Holding Back a Flood

As California moves toward reintroducing beavers, landowners have turned to artificial beaver dams to protect their properties.

When the Sheep Fire swept through nearly 30,000 acres in and around Susanville, California in August, 2020, Hannah Tangeman’s Hulsman Ranch was badly burned. The ranch, which she part-owned and operated, had been in her family since the 1800s. Tangeman was worried that mudslides and flooding would soon follow suit on her 100 acres of cattle land, forests, and alfalfa fields. With all the vegetation burnt, there was no longer anything holding the soil together.

A conservation crew installs a beaver dam analog at Woods Creek, a tributary of the Cispus River in Washington State. Beaver dam analogs are structures intended to mimic the form and function of natural beaver dams. Photo courtesy of Cascade Forest Conservancy.

A little more than a year later, in October, 2021, a powerful bomb cyclone hit Susanville, along with the rest of the Western United States and Canada. Fearing her house might be swept away during one flash storm, Tangeman fled her property and waited out the weather at a friend’s home. When the rains eased, Tangeman went back up to the ranch to see what the storm had done to her land. Parts of the main house flooded, and areas of the ranch were stripped clean of plant-life. But to her great surprise, the land near the stream was almost completely preserved. It seemed like a miracle, but the closer she looked, Tangeman realized it may have been more than good fortune. The parts of her land that escaped destruction were downstream from a couple Beaver Dam Analogs, man-made structures she and the company Symbiotic Restoration built the year prior that mimic a beaver dam and can slow and attenuate floodwaters. “I was stunned,’’ Tangeman says. “I was absolutely stunned.”

Tangeman’s battle with fire and flood is not unique. Ranchers across the American West, faced with ever more unpredictable and extreme weather events, are seeking any means to protect themselves and their lands in the face of the climate crisis. One such tool, strangely, is beavers.

Today, beavers are recognized as a keystone North American species for their ability to create and maintain diverse habitat, including wetlands that are far more resistant to extreme flooding. But by the 1800s they were hunted to near extinction by fur traders. California is only now moving toward their reintroduction. Many landowners, however, have no time to wait for these ecosystem engineers to reestablish themselves in the landscape. Many others prefer not to have beavers on their property at all. So, as scientists develop a comprehensive beaver reintroduction plan, some have turned to Beaver Dam Analogs (or BDA’s), to help mitigate the worst impacts these storms and droughts have on their lands. Preventing extreme flooding on her property was the initial push for Tangeman to explore BDAs.

After a severe storm in 2017 caused devastating flooding on Hulsman Ranch, damaging barns, homes, and forests like she had never seen in her life, Tangeman, with guidance from Tiffany Russel, a biologist with the National Resource Conservation Service and Point Blue, decided to try out a few BDAs on her property. With help from Symbiotic Restoration, Tangeman wove bits and pieces of sticks into standing posts to build a dam hoping not too much of the stream would be torn apart in whatever floods were to come.

Beavers create and maintain diverse habitat, including wetlands that are far more resistant to extreme flooding. Photo of a beaver dam on the Pacific Northwest’s Snake River by enjoiskate8 / Flickr.​

But BDA’s do more than flood mitigation. Similar to a beaver dam, though not quite as effective, this waist high structure helps slow down rushing water, captures sediment, cleans up the water in a stream, and creates havens for wildlife in the midst of wildfires. BDA’s even hold more water in the stream itself, meaning an ephemeral stream that has a BDA will thrive for a longer portion of the year. In some cases in Utah, Oregon, and Idaho, BDA’s have led to the reintroduction of beavers, who end up adopting the artificial dams and increasing the volume and size of streams by up to 1200 percent, according to a study in Science Magazine.

These benefits, along with helping create more stable streams for endangered salmon species, make BDAs a powerful tool for conservation, restoration, and even preservation of lands, especially in the ever-parched West. Its simple design also makes it one of the cheapest options for landowners. All it takes to build one is a few fairly straight and strong pieces of wood (often douglas fir) tamped firmly into a small streambed and then woven through with willow sticks, or some other similarly pliable material.

“Low tech approaches to meadow and stream restoration are more affordable, put money in more hands, and are less detrimental to the landscape.” said Garrett Costello, one of the founders of Symbiotic Restoration.

Beavers are still a divisive rodent in some parts of the American West because their dams alter habitats and can flood areas humans want dry. Even Tangeman said she is worried about the possibility of beavers on her property eating too much vegetation growing back after the Sheep Fire. And so, BDAs are a greatly accepted alternative in agricultural communities. Whereas a beaver may help a landowner, it also might build dams that continually plug up a necessary culvert or dike, adding to a rancher’s workload. This makes BDA’s a much easier option to manage.

California recently budgeted for a group of scientists to study where it might be best to relocate and reintroduce beavers in the state. But with or without beavers, BDA use seems to be growing. Costello, whose company installs BDAs on properties, said he’s seen a big increase in demand. “I started my company in 2018 and the last few years have been very busy,” he said.

While this fire season in California has been relatively tame compared to the last two years, the likelihood of larger, more damaging fires is only a matter of time. And more floods will surely follow in the seasonal desert climates of California. BDAs, and beavers, may help bring some stability to lands that are likely to see much less of it in the future.

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