(a) Stormwater and all other unpolluted drainage shall be discharged to such sewers as are specifically designated as storm sewers, or to a natural outlet approved by the director of public works and engineering. Industrial cooling water or unpolluted process waters may be discharged on approval of the director of public works and engineering, to a storm sewer or natural outlet.
(b) A combination of storage and controlled release of stormwater runoff shall be required for all commercial and industrial developments of one acre or more in area, for all multiple-family residential developments of two (2) or more acres in area, and for all single-family developments of five (5) acres or more in area. Notwithstanding the area limitations stated above, multiple-family residential developments, commercial developments and industrial developments shall be required to provide storage and controlled release of stormwater runoff when the development is located within two hundred feet (200') of an existing storm sewer, or when the development results from a change in use, a change in zoning classification or the granting of a special use.
(c) The release rate of stormwater from all developments requiring detention shall not exceed the stormwater runoff rate from the area in its natural undeveloped state. A release rate of not greater than that calculated from a storm of 3-year frequency with a runoff rate coefficient of fifteen one-hundredths (0.15) will be acceptable unless the applicant can show by detailed calculations which are acceptable to the village engineer that the discharge rate of the natural outlet channel serving the area is greater.
(d) Storm sewer systems shall have adequate capacity to bypass through the development the flow from all upstream areas for a storm of design frequency assuming that the land is in a fully developed state under present zoning or zoning proposed under the village's comprehensive plan. The bypass flow rate shall be computed utilizing a runoff coefficient of not less than thirty five one-hundredths (0.35). An allowance, equivalent to the reduction in flow rate provided, will be made for upstream detention when such upstream detention and release rate has previously been approved by the village and has been constructed.
(e) The live detention storage to be provided shall be calculated on the basis of the 100-year frequency rainfall, as published by the U.S. weather bureau for this area. The detention volume required shall be that necessary to temporarily store the runoff of 100-year rainfall, for any and all durations, from the fully developed drainage area tributary to the reservoir, less that volume discharged during the same duration at the approved release rate.
(f) In the event the downstream sewers are inadequate to receive the release rate hereinabove provided, then the allowable release rate shall be reduced to that rate permitted by the receiving downstream sewers and additional detention as determined by the village engineer shall be required to store that portion of the runoff exceeding the capacity of the receiving sewers.
(g) Plans, specifications and calculations for stormwater detention facilities as required hereunder, shall be submitted to the village engineer for approval prior to the commencement of construction. (Ord. 0-13-51, 11-4-2013)