Technical Manual for 
Dam Owners 
Impacts of Animals on Earthen Dams
FEMA 473 / September 2005

Twenty-five states across the U.S. can write headlines of dam failure caused by nuisance 
wildlife intrusions, and many dam owners find the struggle to adequately manage nuisance 
wildlife at their dams a never-ending story. The Federal Emergency Management Agency 
(FEMA) has funded the development of this manual with the understanding that safe dam 
operation includes comprehensive, state-of-practice guidance on timely inspection and observation 
of wildlife damages, accurate wildlife identification and mitigation, and appropriate 
dam design, repair, and preventive measures. It is hoped that the information and methods 
contained in this manual will compose the core of dam management routines practiced by 
dam specialists across the country. Armed with education and diligence, dam specialists can 
prevent animal intrusion dam failure from becoming headline news. 

Technical Manual for 
Dam Owners
Impacts of Animals on Earthen Dams

i
Table of Contents
1.0 Introduction and Purpose of Manual ...........................................................................1
1.1 Background ............................................................................................................1
1.2 Target Audience, Purpose, and Application of This Manual .....................................2
1.3 Technical Resources Cited .......................................................................................3
2.0 Impacts of Wildlife on Earthen Dams .......................................................................4
2.1 Background ............................................................................................................4
2.2 Hydraulic Alteration ................................................................................................5
2.3 Structural Integrity Losses ......................................................................................6
2.4 Surface Erosion .......................................................................................................6
3.0 Dam Inspection From Two Perspectives: Engineering Function and Biological 
Potential .....................................................................................................................8
3.1 Wildlife and the Earthen Dam ...............................................................................8
3.2 Two-Perspective Dam Inspection Methodology .....................................................9
3.2.1 Zone 1: Upstream Slope Area .......................................................................9
3.2.2 Zone 2: Dam Crest Area ............................................................................10
3.2.3 Zone 3: Upper Downstream Slope Area ....................................................12
3.2.4 Zone 4: Lower Downstream Slope Area .....................................................13
3.2.5 Zone 5: Downstream Toe Area ...................................................................13
3.2.6 Zone 6: Spillway, Outlets, and General Areas ............................................14
4.0 Overview and Identification of Nuisance Wildlife .................................................15
4.1 The Importance of Accurate Wildlife Identification .............................................15
4.2 Identifying Nuisance Wildlife ............................................................................17
4.2.1 Muskrat Overview ....................................................................................17
4.2.2 Beaver Overview .......................................................................................19
4.2.3 Mountain Beaver Overview ......................................................................22
4.2.4 Groundhog Overview ..............................................................................24
4.2.5 Pocket Gopher Overview .........................................................................26
4.2.6 North American Badger Overview ............................................................29
4.2.7 Nutria Overview .......................................................................................31
4.2.8 Prairie Dog Overview ...............................................................................33
4.2.9 Ground Squirrel Overview .......................................................................35
4.2.10 Armadillo Overview ...............................................................................37
4.2.11 Livestock Overview ................................................................................39
4.2.12 Crayfish Overview ..................................................................................41
4.2.13 Coyote Overview ....................................................................................42
4.2.14 Moles and Voles Overview ......................................................................44
4.2.15 River Otter Overview .............................................................................47
4.2.16 Gopher Tortoise Overview ......................................................................48
4.2.17 Red Fox and Gray Fox Overview ............................................................50
4.2.18 Canada Goose Overview .........................................................................52
4.2.19 American Alligator Overview ..................................................................54
4.2.20 Ants Overview ........................................................................................55
5.0 Dam Repair and Intrusion Prevention Through Design ........................................57
5.1 Conformity to the Clean Water Act of 1972 .........................................................57
5.2 The Role of Vegetation Management ...................................................................58
5.3 Burrow Repair Procedures ..................................................................................58
5.3.1 Restoration Measures ................................................................................58
5.3.2 Preventive Measures .................................................................................59

ii
5.4 Dam Repair Zones ...............................................................................................59
5.4.1 Dam Repair Zone 1 .................................................................................60
5.4.2 Dam Repair Zone 2 ..................................................................................62
5.4.3 Dam Repair Zone 3 ..................................................................................62
5.4.4 Dam Repair Zone 4 ..................................................................................63
5.4.5 Dam Repair Zone 5 ..................................................................................63
5.5 Professional Dam Safety Review ..........................................................................64
5.6 Sequenced Repair Program .................................................................................64
5.7 Mitigation Through Design ................................................................................64
5.7.1 Muskrat ...................................................................................................64
5.7.2 Beaver ......................................................................................................66
5.7.3 Mountain Beaver ......................................................................................68
5.7.4 Groundhog ..............................................................................................68
5.7.5 Pocket Gopher .........................................................................................68
5.7.6 North American Badger ............................................................................68
5.7.7 Nutria .......................................................................................................68
5.7.8 Prairie Dog ..............................................................................................68
5.7.9 Ground Squirrel .......................................................................................68
5.7.10 Armadillo ..............................................................................................69
5.7.11 Livestock ................................................................................................69
5.7.12 Crayfish ..................................................................................................69
5.7.13 Coyote ....................................................................................................69
5.7.14 Mole and Vole .........................................................................................69
5.7.15 River Otter .............................................................................................69
5.7.16 Gopher Tortoise .....................................................................................70
5.7.17 Red and Gray Fox ...................................................................................70
5.7.18 Canada Goose .........................................................................................70
5.7.19 American Alligator .................................................................................70
5.7.20 Ants ........................................................................................................70
5.8 Monitoring ........................................................................................................70
6.0 Mitigating Damaging Wildlife ................................................................................71
6.1 Compliance with State and Federal Regulations ..................................................71
6.1.1 Conformity to Federal Regulations ...........................................................71
6.1.2 Conformity to State Regulations ...............................................................72
6.2 Muskrat Management Methods ..........................................................................73
6.2.1 Muskrat Control Through Habitat Modification .......................................73
6.2.2 Muskrat Control Through Trapping ...........................................................73
6.2.3 Muskrat Control Through Fumigants .......................................................75
6.2.4 Muskrat Control Through Toxicants ..........................................................75
6.2.5 Muskrat Control Though Frightening .......................................................76
6.2.6 Muskrat Control Through Repellents ........................................................76
6.2.7 Muskrat Control Through Shooting .........................................................76
6.3 Beaver Management Methods ..............................................................................76
6.3.1 Beaver Control Through Habitat Modification ..........................................76
6.3.2 Beaver Control Through Trapping .............................................................76
6.3.3 Beaver Control Through Fumigants ..........................................................77
6.3.4 Beaver Control Through Toxicants ............................................................77
6.3.5 Beaver Control Through Frightening ........................................................77
6.3.6 Beaver Control Through Repellents ..........................................................77
6.3.7 Beaver Control Through Shooting .............................................................77

6.4 Mountain Beaver Management Methods .............................................................77
6.4.1 Mountain Beaver Control Through Habitat Modification .........................77
6.4.2 Mountain Beaver Control Through Trapping .............................................77
6.4.3 Mountain Beaver Control Through Fumigants .........................................77
6.4.4 Mountain Beaver Control Through Toxicants ............................................78
6.4.5 Mountain Beaver Control Through Frightening ......................................78
6.4.6 Mountain Beaver Control Through Repellents .........................................78
6.4.7 Mountain Beaver Control Through Shooting ...........................................78
6.5 Groundhog Management Methods ......................................................................78
6.5.1 Groundhog Control Through Habitat Modification ..................................78
6.5.2 Groundhog Control Through Trapping ....................................................78
6.5.3 Groundhog Control Through Fumigants ..................................................78
6.5.4 Groundhog Control Through Toxicants ....................................................78
6.5.5 Groundhog Control Though Frightening .................................................78
6.5.6 Groundhog Control Through Repellents ................................................79
6.5.7 Groundhog Control Through Shooting ..................................................79
6.6 Pocket Gopher Management Methods .................................................................79
6.6.1 Pocket Gopher Control Through Habitat Modification .............................79
6.6.2 Pocket Gopher Control Through Trapping ................................................79
6.6.3 Pocket Gopher Control Through Fumigants .............................................80
6.6.4 Pocket Gopher Control Through Toxicants .............................................80
6.6.5 Pocket Gopher Control Through Frightening ............................................81
6.6.6 Pocket Gopher Control Through Repellents ............................................81
6.6.7 Pocket Gopher Control Through Shooting .............................................82
6.7 North American Badger Management Methods ...................................................82
6.7.1 North American Badger Control Through Habitat Modification ...............82
6.7.2 North American Badger Control Through Trapping .................................82
6.7.3 North American Badger Control Through Fumigants ...............................82
6.7.4 North American Badger Control Through Toxicants .................................82
6.7.5 North American Badger Control Through Frightening ............................82
6.7.6 North American Badger Control Through Repellents ...............................82
6.7.7 North American Badger Control Through Shooting .................................82
6.8 Nutria Management Methods ..............................................................................82
6.8.1 Nutria Control Through Habitat Modification ..........................................82
6.8.2 Nutria Control Through Trapping ............................................................83
6.8.3 Nutria Control Through Fumigants ..........................................................83
6.8.4 Nutria Control Through Toxicants ............................................................83
6.8.5 Nutria Control Through Frightening .......................................................83
6.8.6 Nutria Control Through Repellents ..........................................................83
6.8.7 Nutria Control Through Shooting ............................................................84
6.9 Prairie Dog Management Methods ......................................................................84
6.9.1 Prairie Dog Control Through Habitat Modification ..................................84
6.9.2 Prairie Dog Control Through Trapping .....................................................84
6.9.3 Prairie Dog Control Through Fumigants ..................................................84
6.9.4 Prairie Dog Control Through Toxicants .....................................................85
6.9.5 Prairie Dog Control Through Frightening .................................................85
6.9.6 Prairie Dog Control Though Repellents ....................................................85
6.9.7 Prairie Dog Control Through Shooting ....................................................85
6.10 Ground Squirrel Management Methods .............................................................85

6.10.1 Ground Squirrel Control Through Habitat Modification .........................86
6.10.2 Ground Squirrel Control Through Trapping ............................................86
6.10.3 Ground Squirrel Control Through Fumigants .........................................86
6.10.4 Ground Squirrel Control Through Toxicants ...........................................86
6.10.5 Ground Squirrel Control Through Frightening .......................................87
6.10.6 Ground Squirrel Control Through Repellents .........................................87
6.10.7 Ground Squirrel Control Through Shooting ...........................................87
6.11 Armadillo Management Methods ......................................................................87
6.11.1 Armadillo Control Through Habitat Modification ...................................87
6.11.2 Armadillo Control Through Trapping ......................................................87
6.11.3 Armadillo Control Through Fumigants ...................................................88
6.11.4 Armadillo Control Through Toxicants ....................................................88
6.11.5 Armadillo Control Through Frightening ..................................................88
6.11.6 Armadillo Control Through Repellents ...................................................88
6.11.7 Armadillo Control Through Shooting ....................................................88
6.12 Livestock (Cow, Sheep, Horse, Pig, and Wild Pig) Management Methods ..........88
6.12.1 Livestock Control Through Habitat Modification ....................................88
6.12.2 Livestock Control Through Trapping .......................................................88
6.12.3 Livestock Control Through Fumigants ....................................................89
6.12.4 Livestock Control Through Toxicants ......................................................89
6.12.5 Livestock Control Through Frightening ..................................................89
6.12.6 Livestock Control Through Repellents ....................................................89
6.12.7 Livestock Control Through Shooting ......................................................89
6.13 Crayfish Management Methods .........................................................................89
6.13.1 Crayfish Control Through Habitat Modification ......................................89
6.13.2 Crayfish Control Through Trapping ........................................................89
6.13.3 Crayfish Control Through Fumigants ......................................................89
6.13.4 Crayfish Control Through Toxicants .........................................................89
6.13.5 Crayfish Control Through Frightening .....................................................89
6.13.6 Crayfish Control Through Repellents .......................................................89
6.13.7 Crayfish Control Through Shooting .........................................................89
6.14 Coyote Management Methods ...........................................................................89
6.14.1 Coyote Control Through Habitat Modification .......................................89
6.14.2 Coyote Control Through Trapping ..........................................................89
6.14.3 Coyote Control Through Fumigants ........................................................90
6.14.4 Coyote Control Through Toxicants ..........................................................90
6.14.5 Coyote Control Through Frightening ......................................................90
6.14.6 Coyote Control Through Repellents .......................................................90
6.14.7 Coyote Control Through Shooting ..........................................................90
6.15 Mole and Vole Management Methods ...............................................................90
6.15.1 Mole and Vole Control Through Habitat Modification .............................90
6.15.2 Mole and Vole Control Through Trapping ...............................................90
6.15.3 Mole and Vole Control Through Fumigants ............................................91
6.15.4 Mole and Vole Control Through Toxicants .............................................91
6.15.5 Mole and Vole Control Through Frightening ..........................................91
6.15.6 Mole and Vole Control Through Repellents .............................................91
6.15.7 Mole and Vole Control Through Shooting ...............................................91
6.16 River Otter Management Methods ....................................................................91

6.16.1 River Otter Control Through Habitat Modification .................................91
6.16.2 River Otter Control Through Trapping ....................................................92
6.16.3 River Otter Control Through Fumigants ..................................................92
6.16.4 River Otter Control Through Toxicants ...................................................92
6.16.5 River Otter Control Through Frightening ...............................................92
6.16.6 River Otter Control Through Repellents .................................................92
6.16.7 River Otter Control Through Shooting ...................................................92
6.17 Gopher Tortoise Management Methods .............................................................92
6.17.1 Gopher Tortoise Control Through Habitat Modification .........................92
6.17.2 Gopher Tortoise Control Through Trapping .............................................92
6.17.3 Gopher Tortoise Control Through Fumigants .........................................92
6.17.4 Gopher Tortoise Control Through Toxicants ............................................92
6.17.5 Gopher Tortoise Control Through Frightening ........................................92
6.17.6 Gopher Tortoise Control Through Repellents ..........................................92
6.17.7 Gopher Tortoise Control Through Shooting ............................................92
6.18 Red Fox and Gray Fox Management Methods ...................................................93
6.18.1 Red Fox and Gray Fox Control Through Habitat Modification .................93
6.18.2 Red Fox and Gray Fox Control Through Trapping ...................................93
6.18.3 Red Fox and Gray Fox Control Through Fumigants ................................93
6.18.4 Red Fox and Gray Fox Control Through Toxicants ..................................93
6.18.5 Red Fox and Gray Fox Control Through Frightening ..............................93
6.18.6 Red Fox and Gray Fox Control Through Repellents ................................93
6.18.7 Red Fox and Gray Fox Control Through Shooting ...................................93
6.19 Canada Goose Management Methods ................................................................93
6.19.1 Canada Goose Control Through Habitat Modification .............................93
6.19.2 Canada Goose Control Through Trapping ...............................................94
6.19.3 Canada Goose Control Through Fumigants .............................................94
6.19.4 Canada Goose Control Through Toxicants ...............................................94
6.19.5 Canada Goose Control Through Frightening ..........................................94
6.19.6 Canada Goose Control Through Repellents .............................................95
6.19.7 Canada Goose Control Through Shooting ...............................................95
6.19.8 Other Methods of Canada Goose Control ................................................95
6.20 American Alligator Management Methods .........................................................95
6.20.1 American Alligator Control Through Habitat Modification .....................95
6.20.2 American Alligator Control Through Trapping ........................................95
6.20.3 American Alligator Control Through Fumigants .....................................95
6.20.4 American Alligator Control Through Toxicants .......................................95
6.20.5 American Alligator Control Through Frightening ...................................95
6.20.6 American Alligator Control Through Repellents .....................................95
6.20.7 American Alligator Control Through Shooting .......................................96
6.21 Ant Management Methods ................................................................................96
6.21.1 Ant Control Through Habitat Modification .............................................96
6.21.2 Ant Control Through Trapping .................................................................96
6.21.3 Ant Control Through Fumigants .............................................................96
6.21.4 Ant Control Through Toxicants ...............................................................96
6.21.5 Ant Control Through Frightening ............................................................96
6.21.6 Ant Control Through Repellents ..............................................................96
6.21.7 Ant Control Through Shooting ................................................................96

7.0 Fiscal Considerations for Managing Animal Damage on Earthen Dams ................97
7.1 Fiscal Considerations for the Reluctant Dam Owner ............................................97
7.2 Fiscal Considerations of the Willing Dam Owner ................................................97
7.3 Overcoming the Economic Hurdles ....................................................................98
8.0 References ..............................................................................................................102
Appendix A .....................................................................................................................105
Appendix B .....................................................................................................................109

1
Chapter 1. Introduction and Purpose of Manual
1.0 Introduction and 
Purpose of Manual
1.1 Background
In 1999, the Federal Emergency Management Agency 
(FEMA) and the Association of State Dam Safety Officials 
(ASDSO) jointly conducted research and a workshop to 
shed light on the national problem of animal intrusion 
damage to earthen dams and the resulting safety issues. The 
FEMA/ASDSO survey and workshop united dam owners, 
engineers, state and federal regulators, wildlife managers, 
foresters, and academia to form an educated and experienced 
front against the growing problem of earthen dam 
damage and failures due to animal intrusion. The information 
generated by roundtable discussions and survey 
answers indicates that while most states recognize animal 
intrusion as a problem, only a handful know of guidance 
on dams and wildlife management practices available to 
the dam professionals and owners. Based on input from 
the dam communities, FEMA/ASDSOs mission to develop 
a guidance manual on the proper management of nuisance 
wildlife in the earthen dam environment became clear.
To determine the information needs of the dam community
and therefore the most appropriate focus of this 
manualFEMA/ASDSO issued a survey in 1999 and used 
the survey input from the 48 state dam safety officials 
representatives and 11 federal agencies representing the Interagency 
Committee on Dam Safety (ICODS). Additionally, 
a second survey was issued in 2003 to identify the current 
needs of each state, determine what nuisance wildlife and 
damages the states encounter, and understand which mitigation 
methods are being used with success or failure. Four 
main ideas emerged from the two survey efforts; these ideas 
consequently steered the direction of this manual:
Cumulatively, the states indicated a range of problems 
caused by numerous wildlife species relative to the 
operation of dams. This manual discusses 23 species 
with regard to their habitat, behavior, threat to dams, 
food habits, identifying characteristics, and management 
options: Muskrat, Beaver, Mountain Beaver, Groundhog, 
Pocket Gopher, North American Badger, Nutria, Prairie 
Dog, Ground Squirrel, Armadillo, Livestock (cow, sheep, 
horse, pig and wild pig), Crayfish, Coyote, Moles and 
Voles, River Otter, Gopher Tortoise, Red Fox and Gray 
Fox, Canada Goose, American Alligator, and Ants. 
While the states are fully aware of the potential adverse 
impacts wildlife activity can have on earthen dams (such 
as failure), private dam owners and local dam operators 
are often not aware of potential problems, and thus may 

Dam Owners Manual to Animal Intrusion of Earthen Dams
2
not conduct inspections with wildlife damage in mind. 
Local dam owners may not typically mitigate existing 
wildlife intrusion problems or prevent them in the 
future.
States want to know how other states are successfully 
mitigating wildlife damages. Further, mitigation and 
prevention guidance should be developed and conveyed 
to the dam communities. 
Guidance booklets for local dam owners are needed to 
assist dam inspectors in identifying and mitigating animal 
intrusion issues.
Out of 48 states that responded to FEMA and ASDSO surveys, 
25 document nuisance animals as the cause of dam 
failures or unsafe dam operations in their states. The U.S. Bureau 
of Reclamation, the National Park Service, and the U.S. 
Department of Agriculture document several similar cases 
at the federal level. State dam safety officials and federal 
agencies agree that animal burrows within dams can cause 
substantial and costly damage if left unmitigated and are 
consequently a major concern.
1.2 Target Audience, Purpose, and 
Application of This Manual
This manual provides technical guidance to dam specialists 
(including dam owners, operators, inspectors, state dam officials, 
and consulting engineers) in areas of focus identified 
through the two survey efforts and workshop. The purposes 
of this manual are to:
Assist dam specialists in understanding the impacts wildlife 
can have on earthen dams.
Provide dam specialists with basic information on habitat, 
range, description, and behavior of common nuisance 
wildlife to aid in their proper identification at the 
dam. 
Describe state-of-practice methods to prevent and mitigate 
adverse wildlife impacts on earthen dams. 
Provide state-of-practice design guidance for repair and 
preventive design associated with nuisance wildlife intrusion.
It is envisioned that the entire dam specialist community 
will use this manual to augment their routine duties in 
earthen dam management. This manual is presented as 
a process toward dam inspection and management that 
includes wildlife damage identification and control. This 
manual provides technical information and guidance on: 
How wildlife damage adversely affects the safe operation 
of earthen dams; specifically, hydraulic alteration, internal 
and external erosion, and structural integrity losses 
(Chapter 2.0).
Dam inspections that incorporate a biological component 
to sensitize dam specialists to the aspects of their dams 
that attract wildlife and to understand where nuisance 
wildlife are likely to occur on the dam (Chapter 3.0).
Biological data for specific nuisance wildlife to assist 
the dam specialist in identifying which nuisance wildlife 
inhabits the dam. Biological data will also assist in 
controlling nuisance wildlife (e.g., listed food sources can 
be removed to encourage the animal to leave the area) 
(Chapter 4.0).
25: number of states that 
indicate animal activity 
has caused or contributed 
to unsafe dam operation 
or outright failure within 
the state. 
9: number of states 
aware of information or 
guidance on the effects of 
animal activity on dams. 

