The size and capacity of all drainage structures shall be computed using the "rational method". The minimum length of culverts shall be at least equal to the distance from edge of shoulder to edge of shoulder, plus six times the vertical distance from the edge of shoulder to the flow line of the culvert less end section length. No driveway culvert shall have a diameter of less than 12 inches, and no crossroad culvert shall have a diameter of less than 15 inches. In no case shall a driveway culvert be less than 24 feet in length. Material in culverts which exceed 50 feet in length shall be limited to those permitted for storm sewers as specified in the standard specifications, culvert materials shall be circumferentially corrugated metal pipe minimum gauge 16, riveted or as directed by the Supt. of Public Works. All crossroad culverts and driveway culverts shall have end protection in the form of either concrete headwalls or prefabricated end sections as follows:
(A) Single pipe culverts sizes 10" to 18" in diameter must have flared end sections or cast-in-place reinforced concrete headwalls (IDOT Standard 1976)
(B) Single pipe culverts 21" and larger must have cast-in-place reinforced concrete headwalls (IDOT Standard 1976, 1997 or 2093-1).
(C) Double pipe culverts sizes 10" and 12" may have flared end sections or cast-in-place reinforced concrete headwalls (IDOT Standard 2102-1, adjust dimensions as necessary)
(D) Double pipe culverts sizes 15" and larger must have cast-in-place reinforced concrete headwalls (IDOT Standard 2102-1, 2103-1)
(Ord. 1995-0-25, passed 12-26-95)