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APPENDIX B: SEA LEVEL RISE SCENARIO MAPPING METHODOLOGY <br />1) The LiDAR (Light, Detection and Ranging) data was obtained from the Senior GIS/LiDAR Analyst at PSRC for <br />the areas under consideration. <br />2) Tide data for leaf -off months (December - April) was obtained from the National Oceanographic and <br />Atmospheric Administration (NOAA) Tides and Currents and averaged to find the Mean Higher High Water <br />(MHHW) elevation. According to the Department of Ecology, the Mean Higher High Water is: <br />"the arithmetic average of the elevations of the higher high waters of a mixed tide over a specific <br />19-year period." <br />3) Based on the field observations of Doug Canning, University of Washington Climate Impacts Group, 1.25ft was <br />added to the MHHW elevation to find the Ordinary High Water (OHW) elevation. This represents the current <br />shoreline. According to the Department of Ecology, the ordinary high water is: <br />"that mark that will be found by examining the bed and banks and ascertaining where the <br />presence and action of waters are so common and usual, and so long continued in all ordinary <br />years, as to mark upon the soil a character distinct from that of the abutting upland..." <br />4) The worst case flood scenario for Seattle was determined by using the highest water level recorded at <br />the Seattle NOAA gauge in over 100 years. <br />5) The Times and Int spatial analyst tools were used to transform the raster grid into an integer format without <br />losing necessary data accuracy. The grid must be in the integer format in order to execute one of the commands <br />to create the ordinary high water, sea level rise and flood scenarios. <br />6) The command line window was used to enter in several commands to create the ordinary high water base <br />layer, the sea level rise scenarios and the flood scenarios. <br />a) The ExtractByAttributes command was used to extract the cells below the threshold height above <br />NAVD88 zero. <br />b) The RegionGroup command was used to group together the cells that were hydrologically connected <br />to the Puget Sound. <br />c) The ExtractByAttributes command was used to extract out the group of cells that were hydrologically <br />connected to the Puget Sound. <br />d) The ExtractByAttributes command was used to create a mask based on the ordinary high water raster. <br />e) The ExtractByMask command was used to select out the cells from the product of item 6c that are <br />above the ordinary high water and below the threshold height. <br />L-26 <br />Appendix L: Climate Change Background <br />