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A2-S SHALLOW FLOODING STUDY PROCEDURES A, General Guidelines The general guidelines cited are applicable to all areas of shallow flooding, They are indicative of the general approach taken to the study of shallow flooding problems in order to fulfill the requirements of the NFIP, ( Small-scale topographic variations should be averaged across inundated areas in determining depths to keep the effort and results commensurate with the obtainable accuracy of shallow flooding study methods, Flood hazard zone designations should extend across the entire inundated area, without separate designation of X zones at the edges of AD or AH zones, Thus, X zones should be used only when the average depth across the entire inundated area is less than 1 foot, An AO zone should not be used at the edge of an AE zone where the depth is less than or equal to 3 feet. Shallow flooding is often characterized by highly unpredictable flow direction because of low relief or shifting channels and debris loads, Where such conditions exist, the entire area susceptible to this unpredictable flow should be delineated as an area of equal risk, Small-scale topographic relief that is not evident on existing topographic .mapping and that might lead to "islands" of one flood hazard zone within larger areas of another should be ignored, Individual property owners will be issued Letters of Map Amendment in this situation when necessary, Shallow flooding areas are designated as Zones AD or AH depending on the relative accuracy with which flood depths or elevations can be determined.. Ponding areas with a constant flood elevation are always delineated as Zone AH with a BFE. Areas of sheet runoff are usually delineated as Zone AD with average flooding depths above the ground surface indicated on the work map, However, where the slope of the water surface is extremely low and uniform BFEs can be established for large land areas, Zone AH with a BFE is preferred. Average depths and elevations should be rounded to the nearest whole foot. The 10-, 50-, or SOO-year flooding delineations, floodways, and profiles should not be determined in shallow flooding areas. If these items can be readily determined, shallow flooding procedures should not be used, Historical information, local citizen reports, existing physical features, and previous reports discovered during the bibliography search should all be assessed for information on possible flooding conditions. Where any information shows possible local flooding depths, or other hazards more severe than those determined by the study procedures in these Guidelines, that information and reference must be included in the FIS Report to fully alert the community to the potential hazard, A2-3