FIRM Support for Accurate Maps

GIS-revised floodplain boundaries create benefits for homeowners and businesses in Winnebago County, Wis.

by / October 31, 1999 0
Four years and $50 million after enacting the Statewide Land Information System in Wisconsin, the state Legislature asked to see some tangible benefits from the enterprise. In response, the State Land Information Board pointed to Winnebago County, one of the first to develop a GIS-based land information system (LIS). In the process of developing the countywide system, Winnebago created a floodplain-boundary profile far more accurate than the existing Flood Insurance-Rate Maps (FIRMs) required by the Federal Emergency Management Agency (FEMA). FIRMs are used by the county and by mortgage lenders to identify buildings within the floodplain. Owners of such buildings must conform to floodplain zoning ordinances and carry expensive flood insurance. The new profile shows
that more than 2,000 buildings on the old FIRM are actually out of the floodplain.

FEMA approval of the new Winnebago County floodplain-boundary profile will mean millions in flood-insurance savings and increases in property values for the affected homeowners and businesses. It will eliminate the need for property owners incorrectly shown on existing FIRMs as on the floodplain, to go through the expensive process of proving they are not. It will also result in the adoption by FEMA of more accurate FIRMs.

Winnebago's LIS is the result of a four-year, coordinated effort by seven municipalities to modernize land- and infrastructure-management needs of city and county agencies, and enable government, utilities, and private enterprise to share specific data resources via an open software environment. The system is expected to increase government efficiency and public service by eliminating duplication of land-record operations and standardizing data storage management. Also it will enable county zoning to expedite evaluation of land-use restrictions, and give taxpayers access to property-tax information via the Web.

One-Third in Floodplains

Winnebago County is in east-central Wisconsin, along the western shore of Lake Winnebago, the largest lake in the state. According to 1998 Census estimates, the population is 154,000, mainly centered around Oshkosh, the county seat, and near the towns of Neenah and Menasha. Nearly a third of the county's 500 square miles -- including Lake Winnebago, two smaller lakes, the Fox and the Wolf rivers, and numerous streams -- are floodplains. Rain and snow together annually average 30 inches, and in the past, heavy rains have caused flooding in certain areas of the county.

Until development of the Winnebago LIS, federal and state law required the county to base floodplain zoning ordinances on FIRMs produced by FEMA. Where and how new structures could be built depended on whether the FIRM showed the building to be in or out of a floodplain. Mortgage lenders used FIRMs to require flood insurance on buildings in flood-prone areas, to reduce the need for disaster assistance when devastating floods occurs. However, County Zoning Administrator Robert Braun said the Zoning Office is now using the new map developed by the Wisconsin Department of Natural Resources (WDNR) to determine the location of buildings, relative to a floodplain.

The Problem with FIRMs

Braun pointed out that the old FEMA maps were drawn at a scale that makes locating a property virtually impossible. "There's no way to get parcel specific at 1:24,000 [1 inch = 2,000 feet]; the width of a line on a FIRM can represent as much as 50 to 100 feet, depending on how thick the ink was when it came out of the pen."

Ben Niemann, professor of urban and regional planning at the Land Information and Computer Graphics Facility at the University of Wisconsin, Madison, agreed. "FEMA uses 1:24,000 quadrangles to draw the delineation -- you're talking about contour intervals of 10 feet. It is very difficult to draw a floodplain using that scale of map, especially in Winnebago County, where the topography is so flat. Although the margin of error can be quite large, the FIRM is still the determinant of whether or not a building is in the floodplain," he said. "A resident whose building was obviously on top of a hill might still have to buy floodplain insurance. The only way out of the flood-insurance program is to have a surveyor actually survey in the flood elevation relative to the building site, and that's expensive, about $5,000. Winnebago County knew that. That's why they went for a higher-resolution database with two-foot contour intervals. [1 inch = 400 feet] The LIS map is much more indicative of where the flood might actually go."

Potential Cost Savings

Braun explained that with the LIS, it is possible to zoom in to one specific parcel, and through the use of background aerial photography or on-screen data layers, see the relationship between the flood plain and whatever structures happen to be on the property. "For example, by looking at the digital information, insurance companies can now accurately determine whether or not structures on the property are within the floodplain. Whereas on the old Z-fold maps, it was, here's this great blob and we have no accurate way to scale things off, so we're just going to say, 'Yeah, OK.' Now we can say, 'Here's the area on the property that's not in the floodplain. If you want to build somewhat cheaper and not be subject to the basement restrictions, etc., build in this area, and you won't have to comply with floodplain requirements.' There's a potential cost savings here for home- owners and businesses."

Charting the Waters

Approving floodplain mapping is WDNR's responsibility. The agency also reviews new engineering studies for floodplain mapping, provides technical support to the counties, and assists them in integrating floodplain mapping into their LIS. Floodplain Engineer and GIS Specialist Alan Lulloff said the old floodplain-boundary profile was drawn using 10-foot contours. "That eliminated any possibility of the old profile matching the new two-foot contour data in the county's LIS." Lulloff then requested and received a $20,000 grant from FEMA to redelineate the floodplain boundaries.

In drawing the new floodplain profile, Lulloff brought established flood elevations into the grid package in ArcInfo to establish the projected water level of a "100-year flood," and create a representation of the flood surface. He then compared the flood surface to the LIS topography to determine which land points in a 100-year flood would be dry and which would be wet. The "wet" areas were then converted to polygons that outlined the new floodplain boundary. The project was completed in little over a year and a half.

Although WDNR has received concurrence from FEMA to use the revised floodplain map for zoning purposes, Lulloff stressed that formal approval from FEMA is pending revision of the flood insurance-rate map and publication of a new one.

Tangible Benefits

The impact of the redelineation is tangible; of the 5,700 buildings shown on the original FIRMs to be in a floodplain, the new map shows 2,400 of them to be outside, and 1,300 that were thought to be safe are actually inside the floodplain. FEMA's acceptance of the new floodplain delineation will mean an increase in property values for those outside, plus a significant flood-insurance savings. According to the Planning and Zoning Office, the cost of flood insurance over the life of a 30-year mortgage is about $12,000. For owners of the 2,400 structures, FEMA approval will mean a savings of $28.8 million. Owners of 1,300 homes may see a drop the value of their properties, but they will now have something they do not currently have, flood-insurance protection.

"Modern information technology," Niemann said, "is enabling government to spread the cost of flood insurance more equitably. It's a way of government being more responsive to the needs of real people. If you don't need flood insurance, why should you be paying for it? On the other hand, data shows that if you're in a flood-prone area, you'll likely be flooded once in 30 years. This would suggest you do want insurance."

Niemann added that FEMA is in the process of putting together a nationwide program to do what they have done in Winnebago County, support redelineation of floodplain profiles. "As urbanization has expanded outward, FEMA is finding that their maps are inadequate to deal with these problems. They're talking real big money."

What it Takes

Braun said redelineating the floodplain was time-intensive in terms of setting up the data and doing the modeling based on contours. "I don't know that it is something that a specific municipality would have the time or personnel to do. It needs to be coordinated, let's say through a state planning agency with computer facilities. Certainly, the private sector could provide this kind of assistance. As long as things are done within FEMA parameters, everyone will end up with a better product."




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Bill McGarigle is a writer, specializing in communications and information technology. He is based in Santa Cruz, Calif. E-mail him.