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

Mark A. Merrifield (), Mele Johnson, R. T. Guza, Julia W. Fiedler, Adam P. Young, Cassandra S. Henderson, Athina M. Z. Lange, William C. O’Reilly, Bonnie C. Ludka, Michele Okihiro, Timu Gallien, Kyle Pappas, Laura Engeman, James Behrens and Eric Terrill
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Mark A. Merrifield: Scripps Institution of Oceanography UCSD
Mele Johnson: Scripps Institution of Oceanography UCSD
R. T. Guza: Scripps Institution of Oceanography UCSD
Julia W. Fiedler: Scripps Institution of Oceanography UCSD
Adam P. Young: Scripps Institution of Oceanography UCSD
Cassandra S. Henderson: Scripps Institution of Oceanography UCSD
Athina M. Z. Lange: Scripps Institution of Oceanography UCSD
William C. O’Reilly: Scripps Institution of Oceanography UCSD
Bonnie C. Ludka: Scripps Institution of Oceanography UCSD
Michele Okihiro: Scripps Institution of Oceanography UCSD
Timu Gallien: UCLA Samueli School of Engineering
Kyle Pappas: University of Hawaii At Manoa
Laura Engeman: Scripps Institution of Oceanography UCSD
James Behrens: Scripps Institution of Oceanography UCSD
Eric Terrill: Scripps Institution of Oceanography UCSD

Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards, 2021, vol. 108, issue 3, No 11, 2612 pages

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

Keywords: Coastal flooding; Nearshore model; Wave runup; Warning system; Sea-level rise (search for similar items in EconPapers)
Date: 2021
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DOI: 10.1007/s11069-021-04790-x

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