Beaver Flow Device Studies

1.) Effectiveness of Water-flow Devices as Beaver Conflict Resolution Tools, A Satisfaction Survey of Massachusetts Clients (summary – for a full transcript contact us).

By Mary Spock 2006. 
Center for Animals and Public Policy, Cummings School of Veterinary Medicine at Tufts University


Management of beaver-human conflicts causes much controversy in the Commonwealth of Massachusetts, as does the related law, the Wildlife Protection Act. Over the past decade, numerous devices to control flooding caused by beaver dams have been installed in the state as a means to solve these conflicts. This study reports the results of a survey in which people with first-hand experience with beaver water-flow control devices were asked about their experience with the devices. The study:

  • focuses only on professionally installed devices, as the variation in self-installed devices, both in design and in effectiveness, is too great to yield meaningful answers;
  • was conducted by a party not affiliated in any way with any of the installers of the surveyed devices;
  • shows that people who use the devices are satisfied with them, but also finds an undercurrent of skepticism about them.

A telephone survey of clients found that 93.3% were satisfied with the devices, and 63.3% of respondents claimed the highest level of satisfaction offered as a response, “very satisfied.”

2.) Two Break-through University Beaver Reports, Flow Devices Solve Flooding Problems in Two States.

Two university studies of beaver flow devices, one done in Virginia and another from Massachusetts, are good news for taxpayers, environmentalists and beaver advocates. Flooded roads are the most common type of beaver conflict and, despite growing evidence to the contrary, many government agencies still promote trapping—not flow devices—as the best cure. For example, the Massachusetts wildlife agency has claimed that “…very few beaver problems (only 4.5% in Massachusetts, 3% in New York) can actually be solved with a water level control device.” Now, well-documented reports from two states show that landowners, highway department personnel and others were overwhelmingly satisfied (93 to 100%) with professionally-installed flow devices.

In the Virginia study, funded by the Virginia Dept of Transportation (VDOT) and sponsored by Christopher Newport University, wildlife biologist Stephanie Boyles arranged for Skip Lisle to install flow devices at 14 sites in the flat Coastal Plain. All sites were selected by VDOT because of “chronic beaver damage problems,” According to Boyles later survey of adjacent landowners and VDOT personnel in “Report on the Efficacy and Comparative Costs of Using Flow Devices to Resolve Conflicts with North American Beavers along Roadways in the Coastal Plain of Virginia,” the installations solved all the flooding problems.

The report notes, “the Virginia Dept of transportation (VDOT) spent well over $1,000,000.00 attempting to reduce or eliminate damage attributed to beaver activity along state roads from 2000 to 2005.” Agencies have long considered trapping beavers and destroying dams as the best way to stop the road damage, but because flat-tailed immigrants usually reoccupy the trapped sites such removal is an expensive and short-term remedy. For example, “from 2000 to 2005, Virginia Department of Transportation (VDOT) alone lost $800,000.00 in actual resources and spent more than $900,000.00 to have a federal agency remove over 1,000 beavers and 696 dams at 530 damage sites along roadways in Virginia.”

Boyles’ study, which was part of graduate work at Christopher Newport University, describes flow device installations done by Skip Lisle in 2004 and 2005 and includes a post-installation survey. Boyles obtained funding from the Virginia Dept of Transportation (VDOT) for Lisle to design and install 33 flow devices at 14 sites that were selected by VDOT personnel because of chronic beaver damage problems.

The sites were in seven counties bordered by the Atlantic Ocean and Chesapeake Bay. Anyone involved with beavers always hears the notion that flow devices do not work on flat land, despite some contrary evidence. All the 14 study sites were located in Virginia’s Coastal Plain “to evaluate the premise that flow devices …are ineffective in streams with low gradients.”

This study includes surveys from VDOT personnel and landowners adjacent to the sites about whether flooding occurred before and after the plus the total costs involved before the installations and afterward in the spring of 2006. The two basic types of beaver damage sites were “1.) narrow outlets, such as road culverts… 2.) beaver dams that are not attached to manmade structures. At culverts, Lisle used his wood-framed, usually trapezoidal Beaver Deceiver™ fences that spread water over a long perimeter to reduce the “feel” of running water.”

At dams, Lisle installed his Castor Master™ system of one or more black, corrugated polyethylene pipes. At the pipe inlets he used filters called Round Fences™ that resemble cylindrical cages. Most of the installations were at road culvert where Lisle normally used all three devices as added insurance against beaver plugging. A site on Pope’s Creek needed an extra large Deceiver to enclose four culverts and a similarly huge filter at the pipes’ inlet. But Lisle installed a Round Fence™ alone in June 2004 to protect a vertical culvert directing water underneath Route 1102 at the Blackwater Swamp in Prince George County.

