Date: Feb. 1, 2007
Contacts: Bill Kearney, Director of Media Relations
Michelle Strikowsky, Media Relations Assistant
Office of News and Public Information
202-334-2138; e-mail
FOR IMMEDIATE RELEASE
Flight-Based Laser Technology Should Be Used to Map U.S. Land Elevation
And Improve Accuracy of FEMA Flood Maps
WASHINGTON -- New digital, high-resolution land elevation maps -- created using a proven remote-sensing laser technology -- are needed to support the Federal Emergency Management Agency's effort to modernize the nation's floodplain maps, says a new National Research Council report requested by Congress. The floodplain maps are used by mortgage companies and FEMA's National Flood Insurance Program to determine whether property owners should be required to purchase flood insurance.
FEMA has been partnering with state and local governments in a $200 million-per-year modernization effort to replace paper floodplain maps with digital ones. FEMA sets accuracy requirements for the maps, but it is generally up to state and local governments to provide the data upon which the maps are based. Congress requested the report because of concerns that underlying base map information currently available for much of the nation is not adequate to support the new digital maps.
The committee that wrote the report focused on two layers of floodplain maps: base map imagery and base map elevation. It concluded that there is sufficient two-dimensional imagery available from digital "orthophotos" -- aerial and satellite photographs -- to meet FEMA's standards for mapping landmarks such as streams, roads, and buildings that show the context necessary for mapping flood hazard areas. The committee also endorsed a program known as Imagery for the Nation, a joint federal-state effort to keep orthophoto databases current.
However, there is inadequate elevation information available to map the shape of the land surface in three dimensions, which is critical in determining the likely direction, velocity, and depth of flood flows, the committee said. In fact, most of the publicly available elevation data is more than 35 years old, with 1970 being the average date of origin in the U.S. Geological Survey's National Elevation Dataset. Land development and urban expansion since then have significantly altered the surface. New road embankments and flood drainage structures also affect expected floodwater depths, as does land subsidence, which is particularly significant in coastal areas.
