These standards are for the reconstruction, modification or new construction of bridges, culvert crossings and roadway approaches located in the regulatory floodplain.
(A) A proposed new 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 or recorded easements. The evaluation must be submitted to the IDNR-OWR for review and a permit obtained.
(B) If the proposed new structure will increase upstream flood stages greater than one-tenth foot, the applicant must contact IDNR/OWR for a dam safety permit or waiver. The Director shall be copied on all related correspondence.
(C) Lost regulatory floodplain storage must be replaced as required in § 164.063 except that artificially created storage lost due to a reduction in head loss behind an existing bridge or culvert crossing shall not be required to be replaced, provided no flood damage will be incurred downstream.
(D) Velocity increases must be mitigated by use of appropriate measures to avoid scour, erosion and sedimentation at the structure.
(E) For modification or replacement of existing structures, the existing structure must first be evaluated in accordance with IDNR/OWR Rules (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 shall submit justification to allow the damage to continue and evaluate the feasibility of relieving the structure’s impact. Modifications or replacement structures shall not increase flood stages (0.0 feet) compared to the existing condition for all flood events up to and including the base flood event. The evaluation must be submitted to IDNR/OWR, for review and concurrence before a permit is issued. The County Executive and the Chief Subdivision Engineer shall be copied on all related correspondence.
(F) If any work is proposed in, near or over a public body of water, a permit or letter indicating a permit is not required must be obtained from IDNR/OWR.
(G) The hydraulic analysis for the backwater caused by the bridge showing the existing condition and proposed regulatory profile must be submitted to IDNR/OWR for concurrence that a CLOMR is not required.
(H) (1) Construction vehicles shall cross-streams by the means of existing bridges or culverts.
(2) Where an existing crossing is not available, a temporary crossing that has been issued a permit or waiver by IDNR/OWR shall be constructed in which:
(a) The approach roads will be one- half foot or less above existing grade;
(b) The crossing will allow stream flow to pass without backing up the water above the stream bank vegetation line or above any drainage tile or outfall;
(c) The top of the roadway fill in the channel will be at least two feet below the top of the lowest bank. Any fill in the channel shall be non-erosive material, such as riprap or gravel; and
(d) The access road and temporary crossings will be removed within one year after installation, unless an extension of time is granted by the Chief Subdivision Engineer.
(Ord. 10-164, passed 6-17-2010)