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An ecosystem engineer’s vision: mock beaver dams to restore Wisconsin wetlands
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- Wisconsin has lost half of its historic wetlands, with declining beaver populations playing a role.
- Historic beaver loss disconnected streams from their floodplains, warming waters, sinking water tables and killing plants. Mock dams can mimic the beneficial work of beavers.
- Few mock dam projects exist in Wisconsin, where strict regulations make permitting expensive. But several Midwestern organizations and landowners are starting to experiment with the structures, which are frequently used in the American West.
- A cranberry farmer from Alma Center is on a crusade to restore wetlands in Wisconsin by trailblazing a new path through the state’s arduous permitting system, regardless of the substantive cost.
Jay Dee Nichols stamped and packed stiff willow branches between maple wood posts, with muffled crunches.
At 63, the semi-retired handyman from the Wisconsin city of Black River Falls has trapped beavers before. But he’s never heard of a mock beaver dam — much less constructed one.
“It gives you an appreciation for what beavers do,” Nichols said over the shrill beeping of a skid loader. A scratch on his forearm oozed blood, drying into a scarlet smudge.
“They’re one of the hardest-working animals out there, I guess.”
Nichols’ muck boots sloshed in a pool of water that already was forming behind the freshly constructed beaver dam analog, or BDA. The semi-porous wooden structures are often installed across streams to redirect water or capture sediment.
Nichols and three other workers were as busy as beavers for a week in October constructing 12 of them in a forested wetland.
It’s all part of Jim Hoffman’s latest project.
The BDAs span an unnamed, man-made channel that drains overflow from a reservoir on Hoffman’s cranberry farm, north of Alma Center in Jackson County. The water runs into South Fork Halls Creek, a trout stream where actual beavers have taken up residence.
Hoffman, 60, hopes the BDAs, which could pool up to 1.7 acre-feet of water during floods, improve water quality, stabilize eroded stream banks and enhance wildlife habitat. Most of all, he seeks to trailblaze a path through the state’s onerous dam-permitting process so other Wisconsin landowners can follow in his footsteps.
“There’s a lot of different streams and tributaries that could benefit from this,” Hoffman said.
As average Wisconsin temperatures and precipitation increase in response to climate change, scientists, environmentalists and regulators point to the promise of nature-based solutions.
Enter the beaver.
North America’s largest rodent is infamous for wood munching. Where they chew, wetlands often follow. The natural sponges filter water and offer flood protection.
The U.S. once was home to 60 million to 400 million beavers, which inhabited a range extending from the northern Mexican deserts to the Arctic tundra. But European and American settlers hunted them to near extinction.
As their population dwindled and agriculture and urban development expanded, wetlands disappeared. Wisconsin, like the rest of the country, lost roughly half since the late 1700s.
Without maintenance from nature’s “ecosystem engineers,” many of the nation’s once multi-threaded streams also became single-channeled and incised — disconnected from their floodplains. When this happens, water tables sink, water temperature increases and plants die. If torrential floodwaters funnel through the simple stream systems, they flush out wildlife and wood.
Nature can repair itself, but the process of restoring stream complexity can take millennia. Mock beaver dams can jump-start the process, reducing the timing to mere decades.
They also can slow the flow of runoff and allow watersheds to store more water. Hoffman sees their potential to limit flooding in Wisconsin, potentially saving taxpayer dollars and creating wildlife habitat.
Watershed councils, conservation districts, Indigenous tribes, and state and federal natural resources agencies frequently deploy them in the American West. But their use in Wisconsin, a state with a historically tempestuous relationship with beavers, is novel. Many regulators believe the critters’ dams harm trout, and the state’s fisheries and forestry divisions contract with the U.S. Department of Agriculture to wipe out beavers that live on designated streams.
Fewer than a dozen permitted projects that incorporate BDAs or similar wooden structures have been built in Wisconsin to date. The Department of Natural Resources recently approved two on trout stream tributaries, signaling an openness to test their potential despite concerns from fisheries managers. Construction is underway in other Mississippi River basin states too, including Iowa, Kentucky and Missouri.
Wisconsin regulators generally treat BDAs as dams that impound water, making for an arduous and expensive permitting process.
Hoffman spent more than a year and $20,000 to obtain his permit. He is the CEO of a vast Wisconsin construction company and has a running joke.
“The one thing you never do is call the DNR and ask them, ‘Do I need a permit for this?’” he said.
What are beaver dam analogs?
A healthy streamscape requires space for water to slowly meander. That requires messy wood obstructions like fallen trees and debris-filled logjams.
Much like real beaver dams, the analogs obstruct water and disperse the flow across a wider area. Water pools above and below the dams, and upstream surface height increases.
