Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps portray the height and extent to which flooding is expected to occur, and they form the basis for setting flood insurance premiums and regulating development in the floodplain. As such, they are an important tool for individuals, businesses, communities, and government agencies to understand and deal with flood hazard and flood risk. Improving map accuracy is therefore not an academic question-better maps help everyone. Making and maintaining an accurate flood map is neither simple nor inexpensive. Even after an investment of more than $1 billion to take flood maps into the digital world, only 21 percent of the population has maps that meet or exceed national flood hazard data quality thresholds. Even when floodplains are mapped with high accuracy, land development and natural changes to the landscape or hydrologic systems create the need for continuous map maintenance and updates. Mapping the Zone examines the factors that affect flood map accuracy, assesses the benefits and costs of more accurate flood maps, and recommends ways to improve flood mapping, communication, and management of flood-related data.
Floodplain maps serve as the basis for determining whether homes or buildings require flood insurance under the National Flood Insurance Program run by the Federal Emergency Management Agency (FEMA). Approximately $650 billion in insured assets are now covered under the program. FEMA is modernizing floodplain maps to better serve the program. However, concerns have been raised as to the adequacy of the base map information available to support floodplain map modernization. Elevation Data for Floodplain Mapping shows that there is sufficient two-dimensional base map imagery to meet FEMA's flood map modernization goals, but that the three-dimensional base elevation data that are needed to determine whether a building should have flood insurance are not adequate. This book makes recommendations for a new national digital elevation data collection program to redress the inadequacy. Policy makers; property insurance professionals; federal, local, and state governments; and others concerned with natural disaster prevention and preparedness will find this book of interest.
Floods take a heavy toll on society, costing lives, damaging buildings and property, disrupting livelihoods, and sometimes necessitating federal disaster relief, which has risen to record levels in recent years. The National Flood Insurance Program (NFIP) was created in 1968 to reduce the flood risk to individuals and their reliance on federal disaster relief by making federal flood insurance available to residents and businesses if their community adopted floodplain management ordinances and minimum standards for new construction in flood prone areas. Insurance rates for structures built after a flood plain map was adopted by the community were intended to reflect the actual risk of flooding, taking into account the likelihood of inundation, the elevation of the structure, and the relationship of inundation to damage to the structure. Today, rates are subsidized for one-fifth of the NFIP's 5.5 million policies. Most of these structures are negatively elevated, that is, the elevation of the lowest floor is lower than the NFIP construction standard. Compared to structures built above the base flood elevation, negatively elevated structures are more likely to incur a loss because they are inundated more frequently, and the depths and durations of inundation are greater. Tying Flood Insurance to Flood Risk for Low-Lying Structures in the Floodplain studies the pricing of negatively elevated structures in the NFIP. This report review current NFIP methods for calculating risk-based premiums for these structures, including risk analysis, flood maps, and engineering data. The report then evaluates alternative approaches for calculating risk-based premiums and discusses engineering hydrologic and property assessment data needs to implement full risk-based premiums. The findings and conclusions of this report will help to improve the accuracy and precision of loss estimates for negatively elevated structures, which in turn will increase the credibility, fairness, and transparency of premiums for policyholders.
The Federal Emergency Management Agency's (FEMA) Federal Insurance and Mitigation Administration (FIMA) manages the National Flood Insurance Program (NFIP), which is a cornerstone in the U.S. strategy to assist communities to prepare for, mitigate against, and recover from flood disasters. The NFIP was established by Congress with passage of the National Flood Insurance Act in 1968, to help reduce future flood damages through NFIP community floodplain regulation that would control development in flood hazard areas, provide insurance for a premium to property owners, and reduce federal expenditures for disaster assistance. The flood insurance is available only to owners of insurable property located in communities that participate in the NFIP. Currently, the program has 5,555,915 million policies in 21,881 communities3 across the United States. The NFIP defines the one percent annual chance flood (100-year or base flood) floodplain as a Special Flood Hazard Area (SFHA). The SFHA is delineated on FEMA's Flood Insurance Rate Maps (FIRM's) using topographic, meteorologic, hydrologic, and hydraulic information. Property owners with a federally back mortgage within the SFHAs are required to purchase and retain flood insurance, called the mandatory flood insurance purchase requirement (MPR). Levees and floodwalls, hereafter referred to as levees, have been part of flood management in the United States since the late 1700's because they are relatively easy to build and a reasonable infrastructure investment. A levee is a man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to provide protection from temporary flooding. A levee system is a flood protection system which consists of a levee, or levees, and associated structures, such as closure and drainage devices, which are constructed and operated in accordance with sound engineering practices. 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 (WSTB) 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-elated 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 non-accredited levees, flood insurance pricing and the mandatory flood insurance purchase requirement, mitigation options to reduce risk for communities with levees, flood risk communication efforts, and the concept of shared responsibility. The principal conclusions and recommendations are highlighted in this report.
