Final updated FEMA Flood Insurance Rate Map (FIRM)
The Washington Department of Commerce recommends that classifications of frequently-flooded-areas should include, at a minimum, the 100-year floodplain designations of the National Flood Insurance Program (NFIP). Many Washington communities have received updated FIRMs (often called 100-year floodplain maps). Final updated FIRMs must be adopted into the local floodplain management ordinance for properties in a jurisdiction to retain flood insurance coverage. If your CAO references these maps, be sure it references the most recent update of the FIRMs.
Preliminary updated FIRMs from FEMA
In some jurisdictions, FEMA has issued preliminary updated FIRMs but the process to make these maps final has been delayed. As long as the information is at least restrictive as currently effective maps, we encourage using these preliminary updated maps to regulate floodplains to reduce flood risk and protect floodplain resources.
Local governments can adopt the preliminary updated FIRMs as the areas protected under their CAO. We support using the preliminary maps (until they are superseded by final maps) as best available science in meeting CAO update requirements.
In no case, however, may preliminary FIRMs be used to reduce the area covered or decrease applicable standards required by a currently effective FIRM. If using preliminary FIRMs, local governments should have an appeal or review process allowing for engineering review of preliminary FIRM information that is more restrictive than the current effective FIRM.
Mapping of Channel Migration Zones
Channel Migration Zones (CMZs) are the areas where the river channel is likely to shift or “migrate” over time. Structures and other improvements in these areas are particularly vulnerable to long-term damage.
Shifts in channel location are a vital natural process, creating “off-channel habitat” for salmon and other species. These quiet-water areas can be especially important during high river flows as refuge for juvenile salmon and other species. In many jurisdictions, maps identifying CMZs were produced as part of recent Shoreline Master Program updates.
If Channel Migration Zones have been mapped or identified in policy statements, they should be considered for inclusion in the description of frequently-flooded-areas included in the CAO.
Identification of other flooding areas
Washington Department of Commerce rules recommend local governments consider designating flood areas outside the FEMA mapped 100-year floodplain, which may be threatened by flooding under future conditions. Other examples include the area identified as inundated during the “flood of record,” identification of areas subject to groundwater flooding, or stream systems where the path of flood waters can be unpredictable.