(A) Minor. The Minor drainage system components shall consist of storm drains, street gutters, small open channels, and swales designed to store and convey the peak rate of runoff from the ten year return period precipitation event of critical duration, as determined utilizing the Illinois State Water Survey Bulletin 70 (or the latest revision thereof), and shall generally conform to the requirements of the Village of Mahomet Infrastructure Design Manual.
(B) Major. The Major drainage components, such as open ditches and large surface swales draining 40 acres or more in the area, shall be designed to store and convey stormwater flows beyond the capacity of the minor drainage components. They shall be designed to convey the peak rate of stormwater runoff from a 25 year return period precipitation event.
(C) Excess stormwater passageways.
(1) An excess stormwater passageway shall be provided for the floodplain of all natural water courses and such man-made water courses and storm drainage systems as the Administrator may direct, which shall have adequate capacity to convey the excess stormwater runoff from the tributary watershed. The capacity of this excess stormwater passageway shall be adequate to transport the peak rate of runoff from the 100 year return period storm, assuming all upstream areas are fully developed for uses specifically permitted by existing zoning, and antecedent rainfall in the tributary watershed is average (e.g. Antecedent Moisture Condition II).
(2) No buildings or structures shall be constructed within this passageway; however, streets, parking lots, playgrounds, park areas, pedestrian walkways, open green space, and utility and sewer easements may be considered compatible uses.
(Ord. 15-12-02, passed 12-15-2015)