According to Boyles’ study, “Beaver population control activities were conducted at 10 of 14 sites prior to installations at an average cost of $5969.00 per year, or $994.90 per site, at the six sites where VDOT paid for beaver population control activities.  Following preventative maintenance and beaver population control efforts, 100% of the study sites were re-occupied by beavers. VDOT personnel and landowners also reported that road repairs attributed to beaver-related damage were carried out at five sites prior to installations at a total cost of $145,000.00 and an average cost of $29,000.00 per site.”

Overall, the surveys showed both VDOT and landowners were satisfied with the flow devices’ performance. No beaver trapping was needed after the installations and the average cost annual of maintenance after installation less than $20 per site—0.01% of the previous costs! Huge savings resulted to taxpayers; “Following flow device installations, the estimated cost-benefit ratio was 1 to 8.37, or for every $1 spent, VDOT saved $ 8.37.”

Boyles states, “Given the demonstrated low costs to install and maintain flow devices compared to the high costs of preventative maintenance, road repairs and beaver population control activities, a compelling case can be made to install flow devices in freestanding dams near roads or to protect culverts that beavers could potentially plug. Nevertheless, a more prudent approach may be for transportation agencies to identify conflict sites and install flow devices at sites that have the largest impact on road maintenance and beaver management budgets.

…using flow devices to resolve conflicts with beavers also has tremendous potential ecological and environmental benefits. Every year, transportation departments spend millions of dollars to replace wetlands destroyed in the process of developing new roads. For most wetland restoration projects, the cost per acre is extremely high while success rates are generally low. On the other hand, beavers are successfully restoring wetlands at little to no cost to transportation departments and landowners, except when conflicts occur.

…we could estimate that almost 120 acres of wetlands have been preserved through the use of flow devices in our study.

Meanwhile, in order to advance the “no net loss” wetlands conservation program instituted by U.S government, federal agencies should explore developing programs that reward state transportation departments and cooperating landowners for using non-lethal methods, such as flow devices, to manage beavers while permitting these animals to restore and create valuable wetlands (National Research Council, 2001). An incentive-based program could result in a substantial increase in the restoration of natural wetlands while reducing property damage and maintenance costs.”

At all sites unwanted flooding had occurred prior to Lisle’s work and beaver removal costs had been as high as $1,891 at two sites. Yearly maintenance costs were usually in the $1,000s, up to $43,500 at the Lake Cohoon site. Road repairs were also required at times with the south Pope’s creek site averaging $132,500 in such costs per year. After the installations, no flooding occurred at any of the sites and most sites required only an hour of yearly maintenance.

Over two dozen photos of the installations nicely how devices were adapted to the local terrain with one fence shaped like a comma to fit a meandering stream. Survey Questionnaires given to landowners and VDOT staff are included too. Boyles will be expanding her study this year and generating more detailed data based on feedback received from USDAWildlife Services.

Massachusetts town highway departments funded half the installations in Mary Spock’s study, conducted via the Cummings School of Veterinary Medicine at Tufts University. In “Effectiveness of Water-flow Devices as Beaver Conflict Resolution Tools, A Satisfaction Survey of Massachusetts Clients” Spock, questioned a variety of clients about flow devices installed by three professionals: Skip Hilliker of HSUS, Skip Lisle of Beaver Deceivers Inc. and Mike Callahan of Beaver Solutions. Callahan, the only one based in Massachusetts, had placed 55 of the 51 devices. The types of devices used were trapezoidal culvert fences, pond levelers and leveler/fence systems and one diversion dam. When clients were asked, “Would you use a flow device again?” all responded positively.

Where the issue has been especially controversial “Due to rapid development in Massachusetts, wildlife habitat is shrinking at the rate of about 40 acres per day,”  according to Spock’s 50-page report. She notes that “Trapping long has been part of MassWildlife’s [Massachusetts Division of Fisheries and Wildlife] beaver management plan …”. Yet “As of December 2004, there were only 346 licensed trappers in Massachusetts, and only a third of these are reported as active.” Plus, the 1996 passage of a state ballot initiative that restricted kill trapping “stimulated interest in alternative means to control property damage caused by beaver-related flooding…” As of April 2005, over 400 beaver flow control devices had been installed by just one company, Beaver Solutions.

Internet research (Spock’s paper includes a photo from BWW’s website) was the most common way for Massachusetts clients to learn about flow devices. Two basic types, pond levelers and culvert fences, were installed and both were used together at some sites. (Callahan’s flexible leveler with a cylindrical cage at the pipe inlet is a refinement of Michelle LeClair’s model using a flex pipe with a welded triangular cage at Canada’s Gatineau Park in the 1990s.) At one site, a diversion dam was placed along with a culvert fence. Most “cost between $600 to 1,000” and had been in place for over two years when the survey was done.

