Beaver Damage Preventable With Appropriate Techniques
Originally published February 2003, revised 2007
Beaver damage concerns more Oklahoma landowners than damage caused by any other native wildlife species. Beavers have intrinsic values, but unfortunately they damage some things that we build or grow. Some values of beaver include being enjoyable to watch, creating wetlands, providing fur, controlling trees where undesirable along water, and serving important ecological functions in native plant and animal communities ("web of life" stuff). However, they frequently conflict with human interests when they dam drainages, plug drain or overflow pipes, excavate dens into embankments and girdle or cut desirable woody plants.
Effective lethal beaver control options exist such as trapping with Conibear traps and night shooting. However, both techniques provide only temporary results and are illegal in Oklahoma unless performed by USDA Wildlife Services wildlife damage control specialists or by a person who obtains special training and an Oklahoma Department of Wildlife Conservation (ODWC) Nuisance Beaver Control Permit. Oklahoma Wildlife Services can be contacted at (405) 521-4039 and information about the ODWC Permit can be obtained at (405) 521-3719. Both techniques are legal in Texas without special permits or licenses. Live beaver, carcasses or furs should not be taken into possession in either state without appropriate licenses.
I do not dislike beavers - I dislike their damage. Ideally, we look for ways to prevent beaver damage while coexisting with beavers. Most human-beaver conflicts can be prevented with relatively permanent nonlethal techniques. An October 1997 NF Ag News and Views article addressed box-type parallel bar barriers, which usually prevent beaver plugging of drain and overflow pipes. A July 1991 NF Ag News and Views article addressed wire exclosures for protecting trees. The 1997 article is available on the Noble Research Institute Web site. Both articles can be obtained by contacting the Ag Division Helpline at (580) 224-6500 or one of the Foundation's wildlife and fisheries specialists.
Occasionally, beaver dam around the outside of a properly constructed box-type parallel bar barrier. When this occurs, a perforated intake pipe can be installed on the bottom of the pond or pool, which usually overcomes the problem. An example of such an intake pipe is shown in Figure 1. The intake pipe should have an inside diameter larger than the drain or overflow pipe to minimize reduction in drain or overflow pipe efficiency. The lower end of the intake pipe should be plugged to prevent beaver access to the inside of the pipe. An adequate number of 3/4- to 7/8- inch diameter holes should be drilled in the top half of the lower portion of the pipe so their combined surface area exceeds the surface area of the pipe's end, which minimizes reduction in drain or overflow pipe efficiency. The pipe should be inserted into the box-type parallel bar barrier and anchored to the bottom. After installation, all the 3/4- to 7/8-inch holes should be below the water's surface at normal impoundment water levels to prevent beaver plugging them.
A perforated bottom intake pipe, like the one described above, can be used to lower water level or mostly drain an impoundment or flooded area created by a beaver dam. To install such a pipe, a beaver dam should be cut at the deepest point of the drainage and the pipe inserted with 3 to 6 feet extending beyond the back of the beaver dam. The back of the pipe should be lifted off the ground and it should be higher than the intake end. Beaver usually close the dam over the pipe (if not, the objective is accomplished anyway). The height of the back of the pipe determines the water level in the remaining pool. The pool should be deep enough to completely cover all the 3/4- to 7/8-inch holes when the pipe is not flowing water. If water does not cover the holes, beavers will plug or cover the holes with mud and debris. It is best to maximize the distance between the drilled holes and the dam.
Sometimes, beaver dam along the inside of a properly constructed box-type parallel bar barrier by crawling through a drain or overflow pipe. A flapper gate can be installed on the lower end of a drain or overflow pipe to prevent beavers from entering the pipe. An example of a flapper gate is shown in Figure 2.
Beaver excavation into embankments can be prevented with a layer of riprap on the water side of an embankment. Installation of a riprap barrier is shown in Figure 3. Riprap should extend 4 feet below and 2 feet above normal impoundment water levels. Riprap needs to form a continuous layer because any gaps of exposed soil will allow beaver excavation. If beaver already excavated dens prior to installation of riprap, it is best to remove the beaver population from the site with lethal control techniques before covering their den entrances with rock. If trapped inside an embankment, beaver will try to escape through additional excavation, which may cause more problems.
We have successfully used wire exclosures, box-type parallel bar barriers, perforated bottom intake pipe, flapper gate and riprap barriers at ponds with resident beaver populations on the Foundation's Pasture Demonstration Farm (PDF).