A diversion immersion: How engineers are meeting the challenges of the F-M flood diversion
Editor’s note: In December, the Minnesota Department of Natural Resources granted a conditional permit for the Fargo-Moorhead flood diversion project. Though the project still faces legal challenges from upstream opponents, the permit represents a milestone that significantly boosts the odds of the project being completed.
Engineering firm AE2S is a member of the Project Management Consultant team, which is responsible for the diversion project’s overall direction and management. Eric Dodds, an engineer and AE2S program manager, and Rocky Schneider, an AE2S public affairs strategist, work almost full-time on the project; and in January, they sat down in Fargo with Prairie Business to answer questions about key aspects of the diversion.
Tell us about the public-private partnership, or P3.
Eric Dodds: The project is being delivered by what we call a split delivery. The embankment or dam on the south end will be delivered by the Army Corps of Engineers.
Meanwhile, the channel and all of the bridge crossings will be delivered using this P3 model. So, the P3 developer ultimately will be responsible for finalizing the design, submitting their designs to the Diversion Authority for review, then building the channel and operating it for 30 years.
They also will be responsible for bringing some financing.
The private partner will operate, but the Diversion Authority will own, the channel?
Dodds: Right. The Diversion Authority basically is hiring this private developer/private partner to finish the design and then to build, operate and maintain the channel for 30 years. The private party will get paid back over those 30 years.
What are the advantages of a P3?
Dodds: In the traditional process, the channel would be split into about 30 segments, each of which would be built by the lowest bidder.
In this situation, a P3 is well-suited because the project can be completed in full, which means it’ll be functional earlier than it otherwise would be.
Plus, we have long-term sales tax revenue to call upon, which means while we don't have the money today, we will have it long-term and can tap into it over time.
In other words, we get the facility soon, and we pay it back over a long duration. It's a multi-generational funding approach.
Rocky Schneider: Another important thing is that the Corps has never done a P3 project. This will be a first for the Corps.
So when you look at a huge project such as this one in a relatively small metro area, you might ask, how did we get moved up to where we got the approvals and the funding commitments that we needed?
One reason is that we have a really good congressional delegation, and another is that we latched onto this P3.
America has a backlog of infrastructure projects, and the Corps has been hearing from Congress that we need new ways of doing these things. So the Corps is committed to the P3, too. It’s their way of showing Congress that they are trying something new.
That has really moved us to the top of the pack in Washington as well.
Dodds: And one other really important point is that if you hire a firm only to design and build, you could wind up with poor design and shoddy construction. But this way, the firm also will have to operate and maintain the project for 30 years. Plus, they’ll equity partners who’ll want to get paid back.
That means their incentive is to build it correctly, so that it doesn't fall apart, it's easier to maintain, and it’s reliable over that 30-year period.
Has the P3 partner been selected?
Dodds: Not yet. Assuming legal challenges to the diversion get resolved, the expectation is that the P3 developer – likely, a team consisting of several companies – will be selected in the winter of 2019-20.
Let’s move on to the diversion. How will it work?
Dodds: First off, whenever we talk to a new group about the project, we start by talking about the need. We remind people that we have a flood history, which may seem obvious to those of us who have been here for awhile; but frankly, there are new people who move into Fargo-Moorhead every day, and a lot of them don't know the history.
That’s why I always go back and show pictures from 1997, 2009 and 2011, those big flood events. We’re not sensationalizing, or trying to scare people; we’re just recognizing that hey, there’s a real need here. So we always start with that.
Now, about the operation:
The embankment on the south end includes three different control structures: one at the Red River, one at the Wild Rice River and one at the diversion inlet.
Those three control structures will all have gates that can move up and down.
Normally, the river gates will be open, and the rivers will just flow through underneath them.
But when the flood waters are coming from the south, at some point there will be risk to the community, so the river gates will start to close.
The gates will close to control the flow in town to 37 feet. Anything more than that will be slowed down by the gates; that plus the embankment means water will start being stored upstream.
Ultimately, that upstream water will start flowing to the west, where the gate will let a controlled flow go into the diversion channel.
Then if the water continues to rise, it will continue to flood the ground and spread out over the upstream areas.
So, the embankment or dam holds the water in place, while the gates let controlled flows go downstream?
Schneider: Right. And remember, when most people think of a dam, they think of Hoover Dam or something similar – a concrete structure holding back a big lake.
But in our case, the upstream area will be dry 99.9 percent of the time. In a hundred-year flood, that area is expected to hold water for only about three weeks.
Also, the embankment will be just that: an earthen embankment, probably about the size of a highway-overpass embankment, with grassy sides and maybe some rip-rap rock in places. It’s not a concrete wall.
Tell us about the channel. What are some of its key engineering features?
Dodds: The project will protect against not only the Red River, but also five of its tributaries – including the Wild Rice River, which I’ve mentioned.
The diversion channel will cross the other four tributaries – the Sheyenne, the Maple, the Lower Rush and the Rush.
And the Sheyenne and Maple rivers are going to have aqueduct channels that will carry them across the top of the channel. Those are two of the more interesting structures along the way.
How will they work?
Dodds: It’s much like an interstate highway bridge in which the local street passes over the top. In this situation, the local street is the Sheyenne or the Maple river, and the diversion channel will be underneath.
Under normal conditions, the Sheyenne will meander along its way, and then it’ll get to this open-air aqueduct or “water bridge” that will carry it across the top of the diversion channel. Then it’ll continue to meander on its way after that. Same thing with the Maple River.
Under flood conditions, there will be limits on how much water can flow into the metro or protected area across that water bridge. So as the water gets high, it will overflow into a spillway that will take it into the diversion channel below.
What about the Lower Rush and Rush crossings?
Dodds: Currently, those are very straightened-out and channelized rivers. Most people probably wouldn't even call them rivers.
Right now, they empty into the Sheyenne River up near Harwood, N.D. With this project, they’ll dump directly into the the diversion channel, so all of the flow from the Rush and the Lower Rush will go into the channel.
How about highway crossings?
Dodds: They’ll basically be longer-than-usual bridges, as the distance from edge to edge on the channel is roughly 1,600 feet.
Grand Forks has its Greenway as a result of the flood-protection system. Will the diversion have anything similar?
Schneider: That's an exciting side of the engineering. For example, along the 30 miles of channel, there will be huge piles of the dirt that will have been excavated. These berms won’t really serve a flood protection purpose; they’ll just be piles of dirt. So we can make them into, say, a savannah area with trails meandering through, and we’ll be requiring them to be formatted to accommodate a major trail network, with trailheads and picnic tables and the like.
If you think about it, 30 miles of diversion channel with trails along the whole length – that kind of trail network doesn’t exist anywhere else in North Dakota.
Editor, Prairie Business