Any development, redevelopment, site modification or building modification within a regulatory floodway is subject to the provisions of this section and shall be permitted only if the criteria of this section and applicable requirements of this chapter are met. All floodway modifications shall be the minimum necessary to accomplish the purpose of the project. The development shall also meet the requirements of Section 15.68.080 of this chapter.
A. Floodplain Development Permit. No person, firm, corporation or governmental body not exempted by state law shall commence any development in a floodway without first obtaining a floodplain development permit from the Director.
B. Application. Application for a floodplain development permit shall be made on a form provided by the Director, which shall include at least the information required by Article 3 of the WMO.
C. Review and Approval of Permit Applications. The Director shall be responsible for obtaining from the applicant copies of all other local, state, and federal permits and approvals that may be required for the proposed activity. The Director shall not issue the floodplain development permit unless copies of all required federal and state permits have been submitted by the applicant. A registered professional engineer under the employ or contract of the Village shall review and approve applications reviewed under this section.
D. Preventing Increased Damages; List of Appropriate Uses. No development shall be allowed in a floodway unless it is for appropriate uses that will not cause a rise in the base flood elevation, will not create a damaging or potentially damaging increase in flood heights or velocity and will not be a threat to public health and safety. Only those appropriate uses listed in 17 Ill. Adm. Code 3708 and § 602.27 of the WMO will be allowed. Appropriate uses do not include the construction or placement of any new buildings, structures, fill, building additions, buildings on stilts, fencing (including landscaping or planting designed to act as a fence) and storage of materials except as specifically defined above as an appropriate use.
E. Engineering Criteria for Appropriate Uses in the Regulatory Floodway. Within the regulated floodway as identified on the Countywide FIRMs for Cook County, the construction of an appropriate use will be considered permissible; provided that, the proposed project meets the requirements of § 602.7-9 and 25-28 of the WMO, along with the following engineering criteria, and is so stated in writing with supporting plans, calculations and data by a registered professional engineer; and provided that, any structure meets the protection requirements of Section 15.68.080 of this chapter:
1. Preservation of Flood Conveyance, so as Not to Increase Flood Stages Upstream. For appropriate uses, all effective regulatory floodway conveyance lost due to the project will be replaced for all flood events up to and including the 100-year frequency flood. In calculating effective regulatory floodway conveyance, the following factors shall be taken into consideration:
a. Regulatory floodway conveyance,
'K' = 1.486 AR
2/3 |
n |
where "n" is Manning's roughness factor, "A" is the effective area of the cross-section, and "R" is the ratio of the area to the wetted perimeter (see Open Channel Hydraulics, Ven Te Chow, 1959, McGraw-Hill Book Company, New York);
b. The same Manning's "n" value shall be used for both existing and proposed conditions unless a recorded maintenance agreement with a federal, state or local unit of government can assure the proposed conditions will be maintained or the land cover is changing from a vegetative to a nonvegetative land cover;
c. Transition section shall be provided and used in calculations of effective regulatory floodway conveyance. 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;
i. 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 of the flooded stream's length.
ii. 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 of the flooded stream's length.
iii. When expanding or contracting flows in a vertical direction, a minimum of one foot vertical transition for every ten (10) feet of stream length shall be used.
iv. Transition sections shall be provided between cross-sections with rapid expansions and contractions and when meeting the regulatory floodway delineation on adjacent properties.
v. All cross-sections used in the calculations shall be located perpendicular to flood flows.
2. Preservation of Floodway Storage so as Not to Increase Downstream Flooding. Compensatory storage shall be provided for any regulatory floodway storage lost due to the proposed work from the volume of fill or structures placed and the impact of any related flood control projects. Compensatory storage for fill or structures shall meet the requirements of § 602.7-9 of the WMO.
3. Preservation of Floodway Velocities so as Not to Increase Stream Erosion or Flood Heights. For all appropriate uses the proposed work will not result in an increase in the average channel or regulatory floodway velocities, unless a water resource benefit is realized and unless scour, erosion and sedimentation will be avoided by the use of rip-rap or other design measures.
