No development in the flood fringe shall create a threat to public health and safety.
(A) Submission of data; LOMR. 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.
(B) Compensatory storage.
(1) 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.
(2) The excavation volume shall be at least equal to one times the volume of storage lost due to the fill or structure.
(3) In the case of streams and watercourses, such excavation shall be made opposite or adjacent to the areas so filled or occupied.
(4) All floodplain storage lost below the existing ten-year flood elevation shall be replaced below the proposed ten-year flood elevation. All floodplain storage lost above the existing ten-year flood elevation shall be replaced above the proposed ten-year flood elevation.
(5) 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 city to construct the lowest floor of a residential building below the BFE in the flood fringe. The city shall not issue such a permit unless the applicant has complied with all the criteria set forth in the following divisions.
(1) Compensatory storage shall be provided per division (B) above.
(2) The elevation of the lowest opening in the basement wall (i.e., window wells, access ways) shall be at or above the flood protection elevation (FPE).
(3) The lowest adjacent grade to the foundation shall be at or above the FPE, for a minimum distance of ten feet beyond the outside face of the structure. However, if site conditions are such that this requirement cannot be met, the city may waive the ten-foot minimum setback if a state licensed professional engineer certify 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 city for review. The city 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) The grade around the perimeter of the structure, measured at a distance of 20 feet from the structure, shall be above the BFE. However, if site conditions are such that this requirement cannot be obtained, the city may waive the 20-foot minimum setback distance if a state licensed professional engineer certifies that an alternative method to protect the building from damages due to hydrostatic pressures have 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 for review. In no case shall the setback distance be less than four feet.
(5) The ground around the building shall be compacted fill that meets all requirements of this division (C) and is at least five feet thick under the basement floor slab. Nothing in this division (C)(5) 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 a state licensed professional engineer, as warranted by the site conditions.
(8) The basement floor shall be at an elevation that is no more than five below the BFE.
(9) There shall be a granular drainage layer beneath the floor slab, and minimum of one-quarter horsepower emergency backup sump pump with a backup power supply shall be provided to remove seepage flow. The pump shall be rated at four 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.
(12) If the applicant is unable to meet all of the requirements set forth in divisions (A) and (B) above, the city 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, the 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 a state licensed professional engineer.
(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 18 inches, 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.
(Prior Code, § 157.047) (Ord. 08-023, passed 7-22-2008)