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

Chapter 644, rewritten in its entirety by Ordinance No. 2026-03, requires any development, renovation or addition within Royal Oak to detain stormwater runoff on-site, with the City Engineer administering the requirement (§ 644-4). The exemption in § 644-5A covers only small projects: developments, renovations or additions under 0.14 acre or 6,100 square feet do not need detention at the time of the work, but the owner must record a lien with the City stating that once accumulated improvements exceed that threshold, the detention requirement kicks in on the combined area.

Section 644-6 sets the design target once the threshold is crossed: systems must provide Channel Protection Rate Control (extended detention) for a 1.9-inch rainfall event dewatered over 48 hours, plus Detention Flood Control sized to hold a 100-year, 24-hour storm event. The variable release rate that controls how fast water can leave the site is capped at 1.0 cubic foot per second per acre for developments of two acres or less, dropping to 0.15 cfs per acre for developments of 100 acres or more, with the City Engineer able to require an even lower rate depending on downstream capacity.

Green infrastructure such as bioretention, rain gardens, bio-swales or pervious pavement can substitute for part of the requirement under § 644-7 on sites of an acre or larger where soil infiltration rates support it. Every submittal must carry a Michigan-licensed professional engineer's seal (§ 644-8A) and go to the City Engineering Division for review before construction, with the applicant covering the City's review and inspection costs.