N.C. site offers detailed flood data

As Hurricane Isabel headed toward their coastline, North Carolinians had online access to information detailing the flood-prone areas in their state.

The North Carolina Floodplain Mapping Project is a direct result of the disasterous hurricane season of 1999. Three hurricanes'Dennis, Floyd and Irene'battered the Tar Heel State that September and October. In a two-week period between Aug. 30 and Sept. 16, more than 25 inches of rain were dumped on the state, destroying more than 4,000 homes and leaving thousands of people homeless.

Before the mapping project, 80 percent of the homes destroyed in 1999 were not listed as being in a floodplain on available flood insurance rate maps, said John Dorman, director of the project. Because of this, the homeowners were not required to have flood insurance'and many of them didn't.

Most of the flood insurance maps that were in use then were at least 10 years old and woefully out of date, Dorman said. All of them were paper.

Dorman, who was working for the North Carolina Office of Budget and Management at the time, went to the Federal Emergency Management Agency for help. A year earlier FEMA had launched a program to digitize flood hazard data for all flood-prone areas in the nation.

On Sept. 15, 2000, the first anniversary of Hurricane Floyd, North Carolina and FEMA announced an agreement to develop a program to maintain accurate flood hazard data for the state. FEMA designated North Carolina's government the prime custodian for the state's floodplain maps.

Dorman and his team began a program to build an accurate digital floodplain map of North Carolina. The state's General Assembly allocated $23 million to the floodplain mapping program and FEMA added $6 million.

Dorman estimates the digital mapping system will help the state reduce costs related to flood damage by about $65 million a year.

A cost-benefit analysis of the project showed that the state stood to save considerable money as a result of the more-accurate maps, Dorman said. 'For every dollar we spent on the project, there was a seven-dollar return,' he said.

Lots of data

Fortunately, North Carolina was already rich in geographic information systems and geospatial data, Dorman said. Of the state's 100 counties, 99 had GIS maps. The state has 100 layers of GIS data and is working with the U.S. Geological Survey to collect digital orthophotos of land parcels in North Carolina. The North Carolina Geodetic Survey served as the state's technical lead for the surveying and mapping phases of the project.

The floodplain mapping program chose as the prime contractor Watershed Concepts of Greensboro, N.C., a division of Hayes, Seay, Mattern & Mattern Inc. of Roanoke, Va.

To manage the spatial data, program officials decided to use ArcIMS and ArcSDE from ESRI of Redlands, Calif. Because GIS generates a lot of data, the team bought a storage area network with a capacity of 10T from EMC Corp. of Hopkinton, Mass. The project uses a Unisys ES 7000 enterprise server with 16 Pentium III Xeon processors. The mapping application runs under Microsoft Windows 2000 and uses Windows 2000 Datacenter server.

Watershed Concepts uses light detection and ranging (LIDAR) technology to measure terrain elevation points to create the floodplain maps. LIDAR data collection involves putting a laser scanning system onboard an airplane, along with a Global Positioning System receiver to locate x and y coordinates.

North Carolina's new floodplain maps are accurate to within 25 centimeters, Dorman said.

Users can check the digital maps online at www.ncfloodmaps.com. More than 150,000 people have visited the site since it went online in May of last year, Dorman said.

About the Author

Trudy Walsh is a senior writer for GCN.

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