Natural Hydrologists: Beavers have the unprecedented ability to mitigate drought if people let them

By Katy Spence

Pierre Bolduc, a bear of a man capable of lifting thick, hefty tree trunks onto his shoulder, gestures grandly to a pile of cut logs on a beaver dam behind him. “And here we see the work of the Husqvarna beaver!” he said, referring to the brand name of the chainsaw he uses to facilitate the beavers’ work. Over his shoulder, a beaver lodge sits in the middle of a large pond, constructed out of material Bolduc has delivered to them.

For years, Bolduc has cut down “nuisance” trees that interfere with road signs and electrical lines near his property in Bragg Creek, Alberta, offering up the wood for the beavers’ food and raw materials. The beavers’ dam is now more than 300 feet long.

Pierre Bolduc unloads branches near a beaver lodge.

Sometimes called “nature’s engineers,” the North American beaver (Castor canadensis) is one of the few mammals—including humans—that substantially alters the landscape to suit its own needs. In fact, ecologists consider beavers to be a keystone species because their presence or absence will drastically change an ecosystem. With increasingly extreme weather events, ever-growing human populations, and declining freshwater sources, some beaver advocates believe the animals offer a vital, natural solution for retaining water in ponds and mitigating floods in other riparian ecosystems.

But in the process of building lodges and dams, these large, nocturnal rodents can also wreak havoc on human infrastructure and cost several million dollars’ worth of damage each year in North America.

The industrious, powerful animals become active as the sun sets, talking to each other in whining hums. Their webbed back feet and flat rotor-like tails make them graceful in the water and a little less so on land, where their poor hearing and eyesight make them easy targets. When Bolduc first proposed reintroducing beavers to the landscape, his neighborsnot to mention county officialswere not happy. Beavers had previously clogged a nearby culvert, which, in turn, often washed out the road. They were a nuisance, so the county removed them. Property values, crops and roads in many rural areas have suffered damage from beaver construction sites. Sometimes, the territorial rodents will cut a favorite tree or even kill curious pets.

Yet, the rodents have had a tremendous impact on Bolduc’s pond. After approaching each of his neighbors individually about the beavers to convince them to try his reintroduction experiment, they eventually agreed. He even suggested an alternate solution for the county road: beaver-proof culverts. Unlike standard culverts, which run parallel to the water, these culverts are perpendicular—letting water rise into them like a straw in a glass. If the water gets high enough, it will drain through a connected horizontal pipe that runs underneath the road, preventing floods. Even when the beavers’ dam breached in May 2016 and drained hundreds of thousands of gallons of water, the culvert prevented a flood.

A close-up shot of Pierre Bolduc, who wears an orange hard hat.

Bolduc says the payoff of bucking convention has been a rejuvenated landscape, “an oasis” where he can enjoy other wildlife like moose, cougars and bears. Sitting on a tree-trunk bench beside the beaver pond, he added that the healthy landscape pays him back tenfold in personal fulfillment. And it’s all thanks to the beavers. “Attitude is what needs to be changed,” he said. “Attitude is the key to the success of the rehabilitation of wildlife.”


Humans and beavers share a long history of conflict. Europe’s demand for felt hats from the 1600s to the 1800s drove fierce competition among fur companies in North America, decimating the beaver population. One Canadian company, the Hudson’s Bay Company, instituted a “scorched earth policy” in the early 1800s. Trappers were to kill all beavers south and east of the Columbia River to discourage competing trappers from broaching on their turf. Researchers estimate that between 60 million and 400 million beavers once populated North America. Today, after many conservation efforts, the population has rebounded to approximately 10 million or 15 million beavers

As climate change increases the risk of extreme weather events, some scientists are eyeing beavers as a tool for maintaining volatile watersheds. In 2008, Glynnis Hood, an environmental scientist at the University of Alberta-Augustana who specializes in wetland ecology and the impact of beavers, published a paper describing beavers’ unprecedented ability to mitigate drought. She and her team analyzed fifty-four years of drought data from Elk Island National Park in Alberta and found that where beaver dams were present, there was more water— up to nine times that of a pond or water source without beavers. Because beaver ponds are so much deeper than other ponds, water lasts longer, even in times of drought.

