Data Management Plan

This feature class resides within the SOCECON Feature Data Set of the Maine and New Hampshire 2016 ESI geodatabase. It contains vector polygons representing Natural Hazard human-use resource data for waters and lands within the Maine and New Hampshire 2016 ESI study area.

The vector polygons represent predicted flood inundation in the event of a Category 1, 2, 3, or 4 storm. For each storm category, the level of flooding is binned into anticipated depth of flood waters: <= 3 feet, > 3 feet, > 6, and > 9 feet. These are modeled data, based on the National Hurricane Center’s Sea, Lake and Overland Surges from Hurricanes (SLOSH) model (https://www.nhc.noaa.gov/surge/slosh.php). Raster model data, prepared in 2015, was converted to vector polygons for the purpose of the ESI. These data should be used for planning purposes only.

The ArcGIS feature class (NATURAL HAZARD POLYS) has 2 associated attribute tables, considered as Entities or "Child Items" in this metadata record. Location-specific Type and Source information are stored in these related data tables, SOC_DAT and SOURCES (described below), which are stand-alone tables within the Geodatabase.

This data set is a portion of the ESI data for Maine and New Hampshire - 2016. As a whole, the ESI data characterize the marine and coastal environments and wildlife by their sensitivity to spilled oil, and include information for three main components: shoreline habitats, sensitive biological resources, and human-use resources.

Additional human-use information is provided in other feature class themes within the SOCECON Feature Data Set, including NAVIGATION/MARINE (POINTS, LINES, and POLYGONS), PARKS/MANAGED AREA (POINTS and POLYGONS), POLITICAL/JURISDICTIONAL (POINTS and POLYGONS), RESOURCE MANAGEMENT (POINTS and POLYGONS), and SOCECON (POINTS AND POLYGONS).

Process Steps:

• 2016-08-01 00:00:00 - The original NHC SLOSH data was a raster data layer with a geographic extent from Maine to Texas. The first process step was to subdivide the source raster data into geographic regions corresponding to an area slightly larger than the ESI region’s geographic extent. The resultant data were then converted to polygons within Arcmap, using the conversion tool Raster to Polygon. (Citation: National Storm Surge Online Map Service)
• 2016-08-01 00:00:00 - A tool was developed, automating the next several steps to ensure consistency. The SLOSH polygon data were projected into the appropriate UTM zone, then clipped to the ESI shoreline and converted from multipart to singlepart polygons. The resultant polygons were unioned with a universal polygon representing the entire area of interest. This step enables identification of SLOSH polys that do not correspond to land (either due to the vectorization process or because of differences between the SLOSH model’s shoreline and the ESI shoreline); these polygons are coded for deletion. Area, perimeter and ratio (area/perimeter) is calculated all polygons.
• 2016-08-01 00:00:00 - A field, “INUNDATION”, is added to the feature data table, and a value of “<= 3 ft”, “> 3 ft”, “> 6 ft”, “> 9 ft” calculated based on the grid code value from the raster data set. Small (slivers resulting from vectorization) polygons, not assigned an inundation value, are selected and eliminated – merged with the largest adjacent polygon.
• 2016-08-01 00:00:00 - Shoreline gaps are identified. These are polygons that 1) do not have an inundation value, 2) share a boundary with the shoreline, and 3) share boundaries with polygons that do have an inundation value. These polygons may represent areas where the vectorized SLOSH data did not extend to the shoreline either because of shoreline differences of the raster-vector process. A conservative method was used to avoid attributing shoreline with potential flooding where it was not intended. Only features that had an area of less than 8500 square meters and an area/perimeter ratio less than 15 were selected. These polygons were dissolved into the adjacent flood polygon with the longest length. Because this process was conservative, there are several places where the land nearest the shoreline is not shown as flooding. This is likely not the case, and users need to be aware that these types of areas and small islands may erroneously not highlight flooding potential. Use judgement and consider the flood potential of nearby regions.
• 2016-08-01 00:00:00 - The final polygon data are converted from singlepart to multipart features and they are reprojected into a geographic coordinate system, NAD 83.

Data can be accessed by downloading the zipped ArcGIS geodatabase from the Download URL (see Distribution Information). Questions can be directed to the ESI Program Manager (Point Of Contact).