Sec. 9.3.4. Rules for Interpretation of SFHA Boundaries

  1. Regulatory Flood Protection Elevation
    The Regulatory Flood Protection Elevation (RFPE), fully defined in Chapter 12, is an elevation at which structures and uses within SFHAs are required to be elevated or floodproofed. If there is a conflict between the RFPE definition in Chapter 12 and the provisions of this Article, the definition in Chapter 12 shall control.
  2. FEMA Designated SFHA
    1. The boundaries of FEMA SFHAs shown on the FIRMs are initially determined from information obtained from the U.S. Army Corps of Engineers and presented in the FIRMs and FIS by FEMA.
    2. These boundaries are based on the engineering data that most accurately reflects actual field and hydrologic conditions. Field and hydraulic conditions shall prevail over mapped boundaries shown on FIS profiles.
    3. In areas of official cross-sections, FEMA SFHAs boundaries shall be determined by scaling distances on the FIRMs. Where interpretation of the lateral location of scaled distances is needed to determine the actual field location of these boundaries, the Engineering Services Director and/or his or her designee is directed to make the necessary interpretation of FIRMs applying the following:
      1. The RFPE shall be the controlling factor in determining the location of the outer limits of the floodway fringe or future conditions flood hazard area boundaries; and
      2. Interpretations of floodway boundaries on FIRMs shall be based on the current procedures for interpreting floodways in accordance with FEMA guidelines.
    4. The RFPE for FEMA designated SFHAs is the BFE plus two (2) vertical feet.
    5. When BFE data or floodway data has not been established by FEMA in accordance with Sec. 9.3.3.B.1.b., the Floodplain Administrator and/or his or her designee must obtain, review, and reasonably utilize any BFE data and floodway data available from a federal, state, or other source, including data developed pursuant to Sec. 9.3.6.C. in order to administer the provisions of this Article.
  3. SFHA Based on Drainage Basin Study Maps
    1. Upon approval by the Engineering Services Director and/or his or her designee, drainage basin study maps may supersede flood hazard soil maps or North Carolina licensed soil scientist (NCLSS) determinations. SFHA and flood elevation data shall be obtained from the most current drainage basin study maps or flood studies.
    2. The boundaries of SFHAs shown on drainage basin study maps are determined from information obtained or produced by the City as part of watershed master planning process.
    3. These boundaries are based on the engineering data that most accurately reflects actual field and hydrologic conditions. Field and hydraulic conditions shall prevail over mapped boundaries shown on drainage basin study maps.
    4. In areas of official cross-sections, drainage basin study map SFHA boundaries shall be determined by scaling distances between official cross sections. Where interpretation of the lateral location of scaled distances is needed to determine the actual field location of these boundaries, the Engineering Services Director and/or his or her designee is directed to make the necessary interpretation of drainage basin study maps applying the following:
      1. The RFPE shall be the controlling factor in determining the location of the outer limits of the floodway fringe or future conditions flood hazard area boundaries; and
      2. Interpretations of floodway boundaries on drainage basin study maps shall be based on the current procedures for interpreting floodways in accordance with FEMA guidelines.
    5. The RFPE for drainage basin study map designated SFHAs is the BFE plus two (2) vertical feet.
  4. SFHA Based on Flood Hazard Soils
    1. The outer limits of flood hazard soils may be specifically described by metes and bounds or other means from detailed surveys of a property on which they lie.
    2. When flood hazard soils are present on a property and no encroachment is proposed within flood hazard soils, the extent of the flood hazard soils can be determined one of two ways:
      1. When the extent of the flood hazard soil(s) depicted on the published Wake County or Durham County Soil Survey, whichever is applicable, is not disputed by the applicant, the applicable soil data from the soil survey shall be utilized.
      2. When the extent of the flood hazard soil(s) depicted on the published Wake County or Durham County Soil Survey, whichever is applicable, is disputed by the applicant the outer limit of the flood hazard soil boundary shall be determined by the following:
        1. A NCLSS shall verify the presence and extent of the flood hazard soils on a property as depicted on the published Wake County or Durham County Soil Survey map, whichever is applicable.
          1. When flood hazard soils are present on the property the NCLSS must identify the extent of the flood hazard soils on the property by sealing a statement on a survey (completed by a registered land surveyor licensed in the State of North Carolina) of the property which shall include the RFPE, as further defined and outlined in Chapter 12, and one of the following criteria as applicable:
            1. When the watercourse associated with the flood hazard soil drains one (1) square mile or more, the RFPE shall be the outermost boundary elevation of the flood hazard soils plus five (5) vertical feet; or
            2. When the watercourse associated with the flood hazard soil drains less than one (1) square mile, the RFPE shall be the outermost boundary elevation of the flood hazard soils plus two (2) vertical feet.
          2. When it is determined by a NCLSS that flood hazard soils are not present on the property a report sealed by a NCLSS must be provided to the Floodplain Administrator and/or his or her designee with appropriate supporting evidence including, but not limited to, soil boring locations and soil profiles.
    3. When flood hazard soils are present on a property and an encroachment, including fill, is proposed within flood hazard soils the following shall apply:
      1. The floodway and floodway fringe boundaries shall be identified based upon a flood study provided by the property owner to the Floodplain Administrator and/or his or her designee which consists of an analysis and hydraulic routing methods used by the U.S. Army Corps of Engineers to establish FIRMs. These methods are contained in the FIS for Wake County or Durham County, whichever is applicable, as published by FEMA. Approved interpretations of flood hazard soils boundaries may be described by bearings and distances and drawn with elevations in mean sea level datum given for each cross-section used in the routing computations.
      2. If the property owner chooses not to complete a flood study the entire flood hazard soil area on the property as depicted on the Wake County or Durham County Soil Survey, whichever is applicable, shall be considered floodway and the provisions of Sec. 9.3.7.A. shall apply.
  5. SFHA Boundary Interpretation Requests
    1.  If uncertainty exists with respect to SFHA boundaries, the property owner shall submit a written interpretation request to the Floodplain Administrator and/or his or her designee. The Engineering Services Director and/or his or her designee is authorized to interpret SFHA boundaries and shall do so pursuant to the methods for delineating SFHA boundaries set forth in this Article.
    2. Any appeal of the Engineering Services Director’s and/or his or her designee’s interpretation shall follow the procedures prescribed by law for appeals of administrative decisions, as set forth in Sec.10.2.11.
    3. All final interpretations of SFHA boundaries shall be described on a map(s) or plat(s), which shall then be filed with the Clerk of the Superior Court and with the Register of Deeds of Wake County or Durham County, whichever is applicable. The map(s) or plat(s) shall show the locations of all cross-sections, the elevation at the boundary of the floodway fringe areas, future conditions flood hazard area and flood storage area at the cross-section, the location of a benchmark used for vertical control, its elevation in reference to mean sea level datum, all SFHA boundaries and the source of the SFHA. The map(s) or plat(s) shall also bear the name, title, and professional seal of the person who supplied the survey and the calculation(s) as well as the date the interpretation was finalized, whether by the Engineering Services Director’s and/or his or her designee’s interpretation or appeal thereof.