Washington County, UT Environmental Rules: Stormwater Management (2026)

Washington County Code § 11-5-2 sets the design standard for subdivision storm drainage under Title 11, Subdivision Regulations. Subsection A requires a stormwater system "separate and independent of the sanitary sewage system," with final plans prepared by a licensed engineer and approved by the County Public Works Director before any construction begins. Subsection B bars using an irrigation ditch or canal for stormwater unless the ditch or canal company gives written permission and the channel is improved enough to handle the added flow. Subsection C prohibits open ditches or canals within or adjoining a new subdivision; the subdivider must coordinate with irrigation companies on inspection, cleaning, and maintenance of pipes and culverts, and the Public Works Director must approve specifications for any pipe or culvert crossing a public road.

Subsection D forbids a subdivision from dumping drainage onto adjoining property and requires the developer to submit the drainage plan required under subsection A, with holding and retention basins listed as the preferred method for containing runoff. Subsection E requires fencing or closing off open ditches, canals, waterways, non-access streets, open reservoirs, and other features the Planning Commission judges hazardous, on, crossing, or adjacent to the property being subdivided. A related design-criteria section elsewhere in Title 11 layers on numeric storm-sizing rules for the same subdivisions: an independent storm drain system must be engineered for a 10-year storm with a 12-inch minimum pipe, and major hydraulic structures must handle a 100-year storm. Section 11-5-2 was last amended by Ordinance 2024-1251-O on February 25, 2024.