Sediment accumulates behind the obstructions, sometimes transforming an upstream pool into a wetland and eventually a meadow. But nature’s randomness means beaver dams or analogs can fail.
BDAs are not in themselves a solution, experts say, but tools that initiate natural processes that mend degraded waterscapes.
While their popularity increased in the 2000s, historic drawings indicate that small wicker and log dams were constructed as early as the 19th century to “correct” streams in France.
Construction these days hasn’t changed much, with workers pounding posts directly into a streambed and weaving willow or juniper branches between them. Gaps can be plugged with sediment. The analogs, which are biodegradable and transient, function well when constructed in sequence like natural beaver dam complexes. Proponents hope that using natural materials and hand labor reduces building costs, enabling more miles of restoration.
When human and beaver engineers meet
When Hoffman installed his cranberry marshes more than 20 years ago, a developer taught him an important marketing lesson: christen the business after the resource you are destroying. The developer named his housing division Fox Ridge. Hoffman, in turn, called his cranberry operation Goose Landing.
Yet, in Hoffman’s case, he didn’t necessarily displace geese. Hundreds occupy his reservoir on a given day, leaving droppings that serve as free fertilizer.
The 1,000-acre property serves as a laboratory of earthworks and a wildlife cornucopia.
Hoffman, a Stanford engineer by training, returned to Wisconsin from San Francisco Bay in 1989 and joined the road construction business his great-grandfather started more than seven decades prior, before the United States had an organized highway system.
After starting the cranberry operation, Hoffman mined frac sand, then obtained his commercial fish farming license. Now, he’s stocked the former mining pits — since filled with water — with an angler’s dream: walleye, hybrid muskie, perch, crappie, bluegill and bass.
Hoffman sped past one of the ponds in his Ford Bronco, pointing out the artificial islands he created. To add vegetation, he grabbed trees by their rootballs and shoved them into the virgin soil.
“I like to change my environment,” he said. “I’m an earthmover by character — by business.”
Hoffman’s efforts to “rewild” his land led him to plant turnip and radish plots for deer along with oak trees to recreate a piece of Wisconsin’s historical savannas. He’s replaced row crops with prairie grass and intends to install an osprey nesting box on one of his ponds — even if it means the birds of prey eat his fish.
Mock beaver dams are Hoffman’s latest push.
His interest in them blossomed after he helped a Nordic skiing buddy release an orphan beaver on his property. They constructed a lodge for the two-year-old rodent, tucking in a stuffed teddy bear to keep it company.
“Well, it instantly swam into the pond, and that was the last we saw it,” Hoffman said.
In a section of forest far from the cranberry marshes, the drainage ditch turns into what appears to be a natural stream, which cuts through steep banks.
On both sides lies what resembles a 3- to 4-foot-tall effigy mound running perpendicular across the creek bed. Hoffman wonders if beavers were the original architects.
“It might be hundreds of years old,” he said. “I’m hoping the beavers come back here and say, ‘Well, we almost got a dam built!’”
Mock beaver dams used out West
Science backs Hoffman’s belief in the restoration power of beaver dam analogs. In one of the first major studies, researchers evaluated their trout impacts and potential to reverse stream incision.
Bridge Creek, a high-desert watershed in north-central Oregon, bore the signs of livestock overgrazing and beaver removal. Following severe storms, the main channel gradually disconnected from the landscape’s floodplain — conditions that persisted even 20 years after cattle stopped chomping on surrounding vegetation.
The researchers monitored conditions before and after installing more than 130 BDAs in Bridge Creek. They compared those sections of creek to areas that lacked BDAs — some that beavers called home and others they did not.
Prior to the study, Bridge Creek contained some beaver dams, but they frequently blew out during major floods. Sediment didn’t have time to accumulate and reconnect the channel to the landscape.
But the BDAs acted as reinforcements.
Beaver dams in the study area increased more than sevenfold within the first eight years after the scientists added them.
In the BDA sections, land inundated with water increased by 228% and side channels increased by a whopping 1,216%, considerably more than the Bridge Creek sections that lacked them.
As the analogs rehydrated the aquifer, vegetation increased. Groundwater killed off scrubby plants, such as sagebrush, and water-loving willow trees took root.
Could mock beaver dams block or fry fish?
The impact of beavers on fish remains a hot topic in Wisconsin. For some, it’s axiomatic that beaver dams block trout passage — a belief with a long history.
But that wasn’t a problem at Bridge Creek.
The researchers tagged about 100,000 juvenile trout, enabling antennas to detect fish movement at specific stream locations. They surveyed the stream for more than a decade.
