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Open-File Report O-21-03, Local tsunami evacuation analysis of Gold Beach and nearby unincorporated communities, Curry County, Oregon,
by Laura L. S. Gabel, Fletcher E. O’Brien, and Jonathan C. Allan; 71 p. report, one Esri® geodatabase with internal metadata, external metadata in .xml and .html formats.

PUBLICATION DOWNLOADS

• Report (71 p., 68 MB PDF)
• GIS data bundle: geodatabase plus metadata (10 MB, zip file). Also see metadata links below.
• Complete publication: report, geodatabase, and metadata (76 MB, zip file)
  
  

ABSTRACT
Pedestrian evacuation routes were evaluated for a local tsunami generated by an earthquake on the Cascadia Subduction Zone (CSZ) in the City of Gold Beach and nearby unincorporated communities of Curry County, Oregon. Our analyses focused on a maximum-considered CSZ tsunami event, termed XXL, that could be produced by a locally generated magnitude (Mw) 9.1 earthquake and covers 100 percent of potential variability. We also analyzed evacuation for a slightly smaller local tsunami event covering 95% of potential variability, termed Large (sometimes referred to as L1 in other DOGAMI reports), and generated by a magnitude 8.9 earthquake. Evacuation paths were limited to established roads, trails, and pedestrian pathways designated by local government reviewers as the most likely routes.

To assist in pedestrian tsunami evacuation, we produced maps and digital data that include the following:

• Tsunami wave arrival times for an XXL event,
• Detailed Beat the Wave (BTW) results for the XXL and Large scenarios, including evacuation routes and minimum walking speeds, and
• BTW results for multiple hypothetical scenarios.

The BTW maps depict the minimum evacuation speed required to stay ahead of the tsunami wave for each scenario. For planning purposes, we present a variety of scenarios that increase and decrease evacuation difficulty (due to additional complications and mitigation options, respectively). Model assumptions include:

• Restricting evacuation to pathways rather than permitting cross county travel (i.e., backyard or golf course)
• Applying a 10-minute delay from the start of an earthquake before beginning evacuation to account for:
• the time in which earthquake shaking takes place (3–5 minutes)
• disorientation, shock and collecting family members, go-bags, etc.
• the time required to evacuate a building and reach the nearest road (navigating fallen debris inside building, exiting building, crossing fenced yard, etc.)

In addition to the assumptions listed above, the current conditions scenario also assumes the failure of non-retrofitted bridges. In all cases, the identified minimum speeds must be maintained for the entire time it takes to evacuate from the inundation zone.

Given the model assumptions defined in the Methods section and summarized above, results show that evacuation for most of the region examined is only achievable at relatively fast walking speeds (6 fps, or 4.1 mph) or greater. Those people who find themselves especially far from high ground, such as the beach and the Rogue Shores neighborhood, have the greatest challenge. It will be difficult for evacuees from these locations to reach safety prior to the arrival of the tsunami. Liquefaction and landslides could present additional challenges to evacuation across the region.

In this report, tsunami mitigation refers to actions used to improve the survivability of a local community population. This project is about evaluating ways to help move people out of the tsunami zone in the shortest amount of time possible between the start of earthquake shaking and the arrival of the tsunami. Mitigation options may include adding new evacuation routes, constructing earthquake-hardened roads and trails (that is, built or remodeled to withstand shaking from a major earthquake and liquefaction), enhancing tsunami wayfinding signage along core routes, and/or installing a tsunami refuge, otherwise known as a vertical evacuation structure.

GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.6 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml and .html formatted files.