Grays Harbor County, WA Environmental Rules: Erosion Control (2026)

Chapter 18.06.580 sets the performance standards that apply to any use, structure or clearing activity in a designated erosion hazard area within unincorporated Grays Harbor County. On-site stormwater and drainage work must meet the current edition of the Stormwater Management Manual for Western Washington, the same manual the Washington Department of Ecology issues for construction sites statewide. Builders must minimize modification of the natural slope contour, incorporate stabilization best management practices such as temporary and permanent seeding, mulching, geotextiles, sod stabilization, vegetative buffer strips and preservation of mature vegetation, and stabilize every exposed or disturbed soil surface promptly.

The standards also require minimizing removal of existing vegetation and undergrowth, designing cut and fill slopes to cut erosion, stabilizing conveyance outlets and stream banks, and reducing clearing, grading and impervious surface to the minimum the permit actually needs. Clearing that disturbs soil in an erosion or landslide hazard area is confined to the dry season, May 1 through October 1, though the administrator can extend or shorten that window case by case or on a qualified professional's recommendation. Section 18.06.570(A)(3) separately requires any development proposal on a site with an erosion hazard to submit a written erosion and sediment control plan, prepared to the same Stormwater Management Manual standard, as part of the critical area report before the county will act on the permit. Timber harvest clearing follows an approved forest practices permit instead of these seasonal limits.