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 Thurston County
 Code of Ordinances
 Title 24. CRITICAL AREAS
 Chapter 24.35. SPECIAL REPORTS

  § 24.35.240. Frequently flooded areas—Channel migration hazard area report.  

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  • If the approval authority determines that a proposed project is in an historic channel migration zone of a Type S or F stream and the one-hundred-year channel migration hazard area has not been mapped for the site, the applicant shall identify the location of the one-hundred-year channel migration hazard area on the site as follows:

    A.

    A determination as to whether the one-hundred-year channel migration hazard area is located on site and, if so, the extent of its location, shall be made by a qualified professional proficient in fluvial geomorphology (e.g., possess a graduate degree in geology or physical geography with specialization in fluvial geomorphology, and have at least two years of professional experience) using a reliable methodology to determine channel migration accepted by the resource stewardship department (e.g., as described in Forest Practices Board Manual, Standard Methods for identifying Channel Migration Zones and Bankfull Channel Features, dated 8/2001, as amended, or as described in "A Framework for Delineating Channel Migration Zones," Washington Department of Ecology, 2003 as amended). Maps delineating the one-hundred-year channel migration zone shall be of a scale and format specified by the department.

    B.

    The following areas shall be considered outside of the one-hundred-year channel migration hazard area:

    1.

    Areas separated from the stream channel by a legally established structure that the approval authority, in consultation with a qualified professional, determines will block channel migration. This may include, but is not limited to, dikes and public roads that extend above the one-hundred-year flood elevation which are constructed to remain intact through a one-hundred-year flood. Constraints to channel migration that do not extend above the one-hundred-year flood elevation shall not be considered to limit channel migration unless demonstrated otherwise based on scientific and technical information; and

    2.

    Areas separated from the stream channel by a natural geologic feature, such as a rock outcrop, that the approval authority, in consultation with a qualified professional, determines will stop channel migration.

(Ord. No. 14773, § 3(Att. B), 7-24-2012)