River and coastal floods are among the nation's most costly natural disasters. One component in the nation's approach to managing flood risk is availability of flood insurance policies, which are offered on an individual basis primarily through the National Flood Insurance Program (NFIP). Established in 1968, the NFIP is overseen by the Federal Emergency Management Agency (FEMA) and there are about 5.4 million individual policies in the NFIP. The program has experienced a mixture of successes and persistent challenges. Successes include a large number of policy holders, the insurance of approximately $1.3 trillion of property, and the fact that the large majority of policy holders - 80% - pay rates that are risk based. NFIP challenges include large program debt, relatively low rates of purchase in many flood-prone areas, a host of issues regarding affordability of premiums, ensuring that premiums collected cover payouts and administrative fees, and a large number of properties that experience severe repetitive flood losses. At the request of FEMA, A Community-Based Flood Insurance Option identifies a range of key issues and questions that would merit consideration and further analysis as part of a community-based flood insurance program. As the report describes, the community-based option certainly offers potential benefits, such as the prospect of providing coverage for all (or nearly all) at-risk residents and properties in flood-prone communities. At the same time, many current challenges facing the NFIP may not necessarily be resolved by a community-based approach. This report discusses these and other prominent issues to be considered and further assessed.
Reducing flood damage is a complex task that requires multidisciplinary understanding of the earth sciences and civil engineering. In addressing this task the U.S. Army Corps of Engineers employs its expertise in hydrology, hydraulics, and geotechnical and structural engineering. Dams, levees, and other river-training works must be sized to local conditions; geotechnical theories and applications help ensure that structures will safely withstand potential hydraulic and seismic forces; and economic considerations must be balanced to ensure that reductions in flood damages are proportionate with project costs and associated impacts on social, economic, and environmental values. A new National Research Council report, Risk Analysis and Uncertainty in Flood Damage Reduction Studies, reviews the Corps of Engineers' risk-based techniques in its flood damage reduction studies and makes recommendations for improving these techniques. Areas in which the Corps has made good progress are noted, and several steps that could improve the Corps' risk-based techniques in engineering and economics applications for flood damage reduction are identified. The report also includes recommendations for improving the federal levee certification program, for broadening the scope of flood damage reduction planning, and for improving communication of risk-based concepts.
Flooding is the natural hazard with the greatest economic and social impact in the United States, and these impacts are becoming more severe over time. Catastrophic flooding from recent hurricanes, including Superstorm Sandy in New York (2012) and Hurricane Harvey in Houston (2017), caused billions of dollars in property damage, adversely affected millions of people, and damaged the economic well-being of major metropolitan areas. Flooding takes a heavy toll even in years without a named storm or event. Major freshwater flood events from 2004 to 2014 cost an average of $9 billion in direct damage and 71 lives annually. These figures do not include the cumulative costs of frequent, small floods, which can be similar to those of infrequent extreme floods. Framing the Challenge of Urban Flooding in the United States contributes to existing knowledge by examining real-world examples in specific metropolitan areas. This report identifies commonalities and variances among the case study metropolitan areas in terms of causes, adverse impacts, unexpected problems in recovery, or effective mitigation strategies, as well as key themes of urban flooding. It also relates, as appropriate, causes and actions of urban flooding to existing federal resources or policies.