Dam design specifications and methods that can be 
incorporated into repair of existing dams or new dam 
designs to prevent wildlife intrusions (Chapter 5.0).
Guidelines to determine when wildlife management 
should occur at a dam (beyond dam repair and prevention 
actions) and wildlife management methods that can 
be implemented when control of specific nuisance wildlife 
populations is deemed necessary. Specific methods 
discussed include habitat modification, use of toxicants 
and fumigants, trapping, and shooting (Chapter 6.0). 
The fiscal issues related to appropriate and timely wildlife 
management at earthen dams (Chapter 7.0).
1.3 Technical Resources Cited
The technical information provided in this manual represents 
the most current practices in the areas of wildlife data 
and management and engineering inspection and repair, 
as they relate to nuisance wildlife and their effects on safe 
dam operations. While numerous technical sources are cited 
throughout the document, three main sources form the 
backbone of this manuals technical understanding and recommendations. 
The first source is a manual titled Prevention 
and Control of Wildlife Damage (University of Nebraska, 1994). 
The data contained in the 1994 manual are considered the 
industry standard for pest control, and the manual is used as 
the handbook for those testing for licensure as pest control 
managers. It should be noted that the 1994 manual is under 
revision and a revised version will be completed February 
2005. Until the release of the revised manual, the 1994 edition 
remains the leading guidance literature in this field and 
is accepted as the most current practice in nuisance wildlife 
management (Smith, Pers. comm., 2003; 2004). The second 
source is a booklet called Prevention and Control of Animal Damage 
to Hydraulic Structures (USDA, 1991). The 1991 booklet adapts 
some of the 1994 manual data for application to the dam 
environment. The last source is technical data on remedial 
dam repair design by Dr. B. Dan Marks, as presented in the 
2001 ASDSO West Region Seminar on Plant and Animal 
Penetrations for Earthen Dams (ASDSO, 2001). Many other 
sources are also used throughout this manual to provide a 
cross-reference of data as well as a broad spectrum of information. 

Dam Owners Manual to Animal Intrusion of Earthen Dams
4
2.0 Impacts of Wildlife 
on Earthen Dams
muskrat
burrow
dam crest
water level
groundhog
burrow
dangerously
close burrows
phreatic surface
Figure 2-1. Upstream and downstream burrows can become dangerously close, causing internal erosion that may lead to dam failure. 
Earthen embankment dams are used by private landowners 
and state and federal agencies to store farm water supplies, 
city water supplies, recreational waters, flood waters, and 
wastewater lagoons. Earthen dams rely on a thick placement 
of compacted soils to withstand the water pressure of the 
pool contained behind the embankment. Often constructed 
outside of developed areas, the earthen dam environment 
is usually near a water source and can contain a variety of 
vegetation; given these characteristics, earthen dam environments 
can be naturally conducive to use by wildlife. Wildlife 
inhabiting the dam can alter the dam environment through 
habitat establishment and usebeaver build dams, muskrat 
excavate dens, livestock feed on stabilizing vegetation. The 
natural instincts of wildlife to adapt and use their environment 
toward their survival can compromise the balance 
of engineered functions that maintain the viability of an 
earthen dam. 
The first step in fortifying a dam against unsafe operations 
caused by wildlife damage is to understand what could go 
wrong if wildlife damage is left unchecked. While a dam 
owner may observe a few small burrows on the upstream 
and downstream slopes, it is important to understand that 
potential problems, like those burrows, often run deep 
below the surface. As such, the purpose of this Chapter is to 
discuss adverse engineering effects stemming from nuisance 
wildlife activity. Adverse effects caused by specific wildlife 
(as well as their identification and mitigation) are discussed 
in Chapters 4.0, 5.0, and 6.0.
2.1 Background
Embankment dams are vulnerable to damage from wildlife 
intrusions. Twenty-five states indicate that animal activity 
has caused or contributed to unsafe operation or outright 
failure of an embankment dam. Several animal species excavate 
burrows, tunnels, and den entrances for shelter, while 
other predatory animals will enlarge these structures via 
digging in search of prey. Similarly, herbivorous species will 
forage on vegetation growing on embankment dams. All 
of these occurrences create open areas in the embankment 
fill which are detrimental to the safety and performance 
of embankment dams. Some of these effects can be easily 
identified, such as surface erosion; other effects such as 
internal erosion may not become visible until dam safety is 
jeopardized.

5
Chapter 2. Impacts of Wildlife on Earthen Dams
Embankment dams can be generally categorized as either 
homogeneous (containing one material) or zoned (containing 
multiple materials). Zoned embankment dams usually 
contain a central core designed to produce a lower phreatic 
surface (static water level within a dam embankment) 
within the downstream slope than the theoretical surface 
often assumed for homogeneous embankments. Due to the 
variability of zoned embankments, this manual discusses 
only homogeneous embankments.
2.2 Hydraulic Alteration
The most significant and often least obvious impact of wildlife 
intrusions on embankment dams is hydraulic alteration. 
Hydraulic alteration and its effects can manifest in different 
ways depending on the type and location of intrusion, 
including flownet distortion and physical barriers to flow. 
A distorted flownet may not be a visible problem but it can 
have the most dramatic impact. Flownet is a term referring 
to the theoretical description of water flow through and 
under an embankment dam. The phreatic surface, equal potential 
lines and flow lines associated with a flownet are defined 
by the physical dimensions of the dam, classification 
of 
soils in the dam, and variability of the reservoir normal 
pool. As such, each dam has a unique flownet. The presence 
of animal burrows, either on the upstream or downstream 
slope, can distort the established phreatic surface and impact 
the flownet. As illustrated on Figure 2-2, upstream burrows 
can allow the normal pool elevation to extend into the dam 
embankment, forcing the phreatic surface further into the 
embankment. Likewise, downstream intrusions can allow 
the phreatic surface to day-light higher on the downstream 
slope. The overall effect can be a significant alteration to the 
phreatic surface. Dramatic changes to the phreatic surface can shorten seepage paths, increase seepage volumes, 
decrease the factor of safety against slope failure, and cause 
internal erosion of embankment materials (piping). 
Of these impacts, piping is most often cited as the greatest 
concern among dam safety professionals because it is progressive 
and can rapidly lead to failure of the dam. Piping 
is the uncontrolled movement of soil particles caused by 
flowing water. As shown on Figure 2-3, piping will often 
start in a burrow on the downstream slope. Flowing water 
moves soil particles from the embankment to the burrow, 
leaving a void that is quickly filled with soil particles from 
deeper within the embankment. Because water pressure and 
flow generally increase further into the dam embankment, 
the rate of movement of soil particles will also increase. 
A pipe is rapidly formed extending from the downstream 
slope to the upstream slope. A dam breach is almost certain 
to develop in these instances.
External problems can also arise from wildlife activity 
around an embankment dam. Though hydraulic barriers 
can result from the activities of several species, beaver cause 
perhaps the largest array of adverse effects. To create deep 
waters in which to hide from predators, beavers compact 
felled tree trunks, limbs, and other materials into a mound 
to restrict the natural flow of a water source. As a result, 
the hydraulic function of the dam is altered in several ways. 
First, beaver mounds may block principal and emergency 
spillways and riser outlets, resulting in increased normal 
pool levels and reduced spillway discharge capacity. Second, 
sudden high discharges from the dam could occur if the 
beaver dam fails. Third, beaver dams located upstream of 
the embankment dam can clog water control structures as 
debris from the beaver dam floats downstream. Finally, erosion 
of the downstream toe of the dam can occur as a result 
of elevated tailwater caused by beaver activity.
Homogeneous and zoned 
embankment dams are 
equally susceptible to 
damage from animal 
intrusions. The ultimate 
consequence from the 
intrusions depends on the 
specific engineering and 
biological characteristics 
of an individual dam. 

2.3 Structural Integrity Losses 
Wildlife excavate dens, burrows, and tunnels within embankment 
dams, causing large voids that weaken the 
structural integrity of the dam. Typical voids can range 
from the size of a bowling ball to a beach ball and much 
larger. Heavy rain and snow melt loosen soils surrounding 
a burrow, causing a localized collapse inside the burrow. In 
addition, a burrowing animal may encounter loose zones in 
the embankment (due to variability of constructed embankments) 
during burrow excavation, leading to a localized 
collapse. Animal dens also erode and collapse under the load 
of heavy equipment and other vehicles that use the crest of 
the dam as a throughway.
The collapsing soils will progressively lead to sinkholes or 
depressions appearing on the embankment surface. Because 
burrows can be under several feet of soil, the deformation 
or sinkhole visible at the surface could be several times the 
size of the original burrow. As illustrated on Figure 2-4, 
the collapsed soils can represent a significant portion of the 
dam embankment. Under the right circumstances, localized 
slope instability can result from a collapsed animal burrow. 
Depending on the location and number of collapsed burrows, 
dam safety or operation could be jeopardized. If portions 
of the crest are affected, a loss of freeboard can result, 
thus endangering the dam during storm events. Downstream 
slope failures, regardless of their extent, weaken 
embankment soils and reduce confinement of surrounding 
soils, thereby resulting in further weakening of embankment 
soils. Depending upon site and weather conditions, 
the process can progress slowly or rapidly, potentially leading 
to massive slope instability.
2.4 Surface Erosion
The foraging behavior of some animals on open area vegetation 
associated with dam embankments can reduce or 
eliminate vegetative cover on a dam. This increased feeding 
pressure on the dams vegetative groundcover can lead 
to erosion paths and decreased soil retention on the dams 
crest and slope. In addition, dams that are grazed by livealtered 
phreatic surface
burrow
theoretical
phreatic surface
groundhog den
Figure 2-2. Burrows can alter dam hydraulics by shortening seepage paths.
soil movement
into burrow
process continued 
over time
Figure 2-3. Burrows can lead to piping within an embankment. 

stock often show increased rates of soil erosion because of 
the lack of stabilizing vegetation from grazing and trafficking, 
which can lead to irregular surface erosion and the 
formation of rills and gullies. 
With continued neglect, these areas will require more than 
simple maintenance. In fact, given enough time, external 
erosion can lead to a reduction in freeboard and loss of 
cross section. In turn, these impacts can increase the dams 
vulnerability to damage from high water during large storm 
events.
collapse
theoretical seepage line
Figure 2-4. Burrows can collapse, leading to formation of sinkholes and loss of structural integrity.

Dam Owners Manual to Animal Intrusion of Earthen Dams
8
3.0 Dam Inspection From 
Two Perspectives: 
Engineering Function and 
Biological Potential 
The second step toward fortifying a dam against the effects 
of nuisance wildlife damage is the observation of clues 
left by wildlife in the dam environment. As such, regular 
inspection of the dam that incorporates wildlife activity 
recognition must be conducted by the dam owner, who is 
the first line of defense in protecting earthen dams. While 
the dam inspection is focused primarily on seepage, deformation, 
and structural deficiencies, the inspectors must 
also perceive wildlife clues left behind by dam inhabitants 
whose presence could cause trouble down the road. Toward 
this goal, this Chapter details an inspection procedure that 
pairs engineering inspection with key biological considerations 
to assist the dam specialist in viewing the dam from 
both perspectives (this methodology should be applied using 
the specific wildlife clues data presented in Chapter 4.0 
of this manual). 
3.1 Wildlife And The Earthen Dam 
Through their natural desire to create dens, search for food, 
or escape predators, wildlife can cause a host of adverse 
impacts to an earthen dam which can lead to dam failure 
(refer to Chapter 2.0 of this manual for detail on the adverse 
impacts of wildlife activities). Though earthen dams are 
manmade, wildlife interacts with the earthen dam environment 
as if it were natural field or forest. To protect their 
dams, dam owners should know the biological potential of 
their damscan wildlife find a suitable environment at the 
dam, and if so, which kind of wildlife will inhabit which 
locations of the dam? In answering these questions, it is 
helpful to know the characteristics that compose favorable 
habitat, and to realize that dams with diverse vegetation 
and site features often support a wide variety of wildlife. 
In assessing the dam for its biological potential, review the 
following relative to the dam area and surrounding areas 
(adapted from Benyus, 1989):
Vegetation Vitality: Do the dam and adjacent areas contain 
dense vegetation at all levels (e.g., grass, shrub, and 
tree)? In general, greater variety of dense vegetation at 
levels ranging from groundcover to understory to canopy 
(regardless of vegetation type) allows for a greater variety 
of wildlife to inhabit the area. Small mammals, such as 
those discussed in this manual, prefer sites with adequate 
vegetation cover to hide from predators (see Chapter 5.2 
for a discussion on appropriate vegetation at a dam).

9
Chapter 3. Dam Inspection from Two Perspectives: Engineering Function and Biological Potential
Mini-habitats: Do the dam and surrounding area offer 
vegetative diversity? Different landscapes such as prairie 
and forest? Sun and shade? Deep and shallow water? An 
environment with a mosaic landscape provides several 
habitat types in one area, which can support a wider 
variety of wildlife.
Transition Zones: Is there a clear edge between one 
habitat type and another? At the dam environment, the 
dam area (a lake/pond environment) may be surrounded 
by a grassy field environment, a shrub edge, or a forested 
environment. The junction where two environments 
meet is called an edge, and edges are the most heavily 
trafficked areas in an environment (a good place to view 
the wildlife in and around the dam area) because they 
provide safe travel corridors between the two habitat 
types and create a more diverse habitat than either of the 
two habitat types. 
Size: Does the dam environment provide a large land area 
that allows wildlife to meander without having to cross 
roadways or come into contact with people? Most species 
of wildlife prefer large parcels of land that provide habitat 
variety without human influence. 
Unique Characteristics: Does the dam contain unique 
land features? By its very nature, the dam environment 
is unique because it contains a water source. Wildlife 
prefers a constant water source, so dams with a permanent 
pool will be preferable to those with a fluctuating 
pool, such as those used for flood control or irrigation. 
However, any water source will attract wildlife to some 
degree.
3.2 Two-Perspective Dam Inspection Methodology 
The typical dam safety inspection checklist requires observation 
of every dam feature. The checklist is developed by 
an individual states dam safety program or federal organization 
such as the U.S. Bureau of Reclamation, U.S. Army 
Corps of Engineers, U.S. Fish and Wildlife Service, or the 
Federal Energy Regulatory Commission. All inspections 
focus on distinct physical regions, although the inspection 
checklists vary in length, listed inspection items, and required 
observations. Generally, the features are divided into 
clear components including:
Upstream Slope
Downstream Slope
Crest
Embankment-Abutment Contact (Groin)
Principal Spillway
Emergency Spillway
Lake Drain or Outlet Works
Although inspection for animal intrusions is a facet of 
most if not all state inspection checklists, it is certainly not 
a major part of the inspection. Specific guidance on identifying 
animal intrusions or the typical intrusion locations 
of specific animals is not provided on the checklists. An 
inspector lacking this information may be unable to adequately 
inspect their dam for animal intrusions, much less 
adequately identify and mitigate the nuisance animal. As 
such, this manual presents an inspection methodology that 
combines engineering and biological considerations, which 
when viewed together, allow a dam specialist to view the 
dam comprehensively.
For the purposes of this manual, the dam is divided into 
six zones: Upstream Slope, Dam Crest, Upper Downstream 
Slope, Lower Downstream Slope, Downstream Toe, and Spillway, 
Outlets, and General Areas (Figure 3-1). The risk posed 
by animal intrusions is greater in some zones than in others. 
As such, the zones are overlapped to emphasize the critical 
nature of the area and to require inspection of the area 
twice to ensure that biological clues are sighted (ASDSO, 
2001). Further discussion of the six zones relative to risk, 
restoration, and repair of animal intrusions is provided in 
Chapters 5.3 and 5.4. 
When considering animal intrusions, inspection of each 
zone should consider not only physical evidence of an 
animal presence (e.g., burrow entrance), but also the habitat 
and biological factors that attract wildlife to the dam and 
sustain them once they have become established (Figure 
3-2). Understanding both the engineering and biological 
aspects of animal intrusions into embankment dams is critical 
in eliminating or at least controlling the intrusions. 
3.2.1 Zone 1: Upstream Slope Area
Engineering Perspective: The goal of inspecting the upstream 
slope of the earthen dam is to see the entire surface 
clearly. To ensure the inspector views the entire slope 
surface, the inspector must walk back and forth across the 
slope utilizing one of two patterns: zig-zag or parallel. In 
general, the zig-zag method is best for small dams and mild 
slopes (Figure 3-3, shown on page 17). It may prove difficult 
to move in a zig-zag pattern on large dams and steeper 
slopes, and in these cases the parallel pattern is suggested 
(Figure 3-4, shown on page 17). 

While walking the slope, the inspectors should routinely 
stop and view the alignment of the surface by turning their 
gaze a full 360 degrees. Checking the slope frequently and 
from many viewpoints and distances can reveal deficiencies 
and distortions (such as surface distortions or vegetation 
changes) that might otherwise go undetected. The inspectors 
should observe berms on the upstream slope by centering 
their eyes on the line being viewed and moving their 
body from side to side to view the line from several angles. 
This approach will help the inspector identify misalignments. 
A typical dam safety inspection report should comment on 
vegetation, slope protection, erosion, instabilities, and animal 
burrows observed in Zone 1. When specifically considering 
animal burrows and other deficiencies resulting from 
animal activity, the inspector should look for the following: 
animal burrow entrances, mounds of excavated soil, debris 
(evidence of beaver activity), cracks, depressions, erosion, 
sinkholes, paths and ruts, sloughs, slides, and scarps. These 
conditions often indicate damaging animal activity. The 
inspection report should note whether the deficiencies warrant 
monitoring, repair, or further investigation.
Biological Perspective: This zone is primary habitat for 
aquatic burrowers such as muskrat and beaver, which generally 
burrow from 6 inches to 4 feet below the water line 
upward toward the crest. Nutria prefer to dig dens in the 
zone where land and water meet, which could be dominated 
by aquatic vegetation. River otters are often found living 
in abandoned muskrat, beaver, and nutria burrows, and can 
construct slides on slopes and bare areas where they repeatedly 
enter and exit the water. Livestock often traverse the 
upstream slope arealook for hoof tracks, rills, and eroded 
pathways. Canada geese and livestock feed on embankment 
slopes causing eroded areas and ruts. Crayfish and alligator 
may inhabit the banks and shallows of the upstream slope 
area. Ants may dig tunnels in the slope, loosening existing 
cracks. Mountain beaver or armadillo may be found along 
the wet edge of the pond, especially if a forest fringe or 
wooded area is nearby. Moles may hunt in the moist soils 
near the reservoir.
3.2.2 Zone 2: Dam Crest Area
Engineering Perspective: Similar to inspecting the upstream 
slope, the crest can be viewed using either a zig-zag 
or parallel pattern, with the primary goal being to view the 
Zone 1 Upstream 
slope area 
Zone 2 Dam crest area
Zone 3 Upper downstream 
slope area
Zone 4 Lower downstream 
slope area
Zone 5 Downsteam 
toe area
Zone 6 Spillway, outlets 
(not shown)
crest
zone 1
zone 3
zone 4
H/2
zone 2
zone 5
H/3
4
H/2
theoretical seepage line
phreatic surface
Figure 3-1. Dam Inspection Zones.

