Franklin County, WA Environmental Rules: Stormwater Management (2026)

Franklin County's site design standards, inside the Zoning title's general development chapter, put the burden of stormwater management on the developer, not the county storm system. Section 17.72.060 says all storm drainage 'shall be retained on-site,' naming swales, dry wells and French drains as accepted tools, but leaves the final method up to the county engineer's approval, so a lot with heavy clay or a high water table can be required to use a different design than the ones listed. The rule sits inside the same chapter (17.72) that sets yard, height and vision-triangle standards for every zoning district in unincorporated Franklin County, so it applies countywide, from the AP-20 agricultural zones to the C-3 commercial district.

The requirement is enforced through the same land-use permit process as every other Title 17 standard. Franklin County Code Section 17.04.040 makes it a violation to build or use property without the required permits, and Section 17.04.030 lets the planning and building director start with a voluntary-correction notice before moving to civil, and eventually criminal, penalties if a developer refuses to fix an undersized or missing drainage system. For subdivisions, the Planning Commission must find under Section 16.20.070 that 'adequate provisions' exist for drainage ways, including stormwater retention and detention, before it can recommend approval of a preliminary long plat. Planned unit developments carry the same obligation earlier in the process: Section 17.58.120 requires a PUD applicant's final development plan to include preliminary engineering plans for storm drainage before the Board of County Commissioners will grant final approval.