A beaver swims by its lodge in the middle of a lake.

Hood has continued to examine the nuanced effect beavers have on a landscape, as well as how humans respond to them. She’s completing a study that compares costs of different beaver management efforts. The study will contribute to a larger project, called Leave it to Beavers, which aims to reduce human-beaver conflict. The Alberta-based, inter-agency effort uses citizen science to gather information about the long-term effects beavers can have on a landscape. The project is composed of several agencies, including the Alberta Riparian Habitat Management Society, an non-governmental agency informally known as “Cows and Fish.”  Cows and Fish works with landowners and stakeholders to clarify how water flows through different landscapes, especially agricultural areas.

A riparian specialist for Cows and Fish, Lorne Fitch, is trying to spark discussions about living with beavers. He offers a voluntary workshop on how beavers affect the landscape and how humans can peacefully coexist with them. He isn’t interested in pushing people to accept beavers, necessarily. He’s simply holding the door open. “You don’t bring people to the middle,” Fitch said. “You just start them thinking about where their position is and, hopefully, use that and expand their information sources. Maybe they’ll continue to migrate towards the middle.”

Fitch developed a ten-step list of goals, the first of which is building tolerance. Perhaps the most formidable step will be to change government policy in Alberta. The province has no clear policy concerning beavers, leaving confusion over what is permitted and what is not when it comes to relocation and rehabilitation.

Another person on the Leave it to Beavers team is Rachelle Haddock of the Miistakis Institute, based in Calgary, Alberta. The group’s aim is to make scientific research and social issues accessible to land and resource managers. Haddock studied beaver management plans in Utah, Oregon, and Wyoming, and has found that those plans have been successful in many areas. What concerns her most is water allocation. More people and less available water spell trouble, especially in agricultural areas where all the water has already been carefully allotted. “It’s a story about water scarcity and the role that these animals play and keeping water on our landscapes,” she said.

Leave it to Beavers is also studying the costs of beaver reintroduction compared to the cost of building a dam or reservoir. Many people still rely on traditional methods of dealing with beavers: dynamite and backhoes (to kill the animals and destroy their lodges). But these can be costly—and futile. Surviving beavers can rebuild dams and lodges in a couple of days, and most beaver-appropriate habitat will eventually be repopulated by beavers.

 “They’re very polarizing,” Haddock said. “I like to call them the wolves of the wetlands. People either love them or hate them.”


A little farther north, in Alberta’s Beaver County, Duncan Abercrombie, an operations manager for Animal Damage Control, a wildlife control company that serves the city of Edmonton and surrounding areas, often works with folks who want to be rid of beavers. Some of Abercrombie’s duties include kill-trapping, live-trapping, and relocation. On a job for the county, Abercrombie joked with a farmer that Beaver County was living up to its name. The farmers had all wanted beavers a few months ago when water was scarce, Abercrombie said, but the recent influx of rain had somewhat changed their minds. In the following weeks, his truck bed was filled with trapped beavers.

Duncan Abercrombie removes sticks that block water drainage.

His long legs protected in tall rubber boots, Abercrombie unclogs culverts and dismantles dams, careful to remove only a few sticks to restrict drainage and delay the beavers’ response. He cites how smart the beavers are; using obvious trapping methods will make the animals even more difficult to trap in the future. He acknowledges that they can be good for an agricultural landscape, holding water for cows and wildlife in times of drought. But he also pointed out examples of flooded fields and washed-out roads in the county.

“As we grow, we’re consuming their habitat and causing stress on their numbers,” Abercrombie said. Less habitat means beaver overpopulation occurs more quickly, making the animals more susceptible to disease. On top of that, they run out of food faster. Trappers, he believes, help keep those populations in check; his father, a fellow trapper, instilled in him the idea of management and looking at an ecosystem holistically. After working with Glynnis Hood at the University of Alberta-Augustana, Abercrombie added a new management tool to his repertoire: pond-levelling devices.

