Calculating Debits for Wetland Impacts

The Credit-Debit Method (Calculating Credits and Debits for Compensatory Mitigation in Wetlands of Western Washington PDF (6.9 MB), Ecology Publication #10-06-011) is the preferred method for calculating debits associated with proposed wetland impacts when proposing to use the King County In-Lieu Fee.  It is based on the Washington State Wetland Rating System for Western Washington PDF (7.8 MB) (Ecology publication #14-06-029).  This method, however, does not work for every impact.  The Credit-Debit Method cannot be used for impacts to buffers, streams, and other aquatic resources (which instead require an are-based method; see below). 

When using the Credit-Debit Method, it is important to choose the ‘delayed’ temporal loss factor. King County’s In-Lieu Fee Instrument requires initial physical and biological improvements by the third growing season after an applicant purchases a mitigation credit. The credit-debit worksheets include a table of temporal loss factors based on the timing of mitigation (see the debit worksheet Download Excel file (24 KB) on Ecology’s website). The temporal loss factors for in-lieu fee mitigation will range from 3-7 based on the type of wetland impact.

Once the “Debit” worksheet is completed, the applicant will add the debits for improving water quality, hydrologic, and habitat (the three different wetland functions) to determine the total number of credits needed to offset the impact. Applicants using King County’s In-Lieu Fee Mitigation Program do not need to complete the “Credit” worksheet.

Information on Purchasing Credits

Calculating Debits for River, Stream, Shoreline, and Buffer Impacts

For river, stream, shoreline, and buffer impacts, these impacts should be quantified using an area-based method and ratios discussed with regulators. Mitigation can be provided for river, stream, shoreline, and buffer impacts on a case-by-case basis. Please contact the Mitigation Reserves Program to discuss mitigation needs for your impact.

For questions about King County's Mitigation Reserves Program, please contact program staff.