Non-Hydrostatic Modelling to Improve Nearshore Optical Remote Sensing Algorithms: Applications for Surf Zone Hydrodynamics and Morphodynamics

Abstract

Accurate bathymetric data is essential for predicting changes in coastal environments. Traditional surveying methods the seabed provide precise measurements but are limited in coverage and cost. Video remote sensing offers a cost-effective alternative that can capture wave, current, and bathymetric information in dynamic nearshore areas. However, reliable methods are needed to extract accurate data from imagery across various wave conditions. This thesis aims to enhance two retrieval algorithms used to estimate bathymetry and alongshore currents from optical data. Using the non-hydrostatic numerical model SWASH (Simulating WAves til SHore), synthetic wave and current fields are generated to simulate storm events at the US Army Corps of Engineers Field Research Facility in Duck, NC. The simulations complement field observations and offer a new method of identifying sources of error in optical data. The first of these algorithms is cBathy, which faces challenges during large offshore wave conditions, which causes signal interference. By incorporating SWASH-generated water surface elevation data, the errors in depth estimates were reduced, especially in areas of wave breaking. The results of different versions of cBathy are also investigated, which are discussed alongside recommendations for further refinement. The second of these algorithms calculates alongshore current speed, a key driver of bathymetric change. A new version of the Optical Current Meter method (OCM) is developed using SWASH model results and field observations. The updated algorithm lowers measurement error and improves optical measurements across a broader range of conditions. The open-source code is now included in the Coastal Imaging Research Network (CIRN) Video-Currents-Toolbox and is available to other researchers. Informed by the numerical model and field sensor observations, the results provide improved estimates of coastal bathymetry and alongshore currents from optical data, especially during storm conditions that are challenging to monitor.