During-event Tsunami Observations at Crescent City Harbor

We investigated a rare tsunami-induced failure mode at Crescent City Harbor, CA: the transient, full submergence of large concrete floating dock modules without structural breakup. The mission focused on identifying the hydrodynamic mechanism(s)—particularly under-deck pressure deficits and blockage effects—that can overcome residual buoyancy and induce vertical instability under tsunami-driven currents.

The investigation combined during-event observations with rapid post-event reconnaissance. We assembled and time-synchronized harbor water-level records, georeferenced bathymetry/harbor geometry, as-built dock specifications, and high-frame-rate time-lapse video. Methods included: camera calibration and video-based kinematic tracking of freeboard loss and re-emergence; image-assisted current estimation and uncertainty bounds; simplified force-balance and Bernoulli/Venturi analyses for under-deck pressure; and consistency checks against harbor resonance timescales. All processing steps are scripted with documented inputs/outputs and metadata for reproducibility.

The dataset and analyses document a coherent submergence–resurfacing sequence consistent with negative hydrodynamic lift generated by accelerated, constricted flow beneath the dock. Despite large vertical excursions and joint misalignment upon resurfacing, global structural integrity was retained—implicating vertical stability, rather than strength, as the governing vulnerability. The mission yields traceable evidence linking basin-scale forcing, local current amplification, and float response, and distills testable thresholds for future modeling.