LOCAL 100-YEAR FLOODPLAIN MAPS MAY no longer be worth the paper they're printed on. The maps, which contrary to their name actually outline areas subject to a one-in-100 chance of flooding in a given year, are coming under new scrutiny by local governments that use them to determine where to ban or restrict development. Mortgage lenders say they consult the maps to determine which properties need flood insurance. The maps also influence where home builders seek to purchase or develop land.

North Carolina is one state reassessing its flood maps. The state and federal government plan to spend $90 million on new flood maps for the state, with roll-out of the maps to be completed by 2008.

After Hurricane Floyd swamped North Carolina in 1999, many state officials realized that sections of their flood maps were outdated or even missing for many parts of the state. “Eighty percent of all homes damaged or destroyed were not shown in the correct flood zone,” said John Dorman, director of the N.C. Floodplain Mapping Program. “So [homeowners] didn't know to buy flood insurance.”

Technology has improved, and with it, so has the accuracy of the maps. Today, cameras and lasers mounted on airplanes will delineate stream banks and photograph topography, producing maps that are more detailed than any before.

The maps show countless changes in the floodplain, and not all are corrections of previous inaccuracies. The floodplain has grown in the state as areas upstream have been developed. Rainwater that cascades off roads, buildings, and parking lots pushes streams over their banks instead of soaking into the ground.

Other states may follow North Carolina as the impact of the hurricanes and the floods they leave behind sinks in from Florida and other parts of the Southeast.