Maintaining elevation of Upper Mississippi River a well-orchestrated effort

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During the high water of a few weeks ago, the five roller gates at Lock and Dam 9 were out of the water as were the eight tainter gates. The gates at all of the dams the United States Corps of Engineers uses to maintain the flow of the Mississippi River in the St. Paul District were wide open. When standing directly above the gates, one can truly appreciate the huge amount of force the river can have. (Photos by Ted Pennekamp)

The tainter gates at Lock and Dam 9 look similar to the roller gates but are much smaller.

By Ted Pennekamp

 

Maintaining the flow of the Upper Mississippi River through the lock and dam system in order to maintain a nine-foot-deep channel for barge navigation can be quite complex.

The St. Paul District of the Corps of Engineers uses a hinge-point system to control the water levels, said Daniel Fasching, the primary Mississippi River regulator for the St. Paul District.

Fasching explained that the Corps of Engineers in working with the lock masters at each lock and dam use what is known as river elevation rather than the term river stage which is more commonly known to most people. Elevation is based upon mean sea level. River stages, such as the river stage at McGregor, for example, are just local values so that local citizens know what a certain river stage means and how it affects their area. 

“We need to look at the big picture, the overall flow,” said Fasching. “We can’t rely on local stages. “We need to maintain elevation thresholds in order to keep a nine-foot depth.”

In addition to maintaining a nine-foot depth for the barges, Fasching said that a balanced flow at each dam must also be maintained regarding the force of the water. “We need to prevent an unbalanced force that could damage the dam,” he said.

With a rising river, the gates at every dam also need to be raised accordingly, said Fasching. With a receding river, the gates can be lowered as dictated by the flow.

In recent weeks, the river was high and there was minor flooding in the Prairie du Chien area and other parts of Pool 10. During this high water time, Fasching said that all gates at the 10 lower dams in the St. Paul District were wide open in order to let as much water through as possible. 

Contrary to popular belief, the Corps of Engineers does not have Dam 10 at Guttenburg, for example, lower their gates to hold water back during high water events in order to protect Pool 11 at the expense of Pool 10.

“That is one of our biggest misconceptions,” said George Stringham, the public affairs specialist with the St. Paul District of the Corps of Engineers. “We simply don’t have that much control. When the river is up, we want to evacuate as much water as we can.”

Stringham said if a dam were to attempt to hold water back during times of overly high water, the dam would be damaged and the force of the water would cause huge eddies under the dam which would cause vast scour holes. “It would take a lot of money to repair the dam and to fill those holes,” he said. In addition to damaging the dam, the upstream pool would flood massively.

When the flow goes beyond 64,000 cubic feet per second at Lock and Dam 9, for example, all of its five roller gates and eight tainter gates must be out of the water.

“When we can’t control the water level, we have what we call open river conditions,” said Fasching. “There is simply too much water and we have to open all gates and let the river do its own thing.”

The hinge point system of controlling the river elevation includes a primary point and a secondary point. The primary point for Pool 9, which is above Lock and Dam 9, is at Lansing. The secondary point is Lock and Dam 9.

There are 13 dams in the St. Paul District. The upper three are regulated by hydro-electric power. Nine dams are regulated by the hinge point system. Lock and Dam 7 is regulated by the secondary control point only.

All pools have a slant to them from upstream to downstream. When the river rises, it has more of a slant. When it has lower flow, it is flatter.

Orders given by Fasching are what the lock and dam operators hold at the pool gauge at their dam in order to maintain either primary control or secondary control. Water surface elevations held at the locks and dams are flow dependent and can range anywhere between the primary control point elevation and the secondary control point elevation.

When the flow in Pool 9 is less than 33,000 cubic feet per second, the hold elevation at the primary control point at Lansing is 620 feet (plus or minus .2 inches during the navigation season. Plus or minus .3 inches during the non-navigation season). When the flow is between 33,000 and 64,000, the hold elevation is 619 feet at the secondary control point at Lock and Dam 9. When the flow becomes greater than 64,000 cubic feet per second, the river is out of control and all gates are wide open.

“Pool 9 is the biggest pool acreage wise in the St. Paul District,” said recently retired Lock and Dam 9 Lock Master Darrel Oldenburg. “We are normally one of the first to take our gates out of the water during high water events.”

Fasching said that he gives orders to each lock master before 8 a.m. each morning. Fasching’s orders are based upon many factors and the discharge at each dam in turn affects those downstream. With a moderate flow, it will take between 16 and 20 hours to go from Dam 8 to Dam 9. It will take between 8 and 12 hours to go from Dam 9 to Dam 10. 

A change in flow of 1,600 cubic feet per second for 24 hours will change the elevation of Pool 9 by .1 feet. The gates at the dams are usually changed once per day. With higher flows, more regulation is needed.

Fasching must take into account the whole Upper Mississippi River Basin when giving orders, including rain fall totals above all of the pools, the river levels of all tributaries, snow pack, snowfall totals,  wind, water on the ground and gate balance. Wind can change a pool by .1 foot per 10 mph.

Timing is also critical to his calculations. If the Upper Iowa River receives five inches of rain, for example, that can significantly increase the flow for Pool 9 of the Mississippi River, perhaps by as much as 10,000 cubic feet per second depending upon conditions.

A somewhat unpredictable factor for Pool 10 is the fact that the Wisconsin River has several dams that are privately owned by hydro-electric power companies. These dams will sometimes discharge a significant amount of water in a relatively short time frame to suit their needs. 

When the Mississippi River is running low, the dams on it will hold the river back in order to maintain the navigational channel. 

“But, when there is a low flow, we can’t hog all of the water to fit our needs,” said Fasching, who noted that the St. Paul District works in collaboration with the Rock Island District downstream. 

“We pass a lot of information back and forth,” said Fasching. “There are all kinds of factors that play into this. We gather as much data as we can.”

In addition to data gathering and mathematical calculations by the Corps of Engineers, Fasching said that the lock masters at each dam can also use their knowledge and years of experience to change orders if necessary. Lock and dam operators can make up to a 20 percent change in flow during off hours without orders.

“It’s a big team effort, a well orchestrated effort, between the engineers and the guys at the dams,” Fasching said.

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