Sec. 9.3.8. Streets Crossing Watercourses

  1. All streets and driveways or any bridge or culvert associated with any street or driveway, crossing a watercourse, shall be designed and constructed in accordance with City standards.
  2. Street crossings of natural resource buffer yards shall be as close to a perpendicular angle as possible.
  3. Any street, driveway, bridge or culvert associated with any street or driveway, which is located in a SFHA draining less than one (1) square mile and not shown on a FEMA map or located outside a FEMA SFHA, may either increase the flow levels and area of flooding of the 10 through 100 year frequency floods or redirect floodwaters if the following is met:
    1. Copies of recorded drainage easements for flood storage shown on recorded plats adequate to contain the increased flow levels are first submitted to the City; and
    2. Land areas contained within the drainage easement boundaries shall be delineated as flood storage areas.
  4. The following additional standards shall apply to all streets and driveways crossing watercourses draining ten (10) acres or more and which are located inside SFHAs.
    1.  Any street, driveway, bridge or culvert associated with any street or driveway shall pass the 100-year flood crest, under free flow conditions that will not result in any increase in the elevation of the 10- through 100-year floods above those specified in the FIS for Wake County or Durham County, whichever is applicable, as published by FEMA  unless a map revision is completed for the FEMA SFHA. 
    2. If the drainage areas exceed one (1) square mile, the maximum rise allowed for the 100- year flood shall not exceed a total of 0ne (1) foot above the BFE established for flood hazard soil areas or those elevations specified either in the drainage basin study maps or in the FIS for Wake County or Durham County, whichever is applicable, as published by FEMA.  If flood levels are increased, a map revision is needed for FEMA SFHA and drainage easements for flood storage are required for non-FEMA SFHA. 
    3. BFEs for return periods of less than 100-years may be increased to exceed one (1) foot, provided that the portion of the flood increase which is greater than one (1) foot is either limited to the site boundaries of the property of the owner requesting this increase or restricted to flood storage areas shown on a recorded plat.