Spring Flooding Could Swell North Dakota Lake by 50 Square Miles

The cost of flood control in North Dakota’s Devils Lake region has surpassed $1 billion, but the worst could be yet to come this spring if forecast predictions of rises in the lake’s level prove accurate, cautions Paul Todhunter, University of North Dakota professor of geography.

“We’re at a point in the lake level’s rise where the rate of change is dramatic,” he explains. “As bad as things have been, we’re transitioning into a period where there will be greater expansion of the lake’s area for each foot of rise in its level.”

Located in northeastern North Dakota next to the city of Devils Lake, the lake’s level has risen more than 29 feet since a regional wet cycle began in 1993, causing millions of dollars in damage by inundating communities, farms, homes and recreation facilities. Eighteen years ago, Devils Lake covered approximately 70 square miles. During that period, the average increase of area covered was less than 11 square miles per year.

However, Todhunter says the forecast three-foot rise in Devils Lake caused by runoff from heavy snow in the area this winter could increase the lake’s size by more than 50 square miles in a single year.

Comparing the glacially formed Devils Lake Basin’s shape to a bowl, Todhunter explains, “We’ve been filling the deeper part of the bowl. Now we’re moving from that area to the flatter areas. Instead of a bowl-shaped area, we’re filling a platter-shaped area. It’s a more gradual depression that causes the water to spread out more.”

Todhunter warns that Devils Lake has reached a point at which any additional increase in its level will likely result in an exponential increase in the area it covers. He refers to a graph based on U.S. Geological Survey data showing the amount of acreage Devils Lake covers in relation to its elevation above sea level.

From its lowest recorded level of 1,402 feet in 1940 to its current level of near 1,452 feet, the area covered by water is represented by a gradually rising curve. But past the current level, the line’s slope increases sharply, indicating that every increase in the lake’s level will cause it to spread out more.

Todhunter studies natural hazards related to climatology and hydrology. He’s been interested in Devils Lake since it began to rise in 1993, and has conducted research, presented papers and taught courses on the subject. He says Devils Lake in northeastern North Dakota is unusual because it’s a terminal lake, a unique flood hazard in the United States.

Terminal lakes exist in closed drainage basins. While water from rain and melting snow can flow into them, there is normally no natural outlet for water to escape. Like a bathtub that eventually runs over when the water is left running, Devils Lake will naturally overflow into the Red River Drainage Basin when it reaches 1,458 feet above sea level. This has not occurred in recorded history, although there is evidence that it has happened at least twice in the last 10,000 years.

“The basic fact of terminal lakes is that water can only be removed from them by evaporation, which varies relatively little from one year to the next – especially in North Dakota where summers are short,” Todhunter says. “When the water level goes up sharply, it can only be brought down slowly.”

The geologic record of Devils Lake shows that it has never remained at a stable level; it is either rising or falling. During the 1980s and early 90s, falling lake levels were the greatest concern to area residents.

“The wet cycle we have been in not only adds water directly onto Devils Lake by precipitation, but it also increases surface runoff into the lake from streams feeding into it,” Todhunter says. “This surface inflow is the largest source of water input to the lake and is highly variable from year to year.

“Some years, little or no surface runoff occurs, while the water is now gushing into the lake,” he continues. “This means that without artificial removal such as an outlet, it will be some time before the lake levels drop to a less threatening level.”

Although the state of North Dakota has operated an outlet on the west end of Devils Lake since 2005, it has not significantly reduced the lake’s level. Plans are being made to increase its capacity and add another outlet on the lake’s east end. The goal is to prevent an uncontrolled release of water from Devils Lake that would not only cause flooding along the Sheyenne and Red Rivers, but also cause water quality problems.

“They’ve moved a lot more aggressively in the last couple years because the forecast that people said wouldn’t occur is looking a lot more probable,” Todhunter says.

Source: Newswise, University of North Dakota