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This section details special considerations and performance standards for the construction of new bridges or culvert crossings and roadway approaches, or the reconstruction or modification of existing bridges, culvert crossings, or roadway approaches.
(A) The proposed structure shall not result in an increase of upstream flood stages greater than one-tenth foot when compared to the existing conditions for all flood events up to and including the base flood event unless contained within the channel banks, project right-of-way, or recorded easements. The evaluation shall be submitted to the Lake County Stormwater Management Commission for review and concurrence before a site development permit is issued.
(B) If the proposed construction will increase upstream flood stages greater than one-tenth foot, the developer must contact the Illinois Department of Natural Resources, Office of Resources for a dam safety permit or waiver.
(C) Lost regulatory floodway and regulatory floodplain storage must be compensated in accordance with all regulatory floodplain performance standards of this chapter, except that artificially created storage that is lost or displaced due to a reduction in upstream head loss caused by a bridge, culvert, storm sewer, or constructed embankment shall not be required to be replaced, provided no damage will be incurred downstream (see § 151.150).
(D) Velocity increases must be mitigated in accordance with all regulatory floodway performance standards of this chapter except that in the case of bridges, culverts, or on-stream structures built for the purpose of backing up water in the stream during normal or flood flows, velocities may be increased at the structure site if erosion and sedimentation will be avoided by the use of appropriate measures (see § 151.150).
(E) For modification or replacement of existing structures, the existing structure must first be evaluated in accordance with 17 Ill. Adm. Code Part 3708 to determine if the existing structure is a source of flood damage. If the structure is a source of flood damage, the applicant’s engineer must evaluate the feasibility of redesigning the structure to reduce the existing backwater, taking into consideration the effects of flood damage to upstream and downstream properties. Modifications or replacement structures shall not increase flood stages compared to the existing or regulatory condition, whichever is greater, for all flood events up to and including the base flood event. The evaluation shall be submitted to the Illinois Department of Natural Resources, Office of Water Resources or its designee for review and concurrence before a site development permit is issued.
(F) If the crossing is proposed over a public body of water, an Illinois Department of Transportation, Office of Water Resources permit shall be received. (See Appendix I for a list of public bodies of water.)
(G) The hydraulic analysis for the backwater caused by the bridge showing the existing condition and proposed regulatory profile shall be submitted to the Illinois Department of Natural Resources, Office of Water Resources for concurrence that Conditional Letter of Map Revision is not required.
(Ord., § 8.7, passed 10-13-2009; Ord. passed 10-9-2012)