This interview has been lightly edited for clarity.
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Scott Hall:
And I'm Scott Hall with John Latimer. You know, John, if you mention dams, I always think of the five dams on the headwaters, right? Winnie, Leash, Pokegama, Big Sandy, and Cross Lake. But, there was a period between the 1880s and around 1960 when hundreds and hundreds of dams were built on smaller streams than the Mississippi river and waterways. Luther Aadland is a river ecologist and scientist who's worked with the DNR for many years on dam removal. Some of 'em were temporary, like for log drives; We're not talking about those. We're talking about ones six feet or taller. Luther's been working on these for over 25 years, and he joins us now. Hi Luther.
Luther Aadland:
Hello.
John Latimer:
Hey, good morning, Luther. This is John Latimer. Nice to meet you.
Luther Aadland:
Good morning.
Scott Hall:
Thanks for being on our program today, Luther. How did you get onto the idea of removing some of these dams?
Luther Aadland:
Well, some of it started early on. My career initially with the DNR was related to fish habitat and developing the details on what individual species and their different life stages required. And then trying to restore river ecology with river flows and protected flows. And what we came to realize pretty quickly is that you could have really good habitat in a stream, but a downstream dam could eliminate a lot of the fish species that you'd expect to have there by blocking their migrations and recolonization that they routinely do in a river system.
Scott Hall:
Yeah. So, it turns out these dams really do change habitat in a big way, not just the migration (and say, in the spring, for spawning), What are other ways that dams change a waterway?
Luther Aadland:
First of all, they flood out the riverine habitat and replace it with kind of a hybrid between lake and river habitat. In doing so they also block sediment transport. So, sediment accumulates in those reservoirs, they block the flow of woody debris, and that kind of thing. And then the hydraulics, it becomes static water instead of flowing water, which is conducive to algal blooms. So, they can change the water quality as well, but blocking migrations is a huge aspect of that.
Scott Hall:
In the last three or four years we've seen dams removed right around Pine River. I believe over toward Hinckley and Willow River, some dams have been removed. Out in Northwestern, Minnesota, there's some dams there in the Red River watershed. So, tell us about some of the specific projects, and how they were removed. I know there was a component where you had to sell the idea to the communities around these dams who had grown used to having the dams as part of their waterway: they thought this might not be a good thing.
Luther Aadland:
Yeah. Well, first of all, I work statewide for the DNR and now nationally (and in some cases internationally) on rivers around the country. The first dam removals I got involved in were in the mid-1990s and the early 1990s. Part of dam removal is getting the community to think about it. In some cases, we visited with a community and they chose not to go that route. And in some cases, we put in a nature-like fish passage to at least allow fish passage through these dams. But, in a number of cases, after visiting with the community and them deciding not to go that way, we'd get these catastrophic floods and the dam would fail. A lot of the removals are also after dam failure in trying to restore the river and remove the remnants of the dam.
Scott Hall:
Yeah. A lot of these dams are getting old and either need some kind of maintenance or removal. You mentioned fishways, these are ways you can create for a fish to go around a dam while not removing it. Is that how it works?
Luther Aadland:
That's that's right. Actually, there's a couple ways of doing it. On dams that are under 12 feet tall, you can convert that dam into functional rapids. So, that has some advantages in eliminating the dangerous hydraulic undertows below dams but also providing fish passage and habitat. And the other way is to make a channel that kind of emulates a natural channel that goes around the dam and allows the fish to move through.
Scott Hall:
In Pine River, there was a project called Rock Arch Rapids?
Luther Aadland:
This concept was developed in the early 1990s for dams where there's a critical existing function. And sometimes even where we removed dams: because these reservoirs will fill with sediment, it provides a way of stabilizing those sediments. We've used that around the state in those kinds of situations and that kind of initiated use of the same design around the country. So, I've assisted other states, federal agencies, and communities with providing passage around the country using that approach. What the rock arch rapids does is kind of create a step pool channel, which is typical of steep rivers. And it's also the kind of habitat that fish like walleyes, lake sturgeon, red horse suckers, and other species will spawn in. So, if you can't remove the dam, you can at least provide some of the critical habitat that dams often impact.
John Latimer:
When you're talking about dams, does this include things like weirs as well?
Luther Aadland:
Yeah. I mean, dam weirs are just another name for a dam. It doesn't take very high dam to block fish migrations.
John Latimer:
Okay.
Luther Aadland:
So, yeah, that would be included.
John Latimer:
And, to that end, let's say we've got this little Brook trout. With your study on the ecology of rivers and fish movement, how much of the river does he need? Does he use the whole river?
Luther Aadland:
Yeah, that's an excellent question. And it really varies with the species. Some species like sturgeon (even walleyes and catfish) will migrate hundreds of miles. Walleyes don't necessarily go that far, but they do in some river systems. Sturgeon may go a thousand miles. Some of the smaller-bodied fish that we don't think of being migrants do, in fact, migrate a pretty long distance despite their small size.
John Latimer:
Wow.
Luther Aadland:
I kind of relate it to bird migrations, you know. They'll move seasonally, they'll move to spawn, and they'll move to recolonize a river after a drought, fish kill, or other water quality event. It really becomes critical to river systems.
