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Layer: Hurricane Evac Zones, Kent County (ID: 3)

Name: Hurricane Evac Zones, Kent County

Display Field: NAME

Type: Feature Layer

Geometry Type: esriGeometryPolygon

Description: This GIS shapefile depicts Hurricane Evacuation Zones that are recommended to be evacuated from potential worst-case Hurricane Surge Inundation. Areas that may become isolated by worst-case Hurricane Surge Inundation are also included in the Evacuation Zones. Inland areas which may be exposed to fresh water flooding only are not included in the Evacuation Zones. Evacuation Zone “A” is recommended to be evacuated prior to an expected category 1 or 2 hurricane. Evacuation Zone “B” is recommended to be evacuated prior to an expected category 3 or 4 hurricane. Evacuation Zone “C”, which exists only for the City of Providence, is recommended to be evacuated in the unlikely event that the Fox Point Hurricane Barrier was to fail during a worst case category 3 or 4 hurricane. Hurricane surge elevations were determined by the National Hurricane Center using the Boston 2 (PV2) SLOSH model basin, and assumed peak hurricane surge arriving at mean high water.The Evacuation Zones are based on the Hurricane Surge Inundation that can be expected to result from a worst case combination of hurricane landfall location, forward speed, and direction for each hurricane category. For the Hurricane Surge Inundation Areas, see the map series entitled “Rhode Island Hurricane Evacuation Study, Hurricane Surge Inundation Mapping”, May 2009, and the accompanying Hurricane Surge Inundation GIS shapefiles for each of the five coastal Rhode Island Counties. This GIS shapefile was created by the U.S. Army Corps of Engineers, New England District under the National Hurricane Program. Partners in the National Hurricane Program include FEMA, the Army Corps of Engineers, and the National Hurricane Center. SLOSH Model hurricane surge data was provided by the National Hurricane Center. There were three GIS datasets that were used to create this Hurricane Evacuation Zones GIS layer for Rhode Island. The first was the RI Hurricane Surge Inundation Areas GIS layer from the Army Corps of Engineers New England District (one shapefile for each of the five coastal Rhode Island counties: Inundation_Bristol, Inundation_Kent, Inundation_Newport, Inundation_Providence, and Inundation_Washington; all May 2009). The second dataset was the 2010 Census Block polygon shapefile from RI GIS (censusSF1_2010, 3/2012). The third dataset was the RI Towns polygon shapefile, also from RI GIS (ritown5k, 8/2001). All GIS data processing was done in ArcGIS 10.0 ArcInfo. In the first step processing the data the censusSF1_2010 polygon shapefile was loaded into ArcMap along with the Hurricane Surge Inundation shapefiles for each of the five counties. A spatial selection (ArcMap, Selection>Select by Location) was done to select the census block polygons that intersected the category 1 and 2 polygons in each county inundation shapefile. Those census polygons were assigned an EVAC attribute of “A”. Then a spatial selection was done to select the census block polygons for each community that intersected the hurricane category 3 and 4 polygons in the inundation shapefile. Finally an attribute query was done to unselect those polygons with an EVAC attribute of “A”. The remaining selected polygons were assigned an EVAC attribute of “B”. This step resulted in a census block shapefile with EVAC attributes of “A” and “B” indicating which Hurricane Evacuation Zone the census blocks belonged to. The name of this shapefile was “censusSF1_2010_w_Evac_Zones”. The next step used the ritown5k polygon shapefile. An attribute query (ArcMap, Selection>Select by Attribute) was done to select the polygons for each community by the community “Name” attribute, and then save the selected records out as a separate polygon shapefile for each of the 21 study communities. Next the censusSF1_2010_w_Evac_Zonespolygon shapefile was clipped to each of the 21 community polygon shapefiles (ArcMap, Geoprocessing>Clip). This step produced 21 shapefiles named [community name]Step1Clip. Next each of the resulting 21 clipped census shapefiles were unioned with the community polygon shapefile (ArcMap, Geoprocessing>Union). The result of these two steps (clipping and then unioning) was to create a census block shapefile for each community that exactly matched the ritowns5k polygon shapefile. The clipping ensured that the census shapefile did not extend outside of the ritowns5k