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Flooding services

King County, Washington

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Flooding services and information in King County, WA

Floodplain maps

The most current Preliminary Flood Insurance Rate Maps (FIRMs) and Flood Insurance Study (FIS) dated February 1, 2013, show proposed special flood hazard areas that are subject to inundation by the base flood (100-year flood) as well the regulatory floodway.

Preliminary Flood Insurance Rate Maps and Flood Insurance Study

Frequently asked questions about the maps

Why are the maps being updated?
FEMA updates the maps to reflect the most recent flood studies based on new topography and modeling as they become available. This set of maps more accurately depicts floodplain and floodway boundaries and associated information in many areas throughout King County.

What areas are affected by the February, 1 2013 maps?
The Sammamish River and tributaries (Bear Creek, Evans Creek, North Creek, Swamp Creek), Coastal areas (Vashon Island and mainland), White River (from ¼ mile downstream of Highway 410 near Enumclaw to the Outlet Works at Mud Mountain Dam). All other areas in King County are included the Preliminary FIRMs and FIS dated November 6, 2010.

Where can I view printed Preliminary FIRMs and Flood Insurance Study (FIS) reports?
Available at:  King County Water and Land Resources, 201 South Jackson Street, Suite 600, Seattle WA 98104 (contact Ken Zweig, Program Manager) and the following Cities: Algona, Bothell, Burien, Des Moines, Enumclaw, Federal Way, Kenmore, Milton, Normandy Park, Pacific, Redmond, Sammamish, Seatac, Seattle, Shoreline, Woodinville.  Contact city offices for further information.

What is the schedule that will result in Preliminary FIRMs becoming effective?
FEMA will meet with city and county staff from affected communities to discuss the process and technical topics in 2013. Based upon city staff input, a public outreach strategy will be developed that may include public meetings.  After the community coordination meetings, FEMA will initiate a 90 day public appeal period.  If no appeals are submitted, the Flood Insurance Rate Maps and the Flood Insurance Study report will be effective approximately 7-10 months later.

What happens to previously issued Letter of Map Change (LOMC) actions  i.e., Letters of Map Revision (LOMRs) and Letter of Map Amendment (LOMAs)?
FEMA has published a list of 3 categories of LOMCs (see below). The document is available here: Preliminary Summary of Map Actions. Cities have also been provided these lists in conjunction with the mapping and flood study document.

  1. LOMCs Incorporated: One LOMR (SR 202 widening project) is listed as incorporated into the FIRMs.
  2. LOMCs Not Incorporated: LOMCs that have not been incorporated into the PFIRMs because of scale limitations or because the property or structure is located outside the latest floodplain boundary. These LOMCs will be revalidated through a letter from FEMA after the PFIRM becomes effective.
  3. LOMCs Superseded: LOMCs that are no longer in effect due to new detailed flood hazard information or insufficient information to make a determination.

What is King County’s role in the process?
Unincorporated King County is a National Flood Insurance Program community affected by the Preliminary FIRMs and FIS.  King County staff reviewed the FIRMs and sent FEMA comments. King Country will be participating in the community staff meetings with FEMA and will also participate in subsequent a public outreach meetings to assist in providing information to county residents about the preliminary flood insurance study and mapping.

Vashon-Maury Island coastal flood hazard mapping

The work maps (linked below) were submitted to FEMA and included in the February 1, 2013 Preliminary Flood Insurance Rate Maps.


Sheet 1 Sheet 5
Sheet 2 Sheet 6
Sheet 3 Sheet 7
Sheet 4 Sheet 8

Sammamish River

The work maps (linked below) were submitted to FEMA and included in the February 1, 2013 Preliminary Flood Insurance Rate Maps.


Sheet 1 (Lake Washington) Sheet 6
Sheet 2 Sheet 7
Sheet 3 Sheet 8
Sheet 4 Sheet 9
Sheet 5 Sheet 10 (Lake Sammamish)

White River

The work maps (linked below) show the areas from the King-Pierce County line to Stuck River Drive and from SR410 to Mud Mountain Dam. The February 1, 2013 Preliminary Flood Insurance Rate Maps includes only the White River (near Enumclaw) area from approximately 1,275 feet downstream of State Highway 410 to the Outlet Works at Mud Mountain Dam.


