Service Description: Populations isolated during a local tsunami event.

Service ItemId: b06346ee60f44027bed2229c8a986304

Has Versioned Data: false

Max Record Count: 1000

Supported query Formats: JSON

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• Isolated Population Area (0)

Description: The island mapping project is a collaboration of the Cascadia Region Earthquake Workgroup, the Oregon Office of Emergency Management (OEM) and Lane Community College GIS Cooperative Education. Large-format maps showing coastal community infrastructure (roads and facilities) vulnerable in the event of a Cascadia Subduction Zone earthquake and tsunami were used during community workshops to identify populations that will be isolated due to infrastructure damage after a XXL tsunami from a 9.0 Cascadia Earthquake. The coastal areas mapped for this project cover the extent used in the DOGAMI map series Open file report 0-13-06, “Tsunami Inundation Map for a Simulated Magnitude 9 Cascadia Earthquake.” Two series of coastal workshops were held to collect and ground truth maps and data. The five initial workshops were held in June 2014 in Clatsop, Tillamook, Lincoln, Coos, and Curry Counties. During each workshop, participants used large-format maps of the region to identify areas of population that would be isolated due to tsunami inundation and bridge failure. Participants also identified additional assembly areas and facilities that were missing or needed updating. The second series of workshops was held in June 2016 in Clatsop, Tillamook, Lincoln, Lane, Coos, and Curry Counties. In these workshops, participants verified and updated the population islands, located potential landing areas, identified additional assembly areas and other critical facilities. The maps for the workshop in 2014 were created using the tsunami inundation polygon (DOGAMI), roads and bridges (ODOT and US Census), critical facilities: schools, hospitals, police stations, fire stations (DOGAMI), and existing assembly areas (DOGAMI) within the mapping extent. The assumption used for producing the large-format maps is that all facilities and infrastructure (bridges, roads, buildings) within the XXL tsunami inundation would be destroyed. Therefore, the tsunami polygon layer was used and an erase feature to remove the sections of road, the bridges, assembly points, and buildings that were in the inundation area. The roads, bridges, critical facilities, and assembly areas represent only those features that are outside the XXL tsunami inundation. The maps show a transparent tsunami inundation polygon over an aerial image. The population islands identified on the large-format maps were captured as GIS layers and added to the maps for the 2016 workshops. The additional assembly areas and other changes to the critical facilities were edited according to information from the 2014 workshops and included in the 2016 maps. A total of 260 population islands were identified. The islands range in size from 0.002 square miles to 12 square miles. To understand the impact on population, it was necessary to estimate the number of people in the proposed islands. Population was determined using the US Census 2010 block files. This was the most comprehensive data available for the smallest areal extent that covered both urban and rural areas. The total population for the mapped area is 208,277. The population for the area within the tsunami inundation and within the population islands was calculated using the areal allocation method (AAM). This method is used to estimate the population for a portion of a census block when the tsunami inundation line or the population island outline intersects or splits the census block. The population for the portion of the split census block is recalculated based on the change in area from the original block. For example, if the census block is split in half, then the population for the new segment is also halved. The results of the areal allocation method was compared to population estimates generated by DOGAMI Residential Building Proration Method (RBPM) for Tillamook and Curry Counties. This method also used the 2010 Census block data. In this method the population for each block is prorated by the size of the residential buildings in the block. The Residential Building Proration method shows 14,001 people in islands in Tillamook County and 13,767 people in islands in Curry County. The method shows 6,473 people in Tillamook County in the tsunami inundation area and 6,909 people in Curry County in the tsunami inundation area. The centroid of each island was generated and given the Latitude and Longitude in decimal degrees. This file was joined to the Public Land Survey System that includes the Township, Rang, and Section for the index area of the project. Each island centroid can be identified by this location information. Figure three shows the centroid and label for an ilsand in Section 10, T18S, R12W. If more than one centroid occurs in a one mile by one mile section, each is given a fourth identifier, which indicates the island orientation north to south.

Copyright Text: Lynn Songer, Lane Community College

Spatial Reference: 102381 (6868)

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Units: esriFeet

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Supported Operations:   Query   ConvertFormat   Get Estimates   Create Replica