Arapahoe County, CO Environmental Rules: Stormwater Management (2026)

7) folds drainage design into the landscaping chapter rather than a standalone stormwater ordinance. Any detention or water-quality area on a development site needs Engineering Services Division sign-off confirming it matches the approved drainage plan; regional and sub-regional facilities skip that step unless the Board of County Commissioners decides otherwise for a specific project. Ponds with earthen sides, and any pond with a water-quality component, must be graded, planted and irrigated exactly as the County's Stormwater Management Manual specifies -- the LDC repeatedly incorporates the Manual by reference for growing media, vegetation, irrigation and access rather than restating numeric standards itself.

Native-seed or low-water plantings inside detention areas still need functioning automatic or temporary irrigation. Where an in-line detention area sits in the 100-year floodplain, the landscaping requirement can be adjusted to the specific standards of the Mile High Flood District and/or the County's own Engineering Services Division, and every pond must keep a maintenance access route open. The same Manual governs bioretention facilities, sand filters, and grass swales and buffers elsewhere in the same section. Major drainageways -- defined as a flow path with a tributary area of 130 acres or more -- must be kept in their natural state as much as possible, with any stabilization work designed to complement the natural channel, and drainageway flows themselves must comply with the Stormwater Management Manual.

None of this reaches land inside Aurora, Centennial, Littleton or the county's other incorporated cities, which run their own stormwater review under their own codes; it applies only to development on unincorporated county land reviewed by the Public Works and Development Department.