After the Flood

An accurate GIS database of flood hazards could save North Carolina taxpayers millions in disaster aid.

by / January 6, 2004
When Hurricane Floyd ripped through North Carolina in 1999, more than 4,000 destroyed homes were uninsured or underinsured. Much of the blame lay with maps produced by the federal government to show which properties stood in areas at high risk for flooding.

Those maps, state officials said, were badly outdated, so thousands of property owners who should have bought flood insurance hadn't.

"About 80 percent of all the homes either damaged or destroyed were not shown in the special flood hazard areas," said John Dorman, program director at the North Carolina Floodplain Mapping Program.

Development, road construction and natural forces continually reshape a waterway's floodplain. But the printed maps of high-risk areas, which dictate which property owners must carry flood insurance, were about 13 years old when Floyd hit, Dorman said.

Nor did those maps precisely represent the height of the land. In some places, Dorman said, the elevation was off by 10 feet. In the eastern part of the state, a mere two feet could mean the difference between dry land and an entire county underwater.

One year after Floyd, North Carolina launched a major effort to build accurate digital maps of state flood hazard areas. The state became a cooperating technical partner (CTP) within the Flood Hazard Mapping Modernization Program at the Federal Emergency Management Agency. FEMA made North Carolina responsible for the flood insurance rate maps (FIRMs) covering the state's watersheds. The state started developing digital FIRMs (DFIRMs), which it can update as conditions change.

So far, North Carolina has created preliminary versions of DFIRMs for 29 counties, and offers the data on the Web for free. Officials hope to complete DFIRMs for all North Carolina counties by 2007, Dorman said, and also plan to update definitive floodplain maps every 18 to 24 months.

Mandatory Insurance
The main purpose of a FIRM is to help mortgage lenders determine which properties fall into Special Flood Hazard Areas. To get a federally backed mortgage on a property in one of those areas, the purchaser must buy flood insurance. Communities that participate in FEMA's National Flood Insurance Program (NFIP) develop floodplain management plans, with ordinances to regulate development in flood-prone areas. The NFIP helps property owners and renters in participating communities buy flood insurance at moderate rates.

When rising waters ravage uninsured properties, owners often lack money to rebuild.

"It puts the onus back on the community, or the state or federal government, to support those people," Dorman said.

State and local governments are joining the Flood Hazard Mapping Program so after a flood, owners can rely on insurance settlements rather than government aid. That could save North Carolina taxpayers a lot of money, Dorman said, citing a study by the U.S. Geological Survey that determined if the maps were updated and kept current on a statewide basis, a cost avoidance of $56 million per year from flood damage would result.

To get its program going, North Carolina signed a CTP agreement with FEMA. The state Legislature created the Floodplain Mapping Program, and the new program created a Cooperating State Technical Committee. This group of about 50 represents federal, state, county, municipal and private-sector organizations was designed to bring all stakeholders to the table.

North Carolina is developing DFIRMs in three phases. Phase one covers the six river basins in the eastern part of the state. Phase two will focus on another six basins in the Piedmont region, and Phase three will cover the western part of the state.

The Legislature initially funded the program with $23 million, later adding another $9 million to move it into Phase two, Dorman said. FEMA has contributed about $18 million.

The program contracted with two firms -- Watershed Concepts and Greenhorne & O'Mara -- to collect the necessary geographic data, conduct flood hazard modeling, develop the DFIRMs and build the information system to support them. At the heart of this system is a Unisys ES7000 Orion 200 server running Microsoft Windows 2000 Datacenter Server and the Microsoft SQL Server 2000 database. The GIS software comes from ESRI of Redlands, Calif.

The system includes 10 terabytes of storage capacity. To map the entire state, Dorman said, another 10 terabytes to handle the inclusion of high-resolution orthographic maps on the site must be purchased.

Image Files versus Interactive Maps
Web site visitors can view PDF files of DFIRMs and interactive maps linked to the GIS database, which will be more current than the DFIRMs. Under federal regulations, each time a published DFIRM is updated, citizens have 90 days to review it and appeal any features they think are inaccurate, Dorman explained. That requirement makes it impractical to revise DFIRMs every time the database receives fresh information.

Dorman hopes regulations will change one day to make the digital maps the official DFIRMs.

"As changes occur in the development of the community, or in the characteristics of the stream or new roads, you need to update that as quickly as possible so people make good floodplain management decisions," he said.

Under agreements signed with local governments, North Carolina will use GIS data those governments have developed and offer its floodplain data to counties and municipalities. Beyond determining who needs to buy flood insurance, the data will support a host of other applications, such as wetlands, clean water management and preliminary design for road construction, Dorman said.

One rich source of data will be Mecklenburg County, which started working with FEMA on its own floodplain mapping modernization in 1998. Major floods in 1995 and 1997 spurred the county to become a CTP, said Bill Tingle, manager of Mecklenburg County Stormwater Planning. Because the FIRMs in place at the time were based on studies conducted in the late 1970s, some areas inundated by the floods weren't shown in the floodplain, he said.

Floodplain of the Future
Mecklenburg now has DFIRMs for the entire county, and has pushed the program a few steps beyond FEMA's original vision. The county's maps not only indicate the current floodplain, they also show how that plain will evolve in the next 20 to 30 years, based on planned development.

The county can also calculate a "100-year elevation," which refers to the height floodwaters will reach under conditions statistically likely to occur every 100 years.

"When somebody comes in for a building permit, if they're in any part of the floodplain, we look at that 100-year future flood elevation and say, 'Before you get your permit, you're going to have to show us you've built above that future 100-year elevation, so we won't have to worry about folks flooding in the future who build houses today,'" Tingle said.

The county offers this information on its Web site, and also provides elevation data for approximately 4,000 individual buildings in flood-prone areas. Prospective buyers, realtors, appraisers, insurance companies and mortgage lenders use this information, Tingle said.

Mecklenburg County is working with North Carolina on ways to incorporate the county's map data in the statewide project. Integration will be a challenge, since the state uses digital orthographs to develop its base maps, while Mecklenburg uses planametric maps, or line drawings.

"We haven't come up with a final solution for that," Tingle said.

Outside North Carolina, numerous state, regional and local organizations have also signed CTP agreements with FEMA. Alabama is developing the business plan for its floodplain modernization program, said Trey Glenn, director of the state's Office of Water Resources.

The program's benefits extend far beyond flood insurance problems, Glenn said. The map database will provide a fully integrated digital tool with the maps, models and delineations that state and local agencies can use for a wide variety of purposes, he said.

The Southwest Florida Water Management District is lining up consultants and funding to produce DFIRMs for its jurisdiction. The initiative dovetails with the district's other GIS activities, supporting its mission to manage the watershed, said Gordon McClung, engineering manager of the District's Resource Management Department.

"As we're doing what we do in our business, it makes good sense to coordinate with FEMA," McClung said.
Merrill Douglas Contributing Writer
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