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Open-File Report O-16-08, Local tsunami evacuation analysis of Warrenton and Clatsop Spit, Clatsop County, Oregon
by Laura L. S. Gabel and Jonathan C. Allan, 56 p. report, GIS data.

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ABSTRACT from the report:

We evaluated difficulty of pedestrian evacuation in the communities of Warrenton and Hammond and on Clatsop Spit, Clatsop County, Oregon, in the event of a local tsunami generated by an earthquake on the Cascadia subduction zone (CSZ). We examined a maximum-considered CSZ tsunami event covering ~ 100% of potential variability, termed XXL1 and generated by a magnitude 9.1 earthquake. We determined minimum walking times to safety (~ 20 ft beyond the inundation limit) for a moderate walking speed of 4 fps (feet per second, 22 minutes/mile) using least cost distance (LCD) routes determined by slight modification of the anisotropic path distance method of Wood and Schmidtlein (2012) and Wood and others (2016). Four feet per second is the standard speed for pedestrians to cross at signalized intersections. Evacuation was limited to roads and pedestrian pathways designated by local government reviewers as the most likely routes. In order to estimate whether pedestrians can stay ahead of a tsunami along entire routes, we produced tsunami wave advance maps for XXL1, LCD walking time maps (at 4 fps), and “beat the wave” (BTW) maps for the XXL1 scenario; detailed maps are also included for Clatsop Spit, Hammond and Alder Creek, Warrenton, Camp Rilea, and Fort Stevens campground. The BTW maps depict the minimum evacuation speed required to stay ahead of the wave for two levels of increasing evacuation difficulty: 1) all bridges intact, 10-minute delay from start of earthquake before starting evacuation, and 2) only retrofitted bridges intact, 10-minute delay. These minimum speeds must be maintained for the duration that it takes to safely evacuate from the inundation zone. The results show that evacuation from Clatsop Spit and Alder Creek areas is challenging for an XXL1 tsunami. In particular, evacuation from these areas will be extremely challenging for the XXL1 scenario for those with mobility limitations (i.e., those travelling at speeds less than 4 fps). LCD and BTW trials showed that any failure of bridges greatly expands areas that cannot be evacuated. Possible mitigation options include increasing the number of evacuation routes by construction of more earthquake-hardened bridges, the addition of new evacuation routes, and/or installation of tsunami refuges, otherwise known as vertical evacuation structures, in the Alder Creek area and at the tip of Clatsop Spit.


Geodatabase is Esri® version 10.2 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.

Feature dataset: Evacuation_modeling_data
feature classes:

Metadata in .xml file format: