Extremely high winter river flow ‘a real concern’

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By Ted Pennekamp

 

The U.S. Army Corps of Engineers, St. Paul District, is monitoring high water conditions affecting parts of the Upper Mississippi River in Minnesota, Wisconsin and Iowa as a result of historic flows this winter. 

The Corps urges the public to remain vigilant for river flooding. Cities from Winona, Minn., to Guttenberg, Iowa, have an increased chance of localized flooding due to ice dams. 

The high water conditions were created by a combination of ice dams and historic high flows. The current river flows are at levels normally observed in late spring. Irregular temperatures have also prevented ice from forming in a stable way, which compounds the ice dam problem. The ice has blocked the river’s normal flow and forced water out of its banks. It has also reduced Corps water managers’ abilities to actively manage the river water elevations.

“We have never in our record had these sustained high flows over the month of January,” said Dan Fasching, St. Paul District Water Manager for the Upper Mississippi River.

Depending on temperatures and the rate of ice melt, Fasching said there could be more high water in the weeks and months ahead. He added that the Corps is working closely with the National Weather Service and the U.S. Geological Survey to share information relevant to potential flood risk and will continue to monitor high water conditions on the Upper Mississippi River.

“With relatively mild temperatures, the ice never got a chance to form its crust,” said Fasching, who noted there have been some periods when there were cold temperatures for a few days followed by mild temperatures again for several days. “With the fluctuating cold and mild, cold and mild, the river became an ice making machine.”

The result has been huge ice dams in all pools of the Upper Mississippi River. The biggest are in pools 6 and 10. Fasching said the ice dams have added to a unique situation because the water takes a lot longer to get around the ice dams, which forces the river levels in the pools below each dam to continue to elevate. 

“The ice dams have taken away the ability for the locks and dams to control the river flow at all,” said Fasching, who noted that all gates at all of the dams in the Upper Mississippi River have been wide open and will remain so for the foreseeable future. 

“The ice dams are not letting the water go through the pools like normal,” said Fasching. “It makes it extra challenging. We (the lock and dam system) just need to get out of the way. The spring melt is a real concern.” 

The high water in the Upper Mississippi River is also the result of extremely high flows for this time of year. In fact, the Corps of Engineers has never seen a situation like this in the winter whereby extremely high flows combined with temperature swings and large ice dams are producing high water above and below each dam, said Fasching.

“Because the water isn’t moving through each pool like it normally does, the water elevation below each dam ‘tailwater’ rises. At the same time the ‘head,’ the water above the dam, also rises to the point at which it breaks the threshold at which the gates have to be wide open to let more water through.

Where is all of the high flow coming from? Fasching pointed out that 2019 was the wettest year on record for the Upper Midwest. There is a high flow of water coming from the ground. Also, there were heavy rains on New Year’s Eve in Minneapolis and areas north of there. The flow from the New Year’s rain has finally reached Pool 10. All of the combined factors have resulted in a very high base flow.

Lake Superior and the rest of the Great Lakes also remain very high. Lake Superior doesn’t affect the flow of the Mississippi River, but the high lake levels are just another indicator of how wet 2019 was.

In fact, Fasching noted that the volume of water that flowed through Pool 10 in 2019 shattered the all time record. For the year, 77.9 million acre feet of water flowed through Pool 10. 

The former record was 59 million acre feet in 1993. These records have been kept since 1965. The average volume since 1965 is 38 million acre feet.

Fasching said 77.9 million acre feet is enough to fill Mille Lacs Lake, a large lake in Minnesota, more than 28 times.

The U.S. Army Corps of Engineers, along with everyone else, is hoping that there is a gradual spring thaw.

As of Jan. 28, the river stage at the McGregor gauge was 13.6 feet and expected to drop slowly. The threshold at which all gates at Dam 9 near Lynxville need to be wide open is 63,000 cubic feet per second (cfs). The threshold at Lock and Dam 10 is 73,000 cfs. On Jan. 28, the flow at Lock and Dam 9 was estimated at 67,000 cfs. At Lock and Dam 10 it was estimated at 78,000 cfs.

An unusual problem, said Fasching, is because of ice jams in Pool 10, there are flows of 104,000 cfs within Pool 10. 

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