DOGAMI OPEN-FILE REPORT SERIES
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Open-File Report O-23-04, Tsunami Evacuation Analysis of Bandon, Bullards Beach State Park, Langlois, and Floras Lake, Coos and Curry Counties, Oregon, by Laura L. S. Gabel, Fletcher O’Brien, and Jonathan C. Allan; 61 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 City of Bandon and nearby unincorporated communities of southern Coos and northern Curry Counties, Oregon including Bullards Beach State Park, Langlois, and Floras Lake. 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. 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 Beat the Wave 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-country 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 and go-bags
- the time required to evacuate buildings and reach the nearest road (navigating fallen debris inside and exiting building, crossing a 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 limitations defined in the Methods section and summarized above, results vary widely for the region with some areas requiring jog,
run and in some cases
sprint (5.5, 6.8, and 10 mph, respectively). This is due to early wave arrival times and long evacuation distances. Liquefaction and lateral spreading could present additional challenges to evacuation across the region and are not examined in detail.
In this report, tsunami mitigation refers to actions used to improve the survivability of a local 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 (built or remodeled to withstand shaking from a major earthquake and liquefaction), improving tsunami wayfinding signage along core routes, and/or installing a tsunami refuge, otherwise known as a tsunami vertical evacuation structure.
GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.7 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml format files.
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| XXL1_BridgesOut_EvacuationFlowZones |
This polygon feature class shows 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. This layer was created based on the Extra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ)tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least10,000 years.
| .xml |
XXL1_BridgesOut_EvacuationRoutes
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This line feature class shows 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. Symbolize in ArcGIS with arrow at end of each segment to see direction offline. This layer was created based on the Extra-extra-large1(XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years.
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XXL1_BridgesOut_WalkingSpeeds_Roads
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This polygon feature class shows minimum evacuation speeds, in feet per second, 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 data on paved roads. A separate feature class contains data for trails and beach networks. This layer was created based on theExtra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years.
| .xml
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XXL1_BridgesOut_WalkingSpeeds_Trails
| This line feature class shows minimum evacuation speeds, in feet per second, 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 data on trails and beach networks. A separate feature class contains data for paved roads. This layer was created based on theExtra-extra-large1 (XXL1) tsunami scenario, which is a Local Cascadia Subduction Zone (CSZ) tsunami scenario generated by a magnitude 9.1 earthquake. The XXL1 event has an estimated recurrence rate of at least 10,000 years.
| .xml
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