(A) All major drainageways shall be designed as shown on the community storm drainage plan.
(B) Where no drainage plan exists drainage ways shall be designed as follows.
(1) Major waterways. Major waterways are defined as those with a tributary area in excess of four square miles. The major waterways shall be designed for an average flood recurrence interval of 100 years.
(2) Secondary waterways. Secondary waterways are defined as those with a tributary area of between one and four square miles. The secondary waterways shall be designed for an average flood recurrence interval of 25 years.
(3) Minor waterways. Minor waterways are defined as those with one square mile or less of tributary area. The minor waterways shall be designed for an average flood recurrence interval of ten years.
(4) Design flows.
(a) Design flows for secondary and minor drainage facilities shall be computed by the subdivider's engineer by use of the rational formula:
Q = CIA in the urban areas.
Wherein: Q = cubic feet per second
C = run-off coefficient
I = intensity of rainfall, inches per hour
A = tributary area
(b) Drainage structures and their easements shall be adequate to handle the flow from this formula.
(C) Drainage designs shall be accomplished for the subdivider by a professional engineer, registered in the State of Illinois.
(1) The drainage plan and design shall bear the seal of professional engineer.
(2) The drainage plan will be subject to review and the approval of the Village Engineer.
(D) Flows for the design of secondary and minor drainage facilities within urban and suburban areas shall be calculated in accordance with the State Department of Transportation Storm Water Design Manual, latest revision.
(E) In the agricultural areas within the review area of the village but outside the urban area, run-off calculations shall be made using the most appropriate method according to the current state of art of hydrology and current engineering practice, i.e., Cook's or Soil Conservation Service methods.
(2001 Code, § 34-6-34)