First American Spatial Solutions Finds $30B of Properties Exposed to Howard Hanson Dam Vulnerability

To see the full report and a detailed explanation of the river flow scenarios and methodology used to model the exposure, please visit www.faspatial.com/hhd.  The analysis is immediately available as an enhancement to FASS’ Flood Risk Score to help underwriters assess existing portfolio risk and improve underwriting capabilities.

Following a torrential rainfall and subsequent record water volumes in the Howard Hanson Reservoir in January of 2009, the United States Army Corps of Engineers (USACE)  labeled the dam as “unsafe”— a category that describes less than 5 percent of the over 80,000 dams in the U.S. that are in the very worst condition.   The current Federal Emergency Management Agency’s (FEMA) maps do not reflect the possible risk from measures taken to avoid dam breach such as the possibility of opening up the dam. FASS has analyzed multiple flood scenarios to quantify King County’s overall exposure to the Howard Hanson Reservoir to provide homeowners and businesses insight into their exposure and enable insurance carriers to identify their own portfolio risk and modify underwriting policies.   

As permanent flood protection capabilities for the Howard Hanson Dam are sought, FASS will continue to monitor the situation and update its analysis as the anticipated risk and exposure evolve.

Comparison between FEMA/FASS maps for the area of expected impact for the Green River Valley (See map attached for visual):
At the 25,000 cf/s (cubic feet/second) level, FASS suggests that 20 square miles would be inundated with water. At 13,900 cf/s, FASS suggests that roughly 15 square miles would be affected by flooding. If you look at the FEMA zones for the same area, they suggest that 5 square miles would be affected.

According to FEMA, the number of land parcels that would be affected is 1,140. According to FASS, the number of parcels that would be affected at 13,900 cf/s is 4,065 and at 25,000 cf/s is 5,072.