event, that is, “accredited.” Certification is the technical evidence provided by a levee owner to FEMA demonstrating that the levee system meets the requirements to reduce risk from at least the one percent annual chance flood.7

Recognizing the need for improving the NFIP’s treatment of levees, FEMA officials approached the National Research Council’s (NRC) Water Science and Technology Board and requested this study. The NRC responded by forming the ad hoc Committee on Levee and the National Flood Insurance Program: Improving Policies and Practices, charged to examine current FEMA treatment of levees within the NFIP and provide advice on how those levee-related policies and activities could be improved. The study addressed four broad areas—risk analysis, flood insurance, risk reduction, and risk communication—regarding how levees are considered in the NFIP. Specific issues within these areas include current risk analysis and mapping procedures behind accredited and nonaccredited levees, flood insurance pricing and the MPR, mitigation options to reduce risk for communities with levees, flood risk communication efforts, and the concept of shared responsibility. For the full statement of task, see Chapter 1, Box 1-4. The report’s principal conclusions and recommendations are highlighted in bold in this Summary.


After the establishment of the NFIP, efforts to identify the nation’s flood hazard began. Because many flood protection works, mostly levees, had, in the past, successfully passed what had been considered a one percent annual chance flood, both local communities and contractors raised the issue of excluding areas protected by a one percent annual chance or greater structure from the SFHA. As a result, areas behind levees were not labeled on early flood maps as being within the SFHA where levees had provided or were thought to have provided protection from the one percent annual chance flood or had been constructed by U.S. Army Corps of Engineers (USACE) to withstand the one percent or higher annual chance flood.

As the program evolved, levees were required to be certified and accredited in order for the areas behind them to be mapped out of the SFHA. When a levee in a community provides less than 1 percent protection, it is not shown on a FIRM as providing protection and the flood risk is assessed as if the levee does not exist. Not recognizing levees that are not accredited on FIRMs is referred to in this report as a “without levee” analysis. An all-or-nothing approach, this either gives communities credit for a one percent annual chance levee (through exclusion from the SFHA and exemption from the MPR, etc.) or does not; that is, a levee that is not accredited is not recognized on the FIRM.

In 2003, with the support of communities and organizations to improve the quality of flood mapping, FEMA moved forward with a program to modernize maps by converting to a digital format and, when possible, providing a new engineering analysis. During “Map Mod,” FEMA officials became concerned that the levees encountered in this process might not meet the one percent annual chance standard despite being labeled as such. Affected communities, faced with the potential movement of the previously exempt areas into the floodplain and the mandatory requirement to purchase flood insurance at rates that might be the same as areas without protection, argued that some credit should be given to the presence of the deficient levees (i.e., some protection less than the one percent annual chance flood). Members of the Congress urged FEMA to discontinue use of the without-levee analysis in updating FIRMs. In agreement, FEMA is currently developing a new approach, the Levee Analysis and Mapping Procedure (LAMP), to replace the without-levee approach.


Flood risk management represents efforts to continuously carry out analyses, assessments, and related mitigation implementation activities to reduce flood risk. It focuses on assessment of flood hazards, the consequences resulting from flooding, the significance of risks identified, and the development of risk management strategies to deal with flood risk, which is gaining momentum across the global floodplain management community. Effective flood risk management requires use of the best available science in its execution. A flood risk analysis is that


7 Certification may be accomplished by a registered professional engineer or a federal agency with levee responsibilities.

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