Wetland mitigation resources

What is mitigation?

Generally, mitigation means offsetting or countering the adverse environmental effects that developing the land can have on wetlands, rivers, streams, lakes, and other aquatic habitats. Wetland mitigation usually occurs in a sequence of steps or actions.

Wetland compensatory mitigation is one of the last steps in the mitigation sequence where unavoidable impacts to wetland functions are offset by creating, restoring, enhancing, or preserving other wetlands. Use the resources below to apply mitigation sequencing and to select, design, and implement compensatory mitigation.

Mitigation resources

• Identify wetlands on the proposed development site
• Avoid and minimize wetlands impacts
• Characterize wetland functions and values
• Identify mitigation opportunities
  • Understand mitigation options
  • Choose a mitigation site
• Develop and implement a wetland mitigation plan
• Monitor mitigation site success

Identify wetlands on the proposed development site

An on-site inspection is almost always necessary to determine, with certainty, whether wetlands are present. Other information, such as Ecology Wetland Inventory Maps, National Wetland Inventory Maps, county soil surveys, and aerial photos provide indications of where wetlands may exist. However, these might not include all wetlands and might identify areas that were once, but are no longer wetlands.

• Use online mapping tools to get an initial idea of potential wetlands on the property
  • 2016 Modeled Wetlands Inventory (ArcGIS Web Mapping Application): Medium resolution scale map of wetlands in Western Washington. It was developed by NOAA and Ecology, modeled from NOAA's Coastal Change Analysis Program.
  • U.S. Fish and Wildlife Service National Wetland Inventory
  • Coastal Atlas: Make a custom map (choose from more than 100 layers)
• Hire a qualified wetland professional
• Establish the existence (location) and physical limits (size) of the wetlands by conducting a wetland delineation.

Avoid and minimize impacts to wetlands

• Guidance on avoidance and minimization: Information to assist project applicants with understanding the requirements for avoiding and minimizing wetland impacts during development.

Characterize wetland functions and values

Better mitigation through a better understanding of wetland functions and values:

• Wetland rating systems classify wetlands into four categories based on their sensitivity to disturbance, their rarity, the ability to replace them, and the functions they provide. Classification and wetland scores help determine the amount and type of mitigation needed to compensate for impacts to the wetland.
• Focus On: Using the Wetland Rating System in Compensatory Mitigation

Identify mitigation opportunities

In addition to traditional on-site mitigation, there may be other ways to achieve mitigation depending on what can work best for the applicant and the environment. Each option must conform to appropriate local, state, and federal regulations and permits.

Understand mitigation options

Determining which mitigation option, or combination of options, is best for your site must be done on a case-by-case basis. Washington provides a comprehensive range of mitigation options:

• Wetland mitigation banking:  A mitigation bank is a wetland, stream, or other aquatic resource area that has been restored, established, enhanced, or, in certain circumstances, preserved for providing compensation in advance of unavoidable impacts to aquatic resources.
• In-lieu fee (ILF) mitigation: In this approach to mitigation, a permittee pays a fee to a third party in lieu of conducting project-specific mitigation or buying credits from a mitigation bank.
• Advance mitigation: Is constructed in advance of a permitted impact. Advance mitigation can be proposed by any applicant, but the advance compensatory mitigation credits generated by a mitigation effort in advance of impacts can only be used by that same applicant.

In some cases, it may be best to use a combination of onsite and offsite mitigation. An applicant may buy credits from a wetland mitigation bank or pay for in-lieu fee mitigation rather than mitigate for their unavoidable impacts to wetlands onsite. Or, it may be best to provide some functions like onsite water quality and quantity  and compensate for habitat functions offsite.

Choose a mitigation site

Better mitigation through improved site selection:

• 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
• Methods for analyzing landscape processes
  • The Puget Sound Watershed Characterization Project: A regional-scale tool that highlights the most important areas to protect and restore, and those more suitable for development. 

Develop and implement a wetland mitigation plan

• Interagency wetland mitigation guidance: Guidance on wetland mitigation from Ecology, U.S. Army Corps of Engineers and EPA. Part 2 has detailed guidance on how to develop a wetland mitigation plan.
• Wetland Mitigation Bank Use Plan: Guidance to applicants on what to submit for bank use plans.
• In-lieu fee Use Plan: A guide for permit applicants planning on proposing the use of an ILF program as their mitigation option.
• Calculating credits and debits for wetland compensatory mitigation: A tool for calculating when a proposed wetland mitigation project adequately replaces the functions and values lost when wetlands are impacted. It is also known as the Credit/Debit Method.

Monitor mitigation site success

• Requirements for wetland mitigation monitoring
• Wetland mitigation compliance: We follow up on wetland mitigation projects to ensure mitigation requirements are fulfilled.