Land surface reference information describes streams, roads, buildings, and administrative boundaries that show the background context for mapping the flood hazard zone.

Two aspects of mapping need to be considered in this context-defining land surface reference information and land surface elevation. This report presents the committee’s response to its statement of task. A previous study examined uncertainty in flood hydrologic and hydraulic computations (NRC, 2000).īesides the mapping technologies study presented in this report, FEMA has separately engaged the National Academies to undertake a longer-term flood map accuracy study within which the above issues will be addressed more fully. Vertical datums across the nation, but this report does highlight land subsidence as an issue important to Flood Map Modernization (3) mapping technologies other than airborne remote sensing-the committee considered in detail only photogrammetry, light detection and ranging (lidar), and interferometric synthetic aperture radar (IFSAR), which are all aerial mapping technologies, and did not consider land-based mapping technologies (4) uncertainties in flood hydrology and hydraulics-the committee focused on issues related to base map and elevation data and not on hydrologic and hydraulic sources of uncertainty in flood risk assessment. Limitations of time, and the narrow focus of the statement of task, meant that this study did not focus in detail on the following issues: (1) coastal flooding-this involves a different methodology than riverine flooding and since the nation has 60,000 miles of coastlines and about 4.2 million miles of rivers and streams, the committee focused on riverine flooding because that makes up the bulk of Flood Map Modernization (2) geodetic control-the committee did not consider variations in the precision of definition of the survey control points and This study was conducted in a short period of time to enable Congress to consider its conclusions during deliberations on appropriations in the spring of 2007. Identify mapping technologies that are currently available andĭetermine if newer technologies are appropriate and would be of additional benefit to floodplain mapping. Identify the current mapping technologies being used by FEMA to develop flood hazard maps The National Academies requested that an ad hoc committee be established to respond to the following statement of task: This study was commissioned by the National Academies for the purpose of informing Congress and the nation about this issue. Federal flood insurance is required if the property owner has a federally-backed mortgage.ĭuring the annual appropriations hearings for Flood Map Modernization, concerns have been expressed to Congress that the underlying framework data used as input to the flood mapping process is not of adequate quality in much of the nation to properly support the new digital flood map creation. This insurance is designed to provide an alternative to federal disaster assistance to reduce the costs of repairing damage to buildings and their contents caused by floods. This program encourages communities to regulate the land development in their floodplains to avoid flood damages and, in return, allows property owners located in flood hazard areas to purchase federal flood insurance. This work is being carried out by the Federal Emergency Management Agency (FEMA) in collaboration with state and local partners as part of the National Flood Insurance Program (NFIP). Resource limitations have meant that the scope of the effort has been modified to increase map quality by mapping 65 percent of the nation that contains 92 percent of its population.

The goal is to replace paper Flood Insurance Rate Maps (FIRMs) by Digital Flood Insurance Rate Maps (DFIRMs), and to achieve national coverage with these digital maps. The nation is presently making an investment of more than $200 million per year in Flood Map Modernization.

Figuring out base flood elevation