Political furor arises over proposed SW Idaho flood map expansion

As local officials work to boost southwestern Idaho’s economy, the National Flood Insurance Program may expand its flood-plain maps — which could cost residents and business owners millions in additional insurance.

A new NFIP survey of flood structures in the towns of Nampa and Caldwell, Idaho, showed the current flood-plain isn’t wide enough to handle a 100-year flood, according to Scott VanHoff, state coordinator for the NFIP.

With Caldwell in the midst of an ambitious downtown redevelopment process including residential growth along Nampa’s stretch of Indian Creek, future challenges to NFIP’s plans to expand the area’s flood map are looming. Local officials are watching the new survey warily.

“I think we’ll find a way out of this,” Dennis Cannon, economic development coordinator for the city of Caldwell, told the Idaho Press-Tribune.

Meanwhile, Nampa Economic Development Director Cliff Long reported there already is a hold on the city’s housing projects until the implications of the flood-plain designation are resolved.

Should the flood-plain expand, property owners within the flood-plain area would be forced to purchase flood insurance at an average cost of $400 per year, VanHoff said.

Last spring, mountain snowfalls swelled Idaho’s rivers, causing fears of flooding. In northern Idaho, winter wheat farmers saw crops inundated by the rising Kootenai River, subdivision streets south of Sun Valley became an impromptu path for the Big Wood River and residents of Eagle, Idaho, threatened to oust a local homeowners association’s board in a dispute about potential flooding on the Boise River.

In Nampa and Caldwell, VanHoff said new buildings in a potentially expanded flood-plain would have to be built to withstand a 100-year flood, potentially increasing building costs. Yet he downplayed the potential for new regulations to put a dent in municipalities’ aggressive expansion plans.

“It’s not that tough,” VanHoff said, noting that many structures inside the flood-plain in Boise are built to survive rising waters.

Mark Carey, the Federal Emergency Management Agency’s chief of flood-plain management, said maps must reflect the best available science. Despite pressure from economic development officials that may be building against yet-to-be-released maps, he said evaluating flood-plains is a “technical exercise” removed from the forces of political whimsy.

“The current map [in Nampa and Caldwell] is more than 10 years old. We are just trying to update it,” VanHoff explained. “It was requested by the county five years ago and has been a five-year process to get the funding and get this map done.”

FEMA periodically restudies flood areas and produces new maps because hazards change with time.

“There are two main factors that would cause the flood boundary lines to change: One being natural causes — as rivers meander they change the topography of the flood-plain. The other cause is human development — deliberate change to the topography and flood-plain by adding fill or excavating. Over time, the flood-plain itself physically changes, and the flood map needs to change as well to keep up,” VanHoff said.

The greatest contributing factor to the widening of the flood-plain in Nampa and Caldwell, according to VanHoff, is 1984 — the year the existing map was made. “There is a diversion point right at the Canyon county line where the canal water is taken back out of the natural channel of Indian Creek, eventually going down into Lake Lowell. Theoretically, the natural water would continue down the channel and flow through Nampa and Caldwell,” he explained. “The contractor hired to study the flood-plain [in 1984] looked at the routing of the natural floodwater plus the irrigation water from New York Canal routed through Indian Creek. When the contractor looked at that diversion point, he made the assumption that the canal would assist during a flood flow. And at that time, they would have been able to divert almost half of the flood flow.”

Now, post-Katrina, the law requires two things anytime a man-made flood control structure is considered during the process of mapping a flood hazard. It requires structures to be considered in a flood hazard map, to be certified as able to withstand the forces of a 100-year flood and capable of functioning the way it’s intended explained VanHoff. Second, the owner of the structure must sign an agreement that he or she will use it in the manner it was intended to be used to help alleviate flooding.

“We can’t assume [flood structures will work] any more; it must be documented that it can and will be used to alleviate the flood,” he said. “In this case, the New York Canal is owned by the Bureau of Recreation, which will not sign that agreement … So the old map reflected half of the flood going around town, and this map shows 100 percent of the flood going through town.”

Should Idaho officials or local entities object to the map expansion, a technical appeal must be filed to show where the NFIP erred or interpreted data incorrectly and must show what the correct map should look like.

“I expect there might be some slight adjustments, but the new map will be published, and there will be a significant change from the current map,” VanHoff said. There are certainly opportunities for appeals, so long as it is based on scientific data.”

Copyright 2006 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Additional reporting by Britton Wells.