Rodent Control

Contents

Groundhogs and Groundhog Control

Muskrats and Muskrat Control

Eliminating Burrows

Beaver

Hunting and Trapping

Resources

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Why is rodent control necessary?

Rodents such as the groundhog (woodchuck), muskrat, and beaver are attracted to dams and reservoirs, and can be quite dangerous to the structural integrity and proper performance of the embankment and spillway. Groundhog and muskrat burrows weaken the embankment and can serve as pathways for seepage. Beavers are attracted to running water and may try to plug the spillway and raise the pool level. Rodent control or eradication is essential in preserving a well-maintained dam.

If left uncontrolled, these burrows can hollow out and weaken embankments and spillways, increasing the risk of slides, seepage, and failure.


 

Groundhogs

The groundhog is the largest member of the squirrel family. Its coarse fur is a grizzled grayish brown with a reddish cast. Typical foods include grasses, clover, alfalfa, soybeans, peas, lettuce, and apples. Breeding takes place during early spring (beginning at the age of one year) with an average of four or five young per litter, one litter per year. The average life expectancy is two or three years with a maximum of six years.

Occupied groundhog burrows are easily recognized in the spring due to the groundhogs habit of keeping the burrowcleaned out. Fresh dirt is generally found at the mouth of active burrows. Half-round mounds, paths leading from the den to nearby fields, and clawed or girdled trees and shrubs also help identify inhabited burrows and dens.

When burrowing into an embankment, groundhogs stay above the phreatic surface (upper surface of seepage or saturation) to stay dry. The burrow is rarely a single tunnel. It is usually forked, with more than one entrance and with several side passages or rooms from 1 to 12 feet long.

Groundhog Control

Control methods should be implemented during early spring when active burrows are easy to find, young groundhogs have not scattered, and there is less likelihood of damage to other wildlife. In later summer, fall, and winter, game animals will scurry into groundhog burrows for brief protection and may even take up permanent abode during the period of groundhog hibernation. Groundhogs can be controlled by using fumigants or by shooting. Fumigation is the most practical method of controlling groundhogs. Around buildings or other high fire hazard areas, shooting may be preferable. Groundhogs will be discouraged from inhabiting the embankment if the vegetal cover is kept mowed.

Gas cartridges may be purchased at garden supply and hardware stores. Information about the use and availability of gas cartridges may be obtained from county extension offices, or the U.S. Department of Agriculture.


 

Muskrats

The muskrat is a stocky rodent with a broad head, short legs, small eyes, and rich dark brown fur. Muskrats are chiefly nocturnal. Their principal food includes stems, roots, bulbs, and foliage of aquatic plants. They also feed on snails, mussels, crustaceans, insects, and fish. Usually three to five litters, averaging six to eight young per litter, are produced each year. Adult muskrats average one foot in length and three pounds in weight. The life expectancy is less than two years, with a maximum of four years.

Muskrats can be found wherever there are marshes, swamps, ponds, lakes and streams having calm or very slowly moving water with vegetation in the water and along the banks. Muskrats make their homes by burrowing into the banks of lakes and streams or by building houses of bushes and other plants. Their burrows begin from 6 to 18 inches below the water surface and penetrate the embankment on an upward slant. At distances up to 15 feet from the entrance, a dry chamber is hollowed out above the water level. Once a muskrat den is occupied, a rise in the water level will cause the muskrat to dig farther and higher to excavate a new dry chamber. Damage (and the potential for problems) is compounded where groundhogs or other burrowing animals construct their dens in the embankment opposite muskrat dens.

Muskrat Control

Barriers to prevent burrowing offer the most practical protection to earthen structures. A properly constructed riprap and filter layer will discourage burrowing. The filter and riprap should extend at least 3 feet below the water line. As the muskrat attempts to construct a burrow, the sand and gravel of the filter layer caves in and thus discourages den building. Heavy wire fencing laid flat against the slope and extending above and below the water line can also be effective. Eliminating or reducing aquatic vegetation along the shoreline will discourage muskrat habitation. Where muskrats have inhabited the area, trapping is usually the most practical method of removing them.


 

Eliminating a Burrow

The recommended method of backfilling a burrow in an embankment is mud-packing. This simple, inexpensive method can be accomplished by placing one or two lengths of metal stove or vent pipe in a vertical position over the entrance of the den. Making sure that the pipe connection to the den does not leak, the mud-pack mixture is then poured into the pipe until the burrow and pipe are filled with the earth-water mixture. The pipe is removed and dry earth is tamped into the entrance. The mud-pack is made by adding water to a 90 percent earth and 10 percent cement mixture until a slurry or thin cement consistency is attained. All entrances should be plugged with well-compacted earth and vegetation reestablished. Dens should be eliminated without delay because damage from just one hole can lead to failure of a dam or levee.


 

Beaver

Beaver do not necessarily burrow into dams but they will try to plug any spillways, outlets and channels with running water with their cuttings, mud, rocks and debris. Routinely removing the cuttings is one way to alleviate the problem but beaver can rebuild their obstructions overnight. Beaver may also establish large intrusive lodges on the banks or lakes formed by dams.  Trapping beaver may be done by the owner during the appropriate season but beaver can migrate up and down a stream or river system and proliferate where habitat is good. 


 

Hunting and Trapping

Because hunting and trapping rules and regulations vary from state to state the appropriate State Wildlife Agency should be consulted to ensure compliance with state regulations.


 

Resources

ASDSO Resources

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Free Webinar
Introduction to Inspecting Dams for Owners and Operators-2013

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Sample Inspection Forms I
Sample Inspection Forms II
Sample Inspection Forms III

The ASDSO website houses national guidelines on dams. Go to:
DamSafety.Org/ManualsandGuidelines

For more information, videos and tools for dam owners go to:
DamOwner.Org

Watch for training in your area sponsored by ASDSO or your State Dam Safety Office. Access your state’s Dam Safety Program by clicking your state at:
DamSafety.Org/States

 

DHS/FEMA Resources

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Pocket Safety Guide for Dams and Impoundments (FEMA National Dam Safety Program)

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Impacts of Animals on Earthen Dams (FEMA National Dam Safety Program)

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Animal Impacts on Earthen Dams - Owner Intro (FEMA National Dam Safety Program)

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Impacts of Plants on Earthen Dams (FEMA National Dam Safety Program)

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Plant Impacts on Earthen Dams-Owner Intro (FEMA National Dam Safety Program)

Dam Safety: An Owners Guidance Manual (FEMA National Dam Safety Program)

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Identification of Visual Dam Safety Deficiencies (FEMA Training Aids for Dam Safety [TADS])

The Department of Homeland Security and FEMA make several publications and videos available through their websites. Visit their websites below and search "dam safety" for more information.
FEMA.gov
DHS.gov

 

Videos

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Perfect to Imperfect Dam - Maintenance (YouTube, Download)
Piping Failure (YouTube, Download)
Slope Failure  (Youtube, Download)
Identification of Visual Dam Safety Deficiencies
 (FEMA Training Aids for Dam Safety [TADS])

 


 

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