Nature’s engineers can help mitigate effects of drought in the West
By Deanna Drew
As Colorado and the rest of the Southwest grapple with the effects of an ongoing, twenty-two-year drought, scientists are turning to beavers for help restoring moisture to the land.
The American beaver used to be prolific across the Western landscape. Historically in the San Juan Mountains, beaver populations were so plentiful that most mountain streams became beaver wetlands, and broad glacial valleys were filled wall to wall with intricate systems of beaver dams, lodges and canals. Their complex wood workings temporarily flooded the native lands, resulting in an abundance of seasonally wet meadows and lush floodplains, which in turn created rich, wet habitat that supported a large variety of aquatic plant and animal life and a healthy, functioning ecosystem. “If you had visited Telluride a thousand years ago, it would have been an insane wetland with wildlife and birds everywhere, because of the beaver,” says Adrian Bergere, Executive Director of the San Miguel Watershed Coalition.
But by the mid-1900s beaver were nearly trapped to extinction for the fur hat trade. Beaver populations never bounced back: only about 10 percent of the historic population currently inhabit the beaver’s range.
Now, southwestern Colorado is experiencing the longest stretch of drought in more than a thousand years, and the effects of water’s absence is being felt throughout the land. Rivers are shrinking and reservoirs are reaching record lows, and the dwindling water supply for agriculture is reducing farmers’ crops to a fraction of the normal yield. “Before, we had beaver dams,” says Bergere. “But we decided to remove the beavers and tried to replace their work with a system of man-made dams, and it’s not working well.”
The San Miguel Watershed Coalition and other Western conservation groups are working with public lands managers and private landowners to increase beaver populations in Western rivers with the hope their busy work can help recharge groundwater systems and restore water to the land. “Now we’re in drought times and need nature-based solutions. We’re looking at climate-related issues and environmental issues asking: What in nature is not there anymore?”
Some beaver are still present in all stretches of the San Miguel River, from the alpine headwaters above Telluride to the river’s confluence with the Dolores River, some eighty miles below and 7,000 feet lower in elevation. The river travels through ranching and farming communities in Norwood and Naturita before it reaches the red rock desert near the Utah border. “Given half a chance they will repopulate areas where they used to exist.”
Because beaver are still widespread in the watershed, Bergere and other scientists believe there is an opportunity for successful watershed restoration work in the San Miguel. “Let’s bring them back and give them a helping hand.”
Back to analog
Beaver dams are an imperfect weave of riparian-dwelling tree species including aspen, willow, and cottonwood, the beaver’s primary food source. Their dams allow complete stream connectivity and do not prevent aquatic species from getting where they want to go, while creating habitat for juvenile species. Beavers will take a cobbled, fast moving, steep stream and slow it down to allow water to spread out and create wet meadows and ponds for increased water storage.
According to Bergere, it’s the imperfect nature of beaver dams that makes them work so well in the environment. “They recharge groundwater, trap sediment, and create ephemeral ponds that eventually fill in. Then the beaver move to the next spot, find a good site for a lodge or dam and start the cycle over again, creating a healthy landscape for storing water.”
Without beaver dams, the snowpack rages out faster, and rainwater rushes down streams and riverbeds with no impediments to collect and distribute it across the landscape for farming. The rushing water gouges out streambeds, and the incised streams become disconnected from the floodplain with no associated riparian corridor or wetlands. “Sometimes you think of rivers and wetlands as separate things, but they’re really not.”
The fast-moving water creates banks so steep that the beavers can’t get into them, and the streams become so overcharged that their work gets blown away. “It’s bad for sediment, bad for water quality, and bad for the aquatic, terrestrial and bird species that we love.”
Beaver dam analogs are log and wood structures that scientists install to bring back the beaver’s benefits to water users, by slowing water down and creating stores of water that help recharge groundwater by forcing it into the ground and delaying its release until later in the season. “What we can do is step in and install low-tech, process-based restoration work to give the landscape a bit of a helping hand.”
In areas with existing beaver populations, but where there’s too high a gradient for beaver to get back in or a lack of woody debris, scientists drive posts into the river bed, then add mud, willow cuttings, alder, and cottonwood to mimic what the beaver would be using and attract them back to the area. The analogs replicate a beaver dam, slow down the flow and recreate naturally what the landscape looked like historically, giving beaver a chance to reestablish itself in that tributary or section of stream. “Ours will never be as good as what a beaver would build, but it does create positive effects of groundwater recharge and sediment aggregation, ultimately leading to the river’s reconnection to the floodplain which is absolutely crucial to a healthy river.”
Bergere says it’s best to install not just one beaver dam analog by itself, but to plan for several in an area that would be suitable habitat for beaver to reinstate a colony in that tributary or section of stream. “Beavers will adopt the structures and start building their own, so if yours get blown out, it does not really matter because the beavers have now gotten a foothold to reestablish themselves, and will do the restoration work for you.”
Beaver dams benefit tree species, too. When beaver cut trees like willow down, it’s just like propagating a house plant in your home: some cuttings stay and regrow and some go downstream, and recreate more healthy willow populations. “We’re replicating what beavers do. With any luck the natural processes will take it from there.”
In an area where there are no beaver dams or beaver populations are low due to human conflict, you can still gain the benefits of dams without beavers by installing beaver dam analogs. “There’s no guarantee beaver will come back to your property. But if you are out in the desert or ranchland, you can still do this mimicry or analog work to gain their benefits and create wetlands on the land.”
Living with Beaver
When it comes to living with beavers, there are two tools in the toolbox. While dam analogs promote beaver on the landscape to increase water storage, the other is a mitigation or adaptive management technique to coexist with the animals in a mutually beneficial manner.
Beaver dams can reach a point when they are negatively impacting human infrastructure, or impairing drinking water sources. Often in these cases, landowners find themselves continually dismantling the dam to discourage beaver from making a permanent residence, or trapping and relocating or killing the beaver.
A flow device system allows water to pass through a beaver dam, so you don’t have flooding issue, you don’t have to spend your days picking sticks and twigs off the dam, and you don’t have to trap the beaver, which is very time intensive. “For a relatively low cost, you can install a flow device and save a beaver.”
Sometimes called a “beaver deceiver,” a flow device uses a pipe installed through the dam to dictate the level of water in a beaver pond and prevent flooding. A hydrologist will insert a pipe through the dam, with the outlet set at the elevation appropriate to avoid flood impacts, and the inlet set below the surface of the water. This controls the water level, because the water is passing thorough the dam at two points removed from the dam. The beaver’s auditory instinct can’t hear the rushing water because the pipe is under the surface; they can’t find it and don’t know where to plug the leak. “Flow devices are a biological hack,” Bergere admits. “But this way, the beaver can still do what they’re doing, and will keep returning and returning.”
This year, San Miguel Water Coalition is joining forces with the national non-profit American Rivers to expand their beaver restoration work further into the San Miguel watershed. The groups are looking for landowners to partner with, who are interested in working together with beaver to restore environmental, ecological and aesthetic values to the river and land. “Ranchers across the west have adopted these nature-based restoration techniques and are seeing water supplies last up to six weeks longer into the dry season.”
So far, the Coalition has identified eleven sites for beaver dam analogs in the San Miguel Watershed, and Bergere says the list is growing. “Fish, birds, elk, deer…it’s really remarkable what happens when you spread water across the floodplain. If you want a natural wetland complex with ponds on your landscape, this is the most cost-effective way to do it. Restore a natural grade, the beaver adopts the structure, and takes it from there.”