White River (Pacific/Auburn) White River (near Enumclaw)
Sheet 1 (King-Pierce County Boundary) Sheet 1 (SR 410)
Sheet 2 Sheet 2
Sheet 3 Sheet 3
Sheet 4 Sheet 4
Sheet 5 (Stuck River Drive) Sheet 5 (Mud Mountain Dam)


Lower Snoqualmie River and Patterson Creek work maps

The work maps (linked below) were submitted to FEMA and included in the November 2010 Preliminary Flood Insurance Rate Maps.


Lower Snoqualmie River Patterson Creek
Sheet 5 (King-Snohomish County Boundary) Sheet 1
Sheet 6 Sheet 2
Sheet 7 Sheet 3
Sheet 8 Sheet 4
Sheet 9 Sheet 5
Sheet 10 Sheet 6
Sheet 11 Sheet 7
Sheet 12 Sheet 8
Sheet 13
Sheet 14
Sheet 15
Sheet 16
Sheet 17 (Snoqualmie Falls)

*Lower Snoqualmie River Sheets 1-4 are Snohomish County floodplain work maps.

Lower and Middle Green River work maps

New flood boundary maps have been prepared for the Green River between the Duwamish Waterway in Seattle to Flaming Geyser State Park. The information was submitted to the Federal Emergency Management Agency (FEMA) on March 18, 2008 for the purpose of revising flood insurance rate maps. FEMA technically reviewed the work maps and included the hazard mapping in the November 2010 Preliminary Digital Flood Insurance Rate Maps. The reviewed maps have some slight illustrative revisions as compared to the 2008 draft maps. Please note that no technical changes were made to the flood study analyses. The final-reviewed work maps are linked below.


Middle Green River
State Route 18 to Flaming Geyser State Park
(each file exceeds 2Mb)
Lower Green River
Duwamish Waterway to State Route 18
(each file exceeds 5Mb)
Sheet 1 Sheet 1
Sheet 2 Sheet 2
Sheet 3 Sheet 3
Sheet 4 Sheet 4
Sheet 5 Sheet 5
Sheet 6 Sheet 6
Sheet 7 Sheet 7
Sheet 8 Sheet 8
Sheet 9

Map Information & Elevation Certificates
Staff from the River and Floodplain Management Section can assist with the following flood map information by calling 206-477-4727.

  • Whether a property is located within a FEMA mapped Special Flood Hazard Area (SFHA), or flood prone area identified by King County.
  • Flood insurance rating information such as FIRM zone, panel number, suffix, panel date and index date.
  • FEMA elevation certificates if available. King County has elevation certificates for many properties within the SFHA.
  • Regulatory provisions that may apply to the property in question.
  • If available, whether the property has ever suffered any flood damage.

Flood insurance and FEMA (Acrobat PDF format)
This bulletin explains the effect of the Federal Emergency Management Agency (FEMA) on the permitting process of the Department of Permitting and Environmental Review (DPER) and answers some common questions about the National Flood Insurance Program's (NFIP's) impact on development projects.

King County Code >> Critical Areas (Acrobat PDF format)
County definitions and rules on development standards, restrictions, and requirements as well as permitted uses in King County floodplains and other sensitive areas. Codes pertaining specifically to floodplains can be found under sections 21A.24.230 to 21A.24.275 of this document.

Flood map information for realtors, lenders and insurance agents

Online Floodplain Boundary Maps iMAP (high speed Internet connection required)
View and print custom online maps using King County data including parcels, floodway and floodplain boundaries.

FEMA Flood Map Service Center (external link)
The official online location to find all flood hazard mapping products created under the National Flood Insurance Program (NFIP).

For questions about the floodplain mapping, please contact Ken Zweig, Project Manager, River and Floodplain Management Section.