When Congress authorized the National Flood Insurance Program (NFIP) in 1968, it intended for the program to encourage community initiatives in flood risk management, charge insurance premiums consistent with actuarial pricing principles, and encourage the purchase of flood insurance by owners of flood prone properties, in part, by offering affordable premiums. The NFIP has been reauthorized many times since 1968, most recently with the Biggert-Waters Flood Insurance Reform Act of 2012 (BW 2012). In this most recent reauthorization, Congress placed a particular emphasis on setting flood insurance premiums following actuarial pricing principles, which was motivated by a desire to ensure future revenues were adequate to pay claims and administrative expenses. BW 2012 was designed to move the NFIP towards risk-based premiums for all flood insurance policies. The result was to be increased premiums for some policyholders that had been paying less than NFIP risk-based premiums and to possibly increase premiums for all policyholders. Recognition of this possibility and concern for the affordability of flood insurance is reflected in sections of the Homeowner Flood Insurance Affordability Act of 2014 (HFIAA 2014). These sections called on FEMA to propose a draft affordability framework for the NFIP after completing an analysis of the efforts of possible programs for offering "means-tested assistance" to policyholders for whom higher rates may not be affordable. BW 2012 and HFIAA 2014 mandated that FEMA conduct a study, in cooperation with the National Academies of Sciences, Engineering, and Medicine, which would compare the costs of a program of risk-based rates and means-tested assistance to the current system of subsidized flood insurance rates and federally funded disaster relief for people without coverage. Production of two reports was agreed upon to fulfill this mandate. This second report proposes alternative approaches for a national evaluation of affordability program policy options and includes lessons for the design of a national study from a proof-of-concept pilot study.
Alluvial fans are gently sloping, fan-shaped landforms common at the base of mountain ranges in arid and semiarid regions such as the American West. Floods on alluvial fans, although characterized by relatively shallow depths, strike with little if any warning, can travel at extremely high velocities, and can carry a tremendous amount of sediment and debris. Such flooding presents unique problems to federal and state planners in terms of quantifying flood hazards, predicting the magnitude at which those hazards can be expected at a particular location, and devising reliable mitigation strategies. Alluvial Fan Flooding attempts to improve our capability to determine whether areas are subject to alluvial fan flooding and provides a practical perspective on how to make such a determination. The book presents criteria for determining whether an area is subject to flooding and provides examples of applying the definition and criteria to real situations in Arizona, California, New Mexico, Utah, and elsewhere. The volume also contains recommendations for the Federal Emergency Management Agency, which is primarily responsible for floodplain mapping, and for state and local decisionmakers involved in flood hazard reduction.
Sacramento, California, has grown literally at the edge of the Sacramento and American Rivers and for 150 years has struggled to protect itself from periodic floods by employing structural and land management measures. Much of the population lives behind levees, and most of the city's downtown business and government area is vulnerable to flooding. A major flood in 1986 served as impetus for efforts by federal, state, and local entities to identify an acceptable and feasible set of measures to increase Sacramento's level of safety from American River floods. Numerous options were identified in 1991 by the U.S. Army Corps of Engineers (USACE) in a report known as the American River Watershed Investigation. Due to the controversial nature of many of the alternatives identified in that report, study participants were not able to reach consensus on any of the flood control options. In response, the Congress directed the USACE to reevaluate available flood control options and, at the same time, asked the USACE to engage the National Research Council (NRC) as an independent advisor on these difficult studies. In 1995 NRC's Committee on Flood Control Alternatives in the American River Basin issued Flood Risk Management and the American River Basin: An Evaluation. This report outlined an approach for improving the selection of a flood risk reduction strategy from the many available.
