FARGO — Engineers are at work inside a cavernous building observing how water moves through a wooden model — a miniature of a structure that will control Red River flows as part of the mammoth Fargo-Moorhead flood diversion project.
The scale model, housed in a building that resembles an aircraft hangar, resides at a U.S. Army Corps of Engineers research center in Vicksburg, Miss., where technicians specialize in building models so engineers can refine dam designs.
The model of the Red River structure covers an area about 60 feet wide and 100 feet long, simulating an area about half a mile wide and two-thirds of a mile long, at a scale of 1 to 40.
Building a miniature of the structure — the real version will stand almost 80 feet tall — helps engineers to better understand how water will flow in, around and through the gated structure.
Engineers can stare at their computer screens all day, but a model helps them study design tweaks in tangible ways, said Kevin Denn, a hydraulic engineer for the Corps.
“Working with a physical model — that is probably one of the most fun things a hydraulic engineer will get to do in their career,” he said. “There’s no replacement for getting to see and feel that. That’s exciting.”
The Red River structure will be one of three dams along a 21-mile embankment that will control the Red River during extreme floods, diverting some of the flows through a 30-mile channel that will bypass the western metro area.
The dams and embankment will temporarily impound water in an upstream area south of Fargo-Moorhead to minimize impacts downstream. Engineers expect the diversion to operate an average of once every 20 years when the flood stage is 37 feet or higher.
The Red River structure will have a capacity that is more than twice that of the other two control structures, an inlet for the diversion channel and a Wild Rice River control structure.
Corps engineers have been testing the Red River structure model since November and have several more months of experimenting ahead.
“We’ve definitely learned some things that are useful to us in the design effort,” Denn said. “There’s really no replacement for being able to stick your hand in the water and feel how fast it’s moving,” he said.
For example, the model can help engineers determine if a portion of the dam should be longer or shorter, or where to place rocks downstream to prevent erosion.
Engineers have used physical models to guide their designs long before computer modeling became a tool.
“We’re not doing anything that’s necessarily new here,” Denn said. The technicians at the testing center in Mississippi have played a role in designing dams all over the country and even the world.
“They have this expertise that spans decades and generations even,” he said.
It cost $700,000 to build the Red River control structure model. Added costs from alternative testing, requiring further engineering and building time as well as materials, brought the anticipated total to $1.3 million, Denn said.
The model also will be used for demonstrations of how the control structure will work to partners, including the Metro Flood Diversion Authority and Minnesota Department of Natural Resources, he said.
Earlier, Corps engineers worked with technicians at the University of Minnesota on a model to test another diversion feature, an aqueduct that will span the Maple River, to minimize formations of ice jams.
The miniature fails to hint at the dimensions of the Red River control structure, which will approach 80 feet in height.
“The scale and size of these structures, from an engineering perspective at least, is impressive,” Denn said. Because part of the structure will be beneath the ground — or underwater, when operating — the scale will be deceptive. “It’ll be tough to comprehend the magnitude of it.”
Design work on the diversion project, which followed a 2008 feasibility study, began in 2010.
“It’s been a long journey to get to this point,” Denn said.
Model testing is expected to conclude this summer. Design completion for the Red River structure is expected in the late summer or fall of 2021. The goal of officials is to have the $2.75 billion project completed by 2026.