Dam and Bridge Inspections, Solutions Will Take Time

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(TNS) – The situation has improved enough on the Blue Earth River to allow for more assessment of the damaged Rapidan Dam, riverbanks, the County 9 bridge just up from the dam, as well as downstream bridges.

But water flows are still strong and safely doing reconnaissance remains difficult.

“We’ve been in constant contact with (federal and state) agencies,” Blue Earth County Public Works Director Ryan Thilges told the County Board Tuesday.

But he said there will be a long road to documenting damage, filing for disaster aid and preparing environmental studies before the bridge can be repaired or replaced or before deciding if the 114-year-old dam should be removed or stay put.

On Tuesday, Bolton & Menk engineers were at the site to see if the dam had slid or rotated at all.

The Federal Energy Regulatory Commission, which licenses dams, also gave the county permission to have county staff go out on the deck of the dam to do inspections if needed. FERC already had sent its staff out on the deck to look for any major damage that might imminently jeopardize the dam.

The dam used to generate electrical power but hasn’t for several years since a previous flood damaged the power plant. There was still an electrical substation at the dam that Xcel Energy used, but that was destroyed in the recent flood.

The Sheriff’s Office took a boat to bring Thilges to the downriver side of the dam and they were able to do some visual inspection and get partly into the inside of the dam, much of which is hollow, to take some photos. Thilges said sediment kept them from doing too much exploring.

Meanwhile, focus has been on the highway bridge, which was installed in the early 1980s.

The piers of the bridge are on bedrock, but the bedrock is sandstone, which can erode fairly easily under strong water flows. A thick layer of sediment behind the dam had held the piers in place and prevented water from churning at the base of the piers. But much of that sediment washed down the river when the new channel was created. The amount of sediment that has been released from behind the dam is undetermined.

Thilges said they’ve done some “crude” attempts to try to determine how exposed the bottom of the piers are, but it’s difficult with water still flowing fairly strong. The bridge has remained closed since late last month.

“There’re a lot of unknowns about the bridge,” he said.

Whether it would be feasible to repair the bridge or if it needs to be replaced will not be known until water is much lower and inspections can be done. A 2021 estimate put a cost for replacing the bridge at about $8 million, but inflation would likely push that to the $10 million range, Thilges said. If the bridge is replaced, it would be done with more robust footings, he said.

When the Sheriff’s Office was taking him up the Blue Earth River from the Minnesota River, Thilges got a view of the number of of trees and amount of other debris that washed down and snagged on shore or at bridges.

“The amount of debris downstream (of the dam) is mind-boggling.”

He said there is no easy, inexpensive or safe way of removing most of that debris.

County Commissioners Kip Bruender and Vance Stuehrenberg talked about a host of social media posts that were inaccurate or speculation.

“Lots of people want to blame the county,” Stuehrenberg said.

But Thilges said they followed all the emergency procedures and did all they could safely do to safeguard the dam and bridges.

Commissioner Kevin Paap, whose district includes the dam, said Blue Earth County is not the only place in the United States with aging infrastructure. He said more federal aid is needed across the nation to upgrade deteriorating infrastructure, particularly in rural areas.

Paap also praised all the county agencies that kicked into action and have spent long hours dealing with the dam and the other flooding and damage across the county, including Public Works, the Sheriff’s Office, Emergency Management, county administration and others.