Since 2011, Hood has been installing pond-levelling devices in and around the University of Alberta-Augustana area to prevent flooding of trails, farmland, and county roads. The apparatus is essentially a large siphon—a man-made modification to a beaver dam that prevents rising water levels and subsequent floods. Although the basic idea behind the devices has been around for decades, they’ve yet to be adopted as a management solution in many parts of North America.

Two devices on the university campus provide Hood with an easy demonstration of her work. Each is a large plastic pipe with wire cages around both ends. Hood and her assistants dig into the center of the dam, placing the pipe so there is a submerged end in the upstream beaver pond and a free-floating one downstream. The height of the pipe in the dam needs to be at the desirable height of water, so the pond never gets too high. The beavers hear the water through the pipe in the dam, but no amount of sticks and mud placed on top will clog the leak. Its simplicity ensures its lasting success, as the devices rarely need maintenance and can be highly cost-effective.

Glynnis Hood points to a beaver dam that prevents flooding along a ditch.

Hood said one of her greatest successes was one of her first installations. In 2011, she installed a pond leveler near a popular, but flood-prone trail in an Alberta Park. The skeptical park foreman told her that their traditional methods of beaver control—backhoes, dynamite, and trapping—were best, but he let her proceed. The pond leveler has worked without incident since its installation. A year after the installation, Hood overhead the foreman on the phone, telling a peer to consider a pond leveler to solve his own beaver problem. Hood has now helped install more than two dozen devices.


Despite the prevalence of beaver-friendly solutions like the pond leveler and Bolduc’s culverts, many management agencies are reluctant to adopt new and alternative solutions. Leave it to Beavers is working to change minds, while Hood focuses on encouraging good science. There are a number of relatively simple and long-lasting tools for those who wish to find them. Cows and Fish recently published two guides that list relatively simple, long-lasting solutions such as fencing off trees and culverts.

After a summer of helping Hood install devices, Abercrombie is now willing to suggest alternative solutions in areas where beavers have been persistent, and where such efforts could improve the landscape. Most trappers have no desire to kill off a species—their livelihood depends on maintaining healthy populations. However, Abercrombie is hesitant about rehabilitation efforts of groups like Leave it to Beavers that want to reintroduce beavers to many landscapes. As a trapper, he sees what happens when there are too many beavers in an area—they end up in his traps, covered in wounds and scars from fighting with other territorial rodents.

Meanwhile, back on his property in Bragg Creek, Bolduc hopes the beaver colony will expand and create another pond to the north. To encourage them, he played the sound of running water on a set of speakers upstream from where he wanted the new dam. Running water means there’s a leak, and the beavers quickly went to work packing limbs and silt on top of the speakers. Although rains eventually washed the speakers away, the new dam is well underway, right where Bolduc wanted it. His ultimate vision is to have beaver dams all the way up the valley. He’s not worried about objections from his neighbors. He said his beautiful backyard has changed their minds.

Three beavers gnaw on branches left on the lake shore by Pierre Bolduc.

Recent floods and droughts in the region worry water advocates. Water resources are becoming less predictable, which is problematic as both human and beaver populations grow and demand more. Beavers may offer more cost-effective and natural solutions. Alberta’s beaver advocates are busily building networks, intent on changing minds and policy from the ground up. They believe, for example, that the crown of the Continent offers such an opportunity. It is a network of parks, recreational areas, and wilderness that cover approximately 28,000 square miles in southwestern Alberta, southeastern British Columbia, and northwestern Montana. Some beaver advocates feel the area will become a major refuge for wildlife as the climate changes. If people are willing to compromise with beavers now, the result could be a new narrative in which humans and wildlife co-engineer a healthier, more resilient landscape. The biggest unknown is whether or not we can move past old assumptions.

Natural History Magazine published Katy Spence's story in the December 2016/January 2017 double-issue.