VSP Frequently Flooded Areas Resources
We are the floodplain management agency for Washington. We provide guidance on topics related to Growth Management Act designation and protection of frequently flooded areas.
FEMA 100-Year floodplains
Frequently flooded areas include, at a minimum, the 100-year floodplain designations of 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. Due to 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 flood map modernization, 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 though they have not been finalized.
Channel Migration Zones
Channel migration zones (CMZ) 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 for consideration for inclusion in frequently flooded areas in Critical Areas Ordinances. We have guidance on using mapping tools to identify these migration zones (below).
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