Frequently flooded areas resources for VSP planning

FEMA 100-year floodplains

Frequently flooded areas include, at a minimum, the 100-year floodplain designations under the FEMA National Flood Insurance Program. FEMA develops Flood Hazard Rate Maps displaying the 100-year floodplain. The first digital FEMA maps were called Q3 Flood Data, but with advancing technology, these maps are being modernized.

Modernization primarily means the data are being digitized. The new maps are Digital Flood Insurance Rate Maps (DFIRMs). As part of the flood map modernization process, FEMA will only update or produce DFIRMs.

In some places, there are preliminary updated DFIRM maps. We and FEMA encourage the use of preliminary updated maps even if they are not yet final.

Resources

• Critical Areas Ordinance Guidance for Frequently Flooded Areas
• Learn more about map modernization
• FEMA Flood Maps

Map Data

• Ecology's FEMA Flood Data

Data limitations

Not all maps have been or will be modernized. We will add others as they are completed. Contact us to ask about the schedule for completing new maps for your area.

Channel Migration Zones

Channel migration zones are the areas where the river channel is anticipated to shift over time, eroding and flooding new areas. Channel migration is vital to creating off-channel habitat for fish and other species. It can also pose a hazard for residents and property owners.

Channel migration zones should also be considered in VSP since they are recommended to be considered for inclusion in frequently-flooded areas in Critical Areas Ordinances. We have new guidance about using mapping tools to identify these migration zones.

Resources

• Channel Migration Assessment
• The Channel Migration Toolbox: ArcGIS® Tools for Measuring Stream Channel Migration