LONG BEACH Residents and visitors in Long Beach may someday have an artificial big rock they can climb for salvation from a future tsunami following a May 20 Long Beach City Council decision to move ahead with getting a grant for a pilot project.
Tall, man-made structures that look like grassy hill-like berms can be found in Japan as an option for people to seek higher ground in the event of tsunami.
In October, the council authorized city staff to execute a grant application for the amount of $1 million from FEMAs Hazard Mitigation Grant Program for the research, design and ultimately the construction of an earthen berm to be located on the southeast side of Long Beach Elementary.
Last year, Project Safe Haven, a grassroots process to develop ideas and strategies about vertical evacuation, brought together University of Washingtons College of Built Environments, emergency management officials and earthquake and tsunami experts to assess the evacuation needs for Long Beach, Ilwaco, Ocean Park, Tokeland and North Cove. After conducting site visits and soliciting public comment, it was determined that Long Beach was in great need of vertical evacuation structures as there was no higher ground located within the city limits.
There were three evacuation structure options that were considered: buildings, towers and berms. Project Safe Haven documents explain:
Berms are artificial high ground created from soil. They typically have ramps at a 1:4 slope providing access from the ground to the elevated surface. Berms have a large footprint on the landscape, giving the appearance of an engineered and designed hill. A berm can range in size from 1,000 square feet for 100 people up to 100,000 square feet for 10,000 people.
A tsunami evacuation tower can take the form of a simple elevated platform above the projected tsunami wave height, or a form such as a lighthouse, that has a ramp or stairs leading to an elevation above projected wave height. A 500 square foot tower can accommodate 50 people and a 1,000 square foot tower can accommodate 100 people.
A building used as a tsunami evacuation structure has several lower levels that allow the tsunami wave to flow through it or the building is faced in a manner that the structural integrity of the building will support the force of the wave. Tsunami refugees seek safety in the upper floors of the building. Typical tsunami evacuation buildings are hotels or parking structures.
It was determined that evacuation structures would need to be easily accessible on foot within 15 minutes time and be able to hold evacuees for 12 to 24 hours (until there is no longer a threat of incoming waves).
According to the projects report, a tsunami generated by a distant earthquake would allow for a couple hours notice for residents to evacuate or it may not affect our area at all. In contrast, a local earthquake would provide little time for people to react and likely cause a tsunami.
Most lives saved for the money
Though tsunami evacuation berms have not been built in the U.S. before, Community Development Director Gayle Borchard says the city has decided to move forward with the berm idea because a cost-benefit analysis showed that it has the potential to save the most lives with the lowest cost per life saved.
According to Borchard, tsunami waves in the vicinity of the school are estimated to be 20 feet high. FEMA guidelines require the height of an evacuation structure to be the height of the wave plus 30 percent plus 10 feet.
She says the berm would be 34 feet high and would hold at least 500 people.
Were really building a big rock, Borchard explains. It will be about an acre at the base. The refuge area thats high and dry and flat is 5,000 square feet.
Borchard says the berms could be multipurpose, such as using it for a kids play area, a seating area for recreation events, a kite-flying mound, a wildlife viewing area, a place for outdoor music events or possibly a public art display.
The project is estimated to cost around $2 million, and the grant would require the city to provide a 12 percent match around $240,000. Borchard said the school districts donation of land can be considered a $40,000 in kind match.
The last 9.0 Cascadia subduction zone earthquake that shook our area was in January 1700 in a cycle that recurs on average every 300 to 500 years. Some experts predict that it will happen sometime in the next 50 years in the southern portion of the subduction zone in the vicinity of the Oregon-California state line. The northern section near us may have a longer timeline.
Information gathered through Project Safe Haven states that a local subduction zone earthquake will originate approximately 80 miles off our coast and last five to six minutes. It could cause the ground to liquify or drop in elevation by as much as six feet, rendering motor vehicles useless. Tsunami waves would be arriving within about 40 minutes after the shaking stops, with the first wave estimated to be around 22 feet high.