Section 3700.70  Special Provisions for Bridges and Culverts

a)         General Standards for New Bridges and Culverts

            Permits will be granted for new bridges and culverts that would not result in flood damages or potential flood damages outside the project right-of-way due to increases in flood heights or velocities.  Absent contrary evidence, this standard will be considered met if, for the worst-case analysis (see Section 3700.20):

1)         the application shows that:

A)        any water surface profile increase would be contained within the channel banks (or within existing vertical extensions of the channel banks such as within the design protection grade of existing levees or floodwalls) or flood easements; or

B)        in urban areas, the water surface profile increase would not exceed 0.5 feet at the structure, nor 0.1 foot at a point 1000 feet upstream of the structure as determined by the horizontal projection of the increase and the slope of the hydraulic grade line; or

C)        in rural areas, the water surface profile increase would not exceed 1.0 foot at the structure, nor 0.5 feet at a point 1000 feet upstream of the structure as determined by the horizontal projection of the increase and the slope of the hydraulic grade line; and

2)         the application shows that:

A)        any increase in average channel velocity would not be beyond the scour velocity of the predominant soil type of the channel; or

B)        increased scour, erosion and sedimentation would be prevented by the use of riprap or other design measures.

b)         General Standards for Bridge and Culvert Reconstruction

            A bridge or culvert reconstruction project that would meet the following provisions will be permissible.  A reconstruction project that would not meet these provisions must either comply with the general standards for new bridges and culverts or be designed to reduce the induced flood damages to the fullest practicable extent.

1)         The reconstruction (including approach roads) shall be no more restrictive to normal and flood flows than the existing bridge or culvert crossing; and

2)         Documentation must be provided that the existing crossing has not caused demonstrable flood damage.  In the case of public projects, certification by a District Engineer of the Department of Transportation's Division of Highways, a County Engineer (if a Professional Engineer), or a Municipal Engineer (if a Professional Engineer) that the existing crossing has not caused demonstrable flood damage will be adequate documentation.

(Source:  Amended at 38 Ill. Reg. 934, effective December 27, 2013)