Natural wave tank experiment for validating depth inversion algorithm in the intertidal beach

Waves develop by the wind on a wide offshore area and propagate long-distance preserving most of their energy but are dissipated by wave breaking in a relatively narrow shore area. Therefore, on the shore where a considerable amount of energy loss is concentrated through wave breaking, the energy causes active movement of sediment and changes in coastal topography. To understand the complex physical phenomena on the shore, accurate observations of coastal bathymetry are essential. However, observing the water depth on the shore is not an easy task due to the too low water depth and the continuous movement of the water surface by waves. The recent development of camera monitoring techniques makes it possible to observe many processes occurring on the beach such as shoreline changes, longshore currents, wave set-up/down, etc. In particular, Holman et al. (2013) developed cBathy depth inversion algorithm which estimates water depth using dispersion relationship of waves. This algorithm uses the relationship between water depth, wave frequency, and wavenumber to estimate water depth, and it also uses Kalman Filter to avoid the contamination of images due to sun glare, weather conditions, and no waves. By using cBathy, it is possible to observe the beach depth remotely from only water surface information more frequently. Despite the powerful efficiency of cBathy algorithm, comparison with field observations has to be carried out for validation of its algorithm in order to increase its utilization. In this study, we test cBathy algorithm on the intertidal beach on the west coast of Korea. The intertidal beach has tidal ranges over 5 m and can serve as a physical wave tank with a scale of 1 by comparing the bathymetry estimated during high tide with the bathymetry surveyed during low tide. Usually, in the physical model experiment for morphological changes due to waves and currents, the coastal topography is built in a certain reduced ratio in a 3-dimensional wave tank, and fill the water, generate waves and currents, drain the water again, and observe the topographic changes due to waves and currents in detail. The validated depth inversion algorithm at shorter time intervals can be used as input data to the numerical sediment transport & morphological change model, and more accurate beach depth prediction will be possible.