Frequently flooded areas: Critical Areas Ordinance

Counties and cities in Washington are required to periodically review and update their Critical Areas Ordinances (CAOs) under the state Growth Management Act. One element of a CAO is a frequently-flooded-areas chapter. Frequently-flooded-areas include floodplains, as designated by the National Flood Insurance Program, and other areas subject to flooding that perform important hydrologic functions and may present a risk to people and property.

Developing a frequently-flooded-areas chapter

Frequently-flooded-areas chapters must be based on best available science. Key information sources for designation and mapping these areas include:

Updating frequently-flooded-area chapter represents an opportunity to enhance flood safety by improving local standards. Enhanced flood safety steps can include:

Each local government must consider the adequacy of the designation and protection of frequently-flooded-areas within their CAO. In these reviews, it is possible to integrate new information, such as maps or relevant science findings.

Local governments will consider whether to incorporate updates from state statutes, local codes, or best available science into the CAO. An important facet is maintaining consistency with other statutes and programs. CAO reviews also afford local governments the opportunity to make policy and regulation enhancements, particularly policies related to flood hazard management planning.

Basing chapters on best available science

Frequently-flooded-areas chapters must be based on best available science. Some sources of information for mapping frequently-flooded-areas include the following:

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.

Addressing floodplain development

Developing or updating your frequently-flooded-areas chapter can serve as an opportunity to address floodplain development to promote flood safety and ecological habitat protection by developing locally appropriate standards.

Habitat protection

Floodplains provide vital habitat for salmon and other important species. Relevant information may be found in updates to salmon recovery plans, channel migration zone mapping, and other sources.

This information should be considered when developing revised CAO provisions to better protect riparian habitat. These protections may be addressed under the frequently-flooded-areas provisions or within the Fish and Wildlife Habitat Conservation Area provisions of a CAO.

Endangered Species protection

Local governments have responsibility under the Endangered Species Act to prevent harm to listed fish and other species commonly inhabiting floodplains. No adverse effects to habitat function are allowed in areas vital to these species.

FEMA Puget Sound Biological Opinion response

Jurisdictions in the Puget Sound basin must meet the procedural and substantive requirements of the National Marine Fisheries Service Biological Opinion on the NFIP. FEMA has the ultimate authority for determining the adequacy of biological opinion compliance.

The CAO update provides local governments the opportunity to include or reference procedures to implement the biological opinion in their floodplain management regulations or combined floodplain management regulations/CAO. This will help ensure all staff and other parties are aware of these required procedures to comply with the opinion.

Address unique circumstances and climate change

A local government may have unique risks due to the potential for tsunamis, high tides with strong winds, sea level rise, or extreme weather events it may want to address in its frequently-flooded-areas provisions.

Flood risk reduction beyond FEMA minimums

We encourage local governments to go beyond FEMA minimum requirements for floodplain management. Greater protection from floods may be a policy objective that should be incorporated into the CAO. For example, some jurisdictions use the “flood of record” or “freeboard” requiring greater elevations of structures.

Still have questions?

Please contact us if you have any questions. If your jurisdiction wants a CAO update to satisfy both the Growth Management Act and National Flood Insurance Program requirements, we will work with you to accomplish this task.