Surfing Transport of Buoyant Objects Observed in the Nearshore

Free-drifting buoyant objects, including plastics, marine debris, and organisms, move with the wind, waves, and surface currents. These objects also surf on breaking waves; this process adds to the total transport of the objects and can control beaching. Observations of surfing transport are made using small free-drifting buoys called microSWIFTs. The drifters are deployed nearshore at the US Army Corps of Engineers Field Research Facility in Duck, NC, USA, as part of the During Nearshore Events Experiment in October 2021. Surfing events are observed in the drift trajectories of the buoys as “jumps” in the time series of cross-shore position. There are 3,172 surfing events observed, with a median jump amplitude of 8.3 m and a median duration of 2.5 s. These median values are 13 (Formula presented.) of a characteristic offshore wavelength and 32 (Formula presented.) of a characteristic offshore wave period, respectively. The median bulk jump speed (jump amplitude/jump duration) is 82 (Formula presented.) of the linear phase speed for waves in the corresponding jump depth. The buoys' trajectories are simulated using three models of increasing complexity: “Wind-Only,” “Wind and Waves,” and “Wind, Waves, and Surfing.” The surfing process is represented using a probabilistic parameterization. When surfing is included in the models, the terminal location of the modeled objects (on beach or offshore) is correctly predicted in 93 (Formula presented.) of cases compared to 76 (Formula presented.) and 84 (Formula presented.) for the “Wind-Only” and “Wind and Waves” models, respectively. Including surfing also significantly improves the accuracy of the time-to-beach and alongshore beaching location.