Increased Flood Scenarios in San Juan County, WA

Increased Flooding Scenarios in San Juan County, WA Naomy Pérez-Sánchez, Coastal Geomorphologist ESRI Water Conference San Diego, CA – January 30th, 2018 FEMA Regulatory Products Regulatory Products provide accurate flood hazard data to governments, planners, and communities to help with mitigation efforts. They are used as the basis for official requirements, such as determining the flood insurance rating system and constructions standards. Regulatory Products include: • Flood Insurance Rate Maps (FIRMs) • Digital FIRM Database (DFIRMs) and • Flood Insurance Studies (FISs). FEMA Flood Risk Products Flood Risk Products are supplemental to the Regulatory Products. They help planners, community leaders, local governments and the like get a broader view of flooding problems in the community. Some of these Products are coastal-specific. Flood Risk Products include, but are not limited to: Source: FEMA • Changes Since Last FIRM • Flood Depth Grids • Increased Flooding Scenarios This presentation will focus on describing the Increased Flooding Scenarios (IFS) for San Juan County, Washington. San Juan County, WA Geography • Located in the Salish Sea between the US mainland and BC, Canada. • Archipelago of 8 bigger islands (Stuart, Waldron, Orcas, Blakely, Decatur, Lopez, Shaw, and San Juan) and several smaller islands and keys. • San Juan Islands are mostly characterized by steep shorelines. • Approximately 175 land square miles. • 357 shoreline miles studied. Demographics • 2016 Population: 16,339 (Census, 2016) • 2010-2016 Population percent change: 3.6% increase (Census, 2016) Increased Flooding Scenarios • Estimates hypothetical increases above the Base Flood Elevation (BFE) levels associated to a particular annual-chance event (Coastal- Specific Non-Regulatory Datasets, 2014). • Coastal specific product. • Often the IFS is used to create hypothetical scenarios regarding sea-level rise. Base Flood Elevation Source: FEMA, 2016 Methods Create Coastal 1% Annual-Chance Flood Depth Grid • Convert the SFHA shapefile to a raster using the BFE field as the converting factor. • BFE - Elevation DEM. • Delete negative values from the output DEM. *elevations are displayed in NAVD88. 1% annual chance BFEs Methods Create Increased Flooding Scenario Shapefile Source: Coastal-Specific Non-Regulatory Datasets, 2014 Results Roche Harbor, San Juan Island • ~ 200 ft. from Base Flood to Base Flood +3 Results • 5 buildings affected Roche Harbor, San Juan Island Results Orcas Island Airport, Orcas Island Results • ~ 500 ft. from Base Flood to Base Flood +3 • 15 buildings affected Orcas Island Airport, Orcas Island Results Mackaye Harbor, Lopez Island Results • ~ 300 ft. from Base Flood to Base Flood +3 Mackaye Harbor, Lopez Island • 9 buildings affected Results Lime Kiln State Park, San Juan Island Discussion • Improves flood risk awareness. • Because of the county’s steep nature, horizontal flooding will likely not affect people living on cliffs or higher/steeper areas. • Flatter areas are prone to greater horizontal flooding. • Values from dedicated sea-level rise studies can be used for more precise results . • Government, planners, and communities should not rely solely on this tool, but it can be used to assess mitigation actions (buy outs versus elevating structures on piers versus shoreline protection). Limitations • It may not necessarily take into consideration non-linear factors like the terrain morphology, shoreline change, coastal structures, among other. Thank you! Naomy Pérez-Sánchez Coastal Geomorphologist, Atkins Austin, TX 1.512.342.3365 [email protected].

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