Beaver populations have been relatively high for many decades due to lack of extensive trapping and abundant beaver food habitat like aspen. Beaver can cause considerable problems for county road commissions, other government road maintenance personnel, private land owners trying to maintain an access road across a stream crossing, and waterfront land owners with beaver preferred trees in their yards. Beaver create problems by tree cutting, building dams and flooding stream crossing areas, and blocking culverts.
Beaver are especially aggressive in the late summer and fall. As a Michigan Department of Natural Resources fisheries biologist, I dealt with beaver issues for several decades related to excessive beaver damming having such a detrimental affect on trout stream habitat. There is one overwhelming fact of dealing with beaver problems – in the short run you have to remove the beaver to solve the problem.
For many years I have watched road maintenance personnel, railroad maintenance, Department of Natural Resources and Forest Service personnel and private land owners attempt to control beaver flooding, plugged culverts, threatened road grades, and cutting of desirable trees. Any attempt to control these beaver related problems without removing the beaver is futile. Sometimes in the spring or summer a beaver flooding may stay down for a little while but the beaver always rebuilds it and you are back to the problem you started with. In the late summer and fall work crews can unplug a culvert and draw the water down with the beaver still in place, typically the dam will be rebuilt, culvert plugged and the water flooding the next day. In some cases, culvert clearing became a daily chore for road maintenance personnel due to the likelihood that the road could wash out.
We found from years of experience that the best control measure on beaver is to obtain the services of a skilled damage control beaver trapper. Ideally if the beaver problem is not bad yet, you could arrange an experienced trapper to remove all the beaver in that area during the regular trapping season. Unfortunately, beaver problems often crop up well before the late fall trapping season. If the problem is pressing, a free Beaver Damage Control Permit can be obtained from the DNR – Wildlife or Conservation Officer. This allows the land owner or road crew to remove the beaver outside of trapping season if there is proven damage or likely damage (road washout etc.).
Catching beaver during the non-trapping season is more difficult due to their behavior being somewhat different from what many beaver trappers are used to dealing with. Trappers that are capable of catching all the beaver in a colony typically charge to cover their mileage and time. Sometimes interested parties can get names of damage control trappers from the DNR, US Forest Service or your local road commission. Inexperienced trappers will often create more of problem for you in the long run. They can sometimes catch or scare one or two of the young beaver resulting in the rest of colony with adults being much more wary.
A common mistake we heard was land owners stating their intention to remove the beaver by shooting them at dusk or dawn. Research indicates the average beaver colony is about five animals. Anyone trying to shoot all the beaver in a colony when they are all out at one time will find out quickly that is impossible. The most likely scenario is that one or two at most of the less wary young may be vulnerable to shooting and then the rest of the colony will become completely nocturnal. Shooting beaver is not easy since there is very little of the beaver visible when they are swimming in low light. Shooting should only be used as a last option if a remaining beaver is trap shy from past failed trapping efforts.
In the beginning of my DNR career, conservation officers and fire officers (DNR road maintenance responsibility) would blast beaver dams out with dynamite. Times have changed with terrorism resulting in extreme Federal government control over high explosives and dams are not blasted anymore. Another danger of blasting beaver dams is the likelihood of washing out downstream roads, culverts and stream crossings. Obviously, when a large dam (some up over six feet high) is suddenly breached a large head of water rushes downstream. This should be stressed to anyone who intends to breach a beaver dam with water impounded – it can do great damage downstream and any potential problem stream crossings close by downstream should be scouted out ahead of time. The danger of washout is even greater if there is significant gradient downstream with little flood plain to spread out the rapidly outflowing water.
If downstream road crossing is a concern, great care should be taken to draw down the beaver dam very gradually. I used to have two minimum security prison crews removing beaver dams where beaver populations were removed on 250 miles of trout streams in the southwest U.P. to maintain trout stream habitat. We found the best tool to remove beaver dams is a heavy-duty potato fork. Of course, beaver dams rarely washout on their own due to the way they are built. Sticks are more or less thatched together with mud and small rocks. The tangle of sticks and roots is fairly indestructible and is typically “self sealing,” where if sticks are removed the remaining structure stays pretty much intact. To draw the dam down a large number of sticks need to pulled out using the potato fork, eventually the earthen and rock berm in the lower portion of the dam has to be breached. It is not easy work although one determined person in reasonably good shape can breach a normal sized beaver dam. This is where having removed all the beaver becomes really important. It is easier to do this chore if you know the dam will not be immediately rebuilt that night.
As stated earlier, if downstream stream crossings are a concern for removing a large head of water the dam can normally be removed gradually. The best practice is to remove a section of the upper portion of the dam and then let the water flow out down to the level cleared, overnight. The next day another portion of the dam can be removed which allows the entire impoundment of water behind the dam to drain more gradually hopefully avoiding any downstream water damage. If the impoundment behind the dam is large, greater care needs to be taken breaching the dam. The largest beaver dam and impoundment any of my stream habitat crews ever removed was about eight-feet high and we estimated the pond behind to be about 30 acres. Anyone who ever witnessed a river flood or tsunami knows the power of rushing water. The crew leader did not draw this large dam down gradually enough and with great water pressure on the remaining dam from the large impoundment it pushed out an entire section of the dam while they were working on it. Luckily the crew was not hurt although it illustrates that when a large dam has to be removed great care should be taken to only remove enough of the dam to relieve some of the water pressure on the dam over the course of several days.
Road engineers explained to me that in the past road grades that are completely saturated by high water can catastrophically fail. One other option that can be taken on an active beaver dam is installing a “beaver proof culvert” if you only need to draw the water partially down. The concept is to dig out a section of the dam and install a beaver proof culvert. This is typically a relatively large volume PVC or plastic culvert with the upper end blocked off. Holes are drilled in the bottom of the culvert that allows water to flow into the pipe over a larger surface area the beaver don’t instinctively plug. The design for this type of specialized culvert can be found with a normal online search engine. We found that nothing is maintenance free and normal debris and plant material, leaves etc. plug up the underlying holes.
One thing to remember is the easiest way to minimize beaver problems in Northern Michigan is to not create ideal beaver habitat next to stream crossings. Clearcutting aspen and other deciduous trees desirable to beaver near streams can result of 40 years or more of ideal beaver food habitat. Of course, beaver are in the rodent family and they are extremely prolific. If good food habitat (aspen, poplar etc.) is present near water any land owner or maintenance crew will likely have decades of reoccurring problems. The only long-term solution to minimize beaver problems is converting nearshore stream habitat to conifer that the beaver don’t utilize for food.