Unified Development Ordinance, 25th Supplement, December 2022

CHAPTER 9. ​NATURAL RESOURCE PROTECTION | Article 9.3. ​Floodprone Area Regulations

is disputed by the applicant the outer limit of the flood hazard soil boundary shall be determined by the following: i. A NCLSS shall verify the presence and extent of the flood hazard soils on a property as depicted on the publishedWake County or Durham County Soil Survey map, whichever is applicable. a) 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. b) 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: a. 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 forWake County or DurhamCounty, 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

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: a. 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 b. 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. D. 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: a. When the extent of the flood hazard soil(s) depicted on the published Wake County or DurhamCounty Soil Survey, whichever is applicable, is not disputed by the applicant, the applicable soil data from the soil survey shall be utilized. b. When the extent of the flood hazard soil(s) depicted on the published Wake County or DurhamCounty Soil Survey, whichever is applicable,

Supp. No. 25

9 – 30 Pub l i s hed De c embe r 2022

Pa r t 10 : Un i f i ed Deve l opmen t Or d i nanc e C i t y o f Ra l e i gh , No r t h Ca r o l i na