MULTI-HAZARD RISK MAPS FOR COASTAL COMMUNITIES OF WASHINGTON STATE, PACIFIC NORTHWEST OF THE UNITED STATES

Washington Department of Natural Resources – Division of Geology and Earth Resources (WADNR-DGER) partnered with FEMA through their Cooperating Technical Partners (CTP) program to assess annualized losses from flood and other hazards and prepare inputs for FEMA’s coastal Risk Map projects. We use HAZUS-MH analysis to assess losses from earthquake, flood and other potential hazards such as landslide and tsunami in the project areas. The Multi-Hazard Risk mapping (project) areas are on shorelines of the Pacific Ocean and Puget Sound of Washington in Grays Harbor, Pacific, Skagit, Whatcom, Island, Mason, Clallam, Jefferson and San Juan counties.

The HAZUS-MH tool was applied to estimate losses and damages due to floods and earthquakes by building an updated HAZUS inventory database aggregated from county assessor and Census information for risk assessments. We updated general building stocks which are aggregated using Census 2000-2010 blocks/tracts, and generated user-defined facilities database, accounting for each structure in the study areas, for earthquake and flood risk models. We then used the updated (Level 2) inventory data as inputs to the HAZUS-MH software to estimate losses and damages for the counties.

Flood depth grids were used to determine which properties are most impacted by flooding. For example, the HAZUS-MH (flood model) run based on the 1% annual chance event (or 100 year flood) for Grays Harbor County, resulted in a total of $389,861,000 in losses to buildings including residential, commercial properties, and other building and occupancy types. A likely M9 megathrust Cascadia earthquake scenario USGS-ShakeMap was used for the HAZUS-MH earthquake model. For example, the HAZUS-MH (earthquake model) run based on the Cascadia M9 earthquake for Grays Harbor County, resulted in a total of $1,531,798,000 in losses to building inventory including residential, commercial properties, and other building and occupancy types. GIS-based overlay maps of properties exposed to tsunami, landslide, and liquefaction hazards within the communities of the counties will be shown. This ongoing Multi-Hazard Risk mapping project along with its outreach component will further improve local and regional mitigation and emergency response plans in and around the coastal communities in Washington State.