47.5 MB - The Whole Building Design Guide

m FIRMs and Flood Insurance Studies(FISs) are prepared to meet therequirements of the NFIP. For the mostpart, floodplains along smaller streamsand drainage areas (less than 1 squaremile) are not shown.m Especially for older maps, the topographyused to delineate the flood boundary mayhave had contour intervals of 5, 10, oreven 20 feet, which significantly affectsthe precision with which the boundaryis determined. The actual elevation ofthe ground relative to the flood elevationis critical, as opposed to whether an areais shown as being in or out of the mappedflood hazard area.In communities along the Gulf and Atlanticcoasts, facility owners, planners, anddesigners should check with emergencymanagement offices for maps that estimatestorm surge flooding from hurricanes.Local planning or engineering offices mayhave post-disaster advisory flood mapsand documentation of past storm surgeevents. The FIRMs and regulatory designflood elevations (DFEs) do not reflect lowprobability/high magnitude floodingthat may result from a hurricane makinglandfall at a specific location.m Maps are based on the data available at the time they wereprepared, and therefore do not account for subsequentupland development (new development that increases rainfallrunofftends to increase flooding).m The scale of the maps may impedeprecise determinations (many older mapsare 1 inch = 2,000 feet).m Flooding characteristics may have beenaltered by development, sometimes byupland development that has increasedrunoff, and other times by localmodifications that have altered the shapeof the land surface of the floodplain(such as fills or levees).m Local conditions are not reflected,especially conditions that changeregularly, such as stream bank erosionand shoreline erosion.m Areas exposed to very low probabilityflooding are not shown, such as floodingDesigners and property owners in coastalregions should be aware that current FIRMsmay not fully account for natural andmanmade changes to beaches, wetlands,and other coastal environments (e.g., theerosion of protective dunes during thebase flood). Since the original FIRMswere published in the early 1980s, FEMAhas made significant improvements inthe models and methods used to identifycoastal flood hazards. Before any actionis considered, the Flood Insurance Studyreport should be checked to verify that allpertinent hazards have been addressed.A coastal engineer or similar professionalshould be consulted if there are anyquestions concerning the coastal flood data.MAKING CRITICAL FACILITIES SAFE FROM Flooding2-11