Grays Harbor County, WA Environmental Rules: Stormwater Management (2026)

Section 16.20.210 of the Grays Harbor County Code, in the subdivision design chapter, requires every proposed subdivision to make adequate provision for storm water and flood water runoff so that erosion, flooding, sedimentation, and damage to ditches, streams, and natural drainage channels are prevented, both while the subdivision is under construction and once it is fully developed. Subsection A requires drainage facilities adequate to protect roads, lots, and adjacent or downstream property to be installed according to a drainage plan, directs the design to use natural drainage ways wherever feasible, and requires lots to be laid out so they drain positively away from buildings. Any drainage facility approved through the summary short subdivision process must meet the standards in the current edition of the Washington State Department of Ecology's Stormwater Management Manual for Western Washington, the same statewide technical manual the county's mobile-home-park and RV-park chapters point to for their own drainage standards.

Subsection B requires anyone applying for preliminary subdivision approval to submit a drainage plan covering the surface and subsurface water flows entering, moving through, and leaving the property, built to the specifications in Appendix E of Title 16, and the public works division must approve it. Subsection C keeps the storm drainage system separate and independent from any sanitary sewer system. Where a watercourse or drainage channel crosses the subdivision, subsection D requires a drainage easement wide enough for maintenance and erosion control, coordinated with the critical-areas provisions of Chapter 18.06; the county itself takes on no maintenance duty for that easement. The public works director can reduce or waive the drainage-plan requirement under subsection E for low-density subdivisions, at one unit per acre or fewer, if the applicant demonstrates that peak storm water discharge will not increase significantly, existing drainage ways will stay protected within easements, and no property will be affected by runoff during the design storm.