An early warning system for wave-driven coastal flooding at Imperial Beach, CA

Abstract Waves overtop berms and seawalls along the shoreline of Imperial Beach (IB), CA when energetic winter swell high tide coincide. These intermittent, few-hour long events flood low-lying areas pose a growing inundation risk as sea levels rise. To support city response management, an IB warning system was developed. Total water level (TWL) forecasts combine predictions tides sea-level anomalies with wave runup estimates based on incident nonlinear model SWASH. In contrast to widely used empirical formulas that rely significant height peak period, use only foreshore slope for bathymetry, SWASH incorporates spectral forcing uses cross-shore depth profile. TWL using emulator demonstrate skill several days in advance. Observations set thresholds minor moderate flooding. The specific conditions lead flooding, key contributors uncertainty, are identified. forecast is reduced by errors one-dimensional model, lack information variable beach morphology (e.g., protective sand can erode during storms). Model largest most extreme events. Without mitigation, projected rise will substantially increase duration severity street Application approach other locations requires hindcasts forecasts, numerical simulation associated local storms morphology, calibration observations.