MDC testing effective method to limit water levels behind beaver dams

El Dorado Springs, Mo. – Beavers are hard-working and clever engineers when building dams on small streams. They create pools and wetlands that benefit wildlife, but too much water can pose problems for landowners. Missouri Department of Conservation (MDC) biologists are testing a self-built “beaver deceiver” system that can help land managers eliminate problems from water backup behind beaver dams. Landowners who want more wildlife can use the systems to control water levels while keeping benefits the beavers can provide, for free.

Left alone, beavers will build dams higher to raise water levels. But a simple cage and tube system can keep water levels behind a dam steady. A cage can be constructed from wire fencing such as livestock fence panels clipped together around a large plastic drain tube, which is suspended in the cage. The outlet tube is buried in a notch in the beaver dam.

Mike Allen, MDC fisheries management biologist, built and installed a system in a beaver dam on Baker Branch at the Taberville Prairie Conservation Area north of El Dorado Springs. Thus far, beavers have been unable to harm the system or block water from flowing through the cage and tube. The system he built cost less than $1,000, and they can be installed for less than $500.

“They can’t get big materials through the cage,” Allen said, of dam building materials like sticks. “Small materials that they do put in the cage wash away.”

In April, biologists inspected the cage system at Baker Branch and the small wetland the beavers had created. As they approached, a glossy ibis, which is a large wading bird, took flight. Upon closer inspection they saw migrating blue-winged teal and shorebirds using the pool. A pair of Canada geese nested downstream of the dam. Small prairie fish species swam in the pool below the outlet. On the dam were crayfish shells.

Beavers created the prairie wetland habitat along this small headwater stream. Missouri’s grasslands and woodlands were likely covered by thousands of similar wetlands rich with aquatic wildlife and plants before European settlement brought the fur trade and farming that almost eliminated beavers.

Today, beavers damming small streams can cause problems in some situations. Landowners are allowed by regulations to protect property from wildlife damage. Beavers can be trapped and killed to protect crop fields and pastures, or to prevent flooding over roads or blockage of drainage structures such as tubes and culverts. Landowners experiencing issues with beavers can contact MDC for assistance with the removal of beavers.

However, there are ways to co-exist without lethal means.

Once beavers are removed from a stream site, others will eventually move into the territory. The cage and tube system, otherwise known as beaver deceivers, allows beavers to use the stream but keeps water levels low enough to prevent damage to crops and pastures or roadways. Beavers can work non-stop on a dam but still not raise water levels because the cage outlet keeps water flowing downstream. This is an option for both parties to co-exist.

For landowners who want wildlife on their property, beaver dams have benefits. Small creeks with low flow have value for fish and wildlife. But the value is limited if only a narrow, shallow channel has water flow. Beaver dams can hold more water in a stream system. They trap nutrients and sediment, and they create nurturing moist areas for plant growth, increasing the opportunities and niches for other critters above and below the water. Beaver dams also allow fish passage while holding back water. Small fish can still get through the semi-permeable stick-and-mud dams. At high flows, most fish can pass over or around the dams. Beaver dams also eventually fail, flow returns, and new dams are built in other places.

“There wouldn’t be water here if it weren’t for the beaver dams,” said Frank Nelson, MDC wetland systems manager, who inspected the Baker Branch cage outlet set up. “The interaction of water and land is important. Beavers providing wetland habitat within a prairie matrix adds to the biodiversity of Taberville Prairie.”

The pools and wetlands created by beaver dams can provide water storage that becomes a critically important refuge for aquatic life during drought, which is being experienced more widely and more often.

Another benefit for landowners is that beaver dams can sometimes help reduce or eliminate head cutting (gullying) in crop fields. Head cutting is when swift and heavy water flows scour channel bottoms downward and wash away the sides of channels, which can eat into productive crop land and lower the water table. The pools beavers create can reduce erosion at no cost to landowners and help maintain groundwater levels. Landowners can use the cage-and-tube system to manage water levels.

“This requires the landowner to set a little bit aside,” Nelson said. “But the beavers can help with head cuts and hold water during droughts.”

For more information about using the cage and tube system to manage water levels behind beaver dams, contact Mike Allen at 417-876-5792, ext. 1953, or via email at mike.allen@mdc.mo.gov. For guidance and specifications on installing beaver deceivers from The Beaver Institute, visit https://short.mdc.mo.gov/4Av. To learn more about beavers in Missouri, visit https://short.mdc.mo.gov/4dk.