FARGO — Machines are moving earth and driving piles to prepare the ground for what will become a gated concrete structure that will divert water during extreme floods into a diversion channel that will skirt the western metro area.
The Red River inlet, which is being built on a 90-acre site south of Horace, N.D., near the junction of Cass County roads 16 and 17, will be one of three gated structures along a 20-mile embankment that hold water back for the $2.75 billion Fargo-Moorhead diversion.
The inlet’s three steel gates will control the flow of water into a 30-mile diversion channel that will reduce Red River flows through Fargo-Moorhead during extreme floods. Engineers estimate that the diversion will operate, on average, once every 20 years.
“This is essentially the gateway to the diversion channel,” said Terry Williams, an engineer and program manager for the U.S. Army Corps of Engineers, which designed the project and is overseeing its construction.
Work on the $46 million inlet structure started in the spring of 2017 but was halted months later by a federal judge. Construction resumed last year with the judge’s permission while a lawsuit remains pending against the diversion project by upstream opponents in North Dakota’s Richland County and Minnesota’s Wilkin County.
“In a month or two, we’ll have the first concrete pour for the site,” Williams said. “A lot of people are excited to see that first concrete show up.”
Crews will pour 35,000 tons of concrete to form the Red River inlet, including a foundation slab that will be 7 or 8 feet thick, to house the three 50-foot-long control gates.
Ground work also started on another significant feature for the project, the $59 million Wild Rice control structure, located on a 200-acre site south of St. Benedict Church of Wild Rice, also located south of Horace.
“They have done a lot of site prep to date,” Williams said. “They’re excavating where the control structure is going to sit.”
The Wild Rice control structure will require 42,000 tons of concrete for its two 40-foot-long control gates.
Between the two projects, the Corps has approval to carry out $100 million of construction this year on the diversion project. Ames Construction of Burnsville, Minn., is the contractor for both the inlet structure and Wild Rice control structure.
A third gated structure, the Red River control structure, still is being designed. It will be the largest of the three dams along the earthen embankment, which will have an average height of 20 feet as it snakes across the prairie.
“It’s not really as tall as what people might think,” Williams said of the embankment, which she said will resemble the turf-covered levees along the Red River in downtown Fargo.
The diversion’s dams and embankment are designed to withstand the probable maximum flood — a monstrous deluge that would surpass even what the Corps considers the 500-year flood.
In the event of a 100-year flood, 41.3 feet, the inlet and control structures will allow a 37-foot river to flow through Fargo-Moorhead, which permanent levees and floodwalls will handle.
The diversion is designed to allow Fargo-Moorhead to fend off a 100-year flood, which would allow a 40-foot river to pass through the cities, with minimal temporary measures.
If confronted by a 500-year flood, the diversion is intended to enable the cities to deploy emergency measures, such as temporary levees and sandbag barriers, to stay dry.
The biggest flood on record was in 2009, when the Red River crested at 40.84 feet — a flood that, although successfully defended, brought Fargo-Moorhead close to catastrophe and galvanized support for the diversion project.
Next year, the Corps is planning another $50 million to $100 million in construction work on the diversion, followed by another $200 million in 2022, including starting work on the Red River control structure.
The diversion is the largest project the St. Paul District of the Army Corps of Engineers has built since building a series of projects to enable barge navigation on the Mississippi River, Williams said.
“I think you’d have to go back to when we built the locks and dams to find something comparable,” work that was done in the 1920s or '30s, she said.
Altogether, the Corps’ share of the project totals $750 million, including construction of the embankment and three control structures.
“The Diversion Authority is extremely pleased at the progress being made by the Corps of Engineers at the inlet structure and Wild Rice structure,” said Joel Paulsen, the Diversion Authority’s executive director.
This winter, bids will be sought to raise a section of Interstate 29 about 5 feet in an area where water will be temporarily pooled when the diversion operates. Work on the road project will be done the following year, he said.
Bids also will be sought for the first section of the embankment, a portion in North Dakota called the western tieback that will tie into high ground near Horace, Paulsen said.
And, if all goes as planned, work will begin next spring on the diversion channel, he said, a project that will be jointly carried out by the Diversion Authority and a consortium of private companies under an arrangement called a public-private partnership.
“Things are moving along as scheduled on that as well,” Paulsen said.
That timetable assumes that a crucial permit for the project issued by the Minnesota Department of Natural Resources will be upheld, although possibly modified, following a pending administrative appeal.
Finance proposals for the diversion channel, which will determine the cost of that portion of the project, are due Dec. 11. At that point, the precise cost of the project should be known.
“That’s going to be a pretty big milestone,” Paulsen said.
The Corps’ work on the diversion, including design of the Red River structure, has been on schedule despite the disruptions caused by the coronavirus pandemic, Williams said.
Engineers and other staff have, with a little ingenuity, found ways to work collaboratively from home, she said.
“Our teams have figured it out and kept on schedule,” Williams said. “Everybody’s been teleworking and working virtually.”
If the schedule holds, she said, the diversion will be able to go into operation by the spring of 2027.
Once complete, the diversion would mean that a 100-year flood, with a crest of 41.3 feet, would be held to an easily managed 37 feet as the Red River flows through Fargo.
A 500-year flood, or 44.6 feet with emergency measures in place, could be held to 40 feet, a little less than the 2009 record flood.