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Open-File Report O-19-08, Tsunami evacuation analysis of some unincorporated Tillamook County communities: Building community resilience on the Oregon coast,
by Laura L. S. Gabel, Fletcher E. O’Brien, John M. Bauer, and Jonathan C. Allan; 68 p. report, one Esri® geodatabase with internal metadata, external metadata in .xml format.

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ABSTRACT
Pedestrian evacuation routes were evaluated for a local tsunami generated by an earthquake on the Cascadia Subduction Zone (CSZ) in the Tillamook County communities of Cape Meares, Bayocean Spit, Oceanside, Netarts, Cape Lookout State Park, and Neskowin. Our analyses focused on a maximum-considered CSZ tsunami event covering 100% of potential variability, termed XXL and generated by a magnitude 9.1 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:

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 base scenario uses the existing road network and includes a 10-minute delay from start of earthquake before beginning evacuation. Additional challenges to evacuation are discussed, including failure of non-retrofitted bridges and effects from landslides and 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 for most of the Tillamook County communities examined is achievable at a moderate walking speed (4 fps or 2.7 mph). 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. Exceptions to this arise on Bayocean Spit, Cape Lookout State Park, and Neskowin. For the latter, longer distances to high ground and limited evacuation routes make this an especially difficult location to reach safety prior to the arrival of the tsunami. Liquefaction could present a significant challenge to evacuation across the region.

For the purposes of this report, we refer to tsunami mitigation in terms of actions used to improve the survivability of a local community population. Thus, the results presented in this study are 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. Given this context, mitigation options may include adding new evacuation routes, constructing earthquake-hardened roads (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 10.1 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.

Tillamook_County_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. 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. Assume 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 only. .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_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