Sacramento, California, has grown literally at the edge of the Sacramento and American Rivers and for 150 years has struggled to protect itself from periodic floods by employing structural and land management measures. Much of the population lives behind levees, and most of the city's downtown business and government area is vulnerable to flooding. A major flood in 1986 served as impetus for efforts by federal, state, and local entities to identify an acceptable and feasible set of measures to increase Sacramento's level of safety from American River floods. Numerous options were identified in 1991 by the U.S. Army Corps of Engineers (USACE) in a report known as the American River Watershed Investigation. Due to the controversial nature of many of the alternatives identified in that report, study participants were not able to reach consensus on any of the flood control options. In response, the Congress directed the USACE to reevaluate available flood control options and, at the same time, asked the USACE to engage the National Research Council (NRC) as an independent advisor on these difficult studies. In 1995 NRC's Committee on Flood Control Alternatives in the American River Basin issued Flood Risk Management and the American River Basin: An Evaluation. This report outlined an approach for improving the selection of a flood risk reduction strategy from the many available.
This book reviews the U.S. Army Corps of Engineers' (USACE) investigations of flood control options for the American River basin and evaluates flood control feasibility studies for the watershed, with attention to the contingency assumptions, hydrologic methods, and other analyses supporting the flood control options. This book provides detailed comments on many technical issues, including a careful review of the 1991 National Research Council report American River Watershed Investigation, and looks beyond the Sacramento case to broader questions about the nation's approach to flood risk management. It discusses how to utilize information available about flood hazard reduction alternatives for the American River basin, the potential benefits provided by various alternatives, the impacts of alternatives on environmental resources and ecosystems, and the trade-offs inherent in any choice among alternatives which does not lie in the realm of scientists and engineers, but in the arena of public decisionmaking.
Rivers provide about 60 percent of the nation's drinking water and irrigation water and 10 percent of the nation's electric power needs. The multiple and sometimes incompatible services demanded of rivers often lead to policy and management conflicts that require the integration of science-based information. This report advises the U.S. Geological Survey on how it can best address river science challenges by effectively using its resources and coordinating its activities with other agencies. The report identifies the highest priority river science issues for the USGS, including environmental flows and river restoration, sediment transport and geomorphology, and groundwater surface-water interactions. It also recommends two cross-cutting science activities including surveying and mapping the nation's river systems according to key physical and landscape features, and expanding work on predictive models, especially those that simulate interactions between physical-biological processes. The report identifies key variables to be monitored and data-managed. It proposes enhancements in streamflow, biological, and sediment monitoring; these include establishing multidisciplinary, integrated reach-scale monitoring sites and developing a comprehensive national sediment monitoring program. Finally, it encourages the USGS to be at the forefront of new technology application, including airborne lidar and embedded, networked, wireless sensors.
Floodplain maps serve as the basis for determining whether homes or buildings require flood insurance under the National Flood Insurance Program run by the Federal Emergency Management Agency (FEMA). Approximately $650 billion in insured assets are now covered under the program. FEMA is modernizing floodplain maps to better serve the program. However, concerns have been raised as to the adequacy of the base map information available to support floodplain map modernization. Elevation Data for Floodplain Mapping shows that there is sufficient two-dimensional base map imagery to meet FEMA's flood map modernization goals, but that the three-dimensional base elevation data that are needed to determine whether a building should have flood insurance are not adequate. This book makes recommendations for a new national digital elevation data collection program to redress the inadequacy. Policy makers; property insurance professionals; federal, local, and state governments; and others concerned with natural disaster prevention and preparedness will find this book of interest.
Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps portray the height and extent to which flooding is expected to occur, and they form the basis for setting flood insurance premiums and regulating development in the floodplain. As such, they are an important tool for individuals, businesses, communities, and government agencies to understand and deal with flood hazard and flood risk. Improving map accuracy is therefore not an academic question-better maps help everyone. Making and maintaining an accurate flood map is neither simple nor inexpensive. Even after an investment of more than $1 billion to take flood maps into the digital world, only 21 percent of the population has maps that meet or exceed national flood hazard data quality thresholds. Even when floodplains are mapped with high accuracy, land development and natural changes to the landscape or hydrologic systems create the need for continuous map maintenance and updates. Mapping the Zone examines the factors that affect flood map accuracy, assesses the benefits and costs of more accurate flood maps, and recommends ways to improve flood mapping, communication, and management of flood-related data.
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