Best available science for wetlands

Under the state Growth Management Act (GMA), local governments are required to use the best available science in their policies and regulations on wetlands.

To assist local governments in meeting the GMA requirement, we worked in partnership with the Washington Department of Fish and Wildlife to develop a two-volume document on the science currently available about wetlands, their functions, and management.

Although the primary audience is local governments, both volumes are also valuable to those with an interest in protecting and managing wetlands. Both volumes were reviewed by peer experts and the public.

The science is always advancing

Our scientific knowledge is continually changing and we recognized that the 2005 synthesis would need periodic updates. Much of the information presented is still valid but the research in the last decade has provided new data to expand and clarify many of the conclusions made in 2005.

This is especially true for information about the role of buffers in protecting wetland functions. Buffers are one of the most common elements of wetland regulations in critical areas ordinances (CAO), and they are consistently the part of a CAO of most interest and concern to the public.

Limited resources prevent us from expanding our review and update to other issues.

State of the Science update on wetland buffers

The 2013 State of the Science update revisits the conclusions and key points concerning wetland buffers made in the 2005 synthesis of the science for wetlands.

Each conclusion is reviewed with respect to new information published between 2003 and 2012. If the conclusion is still valid, any new references supporting it are noted. If the conclusion needs to be expanded or modified, revised conclusions are presented based on the new information.

In reviewing the recent information, we found some of the more recent studies address issues that were not commonly discussed in the past. New conclusions that can be made from this information are presented as updates to the old conclusions.

Several jurisdictions, including Island and San Juan counties, have developed their own syntheses of scientific research based on some of the more recent information on buffers. These syntheses focus on the wetlands found within their jurisdiction, which may have limited relevance to other areas in the state.

Does the 2013 update affect buffer guidance for local regulations?

Many local jurisdictions have included buffer language in their CAOs based on the information published in the 2005 guidance (Volume 2, Appendices 8-C and 8-D). The 2013 update doesn't address how this new information can be incorporated into critical areas ordinances.

For the 2015-2019 ordinance update cycle, we aren't proposing any changes to the buffer widths recommended in our 2005 guidance.

Related resources

  • Wetland rating systems for Eastern and Western Washington
    The methods for categorizing wetlands using specific criteria were updated in 2004 and 2014. They reflect changes in our understanding how wetlands function and how they are valued.

    The four rating system categories are intended to be used in developing standards for protecting and managing wetlands. Examples of protection standards include the width of buffers necessary to protect the wetland and the ratios needed to compensate for impacts to the wetland. We developed guidance for these protection standards as a part of Volume 2 of the Best Available Science project.
  • Interagency wetland mitigation guidance
    We updated our guidance on mitigation in 2006 to reflect changes in our understanding of wetland science and management.
  • Wetland mitigation resources
    We have updated guidance on several mitigation topics, including site selection and use of alternative mitigation options (in-lieu fees, mitigation banks, and advance permittee-responsible mitigation).