Figure 3-2. The Earthen Dam from Biological and Engineering Perspectives.
Upland Areas. Many species live in the upland 
areas, away from the water. Even the downstream 
slope, abutments, and groin areas of the dam can 
be considered upland in terms of habitat. 
Forest Fringe. The zone between two environments (the 
edge) is the best place to observe those species living at 
and around the dam. The more habitat types at the dam, 
the greater number of species likely to inhabit the dam. 
Mountain beaver or armadillo prefer forested/wooded areas.
Emergency Spillway. Beaver often dam the 
spillway, causing the pond water levels to rise. 
Left Abutment contact.
Inappropriate Vegetation on Embankment. Many 
dams contain vegetation other than mowed grass. 
Improper vegetation provides cover and food supply, 
which encourage animals to inhabit the dam. 
Downstream Slope. This area is often the location where 
groundhogs, coyote, and fox excavate burrows. Canada 
geese will feed on the downstream slope, which could cause 
loss of protective vegetative cover and associated erosion. 
Species that prefer upland areas could be found in this area.
Left Groin.
Discharge Conduit and Outlet Channel. Beaver can dam 
the outlet structure. Aquatic species may inhabit this area 
depending on water flow and availability of vegetation.
Toe of Embankment and right groin.
Erosion Pathways on the Embankment. Livestock 
traverse the embankment creating erosion pathways. 
Right abutment contact.
Crest. Livestock traverse the crest which creates ruts. 
The ceilings of beaver and muskrat burrows in the 
upstream slope are often just below the dam crest. 
Aquatic Fringe. The zone where the bank meets 
the pond usually contains aquatic vegetation 
preferred by many animals such as nutria.
Upstream Slope. Beaver, muskrat, and nutria 
prefer the upstream slope for burrow excavation. 
Alligators, otters, and turtles usually live in the 
shallow waters near the upstream slope. 
Principal Spillway (with riser and trash rack). Beavers 
can block principal spillways by constructing dams.

entire crest from several perspectives and distances. Similar 
to the upstream slope inspection, the inspectors should center 
their eyes on the crest line, moving their body from side 
to side to view the line from several angles. Fixed features 
that can mark horizontal and vertical points along a dam 
can be used as reference lines; guardrails, a row of posts, or 
parapet walls are good reference lines (use caution when 
using man-made reference lines which can be moved). The 
reference line must be viewed from several different perspectives; 
first, the inspectors should sight directly on the 
reference line and then move their body to either side. This 
method will assist the inspector in detecting a change in the 
uniformity of the crest. Zone 2 overlaps Zone 1 on one-half 
of the crest width. This is intentional, and is meant to emphasize 
the critical nature of the area by requiring inspection 
of the area twice (ASDSO, 2001).
A typical dam safety inspection report should comment 
on width, alignment, vegetation, erosion, instabilities, and 
animal burrows observed in Zone 2. When specifically 
considering animal burrows and other deficiencies resulting 
from animal activity, the inspector should observe the 
following: animal burrow entrances, mounds of excavated 
soil, cracks, depressions, erosion, sinkholes, paths and ruts, 
sloughs, slides, and scarps. As with Zone 1, these issues can 
indicate animal activity. The inspection report should note 
whether the deficiencies warrant monitoring, repair, or 
further investigation.
Biological Perspective: Dens of beaver and muskrat are typically 
located just below the crest (look for depressions in 
the crest since the burrow entrance is typically underwater), 
and livestock often traverse the crest (look for hoof tracks, 
rills, gullies, and eroded pathways). Terrestrial wildlife such 
as groundhogs, ground squirrels, pocket gophers, foxes, 
coyote, and badgers may inhabit or hunt in the crest area. 
Moles may dig burrows in the dry, upland area of the upper 
upstream slope/crest that lead to their hunting grounds in 
the cool, moist soils near the reservoir pool. Vehicular traffic 
on crests may discourage wildlife establishment. Additionally, 
the crest is often constructed of well-compacted material, 
which is not attractive to most burrowing wildlife. Ants may 
dig tunnels in the crest, loosening existing cracks.
3.2.3 Zone 3: Upper Downstream Slope Area
Engineering Perspective: Inspecting the downstream slope 
is similar in method to inspecting the upstream slope. It 
is suggested that the downstream slope be viewed from a 
distance at a time of day when the angle of the sun is low 
so that wet areas, which will reflect sunlight, are seen more 
easily. Zone 2 overlaps Zone 3 on one-half of the crest in 
order to draw additional attention to the crest area. 
A typical dam safety inspection report should comment 
on alignment, vegetation, erosion, instabilities, and animal 
burrows observed in Zone 3. When specifically considering 
animal burrows and other deficiencies resulting from 
animal activity, the inspector should observe the following: 
animal burrow entrances, mounds of excavated soil, cracks, 
depressions, erosion, sinkholes, paths and ruts, sloughs, 
slides, and scarps. As with the previous zones, these issues 
can indicate animal activity. The inspection report should 
Figure 3-3. The zig-zag method of inspection is 
best used on small dams and mild slopes.
Figure 3-4. The parallel method of inspection is 
best used for dams with steep slopes.

note whether the deficiencies warrant monitoring, repair, or 
further investigation.
Biological Perspective: This zone is the most attractive 
for terrestrial animal activity and is preferred by groundhog, 
fox, and coyote for burrow and den sites. Prairie dog, 
pocket gopher, ground squirrel, and groundhog may inhabit 
the downstream slope area; if they do, predators such as 
badger, coyote, and foxes may choose this zone as a hunting 
ground. Gopher tortoises, which are strictly terrestrial, 
would prefer this zone as it is dry and located well-above 
the phreatic surface. Look for large dens, burrows, and piles 
of dirt outside of small burrows. Ants may dig tunnels in the 
slope, loosening existing cracks. Livestock and Canada geese 
may graze on the stabilizing vegetation. Moles may inhabit 
this area and dig burrows from the slope area to an adjacent 
outlet or spillway for the moist soils they prefer as a hunting 
ground. Armadillo, mountain beaver, or voles may inhabit 
this area if the dam is improperly vegetated with trees, 
shrubs, or a thick understory.
3.2.4 Zone 4: Lower Downstream Slope Area
Engineering Perspective: Inspection of this zone is similar 
to inspecting the upstream and upper downstream slopes, 
but the inspector should give greater scrutiny to the downstream 
slope below the pool elevation. In most embankment 
dams, the potential for seepage through the embankment 
materials day-lighting on the downstream slope increases 
dramatically further down the downstream slope. As shown 
on Figure 3-1, the theoretical phreatic surface typical for 
homogeneous embankment dams intersects the downstream 
slope. Therefore, the presence of an animal burrow 
in this area could shorten seepage paths, increase hydraulic 
gradients, and ultimately cause internal erosion of the 
embankment materials. A more detailed description of the 
potential impacts from animal intrusions is provided in 
Chapter 2.0.
A typical dam safety inspection report should comment 
on vegetation, erosion, instabilities, seepage, and animal 
burrows. The potential for uncontrolled seepage through 
animal burrows in Zone 4 is significantly greater than in the 
three previous zones. Therefore, seepage observations are 
important in Zone 4. When specifically considering animal 
burrows and other deficiencies resulting from animal activity, 
the inspector should scrutinize the following: animal 
burrow entrances, mounds of excavated soil, concentrated 
seeps, wet/spongy areas, cracks, depressions, erosion, sinkholes, 
paths and ruts, sloughs, slides, and scarps. As with 
previous zones, these issues can indicate animal activity. The 
inspection report should also note whether the deficiencies 
warrant monitoring, repair, or further investigation
Biological Perspective: This zone would also likely support 
terrestrial wildlife as described under Zone 3. Burrows 
constructed in lower Zone 4 (where it overlaps with Zone 
5) will become saturated depending on depth, which is not 
preferred by most burrowing animals; therefore, burrows 
of terrestrial animals (i.e., gopher tortoise, fox, coyote, and 
groundhog) will occur in upper Zone 4. If a resident beaver 
constructs a dam that retains water, then muskrat, beaver, 
and otter will occupy inundated downstream slopes and 
outlet areas. Moles may hunt in the downstream slope if 
soils are moist, and the mountain beaver or armadillo may 
inhabit this area if the vegetation includes trees, shrubs, and 
a thick understory. Ants may dig tunnels in the slope, loosening 
existing cracks. Livestock and Canada geese may graze 
on stabilizing vegetation.
3.2.5 Zone 5: Downstream Toe Area
Engineering Perspective: Inspection of this zone is similar 
to inspecting the upstream slope and upper/lower downstream 
slopes, but Zone 5 is the most critical area because 
of the potential proximity of the phreatic surface to the 
downstream slope in this zone. Therefore, as in Zone 4, the 
presence of animal burrows in this area could shorten seepage 
paths, increase hydraulic gradients, and ultimately cause 
internal erosion of the embankment materials. 
A typical dam safety inspection report should comment 
on vegetation, erosion, instabilities, seepage and animal 
burrows in Zone 5. The potential for uncontrolled seepage 
through animal burrows in Zone 5 is significantly greater 
than in Zones 1 through 3, and somewhat greater than in 
Zone 4. Therefore, seepage observations are critical in Zone 
5. When specifically considering animal burrows and other 
deficiencies resulting from animal activity, the inspectors 
should observe the following: animal burrow entrances, 
mounds of excavated soil, concentrated seeps, wet/spongy 
areas, cracks, depressions, erosion, sinkholes, paths and ruts, 
sloughs, slides, and scarps. As with previous zones, these 
issues can indicate animal activity. The inspection report 
should note whether the deficiencies warrant monitoring, 
repair, or further investigation.
Biological Perspective: Burrows constructed in Zone 5 
will become saturated depending on depth, which is not 
preferred by burrowing terrestrial animals (i.e., armadillo, 

mountain beaver, vole, mole, gopher tortoise, fox, coyote, 
and groundhog). If a resident beaver builds a dam that 
retains water, then muskrat, beaver, nutria, and otter will 
occupy inundated downstream slopes and outlet areas, if 
appropriate vegetation has become established. Ants may 
dig tunnels in the slope, loosening existing cracks. Livestock 
and Canada geese may graze on stabilizing vegetation.
3.2.6 Zone 6: Spillway, Outlets, and General Areas 
Engineering Perspective: The best approach to inspecting 
spillways and outlets is to view all surface and internal areas 
by walking closely along or within the structure, observing 
confined space entry requirements. The inspector should 
enter the conduit and view the internal structure using a 
flashlight, providing the conduit is of the appropriate size 
and in safe repair. The inspector should use binoculars or 
a camera/video camera with the appropriate lens to document 
the conduit condition if the conduit is not accessible 
(e.g., located in the water separated from the shoreline or 
embankment). Underwater features can be viewed via use 
of boats or underwater divers. Shorelines and upstream 
areas should be inspected by walking or using vehicles 
to traverse the inspection areas. Other appurtenant works 
should be inspected up-close. 
Biological Perspective: Beaver will construct dams at the 
spillway locations to capture and reroute water flow. Look 
for gnaw marks in a circular pattern on tree trunks, beaver 
dams, and otters playing in the beaver dam waters. Aquatic 
animals such as muskrat and nutria may be found at these 
locations if the beaver dam retains water, and if sufficient 
aquatic vegetation has become established. Armadillo or 
mountain beaver may inhabit the area if a forest fringe or 
wooded area is adjacent to the water source.

15
Chapter 4. Overview and Identification of Nuisance Wildlife
4.0 Overview and Identification 
of Nuisance Wildlife
The FEMA/ASDSO workshop and 2003 dam safety specialist 
surveys indicate that several species damage earthen dams 
across the nation. This Chapter discusses 23 animals identified 
by the states as presenting the greatest threats to safe 
dam operations. Tracks, photographs, and range maps are 
provided for each animal, as well as a description of the 
specific threats each animal poses to the earthen dam environment, 
its preferred habitat, food habits, behavior, and 
field-identifying tips specific to each animal. It should be 
noted that some information is difficult to present depending 
on the animal (e.g., crayfish tracks) and in these cases, 
such information is omitted.
In a general sense, it is envisioned that a dam specialist will 
use this information to gain a better understanding of the 
wildlife that inhabits a dam. To a greater degree, it is hoped 
that this information will go hand in hand with overall dam 
management to assist a dam specialist in knowing where to 
look for wildlife damage (e.g., burrow sites), indicate which 
animals caused the damage via specific descriptors, and 
lead the dam specialist toward appropriate damage repair, 
prevention, and wildlife management (see Chapters 5.0 and 
6.0 for dam repair, damage prevention, and wildlife management 
methods). 
4.1 The Importance of Accurate Wildlife Identification
During the regular dam inspection detailed in Chapter 3.0 
of this manual, the dam specialist will have viewed the dam 
from both engineering and biological perspectives. In doing 
so, the specialist may have identified burrows just below 
the water-line, observed floating rafts of vegetation on the 
water, trails from the water to the bank, and noted an abundance 
of aquatic vegetation along the shoreline. Application 
of the information in this chapter will assist the dam 
specialist in putting the above clues together to determine 
which animal is damaging the embankment.
Given the dynamic nature of wildlife and its desire to avoid 
human interaction, a dam owner will seldom witness wildlife 
causing damage to dams. However, proper identification 
of nuisance wildlife is critical so that dam repair and wildlife 
management methods can be appropriately and lawfully 
applied to mitigate specific species and their impacts to the 
earthen dam. 
A dam environment that has high biological potential (refer 
to Chapter 3.1 for discussion of biological potential) will 
most likely support several nuisance species; however, not all 

Dam Owners Manual to Animal Intrusion of Earthen Dams
16
species living at the dam are necessarily in need of management. 
To apply mitigation that blankets all animals seen at 
the dam may be a waste of time and money, not to mention 
unnecessarily damaging to the environment. For this reason 
it is important to carefully evaluate the biological evidence 
at the dam to accurately identify the species responsible for 
the damage. For example, beaver and otters often live in the 
same environment, and otters often opt to use beaver dens 
instead of creating their own. In this case, the otter may be 
seen living in the den, but the beaver is the species actually 
responsible for the burrowing activity. Therefore, mitigation 
should be geared toward the beaver, and not necessarily 
the otter, which will live in hollow logs and rock crevices 
just as comfortably. On the other hand, several species may 
be responsible for compromising activities at the dam, and 
dam repair, prevention action, and wildlife mitigation will 
need to be geared toward several species. In essence, application 
of the information provided in this Chapter will assist 
in accurate identification of the problematic species, which 
will help the dam specialist appropriately manage the dam 
without spending unnecessary energy or funds. 
Misidentification of a 
wildlife species may result 
in inadequate mitigation, 
which could allow damage 
to continue, perhaps leading 
to dam failure. As wildlife 
identification can be 
difficult, a dam owner may 
benefit from using a wildlife 
specialist or professional 
trapper to positively identify 
the species so that proper 
wildlife mitigation can 
be developed. Appendix 
A contains state wildlife 
contacts, and state 
trapper information can 
be obtained at www.
nationaltrappers.com. 

4.2 Identifying Nuisance Wildlife 
4.2.1 Muskrat Overview
Muskrat(Ondatra zibethicus) are semi-aquatic rodents with brownish-
black fur and with a body 10-14 inches long and a tail 8-11 inches 
long. Muskrats have large, partially-webbed hind feet and a vertically 
flattened tail, which they use to propel themselves through water. 
Threat to Dams: Muskrats dig fairly large burrows that can 
lead to internal erosion and structural integrity losses in the 
earthen dam. Muskrats will continue to dig upward into the 
embankment as the phreatic surface rises; internal burrows 
can become extensive.
Habitat and Home (Figure 4-1): Muskrat inhabit freshwater 
and saltwater marshes, lakes, ponds, rivers, and other watercourses, 
where water is calm or very slowly moving. Muskrats 
prefer water courses that are about 3-4 feet deep that 
dont freeze completely in the winter and contain abundant 
cattails or aquatic vegetation. Muskrats typically burrow 
Figure 4-1. Muskrat dig dens in the upstream slope, with the entrance tunnel beginning about 6-18 inches below the water line.

Muskrats also build conical houses out of marsh vegetation, but usually excavate and use burrows when inhabiting 
earthen dams and other hydraulic structures (USDA, 1991). 
Detection of muskrat can be difficult if slopes of the dam 
over (see Chapter 5.2 for a discussion on improper vegetation at an earthen dam).
into a dams upstream face. Their burrows begin from 6 to 
18 inches below the water surface, and breather holes and 
escape holes can be observed above the water line. If the 
water level rises, the muskrat will excavate a dry chamber 
by digging higher into the embankment at an upward slant. 
are 
improperly vegetated, as their burrows may be covered 
Food 
Habits: Muskrats are primarily herbivores and prefer to 
feed on cattails, grasses, smartweed, duck potato, water lily, 
sedges, and other aquatic plants. When vegetation is scarce, 
muskrat will feed on bivalves, crustaceans, insects, and 
sometimes fish (University of Nebraska, 1994). 
Behavior: Muskrats can often be seen swimming at any hour 
of the day however they are most active at twilight. Muskrats 
often construct roofs over floating rafts of vegetation 
so that they have a covered place to eat. These huts can be 
found floating on the water and are especially important 
to the muskrat in winter when cooler weather can chill the 
animals naked tail and feet (USDA, 1991; Benyus, 1989).
Field Tip: Listen for a loud splash when nearing the water. 
Muskrats plop into the water when approached to alert 
other muskrat of human activity. Muskrats sometimes hold 
their tails out of the water as they swim (Benyus, 1989). 
Muskrats are considered 
a significant dam 
safety issue in 71% of 
the surveyed states.
Range of the muskrat in North America.
forefoot
hindfoot
walking
In very clear tracks, a small fifth toe can be seen on the 
outside of the front foot pad. All toes, except the nubbin, will 
show claw prints. The muskrats vertically flattened, bare tail 
will create a drag mark in the center of the prints.

4.2.2 Beaver Overview
The Beaver (Castor canadensis) is the largest rodent in North America 
weighing 45-60 pounds, with a body measuring 25-30 inches 
and a tail measuring 9-10 inches. Beavers are typically aquatic 
mammals, with webbed feet that are adapted for swimming and a 
flattened tail. Beavers vary in color but the most common body fur is 
reddish-brown and the belly fur is usually gray (USDA, 1991). 
Threat to Dams: Beaver can cause extensive damage to earthen 
dams by excavating bank burrows, which can cause internal 
erosion or structural integrity losses. Beaver dams constructed 
across spillways can cause adverse hydraulic effects and 
result in flooding or failure of the spillway or the earthen 
dam itself. Beavers often clog the intake and outlet structures 
with their cuttings.
Habitat and Home: (Figures 4-2, 4-3, 4-3A and 4-4): Beaver 
can be found throughout the continental United States 
wherever there is a year-round source of water. However, 
beaver will avoid an aquatic site that does not contain 
preferred foods or have adequate sites for lodges, dens, or 
dams (University of Nebraska, 1994). Beaver lodges are 
easy to identify; they are dome-shaped, built of limbs and 
Beavers are considered 
a significant dam 
safety issue in 67% of 
the surveyed states. 
dam crest
den
Figure 4-2. The ceiling of a beaver den is often just below the crest of the dam.

create tunnels and dens. Beaver tunnel entrances have been 
observed 1-4 feet below the water level. Beavers burrow 
into the dam from below the water line upwards toward the 
crest, where the beaver will excavate their den. The entrance 
interior den being several inches above the water surface. 
All lodges and bank dens have at least two entrances, and 
perhaps four or more (University of Nebraska, 1994).
logs, may reach 5-6 feet above the water line, and be 12-14 
feet wide (Benyus, 1989). Beavers have also been known to 
to the lodge or bank den is typically under water, with the 
Food Habits: Beaver prefer to eat tree species such as aspen, 
willow, poplar, cottonwood, sweetgum, blackgum, and 
pine, although beaver will also eat most woody plants that 
grow near water, as well as herbaceous and aquatic plants. 
Beavers will travel 100 yards or more from their water habitat 
to cut down crops or trees growing in adjacent habitats 
and drag them back to their pond home. Beaver use whatever 
vegetation they dont eat for dam construction (University 
of Nebraska, 1994).
Beaver dens are often 
excavated just below the 
dam crest within the dam. 
A den roof collapse at this 
location can create voids in 
the crest and upstream slope. 
Range of the beaver in the North America.
forefoot
hindfoot
walking
Beaver tracks are not a reliable way to identify their presence due to 
their walking pattern. The beavers hind foot is placed on top of the front 
foots track and the wide tail, which drags along the ground, smears 
both to a point where identification becomes nearly impossible.

Behavior: Beavers construct dams to create a depth of water 
suitable for them to hide from predators as they travel to 
their shore feeding grounds. Beaver use a variety of materials 
to construct these damsthe use of wood, fiber, metal, 
wire, and rocks is not uncommon. Beavers leave their lodge 
at dusk and spend most of the night working (removing 
shoreline trees, constructing dams, gathering food). However, 
in the fall season it is not uncommon to see a beaver 
working in the daytime as they gather food for the winter 
(Benyus, 1989). 
Field Tip: Perhaps the best indication of beaver is their dams. 
Dams are typically a few feet long, but can be up to several 
hundreds of feet long. A second indication is the presence of 
canals, which beaver build in the water to help them transport 
the trees they fell to construct the dams. Gnaw marks 
in a circular pattern on tree trunks are also good indicators 
of beaver, and trees cut by beavers show a distinctive tapered 
cone at the end of the trunk. An audible sign of beaver is the 
loud slap of their horizontally flattened tail on the surface of 
the water to alert other beaver to the presence of predators 
(Benyus, 1989).
Figures 4-3 and 4-3A. Beaver dams can block emergency spillways causing water levels behind the dam to rise.
Figure 4-4. A lodge can reach 5-6 feet above the waterline.
The ranges for beaver, 
nutria and muskrat overlap, 
and their damages can 
appear similar. Careful 
examination of the 
damage, burrows, and 
proper use of the field 
tips listed in this manual 
will assist in accurate 
species identification 
and management. 

4.2.3 Mountain Beaver Overview
Mountain Beaver (Aplondontia rufa) is typically found in 
Washington, Oregon, and portions of California. Mountain beaver 
neither prefer mountainous habitat nor are true beavers. These rodents 
have short, heavy bodies and are dark brown above and lighter 
brown below; they resemble a tailless muskrat. Mountain beavers 
have long, strong claws, which they use to create burrows up to 19 
inches in diameter in wet soil near dense water-side vegetation.
Threat to Dams: Mountain beavers divert waterflow by blocking 
water with vegetation. The shallow location of the 
extensive burrows will often cause the ground to cave in. 
The mountain beavers activities could result in hydraulic 
alteration and structural losses.
Habitat and Home: Mountain beavers prefer habitats in forested 
areas where the canopy is open enough to allow dense 
understory vegetation. If a dam is covered with trees and 
thick understory, then a mountain beaver will likely find 
a comfortable habitat. Within this area, mountain beaver 
prefer moist gullies, and vegetated hillsides or flat areas that 
are not prone to flooding. Habitats dominated by red alder, 
salmonberry, huckleberry, and bracken and sword ferns are 
preferred by the mountain beaver. Mountain beavers dig extensive 
burrows that can cover a quarter-acre, are usually located 
near vegetative cover, and are generally 1-6 feet deep 
with 10-30 open entrances. The burrows contain deep (1-9 
feet) nesting and food chambers usually located about 3 feet 
below ground surface; the chambers can be large, usually 
measuring 2 feet in height and 2 feet in diameter. Mountain 
beavers do not like their burrows to be wet and will leave a 
burrow once it is flooded (University of Nebraska, 1994) 
(Figure 4-5).
food
drying den
nest
waste den
Figure 4-5. The mountain beaver only leaves its den to forage or create new dens.

