Authorities are keeping a close watch on the integrity of the Kennedy Bridge -- the Grand Cities' only remaining link over the flooded Red River.
A Minnesota Department of Transportation crew used sonar equipment Monday to check for underwater erosion around the substructure of the U.S. Highway 2 bridge that connects Minnesota and North Dakota.
"We're not doing this because we think we have a safety concern. We're doing it because it's a critical link," bridge engineer Roger Hille said.
MnDOT plans to continue monitoring the bridge each day until the river drops to a level of 48 feet. On Monday evening, the river stood at 48.82 feet and was expected to rise, the National Weather Service said.
The daily checks will require closing one lane in one direction on the four-lane bridge from 9 to 11 a.m.
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If congestion becomes an issue, crews may switch their work slot to the early afternoon.
Hille said the goal is to detect any structural problems early enough that repairs could be made before closing the bridge becomes necessary.
"We're monitoring for any scour or erosion around the bottom of those substructure units," he said. "Each time we do that, we monitor for any movement on the superstructure on the top as well."
But even if erosion is found, he said, the Kennedy's piles are driven deep enough into the riverbed that the bridge wouldn't have to be shut down.
Hille said Monday afternoon that he had not received the results of that day's sonar check.
Also on Monday, a crew from Collins Engineers, a Chicago-based firm, tested new sonar technology on the Kennedy with MnDOT and on the Sorlie Bridge.
Before the Sorlie reopens, Hille said, MnDOT will check that bridge's substructure for erosion.
"What often happens as the current increases, you get scour erosion around some of the piers or substructure units, and as the current slows down, some of that fills in" with loose material, he said.
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With plans for daily checks of the Kennedy, MnDOT officials are considering how a storm system tracking east across North Dakota could affect the project.
"We've already determined that if road conditions deteriorate or weather conditions deteriorate, we will not monitor on that particular day," Hille said.
Al Grasser, Grand Forks' city engineer, has said the Kennedy would close at a river level of about 52½ feet. The latest predictions show the Red cresting near 51 feet Friday.
