Development in and/or filling of the flood fringe will be permitted if protection is provided against the base flood or 100-year frequency flood by proper elevation, and compensatory storage, and other applicable provisions of this chapter. No use will be permitted which adversely affects the capacity of drainage facilities or systems. Developments located within the flood fringe shall meet the requirements of this section, along with the requirements of section 12-1-9 of this chapter. (Ord. 2007-832, 9-5-2007)
A. Watershed Management Permit:
1. No person, firm, corporation, or governmental body not exempted by law shall commence any development in the SFHA without first obtaining a watershed management permit from the building officer.
2. Application for a watershed management permit shall be made on a form provided by the building officer.
a. The application shall be accompanied by drawings of the site, drawn to scale, showing property line dimensions and legal description for the property and sealed by a licensed engineer, architect or land surveyor; existing grade elevations, using the North American vertical datum of 1988, and all changes in grade resulting from excavation or filling; the location and dimensions of all buildings and additions to buildings; and other applicable requirements of article 3 of the WMO. (Ord. 2015-1061, 3-19-2015)
b. For all proposed buildings, the elevation of the lowest floor (including basement) and lowest adjacent grade shall be shown on the submitted plans and the development will be subject to the requirements of section 12-1-9 of this chapter. (Ord. 2007-832, 9-5-2007)
3. Upon receipt of a watershed management permit application, the building officer shall compare the elevation of the site to the base flood or 100-year frequency flood elevation. (Ord. 2015-1061, 3-19-2015)
a. Any development located on land that can be shown to be higher than the base flood elevation of the current flood insurance rate map and which has not been filled after the date of the site's first flood insurance rate map without a permit as required by this chapter is not in the SFHA and, therefore, not subject to the requirements of this chapter. Conversely, any development located on land shown to be below the base flood elevation and hydraulically connected, but shown on the current flood insurance rate map is subject to the provisions of this chapter.
b. The building officer 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 first flood insurance rate map identification.
4. A soil erosion and sediment control plan for disturbed areas shall be submitted. This plan shall include a description of the sequence of grading activities and the temporary sediment and erosion control measures to be implemented to mitigate their effects. This plan shall also include a description of final stabilization and revegetation measures, and the identification of a responsible party to ensure postconstruction maintenance.
5. The building officer shall be responsible for obtaining from the applicant copies of all other federal, state, and local permits, approvals or waivers that may be required for this type of activity. The building officer shall not issue a permit unless all other federal, state, and local permits have been obtained.
B. Preventing Increased Damages: No development in the flood fringe shall create a threat to public health and safety.
1. LOMR Based On Fill: If fill is being used to elevate the site above the base flood or 100-year frequency flood elevation, the applicant shall submit sufficient data and obtain a letter of map revision (LOMR) from FEMA for the purpose of removing the site from the floodplain.
2. 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 base flood or 100-year frequency flood elevation shall be compensated for and balanced by a hydraulically equivalent volume of excavation taken from below the base flood or 100-year frequency flood elevation.
b. The excavation volume shall be at least equal to 1.5 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 10-year flood elevation shall be replaced below the proposed 10-year flood elevation. All floodplain storage lost above the existing 10-year flood elevation shall be replaced above the proposed 10-year flood elevation.
e. All such excavations shall be constructed to drain freely and openly to the watercourse.
C. Construction Of The Lowest Floor Below The Base Flood Elevation (BFE): A person, who has obtained a letter of map revision based on fill that removes a site in the flood fringe from the floodplain due to the use of fill to elevate the site above the BFE, may apply for a permit from the village to construct the lowest floor of a residential building below the BFE in the flood fringe. The building officer shall not issue such a permit unless the applicant has complied with all the criteria set forth in the following subsections:
1. Compensatory storage shall be provided per subsection B2 of this section.
2. The elevation of the lowest opening in the basement wall (i.e., window wells, accessways) shall be at or above the flood protection elevation (FPE). (Ord. 2007-832, 9-5-2007)
3. The lowest adjacent grade to the foundation shall be at or above the FPE, for a minimum distance of ten feet (10') beyond the outside face of the structure.
4. The grade around the perimeter of the structure, measured at a distance of twenty feet (20') from the structure, shall be above the BFE. (Ord. 2015-1061, 3-19-2015)
5. The ground around the building shall be compacted fill that meets all requirements of this subsection and is at least five feet (5') thick under the basement floor slab. Nothing in this subsection shall be interpreted to require the removal or replacement of fill that was placed as part of a LOMR-F, if such fill consists of material, including soils of similar classification and degree permeability, such as those classified as CH, CL, SC or ML according to ASTM standard D-2487, "Classification Of Soils For Engineering Purposes".
6. The fill material must be homogeneous and isotropic; that is, the soil must be all of one material, and the engineering priorities must be in the same direction.
7. All fill material and compaction shall be designed, certified and inspected by an Illinois registered professional engineer, as warranted by the site conditions.
8. The basement floor shall be at an elevation that is no more than five feet (5') below the BFE.
9. There shall be a granular drainage layer beneath the floor slab, and minimum of one-fourth (1/4) horsepower sump pump with a backup power supply shall be provided to remove seepage flow. The pump shall be rated at four (4) times the estimated seepage rate and shall discharge above the BFE and away from the building in order to prevent flooding of the basement or uplift of the floor under the effect of the seepage pressure.
10. The drainage system shall be equipped with a positive means of preventing backflow.
11. All foundation elements shall be designed to withstand hydrostatic pressure in accordance with accepted engineering practices. (Ord. 2007-832, 9-5-2007)
12. If the applicant is unable to meet all of the requirements set forth in the preceding subsections, the building officer may allow the construction of a basement below the BFE only if the applicant demonstrates that the proposed fill and structure meet the guidelines and requirements set forth in the WMO and FEMA technical bulletin 10-01 and are reasonably safe from flooding. In order to demonstrate that the proposed structure is reasonably safe from flooding, the applicant shall submit a detailed engineering analysis of the proposed fill and foundation wall. The engineered basement study shall be completed in accordance with the latest edition of FEMA technical bulletin 10-01, with the analysis of the fill being prepared by an Illinois registered professional engineer. (Ord. 2015-1061, 3-19-2015)
13. In order to provide the required compensatory storage on site, in no case shall the depth of excavation in the front and side yards of the lot exceed eighteen inches (18"), as measured from the previously existing natural grade. The rear yard shall be permitted to have a greater depth of excavation, if necessary. All such excavation shall be constructed to drain freely and openly to the watercourse or storm sewer system. The use of mechanical means to drain the compensatory storage area will not be permitted. (Ord. 2007-832, 9-5-2007)