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Open-File Report O-15-02, Local tsunami evacuation analysis of Seaside and Gearhart, Clatsop County, Oregon, by George R. Priest, Laura L. Stimely, Ian P. Madin, and Rudie J. Watzig.

Download .zip file (1.28 GB)

Note: This report was produced in tandem with an abbreviated version submitted to Natural Hazards (Priest and others, 2015) that summarizes only the BTW approach applied to Seaside.

DOGAMI publication includes:

geodatabase icon GIS folder:

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 format files.

Seaside_Tsunami_Evacuation_Modeling.gdb:
Feature dataset: Evacuation_modeling_data
feature classes:
BTW_XXL1__AllBridgesIntact_5minDelay (polygon)
BTW_XXL1_RetrofittedBridgesOnly_5minDelay (polygon)
BTW_XXL1_RetrofittedBridgesOnly_10minDelay (polygon)
EvacuationRoutes_XXL1__AllBridgesIntact_HighResolution (polylines)
EvacuationRoutes_XXL1__AllBridgesIntact_LowResolution (polylines)
EvacuationRoutes_XXL1_RetrofittedBridgesOnly_HighResolution (polylines)
EvacuationRoutes_XXL1_RetrofittedBridgesOnly_LowResolution (polylines)


Raster data: Tsunami wave data
XXL1_MaximumTsunamiFlowDepth
XXL1_TsunamiWaveAdvance
L1_MaximumTsunamiFlowDepth
L1_TsunamiWaveAdvance

Metadata in .xml file format:
BTW-AllBridgesIntact_5minDelay.xml
BTW-RetroOnly_5minDelay.xml
BTW-RetroOnly_10minDelay.xml
EvacRoutes-AllBridgesIntact_HighRes.xml
EvacRoutes-AllBridgesIntact_LowRes.xml
EvacRoutes-RetroOnly_HighRes.xml
EvacRoutes-RetroOnly_LowRes.xml
FlowDepth-L1.xml
FlowDepth-XXL1.xml
WaveAdvance-L1.xml
WaveAdvance-XXL1.xml

Text report:

31-page report in PDF format.

Abstract from the report:

We evaluated difficulty of pedestrian evacuation of Seaside and Gearhart, Oregon, in the event of a local tsunami generated by an earthquake on the Cascadia subduction zone (CSZ). CSZ tsunami scenarios explored are 1) a maximum-considered event covering ~100% of potential variability, termed XXL1 and generated by a magnitude 9.1 earthquake, and 2) an event covering ~95% of variability, termed L1 and generated by a magnitude 9.0 earthquake. We determined minimum walking times to safety (within 20 ft of the inundation limit) for a moderate walking speed of 4 fps (22 minutes/mile) using least cost distance (LCD) routes determined by slight modification of the anisotropic path distance method of Wood and Schmidtlein (2012). Four feet per second is the standard speed for pedestrians to cross at signalized intersections. Evacuation was forced onto the 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 L1 and XXL1, a LCD walking time map (at 4 fps) to the east bank of the Necanicum River, a LCD map to the east bank of Neawanna Creek, a LCD map to the lowest point on the Tillamook Head evacuation route, and “beat-the-wave” (BTW) maps for the XXL1 scenario. The BTW maps depict minimum evacuation speed needed to stay ahead of the wave for three levels of increasing evacuation difficulty: 1) all bridges intact, 5-minute delay from start of earthquake before starting evacuation, 2) only retrofitted bridges intact, 5-minute delay, and 3) only retrofitted bridges intact, 10-minute delay. The results show that evacuation of Gearhart is challenging for a XXL1 tsunami but reasonably possible for an L1 event. Evacuation of Seaside seaward of the Necanicum River is extremely difficult for either the XXL1 or L1 scenario for those with mobility limitations (i.e., <4 fps). LCD and BTW trials showed that any failure of bridges greatly expands areas that cannot be evacuated at 4 fps. Possible mitigation options include increasing the number of evacuation routes by construction of more earthquake-hardened bridges in Seaside, extending Salminen Lane in Gearhart, and installation of tsunami refuges, otherwise known as vertical evacuation structures. Although more bridges across the Necanicum River and Neawanna Creek in Seaside would increase evacuation efficiency, the area positively impacted by each additional bridge would be small relative to the area impacted by a tsunami refuge.

Plates folder:

PDF file format.

Plate 1. Evacuation time map of Gearhart and Seaside the for maximum-considered XXL1 tsunami scenario at 4 fps, 48 x 36 inches

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Plate 2. Evacuation time map of Gearhart and Seaside for the L1 or “Large” tsunami scenario at 4 fps, 48 x 36 inches

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Plate 3. Evacuation time map of Seaside for the L1 tsunami scenario at 4 fps – Avenue G and Avenue U bridges out, 30 x 36 inches

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Plate 4. Evacuation time map of Seaside for the L1 tsunami scenario at 4 fps – Avenue A, West Broadway, and Highway 101 bridges out, 30 x 36 inches

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Plate 5. Evacuation time map of Seaside for the L1 tsunami scenario at 4 fps – hypothetical vertical evacuation structure at Seaside Civic and Convention Center, 30 x 36 inches

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Plate 6. Evacuation time map of Seaside for the L1 tsunami scenario at 4 fps – hypothetical vertical evacuation structure at Trendwest (WorldMark) Resort parking structure, 30 x 36 inches

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Plate 7. Tsunami wave advance map of Gearhart and Seaside for the maximum-considered XXL1 tsunami scenario

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Plate 8. Tsunami wave advance map of Gearhart and Seaside for the L1 tsunami scenario

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Plate 9. “Beat the wave” map for the maximum-considered XXL1 tsunami scenario for Seaside – all bridges intact and assuming a 5-minute evacuation delay, 22 x 32 inches

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Plate 10. “Beat the wave” map for the maximum-considered XXL1 tsunami scenario for Gearhart – all bridges intact and assuming a 5-minute evacuation delay, 22 x 32 inches

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Plate 11. “Beat the wave” map for the maximum-considered XXL1 tsunami scenario for Seaside – only retrofitted bridges intact (12th Street and 1st Avenue brides over the Necanicum River; 12th Street and Broadway Street over Neawanna Creek) and assuming a 5-minute evacuation delay, 22 x 32 inches

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Plate 12. “Beat the wave” map for the maximum-considered XXL1 tsunami scenario for Seaside – only retrofitted bridges intact (12th Street and 1st Avenue brides over the Necanicum River; 12th Street and Broadway Street over Neawanna Creek) and assuming a 10-minute evacuation delay, 22 x 32 inches

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Plate 13. “Beat the wave” map for the maximum-considered XXL1 tsunami scenario for Gearhart assuming a 10-minute evacuation delay, 22 x 32 inches

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