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Serving: IA

Beaver dams: Nuisance or conservation practice?

Billy Beck, ISU Extension Everett Johnson, an ISU senior studying animal ecology, stands on the downstream side of an active beaver dam
CHANNEL CHANGES: Everett Johnson, an ISU senior studying animal ecology, stands on the downstream side of an active beaver dam. Note the differences in stream channel width, water surface elevation and water velocities upstream and downstream of the structure.
Conservation Learning Group: Beaver dams can potentially improve water quality and reduce stream bank erosion.

The beaver is often thought of as an industrious construction expert with instinctive engineering skills that creates dams capable of holding back the flow of water in Iowa’s creeks and streams.

For some, this skill is not as welcome as you may think. When a beaver’s dam backs water into a row crop field during a weather event or wet season, farmers are not their biggest fans. In addition, beavers have a voracious appetite for almost anything that grows, including corn. The combined nuisance of crop pilferage and field flooding creates a negative perception of beavers among most farmers.

However, beavers do play an important role in creating habitat for other wetlands creatures through the creation of natural ponds. And the slowing of water flow is one potential remedy for erosion and downstream nutrient transport issues facing Iowa. An additional upside of beaver dams is there is no construction or implementation cost for the farmer.

Finding a balance between these potential conservation benefits while paying attention to farming interests may be a daunting task, but as with most complex challenges, the first step is gathering data for analysis.

According to Billy Beck, assistant professor and Extension forestry specialist at Iowa State University, a new study being conducted through the Iowa Nutrient Research Center at ISU is taking a look at beavers from a conservation perspective, seeking to better understand possible water quality improvements, and the impacts of flooding caused or exacerbated by beaver dams.

Possible water quality benefits

In Iowa, beaver dams are protected from destruction or demolition, unless it is done to protect the owner’s property. During a 2018 Iowa Learning Farms conservation listening session with farmers participating in watershed improvement projects, one farmer related a story about how they had handled a beaver dam issue on his farm.

He remarked that after the beavers were forcefully encouraged to move a dam downstream to reduce field flooding, he participated in nitrate testing above and below their newly constructed dam. To his amazement, the nitrate levels in the water were measured to be some 90% lower below the dam than above.

While this is a single data point, it does provide an indication that slowing the water flow at a point where it doesn’t impact crops can help improve water quality. It is assumed that the beavers were happy with their new home, the farmer was happy that he no longer had a flooding problem, and Iowans should be happy that in this instance there were lower nutrient levels in the water.

“Practices which help to move water off cropland as quickly as possible have helped farmers increase yields and put more acres into production, but in many cases at the cost of topsoil and nutrient loss to our waterways,” Beck says.

“There has been tremendous effort invested in research and practice aimed at conserving soil, and slowing or preventing nutrients from degrading water quality,” he says. “One area that hasn’t had a lot of critical study in Iowa is the potential efficacy of beaver dams as a conservation practice or structure that could naturally contribute to the recovery of compromised waterways.”

More natural streamflow

One other question the researchers are seeking to answer is whether the ponding of water behind a beaver dam also allows heavier particles to settle to the streambed, rather than be carried downstream. If so, over time, this collection of bed materials could raise the channel back to levels that are more compatible with the surrounding natural floodplain.

Everett Johnson, ISUAbandoned dam

SEDIMENT PILES UP: Note the sediment accumulation and difference in streambed elevation above and below this recently abandoned dam.

“Water is a powerful sculpting tool that continuously erodes and carves a path through just about everything,” Beck says. “When we straightened streams, making the water run faster, many carved their way deeper into the earth, reducing connectivity between the channel and its surrounding landscape, while exposing steep, high stream banks subject to collapse and erosion.

“When the streambed is at a more natural elevation in relation to surrounding terrain, sudden floodwaters can spread over a larger area, allowing transported nutrients to settle and be utilized or sequestered by the natural riparian vegetation across the floodplain.”

Natural or constructed ponds and wetlands are proven to be effective in slowing the migration of soil and nutrients from fields into waterways. The ponding of water behind beaver dams is expected to offer similar benefits.

“We hope to be able to quantify the impacts to water quality provided by beaver dams,” Beck says. “We do understand that these creatures don’t always put their dams in the most beneficial sites from a farmer’s perspective. Finding measurable factors that can be analyzed from a cost-benefit angle may influence how farmers view and interact with beavers in their area.”

The likelihood of finding the perfect location for every beaver dam — one which maximizes benefits to all — is relatively low. However, reaching a better understanding of how these natural structures fit into a multifaceted approach to water quality improvement and conservation may contribute to overall progress toward statewide nutrient reduction goals.

Pierce is an Extension Program Specialist with a focus on water quality with Iowa Learning Farms and Water Rocks.


TAGS: wildlife
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