Mapping the Flood Risk

Flood Insurance Rate Maps

The county has partnered with Federal Emergency Management Agency (FEMA) to update and digitize the Flood Insurance Rate Maps (FIRMs) for Snohomish County. The new maps, called Preliminary Digital Flood Insurance Rate Maps (DFIRMS), were adopted by the county in June 2020.

The Preliminary DFIRMS update flood hazard data 

in the Flood Insurance Study (FIS) and FIRMs for areas in Snohomish County subject to riverine and coastal flooding. Products produced in association with the new DFIRMs include a flood risk database and a flood risk report. These products provide information such as:

• Areas of higher flood risk by census block
• Areas of highest expected damage
• Potential future losses to existing structures
• Areas within and upstream of the watershed that may be contributing to flood risks
• Improved risk data for mitigation planning

 In the future, the above information will be used by planners, developers, community officials and emergency managers to support efforts to reduce flood risks and losses and to improve design and construction standards for development in coastal areas.

Technical Support Data Notebooks (TSDNs)

Available TSDNs for flood mapping projects completed in Snohomish County are listed below:

• Lower Skykomish River and Snoqualmie River Floodplain Mapping Project TSDN (PDF)
• Upper Skykomish River Floodplain Mapping Project TSDN (PDF)
• Snohomish River Floodplain Mapping Project TSDN
  • Technical Support Data Notebook (PDF)
  • Memo on Snohomish River Flood Insurance Study (FIS) Revisions (PDF)