Madison County, AL Environmental Rules: Stormwater Management (2026)

8(2) of the Subdivision Regulations is the operative rule for how a developer must handle runoff. At the time the Proposed Plat is filed, the Applicant must also submit Construction Plans containing a Storm Drainage Plan prepared to specific design-storm criteria: minor streets and roadside open ditches are sized to a 10-year storm, while every other street, road, drainage structure and open channel is sized to the 25-year storm. 75 percent must be built of concrete rather than left as earthen channels, and all such channels must include erosion and sedimentation control appropriate to minimize erosion.

Any detention or retention structure has to handle the 10-year, 24-hour, Type II storm event while keeping post-development runoff no greater than predevelopment flows, and must also pass the 100-year storm through a controlled section so it doesn't flood adjoining structures. The plan must map every drainage structure's contributing drainage area with supporting calculations such as curve numbers, runoff coefficients and time of concentration, show easements and rights-of-way for each drainageway, and, if the site lies in a flood zone, tie into the Madison County Flood Damage Prevention Ordinance for base flood elevations and minimum finished floor elevations. The County Engineer reviews and must approve these plans before the plat can proceed to final approval and recording with the Probate Judge.