In all areas of special flood hazard within the Regent Park Floodplain Overlay District where base flood elevation data has been provided pursuant to § 151.04(B) or as outlined in the duties and responsibilities of the local administrator in § 151.24, the requirements of § 151.36 shall apply in addition to the following higher specific standards:
(A) Freeboard.
(1) Freeboard requirements are based on FEMA's Federal Flood Risk Management Standard (FFRMS) Freeboard Value Approach (FVA). This approach establishes a minimum vertical elevation requirement above the base flood elevation for all actions involving development, structure elevation, dry floodproofing, and mitigation reconstruction projects in all areas of special flood hazard. Minimum freeboard shall be provided as either:
(a) Two feet of freeboard shall be added to the base flood elevation; or,
(b) For critical development or critical facilities, a freeboard of three feet shall be added to the base flood elevation.
(2) Freeboard, meeting requirements of § 151.44 (A)(l), shall result in and include a horizontal extension of the base floodplain boundary limits to the point where the ground contour elevation intersects with the extended freeboard elevation as illustrated in Figure 2. All development within the extended horizontal flood boundary limits based on freeboard shall be subject to the freeboard requirements of this chapter.
(B) Compensatory storage.
(1) Compensatory storage, as illustrated in Figure 3, may be provided to offset the loss of flood storage resulting from when fill is used for development or when elevating a structure within areas of special flood hazard, as an option allowed under § 151.44(H).
(2) Compensatory storage should be located onsite and adjacent to or opposite the areas of new floodplain fill. If such placement location is not feasible, hydraulic analysis shall be provided to demonstrate that the proposed location is a hydraulically equivalent site and that the proposed storage volume is sufficient to not result in an adverse impact to adjacent properties. Compensatory storage located on a hydraulically equivalent site provides additional floodable area so that flood elevations, peaks, stages, and velocities of floodwater are not increased and therefore will not adversely impact adjacent properties.
(3) Compensatory storage shall be provided at a minimum ratio of 1.15 cubic yards of excavation for every cubic yard of fill (1.15:1).
(4) The floodplain storage volume lost below the existing 10-year frequency flood elevation must be replaced below the proposed 10-year frequency flood elevation. The floodplain storage volume lost above the existing 10-year frequency flood elevation must be replaced above the proposed 10-year frequency elevation.
(5) Compensatory storage areas shall be designed to drain freely and openly to the channel and not retain water, nor create aquatic life stranding areas.
(6) No area below the elevation of normal channel stage, the waterline of a pond, or other body of water including seasonally high groundwater, can be credited as a compensating excavation volume. Excavation above the base flood elevation is also not allowed for credit as a compensating volume. Additional test pits should be excavated to demonstrate that the proposed compensatory storage will not intercept the seasonal high groundwater table.
(7) A recorded deed and plat restriction are required to prohibit any modification to the compensatory storage areas.
(G) Map maintenance activities. All provisions of § 151.36(I) shall apply with the following exceptions:
(1) The provisions found in § 151.36(I)(1)(a)2. shall also include development that increases the base flood elevation in any amount through placement of a structure or fill; and,
(2) Where FEMA has provided base flood elevation data, a conditional letter of map revision (CLOMR) shall be required for any proposed development that increases or decreases the base flood elevation where measured at any adjacent property boundary, or otherwise alters the floodplain boundary.
(H) Fill. All provisions of § 151.36(M) shall apply with the following exceptions. The placement or stockpiling of fill, whether permanent or temporary, including loose or compacted soils, gravel or rock, within areas of special flood hazard is discouraged due to reduction in flood storage capacity, adversely altered natural drainage patterns, potential for increased flood elevation, stage and velocity increases, erosion and scour, and diminishment of wildlife habitat. The use of fill shall be limited only to the elevation of individual structures and buildings, utilities, infrastructure, and public road crossings. Other methods of elevating structures should be considered first. The following provisions shall apply to all fill placed in the areas of special flood hazard:
(1) Certification with supporting technical data, prepared by a registered professional engineer, licensed in the State of South Carolina, is provided to demonstrate that the fill will not result in adverse impact to other properties upstream, downstream, and adjacent to the development as measured at the property boundary by any increase in base flood elevation, floodway elevation, flood peaks, flood stage, floodwater velocity, scour and erosion/sedimentation, and/or decrease in floodway width or flood storage. The Floodplain Administrator will evaluate each fill encroachment/development and determine which of the following options will be required.
(a) Compensatory storage shall be provided to compensate for all storage lost or displaced in a regulatory floodplain meeting the requirements of § 151.44(B); and/or,
(b) A detailed hydrologic and hydraulic analyses performed in accordance with standard engineering practice that meets or exceeds FEMA's guidelines and standards for flood risk analysis and mapping. The analyses may incorporate compensatory storage at hydraulically equivalent sites within the proposed project area as part of the required demonstration.
(2) If fill results in an adverse impact which results in any increase to the base flood elevation at any adjacent property boundary within a FEMA Special Flood Hazard Area, the applicant shall:
(a) Submit to FEMA, through York County, a CLOMR or other appropriate map change application. A floodplain development permit will not be issued until FEMA has issued the CLOMR. Within 60 days of completion of construction activities, the applicant shall apply to FEMA, through York County, for a letter of map revision (LOMR). The applicant is responsible for all technical submissions and fees required to obtain all official letters from FEMA.
(b) Obtain, and provide copy of, a written and notarized agreement from all affected property owners thereby agreeing to allow their property to be adversely impacted by flood waters resulting from the development.
(3) Fill shall be designed and constructed meeting the minimum requirements of ASCE 24-14 Flood Resistant Design and Construction to be stable under conditions of flooding, including rapid rise and drawdown, prolonged inundation, and flood-related scour and erosion.
(I) Roads, bridges, and culverts.
(1) New roadways constructed within or adjacent to areas of special flood hazard shall be constructed so that the centerline elevation of the finished road surface is no less than two feet higher than the base flood elevation.
(3) Replacement of existing bridges and culverts shall meet the requirements of § 151.36(G), if applicable.
(Ord. 2924, passed 6-3-24)