Jack Eaton contacted the County Water Resources Commissioner, Evan Pratt, and asked what the County storm water requirements were. Jack reported he was told:
The developer proposed drawings state the area of the development is 115,000 sq ft. A 100 yr storm event in Ann Arbor is usually considered to be 4.75 inches in a 24 hour period. That amount, 4.75 inches over 115,000 sq ft is about 45,500 cubic ft of water.To manage both water quantity and quality basins must be designed to capture . . . the 100 year storm event
But in the report by developers of their recent meeting with neighborhood citizens the developer states:
The developer is responsible for storm water management for the entire 2.64 acres. . ....The storm water detention system holds approximately 20,000 cf of water in pipes that are 72” in diameter.We need to ask why there is such a large difference and if the County and the Planning Commission intend to accept the developers calculation.