Royal Oak Township, MI Environmental Rules: Stormwater Management (2026)

Article V of Chapter 8 sets three linked rules. Section 8-109 requires on-site retention for every development and redevelopment in the township and caps site runoff at the agricultural (undeveloped land) rate of 0.2 cubic feet per second (cfs) per acre under a ten-year frequency storm. To size the retention, the Code points to the county drain commissioner's method titled "A Simple Method for Retention Basin Design" dated December 1973, or the drain commissioner's adopted subsequent standard.

The Code prints three retention methods. Retention basins are unfenced, with a side slope no steeper than one vertical on six horizontal and a three-foot minimum flat shoulder between the top of slope and the property line. The basin design is an integral part of the landscape and the property owner maintains it. Parking lots can hold runoff to a height not to exceed eight inches above inlet rim elevations, with an overflow at the maximum elevation six inches below the finished floors of the buildings, no restricted covers on inlets, and an orifice restrictor of proper size on the outlet pipe of the last downstream structure on site. Underground retention uses oversizing of the base storm system, large diameter pipes or underground storage tanks. All on-site facilities must be periodically maintained so sediment does not enter the sewer system.

Section 8-108 deals with roof water. Single-family dwellings cannot have direct connections of eaves troughs and roof downspouts to the sewer system, and the Code recommends discharge into landscaped areas. Multiple-family developments face the same ban, with landscaped discharge required. Commercial and industrial roof drains also cannot connect directly to the sewer system, though a direct connection to the storm system can be allowed with the township engineer's approval where the development is in a separated storm district or site conditions dictate it. Section 8-110 bars direct connection of any stormwater source to sanitary sewers and sends subsurface water from edge drains, sump pumps or other conveyance to a storm sewer or to the surface with positive drainage to an approved point of collection.