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floodplain to be protected from flooding have prevented more than $770 million in flood damage to buildings and their contents (FEMA 1997). Furthermore, NFIP participation has been a very positive force in encouraging communities to plan and regulate all development in the community, not just development in the floodplain. NFIP ensures that the costs of floodplain development (not to be confused with the costs of postdisaster assistance) are borne by the property owner and not by the taxpayer. The property owner assumes these costs in two ways-by paying the higher price of building components that are designed to protect the property from flood damage and by making payments on the annual flood insurance premium on the property. Since flood insurance rates for new construction are required by statute to be actuarial (i.e., based on risk), there is no taxpayer subsidy of this coverage. In other words, as a result of NFIP, property owners must make development decisions based on the true costs to build in the floodplain. Although primarily intended to reduce flood damages, NFIP regulatory requirements also have direct and indirect environmental benefits. Participating communities must review plans for subdivision and other proposals for floodplain development to ensure that the requirements of their floodplain management ordinance are met. While conducting this review, the community has the opportunity to address any environmental issues posed by the development. In terms of the direct environmental benefits, NFIP requires that the floodway-the portion of the floodplain that carries the fastest and deepest water-be free of any intrusions that would raise the water level above a specified point. As a result of such requirements, most flood ways provide wildlife habitat and buffer zones of vegetation that protect water quality. Often communities choose to acquire these areas (or designate them through zoning) for recreation and open space. In October 1990, FEMA introduced the Community Rating System (CRS) to provide a new incentive for activities that reduce flood losses and support the sale of flood insurance. (See Figure 1-2.) CRS recognizes NFIP-participating communities that have gone above and beyond the NFIP minimum requirements by providing a reduction in insurance premiums for all policy holders in the community. The community must demonstrate that it is implementing floodplain management and public information activities that exceed the minimum requirements of NFIP. As of May 1, 1997, 910 communities, representing 60 percent of the NFIP policy base, were participating in CRS. Defining and Mapping the Floodplain FEMA conducts hydrologic and hydraulic analyses and gathers historical data to determine flood risks in communities. The results are presented on Flood Insurance Rate Maps (FIRMs) and in an accompanying Flood Insurance Study text. The text also includes discussions of the flood hazards within the community. The maps and studies are then used to determine which 6 Figure 1-3. Elements of the 100-Year Floodplain i . . FLOOD! . I FRINGE! ! I k ~ IFLOODWAY i . BASHLOOD I . !. ELEVATION 1 I PLAN VIEW C.ROSS SECTION lands are subject to NFIP regulations and local floodplain management regulations. A FIRM shows the 100-year flood boundary. A "lOa-year flood," or base flood, is the flood that has a 1 percent or greater chance of being equaled or exceeded in any given year. The elevation reached by the lOa-year flood is called the base flood elevation (BFE). BFEs are generally defined in relation to height above mean sea level or average depths of flow above the ground surface and are the national standard for flood protection throughout the United States. (See Figure 1-3.) Different mapping methodologies are used depending on the type of floodplain (e.g., a "step backwater moder' is used to identify BFE in riverine areas, and surge or wave-height models are used in coastal areas). BFEs have been established for the purposes of floodplain management regulation and flood insurance ratings. Areas in a community that are within the lOO-year flood boundary are called Special Flood Hazard Areas (SFHAs). NFIP floodplain management regulations must be applied within the SFHA. The purchase of flood insurance is required as a condition for receiving federal financial assistance for any building within the SFHA. In addition to mapping lOa-year flood