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

3, Storm Water Drainage. Every proposed subdivision must include a drainage system, whether a storm sewer, open ditches, culverts, pipes and catch basins, or a combination, with easements dedicated to carry surface water; drainage way easements or land dedication must be provided when needed for flood plain management, erosion prevention, or public access to water bodies. The rate of surface runoff leaving the subdivision 'shall not, in any event, be greater than the rate of runoff existing on the proposed subdivision prior to the proposed development,' and the county can regulate the volume of runoff if downstream properties or water resources would otherwise be unreasonably interfered with.

3(6) goes further for peak flows: an applicant must install all stormwater management facilities necessary so that the 2-year, 10-year and 100-year storm peak discharge rates existing before development are not increased and so that accelerated channel erosion does not result. The code sets a preference order for how to get there, starting with natural infiltration, maximizing vegetated area and minimizing impervious surface, before turning to engineered ponding facilities that must handle both permanent and temporary storage. 3 for any activity within the Shoreland Management Overlay District, so lakeshore and riverfront development is held to the identical runoff and peak-discharge limits.