Food Habits: Mountain beavers are herbivores and eat any 
type of succulent vegetation, with sword fern and bracken 
fern being favorites (University of Nebraska, 1994). Mountain 
beavers will also girdle the base of trees and feed on 
small stems (Figure 4-6). Plants that are gathered by the 
mountain beaver are often dried near the burrow and are 
probably used for storage or nesting material. Mountain 
beavers dry their food by stacking vegetation on a nearby 
log or rock, which is termed haystacking (Figure 4-7). 
Mountain beaver usually feed on plants located within 50 
feet of their burrows (University of Nebraska, 1994). 
Range of the mountain beaver in North America.
hindfoot
Figure 4-6. Mountain beavers girdle trees and feed on small stems.
walking
forefoot
The identifying characteristic of a mountain beaver track is a front foot 
print that has a square heel and a hind print that displays a tapered heel.
Figure 4-7. Mountain beavers dry their vegetation on 
logs, known as haystacking, before moving it into their 
burrows. Haystacks can be up to 2 feet high.

Behavior: Mountain beavers are nocturnal animals. They are 
superb diggers and spend much of the night digging and 
maintaining their labyrinth of burrows. Mountain beavers 
often stack cut vegetation in a burrow entrance, presumably 
to lower the vegetations moisture content before storing it 
in the burrow (University of Nebraska, 1994).
Field Tip: Stem and branch cutting within the vicinity of the 
dam may be a positive sign of mountain beavers. Signs of 
mountain beaver include freshly dug soil and chewed vegetation 
in proximity to a 6 to 8-inch diameter hole. Look 
for haystacks near the burrow entrance and vegetation piled 
in the burrow entrance (Figure 4-8).
Figure 4-8. Ferns and Douglas fir branches placed in a 
burrow is a reliable field sign of mountain beaver. 
4.2.4 Groundhog Overview
Groundhog (Marmota monax) (also known as Woodchuck or Rockchuck) 
are large burrowing rodents that weigh an average of 5 to 10 pounds 
and have an average body length of 16-20 inches. Groundhogs are 
usually grizzled brownish gray, although white and black individuals may 
occasionally be found. The groundhogs forefeet have long, curved claws that 
are well adapted to digging burrows (University of Nebraska, 1994).
Threat to Dams: Groundhog burrows in earthen dams can 
weaken the embankment and act as a pathway for seepage.
Habitat and Home: The groundhog generally prefers open 
farmland and woody or brushy areas adjacent to open land. 
Groundhog burrows are usually located in fields or near 
grassy pastures or meadows, along fence rows, stone walls, 
roadsides, and near building foundations or the bases of 
trees (University of Nebraska, 1994) (Figure 4-9, shown 
on page 31). Groundhogs will burrow into earthen dams, 
generally on the downstream side of the dam, as this environment 
can be similar to their preferred habitat (Michigan 
State University Extension, 1998). Their burrows can be distinguished 
by the large mound of excavated earth deposited 
by the main entrance. Two or more entrances generally exist 
for each burrow system. Burrows are often well-hidden and 
may be difficult to locate.

Food Habits: Groundhogs are strict herbivores. They feed on a 
variety of vegetables, grasses, and legumes, including beans, 
peas, carrot tops, alfalfa, and clover. Groundhogs prefer to 
feed in the early morning and evening hours (University of 
Nebraska, 1994). 
Behavior: Groundhogs are usually only active during the day. 
During warm periods, they can often be found basking in 
the sun near their burrows. Groundhogs are one of the few 
mammals that enter a true hibernation period. Hibernation 
generally occurs from late October or early November to 
late February or March, although the exact timing depends 
on the latitude (University of Nebraska, 1994). New burrow 
construction occurs in late summer (USFS, 1994).
Field Tip: When approached or startled, a groundhog will 
often emit a shrill whistle followed by a low, rapid warble 
(University of Nebraska, 1994). An indicative sign of a 
groundhog burrow is the spring cleaning performed by the 
groundhog, which results in a mound of fresh dirt outside 
the burrow entrance. Adjacent trees may be girdled or 
clawed (Indiana Department of Natural Resources, 2003). 
Look for burrow construction in the late summer months.
Range of the groundhog in the North America.
hindfoot
forefoot
walking
It may be difficult to tell the front and back tracks apart because when 
a groundhog walks, it puts its hind foot in the track of its front foot. 

crest
phreatic surface 
Figure 4-9. Groundhog burrows are extensive and irregular in pattern. 
4.2.5 Pocket Gopher Overview
Pocket Gopher (Geomys spp., Thomomys spp., and Pappogeomys castanops) 
are medium-sized burrowing rodents that weigh an average of 3 to 20 
ounces and have an average body length of 5 to 14 inches. Their fine 
fur is highly variable in color, ranging from nearly black to pale brown 
to almost white. Pocket gophers have fur-lined pouches outside of the 
mouth that are used for carrying food. They have yellowish-colored 
incisor teeth that are always exposed, even when the mouth is closed.
Threat to Dams: Pocket gophers are generally only a threat 
to small earthen dams. They dig burrows that can lead to 
internal erosion and structural integrity losses in the dam. 
The presence of pocket gophers also increases the likelihood 
of badger activity. Badgers are one of the primary predators 
of pocket gophers. Badgers will attempt to dig gophers out 
of their burrows, which can be very destructive to earthen 
dams (See Chapter 4.2.6 for a discussion on badgers). 
Pocket gophers can also damage underground utilities, such 
as irrigation pipes or electric cables (USDA, 1991). 
Habitat and Home: There are 10 species of pocket gopher 
with substantial populations in the United States, but only 
one species is typically found in an area (USFS, 1994). They 
can occupy a wide range of habitats, from low coastal areas 
Pocket gophers are 
considered a significant 
dam safety issue in 23% 
of the surveyed states.

to mountains (USDA, 1991). Horseshoe-, fan- or kidney-
shaped mounds of soil are characteristic evidence of pocket 
gopher burrows. Their burrows are nearly always kept 
closed with an earthen plug (University of Nebraska, 1994) 
(Figure 4-10). 
Food Habits: Pocket gophers are strict herbivores, eating 
all types of forbs, grasses, shrubs, and trees. Roots are the 
major food source, although during the growing season, 
pocket gophers will also eat the above-ground portions of 
plants (University of Nebraska, 1994). 
Behavior: Pocket gophers are solitary animals that spend 
much of their time underground. There is typically only one 
gopher per burrow, except during breeding season (USDA, 
1991). 
Range of the pocket gopher in North America.
Plains (Geomys bursarius), and Botta (Thomomys botta) Pocket Gophers
Northern (Thomomys talpoides), and Yellow-Faced 
(Pappogeomys castanops) Pocket Gophers
Southeastern (Geomys pinetis), and Southern 
(Thomomys umbrinus) Pocket Gophers

Field Tip: Pocket gopher activity can be distinguished from 
that of other burrowing animals by their burrow characteristics, 
particularly the fan-shaped mounds of soil and 
plugged burrow entrances. Pocket gophers will tunnel 
through the snow, pushing soil from below ground into 
the snow tunnels. When the snow melts, the soil casts or 
tubes can be found on the ground surface (USFS, 1994). 
Horseshoe-shaped mounds of soil are created in summer or 
late fall.
hindfoot
walking
forefoot
Pocket gopher tracks will show five toes on the hindfoot and four toes on 
the slightly smaller forefoot. Claw marks are usually well-defined.
plug
gopher mound
plug
gopher tunnel and mound
Figure 4-10. Lateral burrows of the pocket gopher end in a soil mound or a soil plug. 

4.2.6 North American Badger Overview
The North American Badger (Taxidea taxus) is a stocky animal that can 
grow up to 30 inches long. It has grayish yellow fur with pale underparts, 
long claws, a short, bushy tail, and black feet. Badgers can weigh from 
19 to 30 pounds and can be identified by a white stripe that runs from 
its nose to the back of its head (University of Nebraska, 1994). 
Threat to Dams: Badgers are especially adapted for digging 
and dig in pursuit of prey and to construct dens for shelter. 
Badgers can cause severe damage to hydraulic structures. 
Badgers can exacerbate internal and external erosion in an 
earthen dam by enlarging existing burrows of prairie dog, 
pocket gopher, or ground squirrels, all of which can inhabit 
an earthen dam and are a preferred food of the badger. Badger 
dens create large voids in the earthen dam, compromising 
structural integrity.
Habitat and Home: Badgers prefer pastures or rangelands with 
light to moderate cover and few trees. Habitats with sandy 
or porous soils are preferred. Female badgers dig large burrows 
(5-30 feet long) with a large chamber 2-3 feet below 
the ground surface for birthing. Dens have one entrance that 
is usually elliptical in shape (University of Nebraska, 1994).
Food Habits: North American badgers are opportunist omnivores 
that feed on earthworms, mammals, birds, reptiles, 
grains, and fruits. Prairie dog, pocket gopher, and ground 
squirrels are common in badger diets. 
Badgers are considered 
a significant dam 
safety issue in 17% of 
the surveyed states.

Behavior: Badgers are adept at pursuit and capture of ground-
dwelling prey. A typical burrow dug in pursuit of prey is 
shallow and about 1 foot in diameter (University of Nebraska, 
1994). Badgers are mostly nocturnal but will be 
active during the day if the area is quiet. Badgers are usually 
solitary.
Field Tip: Large piles of dirt and rock left near animal burrows 
can indicate badger hunting activity. Badgers maintain 
the condition of their claws by sharpening them on trees or 
fence posts; claw marks can indicate badger presence (University 
of Nebraska, 1994). 
Badger tunnels and dirt 
mounds resulting from 
prey pursuit can cover an 
area the size of a car.
Range of the badger in North America.
hindfoot
walking
forefoot
Badger tracks are similar to coyote tracks, but are distinct in 
the long claw marks on the front feet and the presence of five 
toes. Badger tracks are typically turned inward toward each 
other, and the hindprints are narrower than the foreprints.

4.2.7 Nutria Overview
Nutria (Myocastor coypus) With an average weight of 8 pounds and 
a body length of 24 inches (tail is an additional 16 inches long), 
nutria are larger than muskrat, but much smaller than beaver. With 
a preferred habitat that includes permanent water, nutria are excellent 
swimmers with webbed hind feet, but move awkwardly on land. 
Threat to Dams: Nutria construct extensive burrows as shelter 
in the upstream slope. Burrows can weaken an earthen dam 
to the point of collapse when soil becomes saturated by 
precipitation or high water, or when heavy vehicles cross 
the crest. Nutria are notorious for breaking through water-
retaining levees in Louisiana and Texas (University of 
Nebraska, 1994).
Habitat and Home: Nutria can adapt to a variety of habitats, 
but prefer a semi-aquatic environment and particularly, the 
zone between land and permanent water. This zone is preferred 
for its abundance of aquatic vegetation. For the most 
part, any substantial nutria populations in the United States 
occur in freshwater marshes of coastal areas (University of 
Nebraska, 1994). Nutria are ground-dwellers during the 
summer, preferring to live in dense vegetation. The rest of 
the year nutria live in burrows they have dug, or that have 
been abandoned by armadillos, muskrat, or beaver. Nutria 
construct burrow entrances in vegetated banks of dams and 
waterways; a bank that has a slope greater than 45 degrees is 
a preferred location (University of Nebraska, 1994). Nutria 
burrows can be simple or complex; a complex burrow may 
have several tunnels and entrances at different levels in the 
bank. A burrow system will contain compartments (ranging 
from 1-3 feet across) for resting, feeding, and shelter from 
the weather and predators. Tunnels can be 4-6 feet in length.
In some cases, nutria 
tunnels have been so 
extensive that water flowed 
unobstructed through the 
embankment necessitating 
its complete reconstruction.
Look closely! Nutria are 
aquatic rodents often 
misidentified as either 
a muskrat or beaver. 
Nutria are considered 
a significant dam 
safety issue in 4% of 
the surveyed states.

Food Habits: Nutria prefer aquatic plants such as sedges, 
rushes, cattails, and arrowheads, however the bark of black 
willow and bald-cypress may be eaten in the winter. Nutria 
eat food in a number of places including feeding platforms 
on the water (floating mats of vegetation or even on top of 
beaver and muskrat houses), in the water itself, or on land. 
Behavior: Nutria feed at night when food is plentiful, but will 
feed during the day if food is limited. Nutria can scratch or 
bite aggressively if captured or cornered.
Field Tip: Unlike muskrat or beaver, a nutrias tail is round 
with scant hair, the whiskers are long (around 4 inches) 
and whitish, and nutria have prominent red-orange incisors. 
Trees girdled by nutria will show no teeth marks. 
Range of the nutria in North America.
Nutria construct platforms 
of floating vegetation used 
for loafing, grooming, 
birthing, and escape, 
which are often mistaken 
for muskrat houses.
forefoot
walking
hindfoot
Tracks left by nutria may also have tail drag marks, or sometimes 
chest marks, as a nutria may drag its chest when on land. 

4.2.8 Prairie Dog Overview
Prairie Dogs (Cynomys spp.) are squirrel-like, burrowing rodents 
with squat, muscular bodies and short tails and ears. Their fur is 
sandy brown to cinnamon in color with grizzled black and buff-
colored tips. Adult prairie dogs grow to a length of 13 to 17 inches 
and weigh approximately 2 to 4 pounds (USDA, 1991).
Threat to Dams: Prairie dogs dig burrows that can lead to 
internal erosion and structural integrity losses in earthen 
dams.
Habitat and Home: Prairie dogs prefer grassland or short shrubland 
habitats. They often establish colonies near intermittent 
streams or water impoundments (USDA, 1991). Prairie 
dog burrows are found in open areas with low vegetation. 
Their burrows are distinguished by relatively large holes 
and cone-shaped mounds. Prairie dogs remove the vegetation 
from around their burrows and use it for food or 
nesting material (USDA, 1991). Other animals often make 
their homes in prairie dog burrows, including the federally 
protected black-footed ferret and burrowing owl. 
Food Habits: Prairie dogs eat mostly grass, although they will 
also eat flowers, seeds, shoots, roots, and insects when available 
(University of Nebraska, 1994).
Behavior: Prairie dogs live in large colonies known as 
towns. Each town is made up of a complex series of tunnels 
and may have as many as 20 to 50 burrow entrances. 
Prairie dogs are social animals that are most active during 
the day (University of Nebraska, 1994). 
Field Tip: Look for mounds of earth about 1 to 2 feet high 
that resemble miniature volcanoes. 
Prairie dogs are considered 
a significant dam 
safety issue in 8% of 
the surveyed states.

Range of the prairie dog in North America.
White-Tailed (Cynomys leucurus), and Mexican 
(Cynomys mexicanus) prairie dogs
Black-Tailed (Cynomys ludovicianus), and Gunnison 
(Cynomys gnnisoni) prairie dogs
hindfoot
walking
forefoot
Prairie dog tracks will show five toes on the hindfoot 
and four toes on the slightly smaller forefoot. 

4.2.9 Ground Squirrel Overview
Ground Squirrel (Spermophilus spp.) are small to medium-sized burrowing 
rodents. Twenty-three species of ground squirrels live in the United States 
(University of Nebraska, 1994). They vary is size, with lengths ranging 
from 6 to 20 inches and weight ranging from 0.25 to 2.5 pounds. They 
also vary in color, ranging from brown to reddish brown to gray. Some 
species have markings, such as spots or stripes. Some species have long 
bushy tails, while others have short tails with short hair (USDA, 1991).
Threat to Dam: Ground squirrels dig burrows that can lead to 
internal erosion and structural integrity losses in earthen 
dams. The presence of ground squirrels also increases the 
likelihood of badger activity. Badgers will pursue ground 
squirrels into their burrows, which can be very destructive 
to earthen dams (USDA, 1991). 
Habitat and Home: Ground squirrels can be found in at least 
27 states west of Ohio. They occupy a wide range of habitats 
from low coastal areas to mountains. Ground squirrels keep 
their burrows unplugged. Specific burrow design varies 
with species, soil type, habitat and climate. Some species 
of ground squirrels are colonial, which means that several 
individuals live in the same burrow system. These systems 
consist of clustered, above-ground mounds that resemble 
prairie dog burrows. They are generally easier to spot than 
the burrows of solitary ground squirrel species, which tend 
to be scattered and inconspicuous (USDA, 1991). 
Range of the ground squirrel in North America.
Richardson (Spermophilus richardson), and Wyoming 
(Spermophilus elegans) ground squirrels
Columbian (Spermophilus columbianus), Franklin (Spermophilus 
franklinii), California (Spermophilus beecheyi), and 
Mexican (Spermophilus mexicanus), ground squirrels

Range of the ground squirrel in North America (continued).
Townsend (Spermophilus townsendi), Thirteen-lined 
(Spermophilus tridecemlineatus), and Round-tailed 
(Spermophilus tereticaudus) ground squirrels
Belding (Spermophilus beldingi) and Spotted 
(Spermophilus spilosoma) ground squirrels
Rock (Spermophilus variegatus) ground squirrels
Washington (Spermophilus washingtoni), Idaho (Spermophilus 
brunneus), and Uinta (Spermophilus armatus) ground squirrels

Food Habits: Ground squirrels mostly eat plant material, although 
some species may also eat insects, eggs, carrion, and 
other animal material (USDA, 1991).
Behavior: Ground squirrels are only active during the day, 
and they are most active during mid-morning and late 
afternoon. They hibernate in the winter, and most species 
estivate in summer as well (USDA, 1991). 
Field Tip: During warm months, ground squirrels are quite 
active during the day and can be easily spotted. Unplugged 
burrows are a distinctive characteristic of ground squirrel 
inhabitation (USDA, 1991).
forefoot
walking
hindfoot
Although ground squirrel tracks will vary in size, they generally show five 
toes on the hindfoot and four toes on the smaller and rounder forefoot.
Ground squirrels are 
considered a significant 
dam safety issue in 15% 
of the surveyed states.
4.2.10 Armadillo Overview
The Armadillo (Dasypus novemcinctus) is a medium-sized animal, 
about 8 to 17 pounds, with a protective, armor-like shell on its head, 
body, and tail. It has nine movable bands across its back, and the tail is 
covered with a series of overlapping rings. The armadillo has a small head 
with a long, narrow, piglike snout (University of Nebraska, 1994). 
Threat to Dams: Armadillos dig burrows that can result in 
internal erosion and structural integrity losses in dams.
Habitat and Home: It prefers forest, woodland and brush 
habitat, as well as areas near creeks and rivers. The armadillo 
will also inhabit areas with rocks, cracks, and crevices that 
are suitable for burrows (University of Nebraska, 1994). 
Armadillos generally dig burrows 7 to 8 inches in diameter 
and up to 15 feet in length. They can be found in rock piles, 
around stumps, brush piles, or terraces around brush or 
dense woodlands. Armadillos usually have more than one 
den in an area (University of Nebraska, 1994). 

Food Habits: The armadillo primarily eats insects and their 
larvae. They also feed on spiders, earthworms, scorpions, 
and other invertebrates. To a lesser extent, they may eat some 
fruit and vegetable matter (University of Nebraska, 1994). 
Behavior: During the summer, the armadillo is active from 
twilight through early morning hours, but in the winter, it 
is usually only active during the day. The armadillo has poor 
eyesight, but a keen sense of smell. It can run fast when in 
danger and is also a good swimmer (USDA, 1991). 
Field Tip: Characteristic signs of armadillo activity are shallow 
holes, about 1 to 3 inches deep and 3 to 5 inches wide, dug 
in search of food (University of Nebraska, 1994).
Armadillos are considered 
a significant dam 
safety issue in 4% of 
the surveyed states.
Range of the armadillo in North America.
hindfoot
walking
forefoot
Armadillos have four toes on their forefeet and five toes 
on their hindfeet, although not all toes may show up in 
their tracks. Sharp claw marks are often visible.

4.2.11 Livestock Overview
Livestock can include cattle, horses, sheep, goats, and pigs of all varieties, 
domesticated and wild. Livestock exist widely across the United States 
and utilize earthen dams and farm ponds for grazing and drinking. 
Threat to Dams: Livestock can damage an earthen dam by 
removing stabilizing vegetation through grazing, trampling, 
and rooting. External erosion can occur without vegetative 
cover, and erosion pathways can be created as livestock traverse 
the embankment (Figures 4-11 and 4-12). Damages 
are most severe in arid regions, and damage is often not 
noted until the wet season when precipitation collects in 
holes and along erosion pathways. Livestock carcasses could 
alter or block water flow if located at control structures. 
Wild pigs commonly damage farm ponds and can cause 
substantial damage to a grassy area in a single night (University 
of Nebraska, 1994).
Habitat and Home: Livestock can occur anywhere in the 
United States. In some cases, several livestock species will 
graze in one area. Wild pigs can exist in a variety of habitats 
but prefer dense brush or marsh vegetation as cover. Wild 
pigs are often found inhabiting livestock-producing areas 
(University of Nebraska, 1994).
Food Habits: Most livestock, including cows, sheep, goats, and 
horses, are grazers. Pigs, however, generally root for underground 
vegetation, in addition to feeding on acorns and 
Livestock are considered 
a significant dam 
safety issue in 25% of 
the surveyed states.

other mast. Livestock disturb soil and vegetation through 
their feeding methods. 
Behavior: Location to a water source is considered the primary 
influence on livestocks activity within a given grazing 
area, followed by desirable forage and topography of 
the grazing area. In hot weather, pigs will wallow in ponds, 
springs, or streams that contain or are near vegetative cover. 
Field Tip: Livestock are easily identified as they are often 
intentionally grazed on lands near farm dams. Wild pigs are 
obvious if observed, otherwise look for wallows. 
Range of livestock, and wild pigs in North America.
hindfoot
walking
Figure 4-11. Livestock can cause external erosion by 
creating ruts and erosion paths via hoof traffic.
forefoot
Tracks can be used to identify wild pigs. Tracks are generally 
not needed to identify other types of livestock since they are 
often intentionally grazed on lands near farm dams. 
One milk-producing Jersey cow can 
drink up to 12 gallons of water a day. 
Herds of dairy cows typically include 
50 to 100 animals. Thats a lot of 
hoof-traffic at an earthen dam!
Figure 4-12. Livestock can remove stabilizing 
vegetation through grazing and hoof traffic.

