Frequently flooded areas: Critical Areas Ordinance

Counties and cities in Washington are required to periodically review and update their Critical Areas Ordinances (CAO) 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 FEMA National Flood Insurance Program, and other areas subject to flooding that perform important hydrologic functions and may present a risk to persons 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 frequently flooded areas include:

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

  • Habitat protection and endangered species protection
  • Developing a Door response to the Puget Sound Biological Opinion for the National Flood Insurance Program
  • Higher regulatory standards beyond the FEMA minimums
  • Unique circumstances
  • Climate change

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 that new information such as maps or relevant science findings can be integrated.

Local governments will consider whether to incorporate updates from state statutes, local codes, or best available science into the CAO. An important facet of these periodic updates is maintaining consistency with other statutes and programs. CAO reviews are also an opportunity for local governments to make enhancements of policy and regulation, 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 FEMA National Flood Insurance Program (NFIP).  Many Washington communities have received updated Flood Insurance Rate Maps (often called 100 year floodplain maps). Final updated FEMA maps must be adopted into the local floodplain management ordinance in order for properties in a jurisdiction to retain flood insurance coverage. If your CAO references FEMA maps, you should update references to final updated maps.

Preliminary updated FIRM maps from FEMA

In some jurisdictions, FEMA has issued preliminary updated FIRM maps, but the process to make these maps final has been delayed. We and FEMA encourage use of these preliminary updated maps in regulating floodplains to reduce flood risk and protect floodplain resources, so long as the information is at least as restrictive as the current effective maps.

Local governments can adopt the preliminary updated floodplain maps as the areas protected under their CAO. We support the use of the preliminary updated maps (until they are superseded by final maps) as best available science in meeting CAO update requirements.

In no case may Preliminary FIRMs be used to reduce the area covered or applicable standards required by a currently effective FIRM. If utilizing 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 be an opportunity to address floodplain development in a way that promotes flood safety and ecological habitat protection through developing locally appropriate standards.

Habitat protection

Increasingly, there is recognition of the importance of floodplains as vital habitat to support salmon and other species. Relevant information may be found in updates to salmon recovery plans, channel migration zone mapping, or other sources.

These sources should be considered in development of revised CAO provisions which 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, for preventing harm to listed fish and other species that commonly inhabit floodplains. No adverse effects to habitat function are allowed in specified areas that are 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 (BiOp) on the NFIP. FEMA has the ultimate authority for determining the adequacy of BiOp compliance.

The Critical Areas Ordinances update provides an opportunity for local governments to include or reference procedures for BiOp implementation in their Floodplain Management Regulations or combined Floodplain Management Regulations/Critical Areas Ordinances. This will help ensure that all staff and other parties are aware of these procedures required to comply with the BiOp.

Address Unique Circumstances and Climate Change

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

Flood risk reduction beyond FEMA minimums

We and FEMA encourage local governments to go beyond the 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 their CAO update to satisfy both the Growth Management Act and National Flood Insurance Program requirements, we will work with you to accomplish this.