(A) Storage areas shall be designed to the satisfaction of the Flood Safety Officer and if possible to provide secondary purposes for recreation, open spaces, parking lot or other types of use that will not be adversely affected by intermittent flooding.
(B) All storm water storage areas must be designed to contain and safely pass storm water runoff. The combined capacity of these storage areas shall be sufficient to contain the storm from the development. The retention facility must be designed for periodic maintenance and energy dissipater shall be provided at points necessary. The combination of storage of the water from a 100-year storm and the design release rate shall not result in a storage duration in excess of 72 hours.
(C) The pending of storm water runoff shall not exceed a depth of one foot on a pedestrian mall area or one and one-half feet maximum in parking lots. Where these areas are used for pending, the maximum depth should occur in the most remote and least used areas.
(D) The drainage and grading design shall be prepared to insure that in a 100-year storm the depth of water runoff in any street, alley or pedestrian mall will not exceed the level of the first floor of any building.
(E) For a 100-year storm, the pending of surface water on local, collector and arterial streets must not exceed a depth of 18 inches at the gutter; water exceeding this shall be designed to overflow into an excess storm water passage. The maximum velocity of water in the deepest part of the gutter shall be ten feet per second and paved gutters shall have a minimum grade of 0.5%.
(F) Overflow for each storm water storage area shall be provided in the event a storm in excess of the design capacity occurs. The overflow shall be constructed to function without specific attention and shall become part of the excess storm water passage.
(G) Where rooftop storage of excess storm water is provided, the building shall be provided with adequate structural design to insure that roof failure does not occur. Overflow areas shall be provided so that the weight of stored storm water will not exceed the structural capacity of the roof.
(H) For wet pond storage areas when calculating the storage capacity, only the volume available to store excess storm water shall be considered. Permanent water storage does not constitute control of excess storm runoff.
(Ord. 14-79, passed 10-16-1979) Penalty, see § 155.99