Scott Hall:
One aquatic animal that I don't think is moving very fast, but you've found these dams have had a huge impact on, is the population of mussels. How are mussels affected by dams?
Luther Aadland:
Yeah. Of course, mussels are really important for water quality because they filter our water and provide all sorts of functions for biological diversity. Mussels depend on fish typically to reproduce. So, they produce glochidia that are kind of baby mussels <laugh>, but they look like PAC-man <laugh>. They'll latch onto a fish. The mussel will attract them with a lure, and when the fish comes close, they'll release these PAC-men-like larvae, and they'll attach to the fish's gills. They don't really harm the fish; they'll hang on and extract some nutrients for a couple weeks and then they'll fall off and form a new mussel bed. So, their way of getting around is hitching a ride with a fish.
Scott Hall:
Wow. That's an amazing adaptation, isn't it? And of course, if the fish can't move as a result of a dam, the mussels won't be moving either. Another thing: somebody wanted me to ask you about wild rice and the possible impact of dams on our wild rice.
Luther Aadland:
Yeah. I harvest wild rice myself, and I worked with the tribes on this because the rice is very important to them. Wild rice is often found on lakes and wetlands and in these river networks. And they do well with disturbance events and seasonal fluctuations. When we build a dam, we often stabilize those water levels and that's not always so good for rice. Often, it'll make the water too deep for the rice to germinate, and that kind of thing. So, in several cases, we've removed dams and restored wild rice beds by allowing that those natural fluctuations to occur.
Scott Hall:
So, these aquatic animals and plants, I mean, they've adapted to the natural dam-less waterways over thousands of years and they can thrive. In other words, the impact of our dam removal will be good for the aquatic wildlife, if not, uh, we built them for water power, we built them for controlling drought and all that. How would you describe the dam building period? We know about the big dams on the headwaters, but how many dams are still out there, do you think? And do you think this is gonna be a long-term project?
Luther Aadland:
Yeah. Absolutely. Dams have a lifespan of about fifty to maybe a hundred years, depending on the dam. Big dams, of course, are built to last a little bit longer. But we really started building dams in Minnesota about the mid-1800s and many of those washed out. And they continue to wash out as they age and we get these bigger floods. But there are roughly 2,000 dams in the state...
Scott Hall:
Oh!
Luther Aadland:
...Including the ones that aren't as big or noticeable. So, there's a lot of dams. And, yeah, we've removed around 50 of 'em in Minnesota. <Laugh> So there's a lot of fragmented rivers still from the number of dams that we've got out there.
John Latimer:
When you remove a dam, I'm curious what effect it has on the river. And, I suppose it depends on the river, but if you take the Cannon River (it's one I'm familiar with because as a kid, we used to go down and visit my cousins who lived near Vasa and there was a dam there), but if you take one dam out of the river, does that change the river significantly? Or do you need to go from headwaters to mouth and take them all?
Luther Aadland:
Well, just as an example, I assisted on work around the state with some of the early dam removals, but one we were really interested in was the Red River Basin, which is a good size river with thousands of miles of tributaries. And we started on one in Fargo-Moorhead where we made it into rapids and people said, "well, why do you care about fish passage? It's got a dam a few miles upstream and a dam a few miles downstream." And that project was successful and led to a series of dam removals and conversions of dams to rapids. And now, the river is connected for 350 miles from near Fergus Falls to Drayton.
Scott Hall:
And the Drayton dam is about to be replaced with rapids as well. So, at that point, we'll add another nearly 200 miles of connected river just on the main stem. And then we've done this on tributaries. So yeah, sometimes you have to think big and work on that whole connectivity of that river system, where we get connections of the smaller streams to the big ones. A dam can cause a loss of almost half of the native fish species. We've shown that once we remove it, we can bring back on average about nearly 3/4ths of those missing species...
Scott Hall:
Wow.
Luther Aadland:
...And, in some cases, a hundred percent of the native species.
Scott Hall:
Wow. That's great. We're speaking with Luther Aadland, he's a river scientist and ecologist with DNR. He's led the removal of over 50 dams on streams in Minnesota. Finally, one thing we haven't mentioned but we probably should, is that dams can be dangerous. How so?
Luther Aadland:
I mentioned the Midtown dam in Fargo-Moorhead. That, on average, had drowned one person every two years since it had been built. What it does is set up a high-velocity flow coming off the dam that drives almost vertically into the water below the dam, and creates this current that can suck you right under. We had a dam, Marsh Lake, that drowned 300 pelicans. And pelicans are obviously a lot better swimmers than we are. Yeah. By replacing that with rapids we eliminated those dangerous undertows to where I've paddled my kayak through many of these that we've done. And with no fears of being pulled under, like I would've at a low head dam.
Scott Hall:
Well, Luther thanks for introducing us to dam removal, and also telling us this is an ongoing thing, so people should be aware of this. Thanks for being on our program today.
Luther Aadland:
You're welcome. And thank you.
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You can read more about dam removal here, or read some of Luther's papers here.
