Engineers weren’t thinking of flood control when they dammed the Sheyenne north of Valley City
VALLEY CITY, N.D. – Years of severe flooding in the lower Sheyenne River Valley has made the true purpose of Baldhill Dam somewhat of an afterthought these days.
After all, when communities downstream are faced with record flood upon record flood, no one seems to be very concerned about a lack of water.
But when Baldhill Dam was constructed in 1944, the authorized purpose for the project was all about water supply. At that time, residents in eastern North Dakota had more reasons to fear long-term drought than consistent flooding.
Only a fraction of Baldhill Dam’s original purpose was meant to alleviate flood threats downstream on the Sheyenne River.
Now, in the midst of a 20-year wet cycle that rages on, the function of Baldhill Dam has shifted more toward protection than supply, but its authorized purpose remains in place.
For Operations Supervisor Rich Schueneman and other Army Corps of Engineers staff at Baldhill Dam, they have no choice but to do things by the book.
At capacity, Baldhill Dam can hold back up to 100,000 acre-feet of water in picturesque Lake Ashtabula, more than 10 miles north of Valley City.
The man-made lake functions as a reservoir, about 27 miles long and tucked away in the hills and valleys that sometimes mask the Sheyenne River.
The Flood Control Act of 1944 authorized construction of Baldhill Dam as a way to ease concerns about a limited water supply for blossoming cities in eastern North Dakota, like Fargo and Grand Forks.
As a tributary to the Red River, the Sheyenne provides convenient access to a regional water supply.
Lake Ashtabula and the control structures at Baldhill Dam ensure that at least some water will always be available if the cities should call upon it.
Operations at Baldhill Dam, as with other federally managed dams, are governed by a water control manual, comprised of several hundred pages of procedures and protocol that corps staff are mandated to follow.
The manual also dictates the priorities for which Baldhill Dam was constructed, Schueneman said.
Of the dam’s total purpose:
– 38 percent is to provide municipal water supply for cities, like Fargo, Grand Forks, Valley City, West Fargo and Lisbon.
– 31 percent is for rural water supply.
– 23 percent is for municipal pollution abatement to help flush out the riverbed when needed.
– Lastly, just 8 percent is for flood control.
“We operate projects according to their authorized purposes,” Schueneman said. “(People) assume that this project is strictly flood control. It’s not.”
Nonetheless, the heightened need for flood protection in recent years prompted the corps to increase the available level in the reservoir by 5 feet in 2004.
That alone roughly doubled the available amount of water storage that could be used specifically for flood control, from 35,000 acre-feet up to 70,000 acre-feet.
To balance the need for flood control with the requirements to maintain a supply of water, Schueneman said the corps’ operations manual dictates what levels Lake Ashtabula should be at throughout a given year.
The authorized levels range from a base elevation of 1,257 feet up to a maximum of 1,271 feet. Above that height, an uncontrolled overflow out of the reservoir would occur.
“Because this project was originally made to be a water supply project, we have to maintain a conservation pool level in the summer,” Schueneman explained. “You need to be able to supply that water at any time.”
To that end, Schueneman said he’s required to keep Lake Ashtabula at an elevation level of 1,266 feet throughout the summer after the spring melt ends.
“We’d have this water here, and we could release it if communities needed it,” he said.
Every Oct. 1, the corps begins to draw down the reservoir in preparation for winter and the following spring’s melt.
The goal is to reduce the water level to 1,262.5 feet, providing about 3.5 feet of extra freeboard by March, Schueneman said.
The corps will release water through Baldhill Dam at levels deemed appropriate to both draw down the reservoir but not unnecessarily inundate downstream communities, he said.
The corps can adjust releases from Baldhill Dam, depending on the moisture levels in the snowpack, Schueneman said.
In cooperation with the National Weather Service and the U.S. Geological Survey, the corps takes snow surveys during the winter months to gauge how much moisture they might be dealing with come spring, he said.
For instance, if there are 2 to 3 inches of water in the snowpack, procedures allow the corps to reduce the lake level to the authorized minimum of 1,257 feet.
“We can’t go lower because, according to the plan, we’re not allowed to go lower than that,” Schueneman said. “If we want to go lower than that, we need to seek a deviation from our division office (in Mississippi).”
Coincidentally, that’s exactly what the near-record flood of 2011 required.
A moisture-filled snowpack plus heavy spring rains led to a significant flood threat along the Sheyenne River Valley last spring.
For the first time in the project’s 60-year history, officials at Baldhill Dam received approval to deviate from their authorized operating manual so they could lower Lake Ashtabula beyond the approved minimum and attempt to compensate for the expected flood threat.
Schueneman said officials sought to draw down the reservoir an additional 2 feet – down to 1,255 feet – but the spring melt began only halfway through the process.
Because of the V-shaped features of Lake Ashtabula, the simple laws of science mean: The lower the water level, the less storage is gained from reducing that water level further.
The benefit of drawing down the water by an extra foot equated to reducing the flood stage in Valley City by one-tenth of a foot.
The Sheyenne River crested in Valley City on April 14, 2011, at 20.55 feet, dangerously shy of the 2009 historic record of 20.69 feet.
As the flood threat struck Valley City last spring and again in a rare summer event in August, officials at the Army Corps of Engineers came under fire.
Residents questioned why the corps wasn’t drawing down Lake Ashtabula sooner during the winter of 2010-11 and why the releases weren’t greater to prevent the surprise of a tough flood flight.
The answers lie in the corps’ own operating manual, which officials cannot deviate from without rare exception.
Schueneman said managing the dam remains a constant challenge for the corps.
Inflows into Lake Ashtabula from drainage in the upper Sheyenne Valley help determine how much the corps should release through the dam and how much storage could be used up in the reservoir instead.
Corps officials also factor in preparation efforts downstream and whether communities, like nearby Valley City, have time to put sandbag dikes and levees in place before the floodwaters arrive.
Under normal circumstances, Schueneman said, it takes as little as 12 hours for waters to reach Valley City from Baldhill Dam.
Help or hurt
Dams don’t guarantee absolute flood protection for downstream communities, as the flood fights in 2011 showed in Valley City, Bismarck and Minot.
But the control structures can help ease the blow of the floodwaters by taking some of the edge off.
Take the situation at Lake Ashtabula last spring.
“We had over 10,000 cubic feet per second coming into the lake that would’ve otherwise gone downstream through Valley City through Lisbon and all the way down,” Schueneman said. “We were able to reduce that to 7,000 cfs.
“Would Valley City have been able to prepare if the dam isn’t there to take the peak off those inflows and reduce them?” Schueneman said, adding: “People have to judge that themselves.”
Kristen Daum reports for The Forum of Fargo-Moorhead.