I02-22

Tsunamis are rare events often accompanied by advance warning. Where horizontal evacuation out of the tsunami inundation zone is neither possible nor practical, a potential solution is vertical evacuation above rising waters into buildings and other structures with the strength and resilience necessary to resist the effects of tsunami waves. A vertical evacuation refuge is a structure or earthen mound designated as a place of refuge in the event of a tsunami, with sufficient height to elevate evacuees above the tsunami inundation depth, designed and constructed to resist tsunami load effects.

Location of Source	Approximate Warning Time (t)
Far-source-generated tsunami	t > 3 hours
Mid-source-generated tsunami	1 hour < t < 3 hours
Near-source-generated tsunami	t < 1 hour

The average, healthy person can walk at approximately 4 miles per hour. However, some members of the community may have restricted ambulatory capability due to age, health, or disability. The average pace (ambulatory speed) of a mobility-impaired population can be assumed to be 2 miles per hour.

Warning Time	Ambulatory Speed	Travel Distance	Maximum Spacing
3 hours	2 miles per hour	6 miles	12 miles
1 hour	2 miles per hour	2 miles	4 miles
1⁄2 hour	2 miles per hour	1 mile	2 miles
1⁄4 hour	2 miles per hour	1⁄2 mile	1 mile

The vertical evacuation refuges illustrated below by number are located some distance inland from the coastal shoreline and each circle has a radius of 4 miles.

Structure No. 1 is located adjacent to the harbor and a container terminal. Impact forces from ships, barges, boats, shipping containers, and other waterborne debris have the potential to be very large. Locations with additional sources of large, possibly buoyant, debris increase the chances of impact by one or more waterborne missiles, and increase the potential risk to the structure.

Structure No. 2 is located off to the side of the harbor and adjacent to a parking lot. This structure would need to be designed for debris consistent with the use of the parking lot and surrounding areas, which could include cars, trucks, and recreational vehicles.

Structure No. 3 is immediately adjacent to a gas station. In past tsunamis, ignition of flammable chemicals or other floating debris has resulted in significant risk for fire in partially submerged structures.

Structure No. 4 is adjacent to a waterfront park facility. This location can be ideal, as the potential for waterborne debris can be relatively low. Possible hazards could include debris from park structures, naturally occurring driftwood, or larger logs from downed trees. This area has a higher potential for tourists and visitors unfamiliar with the area and would require additional signage to inform park users what to do and where to go in the event of a tsunami warning.

Structure No. 5 is adjacent to an emergency response facility. Co-locating at such facilities can provide opportunities for direct supervision by law enforcement and monitoring and support of refuge occupancies by other emergency response personnel.

Structure No. 6 is intended to aid evacuees in taking advantage of naturally occurring high ground at two locations.