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 provisions of this chapter are met. No use will be permitted which adversely affects the capacity of drainage facilities or systems, including the temporary storage of materials for more than seven (7) calendar days. Developments located within the flood fringe shall meet the requirements of this section, along with the requirements of section 14-1-9 of this chapter.
A. Development Permit: No person, firm, corporation or governmental body not exempted by state law shall commence any development in the SFHA without first obtaining a development permit from the community development director and director of engineering.
1. Application for a development permit shall be made on a form provided by the community development director and director of engineering. 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, or land surveyor; existing grade elevations in 1988 NAVD and all changes in grade resulting from excavation or filling; the location and dimensions of all 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 14-1-9 of this chapter.
2. Upon receipt of a development permit application, the director of engineering shall compare the elevation of the site to the base flood or 100-year frequency flood elevation. Any development located on land that is higher than the base flood elevation as determined pursuant to section 14-1-5 of this chapter is not in the SFHA and, therefore, not subject to the requirements of this chapter. The building official 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 effective FIRM.
3. A soil erosion and sedimentation control plan for disturbed areas shall be submitted. This plan, including all calculations, 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.
4. The community development director shall be responsible for obtaining from the applicant copies of all other local, state and federal permits, approvals or permit not required letters that may be required for this type of activity. The community development director shall not issue a permit unless all other local, state and federal permits have been obtained.
B. Preventing Increased Damages: No development in the flood fringe shall create a threat to public health and safety.
1. Remove Site From Floodplain: 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: 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 or excavation taken from below the base flood or 100-year frequency flood elevation. The excavation volume shall be at least equal to one and one-tenth (1.1) times the volume of storage lost due to the fill or structure. In the case of streams and watercourses, such excavation shall be made in a hydraulically equivalent area to the areas so filled or occupied. 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 and under the 100-year elevation. All such excavations shall be constructed to drain freely and openly to the watercourse.
3. Construction Of The Lowest Floor Below The Base Flood Elevation (BFE): A person who has obtained a letter of map revision based on fill (LOMR-F) 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 city of Des Plaines to construct the lowest floor of a residential building below the BFE in the flood fringe. The building official shall not issue such a permit unless the applicant has complied with all the criteria set forth in the following subsections:
a. Compensatory storage shall be provided.
b. The elevation of the lowest opening in the basement wall (i.e., window wells, accessways) shall be at two feet zero inches (2'0") above the base flood elevation (BFE).
c. 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. However, if site conditions are such that this requirement cannot be met, the building official may waive the ten foot (10') minimum setback if an Illinois licensed professional engineer certifies that an alternative method to protect the building from damage due to hydrostatic pressures has been met. The certifications shall be in the form of a detailed soils and structural design analysis, which shall be submitted to the building official for review. The building official may require such additional documentation as necessary to prove that the proposed shorter setback distance will keep the structure reasonably safe. In no case shall the setback distance be less than four feet (4').
d. The grade around the perimeter of the structure, measured at a distance of twenty feet (20') from the structure, shall be above the BFE. However, if site conditions are such that this requirement cannot be obtained, the building official may waive the twenty foot (20') minimum setback distance if an Illinois licensed professional engineer certifies that an alternative method to protect the building from damages due to hydrostatic pressures has been met. A detailed soils analysis and structural design proving that a shorter setback distance will keep the structure reasonably safe from flooding, shall be submitted to the city of Des Plaines for review. In no case shall the setback distance be less than four feet (4').
e. 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 an 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".
f. 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.
g. All fill material and compaction shall be designed, certified and inspected by an Illinois licensed professional engineer, as warranted by the site conditions.
h. The basement floor shall be at an elevation that is no more than five feet (5') below the BFE.
i. 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.
j. The drainage system shall be equipped with a positive means of preventing backflow.
k. All foundation elements shall be designed to withstand hydrostatic pressure in accordance with accepted engineering practices.
l. If the applicant is unable to meet all of the requirements set forth in the preceding subsections of this section, the building official 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 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 licensed professional engineer.
m. 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.
Elevation certificates will be required for all development within the 100-year floodplain that requires the issuance of a building permit by the city, or as directed by the director of public works and engineering.
C. Repair, Modification, Reconstruction: For repair of damaged homes, modification of existing homes, or reconstruction/replacement of existing homes, see subsections 14-1-9C1b and C2b of this chapter. (Ord. M-15-16, 6-6-2016)