanding how human-influenced systems can be altered to restore dynamic coastal processes and barrier island evolutionary pathways.