Professional societies and federal agency consortia are appropriate entities to lead development of these standards; funding to support these efforts should be considered as part of a nationwide effort.
The committee reached its conclusion that Elevation for the Nation is needed for two main reasons: first, for the nation as a whole the existing elevation data are so old, and the gap between their accuracy and the accuracy required for floodplain mapping is so great, that the need for new elevation data is clear; and second, the required elevation mapping technology exists and has been commercially deployed such that implementing Elevation for the Nation is technically feasible. Regardless of whether “best-available” elevation data are used or new elevation data are acquired for a flood study, informed judgments must be made about the appropriateness of these datasets and their influence on flood data computations. The committee recognizes that Elevation for the Nation will involve significant expense, perhaps as much as the existing Flood Map Modernization program. It is for Congress and others to determine whether this expense is justified in the context of national spending priorities. Certainly the data arising from Elevation for the Nation will have many beneficial uses beyond floodplain mapping and management.
The current study was conducted in a short time to address very specific questions about the mapping technologies used to produce floodplain maps. As such, the committee did not have the resources or scope to examine in detail many important issues related to flood map accuracy. The committee suggests, for example, that analysis of a selection of updated flood maps could be useful to compare the quantitative effects of using lidar versus using conventional 10-meter or 30-meter NED information derived from USGS topographic maps to provide the elevation data. In a new, two-year study, beginning in early 2007, FEMA has separately requested the National Academies to undertake a distinct evaluation of flood map accuracy, including an examination of the whole range of uncertainty in flood mapping arising from uncertainty in flood hydrology and hydraulic modeling, as well as uncertainty in land surface elevation. The committee hopes that the present report provides solid input to the upcoming study and helps to further objective examination of the most cost-effective methods needed to support the nation’s floodplain mapping and management.