The costs for improving flood maps would come from collecting, updating, modeling, and analyzing the flood-related data; increasing construction of property and businesses; losing land to development; updating regulations; and informing the public of changes. The committee found that these costs would be outweighed by benefits of more accurate flood maps, including reduced loss of life, property, and businesses; more efficient planning and response for emergency services; and preservation of natural functions of floodplains. In addition, better maps would provide more reliable measures of flood hazard, which would enable more targeted land-use regulations and structures to be insured at appropriate levels. Maps that include estimates of the height flood water will rise or exceed during a 100-year flood provide significantly more benefits than those that do not.
FEMA commonly produces maps using data from the U.S. Geological Survey National Elevation Dataset (NED), which is developed from airborne and land surveys. However, map accuracy would be increased by updating and generating information using high-accuracy topographic data, such as that generated by "lidar," which measures elevation using aircraft-mounted lasers, the committee said. For the three topographical regions studied, differences in ground elevation measurements by lidar and NED were about 12 feet, with the lidar heights measuring both higher and lower than the NED. These differences significantly affect predicting the extent of flooding, the committee stated. Overall, the total areas of floodplains defined from lidar and from the NED were similar in two study regions and differed in shape by 20 percent in one study region. As lidar data coverage is sparse, FEMA should increase collaboration with federal, state, and local government agencies to acquire lidar data
|Contact: Jennifer Walsh|
National Academy of Sciences