Nearshore bathymetry from video and the application to rip current predictions for the Dutch Coast

Abstract

This paper demonstrates the potential use of nearshore bathymetry estimated from video data in a coastal operational model for the Dutch Coast, which provides daily forecast of waves, water levels and (rip) currents. Two video techniques to obtain beach bathymetry from video data- Beach Wizard and CBathy are validated against jet ski surveyed bathymetry. Both methods show good agreement with surveyed data, and bathymetric features of the beach are adequately produced. To assess the applicability of video-derived bathymetry for the purpose of rip current predictions, a model is built for Egmond aan Zee in The Netherlands, in which rip current predictions based on video-derived bathymetry are compared with those based on the jetski survey. Results show that predicted maximum mean offshore-directed (rip) velocities are in good agreement when using surveyed bathymetry (reference model) and video-derived bathymetry. Finally, to address the rip current forecasting skill, this local model is forced by wave boundary conditions obtained from a larger-scale wave prediction model, in addition to the bathymetry from video. Results show that useful information can still be obtained regarding the rip currents' flow where maximum offshore-directed velocities obtained from the predictive model resemble adequately rip currents pattern in the reference model. This paper will discuss each component of the model system and the validation result on hindcasting and forecasting rip currents.