Devils Lake issues remain
Richard Betting, Valley City
“Lake Ashtabula full. Baldhill Dam under water.”
If that were the newspaper headline yesterday, people downstream on the Sheyenne would probably already have suffered a 1,000-year flood event. They would also be worried about other floods to follow. But since Devils Lake fell three feet last year, probably won’t rise much higher than that this year, and the Tolna Coulee might not overflow and erode, people downstream don’t appear to be too worried.
They should be. Here’s why.
You remember that last year the U.S. Army Corps of Engineers built the Tolna Coulee Control Structure to prevent Devils Lake from overflowing “catastrophically,” they said. That was predicted to happen after the next big rain event.
When Devils Lake rises and overflows, the Corps claims that the Tolna Coulee could erode, even though studies show the coulee has never eroded before. The control structure is the problem.
The Corps/State Water Commission Control Structure is 120 feet long and 12 feet tall, about the size of some of the bridges in Valley City. You can visualize how much water flowed through the city and those bridges in 2009 and 2011.
So in the future when Devils Lake rises and overflows through the Tolna Coulee control structure, here’s what will happen.
According to the U.S. Army Corps of Engineers’ operating plan for the control structure, as the coulee erodes, the “logs” in the structure will be removed one at a time to encourage more erosion. Erosion of the Tolna Coulee will be encouraged to continue until Devils Lake falls to the elevation of 1,446 feet msl. At that point both Stump Lake and Devils Lake will be at the same elevation, and all of the water above that level would have flowed into the Sheyenne River.
In other words, all of the water in Devils Lake above 1,446 feet msl-about 1,200,000 acre feet, or twice as much as entered Devils Lake from the upper basin in either 2009 and 2011-will have flowed through the Tolna Coulee and down the Sheyenne. It would take 200 days at a flow of 3,000 cfs to remove that much water from the lake. You can imagine what that would do downstream along the Sheyenne, since it would be added to what would already be in the river.
The immediate problem would be that when Devils Lake rises to the elevation of 1,458 feet above mean sea level and the Tolna Coulee erodes 12 feet, down to the elevation of 1,446 feet msl, the control structure will not be rebuilt, Corps rules state.
It would be similar to water in Lake Ashtabula rising and overtopping Baldhill Dam. The water formerly held in the lake would flow immediately through and into the Sheyenne River. There would be no stopping the flow, no control.
The same thing would be true of the Tolna Coulee control structure. The Corps’ operating plan for the Tolna Coulee states: “Once stop logs are removed from the structure to allow discharge, they will not be replaced for the purpose of holding water in Stump Lake.”
After erosion to an elevation of 1,446 feet msl, both Stump Lake and Devils Lake will be at the same elevation. And all of the water that flows into Devils Lake after that will flow immediately into Stump Lake. Then on into the Sheyenne. Neither Devils Lake nor Stump Lake would hold water back as neither would be a reservoir above the elevation of 1,446. The so-called “control structure” would be an empty skeleton.
Devils Lake’s elevation would have been effectively reduced by twelve feet. Its capacity would have been reduced by over 1,200,000 cubic feet of water. After the erosion of the Tolna Coulee, all of the water above an elevation of 1,446 would flow into the Sheyenne continually. For comparison, that much water would fill Lake Ashtabula about 15 times.
The most significant effect of the Tolna Coulee operating plan will be that the Sheyenne River will have become a drainage ditch for all of Devils Lake and all of the 3,810 square miles of the upper basin of Devils Lake.
As written, the plan will create a disaster downstream. People living along the Sheyenne who will be affected by the Tolna Coulee drainage ditch plan should ask both Gov. Jack Dalrymple and the Corps to revise the operating plan now, before Tolna Coulee erosion occurs. Now, before Devils Lake rises again and common sense and science are again ignored.