As floodwaters ease, roads and bridges show damage

CHICAGO (Reuters) - Floodwaters that have inundated the Midwest rolled south on Friday, leaving officials where the water was receding with the daunting task of rebuilding roads and bridges vital to farms and factories.

In Iowa, the state hit earliest and hardest by the disaster, a state Department of Transportation spokeswoman said engineers still did not know exactly how many miles (km) of roads and how many bridges need replacement.

"They haven't even tried to do that because they're still in response mode," Dena M. Gray-Fisher said.

Quantifying how much the disruption to Iowa's transport system has cost businesses is a task officials may never get their arms around, she said.

The state warned this week that many of the closures and detours prompted by the flooding will remain in place for "an extended period of time because of the extensive damage."

Iowa has set up an online photo gallery (here) highlighting the destruction caused by the worst flood to hit the region in 15 years.

Experts said a far more challenging task than quantifying the damage is inspecting bridges that look fine but may have been damaged by raging waters that attacked their abutments, bearings, pillars and footings -- and in some cases washed over their railings and decks.

"Bridges are not intended or designed to have water coming over top of them," said Conn Abnee, executive director of the National Steel Bridge Alliance, a trade group for fabricators.

EARLY SCRUTINY

Bridges make up a tiny faction of the overall roadway mileage affected by the disaster.

But bridges, particularly those over waterways, will be the focus of much of the early scrutiny and repair because the effects can be catastrophic when they fail.

In August last year, a 40-year-old bridge over the Mississippi River collapsed in Minneapolis, killing 13 people and injuring scores of others.

"It's a fairly involved and time-consuming physical exam that all these bridges have to undergo in order to make sure they can handle the load they handled before," said Doug Hecox, a spokesman for the Federal Highway Administration, a division of the U.S. Department of Transportation. "Most will be fine."

Inspectors are expected to check the bridge's surface to see if it is still attached to the bridge itself, and the concrete and steel girders and bearings holding its superstructure.

They also would conduct underwater inspections where the bridge's supporting pillars and abutments meet the river bottom to make sure floodwaters did not "scour" away their support.

Flood-caused scouring was cited when an interstate highway bridge near Albany, New York, collapsed in April 1987 during a flood, killing 10 people.

Since then, the federal government has required states to identify scour-prone bridges and regularly inspect and maintain them. As a result, engineers in Iowa and other states are in good shape as they work in coming weeks, Gray-Fisher said.

Iowa has more than 2,100 bridges over waterways, but fewer than 200 are considered likely to scour.

For years, those bridges have been monitored by all kinds of gauges that measure the hydraulic forces that the structures face in real time.

But that sort of system does not exist for the nation's roads and highways. So identifying roads that look fine but were undermined by flooding will be tougher, said Hecox of the Federal Highway Administration.

"Roads are probably going to be the bigger task simply because there's more of them and sometimes the damage can be a little harder to spot," he said.

(Editing by Peter Bohan and Xavier Briand)