Section 3700.60  Departmental Standards

a)         Except as provided in Section 3700.70, construction that would result in an obstruction to flood flows or a reduction in flood storage capacity in a delineated floodway will not be permitted unless the application shows the criteria of subsection (b) are met.

b)         Permits will be granted for construction that would not singularly or cumulatively 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 0.1 foot; or

C)        in rural areas, the water surface profile increase would not exceed 0.5 feet; 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.

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