The scientists determined that the installation of mock beaver dams increased the survival, density and reproduction of juvenile trout. They detected no changes to upstream migration in the tagged trout despite the massive increase in human and beaver-made dams. Several spawners passed through upwards of 200 during their migration.
Other studies conducted in California concluded trout easily cross BDAs, either by jumping or swimming up side passages.
Another objection to beaver dams stems from the belief they invariably increase stream temperature: Beaver ponds increase a stream’s surface area, which is warmed by the sun.
But at Bridge Creek, water temperature remained constant or decreased, even during summer. The researchers suggested that pooled water upstream of the dams percolated into the ground, forcing cool groundwater to upwell downstream and mix with that on the surface. An offset to the sun.
The complexes affected temperatures in other ways.
On one hand, they buffered water temperatures. Stream temperatures periodically fluctuate with day-night cycles and across seasons, but the mock beaver dams compressed the rises and falls. On the other hand, the complexes created variety, filled with warm and cold spots, offering fish a buffet to choose from.
Some studies have documented downstream warming from the analogs. And others from the upper Midwest have documented increased temperatures below natural beaver dam complexes and in beaver ponds, but academics have questioned the research’s scientific rigor.
Nick Bouwes, a Utah State University faculty member who worked on the Bridge Creek study and co-authored a manual that many consider the BDA bible, agrees that the structures could block fish or raise water temperatures in certain ecosystems in his native Wisconsin.
But until there is solid evidence, he said, ultimately those remain assumptions that should be studied.
“It makes you wonder what fish did 3- or 400 years ago when there was an order of magnitude more beaver and an order of magnitude more fish in these systems,” Bouwes said.
Upholding the public trust
In September, Mike Engel, a U.S. Fish and Wildlife Service biologist, oversaw the installation of beaver dam analogs at Briggs Wetland near Beloit, Wisconsin.
The workshop brought together ecologists, consultants, resource managers and regulators from local, state and federal agencies, most of whom dipped their toes into BDA waters for the first time.
Although passionate about such tools, Engel says beavers and BDAs aren’t a panacea for all degraded wetlands or a warming climate.
“There’s certainly people who will grab a hold of the cute, fuzzy critter and like the idea,” Engel said, standing atop a beaver dam that formed a network of ponds adjacent to the Briggs property. “But I think more people will be interested in managing the amount of water they have — whether they need more or they need less due to climate change.”
In other words, what would a well-functioning watershed look like, and what tools and techniques can achieve those ends? The case for mock beaver dams depends on the setting.
“Out West, they have miles and miles and miles of public land,” said Thomas Nedland, who conducts wetland and waterway permitting with the Wisconsin Department of Natural Resources.
If the BDAs fail, “all the water that’s backed up ends up going into the woods or the floodplain” without risk to infrastructure, he said.
“That’s not quite the setting we have here in Wisconsin.”
Such projects might lead to conflicts with property owners, especially if beavers move in and enlarge the structures. They might swamp adjacent corn fields or flood a road or backyard.
Wisconsin’s public trust doctrine also requires regulators to consider the public’s access to natural resources when making permitting decisions. The Department of Natural Resources may impose requirements to maintain the rights to boat, swim and fish, even on artificial ditches that are considered navigable waterways.
Hoffman’s project rang alarm bells for the local county conservationist, who fears the BDAs will attract beavers to the area, leaving floods and unfishable streams in their wake.
Getting the dam permit
State regulators must consider many factors in considering a beaver dam analog.
Throwing some sticks across a streambed is relatively simple, but several Wisconsin installations have relied upon consultants, federal workers or nonprofit organizations to navigate permitting.
“They’re really important devices. They have a lot of functionality. They’re very simple and inexpensive to install,” said Hoffman’s contractor, Clay Frazer, a restoration ecologist.
“And they’re way too complicated to permit right now for the average person.”
The Wisconsin Department of Natural Resources required Hoffman to conduct hydrologic modeling and topographic surveying before regulators approved his BDAs, which stand roughly 3 feet high.
To satisfy regulators that the analog wouldn’t overturn when water pooled behind it, he had to load test the wooden posts.
Joel Pennycamp, a Hoffman Construction Company employee, strapped a scale around the top of one. Hoffman stood on the streambank holding onto the end of a neon orange string that stretched across the BDA. When Pennycamp tugged, each post could move no more than an inch.
Analog proponents say the rigid requirements to build transient structures unnecessarily increase costs and dampen enthusiasm to use nature-based solutions for landscape repair. A potentially laborious permitting process also misses the broader point that process-based riverscape restoration is unpredictable.