4.2.12 Crayfish Overview
Crayfish (Cambarus spp.) resemble miniature lobsters. There 
are over 300 species of various sizes, shapes, and colors in 
the United States (University of Nebraska, 1994). 
Threat to Dams: Crayfish burrow into earthen dam embankments; 
extensive burrowing may cause internal erosion and 
structural integrity losses. 
Habitat and Home: Crayfish are found in a variety of fresh water 
habitats, including streams, rivers, ponds, lakes, swamps, 
and wet meadows (Peckarsky et al, 1990). Crayfish burrows 
are usually located along the shoreline close to the waters 
edge. They may be anywhere from a few inches to three 
feet deep. The opening is generally about  to 2 inches in 
diameter with a cone-shaped mound, known as a chimney, 
plugging the burrow (Virginia Cooperative Extension, 
2001a) (Figure 4-13).
Food Habits: Crayfish eat both living and dead plant and animal 
material. Almost half of their diet consists of bottom-
dwelling worms and insects. The rest of their diet consists of 
Crayfish are considered 
a significant dam 
safety issue in 4% of 
the surveyed states.
Figure 4-13. A crayfish burrow is a cone-shaped mound or chimney made with mud pellets.

living and decaying aquatic vegetation (Virginia Cooperative 
Extension, 2001a).
Behavior: A crayfish will molt several times in its short lifespan. 
They can be quite aggressive towards each other and 
toward anything they perceive as a threat (Peckarsky et al, 
1990). Most crayfish dig burrows to use as a refuge from 
predators and as a resting place during molting and inactive 
periods (Virginia Cooperative Extension, 2001a). 
Field Tip: Crayfish stay in their burrows or in mud bottoms 
during cold weather. They will emerge, and be easier to 
spot, once the water warms up (Virginia Cooperative Extension, 
2001a). 
Range of the crayfish in North America.
4.2.13 Coyote Overview
The Coyote (Canis latrans) is a member of the dog family, and in size 
and shape, it resembles a small German shepherd, with erect pointed 
ears, slender muzzle, and a bushy tail. Coyotes are generally brownish-
gray with a lighter colored belly, although this varies widely across local 
populations. In the west, adult males typically weigh 25 to 45 pounds 
and adult females typically weigh 22 to 35 pounds. Coyotes in the east 
are usually larger, with adult males weighing about 45 pounds and adult 
females weighing about 30 pounds (University of Nebraska, 1994).
Threat to Dams: Although coyotes do not pose a large threat 
to earthen dams, den construction or enlargement, and 
digging out prey that live at the dam can cause structural 
integrity losses.
Habitat and Home: Coyotes exist in virtually any type of habitat, 
arctic to tropic. High densities of coyotes even appear in 
the suburbs of major western cities such as Los Angeles and 
Phoenix. Their dens are often found in steep banks, rock 
crevices, sinkholes, and underbrush, as well as open areas. 
Dens are usually located close to water. Coyotes will often 
dig out and enlarge burrows of other animals. Size of coyote 
dens varies from a few feet to 50 feet, and each den often 
has several openings (University of Nebraska, 1994).
Coyote are considered 
a significant dam 
safety issue in 4% of 
the surveyed states.

Food Habits: Coyotes eat a variety of animals, insects, fruits, 
and vegetables (University of Nebraska, 1994).
Behavior: During hot summer months, coyotes are most active 
at night and during the early morning hours. During 
cooler weather, and in areas with minimal human activity, 
coyotes may be active throughout the day. Coyotes have 
good eyesight and hearing and a keen sense of smell. Their 
adaptable behavior and social system allows them to survive, 
and even flourish, in the presence of humans (University of 
Nebraska, 1994).
Field Tip: Coyotes can often be identified by their tracks, 
although it should be noted that regular dog tracks are often 
mistaken for coyote tracks. Coyote dens are often located in 
the downstream slope. 
Range of the coyote in North America.
hindfoot
walking
forefoot
Badger tracks are often confused with coyote tracks, but note that 
coyotes only have four toes on each foot, while badgers have five toes. 

4.2.14 Moles and Voles Overview
Moles (Scapanus spp.) are small insectivores that are often confused with 
voles, shrews, and pocket gophers. Moles, however, can be distinguished 
by their hairless, pointed snout, small eyes, and webbed forefeet. There 
are seven different species of moles living in the United States. Adult 
males grow to a length of about 7 inches and weigh about 4 ounces; 
adult females are slightly smaller (University of Nebraska, 1994). 
Voles (Microtus spp.) also known as meadow mice or field mice, are 
compact rodents with short legs and short tails. There are 23 species of 
voles in the United States. Most are gray or brown, and about 4 to 8 
inches long; although both size and coloration varies across species. 
Threat to Dams: Earthen dams may provide good hunting 
grounds for moles. Although they usually make their home 
burrows in dry, upland areas, they prefer to hunt in areas 
that are cool and moist. They construct tunnels from their 
dens to their hunting grounds. If located in an earthen 
dam, these tunnels may cause internal erosion and structural 
integrity losses. When present in large numbers, voles 
may also cause damage to earthen dams. They dig extensive 
burrow systems that could lead to internal erosion and 
structural integrity losses in the dam (University of Nebraska,
1994).
Habitat and Home: Moles can be found across most of the 
United States. As mentioned above, they generally construct 
their burrows in dry, upland areas. Deep runways connect 
their dens to their hunting grounds (University of Nebraska, 
1994) (Figures 4-14 and 4-15, shown on page 51). 
Voles can also be found across most of the United States. 
They prefer areas of heavy ground cover, although they can 
survive in a wide variety of habitats. Burrow systems consist 
of a series of tunnels and surface runways, and often have 
several entrances (University of Nebraska, 1994) (Figure 
4-16, shown on page 51).
Food Habits: Moles primarily eat insects, grubs, and worms. 
Voles are mostly herbivorous, primarily eating grasses and 
forbs. Voles will also occasionally eat snails, insects, or animal 
remains (University of Nebraska, 1994).
Moles and voles are 
considered a significant 
dam safety issue in 10% 
of the surveyed states.

Behavior: Moles are solitary animals, and they spend most of 
their time underground. They are active through all seasons 
of the year. Voles are also active throughout the year, both 
day and night. They are excellent swimmers and often try 
to escape from predators through the water (University of 
Nebraska, 1994). 
Field Tip: Moles push up volcano-shaped mounds of soil 
when they are building tunnels. The mounds may be anywhere 
from 2 to 24 inches tall. Surface tunnels or ridges are 
also an indication of mole activity. Voles can be identified by 
their extensive surface runway systems. These runways are 
generally 1 to 2 inches in width. 
Range of the mole in North America.
Range of the vole in North America.

mole ridges
mole hill
Figure 4-14. Mole burrows form ridges visible from the surface.
Figure 4-15. Moles push dirt vertically to the surface, which forms a mound.
entrance to 
underground 
runway system
Figure 4-16. Voles are most easily identified by an extensive surface runway system with many burrows.

4.2.15 River Otter Overview
The River Otters (Lutra canadensis) sleek body, short legs, webbed 
toes, and tapered tail help it thrive in its aquatic environment. 
Otter fur is thick and shaded from brown to near black on most 
of the body, with a lighter brown to beige on the belly, chin, 
throat, cheeks, and chest (University of Nebraska, 1994). 
Threat to Dams: Otters sometimes dig bank dens for shelter 
with an underwater entrance for use in the winter and 
an above-water entrance for use in the summer (Benyus, 
1989). Dens can cause large voids in the dam embankment, 
and underwater entrances provide pathways for internal 
erosion and wave action if water levels rise into the embankment 
den. 
Habitat and Home: Otters are associated almost invariably with 
water environments no matter the water type: fresh, brackish, 
or salt. Water quality, available fish forage, and available 
den sites are the most important factors in determining 
otter habitat. Otters can be found in lakes, rivers, streams, 
bays, estuaries and associated riparian habitat. Otters most 
often utilize existing bank dens and lodges constructed by 
beaver, muskrat, and nutria. Otherwise, otters use hollow 
logs and rock crevices as their shelter and construct natal 
dens on small streams that lead to major drainages (University 
of Nebraska, 1994).
Food Habits: Otters prefer fish of several varieties, but also 
feed on shellfish, crayfish, reptiles, and amphibians. 
Behavior: Otters spend most of the day feeding and participating 
in group play. Otters are superb swimmers and very 
alert.
Field Tip: Look for slides into the water or snowbank (in 
winter) where otters play. Look for haul-outs, worn areas 
along the bank where otters consistently pull themselves out 
of the water. If this area is indeed a haul-out, there will be a 
trail leading away from the haul-out to a patch of trampled 
vegetation where otters roll around to dry themselves after 
a swim or to leave their scent (Benyus, 1989). Listen for the 
blow and sniff sounds of a surfacing otter.
River otters are considered 
a significant dam 
safety issue in 4% of 
the surveyed states.

hindfoot
walking
forefoot
The inner toe of the otters hind paw juts out to the side.
Range of the river otter in North America.
4.2.16 Gopher Tortoise Overview
Gopher Tortoise (Gopherus polyphemus) are large, terrestrial tortoises 
with a shell length of 10 to 15 inches that weigh about 9 pounds. The 
gopher tortoise is a protected species and a permit is always required to 
possess, study, remove, or relocate a specimen (Gopher Tortoise Council, 
2001). The burrows of the gopher tortoise are also protected by law. Over 
360 animal species have been documented inhabiting a gopher tortoise 
burrow so use caution when investigating a burrow. Many of the species 
which coexist in or use gopher tortoise burrows are also protected by 
state and federal laws, such as the burrowing owl and indigo snake. 
Threat to Dams: The gopher tortoises strong claws make it an 
effective burrower. Burrows can be 40 feet long and 10 feet 
deep and will include a spacious chamber used to cool off 
during the heat of the day (Gopher Tortoise Council, 2001). 
Gopher tortoise burrows can cause structural integrity 
losses. 
Tortoises are considered 
a significant dam 
safety issue in 4% of 
the surveyed states.

Habitat and Home: Gopher tortoises prefer to dig their burrows 
in dry, upland habitats especially where saw-palmetto 
is present in the understory and sandy soils dominate. 
Gopher tortoises can live in grassy areas, pastures, and old 
fields as long as there are well-drained sandy soils, herbaceous 
plants, and sunny, open areas for nesting and basking 
(Gopher Tortoise Council, 2001). Look for burrows on the 
southeastern side of sandy hills (such as old dunes that are 
covered in vegetation) at a 30-degree angle from the surface 
(Benyus, 1989; Enchanted Forest Nature Sanctuary, 2003). 
The burrow entrance, or apron, will be marked by a characteristic 
mound of loose sand. The downstream slope and 
toe of a dam may be suitable for gopher tortoises, as might 
a forest fringe in a dam area.
Note: In some cases, snapping turtles may hibernate or 
lay eggs in an existing muskrat den and as such, are often 
identified as the responsible burrowing animal. In truth, 
turtles are more correctly simply associated with burrowing 
animals, rather than responsible for burrows. Depending on 
its size, the snapping turtle may enlarge an existing muskrat 
den. 
Food Habits: Primary food sources of the gopher tortoise 
include low-growing grasses, herbs, and berries. 
Behavior: Gopher tortoises emerge from their burrows in the 
morning to feed and return to the burrows if temperatures 
get too hot or cold. 
Field Tip: Look for large mounds of loose sand created as the 
gopher tortoise digs its burrow. 
Range of the gopher tortoise in the United States.
An east-central Florida 
study indicates that a male 
gopher tortoise constructs 
and uses an average of 
17 burrows. Some males 
construct and use as 
many as 35 burrows.
The shell of the gopher tortoise may obliterate some of the track as it drags.

4.2.17 Red Fox and Gray Fox Overview
The Red Fox (Vulpes vulpes) is dog-like in appearance with large pointed 
ears and an elongated pointed muzzle. It typically has a light orange-red 
coat with lighter colored underfur, black legs, and a white-tipped tail. Coat 
coloration can vary from red to gray to black, but the tail tip is always 
white. Adult red foxes can weigh anywhere from 7.7 to 15.4 pounds; males 
are about 2.2 pounds heavier than females (University of Nebraska, 1994).
The Gray Fox (Urocyon cinereoargenteus) has a long, bushy tail with 
a black tip. It is salt-and-pepper gray over most of its body, with some 
rusty yellow spots on the sides of the neck, back of the ears, legs and feet. 
Adult gray foxes weigh about 7 to 13 pounds, and measure about 32 to 
45 inches from nose to tip of tail (University of Nebraska, 1994).
Fox are considered a 
significant dam safety 
issue in 4% of the 
surveyed states.

Threat to Dams: Foxes do not pose a great threat to earthen 
dams. It is possible that they could cause damage by digging 
out burrowing animals for food. This type of damage 
may be prevented with good rodent control and vegetative 
management.
Habitat and Home: The red fox prefers open country with 
moderate cover, although it is generally adaptable to any 
habitat within its range. Red foxes are commonly found 
in urban areas. They may either dig their own dens or use 
abandoned groundhog or badger burrows. The gray fox 
prefers areas of dense cover such as swamp land or thickets. 
Gray foxes can also be found in urban areas. They commonly 
use wood piles, rocky outcrops, or hollow trees as den 
sites (University of Nebraska, 1994). 
Food Habits: Foxes mostly eat rabbits, mice, bird eggs, insects, 
and fruit (University of Nebraska, 1994). 
Behavior: Foxes are solitary animals that are most active during 
twilight and early morning hours. They have a variety of 
calls that sound like barks, screams, howls, yaps, growls, and 
hiccups (University of Nebraska, 1994).
Range of the red fox in the North America.
Range of the gray fox in North America.

Field Tip: Fox dens may be identified by several 10-inch wide 
entrance holes, with sandy aprons of soil spilling from them 
(Benyus, 1989).
hindfoot
hindfoot
walking
forefoot
walking
Tracks of red fox.
forefoot
Tracks of gray fox.
4.2.18 Canada Goose Overview
The Canada Goose (Branta canadensis) is a large bird that grows to a 
height of 2 to 3 feet and weighs approximately 10 to 12 pounds. It has a 
grayish-brown body and wings; black feet, bill and neck; a white underside; 
and a white patch on each cheek (USDA, 2003). There are 11 subspecies 
that live in the United States (Virginia Cooperative Extension, 2001b). 
Threat to Dam: Canada geese build their nests near water. If 
they choose to nest on or near an earthen dam, their nesting 
and feeding activities could cause external erosion. 
Habitat and Home: Canada geese are found across the United 
States. Many Canada geese spend their summers in Canada 
and migrate south to the United States during the winter. 
Some geese, known as resident Canada geese, spend most 
of the year in the same general area and fly only far enough 
to find food or open water (Virginia Cooperative Extension, 
2001b). Canada geese nest in areas near open water, such 
as swamps, marshes, meadows and lakes. Nests are typiCanada 
geese can cause 
erosion from over-
grazing similar to that 
caused by livestock. 

cally made from weeds, twigs, grass, moss, and pine needles 
(University of Michigan Museum of Zoology, 2002). 
Food Habits: Canada geese eat a variety of grasses and aquatic 
plants. They will also eat crops such as corn, soybeans, and 
wheat. Young Canada geese require more protein, and will 
consequently eat insects, small crustaceans, and mollusks 
(Virginia Cooperative Extension, 2001b). 
Behavior: Canada geese are social animals that communicate 
to each other through a series of calls. They tend to be aggressive 
birds, particularly the males. They will vigorously 
defend their territory, nests, and eggs from intruders (University 
of Michigan Museum of Zoology, 2002). 
Field Tip: Canada geese can be easily identified by the white 
patches on their cheeks. In absence of the birds themselves, 
Canada geese can be identified by their long, black, cylindrical 
droppings. 
Range of the Canada goose in North America.

4.2.19 American Alligator Overview
The American Alligator (Alligator mississippiensis) is one of the largest 
animals in North America. Adult males can grow to a length of 14 feet 
and weight up to 1,000 pounds. Adult females can grow to a length of 10 
feet and weigh up to 250 pounds. They have a rounded snout and black 
and yellow-white coloration (University of Nebraska, 1994). Alligator 
hunting is allowed in several states under strict quota or licence guidelines.
Threat to Dam: Alligators sometimes dig burrows or dens 
for refuge from cold temperatures, drought, and predators. 
These burrows can cause internal erosion and structural 
integrity losses in earthen dams (University of Nebraska, 
1994).
Habitat and Home: Alligators can be found in almost any 
type of fresh water, including wetlands, lakes, canals, and 
streams. They will occasionally inhabit brackish or salt water 
environments (University of Nebraska, 1994).
Food Habits: Alligators will prey upon whatever creatures are 
most available, including fish, turtles, birds, mammals, and 
other alligators. Alligators are opportunistic feeders and will 
eat carrion if it is available and they are sufficiently hungry. 
If they are near human environments, they may also eat pets 
and livestock (University of Nebraska, 1994).
Alligators are considered 
a significant dam 
safety issue in 2% of 
the surveyed states.

Behavior: Because they are cold-blooded, alligators are most 
active when the temperature is warm. When the temperature 
drops below 700F, alligators will stop feeding, and 
when the temperature drops below 550F, they become 
dormant. Alligators are not typically aggressive toward humans, 
but they can and will attack if provoked (University 
of Nebraska, 1994). 
Field Tip: Alligators are large animals, but they blend into 
their surroundings. It is important to be vigilant and cautious 
around any water body in the alligators range. 
Range of the American alligator in North America.
4.2.20 Ants Overview
Ants (Formicidae spp.) are small insects that live in large colonies. The 
body of an ant is clearly divided into three sections. Many different species 
of ants live in the United States. Color and size varies widely across 
species (University of Florida Cooperative Extension Service, 2002). 
Threat to Dam: Ants often build their homes underground. 
Their colonies consist of a complex series of tunnels that 
excacerbate existing cracks and can soften the embankment, 
threatening the structural integrity of an earthen dam.
Habitat and Home: Ants can be found across the United States 
in a variety of habitats. Most ants live in the soil, although 
some also live in wood or in the cavities of plants (University 
of Arizona, 1997). 
Ants are considered a 
significant dam safety 
issue in 4% of the 
surveyed states.

Food Habits: Ants eat a variety of foods, including plants, sugars, 
seeds, and small insects (University of Florida Cooperative 
Extension Service, 2002). 
Behavior: Ants are social animals. They live in colonies comprised 
of one or a few queens and many workers. Some ants 
have a potent sting (University of Arizona, 1997).
Field Tip: Small mounds of soil are often indicative of ant 
inhabitation. 
Range of the ant in North America.

57
Chapter 5. Dam Repair and Intrusion Prevention Through Design
5.0 Dam Repair And Intrusion 
Prevention Through Design 
Once the inspection is completed according to the guidelines 
(refer to Chapter 3.0) and considering the biological 
perspectives presented in Chapter 4.0, the dam specialist 
will need to take action relative to damages found at the 
dam. Specifically, the dam owner will need to repair burrow 
or beaver dam damage, and determine the appropriate level 
and type of prevention action (e.g., reinforced concrete wall 
and slab system on upstream slope to prevent muskrat burrows). 
This Chapter first outlines burrow repair procedures, 
followed by a discussion of each earthen dam zone (which 
corresponds to the zones described in Chapter 3.3 of this 
manual) with regard to the relative priority of prevention 
action for each zone. Lastly, design options to mitigate and 
prevent future animal intrusions are presented for each 
wildlife species. The prevention methods in this chapter 
relate to modification of the dam or its structures; a discussion 
of prevention through animal control methods (e.g., 
trapping) is presented in Chapter 6.0. 
The majority of the prevention action design criteria of this 
Chapter are meant to be incorporated when major features 
of the dam can be easily altered such as during new dam 
construction or dam repair construction, when the majority 
of the dam or a large portion of the dam will be reworked. 
The input of a professional engineer is required to ensure 
proper design and construction of prevention actions. 
5.1 Conformity to the Clean Water Act of 1972
The Clean Water Act of 1972 (CWA) is the primary guidance 
for protecting surface water quality in the United 
States. The goals of the CWA are to restore and maintain the 
chemical, physical, and biological integrity of the nations 
waters so that they can support the protection and propagation 
of fish, shellfish, and wildlife and recreation in and 
on the water. Towards these goals, the CWA sets water quality 
standards for waterbodies, which are upheld by antidegradation 
policies and programs, ambient monitoring, and 
pollutant load reduction strategies as necessary. 
In the dam environment, extensive vegetation removal, burrow 
excavation and repair, and dam restoration measures 
could trigger the CWA if dredged or fill materials could 
be deposited into wetlands or Waters of the United States. 
As such, all remediation activities must be completed in 
accordance with the CWA and its provisions, and coordination 
with the State Dam Safety Official and the State Water 
Resources Agency is required.

