TSUNAMI HAZARD ANALYSIS AND PRODUCTS FOR HARBORS IN CALIFORNIA

In the aftermath of the 2011 Tohoku Japan tsunami, which caused $100M in damage to 27 harbors in California, the State entered into a partnership with FEMA to address tsunami hazards within the State’s 70+ harbors and ports. California worked with engineers at the University of Southern California and State Lands Commission to develop products that improve maritime preparedness, response, mitigation, and recovery.

For preparedness and response, the challenges were to determine: 1) the relationship between tsunami currents and damage potential; and, 2) the threshold tsunami wave heights which create damaging currents within each harbor. Based on current velocity measurements from post-event modeling at known damage locations, velocity categories were established for minor (3-6 knots), moderate (6-9 knots), and major (>9 knots) amounts of tsunami damage. For each harbor, five scenarios with different incoming tsunami wave heights were modeled, current-related damage potential maps were created, and response plans called “playbooks” were generated. During future tele-tsunamis, real-time tsunami forecast wave heights will be used to determine which scenario plan from the playbook should be implemented by the harbors. Harbor managers can reference these plans in real time to determine which docks, boats, and infrastructure require the appropriate response actions prior to tsunami arrival.

To address tsunami mitigation, evaluations are being completed to determine the impacts of currents on dock cleats and pile guides, and from movement of sediment and debris. Harbor Improvement Reports (HIRs) summarize these findings and outline direct mitigation activities for inclusion in Local Hazard Mitigation Plans. These HIRs were used by some harbors to apply for 2017 Hazard Mitigation Grant funding.

Recovery guidance assists harbor managers with both short- and long-term recovery issues. Short-term problems, addressed immediately after an event, include removing floating and sunken debris and setting up temporary moorings where docks are damaged. Long-term recovery issues require plans for sediment removal, reconstruction, and streamlining regulatory paperwork. Harbors that have recovery plans will initiate work more quickly and reduce the loss of business and revenue over the long run.