Aqueducts are a rare feature in northern climates because they can freeze. Engineers working on the Fargo-Moorhead flood diversion project solved this issue by tapping into geothermal energy, a cost effective solution for the remote location.
This article is from the Inforum.
By Patrick Springer
FARGO — One of the most complex challenges engineers had to overcome in designing the Fargo-Moorhead flood diversion project is how to enable the Sheyenne and Maple rivers to cross the channel that will bypass the metro area.
The obvious is to build a pair of aqueducts, elevated structures that might be thought of as bridges to carry water.
But the engineers had to solve some problems, including how to prevent the water from freezing in frigid winter temperatures and how to avoid adverse impacts to fish, an environmental requirement.
Aqueducts are nothing new. They’ve been used for thousands of years, and date back to ancient Rome.
The solution the engineers found to avoid the buildup of ice in the aqueducts: geothermal energy, a source that taps heat from underground.
The aqueducts were designed and will be built by the Red River Valley Alliance, the international consortium of private construction companies that is in partnership with the Metro Flood Diversion Authority.
Because of the challenges in preventing freezing, aqueducts are rare in northern climates. In fact, as far as diversion officials are aware, the two aqueducts could be the northernmost anywhere.
“They will be, as far as I know, the only heated aqueducts structures in the world,” said Joel Paulsen, executive director of the Diversion Authority.
“There’s nothing like this in the region,” although there are similar aqueducts in the Netherlands, he said. “Nothing in North America that I’m aware of of this magnitude.”
The aqueducts were designed with longevity in mind. “These structures will never go away,” Paulsen said, adding their lifespan would be about 100 years, when replacements would be needed.
Engineers for the Red River Valley Alliance determined that geothermal energy was the most cost-effective heating source, given the remote locations for the aqueducts.
Electricity will be required to pump heated water from underground to the surface. But the natural heat from the earth will do the rest of the work. Tubes will be embedded within concrete poured to build the aqueducts to carry the heated water.
The estimated cost for the two aqueducts is $15 million, less than the $20 million budgeted, Paulsen said.
Environmental regulations require that the aqueducts not cause any adverse effects for fish, posing several design challenges. “We have to mitigate everything we do,” he said.
“We always knew there would be issues with fish passage on the aqueducts,” Paulsen added.
Site preparation for the Maple River aqueduct is getting started, with preparations for the Sheyenne River aqueduct to follow later this year.
Among other touches, rocks will be anchored to the channel. “It won’t just be a concrete flume,” Paulsen said, referring to the aqueducts.
On the Sheyenne, 2 miles upstream from the aqueduct, engineers have designed a mitigation project that will widen the river channel and create “benches” where fish can linger in areas with slower river flows.
The bench areas would include “woody structures” and shrubs to create habitat for fish and to slow the velocity of the water during floods.
The mitigation area for the Sheyenne falls outside the project’s footprint, so land rights will have to be acquired, Paulsen said. Diversion officials have met with landowners on both sides of the river in the mitigation area.
“Some of them were not very happy about this at all,” he said. Officials are working to achieve the “least impactful option,” and the land acquisition process has begun, Paulsen said. “A few hundred acres at the most” will be needed.
Mitigation for the Maple falls within the project area, so no additional land is required.
Fish species in the Sheyenne include northern pike, walleye, yellow perch, channel catfish and white bass. Maple River fish species include channel catfish, walleye, carp, yellow perch, northern pike and yellow bullhead.
“We actually are making it probably better for the fish than existing conditions,” Paulsen said.
The plans have been reviewed by the U.S. Army Corps of Engineers, North Dakota Game and Fish Department and the Minnesota Department of Natural Resources.
Design of the aqueducts required extensive computer modeling to calculate river flows as they enter, pass through and exit the structures — challenges that project officials have discussed for a decade, Paulsen said.
“Nobody really knew how to do it,” until extensive design work and computer modeling was completed, he said.
The 7.4-mile Sheyenne Diversion, completed in 1992, will be modified to increase fish passage during floods, Paulsen said.
During floods, water that can’t be accommodated by the aqueducts will flow into the diversion channel via spillways, part of the project's "passive" flood control features .
As a result, areas near both rivers will have 100- to 500-year flood protection, including areas in West Fargo and Horace south of Interstate 94 that will be protected against a 100-year flood. Areas protected by the Sheyenne Diversion, which now are protected against a 100-year flood, will have 500-year protection, Paulsen said.
Along the Maple River, an area north of West Fargo and areas of rural Cass County will receive protection up to a 500-year level, he said.
ASN Constructors, the construction arm of the Red River Valley Alliance, has awarded six bridge construction contracts to Industrial Builders for road crossings on the northern reach of the 30-mile diversion channel now under construction.
Work on the bridges will start this summer, Paulsen said.
So far, ASN has completed 4 miles of the channel excavation, and has started to move equipment west of Interstate 29 to continue the work, he said. “It’s going well,” Paulsen added.
Besides the diversion channel, work continues on other diversion project features, including the three control structures that will regulate the flow of floodwater into the channel.
The largest of the three, the Red River structure, was the last to start construction. Workers are pouring concrete. In one recent pour, crews poured 2,600 cubic yards of concrete — roughly 370 cement truck loads, with trucks from Fargo and Wahpeton involved.
The $3.2 billion diversion is scheduled for completion by spring of 2027. The project is expected to reach peak construction in 2025.