In riverine Floodplains, where no Floodways have been identified, no Development shall be permitted unless the cumulative effect of the proposals, when combined with all other existing and anticipated uses and Structures, shall not significantly impede or increase the flow and passage of the floodwaters nor significantly increase flood heights. The Development must meet all applicable requirements of this Chapter and 17 Ill. Adm. Code Part 3700.
A. Floodway Permit.
1. In addition to a floodplain development permit, work within an IDNR/OWR Jurisdictional Stream shall require either a floodway permit from IDNR/OWR, documentation that the projects meets the conditions of a Statewide Permit listed in Section 4-12-7(B)(3), or a letter from IDNR/OWR stating no permit is required. In addition to the requirements of Section 4-12-3, the application for a floodplain development permit shall also include the following information:
a. A detailed description of the proposed activity, its purpose, and intended use;
b. Site location (including legal description) of the property, drawn to scale, on the FIRM, indicating whether it is proposed to be in an incorporated or unincorporated area;
c. Anticipated dates of initiation and completion of activity;
d. Plans of the proposed activity shall be provided which include as a minimum:
(1) A vicinity map showing the site of the activity, name of the waterway, boundary lines, names of roads in the vicinity of the site, graphic or numerical scale, and north arrow;
(2) A plan view of the project and engineering study reach showing existing and proposed conditions including principal dimensions of the Structure or work, elevations, using the NAVD 88, adjacent property lines and ownership, drainage and Flood control easements, distance between proposed activity and navigation Channel (when the proposed construction is in or near a commercially navigable body of water), Floodplain limit, location and orientation of cross-sections, north arrow, and a graphical or numerical scale;
(3) Cross-section views of the project perpendicular to the flow of floodwater and engineering study reach showing existing and proposed conditions including principal dimensions of the work as shown in plan view, existing and proposed elevations, normal water elevation, 10percent annual chance Flood elevation, BFE, and graphical or numerical scales (horizontal and vertical); and
(4) A seeding or stabilization plan for the disturbed areas.
e. Engineering calculations and supporting data shall be submitted showing that the proposed work will meet the criteria of Section 4-12-7(B).
f. Any and all other federal, state, and local permits or approvals that may be required for this type of Development.
2. Based on the best available existing data according to federal, state, or other sources, the Director of Public Works shall compare the elevation of the site to the BFE.
a. Should no BFE information exist for the site, the developer's engineer shall calculate the BFE according to Section 4-12-4.
b. The Director of Public Works shall maintain documentation of the existing ground elevation at the Development site and certification that this ground elevation existed prior to the date of the site's current FIRM's Floodplain identification.
B. Preventing Increased Damages.
1. No Development in the Floodplain, where a Floodway has not been determined, shall create a damaging or potentially damaging increase in Flood heights or velocity or threat to public health, safety and welfare or impair the natural hydrologic and hydraulic functions of the Floodway or Channel or impair existing water quality or aquatic habitat. Construction impacts shall be minimized by appropriate mitigation methods as called for in this Chapter.
2. Within all riverine Floodplains where the Floodway has not been determined, the following standards shall apply:
a. The developer shall have a Licensed P.E. state in writing and show through supporting plans, calculations, and data that the project meets the engineering requirements of Section 4-12-6 for the entire Floodplain.
b. As an alternative, the developer should have an engineering study performed to determine a Floodway and submit that engineering study to IDNR/OWR and FEMA for acceptance as a Designated Floodway.
c. Upon acceptance of the Floodway by IDNR/OWR and FEMA, the developer shall then demonstrate that the project meets the requirements of Section 4-12-6 for the Designated Floodway.
d. A Development permit shall not be issued unless the Applicant first obtains an IDNR/OWR permit or a determination has been made that an IDNR/OWR permit is not required.
e. Permits for Dams.
(1) Any work involving the construction, modification, or removal of a Dam per 17 Ill. Adm. Code Part 3702 (Rules for Construction of Dams) shall obtain an IDNR/OWR permit prior to the start of dam construction.
(2) If the Director of Public Works finds a Dam that does not have an IDNR/OWR permit, the Director of Public Works shall immediately notify the IDNR/OWR Bartlett office.
(3) If the Director of Public Works finds a Dam which is believed to be in unsafe condition, the Director of Public Works shall immediately notify the owner of the Dam, the IDNR/OWR Bartlett office, and the Illinois Emergency Management Agency.
3. The following activities may be permitted without a Licensed P.E.'s review or calculation of BFE and Designated Floodway. Such activities shall still meet the other requirements of this Chapter.
a. Bridge and culvert crossings of streams in rural areas meeting conditions of IDNR/OWR Statewide Permit No. 2;
b. Barge fleeting facilities meeting conditions of IDNR/OWR Statewide Permit No. 3;
c. Aerial utility crossings meeting conditions of IDNR/OWR Statewide Permit No. 4
d. Minor boat docks meeting conditions of IDNR/OWR Statewide Permit No. 5;
e. Minor, non-obstructive activities meeting conditions of IDNR/OWR Statewide Permit No. 6; activities (not involving fill or positive change in grade) are covered by this permit;
f. Outfall Structures and drainage ditch outlets meeting conditions of IDNR/OWR Statewide Permit No. 7;
g. Underground pipeline and utility crossings meeting the conditions of IDNR/OWR Statewide Permit No. 8;
h. Bank stabilization projects meeting the conditions of IDNR/OWR Statewide Permit No. 9;
i. Accessory Structures and additions to existing residential Buildings meeting the conditions of IDNR/OWR Statewide Permit No. 10;
j. Minor maintenance dredging activities meeting conditions of IDNR/OWR Statewide Permit No. 11;
k. Bridge and culvert replacement Structures and bridge widenings meeting conditions of IDNR/OWR Statewide Permit No. 12;
l. Temporary construction activities meeting conditions of IDNR/OWR Statewide Permit No. 13;
m. Special Uses of Public Waters meeting conditions of IDNR/OWR Statewide Permit No. 14; and
n. Any Development determined by IDNR/OWR to be located entirely within a Flood Fringe area shall be exempt from State Floodway permit requirements.
4. The Flood carrying capacity of any altered or relocated watercourse shall be maintained.
5. Compensatory Storage.
a. Whenever any portion of a Floodplain is authorized for use, the volume of space which will be occupied by the authorized fill or Structure below the BFE shall be compensated for and balanced by a hydraulically equivalent volume of excavation taken from below the BFE.
b. The excavation volume shall be at least equal to 1.1 times the volume of storage lost due to the fill or Structure.
c. In the case of streams and watercourses, such excavation shall be made opposite or adjacent to the areas so filled or occupied.
d. All Floodplain storage lost below the existing ten percent (10%) annual chance flood elevation shall be replaced below the proposed ten percent (10%) annual chance Flood elevation. All Floodplain storage lost above the existing one hundred percent (100%) annual chance Flood elevation shall be replaced above the proposed one hundred percent (100%) annual chance Flood elevation. All such excavations shall be constructed to drain freely and openly to the watercourse. (Ord. 3852, 1-10-2022)