Introduction to non-lethal beaver management for culverts and other surface water facilities
Beaver management issues
Beavers maintain wetland systems in the landscape. Their activities may change watercourses, raise watertables, and create new habitats for plants, fish, and other wildlife. There are impressive examples in arid climates of streams returned to year round flows with the addition of beavers back into the system. In the Pacific Northwest, beaver ponds are critical for slowing stormwater runoff, trapping sediments, and maintaining summer base flows among other ecological benefits. Recent studies indicate that coho that are reared in beaver ponds find more food, refuge from floods and predators, and may be twice the size of juveniles that are not reared in beaver ponds. To date, artificial structures and "restored" wetlands do not provide comparable levels of ecological functions as wetlands created and maintained by beavers. In addition, beavers maintain wetlands at a significantly lower cost than humans have been able to achieve.
In human-managed landscapes beavers can create several problems. The most common problem is plugging road culverts which causes the water to rise on one side of the road, flooding the road and potentially undermining the road bed. Culverts are easy to plug and difficult to unplug resulting in continuous and expensive road maintenance costs. The rising waters behind a beaver dam or a plugged culvert also results in land being flooded. Depending on the topography and the surrounding land uses, this problem may become quite serious. Finally, beavers are frequently implicated in the loss of trees around the edges of their ponds. In some cases, these trees may be special landscape trees or valuable orchard trees.
Historically, the most common response to beaver conflicts has been trapping and removal. Trapping can be quite expensive and is never a one-time solution to the problem. Even if an entire beaver family is removed from a site, new beavers are constantly dispersing across the landscape looking for suitable homes. If a place was suitable for one family of beavers, more will quickly move in to replace those removed by a trapping campaign. In addition, if beavers are removed from a system, the wetland area will likely degrade and the ecological functions of the area will decline. Fortunately, more permanent solutions are quite simple.
Beavers fell trees for food and for materials to create dams and lodges. They typically only fell trees within 200' of the shoreline and usually much closer since they are very vulnerable to predators when on land. Therefore, problems with beavers cutting trees are easily and permanently solved by wrapping important trees with chicken wire or hardware cloth within the riparian zone. Beavers do not climb well so the fencing only needs to be 3 to 4 feet high. Do not wrap trees very tightly as they need room to grow.
To protect larger areas or newly replanted restoration areas, erect a temporary fence of chicken wire or a similar fencing material. Again the fence only needs to be about 3 to 4 feet high, but it should be securely staked to the ground to prevent the beavers from crawling under it or pushing it over. Once plants at a restoration site have established themselves, they should be able to withstand some beaver activity. Typical shoreline tree species such as willows thrive with beaver cuttings resulting in denser growth patterns that benefit a variety of nesting songbirds.
Flooding and damming problems can be countered effectively with well-designed, well-made flow control devices. Skip Lisle, wildlife biologist with the Penobscot Nation in Maine, has devised the "beaver deceiver" flow control device that is shown in the Peterson Pond installation. He has also installed devices of his design at 18 culvert sites on the 130,000 acre Penobscot Nation lands. Beaver-related road maintenance costs had previously been a major cost as most of the land is forested and supports a large population of beaver. For the past 6 years, after installation, road maintenance costs in the Penobscot Nation due to beaver conflicts have been virtually non-existent. Beaver colonies continue to thrive near the devices and to maintain the wetlands and associated ecological benefits at no additional cost.
The Peterson Pond installation is composed of three components, a receiver fence, a pipe, and a round fence. The receiver fence serves to exclude the beaver from the outlet of the pond. In many situations all that might be required would be a receiver fence to exclude the beavers from a culvert opening. Where a receiver fence must be smaller than desired because of site characteristics, then a pipe and round fence might be added. The pipe extends upstream from the receiver fence and then the upstream end of the pipe is protected by a round fence.
Before attempting installation of any devices in streams and wetlands, please be sure to get all the proper permit approvals. In Washington, a Hydraulic Permit Approval is required from the Washington Department of Fish and Wildlife and there may be local county or city permits required as well. In the Puget Sound region, additional federal permits may also be required if the proposed work is located on larger stream systems in watersheds where Chinook salmon may be present.