An ecosystem engineer’s vision: mock beaver dams to restore Wisconsin wetland

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By Bennet Goldstein
Wisconsin Watch

Jay Dee Nichols stamped and packed stiff willow branches between maple wood posts, with muffled crunches.

At 63, the semi-retired handyman 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. “They’re one of the hardest-working animals out there.”

Nichols’ muck boots sloshed in a pool already 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 — 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. The water runs into South Fork Halls Creek, where actual beavers live.

Hoffman, 60, owner of Hoffman Construction, hopes the BDAs 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.

“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 promise in nature-based solutions.

Enter the beaver.

Where they chew, wetlands often follow.

The U.S. once was home to 60 million to 400 million beavers before 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.

Without maintenance from nature’s “ecosystem engineers,” many of the nation’s once multi-threaded streams also became disconnected from their floodplains. When this happens, water tables sink, water temperature increases and plants die.

Nature can repair itself, but the process of restoring stream complexity can take millennia. Mock beaver dams can jump-start the process.

They can slow the flow of runoff and help watersheds store more water. Hoffman sees their potential to limit flooding in Wisconsin and create wildlife habitat.

Government agencies and watershed councils 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 contracts with the U.S. Department of Agriculture to wipe out beavers that live on designated streams.

Wisconsin is home to fewer than a dozen BDA projects.

State 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 (Wisconsin Department of Natural Resources) and ask them, ‘Do I need a permit for this?’” he said.

When human and beaver engineers meet

A healthy streamscape requires space for water to slowly meander.

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.

Workers pound posts directly into a streambed and weave branches between them. Gaps can be plugged with sediment.

Hoffman’s 1,000-acre property, which includes his Goose Landing cranberry marsh, is a wildlife cornucopia. Hundreds of geese occupy his reservoir on a given day.

A Stanford engineer by training, he returned to Wisconsin from San Francisco Bay in 1989 to join his family’s road construction business.

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 walleye, hybrid muskie, perch, crappie, bluegill and bass.

“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.

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.

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.

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.

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.

The impact of beavers on fish remains a hot topic in Wisconsin, especially a debate over whether beaver dams block trout passage.

That wasn’t a problem at Bridge Creek, where researchers tagged about 100,000 juvenile trout and surveyed the stream for more than a decade.

Installing mock beaver dams increased the survival, density and reproduction of juvenile trout, researchers found. They detected no changes to upstream migration.

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 or otherwise affect fish in certain ecosystems in his native Wisconsin.

But those are only assumptions until they are 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.

Mock dams not a panacea

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.

Although passionate about them, 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. “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. “That’s not quite the setting we have here in Wisconsin.”

Such projects might lead to property conflicts, especially if beavers move in and enlarge the structures. They might swamp adjacent corn fields or flood a road or backyard.

Getting the dam permit

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.

Analog proponents say the rigid requirements to build transient structures unnecessarily increases costs and dampens enthusiasm to use nature-based solutions for landscape repair.

“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 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 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.”

Hoffman’s stream tributary may be artificial, but the state still considers its waters navigable and thus protected under Wisconsin’s public trust doctrine. 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.

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.”

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.”

This story is a product of Wisconsin Watch. It was produced in partnership with the Mississippi River Basin Ag & Water Desk with support from the Solutions Journalism Network.