Best available science for wetlands

Under the state Growth Management Act, local governments are required to use the best available science to develop their policies and regulations for managing and protecting wetlands in their jurisdictions.

To help local governments meet the Growth Management Act requirement, we worked in partnership with the Washington Department of Fish and Wildlife and developed a two-volume document on the science currently available about wetlands, their functions, and management. Both volumes were reviewed by peer experts and the public.

Volume 1: A Synthesis of the Science, March 2005
Synthesis of the science regarding freshwater wetlands
Volume 2: Guidance for Protecting and Managing Wetlands, April 2005
Translation of the science synthesized in Volume 1 into guidance for local governments

Although the documents were primarily written for local governments, both volumes are also valuable to those interested in protecting and managing wetlands.

Science is always advancing

Our scientific knowledge is continually changing and we recognized that the 2005 documents would need periodic updates. Much of the information presented in Volume 1 is still valid but research since 2005 provides new data to expand and clarify many of the original conclusions.

This is especially true for information regarding the role of buffers in protecting wetland functions. Buffers are one of the most common elements of wetland regulations and they are consistently the part of a critical areas ordinance of most interest and concern to the public. While we have not had resources to publish a comprehensive update, we continue to review and provide technical support on specific issues.

State of the Science update on wetland buffers

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

Update on Wetland Buffers: The State of the Science (October 2013)

We reviewed each conclusion with respect to new information published between 2003 and 2012. If the conclusion was still valid, any new references supporting it were noted. If the conclusion needed to be expanded or modified, we presented revised conclusions based on the new information.

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

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

Related guidance based on best available science

Wetland guidance for critical areas ordinance updates
Guidance for local jurisdictions working on designating and protecting wetlands as critical areas under the state Growth Management Act. Updated in 2022, it includes recommendations for wetland protection based on best available science, such as buffers and mitigation options.
Interagency wetland mitigation guidance
A two-part interagency document providing guidance on wetland mitigation. Part 1 was updated in 2021 to reflect changes in our understanding of wetland science and management.

Related tools based on best available science

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 of how wetlands function and how they are valued.

The four rating system categories are intended to be used to develop standards for protecting and managing wetlands. Examples include buffer widths necessary to protect the wetland and the ratios needed to compensate for wetland impacts. We developed guidance for these protection standards as a part of Volume 2 of the Best Available Science project.
Characterizing wetland buffers
This manual provides procedures to assess compliance with wetland buffers required at the state and local levels. It can be used by state agencies and local governments to characterize both the implementation and the effectiveness of their required wetland buffers. The results can also be used to inform management decisions about wetland buffer policies and regulations.
Calculating credits and debits for compensatory mitigation in wetlands
We developed a tool to calculate when a proposed compensatory wetland mitigation project will adequately replace the functions lost due to wetland impacts. This tool, Calculating Credits and Debits for Compensatory Mitigation (referred to as the Credit-Debit Method), applies only to freshwater wetlands.
Selecting wetland mitigation sites using a watershed approach
Recommendations on how to apply a watershed approach when selecting sites and in choosing between on-site and off-site mitigation (western Washington version | eastern Washington version).
Puget Sound watershed characterization tool
Watershed characterization is a tool for including watershed conditions in the planning process. Watershed characterization information can help identify areas that are more appropriate for wetland restoration and mitigation. It also includes links to other examples and guidance.

Contact information

Amy Yahnke
Senior Wetland Scientist
amy.yahnke@ecy.wa.gov
360-688-4263