Review of impervious surfaces continues
By Grace Lovins
Discussions on developing a new definition of “impervious surfaces” for Birmingham’s zoning ordinance continued during the Wednesday, November 13, planning board meeting, leading to debate over surface examples listed in the definition.
Birmingham’s Planning Board began reviewing the definition of impervious surfaces in the city’s zoning ordinance back in September after staff requested direction on how the definition could be changed to better fit the city’s sustainability and development goals.
Planning director Nick Dupuis wrote in a memorandum, included in the meeting packet, that impervious surfaces play a role in the preservation of natural and green space and have implications for public health, environmental sustainability and urban heat island effects.
The city’s ordinance currently defines such surfaces as any material that prevents infiltration of surface water, which includes concrete, asphalt, stone and similar materials. Using example definitions from other communities, Oakland County’s stormwater standards and Southeast Michigan Council of Government’s (SEMCOG) low impact development manual, staff was able to broaden the current definition.
Dupuis’ proposed definition reads “a surface that prevents the infiltration of water into the ground such as all roofs, streets, sidewalks, driveways, parking lots, highly compacted soils and gravel.”
Discussions on Dupuis’ definition mostly revolved around the inclusion of gravel. Alternate board member Jason Emerine, filling in for Scott Clein, argued that the word should be removed, saying it’s too general and too restrictive.
“The perviousness of gravel depends on the gradation of said gravel,” said Emerine. “[The size of the gravel] has a huge impact on whether gravel is impervious or not.”
Emerine suggested using SEMCOG’s definition in their low impact development manual which includes everything in Dupuis’ proposed definition aside from gravel. Most of the board said they were comfortable removing the word and explained they trusted Emerine’s opinion based on his professional expertise on the topic.
The board did not take any formal action to move the definition to a public hearing, but Dupuis will be returning with a new draft during the board’s Wednesday, December 11, meeting for another study session.
