COASTAL FLOODING & SOLUTIONS, Workshop Case Studies
Real-Time Tsunami Evacuation and Maritime Response Decision-Support Tools
All coastal entities: 20 counties, 100 cities, and 70 harbors/ports
California Geological Survey
California’s experience during the 2011 Tohoku-Oki tsunami led coastal emergency managers and harbor officials to request more detailed information on the estimated flood levels and impacts for distant-source tsunamis. To help address this, decision-support tools known as “playbooks” have been developed to plan for tsunami scenarios of various sizes and source locations.
Tsunami evacuation playbooks can be useful for partial evacuations when there is sufficient time to implement a partial or secondary evacuation. To help determine what level of evacuation is warranted, an analytical tool called the “FASTER” approach predicts the “total water” flood elevation compared to Mean Sea Level. FASTER is an acronym for the various factors influencing flooding, including the tsunami Forecast Amplitude, Storm, Tides, Error, and Run-up potential. Based on the FASTER flood elevation level, a minimum playbook evacuation plan is recommended for over 100 coastal communities in real-time.
For ports and harbors, the real-time playbook recommendation process is similar except that the tsunami scenarios are selected based on the anticipated tsunami forecast amplitude alone. Five tsunami scenarios of different initial tsunami amplitude have been created showing where damaging currents are likely to occur during that scenario. These scenarios typically range in tsunami amplitude from 0.3 meters to 1-2 meters or greater for the 70 ports and harbors vulnerable to tsunamis.
Use of these tsunami decision-support tools prior to the arrival of a distant source tsunami can help communities be more consistent in their response activities and reduce dependence on an all or nothing response approach.
Playbook products have been integrated into many city, county, port, and harbor emergency response plans statewide. The real-time use of the product by harbor officials occurred during the September 16-17, 2015 tsunami generated by a magnitude 8.3 earthquake off the coast of Chile. CGS and Cal OES have run an playbook communications exercise with community and harbor officials annually since 2015.
The following are challenges or gaps in this work: 1) additional tide gauges are needed along the California coast to better forecast and monitor tsunami amplitudes/activity; 2) we would like to use a better approach than the ETSS to forecast swell and storm surge along the coast; 3) forecasted tsunami amplitude information should be provided more quickly than the 1-3 hour window it presently has through the National Tsunami Warning Center; 4) deployment of ADCP instruments in harbors would allow us to test our tsunami model currents; and 5) the Covid-19 pandemic has reduced the State's capability to coordinate with community and harbor officials.