Dam Owners Manual to Animal Intrusion of Earthen Dams
58
5.2 The Role of Vegetation Management
Proper vegetation management is a cornerstone of effective 
wildlife intrusion management. In most cases, wildlife will 
not inhabit an earthen dam that does not provide vegetation 
for food supply, protective cover, or shelter. If a variety 
of vegetation exists at the dam, then wildlife will choose 
to inhabit the earthen dam environment over other areas 
lacking in vegetation or without a water supply. Ideally, the 
earthen dam environment will contain appropriate grass 
species maintained such that dam inspections can be conducted 
easily without visual obstruction of the embankment 
and other appurtenant structures. Vegetation such as dense 
groundcover and thick, woody trees and shrubs not only 
hinder dam inspections, but can also obscure indicators of 
potential performance problems such as animal burrows, 
settlement, depressions, cracks, and similar issues. If vegetation 
is too thick, animal burrows can go undiscovered and 
proper animal intrusion mitigation may not occur. 
In general, it is advised to limit vegetation at the earthen 
dam to low-growing native grass that is mowed regularly, 
and to keep the embankment and spillway inlet and outlets 
free of vegetation. Vegetated emergency spillways should be 
maintained in a similar fashion as the dam embankment. 
Maintained grass will accommodate thorough inspections 
and limit the number of wildlife species that can easily 
inhabit the dam. If a dam contains vegetation other than 
appropriate grasses, then the dam owner should complete 
mitigation and management as outlined in the FEMA document, 
A Technical Manual on the Effects of Tree and Woody Vegetation Root 
Penetrations on the Safety of Earthen Dams (FEMA, 2002) and the 
FEMA brochure, Dam Owners Guide to Plant Intrusion of Earthen 
Dams (FEMA, 2003). 
5.3 Burrow Repair Procedures
Repair actions can be separated into two categories: restoration 
measures and preventive measures. As the names imply, 
restoration measures address repairing a deficiency, whereas 
preventive measures prevent or avert future damage in the 
area. Specific restoration and preventive measures applicable 
for various locations in the dam are discussed below.
5.3.1 Restoration Measures
Damage from animal intrusions can occur throughout the 
dam. The damage can include removal of surface vegetation, 
rutting, and burrowing. Regardless of the damage location, 
applicable restoration options depend upon the judged 
severity of the damage. 
Filling Ruts and Near Surface Deformation
Ruts, near surface deformation, and loss of vegetation can 
be the result of frequent animal crossings, most likely by 
livestock. Repair of these deficiencies is generally considered 
not critical. However, if left unattended for a sufficiently 
long period of time, these deficiencies can result 
in a progressive loss of vegetation and surface soils due to 
erosion. In extreme cases, the damage can lead to increasing 
amounts of erosion in localized areas, jeopardizing performance 
and requiring significant maintenance. Timely repair 
of ruts and vegetation loss can save considerable effort and 
expense later.
The repair methodology for ruts, surface deformation, and 
vegetation loss includes the following steps:
Fill the rut with soil of a similar type to that of the dam 
embankment. Overfill the rut slightly to account for 
compaction of the fill material. 
Compact the soil using hand held or walk behind equipment. 
In order to achieve reasonable compaction, the fill 
material should not contain particle sizes greater than 
1 inch in diameter. For larger ruts, and ruts created by 
vehicles, larger diameter material may be acceptable. The 
compacted surface should be smooth and level with the 
surrounding ground.
Revegetate the area with grass species appropriate for the 
region (see Chapter 5.2).
Filling Burrows
Methods for repairing or filling an animal burrow are essentially 
limited to two basic types. The first method considers 
filling the burrow without excavation while the second 
method considers excavating the burrow and backfilling the 
area. Details for each method are discussed below.
Observed burrows without signs of embankment distress 
(e.g., cracking, slumping) in the area may simply require 
filling with an impervious material or cementious grout. 
To fill the entire burrow, a process often referred to as 
mud-packing can be applied. This method consists of 
placing one or two lengths of metal stove or vent pipe vertically 
into the burrow. When the pipe is properly sealed, a 
slurry of 90% earth and 10% concrete, plus an appropriate 
amount of water to make the slurry flow, is placed in the 
pipe and allowed to flow into the burrow (Virginia Dam 

Safety Program, 2003). The last 6 inches is filled with dirt 
that will support grass growth.
On the other hand, signs of embankment stress surrounding 
a burrow may indicate massive soil movement into the burrow. 
In these cases and at the owners discretion, complete 
removal of the burrow is preferred. Shovels or backhoes 
could be necessary during excavation depending upon the 
burrow location, size, and depth. Excavation limits will be 
defined by the burrow size and location as well as the density 
and type of embankment material. Prior to excavation, 
dam safety professionals and dam owners should examine 
potential consequences of soil removal, including slope 
instability and increased hydraulic gradient. The completed 
excavation should be thoroughly inspected for adequate 
removal of the animal burrow. Voids remaining from an 
animal burrow can develop into potential internal erosion 
pathways or sinkholes.
Once excavation is complete, the resulting hole must be 
properly backfilled in a timely manner. Acceptable backfill 
material should consist of soil types (e.g., sand, clay, etc.) 
similar to that of the surrounding embankment. If desired, 
laboratory index testing such as grain size and Atterberg 
Limits of the backfill and embankment materials may be 
performed. To achieve adequate compaction of the backfill 
materials, necessary laboratory testing of backfill materials 
should include a maximum dry density determination by 
either the Standard or Modified Proctor test (ASTM D-698 
or ASTM D-1557). Backfill material should be compacted to 
a minimum of 95% of the maximum dry density and within 
+/- 2% of the optimum moisture content, as determined 
by ASTM D-698. The completed backfilled surface should 
be smooth and approximately level with the surrounding 
ground surface. Backfill should be placed and compacted in 
lifts of no more than 8 inches thick. A 2 to 4-inch gap can 
be left between the top of the completed backfill surface 
and surrounding ground surface to accommodate topsoil. 
The final step is to revegetate the disturbed area. Native 
grass species appropriate for embankment dam slopes 
should be provided (see Chapter 5.2). 
5.3.2 Preventive Measures
For a specific animal intrusion or animal related deficiency, 
appropriate preventive measures are highly dependent on 
the affected areas location on the dam. Therefore, common 
preventive measures are discussed in the context of the 
Repair Zone in the following section. The use and effectiveness 
of preventive measures should be assessed by the dam 
owner in conjunction with a dam safety professional. It may 
not be cost effective to employ these measures for treatment 
of animal intrusions alone; however, coincident benefits 
such as protection against wave erosion and plant intrusion 
may make the measure more fiscally viable.
5.4 Dam Repair Zones
As discussed in this manual, a variety of animals can damage 
an embankment dam. The damage can be surfical with 
minor impact to dam safety or performance, or the damage 
can directly threaten the integrity of the dam, potentially 
leading to failure. However, all animal impacts should be 
considered undesirable and must be repaired. Dam regulators, 
owners, and engineers should develop an understanding 
of the potential impact of an animal intrusion to 
properly evaluate its impact on the safety and performance 
of the dam (refer to chapter 2.0 for a discussion on animal 
intrusion impacts).
Prioritization of necessary repairs is critical to maintain a 
proactive approach to repair and maintenance of a dam. 
With limited available capital, many dam owners may delay 
or avoid necessary dam repairs. In addition, routine safety 
inspections by either regulatory personnel or consulting 
engineers tend to overwhelm dam owners by listing all observed 
deficiencies without a clear indication of the relative 
importance or seriousness of each deficiency. The relative 
importance and criticality of a specific deficiency depends 
on the size and nature of the observation (length, width, 
depth, area, etc.) as well as its location. 
Developing a well-defined methodology for evaluating 
observed deficiencies will permit dam safety professionals 
to accurately communicate repair prioritization to dam 
owners. Chapter 3.0 describes an inspection process that 
considers both engineering and biological perspectives for 
a dam divided into five distinct zones. These dam zones corA 
local dam safety 
professional should be 
notified prior to any 
excavation activities in 
an embankment dam.

respond to specific physical areas of the dam as illustrated 
on Figure 5-1 (ASDSO, 2001). The intent of the zones is to 
differentiate and prioritize animal intrusion damages based 
on their potential impact to dam safety or performance. 
Depending on the type of animal intrusion or deficiency 
observed, one or more zones may be considered critical 
and require near term or immediate repair. However, these 
critical zones will vary with the dam as well as the dam 
inspection. Therefore, the zones are not ordered by their 
importance; rather they are simply ordered from upstream 
to downstream. 
The following sections provide a description of each repair 
zone, potential damage from animal intrusion, and suggested 
preventive measures. These descriptions are limited 
to animal intrusions and their impact to embankment dams. 
However, other deficiencies such as plant intrusion and 
erosion can occur within each repair zone. Where appropriate, 
restoration and preventive measures should consider all 
observed deficiencies in the area.
5.4.1 Dam Repair Zone 1 
Zone 1 begins on the upstream slope at a point approximately 
4 vertical feet below the normal pool elevation and 
extends to the center of the crest. A 4-foot vertical distance 
was recommended by Marks, et.al. (ASDSO, 2001) to account 
for average fluctuations in the normal pool and typical 
underwater animal burrows. The size of Zone 1 can vary 
significantly from dam to dam because it depends upon the 
distance between the crest elevation and the normal pool 
elevation. This distance is often referred to as freeboard. 
The relative importance of Zone 1 depends upon the crest 
width and freeboard. For a dam with a wide crest and large 
freeboard, animal intrusion within Zone 1 becomes less 
critical. However, as the crest narrows and freeboard lessens, 
the importance of repairing deficiencies in Zone 1 increases 
rapidly. 
The most common animal intrusions within Zone 1 are 
muskrat burrows in which the burrow entrance is underwater 
as shown on Figure 5-2. However, other intrusions are 
possible depending upon the specific characteristics of the 
Zone 1 Upstream slope area 
Zone 2 Dam crest area
Zone 3 Upper downstream slope area
Zone 4 Lower downstream slope area
Zone 5 Downsteam toe area
Zone 6 Spillway, outlets (not shown)
crest
zone 1
zone 3
zone 4
zone 2
zone 5
H/3
4
H/2
theoretical seepage line
Figure 5-1. Remedial dam repair zones.

dam and reservoir that include geographic location of the 
dam, proximate vegetation, and prevailing weather patterns. 
Zone 1 is also susceptible to other forms of deterioration 
including wave erosion, vehicle access, surface water erosion, 
and plant intrusion.
To effectively repair animal intrusions in Zone 1, the 
reservoir pool must be lowered as far below the observed 
deficiencies as necessary to allow proper access during construction. 
If the dam owner is unable or unwilling to lower 
the reservoir pool, then the repair costs will likely increase 
dramatically to account for necessary water management 
and diversion.
Preventive measures acceptable for use along the upstream 
slope generally consist of hardened or structural features. 
The intent is to provide a physical barrier to the animal, 
thus making the area much less attractive as a burrow site. 
These features include riprap, concrete facing, revetment 
mats, gabions, large gauge wire mesh, and mechanically 
stabilized earth walls among others. With proper design and 
installation procedures, each of the methods can be successful. 
Two of the more common measures are riprap and 
concrete facing because they are relatively simple to design 
and provide protection from wave action and plant intrusion 
as well as animal intrusion. 
A typical cross section of riprap, shown on Figure 5-3 
(Ohio DNR, 1999) should consist of a layer of rock 
riprap overlying bedding material and filter material or 
a geotextile separator. Limits of the protection should 
extend at least 4 feet below the normal pool elevation 
and several feet above depending on estimated wave 
heights and average reservoir fluctuation. Rock size and 
layer thickness will vary significantly from dam to dam 
depending on the reservoir size, prevailing winds and 
other physical characteristics of the area. Therefore, material 
(e.g. riprap, bedding and filter) sizes and layer thickness, 
must be based on the anticipated wave action, ice 
thickness, and compatibility with neighboring materials. 
A number of guidelines including Technical Release No. 
69 developed by USDA, Natural Resources Conservation 
Service can assist dam safety professionals in detailed 
design for riprap slope protection.
A typical cross section of concrete facing as shown on 
Figure 5-4 (Ohio DNR, 1999) will resemble riprap in 
that the concrete will overlie a filter material. As with 
riprap, the concrete facing limits should extend at least 
zone 1
crest
wave 
erosion
vehicle/animal ruts
new burows
elevated 
seepage line
burrow entrance
old burrows
theoretical 
seepage line
Figure 5-2. Zone 1 Pentration Problems.
top of
embankment
upstream slope
rock riprap
lowest anticipated pool
gravel bedding
filter material
(sand or filter fabric)
Figure 5-3. Riprap Repair in Zone 1.
top of
embankment
upstream slope
concrete 
facing
lowest anticipated pool
filter material
(sand or filter fabric)
Figure 5-4. Concrete Facing in Zone 1.

4 feet below the normal pool elevation and several feet 
above, depending on estimated wave heights and average 
reservoir fluctuation. Concrete thickness, compressive 
strength, and reinforcing depend on wave action, freeze/
thaw cycles and other factors.
Regardless of the measure selected, proper implementation 
requires specific design recommendations from a qualified 
dam safety professional.
5.4.2 Dam Repair Zone 2
Repair Zone 2 corresponds to the limits of the dam crest 
and, therefore, overlaps with Zone 1 by one-half of the 
crest width. Overlapping a portion of Zone 1 with Zone 
2 emphasizes the importance and critical nature of both 
zones. This overlap essentially suggests that both zones be 
inspected twice during a dam safety inspection. 
As with Zone 1, the relative importance of Zone 2 depends 
upon the crest width and freeboard. For a dam with a wide 
crest and large freeboard, animal intrusion within Zone 
2 becomes less critical. However, as the crest narrows and 
freeboard lessens, the importance of repairing deficiencies 
increases rapidly. These intrusions may include terrestrial 
animal burrows such those made by groundhog, but most 
typically include ruts and other minor deformations. Zone 2 
is also susceptible to other forms of deterioration including 
vehicle access, surface water erosion, and plant intrusion.
Restoration of animal penetrations within Zone 2 should 
follow the guidelines presented in Chapter 5.3. Any excavation 
activities within a dam embankment should be coordinated 
with a dam safety professional. 
Applicable preventive measures for Zone 2 include hardening 
the crest surface with stone, concrete, or asphalt. These 
measures tend to prevent rutting from animal and vehicular 
traffic. Design of these measures depends upon the specific 
characteristics of the dam and expected loading conditions. 
5.4.3 Dam Repair Zone 3
Repair Zone 3 begins at the crest centerline and extends to a 
point on the downstream slope equivalent to one-third the 
structural height of the dam below the dam crest elevation. 
As with Zone 2, Zone 3 overlaps Zone 2 by one-half of the 
crest width to emphasize the importance of the dam crest 
area. However, the remaining portion of Zone 3 is typically 
considered the least critical dam repair zone relative to dam 
safety issues (ASDSO, 2001). The phreatic surface and zone 
of saturation within the embankment are generally below 
the depths of average animal burrows and should not interfere 
with restoration activities.
Zone 3 is the most attractive area for burrows of terrestrial 
animal, including groundhog, fox, and coyote. Similar to all 
other zones, Zone 3 is also susceptible to other forms of deterioration 
including vehicle access, surface water erosion, 
and plant intrusion.
Restoration of animal penetrations within Zone 3 should 
follow the guidelines presented in Chapter 5.3.1 and as 
shown on Figure 5-5. Any excavation activities within a 
dam embankment should be coordinated with a dam safety 
professional.
Applicable preventive measures for Zone 3 (beyond the 
limits of Zone 2) are limited. Use of hardening materials 
such as stone, riprap, or concrete is generally discouraged 
by dam safety professionals because they obscure the 
surface and prevent detailed inspection. Installation of wire 
mesh or fencing (e.g., chain link fencing) directly on the 
ground surface can effectively deter to burrowing animals. 
With properly sized openings, the wire mesh deters animal 
intruders and accommodates inspection of the area. However, 
these materials can represent an obstacle to routine 
maintenance activities such as mowing and be viewed as a 
tripping hazard. 
crest
zone 3
burrow/den - excavate, 
backfill, compact and seed 
or fill with cementious grout 
and top with dirt and seed
zone 2
H/3
Figure 5-5. Zone 2 and 3 Repair Procedures.

5.4.4 Dam Repair Zone 4
Repair Zone 4 extends from the point on the downstream 
slope that is one-third the dams structural height below the 
crest to the toe of the downstream slope. Zone 4 is one of 
the two most critical dam repair zones relative to dam safety 
issues because of the proximity of the phreatic surface and 
zone of saturation to the embankment slope. 
Animal and plant intrusions within this repair zone should 
be of major concern to dam owners and dam safety professionals. 
Any animal intrusion or dam penetration should be 
thoroughly evaluated for potential impact to dam safety and 
for the required repair. 
Restoration of animal burrows within Zone 4 should follow 
procedures presented in Chapter 5.3. However, due to the 
proximity of the phreatic surface to the animal burrow, the 
increased potential of soil migration and, therefore controlling 
water in the restored burrow must be considered. As 
shown in Figure 5-6, the use of filter materials within the 
backfilled burrow can control internal erosion, and with 
small diameter plastic piping, can manage the flow of water 
in the area. 
Similar to Zone 3, use of hardening materials such as stone, 
riprap, or concrete is generally discouraged by dam safety 
professionals because they obscure the surface and prevent 
detailed inspection. The use of wire mesh or fencing as discussed 
for Zone 3 is also applicable to Zone 4. It is essential 
that restoration and preventive measures in Zone 4 undergo 
review from a dam safety professional prior to implementation. 
5.4.5 Dam Repair Zone 5
Repair Zone 5 begins at the mid-height of the downstream 
slope and extends to a distance of one-half of the dams 
structural height horizontally beyond the downstream toe. 
Zone 5 overlaps a large portion of Zone 4 to emphasize the 
most critical portions of both zones and heighten scrutiny 
during inspection. Zone 5 is typically considered the most 
critical zone relative to dam safety issues (ASDSO, 2001) 
because the interception of the phreatic surface and downstream 
slope is typically located in this zone for homogeneous 
dams. 
zone 5
H/2
zone 4
excavate 
and backfill
burrow/den
livestock paths - fill with soil compact 
the soil, and 
revegetate the area
install
filter/drain
system
2H/3
outlet pipe
Figure 5-6. Zone 4 and 5 Repair Procedures.

Animal and plant intrusions in this zone often develop into 
serious conditions involving seepage and piping that are 
progressive and can lead to dam failure if left untreated. The 
installation of filter and drain systems to control soil migration 
and manage seepage must be considered in Zone 5. 
Similar to Zone 3 and 4, the use of wire mesh of fencing to 
deter animal intruders can also be considered in Zone 5. It 
is essential that restoration and preventive measures in Zone 
5 undergo review from a dam safety professional prior to 
implementation.
5.5 Professional Dam Safety Review
Construction or repair activities on an embankment dam 
should be reviewed by a dam safety professional prior to 
initiation. Due to the complexity of interaction among 
animal penetrations, the phreatic surface, slope stability, and 
other deficiencies, the impact of excavation activities on a 
dam can be unpredictable without thorough review by a 
qualified professional. This review should include the following 
elements at a minimum:
Evaluation of the existing dam relative to the position of 
the phreatic surface and slope stability through review of 
pre-existing inspection reports, design drawings, design 
memoranda, and owner observations.
Assessment of the impact of excavation given the phreatic 
surface position and physical characteristics of embankment 
materials (material type, density, plasticity, etc.). 
Evaluation of the restoration and preventive scheme 
proposed.
5.6 Sequenced Repair Program
Currently, dam safety inspections provide a comprehensive 
list of deficiencies observed at the time of the inspection. 
The list is generally separated into physical areas of the dam 
including the upstream slope, crest, downstream slope, 
emergency spillway, and principal spillway. However, in 
most cases, the list is not prioritized for the dam owner. 
Consequently, the dam owner is left with a long list of deficiencies 
with little guidance on immediate, near-term, and 
long-term repair items. 
Considering that most dam owners do not have the financial 
means to address all deficiencies quickly, a prioritization 
methodology should be established for dam repair. The following 
sequence is one that provides the owner, regulator, 
and dam safety engineer with a reasonable opportunity to 
effectively evaluate the condition of an earthen dam (ASDSO, 
2001). It must be noted that the following sequence 
is intended for general guidance only. Specific dam inspections 
may substantially deviate from the following sequence 
based on the needs and requirements of the individual dam. 
Year 1. (from date of last inspection) Repair animal 
penetrations that exhibit seepage, soil migration, or have 
caused slope instability in Zones 1, 4, or 5. Preventive 
measures should be installed where appropriate.
Year 2. Repair penetrations in Zones 2 and 3. If deemed 
necessary, initiate investigation, analysis, and preliminary 
design of major repair activities. 
Year 3. Complete design and begin construction of major 
repair activities.
Year 4. Complete construction of major repair activities 
and establish an operation and maintenance program 
that will manage animal intrusions and penetrations on a 
frequent and regular basis. 
If dam failure is judged imminent or if dam safety or operation 
has greatly diminished, the above sequence may not be 
applicable. In these cases, a dam safety professional must be 
advised of the situation to develop a revised schedule.
5.7 Mitigation Through Design 
5.7.1 Muskrat 
Some of these design criteria are referred to as overbuilding 
however, they are generally effective at preventing 
serious muskrat burrow damages. The design measures 
are adapted from the following references: University of 
Nebraska, 1994; University of Missouri Extension, 1999; 
ASDSO, 2001; Connecticut DEP, 1999; USDA, 1991; and 
South Carolina DNR, 2003. 
Construct the upstream slope of the dam to a 3H to 1V 
slope. Muskrats favor steep slopes so gentle slopes will be 
less attractive (Figure 5-7). 
Construct the downstream slope of the dam at a 2H to 
1V slope with a crest width of not less than 8 feet, preferably 
10 to 12 feet. 

