A Kinematic Approach for Rip Current Identification from ADCP Observation Data at Haeundae Beach, Korea

Abstract In May 2023, direct observations of rip currents were conducted at Haeundae Beach, Korea, over a two-day period at six different stations using upward-facing Acoustic Doppler Current Profilers (ADCPs). The depth-averaged cross-shore velocity data were low-pass filtered with a 30-s cutoff period to eliminate wave-related motions. By applying 15-min boxcar averages, correlation analyses were performed to examine the relationship between three types of flow (cross-shore, onshore, and offshore) and three environmental factors (tide, wave, and wind). The analysis revealed that only one (R2-3) of the six stations had a high likelihood of rip current occurrence. Rip currents were defined as regions of offshore flow within the low-pass filtered time series of cross-shore velocities. For each identified rip current, three key kinematic features—maximum speed, duration, and distance—were estimated. Using specific thresholds for these features, hazardous rip currents were determined. Station R2-3 was the only station where hazardous rip currents were observed, which is consistent with the findings of the correlation analysis. Additionally, swells with a 15-s period were detected exclusively at R2-3 during the period of the hazardous rip currents, suggesting their significant role in the development of the observed rip currents. Furthermore, both Rip Index from the Rip Current Monitoring and Warning System and the CCTV Score from the Rip Current Checklist exceeded threshold values during this period, reinforcing the reliability of the method used. The potential influence of bound infragravity waves on the duration and variability of these rip currents was discussed. The rip currents observed at Haeundae Beach could be categorized as the "focused" type.