Lincoln County, SD Environmental Rules: Stormwater Management (2026)

Under Lincoln County Code § 152.096, a developer's drainage plan must show all drainage facilities, including on-site detention, drainageways, detention ponds and drainage channels, and must expand to cover neighboring properties in the same drainage basin when upstream or downstream impacts are possible. A natural or established watercourse requires a minimum 40-foot easement. The plan must model the five-, 25- and 100-year storm events for both pre- and post-development conditions, and the post-development flow rate leaving the subdivision cannot exceed the pre-developed rate at any location, as reviewed and approved by the county.

Detention ponds and outlet control structures must be sized to mitigate the increased flowrate for those same storm events, with detention storage beginning at an elevation tied to the discharge point, floodplain, wetland elevation or top of bank. Driveway culverts are designed for the five-year storm; any driveway culvert larger than the 18-inch minimum must be built by the developer along with the road improvements, while roadway culverts, drainageways and road ditches are generally designed for the 25-year storm. A maintenance agreement covering all drainage facilities and natural watercourses must be filed with the plat, and each lot owner is responsible for installing and maintaining the driveway culvert unless the developer already installed it. Concentrated discharge onto adjacent land requires written permission from that landowner, a drainage easement, or approved energy dissipation methods.