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

02 of the 1993 Revised Subdivision Ordinance (MC23-93, revised 7/22/2008) requires every subdivision drainage plan to show existing and proposed contour lines and the full surface water drainage system, including any major alteration of the existing pattern. Drainageways and detention ponds must be sized for a 25-year storm occurrence, and the contour interval has to be detailed enough that the Planning Director and Highway Superintendent can verify the final drainage pattern before signing off. The plan must mark the boundaries of every drainage easement and detention pond, and a maintenance agreement covering upkeep of the ponds has to be filed with the plat itself, not left to a side letter.

Individual lot drainage must tie into the general surface pattern for the area, and the ordinance specifically bars concentrating storm runoff from one lot onto an adjacent lot. Surface water cannot be routed across or around any street intersection. Driveways get their own rule: they cannot inhibit or restrict the flow of surface water, and each lot owner is responsible for installing and maintaining a culvert under the driveway once construction starts. 02(A) lets the County require the developer to expand the plan to cover other affected properties both upstream and downstream.

01 requires plat approval before any building permit issues on the site. 02 if strict application would cause real hardship, but the variance still has to preserve the ordinance's general intent.