4. Construction of New Bridges or Culvert Crossings and Roadway Approaches. The proposed structures shall not result in an increase of upstream flood stages when compared to the existing conditions for all flood events up to and including the one hundred (100) year frequency event, unless the area of the increased flood stages is under the ownership or control of the applicant.
a. The engineering analysis of upstream flood stages shall be calculated using the flood study flows, and corresponding flood elevations for tailwater conditions for the flood study specified in Section 15.68.040 of this chapter.
b. Lost floodway storage shall be compensated for in accordance with subsection (E)(2) of Section 15.68.060.
c. Velocity increases shall be mitigated in accordance with subsection (E)(3) of Section 15.68.060.
d. If the crossing is proposed over a public water that is used for recreational or commercial navigation, an IDNR/OWR permit must be obtained by the applicant.
e. The hydraulic analysis for the backwater caused by the bridge showing the existing conditions and proposed regulatory profile shall be submitted to IDNR/OWR for concurrence that a CLOMR is not required by subsection E of Section 15.68.060.
f. All excavations for the construction of the crossing shall be designed per subsection (E)(8) of Section 15.68.060.
5. Reconstruction or Modification of Existing Bridges, Culverts and Approach Roads.
a. The bridge or culvert and roadway approach reconstruction or modification shall be constructed with no more than one-tenth foot increase in backwater over the existing flood profile for all flood frequencies up to and including the one hundred (100) year event, if the existing structure is not a source of flood damage.
b. If the existing bridge or culvert and roadway approach is a source of flood damage to buildings or structures in the upstream floodplain, the applicant's engineer shall evaluate the feasibility of redesigning the structure to reduce the existing backwater, taking into consideration the effects on flood states on upstream and downstream properties.
c. The determination as to whether or not the existing crossing is a source of flood damage and should be redesigned shall be prepared in accordance with IDNR/OWR Rules 17 Ill. Adm. Code 3708 (Floodway Construction in Northeastern Illinois) and submitted to IDNR/OWR for review and concurrence before a permit is issued.
d. Hydraulically equivalent compensatory storage shall be required to mitigate any potential increase in flow or flood elevations due to the removal or modification of an existing bridge or culvert.
6. On-Stream Structures Built for the Purpose of Backing Up Water. Any increase in upstream flood stages greater than zero feet when compared to the existing conditions, for all flood events up to and including the one hundred (100) year frequency event shall be contained within the area under the ownership or control of the applicant. A permit or letter indicating a permit is not required must be obtained from IDNR/OWR, dam safety section, for a dam safety permit or waiver for any structure built for the purpose of backing up water in the stream during normal or flood flow. All dams and impoundment structures as defined in Section 15.68.020 of this chapter shall meet the permitting requirements of 17 Ill. Adm. Code 3702 (Construction and Maintenance of Dams).
7. Floodproofing of Existing Habitable, Residential and Commercial Structures. If construction is required beyond the outside dimensions of the existing building, the outside perimeter of the floodproofing construction shall be placed no further than ten (10) feet from the outside of the building. Compensation of lost storage and conveyance will not be required for floodproofing activities.
8. Excavation in the Floodway. 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. 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.
a. 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 of the flood stream's length;
b. 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 of the flooded stream's length;
c. When expanding or contracting flows in a vertical direction, a minimum of one foot vertical transition for every ten (10) feet for stream length shall be used; and
d. Erosion/scour protection shall be provided inland upstream and downstream of the transition sections.
9. Seeding and Stabilization Plan. For all activities located in a floodway, a seeding and stabilization plan shall be submitted by the applicant.
10. General Criteria for Analysis of Flood Elevations.
a. The flood profiles, flows and floodway data in the regulatory floodway study, referenced in Section 15.68.040 of this chapter, shall be used for analysis of the base conditions. If the study data appears to be in error or conditions have changed, the IDNR/OWR shall be contacted for approval and concurrence on the appropriate base conditions data to use.
b. If the one hundred (100) year regulatory floodway elevation at the site of the proposed construction is affected by backwater from a downstream receiving stream with a large drainage area, the proposed construction shall be shown to meet the requirements of this section for the one hundred (100) year frequency flood elevations of the regulatory floodway conditions and conditions with the receiving stream at normal water elevations.
c. If the applicant learns from IDNR/OWR, local governments, or a private owner that a downstream restrictive bridge or culvert is scheduled to be removed, reconstructed, modified, or a regional flood control project is scheduled to be built, removed, constructed or modified within the next five years, the proposed construction shall be analyzed and shown to meet the requirements of this section for both the existing conditions and the expected flood profile conditions when the bridge, culvert or flood control project is built.
