BEAVERS AND CULVERTS: Damage control does not require killing them
(from Maine Townsman, June 2001)
By Antoinette Mancusi, Technical Advisor, MMA

On May 23 in Orrington, Maine a large beaver dam let go.  The water that was released washed out a portion of a local road, causing an estimated $200,000 worth of damage (although initial estimates were as high as $1.5 million).  On a scale of beaver problems this was a calamity.  Town Manager Dexter Johnson, who is still very occupied in dealing with the aftermath, reports that the pond area created by the dam might have covered as much as 50 acres in area. Two theories exist for the dam collapse. One alleges human tampering with the dam the other the lack of beaver present to tend to the dam because of trapping and/or relocation.

Luckily most beaver build-up problems (a.k.a., beaver nuisances) do not even come close to the scale of the Orrington incident.  The most common problems associated with beavers occur when beavers build dams within or in front of culverts found under roads.  There are several theories explaining why beaver are drawn to culverts.  One theory proposes that beavers, which are natural born engineers, may see culverts as a hole in a dam in need of reparation.  Beavers then plug the hole and when conditions are right, road flooding may occur.  Another theory suggested by regional wildlife biologist, Keel Kemper of Maine Inland Fisheries and Wildlife Department (IFW), suggests that beavers are drawn to culverts because they are drawn to natural constrictions in a watercourse.  These are just two of many theories and there undoubtedly exist a variety of other factors that may draw the beaver.  Regardless of the specific reasons behind the dams – the fact remains – beaver are here to stay and municipalities and road crews must find creative measures to resolve beaver and culvert conflicts.

So how do municipalities control beaver build up and can such controls occur without killing beaver and destroying precious beaver habitat?  Regardless of the method of control selected, proactively dealing with the problem, i.e., as soon as it becomes apparent, is probably the best way to go.  Waiting until the beaver population has become a colony augments the cost and level of difficulty attributed to remediation of the nuisance.

“Managing Nuisance Beavers Along Roadsides – A Guide for Highway Departments” by Paul G. Jensen and Paul D. Curtis from the Department of Natural Resources, Cornell University and David L. Hamelin from the Division of Fish, Wildlife, and Marine Resources, New York State Department of Environmental Conservation (1999), is a comprehensive resource on the topic replete with schematic diagrams of devises and other engineering considerations. (Refer to the additional “resources list” at the end of this article for other resources).  “Managing Nuisance Beavers Along Roadsides – A Guide for Highway De-partments” can be accessed at the following a web site:

According to the authors of this guide, proactive strategies for roadside nuisance beaver management include:

• At sites where beavers are present in the stream or watershed but have not obstructed the culvert pipe, measure its size and evaluate its probability of being plugged. Just because beavers have not plugged a pipe in the past does not mean they will not do so in the future. Catalog these sites for future culvert replacement plans. At sites where beavers are not present in the roadside area, measure and catalog current habitat conditions at each stream crossing. This process can be done over several years.

• Document the size of the culvert inlet, stream gradient, and percent open area. If money is allocated for proactive replacement of culvert pipes, rank sites based on the probability of beaver presence. 

• When planning and designing roads, evaluate site conditions to assess potential beaver habitat. If beavers may be present in the area, consider road (height of base) and culvert (type, size) characteristics that will minimize potential beaver problems in the future.

In addition to experts agreeing on the importance of proactive planning, experts also agree that beaver problems can be controlled without killing the beaver.  Killing beaver is actually only a short-term solution, as they tend to come back.  Furthermore, the destruction of beaver may reduce the value of natural wildlife habitat, which is vital to the pristine essence of Maine.  Albeit not all beaver sites are of “high natural resource value”, as Kemper of IFW explained.  Municipalities must evaluate measures used in resolving beaver issues relative to the value of the resource they seek to preserve.

So, what are some of the options?  According to IFW staff wildlife biologist, Henry Hilton, alternatives in order of descending priorities include:

1. Prevention:  build roads and structures to accommodate beaver activity; identify and rectify potential problems before they become costly and difficult to correct.

2. Address beaver problems by controlling the flow of water via siphon pipes, diversion fencing, etc.  (Kemper of IFW also strongly encourages always “ placing fencing in front of culverts).

3. Use other non-lethal procedures, including live trap/transfer to more appropriate locations when possible.

4. Use lethal control as a last resort.

Hilton adds, “From the experience of Inland Fisheries and Wildlife Department, lethal control can be minimized dramatically without increasing risk of damage by flooding.  Regional wildlife biologists are available to assist municipalities, road crews and supervisors in determining non-lethal options to beaver control.”  Municipalities should contact their closest IFW regional office for beaver control assistance.  (see sidebar listing regional IFW office telephone numbers.)

Another resource that may be available to municipalities is the USDA, Cooperative Beaver Management Program, which works in conjunction with IFW.  Ed Butler, state director for USDA, Wildlife Services (of which the Cooperative Beaver Management Program is part) explains that the USDA staff works with IFW across the state to remedy beaver problems.  All but two IFW regional offices (Strong and Gray) have USDA staff actually assigned to them. 

Butler explains that most beaver problems his office deals with are solved using non-lethal methods or controls.  He also added that because the Cooperative Beaver Management Program resources are limited, the Cooperative selects projects undertaken on a case-by-case basis.  Although the USDA program does not currently charge for materials needed for beaver diversion devices, the USDA does charge a rate of $12 an hour for labor on such projects per person assigned (normally only one person is assigned at each project).  An average project can take anywhere from a half day to an entire day and wind up costing from $50 to $200 for labor. 

Another avenue municipalities may explore is the use of Urban-Rural Initiative Program (URIP) funds toward capital improvement projects that can include beaver problem remediation under certain circumstances.  Peter M. Coughlan, director of the Community Services Division for the Maine Department of Transportation explains that "the purpose of a capital improvement is to spend the funds on a long-term repair to a road that will generally result in a ten-year life expectancy of the repair.  If a particular road is subject to the damaging effects of a beaver dam or culvert blockage such as a continued saturated road base, constant erosion, washouts and flooded periods, then the use of URIP funds for the construction (not maintenance) of a 'system' would be an appropriate expense."  Municipalities wishing more information on the use of URIP funds are encouraged to contact the Department.

Regardless of the option selected for addressing beaver “issues,” municipalities and their road crews must remember that unauthorized killing of beaver or destroying or tampering with beaver dams is illegal under Maine law (12 M.R.S.A. § 7504, 38 M.R.S.A. § 480-Q) and IFW wardens are authorized to prosecute such offenses.



Additional Resources

Web Sites:   (not active link)  

Inland Fisheries & Wildlife Regional Offices: 

1.        Gray  657-2345

2.        Sidney  547-5300

3.        Greenville  695-3756

4.        Ashland  435-3231

5.        Machias  255-4715

6.        Strong  778-3324

7.         Enfield  732-4132