Corps lowers river for inspections and rare public viewing

Photo By Elizabeth A Stoeckmann | Brad Perkl, U.S. Army Corps of Engineers, St. Paul District archaeologist, explains the historical importance of the falls to visitors in Minneapolis, Oct. 6.  

MINNEAPOLIS, MN, UNITED STATES

10.06.2020

Courtesy Story

U.S. Army Corps of Engineers, St. Paul District

The bottom of the Mississippi River is not something Minnesotans see every day, but routine inspections provided more than 5,400 visitors a rare look into the original structure and foundation of the river Oct. 3-6.

The U.S. Army Corps of Engineers, St. Paul District dropped the navigation pool 12 feet on the Mississippi River between Upper St. Anthony Falls and Lower St. Anthony Falls Lock and Dam for a periodic inspection.

It was great to see so many people come out to look at the river in its drawn-down condition,” said Nan Bischoff, project manager. “People were interested to see the exposed riverbanks, bridge foundations and shoals.”

The purpose of the inspection was to safely inspect facilities that are normally underwater. Corps engineers focused on a detailed examination of the dam’s concrete, mechanics and overall structure. The last periodic inspection at this site occurred in 2015.

“The drawdown is a rare event that provides inspectors and maintenance staff an opportunity to see below water features,” said Doug Crum, dam safety project manager. “The drawdown was initiated for inspection of the Corps facilities that are under consideration for property transfer with an ongoing disposition study.”

Partnerships

During the three-day drawdown, the district worked hand-in-hand with its partners to inspect their facilities.

Representatives from the City of Minneapolis were given a back-stage tour to increase their awareness of how the Upper St. Anthony Falls project functions and what’s involved in future maintenance should they agree to become the site owner, Bischoff explained.

“It’s important to know how the intermediate pool levels affect not only the Corps structures, but also those of Xcel Energy, the University of Minnesota, Brookfield Power and the City of Minneapolis,” she said.

Facility owners with infrastructure along the intermediate pool such as the University of Minnesota’s St. Anthony Falls laboratory depend on the river to conduct research and power companies

Xcel Energy and Brookfield depend on it for hydroelectric power. Xcel Energy’s Hennepin Island plant has operated since 1908 and Brookfield’s plant, located in the auxiliary lock chamber at the lower dam, has operated since 2011.

Using drone technology, Barr Engineering took advantage of performing inspections of the mill race canal, Bassett Creek Tunnel’s outlet structure, the University of Minnesota’s steam plant, and the Lower St. Anthony Falls earth embankment. Collins Engineering and LBH, Inc., also used drones to inspect the Stone Arch Bridge for the Minnesota Department of Transportation.

The drawdown event was scheduled in fall when the river flows are typically lower than in spring/summer months and the weather is more desirable than winter months, Crum explained.

“The sunny, 70 degree forecast was the perfect condition for the periodic inspection,” he said. “Water Control Corporation hosted informative conference calls with interested stakeholders and provided adjacent property owners a chance to survey their river fronts and infrastructure.”
The rich development history of the falls dates back to the 1840s.

Brad Perkl, archaeologist, explained to guests that the falls are the birthplace of Minneapolis and are an important place for Minnesota’s native american communities. The falls were first observed by Father Louis Hennepin in 1680, about 1,000 feet downstream from where they were stabilized in 1887 (at their present location). Geologists have traced the falls migration at least from the confluence with the Minnesota River at St. Paul.

“My job is to protect these resources and document history,” Perkl said.

During the event, the Corps also partnered with the National Park Service and Minnesota Department of Natural Resources to have biologists in the area to help rescue any fish and/or mussels impacted by the drawdown.
National Park Service rangers led visitors onto the lock walls and described how the falls changed the course of history in the area and of the nation.

“What a beautiful day to experience the surrounding mill district,” said a mom and her daughter at the completion of their visit. “It was interesting to read and learn about the history.”

The Corps of Engineers’ dam safety program is focused on ensuring projects deliver intended benefits while reducing risks to people, property and the environment.

• Date Taken: 10.06.2020
• Date Posted: 12.23.2020 08:53
• Story ID: 385686
• Location: MINNEAPOLIS, MN, US