Columbia County residents might be asked to finance $21 million in stormwater control programs due to an outdated floodplain survey in areas that now include West Lake and other developed neighborhoods.
According to a preliminary report by Davis & Floyd, a Charleston, S.C., consulting firm employed by the county, floodplain levels in much of the Reed Creek basin are too low to protect property and public safety.
"Based on very preliminary results from their computer modeling, there could be a very dramatic increase in floodplain elevations along Reed Creek," said Columbia County Commission Chairman Pete Brodie.
That increase could place an undetermined number of homes and land parcels within 100-year flood levels, complicating land-use designations and raising insurance costs.
"What this means is, areas not currently in floodplains could later be in floodplains," Mr. Brodie said. "There could be implications for residents within a newly defined floodplain, especially in terms of flood insurance."
Many areas, according to the consultants, require elevating floodplain levels 41/2 to 6 feet. Because of the far-reaching consequences of such a change, the county is seeking other opinions on Davis & Floyd's figures.
"The work is still in progress," Mr. Brodie said. "We're having additional third-party confirmation of the engineering and modeling before we decide what to do."
West Lake developer Carl Sanders Jr. is enlisting his own consultant, Martin Becker, to evaluate the Davis & Floyd report independently of the county.
"We're at least trying to learn their methodology, especially since we've had some experience with floodplain issues," said Mr. Sanders, who successfully petitioned the Federal Emergency Management Agency for floodplain changes along land he owns in North Augusta. "I think this thing is still a moving target."
As a partial alternative to raising floodplain elevations, Davis & Floyd recommend a series of public works projects costing $21 million, not including costs for land and right of way.
That figure is an early estimate and likely can be reduced, said Jim Leiper, Columbia County's engineering director.
Projects include renovating a 4,000-foot stormwater canal near Stevens Creek Road, retention ponds, bridges, culverts and the dredging, widening and deepening of channels.
Some of the public works projects could double as recreation facilities.
"It's our goal to make some of these multiple-use facilities," Mr. Leiper said. "We're talking ball fields, maybe, and forms of passive recreation."
Affected areas include Bowen Pond, West Lake, Foxfire, Blue Ridge, Fury's Ferry Road, Forest Creek, Old Evans Road, Mullins Pond, undeveloped areas along Washington Road and Springlakes subdivision.
Current floodplain measurements were established in the 1970s by the Army Corps of Engineers and used by the Federal Emergency Management Agency to draft floodplain maps, Mr. Leiper said.
"It was done with a rural modeling scenario then, and now we have a more urbanized area," he said. "It's becoming apparent that what was used to let homes be built in a lot of these areas leaves a lot to be desired."
Rapid development rarely occurs without consequences, such as the need to change floodplain elevations, said Jim Parker, spokesman for the Corps of Engineers.
"Obviously, the more you build, and the more concrete you put down, and the more trees and vegetation that's removed, the more drainage and runoff there is and the bigger the opportunity becomes for flood events," he said. "You see that over and over in areas that are heavily developed."
Financing a major stormwater infrastructure program likely would require the creation of a stormwater utility account, Mr. Brodie said. Such a proprietary account would issue revenue bonds to finance infrastructure.
Money to repay those bonds, he said, could be derived from a surcharge to county water and sewer users. It is too early to gauge how much such a surcharge might be, Mr. Brodie said.
The stormwater problem, although costly to mitigate, is not unusual in areas where development spreads rapidly, Mr. Leiper said.
In Richmond County, for example, along flood-prone Rae's Creek and Crane Creek, more than $14 million in local sales tax money has been spent on flood control projects in the past decade.
Twenty-seven neighborhoods lie totally or partially in the flood plains of Rae's Creek and its tributaries. Many of the 150 homes in the plain will flood when it rains more than four inches in a short time.
Floodplain elevations are significant because development is severely restricted.
"No more than 50 percent of a lot can be in a 100-year floodplain, and the finished floor elevation of any structure must be one foot above the 100-year level," Mr. Leiper said.
The potential implications for Columbia County homeowners, he said, are complex and - for now - undetermined.
"It's under assessment," Mr. Leiper said. "We want to make sure everyone has a full understanding of the consequences so commissioners can make informed decisions on which course to take."