In the long run, significant stretches of Florida coastline are likely to end up underwater, according to climate scientists. But in the short run, your odds of experiencing a flood amount to a crapshoot. In defining official flood zones, insurance authorities have to take their best guess — and sometimes, their first efforts at gauging the risk aren't very precise. As the Federal Emergency Managment Agency (FEMA), in cooperation with the U.S. Army Corps of Engineers, pursues a multi-year effort to create new flood maps around the U.S., localities typically don't like the new versions of the maps that FEMA puts out for public review. And where localities have the resources to take their case to FEMA, they often succeed in having FEMA re-draw the lines. Sometimes, the changes can make a big difference.
That's what happened in Palm Beach County, according to a report in the Sun-Sentinel (see: "How Palm Beach County saved residents millions of dollars by fighting FEMA on flood maps," by Ron Hurtibise). Hampered by funding cuts, FEMA's map-revision effort was plagued by delay. And when revised maps finally arrived, according to Palm Beach officials, they were already outdated. Local experts Ralph Wall and Ken Todd told the Sun-Sentinel the proposed maps were "riddled with inaccuracies." "Wide swaths of land in the central and western sections of the county were suddenly designated as high-risk flood zones," the paper reported. "If the maps were finalized, tens of thousands of property owners who hadn't been in such zones for decades would suddenly be forced to buy mandatory flood insurance policies costing hundreds, and possibly thousands, of dollars each year."
"They relied on a couple old studies where there was no data or that used old data from 30 years ago," Todd told the paper. "They told us they didn't have the funding to collect new data and that's the best information they had." Said Wall, "We had communities of literally thousands of homes — in Andros Isles, Baywinds, Riverwalk — that were lumped into [high–risk flood zones]."
In response to pressure from local officials, FEMA has taken the proposed maps back for a new look — and, after the review, removed tens of thousands of properties from designated high-risk areas. After more comment, however, FEMA took those maps back too, and has now come up with yet another proposed revision.
After engaging in this back-and-forth for years, Palm Beach County officials have decided to take matters into their own hands. With FEMA's agreement, the county has embarked on a multi-year effort to create highly accurate maps of the region's terrain using LIDAR (light detection and ranging), a method that employs laser range-finding devices mounted on aircraft.
"LiDAR (light detection and ranging) technology is a remote sensing tool that uses laser pulses to collect detailed elevation information," explains the Palm Beach County website (see: "USGS Grant to Help Fund LiDAR Mapping Project"). "By measuring the amount of time it takes for the laser pulse to travel from and reflect back to the aircraft, LiDAR can accurately map elevations of features on land. Global Positioning Systems (GPS) on board the aircraft and on the ground near the survey area provide positioning of the laser pulse. Multiple pulses at each location return multiple elevations including tree canopy, rooftops and ground surface."
"This stuff is not an overnight thing," Ken Todd told the Sun-Sentinel. "But we're going to have really good maps when it's done."