“You don’t have to be an engineer. You don’t have to be able to operate large machinery. You’re not going to completely redesign a stream to what you think it should be,” Bouwes said. “Let the stream figure it out.”
One permitting difficulty stems from, in several instances, the state’s classification of the porous structures as dams. Regulators and applicants debate a principle point: Does a mock beaver dam actually impound water or, as researchers say, merely slow or delay it? State employees say they lack latitude to interpret because BDAs, plain and simple, fit the legal definition.
“I often hear back from applicants and they’re like, ‘Well, it’s not very big,’ or, ‘It’s not intended to be there for long,’ or whatever,” said Uriah Monday, a state dam safety engineer. “But they always acknowledge that they need that pool of water to create the energy it’s going to take to do whatever they’re trying to achieve.”
For instance, he said, a raised pool of water is necessary to saturate wetlands, carve stream meanders and trap sediment upstream.
Hoffman’s stream tributary may be artificial, but the state still considers its waters navigable and thus protected. Normally, when dams obstruct public passage, the Department of Natural Resources requires the posting of a portage route.
For now, the agency isn’t requiring it, but Hoffman hopes to run with the idea.
“So I’m having some signs made up for the beavers in case they get confused when they’re swimming upstream and hit the dam,” he said, grinning widely.
The department also has authorized BDAs through a streamlined general permitting process. Hoffman’s mock beaver dams, however, did not meet the criteria to qualify.
“I don’t blame the DNR for it,” he said. “It’s just that they don’t have a system to accommodate our request.”
Kyle Magyera, who performs government outreach with the Wisconsin Wetlands Association, believes regulators should carve out exceptions from the dam rules.
Monday thinks the existing permitting system can work, as it already has, and will ease as the department learns more about the structures. That will include monitoring at Briggs Wetland and Goose Landing.
“We’re actually hopeful too,” Nedland said. “If there’s an efficient, cost-effective way for people to do these kinds of projects in a much easier way that results in less disturbance to the landscape, like boy, that’s a win.”
BDA permitting challenges are not unique to Wisconsin. Even the Bridge Creek researchers were unable to conduct a follow-up round of restoration due to regulatory hurdles.
“It seems like every state, you have to go through the growing pains of getting people familiar with these approaches,” Bouwes said. “When they see what we’re actually doing — we’re throwing sticks in the stream to slow the water down — they become a lot more comfortable with it.”
Balancing human and beaver needs
By mid-afternoon at Hoffman’s farm, evidence of the day’s construction littered the ground adjacent to the channel where the BDAs stood: empty plastic Powerade bottles, gasoline cans, a chainsaw.
Before getting off work for the day, Nichols and Pennycamp loaded it onto a utility vehicle. Hoffman, meanwhile, browsed through a printout of his state-issued permit, reviewing the details through reading glasses he perched across his nose.
“‘The water is a cool-cold headwater. The proposed dam will not result in significant adverse effects on this resource upon compliance with the conditions in the order,’” he read aloud. “In other words, don’t flood too much, don’t warm the water up too much. Okay, well we’ll debate that later.”
He flipped the page.
The beavers living at Hoffman’s farm are dispersing across the property. One colony chewed down some of his pines and aspens and plugged a culvert, expanding the shoreline as part of a project Hoffman didn’t plan.
It doesn’t bother him because he has more trees to spare and wants to live among the rodents, but he doesn’t begrudge beaver-bothered people. The critters create profound impacts.
Humans and beavers share a common drive to engineer their environment to live.
“We’ve got to find a way to balance the different needs of each species,” Hoffman said. “You know, us included.”
Why is he doing all this? Permitting, pounding, portage-routing. Really, why bother?
Hoffman’s campaign is more than just a new permitting process. It’s an exhortation to the state to reconsider its treatment of beavers. If he can show that mock beaver dams don’t heat the water or block fish, perhaps the state will stop removing beavers and their dams from trout streams.
“We’re going to hopefully show to them that the beavers in the ecosystem are actually beneficial,” Hoffman said.
Going through the trouble is simply part of a kindred ecosystem engineer’s balancing act.
This story was produced in partnership with the Mississippi River Basin Ag & Water Desk, an editorially independent reporting network, of which Wisconsin Watch is a member. It was also reported with support from the Solutions Journalism Network, a nonprofit organization dedicated to rigorous and compelling reporting about responses to social problems. Sign up for Wisconsin Watch’s newsletter to get our news straight to your inbox.
An ecosystem engineer’s vision: mock beaver dams to restore Wisconsin wetlands is a post from Wisconsin Watch, a non-profit investigative news site covering Wisconsin since 2009. Please consider making a contribution to support our journalism.