The normal water level in the pond should be at least 3 
feet below the top of the dam and the spillway should 
be wide enough that relatively frequent storms (less than 
the 10 year storm event) will not increase the level of the 
water for any length of time. 
Design for a minimum width of 20 feet at normal water 
level.
Bind soil adequately by sodding well.
Protect the crest from muskrat by applying compacted 
dense-graded aggregate base course 4 to 6 inches thick.
Construct a 10-foot-wide shelf projecting from the face 
of the dam into the reservoir at the water line. This shelf 
will act as a muskrat barrier and also reduce wave action 
erosion.
Place stone rip-rap underlain by fine filter stone and 
geotextile (high strength, non-woven) extending from 3 
to 4 feet below the water line to 1 foot above the water 
line. Riprap size and thickness will depend upon specific 
reservoir characteristics. The riprap will prevent muskrat 
from burrowing into the dam.
Use an appropriate gabion wall system and/or enlarged 
reinforced concrete outlet works structures to act as exclusion 
systems at the toe of the downstream slope.
Embed 1 to 2-inch welded wire or chain link fencing 
into the dam upstream face. Mesh wire should extend 
from 3 to 4 feet below the water line to 1 foot above the 
water line. Lay the wire flat against the banks and fasten 
it down every few feet to secure the wire. It is likely that 
portions of the mesh below the water surface will corrode 
over time and require replacement. 
Using a narrow trenching machine, cut a vertical trench 
extending the full length of the embankment in the 
centerline of the earth fill. The trench should extend from 
3 to 4 feet below the water line to 1 foot above the water 
line. Fill the trench with concrete to create a core that 
will prevent muskrat from digging through the embankment.
sod cover
Proper Embankment Construction
1
1
gentle slope 
discourages burrowing
2
3
3
20 minimum
normal water level
less than 3
(does not rise more than 6)
23 perferred
Improper Embankment Construction
new den
flooded den
high water level
less than 20
normal water level
more than 6
steep bank encourages burrowing
any slope steeper than 3 to 1 
should be avoided
Figure 5-7. Proper dam construction can reduce muskrat damage. 

Design water control structures with a concrete apron to 
prevent muskrat burrows from damaging these facilities.
Several of the above design components indicate placement 
of the barrier 3 to 4 feet below the water line of the normal 
pool. It should be noted that if the barriers are not placed 
at least 3 feet (and preferably 4 feet) below the water line, 
then the muskrat will burrow underneath the barrier and 
penetrate the embankment; failure of the slope protection 
system and embankment damages will result.
5.7.2 Beaver 
Structures or techniques to prevent beaver damage can often 
be included in initial engineering plans or added during 
dam upgrades and repairs. The following techniques have 
been adapted from the following references: University of 
Nebraska, 1994; North Carolina State University, 1994; Wilson, 
2001; New York State DEC, 2002; Porter, 2003; Barnes, 
1991; Virginia Cooperative Extension, 2000; and FEMA, 
2000.
Gently slope the embankment (3H to 1V or flatter) to 
discourage burrowing and minimize the probability of 
beaver dam construction.
Install spillway risers so that they open upstream instead 
of toward the dam.
Place riser structures far from the face of the dam in the 
deepest water possible.
Protect large risers from clogging by installing mesh 
bars (at least 5 inches square) or hog pen panel (4 x 4 
inches). This will prevent beaver from entering the trash 
rack.
Protect intakes with a deep water cage or fence to prevent 
plugging. 
Replace the standard manhole cover on top of the riser 
tower with a beehive grate. This cast iron dome allows 
drainage during high water events, even if the lower 
orifices are blocked. 
Install a single strand, high-tensile electric wire across 
active beaver paths or around the shoreline just above the 
slope where beavers would exit the water. The electric 
wire should be staked about 3 to 4 inches above the soil 
surface and can be powered by a direct 110-volt charger 
or a rechargeable battery pack. After repeated shocks, the 
beaver will usually relocate to another area. Public safety 
issues and concerns must be addressed when considering 
this option.
Install fencing around outlets to prevent plugging. Secure 
the fence to the reservoir bottom with metal posts. Fencing 
should be about 5 feet high, made of heavy-gauge 
woven wire with no larger than 6-inch openings. It 
should extend 10 to 20 feet out from the outlet. Before 
installing the fence, debris should be removed from the 
outlet (Figure 5-8). 
The South Carolina Dam 
Safety Office indicates 
that using siphons and 
other non-trickle 
principal spillway systems 
may be effective against 
beaver, but their success 
is not documented. 
Figure 5-8. Install fencing around culverts and outlets 
to prevent beavers from blocking flow.

Avoid These Water Level Control Devices at Dams
Because these devices require partial obstruction of spillways or outlet pipes, their use at a dam 
should be strictly prohibited. Obstruction of spillways or outlets can cause reservoir levels to rise 
resulting in overtopping of the dam, erosion of earthen spillways and other detrimental impacts.
Elbow and standpipe are 
optional. Needed only to manage 
water-level if maintaining 
pond is an objective
1 re-bar
6 long
beaver dam
8 diameter
40 PVC pipe
intake device
20
pond side
T-joint tilted with a drain 
plug may replace elbow
Figure 5-9. The Clemson Beaver Pond Leveler is a passive but effective means to control water levels through a beaver dam.
beaver dam
flow
15-20 cm green logs
lashing (wire or rope)
Figure 5-11. PVC Beaver Drain Pipe
beaver dam
roofing tin
green sticks separate 
logs to allow water flow
Figure 5-10. A 3-log drain manipulates 
water levels through a beaver dam.
Figure 5-12. Massachusetts Beaver Pond Leveler

Install a layer of riprap on the upstream side of the 
embankment to prevent burrowing. The riprap should 
extend from 4 feet below to 2 feet above normal water 
levels. 
5.7.3 Mountain Beaver
It may be possible to exclude mountain beavers from a dam 
by installing a rabbit-proof fence (chain-link, chicken wire, 
etc.) around the embankment. The bottom of the fence 
must be tight against the ground or, for better protection, 
buried about 1 to 2 feet (Pehling, 2003).
5.7.4 Groundhog 
It is possible to discourage groundhogs from burrowing 
in an earthen dam by armoring the structure with rock or 
other hard materials (Michigan State University Extension, 
1998). 
It is also possible to exclude groundhogs from an earthen 
dam by installing a fence around the area of concern. 
Groundhogs are good climbers so the fence should be at 
least 3 feet high and made of heavy poultry wire or 2-inch 
mesh woven wire. To prevent burrowing underneath the 
fence, it should be buried 10 to 12 inches into the ground 
or bent into an L-shaped angle (pointing away from the 
excluded area) buried 1 to 2 inches into the ground. For 
added protection, an electric wire placed 4 to 5 inches off 
the ground and 4 to 5 inches away from the fence may be 
installed (University of Nebraska, 1994). Public safety issues 
and concerns must be addressed when considering this option.
5.7.5 Pocket Gopher 
Fencing is of limited use for protecting earthen dams from 
pocket gophers; the method is expensive and generally not 
practical because pocket gophers burrow so deeply underground. 
However, if fencing is used to exclude pocket gophers 
from the dam, it should be buried at least 20 inches 
into the ground and extend 6 to 8 inches above the ground 
(USDA, 1991).
5.7.6 North American Badger
Fencing may be used to exclude badgers from an earthen 
dam. The fence should be made of mesh wire and it should 
be buried to a depth of 12 to 18 inches to prevent badgers 
from burrowing underneath. This control method may not 
be practical for protecting large areas because installation 
can be costly and time consuming (University of Nebraska, 
1994).
5.7.7 Nutria
There are several design measures that can be implemented 
to reduce nutria damage. 
Install fencing around the dam embankment. Fences 
should be about 4 feet high with at least 6 inches of 
fencing buried underground.
Armor the embankment with riprap to discourage burrowing.
Contour embankment slopes to an angle less than 45 to 
discourage burrowing. 
5.7.8 Prairie Dog 
The use of fencing to exclude prairie dogs from a dam is 
a potential management tool, although it is rarely practical 
because prairie dogs burrow so deeply underground. If 
fencing is chosen as a control method, a tight-mesh, heavy-
gauge, galvanized wire fence should be used, with 2 feet 
buried in the ground and 3 feet remaining above ground 
(University of Nebraska, 1994).
Visual barriers may also discourage prairie dogs from inhabiting 
an area. Prairie dogs prefer areas of low vegetation 
to provide a clear view of their surroundings and to improve 
their ability to detect predators. Objects such as fences 
or hay bales that are strategically placed to block prairie dog 
views may reduce suitability of the habitat. High construction 
and maintenance costs generally reduce the viability of 
this option (University of Nebraska, 1994).
5.7.9 Ground Squirrel
Fencing is not usually a practical method of control for 
ground squirrels because they are able to climb over or burrow 
under most exclusion structures. Routine weed control 
and vegetative management may limit some damage, but 
the effectiveness of this method is usually limited as well 
(USDA, 1991).

5.7.10 Armadillo 
It is possible to exclude armadillos from an earthen dam by 
installing a fence or barrier around areas of concern. Armadillos 
can both climb and burrow so the fence should be 
slanted outward at a 40 angle with a portion buried underground 
sufficient to maintain the fences pitch. 
5.7.11 Livestock
Fencing is a highly effective method of protecting earthen 
dams from domestic livestock and is moderately effective 
with free-ranging or wild grazing animals (USDA, 1991). 
Heavy wire fences, wooden post fences, or electric fences 
may be used (University of Nebraska, 1994).
5.7.12 Crayfish
No design techniques are effective at discouraging crayfish 
inhabitation.
5.7.13 Coyote
Fencing can be used to 
exclude coyotes from a 
dam. Both wire and electric 
fences will work, and 
a combination of the two 
will probably be most effective. 
Net wire fences 
should be about 5 feet high 
with barbed wire at ground 
level or a buried wire 
apron. Horizontal spacing 
of the mesh should be less than 6 inches and vertical 
spacing should be less than 4 inches. Electric fences usually 
consist of strands of smooth, high-tensile wire stretched to 
a tension of 200 to 300 pounds. Studies have shown that 13 
strands of charged wire effectively protected pastures from 
coyote predation (University of Nebraska, 1994). 
5.7.14 Mole and Vole
Fencing may be useful for mole control in small dams. The 
fence should be made of rolled sheet metal or hardware 
cloth, with at least 12 inches buried underground and 12 
inches extending aboveground. It is also possible to discourage 
moles from burrowing in an earthen dam by packing 
the soil with a roller to reduce soil moisture. This will 
reduce the habitats attractiveness to moles (University of 
Nebraska, 1994).
Fencing of large-scale areas is generally not a cost-effective 
method of vole control (University of Nebraska, 1994). 
5.7.15 River Otter
Fencing may be used to exclude river otters from an earthen 
dam. The fence should be constructed of mesh wire (3 x 3-
inch or smaller) or hog-wire. Dam owners should regularly 
check the fence to ensure that it has not been spread apart 
1/4 x 4 1/2 carriage bolt
galvanized woven wire
72
galvanized
fencing
3 treated pole
7 long
60
56
Studies have shown that 
13 strands of charged wire 
effectively protected pastures 
from coyote predation.
28
23 apron
(old fencing)
Figure 5-13. Installation of a net fence with wire overhang 
and buried apron is an effective coyote exclusion method.

or raised to allow otters to enter (University of Nebraska, 
1994). 
5.7.16 Gopher Tortoise 
Fencing the dam embankment may be practical for protecting 
small areas from gopher tortoise damage (University of 
Nebraska, 1994). 
5.7.17 Red and Gray Fox
Fencing can be used to exclude foxes from an area of concern. 
Both wire and electric fences will work, and a combination 
of the two will probably be most effective. Net wire 
fences should be constructed so that all openings are less 
than 3 inches. The bottom should be buried 1 to 2 feet into 
the ground with at least 1 foot above ground. For an effective 
electric fence, there should be at least three charged 
wires spaced 6 inches, 12 inches, and 18 inches above the 
ground (University of Nebraska, 1994).
5.7.18 Canada Goose
It is often possible to discourage Canada goose inhabitation 
by installing fencing, rock barriers, or vegetative barriers 
around shorelines. Fencing can be constructed out of a variety 
of materials including mylar tape, metal mesh, plastic or 
synthetic mesh, electric wires, or wood. Fences should be at 
least 25 inches tall and should not contain openings greater 
than 3 inches (Virginia Cooperative Extension, 2001b).
5.7.19 American Alligator 
Fencing may be used to exclude alligators from earthen 
dams. The fence should be at least 5 feet high with the top 
edge angled outward (University of Nebraska, 1994).
5.7.20 Ants
There are no exclusion methods or design measures effective 
against ant inhabitation
5.8 Monitoring 
Once a dam specialist identifies the burrow and the species 
creating or occupying it, the burrow(s) would be filled and 
a prevention technique implemented as appropriate. The 
next step to maintaining safe dam operation is to monitor 
the effectiveness of the remedial action (e.g., has the rip-
rap effectively deterred muskrat activity?). In many cases, 
regular dam inspections and swift burrow mitigation (and 
preventive actions when needed) will adequately preserve 
safe dam operations. However, it is possible for a dam to 
become overrun by nuisance animals, or for several species 
to cumulatively compromise safe dam operations. In these 
cases, repair actions are only partial solutions. Monitoring 
can help the dam owner determine whether additional 
mitigation is necessary. 
In general, it is recommended that the dam owner inspect 
the dam once every 3 months after first finding and repairing 
animal damage. The frequency is aimed at confirming 
the animal has not returned to the dam once the burrow is 
removed. Once burrows are identified, the owner should 
consider implementing a preventive action if a burrow 
occurred in one of the critical dam zones (see Chapter 5.4 
for a discussion on animal burrows in critical dam zones). 
Understanding the potential fiscal limitations of dam owners, 
the most realistic approach is to use the fewest actions 
needed to ensure dam safety. As a guideline, if the dam 
owner finds new animal burrows in the dam on two consecutive 
inspections following repair and preventive actions, 
then implementing a wildlife control strategy is probably 
necessary to maintain safe dam operations (see Chapter 6.0 
for a discussion on wildlife control).

71
Chapter 6. Mitigating Damaging Wildlife 
6.0 Mitigating Damaging Wildlife 
This chapter of the manual details methods for managing 
wildlife populations. General wildlife management information 
is provided first, followed by specific management 
information for the 23 species considered in this manual. 
The application of this data in the dam environment can be 
beneficial and at times necessary to protect human populations 
from the disastrous effects of dam failure. However, 
applied indiscriminately, these methods can adversely affect 
the dam environment, protected wildlife species, and 
even human populations. For this reason, nuisance wildlife 
management practices should be implemented only with 
coordination and input from state and federal wildlife 
agencies and the county agent responsible for toxicant and 
fumigant registration and application (Appendix A contains 
state wildlife contacts). 
6.1 Compliance with State and Federal Regulations
6.1.1 Conformity to Federal Regulations
As the vast majority of surveyed states indicate, the dam 
owner is responsible for the identification and mitigation 
of nuisance wildlife at dams. Although the dam owner is 
empowered by the state dam safety official to manage a 
dam toward safe operation, the dam owner must abide by 
applicable federal and state regulations when implementing 
nuisance wildlife management measures. The Endangered 
Species Act of 1973 (ESA), the Migratory Bird Treaty Act 
of 1918 (MBTA), and the Federal Insecticide, Fungicide, 
and Rodenticide Act of 1996 (FIFRA) are three federal laws 
that must be complied with during application of wildlife 
management methods. The ESA protects species of plants 
and animals that are in danger of extinction. Under the ESA, 
it is illegal for anyone to take a species listed as threatened 
or endangered. 
The ESA defines take as, to harass, harm, pursue, hunt, 
shoot, wound, kill, trap, capture, or collect or attempt to engage 
in any such conduct (USFWS, 2002a). The MBTA was 
established to conserve migratory bird species in the United 
States and prohibits the hunting, trapping, possession, and 
transfer of listed species except under the terms of a valid 
permit or during authorized hunting seasons (USFWS, 
2002b). 
Species that are discussed in this manual and protected under 
the ESA and the MBTA include: 

Dam Owners Manual to Animal Intrusion of Earthen Dams
72
Gopher Tortoise (Gopherus polyphemus). This species is listed 
as Threatened under the ESA throughout its range of 
Mississippi, Louisiana, and portions of Alabama, and is 
protected by state laws in Alabama, Georgia, Florida, and 
South Carolina.
The American Alligator (Alligator mississippiensis). This 
species is listed as Threatened by Similarity of Appearance 
to a Threatened Taxon under the ESA throughout 
its range of Alabama, Arkansas, Florida, Georgia, Louisiana, 
Mississippi, North Carolina, Oklahoma, South 
Carolina, and Texas. This designation means that the 
American Alligator is protected under the ESA because 
of its similarity in appearance to the American Crocodile 
(Crocodylus acutus). The American Crocodile is classified as 
Endangered under the ESA. The USFWS determined that 
in order to adequately protect the American Crocodile, 
which is often mistaken for the American Alligator, the 
USFWS must also protect the American Alligator. Therefore, 
though populations of the American Alligator are 
healthy throughout its range, it is afforded full protection 
under the ESA.
Point Arena Mountain Beaver (Aplodontia rufa nigra). This 
subspecies is listed as Endangered throughout its range of 
California. 
Utah Prairie Dog (Cynomys parvidens). This species is listed 
as Threatened throughout its range of Utah. 
Northern Idaho Ground Squirrel (Spermophilus brunneus brunneus). 
This subspecies is listed as Threatened throughout 
its range of Idaho. 
Canada Goose (Branta canadensis). This species is protected 
under the MBTA throughout its range of the United 
States.
If dam owners suspect that one of these species is damaging 
the earthen dam, then the dam owner must contact the 
USFWS and the state wildlife agency to discuss management 
options. While it is often possible to relocate these animals 
with permits and guidance from the USFWS and the state 
wildlife agency, the permitting agency must be consulted 
prior to taking any action. It should be noted that the list of 
protected species can and does change, and regular contact 
with an agency is required to ensure that no protected species 
are adversely affected. 
While difficult to predict each potential circumstance, there 
may be cases when management of a species not protected 
by the ESA or MBTA may result in the illegal taking of a 
protected species that is associated with the targeted nuisance 
species. For example, the endangered black-footed 
ferret (Mustela nigripes) depends on the burrows of prairie 
dog colonies for survival. Mitigation against the prairie dog 
may impact the ferret. Similarly, the eastern indigo snake 
(Drymarchon corais couperi) is afforded refuge by gopher tortoise 
burrows; thus, managing a dam for the tortoise could 
have secondary effects on the indigo snake. As some species 
show interdependencies on others, it is recommended 
that coordination with state and federal wildlife agencies be 
conducted before management of any species, protected or 
not, occurs. 
Last, FIFRA divides pesticides, including toxicants and 
fumigants, into two categories: General Use Pesticides and 
Restricted Use Pesticides. General Use Pesticides will not 
ordinarily cause unreasonable adverse effects on the user or 
the environment when used as directed and as such, they 
are commercially available to the public. Restricted Use 
Pesticides, however, could cause adverse effects to the user 
or the environment even when used correctly. Restricted 
Use Pesticides can only be purchased by a certified pesticide 
applicator and applied by or under the supervision of 
a certified pesticide applicator, in accordance with FIFRA. 
Appropriate disposal of pesticide containers is also required.
6.1.2 Conformity to State Regulations
Certain wildlife species are protected by the state even 
though they are not listed as Federally threatened or endangered; 
each state determines its own regulations with 
regard to protected species. Furthermore, hunting and 
trapping regulations in regard to furbearer, game, and non-
game species vary from state to state. For these reasons, it 
is recommended that a dam owner contact the appropriate 
state wildlife agency for information about mitigation of 
wildlife species, and hunting and trapping seasons, licenses, 
and permits before attempting to remove an animal from 
the dam environment or before any wildlife management 
actions are taken. As with federal laws, the list of protected 
species can change from year to year and regular contact 
with an agency is required to ensure that no protected species 
are adversely affected. 
Finally, legal use of specific toxicants and fumigants varies 
from state to state; one state may allow a toxicant that is 
banned in another. As such, it is recommended that coor

dination with the state wildlife agency or county agent be 
conducted to determine which substances are allowed for 
use in each state. If toxicants or fumigants are selected as the 
management option, it is recommended that:
The substance is used according to direction and precaution;
The substance is stored securely in original containers 
away from children, animals, food, and feed;
The substance is applied so as not to endanger humans, 
livestock, crops, beneficial wildlife, or water supply, or 
leave illegal residues; 
Excess substance is not dumped, and associated equipment 
is not cleaned near ponds, streams, or wells; and 
Substance containers are disposed of properly at an appropriate 
landfill facility.
6.2 Muskrat Management Methods 
6.2.1 Muskrat Control Through Habitat Modification 
(South Carolina DNR, 2003; University 
of Nebraska, 1994; Michigan State 
University Extension, 1998; USDA, 1991)
Mow regularly to remove food supply. Specifically, remove 
cattails, arrowhead, and other plants that grow on the fringe 
of the reservoir. 
Implement an aquatic vegetation control program to 
reduce aquatic vegetation preferred by the muskrat for food 
and cover. Muskrat populations can be effectively managed 
by eliminating food sources. The vegetation control program 
can be achieved through several management approaches: 
Herbicides are widely used to control aquatic vegetation. 
Out of the 200 herbicides registered with the U.S. 
Environmental Protection Agency, only 8 are available 
for aquatic uses, and only 6 of those 8 are widely used 
(2 herbicides are limited to use in 17 western States 
irrigation systems under Bureau of Reclamation control). 
Coordination with the state agency responsible for 
aquatic plant management is required to ensure that the 
appropriate herbicide is selected based on management 
goals and that herbicides are lawfully applied.
Hand Removal of preferred muskrat vegetation can be 
implemented; however this method is labor-intensive 
and needs to be repeated frequently to keep vegetation, 
especially perennial plants, under adequate control. Hand 
removal can be combined with herbicide application.
Mechanical Removal utilizes small and large weed harvesters 
to remove vegetation around the shoreline. This method 
achieves immediate vegetation control in small dams 
and does not carry water-use restrictions after treatment, 
unlike herbicide application. However, weed harvesters 
cannot be used in all environmentsfor example, 
obstructions may preclude harvester use. This method 
is usually higher in cost, slower, and less efficient than 
other available methods.
Manipulate water levels in the reservoir to create an 
undesirable habitat for the muskrat. A 2-foot drawdown in 
the reservoir during the winter months can be an effective 
muskrat management tool. Drawdown allows a dam specialist 
to identify and repair muskrat holes in the upstream 
slope (refer to Chapter 5.3.1 for burrow repair discussion), 
and may drive away resident muskrats, which need adequate 
water levels. It is recommended that muskrats be trapped 
and removed during the drawdown; however, trapping and 
relocation should be coordinated with the appropriate state 
agency, since a permit may be required. 
A secondary benefit of water level manipulation is the potential 
drying and freezing of aquatic plantsthe muskrats 
primary food supplyas the plants are exposed to air. It 
should be noted that some aquatic plants are tolerant of 
drawdown and may actually increase after a drawdown; 
therefore, drawdown as a primary aquatic plant management 
method is not recommended.
6.2.2 Muskrat Control Through Trapping 
(University of Nebraska, 1994; 
South Carolina DNR, 2003)
The most effective types of traps for muskrat include the 
Conibear traps No. 110 and 120, and leghold traps like the 
long spring No. 1, 1 or 2, and similar coil spring traps 
(Figure 6-1 and 6-2). The Conibear traps are preferred 
because they are effective in shallow and deep water settings, 
easy to set up, and kill the muskrat quickly, preventing 
escapes. The Conibear and leghold traps are most effective 
when set close to the den entrance in the runs or trails 
carved into the reservoir bottom by the muskrats hind feet. 
Runs can be easily seen in clear water, or can be felt with 

