For people whose business is to worry about flooding, there's no debate the Federal Emergency Management Agency (FEMA) needs to keep its flood maps current. But as Congress discusses the future of the National Flood Insurance Program (NFIP), not everyone agrees on the best way to modernize those maps or pay for the effort.
Congress created the NFIP in 1968 to reduce disaster assistance costs after floods by providing insurance on properties that are at high risk of flooding, so fewer owners will need government aid. The program also helps state and local governments manage floodplains so fewer properties are constructed in the way of rising waters. To support those two goals, FEMA works with state and local governments across the U.S. to map floodplains.
FEMA's Floodplain Insurance Rate Maps (FIRMs) indicate Special Flood Hazard Areas (SFHAs) - terrain where, in any given year, the chance that a stream will inundate the land is 1 percent or more. Anyone seeking a federally insured mortgage on a property in an SFHA must have flood insurance, which the NFIP subsidizes.
Insurance agents and lenders use FIRMs to determine which properties require the insurance. State and local governments use them in development planning and flood mitigation programs. Unfortunately in a community with ongoing development, the job of mapping the floodplain is never done.
"As farm fields and forests are turned into rooftops and parking lots, it destroys trees," said Larry Larson, executive director of the Association of State Floodplain Managers (ASFM) in Madison, Wis., adding that with fewer roots to drink up the water, more water runs into the nearest stream. "The flood level of that stream may go up significantly. As it does, the boundary of the 100-year floodplain expands to embrace more properties."
Homeowners continuously complain that their maps are obsolete, said David Maune, senior project manager for remote sensing at Dewberry, a Fairfax, Va. planning, design and program management firm whose expertise includes geographic information.
"I think something like 25 to 30 percent of flood claims are from people outside the special flood hazard areas," Maune added.
This creates a problem because many of these people don't carry flood insurance since, according to the FIRMs, they don't need it.
Funding Running Out
For a long time, FEMA had only $50 million per year to produce and update flood maps, Larson said. In 2003, Congress boosted that budget to $200 million a year, but only for the five-year period ending in 2008.
"Unless some additional authorization and appropriation is provided, FEMA will drop back to that $50 million a year," Larson cautioned, "and once again our maps will quickly become outdated."
A bill introduced in the U.S. House of Representatives in March proposed raising that funding to $400 million per year for fiscal 2008 through 2013. The Flood Insurance Reform and Modernization Act of 2007 directs FEMA to establish an ongoing program to review, update and maintain the FIRMs.
Among other items, it also requires FEMA to raise the NFIP's insurance coverage limits; phase out insurance subsidies for vacation homes, second homes and nonresidential properties; and submit annual financial reports on the NFIP.
Although FEMA ultimately is responsible for keeping flood maps current, state and local governments, working with private-sector partners, do the bulk of the work and share the costs with the federal government, Larson said.
When engineers study updating the FIRMs, hydrology and hydraulics receive significant attention. The first asks, "If X inches of rain fall, what volume of water will that add to the local stream?" The second asks, "When you add that volume of water, how high will the stream rise?"
A third factor is land elevation, or topography. Topography matters because, for example, if a house stands atop a knoll that puts it 10
feet higher than the surrounding land, it's less likely to flood than another house the same distance from the river on lower ground.
During hearings before the House Financial Services Subcommittee in June, Maune testified that as FEMA updates the FIRMs, it should include elevation data collected using the latest geospatial technologies.
Maune spoke on behalf of MAPPS (originally called the Management Association for Private Photogrammetric Surveyors), an association of private firms that provides spatial data and GISs. These firms provide technology and services to governments when they update their flood maps.
In particular, MAPPS favors using light detection and ranging (lidar) technology to collect new topographic data. In a lidar system, sensors installed on a plane emit 150,000 pulses of laser light per second, scanning the terrain below to collect elevation data. Software then eliminates readings obtained from foliage and structures to calculate the elevation of the bare ground.
Efficient and Accurate
The most accurate way to collect elevation data is on the ground, using traditional surveying techniques, said John Dorman, director of the North Carolina Floodplain Mapping program. Still, he said, lidar can cover a great deal more ground at a lower cost, and it's much more accurate than the method the U.S. Geological Survey (USGS) used to collect much of the topographic data used in today's FIRMs.
That's why the Floodplain Mapping Program used lidar to collect elevation data for all of North Carolina. "We have accuracy that people really can't beat," Dorman said. "It feeds really well into the engineering model."
North Carolina funded the collection of elevation data with $5 million from the Innovative Partnerships program at USGS and completed the work in 2005.
Some elevation data used in today's FIRMs dates from the 1970s, when the USGS used photogrammetric technology, Maune said. Lidar offers the ability to represent changes in elevation much more precisely, he said. Precision is especially important in very flat terrain such as coastal Florida, where a half-foot of elevation could mean the difference between hurricane-related flooding staying near shore or rushing far inland.
Though Larson agrees that collecting more accurate elevation data is a good idea, he doesn't share Maune's sense of urgency on the issue. "New topo, better topo, is always useful," he said, "although there are many, many areas of the country where good topo, beyond the national minimums, already exists."
In some communities, new topographic data would provide better maps, Larson said. "The engineering wouldn't be any better, but it makes the depiction better."
For ASFM, the big concern is that money for acquiring new elevation data should not come from FEMA's mapping program budget.
"There simply isn't enough there," Larson said.
Along with North Carolina, several other states have raised their own funds to acquire new topographic data using lidar. But all states and local communities, and many other federal agencies besides FEMA, need this data for a variety of purposes.
"I believe that there needs to be federal funding, either through FEMA or through USGS, that allows states to partner and share the costs, but also share the benefit of the data," Dorman said. "I don't think the federal government has its ducks in a row now, but that's the approach that needs to be taken."
"Nobody is arguing that FEMA ought to solve what is basically a nationwide problem," Maune said. "It's something that OMB [Office of Management and Budget] is going to have to work out with a lot of different appropriations."
Bio: Contributing Writer Merrill Douglas is based in upstate New York. She specializes in applications of information technology.