11. Conditional Letter of Map Revision. If the appropriate use would result in a change in the regulatory floodway location or the one hundred (100) year frequency flood elevation, the applicant shall submit to IDNR/OWR and to FEMA all the information, calculations and documents necessary to be issued a conditional regulatory floodway map revision and received from IDNR/OWR a conditional approval of the regulatory floodway change before a permit is issued. The final regulatory floodway map will not be changed by IDNR/OWR until as-built plans or record drawings are submitted and accepted by FEMA and IDNR/OWR. In the case of nongovernmental projects, the municipality in incorporated areas and the county in an unincorporated area shall concur with the proposed conditional regulatory floodway map revision before IDNR/OWR approval can be given. No filling, grading, dredging or excavating shall take place until a conditional approval is issued. Once a CLOMR has been issued, a permit may be issued for site grading and structures necessary in the area of the map change to achieve the final LOMR. Upon completion, the applicant shall submit as-built certifications, as required by FEMA, to achieve a final LOMR prior to the release of final development permits. The regulatory floodway map will be revised upon acceptance and concurrence by IDNR/OWR and FEMA of the as-built plans, and the effective date of the LOMR is reached.
12. Professional Engineer's Supervision. All engineering analyses shall be performed by or under the supervision of an Illinois registered professional engineer, retained by the applicant.
F. State Review in delegated communities. For those projects listed below located in a regulatory floodway, the following criteria shall be submitted to IDNR/OWR for their review and concurrence prior to the issuance of a permit:
1. IDNR/OWR will review an engineer's analysis of the flood profile due to a proposed bridge pursuant to subsection (E)(4) of Section 15.68.060.
2. IDNR/OWR will review an engineer's determination that an existing bridge or culvert crossing is not a source of flood damage and the analysis indicating the proposed flood profile, pursuant to subsection (E)(5) of Section 15.68.060.
3. The IDNR/OWR will review alternative transition sections and hydraulically equivalent storage pursuant to subsections (E)(1), (2) and (8) of Section 15.68.060.
4. The IDNR/OWR will review and approve, prior to the start of construction, any Department projects, dams (as defined in Section 15.68.120 of this chapter) and all other state, federal and local units of government projects, including projects of the Village.
G. Other Permits. In addition to the other requirements of this chapter, a Floodplain development permit for a site located in a floodway shall not be issued unless the applicant first obtains a permit or written documentation that a permit is not required from IDNR/OWR, issued pursuant to 615 ILCS 5/5, et seq.
H. Dam Safety Permits. Any person performing work involving the construction, modification or removal of a dam (as defined in Section 15.68.020 of this chapter) pursuant to 17 Ill. Adm. Code 3702 (Rules for Construction of Dams) shall obtain an IDNR/OWR Dam Safety Permit prior to the start of construction of a dam. If the Director finds a dam that does not have an IDNR/OWR permit, the Director shall immediately notify the Dam Safety Section of IDNR/OWR. If the Director finds a dam that is believed to be in an unsafe condition, the Director shall immediately notify the owner of the dam, IDNR/OWR, Dam Safety Section, and the Illinois Emergency Management Agency (IEMA).
I. Activities That Qualify for a Regional Permit from IDNR/OWR. The following activities may be permitted without a registered professional engineer's review, provided they meet the other requirements of this chapter.
1. Underground and overhead utilities that:
a. Do not result in any increase in existing ground elevations;
b. Do not require the placement of above ground structures in the floodway;
c. In the case of underground stream crossings, the top of the pipe or encasement is buried a minimum of three feet below the existing stream bed; and
d. In the case of overhead utilities, no supporting towers are placed in the watercourse and are designed in such a fashion as not to catch debris.
2. Storm and sanitary sewer outfalls that:
a. Do not extend riverward or lakeward of the existing adjacent natural bank slope;
b. Do not result in an increase in ground elevation; and
c. Are designed so as not to cause stream erosion at the outfall location.
3. Construction of sidewalks, athletic fields (excluding fences), properly anchored playground equipment and patios at grade.
4. Construction of shoreline and streambank protection:
a. When such construction does not exceed one thousand (1,000) feet in length;
b. When materials used in such construction are not placed higher than the existing top of bank; and
c. When materials used in such construction are placed so as not to reduce the cross-sectional area of the stream channel or bank of the lake. (Prior code § 28.06)
(MC-4-2021, § 2, Amended 8/3/2021; MC-5-2018, Amended, 08/07/2018: MC-5-2014 § 21, 04/17/2014; MC-2-2008, Amended, 05/06/2008)