Sec. 9.3.3. Special Flood Hazard Areas

  1. Types of Special Flood Hazard Areas
    There are four (4) primary SFHAs within the City.
    1. FEMA designated SFHA
      If FEMA designated SFHA boundaries overlap with the boundaries of another SFHA, FEMA designated SFHA boundary interpretations and standards shall prevail.
    2. Drainage Basin Study Maps
      A drainage basin study map shall supercede the boundaries of flood hazard soils.
    3. Flood Study Maps
      A site-specific flood study map shall supercede the boundaries of flood hazard soils.
    4. Flood Hazard Soils
       
  2. Establishing Special Flood Hazard Areas
    1. FEMA Designated SFHA
      1. FEMA designated SFHAs are those identified under the Cooperating Technical State (CTS) agreement between the State of North Carolina and FEMA in its flood insurance study (FIS) and its accompanying FIRM for Wake County or Durham County, whichever is applicable.
      2. The most recent FEMA SFHA maps and FIRMs officially adopted by the State of North Carolina and/or FEMA, with accompanying supporting data, including Letters of Map Amendment or Revision, are adopted by reference and declared to be a part of the UDO. Copies of the effective versions of these maps shall be maintained for public inspection as provided in N.C. Gen. Stat. § 160D-105.
      3. FEMA SFHAs are areas that have the potential to be inundated with flood waters during the 100-year storm event or the 1% annual chance. These SFHAs include contributing drainage areas of at least 1 square mile (640 acres).
      4. FEMA designated SFHAs are divided into three (3) primary areas:
        1. Floodway areas;
        2. Floodway fringe areas; and
        3. Future conditions flood hazard areas.
    2. SFHA Based on Drainage Basin Study Maps
      1. SFHAs also include City prepared drainage basin studies. These studies are defined through standard engineering analysis by the City’s Engineering Services Department, but which have not been incorporated in the FIRM. This includes detailed flood information generated as a requirement of Sec. 9.3.3.B.1.a.
      2. Drainage basin studies are completed by the City (or their designee) and accepted by the City to produce maps that supplement the FIRMs. These drainage basin study maps use the same FEMA SFHA criteria but for contributing drainage areas of less than 1 square mile (640 acres).
      3. The most recent drainage basin study maps approved by the City’s Engineering Services Department with accompanying supporting data are adopted by reference and declared to be part of the UDO.
      4. Drainage basin study maps designated SFHAs are divided into two (2) primary areas:
        1. Floodway areas; and
        2. Floodway fringe areas.
    3. SFHA Based on Flood Study Maps
      1. SFHAs also include flood studies prepared for specific sites. These studies are defined through standard engineering analysis but have not been incorporated in the FIRM.
      2. Flood studies are completed by applicants and must be reviewed and accepted by the City.
      3. Comprehensive Flood Studies are required for sites with stream(s) draining 100 acres or more. Comprehensive Flood Study maps’ designated SFHAs are divided into two (2) primary areas:
        1. Floodway areas; and
        2. Floodway fringe areas.
      4. Comprehensive Flood Studies or Simple Flood Studies are required for sites draining equal to or greater than 25 acres and less than 100 acres. Simple flood study maps only contain one category of SFHA; the entire 100-year flood boundary shall be considered floodway and the provisions of Sec. 9.3.7.A. shall apply.
    4. SFHA Based on Flood Hazard Soils
      1. Flood hazard soils are illustrated on maps published in the Wake County or Durham County, North Carolina Soil Survey, whichever is applicable, prepared by the U.S. Soil Conservation Service and the North Carolina Agricultural Experiment Station. Flood hazard soil types are listed in the definition of flood hazard soils in Chapter 12, Definitions.
      2. Maps depicting flood hazard soils with all explanatory matter attached to them are adopted by reference and declared to be part of the UDO.
      3. SFHA for flood hazard soils shall only apply when the flood hazard soils drain greater than or equal to 5 acres of area.