Greenwood, IN Environmental Rules: Stormwater Management (2026)

Sec. 9-150 explains that the City created the Department of Stormwater Management to protect public health, safety, and welfare and to keep Greenwood compliant with its NPDES Stormwater Discharge permit under the federal Clean Water Act, 33 U.S.C. §§ 1251-1387. If a project sits in a Johnson County Regulated Drain Watershed, the applicant must also satisfy the Johnson County Surveyor's Office before the City issues any permit. Sec. 9-156 then sets the technical standard: because streams and drainage channels serving the district lack capacity for continued urbanization, new business, institutional, commercial, industrial, and residential subdivision developments must store and control the release of excess runoff, with detention basins sized so post-development discharge does not exceed pre-development discharge for the 2-year, 10-year, and 100-year storm events.

Storm sewers, inlets, and swales must handle a 24-hour, 10-year return storm at minimum, while ditches must carry the 100-year event within their banks or a designated easement, and no detention facility may sit within the 100-year floodplain. The Board of Public Works and Safety can waive controlled-runoff requirements only for minor subdivisions and parcelization after investigation. All calculations must follow the City's Stormwater Technical Manual, and the Stormwater Department may require more restrictive design storms for individual developments.