Iowa flood maps get decent marks February 2, 2009Posted by Bahadir Sahin in English, Haber (News).
Tags: aerial LIDAR, flood maps, Iowa's DNR GIS Section
Johnson County’s flood map exceeds national standards and Linn County’s soon will, according to a new report from the National Research Council.
Federal Emergency Management Agency flood maps matter because they determine how much property owners have to pay for flood insurance. Those in high-risk areas pay higher premiums than those in low-risk areas.
Iowa is further along than most states in building accurate flood maps.
While almost 80 percent of the maps in the country don’t meet FEMA standards, most of the flood maps in Eastern Iowa do, according to the report sponsored by FEMA and the National Oceanic and Atmospheric Administration.
Also, the report’s key recommendation is for officials to use aerial LIDAR, or Light Direction and Ranging, to gather precise topographical information for the maps. The data is gathered by scanning an area with lasers mounted in aircraft.
The Iowa Department of Natural Resources is already halfway through a $4.3 million statewide LIDAR project.
When it is complete, Iowa and North Carolina will be the only states to have collected such complete topographical information, said Chris Ensminger, Iowa’s DNR GIS Section Supervisor.
“We’d like to have most of it done by the end of 2009,” Ensminger said, explaining that the flyovers can only be completed when the trees and ground are bare. “It gives all the materials we need to go into the models … but you still have to do tons of work.”
He said it may be another 10 years before the updated topographical information is combined with hydrology studies to model what parts of Iowa’s flood plains will be flooded at which river levels.
Most old flood maps are based on what’s called the U.S. Geological Survey National Elevation Dataset, developed from airborne and land surveys. But the information is far less precise than FEMA considers acceptable for flood plain mapping.
FEMA’s Map Modernization Program, funded for fiscal years 2003 to 2008, was supposed to result in digital flood maps for 92 percent of the continental U.S. population.
But even after an investment of more than $1 billion, only 21 percent of the population will have maps that meet or exceed FEMA’s own standards, the report said.
Johnson County’s flood map was updated in 2007 as part of the modernization program, Johnson County GIS Coordinator Rick Havel said.
In Cedar Rapids, a new flood map should be finalized in about a year.
The city hired mapping companies in 1995, 2000 and 2005 to shoot aerial pictures that would give officials more accurate topographical maps of the city and passed that information on to FEMA.
While the city didn’t use LIDAR, Ensminger and Cedar Rapids Public Works Director David Elgin said the new flood map here will be just as accurate as one based on LIDAR.
“I’m doubting what it would be worth redoing,” Ensminger said.