(a) Standards for streams without established base flood elevations and/or floodways. Located within the areas of special flood hazard established in § 8-24, are small streams where no base flood data has been provided or where no floodways have been identified (Flood Zone A). The following provisions apply within such areas:
(1) No encroachments, including fill, new construction, substantial improvements or new development shall be permitted within 100 feet of the stream bank unless certification with supporting technical data by a S.C. registered professional engineer is provided demonstrating that such encroachments shall not result in any increase in flood levels during the occurrence of the base flood discharge.
(2) If § 8-39(a)(1) is satisfied and base flood elevation data is available from other sources, all new construction and substantial improvements within such areas shall comply with all applicable flood hazard ordinance provisions, and shall be elevated or floodproofed to the elevations established in accordance with § 8-30(c). Data from preliminary, draft and final flood insurance studies constitutes best available data. Refer to FEMA Floodplain Management Technical Bulletin 1-98 Use of Flood Insurance Study (FIS) Data as Available Data. If an appeal is pending on the study in accordance with 44 CFR Ch. 1, Part 67.5 and 67.6, the data does not have to be used.
(3) When base flood elevation data is not available from a federal, state, or other source, one of the following methods may be used to determine a BFE, subject to approval by the local administrator. For further information regarding the methods for determining BFEs listed below refer to FEMA's manual Managing Floodplain Development in Approximate Zone A Areas. See §§ 8-30(c) and 8-40(c) for specific flood study requirements.
a. Contour interpolation.
1. Superimpose approximate Zone A boundaries onto a topographic map and estimate a preliminary BFE; and
2. Add ½ of the contour interval of the topographic map to determine the final BFE.
b. Data extrapolation. A BFE can be determined if a site is located within 500 feet upstream of a stream reach for which a 100-year profile has been computed by detailed methods, and the floodplain and channel bottom slope characteristics are relatively similar to the downstream reaches. No hydraulic structures shall be present.
c. Hydrologic and hydraulic calculations. Perform hydrologic and hydraulic calculations to determine BFEs using FEMA approved methods and software.
(4) In all areas of special flood hazard where base flood elevation data are not available, the applicant shall provide a hydrologic and hydraulic engineering analysis that generates base flood elevations for all subdivision proposals and other proposed developments containing at least 30 lots or 3 acres, whichever is less.
(b) Standards for streams with established base flood elevations, but without floodways. Along rivers and streams where base flood elevation (BFE) data is provided but no floodway is identified for Special Flood Hazard Area on the FIRM or in the FIS, the following provisions apply within such areas:
(1) No encroachments including fill, new construction, substantial improvements, or other development shall be permitted unless a flood study is provided with supporting technical data by a SC registered professional engineer identifying the floodway boundary. Refer to § 8-37 for floodway restrictions.
(Ord. 4085, § 2, passed 2-20-2007; Ord. 4631, § 2, passed 6-17-2014; Ord. 5031, passed 11-6-2018; Ord. 5276, passed 4-6-2021)