LINCOLN — Special sonar equipment used for underwater inspections of Missouri River bridges this summer detected scouring as deep as 40 feet in some places.
As startling as that sounds, motorists don't have to worry about shaky supports when bridges reopen in the coming months, said Mark Traynowicz, state bridge engineer with the Nebraska Department of Roads.
"Not when you figure some of the piers and supports go down 80 to 100 feet or more" and are sunk into bedrock, he said Tuesday.
While transportation departments in Iowa and Missouri race to complete emergency repairs before winter weather brings construction to a halt, all Nebraska has to do is wait to drop bridge barricades at Decatur, the Mormon Bridge in northeast Omaha, Nebraska City, Brownville and Rulo.
In other words, just as soon as flood-damaged highways are repaired east of the river, the traffic will flow again.
For the most part, Nebraska highways stayed dry this summer. That's because floodwater followed the path of least resistance, flowing toward lower elevations in Iowa and Missouri, Traynowicz said.
As the flood overtopped or broke through levees on the eastern side of the river, it was like a pressure release valve that directed even more water away from Nebraska.
That doesn't mean Nebraska escaped damage to county roads, cropland and houses. But the state was relatively unscathed when it comes to highways.
The exception was at Niobrara in northeastern Nebraska.
The Standing Bear Bridge was the only one that closed because of water covering a Nebraska highway. The bridge, which connects Nebraska and South Dakota via Highway 37, has since reopened.
The Nebraska Roads Department also spent about $100,000 to raise Nebraska 12 south of Niobrara, said spokeswoman Mary Jo Oie. The highway was closed east and west of the community because of high water, but it has since reopened in both directions.
A weight restriction remains on a portion of the highway west of Niobrara, but otherwise, guardrail replacement and pavement patching were the only repairs required, Oie said.
Because of the flood's volume and duration, bridge engineers weren't sure how the structures would stand up, Traynowicz said.
The U.S. Geological Survey used sonar boats to monitor the river during the peak of the flooding, and bridge engineers accompanied them to get a look at abutments and piers.
An abutment is a bridge's first support structure while piers are the pillars that stand in the river channel. The flood damaged none of those key structures on any of the bridges, Traynowicz said.
"Because the Missouri River is a navigable river. . .the bridges are designed to take an impact from a vessel," he said. "All of those bridges are basically built very, very stout."
But the flood was stout, too.
It has eroded the embankment on the Iowa side of the private toll bridge at Decatur, Neb., which is owned by the Burt County Bridge Commission. Once the river drops low enough and the embankment can be restored, the bridge will reopen, Traynowicz said.
Roads officials in Iowa hope to reopen all flood-damaged highways to at least limited traffic by the end of the year if weather conditions allow, said Dena Gray-Fisher, the Department of Transportation's spokeswoman.
The first to reopen most likely will be Iowa Highway 175 west of Onawa, which connects to the Decatur bridge.
Part of Iowa Highway 2 west of Interstate 29 is expected to remain submerged until the middle of October. But officials think it will be possible to reopen at least one lane in each direction by late December, which would be a welcome development in Nebraska City.
Reopening the damaged stretch of Interstate 680 represents the greatest challenge, because it will have to be replaced.
"We know we need to help with economic recovery," Gray-Fisher said. "It's been very devastating to everybody in the region. We want to get traffic flowing again as quickly as possible, keeping safety in mind."
Southeast Nebraskans got some good news this week when the Missouri Highways and Transportation Commission awarded a $3.3 million contract for repairs to U.S. Highway 136. The highway connects Brownville, Neb., and Rock Port, Mo.
The flood opened four gaps in the highway pavement. Emergency repairs to three of the gaps are scheduled to be completed by Oct. 15.
The highway commission is working to establish a repair timetable for U.S. Highway 159, which connects to the Rulo, Neb., bridge, said Mike Rinehart, area engineer for the commission's Northwest District. The flood cut through the highway in at least three places.
World-Herald staff writer Nancy Gaarder contributed to this report.
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