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Open-File Report O-18-06, Tsunami evacuation analysis of Pacific City, Tillamook County, Oregon,
by Laura L. S. Gabel, Fletcher O'Brien, and Jonathan C. Allan; 54 p. report, including tabloid-sized maps in appendices, one Esri® geodatabase with internal metadata, external metadata in .xml format.

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ABSTRACT
We evaluated pedestrian evacuation in the communities of Pacific City, Nestucca Spit, Woods, Tierra Del Mar, and Sand Lake, Tillamook County, in the event of a local tsunami generated by an earthquake on the Cascadia subduction zone (CSZ). Our analyses focused on 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 (defined as ~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 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 (U.S. Department of Transportation, 2012). Evacuation paths were limited to roads, trails, and pedestrian pathways designated by local government reviewers as the most likely routes.
To estimate whether pedestrians can stay ahead of a tsunami along the evacuation routes, we produced maps of:

The BTW maps depict the minimum evacuation speed required to stay ahead of the tsunami wave given a variety of scenarios that will increase evacuation difficulty. The primary scenario uses the existing road network and includes a 10-minute delay from start of earthquake before beginning evacuation. Additional challenges to evacuation are examined, including failure of non-retrofitted bridges and effects from liquefaction. 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 limitations defined in the Methods section, results show that evacuation of the entire region is achievable at a moderate walking speed (4 fps) whether or not the bridge network remains viable. Even for those with mobility limitations (i.e., those who cannot travel at speeds more than 4 fps), safety can be reached ahead of the wave from nearly every location within the community boundaries. Liquefaction, however, is shown to present a significant challenge to evacuation across the region. Finally, long distances to high ground and difficult walking conditions result in evacuation challenges for Nestucca Spit.

Possible mitigation options include increasing the number of evacuation routes by constructing more earthquake-hardened bridges (built or remodeled to withstand shaking from a major earthquake); adding new evacuation routes; and/or installing a tsunami refuge, otherwise known as a vertical evacuation structure, on Nestucca Spit.


GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA

Geodatabase is EsriĀ® version 10.1 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.

Pacific_City_Tsunami_Evacuation_Modeling.gdb (GIS data bundle zip file)
   rasters
         MaxTsunamiFlowDepth_XXL1 The maximum tsunami flow depth raster shows the maximum tsunami flow depths estimated for a maximum-considered XXL1 tsunami caused by a magnitude 9.1 CSZ earthquake. Data are from DOGAMI Open-File Report O-13-17. Flow depths were not directly incorporated into the evacuation difficulty analysis but are included in this report to assist in the evaluation of mitigation options. .xml
         TsunamiWaveArrival_XXL1 The tsunami wave arrival time raster shows estimated wave arrival times for a maximum-considered XXL1 tsunami caused by a magnitude 9.1 CSZ earthquake. The tsunami starts toward shore at the moment the earthquake starts, but the shaking from the earthquake can last three to five minutes. Wave arrivals are shown as the time when wave depth reaches 6 inches or greater at any location, and arrivals are timed from the start of the earthquake. .xml
 
  feature dataset - L1_BridgesOut
We calculated BTW results for the Large tsunami scenario, termed L1, which covers 95% of potential variability and is generated by a magnitude 9.0 earthquake. This provides alternative safety destinations for areas where evacuation from XXL is unlikely.
         L1_BridgesOut_EvacuationFlowZones Polygons. Evacuation flow zones depict the nearest safety destination for every point in the inundation zone (on the road and trail network) assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. .xml
         L1_BridgesOut_EvacuationRoutes Polylines. Evacuation routes depict the most efficient routes to safety for every point in the inundation zone (on the road and trail network) assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. .xml
         L1_BridgesOut_WalkingSpeeds_Roads Polygons. Polygons. Minimum evacuation speeds needed to stay ahead of the wave assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains BTW data on paved roads. .xml
         L1_BridgesOut_WalkingSpeeds_Trails Polylines. Minimum evacuation speeds needed to stay ahead of the wave assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains BTW data on trails and beach networks only. .xml
 
   feature dataset - XXL1_BridgesIn
Analyses focused on a maximum-considered Cascadia Subduction Zone tsunami event covering 100% of potential variability, termed XXL1 and generated by a magnitude 9.1 earthquake. Assumes the existing road, trail, and bridge network remains intact.
         XXL1_BridgesIn_EvacuationFlowZones Polygons. Evacuation flow zones depict the nearest safety destination for every point in the inundation zone (on the road and trail network) assuming the existing road, trail, and bridge network remains intact. .xml
         XXL1_BridgesIn_EvacuationRoutes Polylines. Evacuation routes depict the most efficient routes to safety for every point in the inundation zone (on the road and trail network) assuming the existing road, trail, and bridge network remains intact. .xml
         XXL1_BridgesIn_WalkingSpeeds_Roads Polygons. Minimum evacuation speeds needed to stay ahead of the wave assuming the existing road, trail, and bridge network remains intact. This feature class contains BTW data on paved roads. .xml
         XXL1_BridgesIn_WalkingSpeeds_Trails Polylines. Minimum evacuation speeds needed to stay ahead of the wave assuming the existing road, trail, and bridge network remains intact. This feature class contains BTW data on trails and beach networks only. .xml
 
   feature dataset - XXL1_BridgesOut
Analyses focused on a maximum-considered Cascadia Subduction Zone tsunami event covering 100% of potential variability, termed XXL1 and generated by a magnitude 9.1 earthquake. Assume all non-retrofitted bridges within the inundation zone fail due to earthquake shaking.
         XXL1_EvacuationFlowZones Polygons. Evacuation flow zones depict the nearest safety destination for every point in the inundation zone (on the road and trail network) assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. .xml
         XXL1_EvacuationRoutes Polylines. Evacuation routes depict the most efficient routes to safety for every point in the inundation zone (on the road and trail network) assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. .xml
         XXL1_EvacuationTime4fps_Roads Polygons. Time required to reach the nearest safety destination for every point in the inundation zone based on a standard walking speed of 4 ft/sec assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains BTW data on paved roads only. .xml
         XXL1_EvacuationTime4fps_Trails Polylines. Time required to reach the nearest safety destination for every point in the inundation zone based on a standard walking speed of 4 ft/sec assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains Beat the wave (BTW) data on trails and the beach only. .xml
         XXL1_WalkingSpeeds_Roads Polygons. Minimum evacuation speeds needed to stay ahead of the wave assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains BTW data on paved roads only. .xml
         XXL1_WalkingSpeeds_Trails Polylines. Minimum evacuation speeds needed to stay ahead of the wave assuming all non-retrofitted bridges within the inundation zone fail due to earthquake shaking. This feature class contains BTW data on trails and beach networks only. .xml