MSU professor outwits beavers after 10-year struggle against dams

October 5, 2005

STARKVILLE, Miss.–After fighting a 10-year battle of wits against beavers, David Smith believes he finally has found a way to keep water flowing through pesky dams they erected on his family’s Rankin County property.

“It’s a matter of trying to outsmart that critter and he’s pretty shrewd,” said Smith. “The animal is nocturnal and you don’t see them”–just the results of their work.

A longtime professor of agricultural and biological engineering at Mississippi State, Smith said beavers for years have been building dams across drainage channels on a few hundred acres of family-owned timberland at Richland Creek on the Pearl River.

The rodents come in at night and build dams up to 20 feet wide across ditches that ordinarily keep water draining naturally across the land, he explained. The dams create water pools in which they can fish for food and provide space for building lodging hutches.

“Water was backing up on our family land,” said Smith, a native of the Richland community just south of Jackson. “It causes upstream damage to timber, crops and recreational areas, and the stagnant water attracts snakes.”

Trying to control the beavers by killing or trapping them had proven futile, he noted, and the furry, buck-toothed varmints quickly rebuilt dams that had been destroyed.

“Once you tear down an active dam and the fresh water starts flowing, it’s like a red flag to the beavers,” he said. “I’ve seen ’em swimming back upstream to repair a dam, even before dark.

“I tried to get a solution to this problem for 10 years,” said Smith, a machinery design and development research specialist in the university’s department of agricultural and biological engineering since 1983.

He has not been alone in his struggle against the gnawing menace.

According to Kris Godwin, wildlife services director for the U.S. Department of Agriculture’s Animal Plant Health Inspection Service in Mississippi, beavers cause millions of dollars in damage to the timber industry, roads, private property, and agriculture throughout Mississippi and the Southeast.

“Beavers cause damage not only from building dams that impede water flow, but also from digging and burrowing into structures such as road beds, and pond and lake levees,” added the MSU-based overseer of Mississippi’s Beaver Control and Assistance Program.

“They also cause extensive damage to timber and landscaping by chewing trees and shrubs,” Godwin added.

In certain situations, experts say water level control devices may be effective in reducing flooding to a tolerable level for landowners, while maintaining suitable beaver habitat. That involves placing some type of device through a dam to keep the water flowing without disrupting the beavers’ normal activities.

That’s easier said than done, as Smith found out over a decade of weekends and holidays spent wading through murky drainage waters and digging into beaver dams–all the time keeping an eye out for water moccasins–while jury-rigging a trial-and-error solution to the problem that had plagued him for so long.

He tried burying three or four 10-foot lengths of four-inch PVC pipe into a cutaway part of the dam, but the beavers would just build back over the pipe.

“They’d also cover the upstream end of the pipe with mud and sticks,” he said.

Next, he placed a six-foot diameter of “hog wire” around the upstream end of the pipe, but the beavers “simply built a dam around the hog-wire circle to prevent water from entering.”

He tried using PVC pipe only one-inch in diameter to keep the water flow rate and noise low, placing the upper end of the pipe 20 feet upstream from the dam. Beavers didn’t stop it up, but a variety of floating objects such as leaves and small sticks did.

Finally, Smith installed a system of four PVC pipes, each one 10 feet long (for a total length of 40 feet) and four inches in diameter. Two rows of three-quarter-inch holes are drilled along the first 10-foot section upstream. The sections are placed beneath the surface of the water with the holes directed away from the bottom. The end of the pipe is sealed off with mesh wire or duct tape, or a 90-degree elbow or tee cap.

“The idea is that the beaver won’t be able to get in there and plug up the little holes,” he said. “You can go to a hardware store and buy the PVC pipe–sewer pipe with the holes already drilled and the solid lengths.”

Smith said he installed one device in each of six dams on his property about 18 months ago with help from his two sons, and all seem to be working as they should.

“Apparently, the flow through the holes is low enough that the beavers can’t detect it,” he said. “I’ve seen no evidence that they’ve tried to plug the holes with mud and twigs.

“It’s been more time-consuming than costly,” he added. “Now, I just want to get the information out to others.”

For more information, contact Smith at (662) 325-7351 or; Godwin at 325-3015 or