“12 private individuals or organization representatives, and 18 municipal employees or volunteers,” answered Spock’s survey, including eight respondents from highway departments that tended to have multiple sites.

Almost a quarter of those who answered the survey had previously tried trapping at the sites with costs varying from $2,000 for eight months at one location to $100 – 200 per beaver for about a dozen animals at other sites. Spock explained, “though satisfied with the devices, most respondents do not see the choice not to trap as an ethical choice, but money- and time-saving solution to their beaver conflict.”

Road or trail flooding was the problem at 55% of the sites. Next came the “potential for flooding” (20%), “land flooding” (16%), “septic, well or groundwater”  (5%), as well as a few sites with both road and land flooding (4%).

Only three installations reported as “not working,” one was a site where beavers were trapped out so there was no high water to be controlled. At another, “The client was a municipal Conservation Commission experiencing flooding on townland. Though the client felt the device was working, the citizens who owned the land surrounding the flooded land were not willing to accept any risk of flooding, and had the beavers trapped.” At the third site, a landowner believed the water was too high “during times of high water, and the cost to augment the leveler/fence would be too great.” Overall, “A telephone survey of clients found that 93.3% were satisfied with the devices…”

71% of the survey respondents had no problems after installations, and of those who needed a device modified, most (69%) liked the results. Modifications involved adding or fine-tuning the pipes to adjust water levels and tightening fences to avoid beavers or turtles getting stuck inside. Beavers built new dams at two sites, yet a client expressed confidence that the same consultant would solve the problem.

“I wish they were a little more aesthetically pleasing: they’re not real sexy,” one person said of the devices. Other comments revealed “a sentiment of distrust running beneath the surface” that Spock attributes to the “lack of solid beaver population data and a lack of understanding of beaver population dynamics, plus the political realities surrounding beaver-human conflicts,” which include being “bombarded with messages from MassWildlife in the media that the beaver population is exploding.”

Massachusetts has long been a hotbed of controversy about beaver management, starting well before the 1996 passage of The Wildlife Protection Act that restricted the use of kill-traps. Although the Act allows use of conibear traps with a permit, new bills to weaken the “ban” have been introduced each year. Public distrust of beaver flow devices has been fomented by statements from MassWildlife (Massachusetts Division of Fisheries and Wildlife) such as “One significant drawback is that very few beaver problems (i.e.: 4.5% in Massachusetts: 3% in New York) can actually be solved with a water level control device.”  Although Spock’s study “sought answers solely based on the performance of the flow devices,” she states “the evidence that flow devices work should prompt the agency to revise its official statement on them…”

Spock explains that the agency’s prediction that “the state’s beaver population would continue to grow exponentially” is unrealistic, according to a long-term study of beaver in the state’s Quabbin Reservation and limiting factors such as available habitat, natural mortality and territoriality. None of these factors were used in a provocative 2004 “Beaver Growth Population” chart from MassWildlife. “Looking at this growth model,” Spock comments, “we can see that with no mortality at all, and 100% of beavers breeding, the population should have grown from MassWildlife’s own population estimate of 24,000 in 1996 to 240,000 in 2006.” No estimate is available for 2006, but, in 2005 a MassWildlife biologist estimated the state’s beaver population at “more than 70,000.” 

Spock notes that “70,000 comes nowhere within shouting distance of the alarmist 240,000 figure. Yes, the population is growing in habitats in the state that are favorable to beaver. But trapping didn’t control the population before 1996 and reintroduction of body-gripping traps or a longer season won’t control it now. The maximum number of beaver reported trapped by MassWildlife between 1985 and 1996 was 2083 in 1994, while the population range given for 1994 was 15,300 to 22,365 beaver, and this increased, regardless of the trapping, to 18,000 to 23,187 in 1995”  [an appendix has documents with relevant statistics].

National Research Council. 2001. Compensating for wetland losses under the CleanWater Act, a report of the National Academy of Sciences. National Academy Press, Washington, D.C., U.S.A.

3.) A Report on the Efficacy and Cost of Using Flow Devices to Resolve Conflicts with North American Beavers along Roadways in the Coastal Plain of Virginia.

4.) Solving Beaver Flooding Problems Through the Use of Water Flow Devices

5.) An Analysis of the Efficacy and Comparative Costs of Using Flow Devices to Resolve Conflicts with North American Beavers Along Roadways in the Coastal Plain of Virginia

6.) America’s Best Beaver Program

7.) Control of Beaver Flooding at Restoration Projects

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