Changes on the DFIRMs


Changes to the maps include:

  • Revised floodplain boundaries for all detailed (Zone AE) study areas in the county.
  • The incorporation of new detailed studies for the Skykomish River, Sultan River, Snoqualmie River, and portions of the Snohomish River and North Fork Skykomish River. Please note that new detailed studies often change the Base Flood Elevations (BFE) in areas because of updated hydrology, refined topography, and changed conditions in the watershed.
  • The incorporation of new approximate studies for the South Fork Skykomish River and portions of the North Fork Skykomish River.
  • Changes to areas that have not received a new detailed study, but for which new topographical data became available. In these cases the floodplain boundaries were redelineated using the new topography.


The new Digital Flood Insurance Rate Maps (DFIRMs) include proposed changes in flood zones for the areas shown on the chart (PDF).

The revised maps are based on decades of rainfall and river gauge information, new hydraulic models, and recent topographic data.


The changes may affect mortgage loan requirements and flood insurance rates for those properties in areas proposed for adjustment. Please see the Federal Emergency Management Agency (FEMA) summary on how map changes can affect flood insurance. Other resources include: