Development of a lidar-based real-time monitoring system for wave runup and overtopping

Wave runup and overtopping pose significant risk to coastal areas and need continuous monitoring to support disaster mitigation. We propose a real-time coastal monitoring system employing Light Detection and Ranging (lidar) technology. The system was tested at two beaches facing the Sea of Japan over two winter seasons. Both sites experienced heavy snow, rain, and steam fog, and the presence of coastal structures further complicated the accurate shoreline detection. The lidar-based measurements were validated by shoreline positions derived from videos taken by surveillance cameras synchronized with the lidar scanners. While the lidar-based shoreline positions tended to be slightly seaward, the runup height measurements showed strong agreement with the camera-based data. Root mean squared difference (RMSD) values of the runup heights were approximately 0.35 m at the gravel beach, where the wave runup heights reached 5 m several times. At the composite beach of sand and gravel, the RMSD values were below 0.2 m, with maximum runup heights reaching 2.5 m. The system also demonstrated the capability to detect wave overtopping at a seawall under severe storm conditions. The findings demonstrate that the proposed system can provide quantitative data on wave runup and overtopping, offering valuable support for coastal management.