(A) When excavation is proposed in the design of bridges and culvert openings, including the modifications to and replacement of existing bridge and culvert structures, or to compensate for lost conveyance for other appropriate uses, transition sections shall be provided for the excavation.
(B) The following expansion and contraction ratios shall be used unless an applicant’s engineer can prove to IDNR-OWR through engineering calculations or model tests that more abrupt transitions may be used with the same efficiency:
(1) When water is flowing from a narrow section to a wider section, the water should be assumed to expand no faster than at a rate of one foot horizontal for every four feet (4:1 expansion) of the flooded stream’s length;
(2) When water is flowing from a wide section to a narrow section, the water should be assumed to contract no faster than at a rate of one foot horizontal for every one foot (1: 1 contraction) of the flooded stream’s length;
(3) When expanding or contracting flows in a vertical direction, a minimum of one foot vertical transition for every ten feet (10: 1 vertical transition) of stream length shall be used;
(4) Erosion/scour protection shall be provided inland upstream and downstream of the transition sections.
(Ord. 3187, passed 1-22-19) Penalty, see § 152.999