Farmington Hills, MI Environmental Rules: Flood Elevation Requirements (2026)

City Code Sec. 33-320 adopts Section I of the Oakland County Water Resources Commissioner's Stormwater Engineering Design Standards, as amended, as Appendix B, and Sec. 33-321 substitutes 'City of Farmington Hills' wherever the standards say 'OCWRC' or 'County,' making the freeboard rule directly enforceable citywide. Appendix B, Section III, Part F (General Detention Basin Requirements) states: 'One foot of freeboard shall be provided above the 100-year stormwater elevation. 50' shall be provided between the 100-year storage elevation and the emergency overflow spillway,' and requires a primary overflow structure, standpipe or overflow manhole, with its rim set at the 100-year storm elevation.

The same Part requires basin side slopes no steeper than 1 foot vertical to 6 feet horizontal for a wet basin and 1 to 4 for a dry basin unless fenced, and recommends a permanent 15-foot natural-vegetation buffer strip beyond the freeboard elevation around every stormwater storage facility, to be written into subdivision restrictions or the master deed. Separately, Appendix B, Section III, Part C sets a 2-foot minimum 100-year flood-stage freeboard to the underside of any bridge crossing a county drain, with footings kept below the frost line.

Sec. 33-320(b) allows variances from the channel protection performance standards only under the alternative standard in the Michigan Department of Environment, Great Lakes, and Energy's stormwater permit dated June 24, 2021. These freeboard and detention standards apply to subdivision plat approvals reviewed by the Oakland County Water Resources Commissioner before final construction plans are accepted.