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.  

Merrill Douglas  |  Contributing Writer