shapefile, and the unioning ensured that the census shapefile completely filled the area of the ritowns5k shapefile. This step produced 21 shapefiles named [community name]Step2Union. Next each of the 21 [community name]Step2Union shapefiles was copied and renamed [community name]HurricaneEvacuationZonesDraft2012. Next each of the 21 [community name]HurricaneEvacuationZonesDraft2012 shapefiles was manually edited. The purpose for this step was to cut census blocks where appropriate to avoid entire large census blocks from being included in an Evacuation Zone when only a small portion of the census block may be impacted by hurricane surge inundation. Another purpose for manual editing was to include areas that may become isolated by hurricane surge inundation. GIS basemaps including roads and aerial photos were used in this step as a visual aid. During this editing step, consideration was given to making the Hurricane Evacuation Zones match at community boundaries. In a few cases communities provided their own Hurricane Evacuation Zone shapefiles, and those shapefiles were used to guide the above manual editing process. This completed the processing and creation of this Hurricane Evacuation Zones GIS layer for Rhode Island. A special case existed in the City of Providence due to the Fox Point Hurricane Barrier. The top of the barrier is at elevation 24.18 feet NAVD88. According to the National Hurricane Center’s SLOSH model, which was used to create the Hurricane Surge Inundation Areas cited in process step 1, the peak worst-case category 2 hurricane surge water surface elevation just seaward of the barrier is 14.7 feet, and the peak worst-case category 3 hurricane surge water surface elevation just seaward of the barrier is 19.6 feet NAVD88. These are still-water elevations, and do not include wave runup. Therefore, the worst-case category 2 & 3 still-water surge would not be expected to overtop the barrier. Waves on top of the category 3 surge could overtop the barrier, but no wave runup analysis was done. Finally, the peak worst-case category 4 hurricane surge water surface elevation just seaward of the Fox Point Hurricane Barrier is 26.6 feet NAVD88. Therefore, the worst-case category 4 still-water surge would overtop the barrier. A hydraulic analysis was done to examine the resulting water surface elevation behind the barrier that would result from overtopping of the barrier during a worst-case category 4 hurricane. The National Hurricane Center provided still-water surge data in 10 minute increments, which was used to calculate the estimated overtopping water volume. The analysis concluded that the resulting water surface elevation behind the barrier could reach elevation 12.9 feet NAVD88 as a result of the overtopping. As a result, behind the barrier, Evacuation Zone “B” was drawn to include census blocks below elevation 12.9 feet NAVD88 feet (with some judgment used to include entire blocks even if only a portion of the block was below that elevation). A third Evacuation Zone “C” was created to include all areas behind the barrier beyond Evacuation Zone B that would be inundated by the worst-case category 4 surge elevation of 26.6 feet NAVD88 (again with some judgment used to include entire blocks even if only a portion of the block was below that elevation). Evacuation Zone “C” represents the area behind the barrier recommended to be evacuated in the unlikely event that the Fox Point Hurricane Barrier was to fail during a worst case category 3 or 4 hurricane. A more detailed discussion of the hydraulic analysis is contained in the Hurricane Evacuation Study Technical Data Report.

Copyright Text: This GIS shapefile was created by the U.S. Army Corps of Engineers, New England District under the National Hurricane Program. Partners in the National Hurricane Program include FEMA, the Army Corps of Engineers, and the National Hurricane Center. SLOSH Model hurricane surge data was provided by the National Hurricane Center.

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MaxRecordCount: 1000

Supported Query Formats: JSON, geoJSON

Min Scale: 0

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Supports Advanced Queries: true

Supports Statistics: true

Has Labels: true

Can Modify Layer: true

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Use Standardized Queries: true

Supports Datum Transformation: true

Extent:
Drawing Info: Advanced Query Capabilities:
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Type ID Field: null

Fields:
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