Team Checks Traffic Bridge Piers

It looks like the SS Minnow, but this boat gets researchers close to potential problems.

A U.S. Geological Survey team is using sonar to see how flooding has impacted piers supporting bridges we travel on daily.

Hydrologist Brenda Woodward is gathering data.

"We do get the intensity of the sonar returned so you do get some sort of a picture of the bottom in addition to the soundings but the main thing is the sonar ping and the time of travel," she said.

The technology is old, developed by the British during World War I but the application is new.

This is the first time sonar has been used to test the integrity of bridge supports in the Missouri River.

"On some of the piers, you can actually see if the footing is showing or if some other structure sticks out a bit, you start seeing some of the tiny details," Woodward said.

The data she records is turned over to Kirk Harvey of the Nebraska Department of Roads.

"Once we get this data we'll know how the river bed's moving," he said. "And then we can compare it to the as-built (original specifications) and determine if the foundation's being undermined or the piling's being exposed."

The sonar takes scans of the river bed along bridge piers to check for erosion or scour that may be caused by rapidly moving river waters.

"We'll see holes, we'll see sand dunes," Rick Wilson of the U.S. Geological Survey team said. "We've actually seen a dune that is over 12 feet high so its like a rolling wave as it goes down the river."

Al Conkling has spent 38 years with the Geological Survey team.

He was nine years old during the 1952 flood.

Conkling said technology makes the job more efficient.

"The old method would take one person several hours and it was labor intensive and now two people in a boat can do it in about half and hour to 45 minutes," he said.

The results are rapid. In a matter of moments, a color chart depicts channel depth and water velocity.

That gives a more clear picture of what's below the surface.

"To make sure that if there is a problem we can identify it and corrective action can be taken," Wilson said.

The Geological Survey team is collecting data at the four Omaha bridges that carry vehicles over the Missouri River.

So far, so good, but the team did find some potential problems at the Decatur bridge in Northeastern Nebraska.

The problem there is not the main support piers in the channel but a possible sinkhole on the Iowa side near a support that is normally on dry ground.


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