Field testing in a 100-acre 
rice field (36 Conibear 
110 traps were set) and a 
60-acre minnow pond (24 
1 leghold traps were set) 
yielded an effective muskrat 
removal rate of 93.3% and 
87.5% for the Conibear 
and leghold traps, 
respectively. All tripped 
traps were 100% effective. 
Leghold Trap
Conibear - Type Body 
Gripping Traps
Figure 6-1. To capture muskrats, leghold traps should be set along runways, den openings, 
or natural resting areas. Conibear No. 110 traps should be set in the water.
trap set in trail 
through rushes
den set
trail set
feed bed set
rock set
Figure 6-2. Muskrat traps can be effectively set in four locations. Bait traps with carrots, potatoes, sweet potatoes, or apples.

the hands or feet in murky or deep water. Poles can be used 
to anchor the trap in front of the den (Figure 6-3). 
Where legal, homemade stovepipe traps can also be effective. 
This type of trap is cheap, simple, and easy to make, but 
it requires more time and effort to set. A trap can be constructed 
by forming sheet metal into a 6 x 6-inch rectangular 
box, 30 to 36 inches long with heavy-gauge hardware 
cloth or welded wire doors. The doors should be hinged at 
the top to allow entry from either end, but no escape out of 
the box. The trap should be set right up against the primary 
den entrance to be most effective.
6.2.3 Muskrat Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are registered for muskrat control.
6.2.4 Muskrat Control Through Toxicants 
(University of Nebraska, 1994)
Zinc phosphide (63% concentration) is the only toxicant 
Federally registered for muskrat control. To make a bait, 
vegetable oil is applied to cubes of apples, sweet potatoes, 
or carrots; the zinc phosphide is sprinkled on top; and the 
ingredients are mixed together thoroughly. The bait is then 
placed at the burrow entrance, on floating platforms (Figure 
6-4), or on feeding houses. Zinc phosphide is a Restricted 
Use Pesticide and may therefore, only be purchased and 
applied by a certified pesticide applicator. Zinc phosphide 
should always be used as directed. Dam owners should contact 
the appropriate state wildlife agency regarding legality 
of toxicant use in their state. 
Anticoagulants such as pivalyl, warfarin, diphacinone, and 
chlorophacinone have also been registered for muskrat 
control in some states. These anticoagulants come in the 
form of a lollipop made of grain, pesticide, and melted 
paraffin. As with zinc phosphide, anticoagulant baits can 
bamboo pole
water line
muskrat den 
entrance
Figure 6-3. Pole set at muskrat den.

be placed at burrow entrances, on floating platforms, or on 
feeding houses. Dam owners should contact their state wildlife 
agency to see which, if any, anticoagulants are registered 
in their state. 
6.2.5 Muskrat Control Though Frightening 
(University of Nebraska, 1994)
Frightening is not an effective method of muskrat control.
6.2.6 Muskrat Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for muskrat control.
6.2.7 Muskrat Control Through Shooting 
(University of Nebraska, 1994)
Shooting can be an effective method of eliminating a few 
individual muskrats. Hunting efforts are most successful 
at dawn and dusk. Dam owners should contact their state 
wildlife agency for information on hunting regulations and 
restrictions. 
6.3 Beaver Management Methods
6.3.1 Beaver Control Through Habitat 
Modification (University of Nebraska, 1994; 
University of New Hampshire Cooperative 
Extension, 1997; USDA, 1994)
Clearing trees and shrubs near the reservoir will reduce potential 
food sources and habitat and may discourage beaver 
inhabitation of a dam. Daily destruction of existing dams 
and removal of dam construction material will sometimes 
cause existing beaver colonies or individuals to relocate. 
6.3.2 Beaver Control Through Trapping 
(University of Nebraska, 1994)
In most situations, trapping is the most effective and economical 
method of controlling beaver damage. Various types 
of traps can be used, but the Conibear No. 330 is generally 
considered the most effective (refer to Figure 6-1 for trap 
types). It is designed primarily for water use, and works 
equally well in deep and shallow areas. Conibear-type 
traps should be set on dry, solid ground to prevent injury 
to the person setting the trap. Once the trap is set, it can be 
pulley system
tie-down
concrete block
Figure 6-4. Toxicant bait platforms.
Researchers in Louisiana 
found that deep water 
beaver dams could be 
removed more effectively 
than shallow water 
beaver dams, and that 
it was more effective to 
remove beaver dams in 
later summer rather than 
early or midsummer. 

moved to the water and anchored down with stakes. Traps 
can be effectively set in front of lodge entrances, in front of 
a hole in the beaver dam, or on underwater beaver trails. 
Leghold traps (No. 3 double spring or larger) are also commonly 
used to capture beavers. This type of trap should be 
used with a drowning set attachment so that the captured 
beaver cannot escape. Proper placement is very important 
with leghold traps. They should be set just at the waters 
edge, slightly underwater, with the pan, jaws, and springs 
covered lightly with leaves or debris. There must be a cavity 
under the pan for the trap to properly trigger. Leghold traps 
are most effective when they are set slightly off-center on 
an underwater beaver trail. 
Snares can also be used to capture beavers. The equipment 
costs less than trapping equipment, and snares can be set 
so that the beaver is caught alive and can then be relocated. 
Snares are frequently set under logs, near bank dens, and 
next to castor mounds. 
Dam owners should contact their state wildlife agency 
regarding trapping regulations and seasons and regulations 
regarding live trapping and relocation. 
6.3.3 Beaver Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are registered for beaver control.
6.3.4 Beaver Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are registered for beaver control. 
6.3.5 Beaver Control Through Frightening 
(University of Nebraska, 1994)
Frightening is not an effective method of beaver control.
6.3.6 Beaver Control Through Repellents 
(University of Nebraska, 1994)
No repellents are Federally registered for beaver control. 
6.3.7 Beaver Control Through Shooting
Shooting may also be used to remove small populations of 
beavers. If permitted by law, night shooting is most effective; 
however, hunting in the early evening and early morning 
hours can also be effective. Dam owners should contact 
their state wildlife agency for information on hunting 
regulations and restrictions. 
6.4 Mountain Beaver Management Methods
The Point Arena mountain beaver is a Federally listed endangered 
subspecies and therefore subject to the provisions of 
the Endangered Species Act. This subspecies is found only in 
California. Dam owners in California who suspect that they 
have a mountain beaver problem should contact the USFWS 
and the California Department of Fish and Game for definitive 
species identification and management guidance.
6.4.1 Mountain Beaver Control Through Habitat 
Modification (University of Nebraska, 1994)
Removal of plants such as sword fern, bracken fern, or salal 
may reduce the attractiveness of a site to mountain beavers. 
6.4.2 Mountain Beaver Control Through Trapping 
(University of Nebraska, 1994)
Trapping is an effective method of controlling mountain 
beavers. The Conibear No. 110 is most commonly used 
(refer to Figure 6-1). The trap should be set in the main 
burrow entrance, anchored with three stakes. Trapping is 
most effective in warm months when mountain beaver are 
most active. 
Live trapping is also possible using double-door wire mesh 
traps such as the Tomahawk. This method of trapping is 
recommended in areas where pets or livestock could accidentally 
be captured. The trap should be placed in the main 
burrow entrance with vegetation arranged along the inside 
and outside of the trap. The trap should be wrapped with 
black plastic and covered with soil to protect the captured 
mountain beavers from the weather. Captured animals 
should be placed in a dry burlap sack and euthanized or 
relocated to an appropriate location. 
Dam owners should contact their state wildlife agency regarding 
trapping regulations and seasons and requirements 
for euthanasia or relocation. 
6.4.3 Mountain Beaver Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are registered for mountain beaver control.

6.4.4 Mountain Beaver Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are Federally registered for mountain beaver 
control. Some toxicants may be registered in certain states, 
though, so dam owners should contact their state wildlife 
agency regarding this option.
6.4.5 Mountain Beaver Control Through Frightening 
(University of Nebraska, 1994)
Frightening is not an effective method of controlling mountain 
beaver.
6.4.6 Mountain Beaver Control Through Repellents 
(University of Nebraska, 1994)
Repellents are effective for controlling mountain beaver that 
are causing damage to trees/seedlings, but this method is 
not practical for preventing damage to earthen dams.
6.4.7 Mountain Beaver Control Through Shooting 
(University of Nebraska, 1994)
Mountain beavers are nocturnal animals that spend most of 
their time below ground; therefore, shooting is not a practical 
method of mountain beaver control.
6.5 Groundhog Management Methods
6.5.1 Groundhog Control Through Habitat 
Modification (Michigan State 
University Extension, 1998)
It is possible to discourage groundhog inhabitation by 
mowing vegetated areas of the earthen dam to remove 
cover.
6.5.2 Groundhog Control Through Trapping (USDA, 
1991; University of Nebraska, 1994)
Trapping is an effective method of controlling limited 
populations of groundhogs. Steel leghold traps (No. 2) 
(refer to Figure 6-1) and live traps are both commonly 
used. Traps should be set at the main burrow entrance or on 
major travel lanes. Live traps, which can be purchased commercially 
or home-built, require bait such as apple slices, 
carrots, or lettuce. Groundhogs captured in live traps should 
be euthanized or relocated to a suitable habitat where they 
will not cause further damage. 
Conibear traps (110, 160, or 220) may also be used in 
certain situations (refer to Figure 6-1). They should not be 
used where they could capture domestic animals or livestock. 
Conibear traps should be set in major travelways or 
at the main entrance of a burrow system. No bait is necessary. 
Dam owners should consult with their state wildlife agency 
regarding specific trapping regulations and requirements for 
euthanasia or relocation.
6.5.3 Groundhog Control Through Fumigants 
(University of Nebraska, 1994)
Use of the commercial gas cartridge is the most common 
method of groundhog control. The cartridge is ignited and 
placed in the burrow with all other entrances sealed. As the 
cartridge burns, it produces carbon monoxide and other 
gases lethal to the groundhog. Gas cartridges are General 
Use Pesticides that can usually be purchased at local farm 
supply stores or pesticide dealers. They should be used with 
caution and in accordance with the directions on the label. 
Aluminum phosphide is a Restricted Use Pesticide that 
may be applied by a certified pesticide applicator to control 
groundhogs. The legal application of aluminum phosphide 
may vary from state to state, so dam owners should consult 
with their state wildlife agency or state pesticide registration 
board before implementing this control method. Aluminum 
phosphide comes in tablet form. Two to four tablets should 
be inserted into the main burrow and then all burrow entrances 
must be tightly sealed. Aluminum phosphide should 
always be used as directed on the label. 
Dam owners should consult with their state wildlife agency 
for information on state and local regulations regarding the 
use of fumigants to control groundhogs.
6.5.4 Groundhog Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are registered for groundhog control. 
6.5.5 Groundhog Control Though Frightening 
(University of Nebraska, 1994)
Scarecrows or other effigies may be installed on or around 
the earthen dam to frighten groundhogs. This method of 
control works best if the scarecrows are moved regularly 
and if there is a high level of human activity around the 
dam.

6.5.6 Groundhog Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for groundhog control. 
6.5.7 Groundhog Control Through Shooting 
(University of Nebraska, 1994)
Shooting is most effective if used as a follow-up to other 
control measures. Groundhogs are considered game animals 
in most states; therefore a hunting license may be required. 
Dam owners should consult with their state wildlife agency 
regarding specific hunting regulations and requirements. 
6.6 Pocket Gopher Management Methods
6.6.1 Pocket Gopher Control Through Habitat 
Modification (Colorado State University 
Cooperative Extension, 2003)
Removal of forbs, through either chemical or mechanical 
treatment, may control some pocket gopher damage. This 
technique is generally effective only for individuals of the 
genera Thomomys, because they prefer the underground storage 
structure of forbs. Other species easily survive on grass 
and therefore will not likely be deterred by this technique.
6.6.2 Pocket Gopher Control Through Trapping 
(USDA, 1994; University of Nebraska, 1994)
Trapping can be extremely effective for pocket gopher 
control in small areas or when used in conjunction with 
toxicants. There are many types of traps available for pocket 
gopher control. The Macabee gopher trap is the most popular, 
but other traps are also commonly used, including the 
Victor Gopher Getter, the Death-Klutch 1 gopher and mole 
trap, and the Guardian gopher trap (Figures 6-5 through 
6-8). Traps may be set in either the main tunnel or in one of 
the lateral tunnels (Figure 6-9). Trapping is most effective 
in the spring and fall, when gophers are pushing up new 
mounds, although it can be done year-round. Dam owners 
should consult with their state wildlife agency regarding 
specific trapping regulations.
Figure 6-5. Macabee gopher trap.
Figure 6-6. Victor Gopher Getter.
thumb latch
jaws
flat metal
piece
body 
shaft
trip lever
Figure 6-7. Death-Klutch 1 gopher and mole trap.
spring
bar
trigger
wire
hold-down
bar
Figure 6-8. Guardian (California box-type) gopher trap.

6.6.3 Pocket Gopher Control Through Fumigants 
(University of Nebraska, 1994)
Aluminum phosphide and gas cartridges are both Federally 
registered for pocket gopher control. They are generally not 
effective though because the gas moves slowly through the 
tunnel system, allowing the fumigant to diffuse through 
the soil and escape to the surface. Carbon monoxide from 
automobile exhaust has proven more effective because of its 
greater volume and pressure. To implement this method of 
control, connect a hose or pipe to the engine exhaust and 
place it in a burrow opening near a fresh soil mound. Tightly 
pack soil around the hose or pipe and allow the engine 
to run for at least 3 minutes. This method is generally 90% 
effective and requires no federal registration. Dam owners 
should consult with their state wildlife agency for information 
on state and local regulations regarding fumigants.
6.6.4 Pocket Gopher Control Through Toxicants 
(University of Nebraska, 1994)
Several rodenticides are currently registered for pocket 
gopher control. Strychnine alkaloid (0.3 to 0.5% active 
ingredient) on grain baits is the most widely used. It is 
classified as a Restricted Use Pesticide and can only be sold 
to and used by a certified pesticide applicator. Applying 1 
to 2 pounds per acre of 0.3 to 0.5% strychnine alkaloid 
grain with a burrow builder should provide an 85% to 95% 
reduction in the pocket gopher population. Zinc phosphide 
(2%) is also a registered toxicant for pocket gopher control, 
though it is less effective than strychnine. Additionally, 
mound
lateral
hole dug
with shovel
main tunnel
Figure 6-9. Traps can be staked in lateral or main pocket gopher tunnels.
Carbon monoxide is 
generally 90% effective 
for pocket gopher 
control and requires no 
Federal registration. 

two anticoagulants (chlorophacinine and diphacinone) are 
registered for pocket gopher control. Bait can be placed in 
a pocket gopher burrow system by hand, using a special 
hand-operated bait dispenser probe or with a mechanical 
burrow builder (Figures 6-10 and 6-11). 
The first step to hand baiting with the bait dispenser is finding 
the main burrow, which is generally located 12 to 18 
inches away from a plugged mound. Once the main burrow 
is located, place the probe over the burrow and push down 
until there is decreased resistance on the probe. Then push 
the button on the bait dispenser to release a metered dose 
of bait. For best results, each burrow should be baited in 
two or three locations. 
The burrow builder is a tractor-drawn device that mechanically 
delivers bait underground. As the burrow builder 
moves along, it makes an artificial burrow, dispenses the bait 
into the newly formed burrow, and then closes up the hole. 
Artificial burrows should be constructed at depths similar to 
those constructed by pocket gophers in the area. 
All toxicant products should be used as directed on the 
label. Dam owners should consult with their state wildlife 
agency regarding legality of toxicant use in their state before 
implementing any control measures. 
6.6.5 Pocket Gopher Control Through Frightening
No frightening methods are effective for pocket gopher 
control. 
6.6.6 Pocket Gopher Control Through 
Repellents (University of Nebraska, 
1994; Witmer et al., 1995)
Repellents may be used to discourage pocket gopher inhabitation, 
although the effectiveness of this method is still 
in question. Initial testing has shown that some predator 
odors, such as coyote or bobcat urine, may effectively repel 
Properly applied, strychnine 
alkaloid can provide an 
85% to 95% reduction in 
a pocket gopher population. 
Figure 6-10. Effective baiting with a bait dispenser requires 
accurately finding the pocket gopher burrow. Use the probe to 
detect the main burrow, which is usually on the plug-side of the 
mound, 8-18 inches away from the plug (USDA, 1994). 
Figure 6-11. A burrow builder mechanically dispenses bait into 
constructed burrows. Adequate soil moisture is needed to form 
effective burrows. Adequate soil can be compressed in the hand 
and rolled gently without crumbling (USDA, 1994).

pocket gophers. Additionally, the mole plant (Euphoriba lathyrus), 
also known as the caper spurge or gopher purge, and 
the castor-oil plant (Ricinus lathyrus) have both been promoted 
as gopher repellents, although there is no scientific evidence 
to support this claim. Use of these plants is not recommended 
because they are poisonious to humans and pets, 
and can grow thickly, obscuring the dam.
6.6.7 Pocket Gopher Control Through Shooting 
(University of Nebraska, 1994)
Shooting pocket gophers is usually not a practical option 
because they spend most of their time below ground.
6.7 North American Badger Management Methods
6.7.1 North American Badger Control Through 
Habitat Modification (University of 
Nebraska, 1994; Texas Wildlife Damage 
Management Service, 1998)
Rodent control will alleviate most problems associated with 
badger damage. Badgers commonly prey on ground squirrels, 
pocket gophers, and prairie dogs. If this food source 
is eliminated, then damage from badger predation will be 
reduced and the badger will often move elsewhere in search 
of food. Dam owners should refer to sections of this manual 
pertaining to management of ground squirrels, pocket gophers, 
and prairie dogs for rodent control guidance. 
6.7.2 North American Badger Control Through 
Trapping (University of Nebraska, 1994; Texas 
Wildlife Damage Management Service, 1998)
Badgers can often be removed from an area through the 
use of cage traps, leghold traps, or snares placed near the 
entrance of an active den. Cage traps require bait, such as a 
dead chicken or large rodent. After a badger is caught alive, 
it should be euthanized or relocated to an area where it will 
not cause further damage. 
Leghold traps (No. 3 or 4) are most effective if attached to a 
drag such as a strong limb or fence post. If leghold traps are 
staked into the ground, it is likely that the badger will dig 
out the trap and escape. 
Snaring involves setting a steel-cable loop in an animals 
path to capture it by the neck, body, or leg. Snares are light-
weight, compact, easy to set, low-cost, and they offer a high 
degree of human safety. Ready-made snares and snare components 
may be purchased from trapping suppliers. They 
must be attached to a solid object so the captured animal 
cannot escape. Snares should not be set where they could 
capture pets or livestock. 
Dam owners should contact their state wildlife agency regarding 
trapping regulations.
6.7.3 North American Badger Control Through 
Fumigants (University of Nebraska, 1994)
No fumigants are registered for badger control.
6.7.4 North American Badger Control Through 
Toxicants (University of Nebraska, 1994)
No toxicants are registered for badger control.
6.7.5 North American Badger Control Through 
Frightening (University of Nebraska, 1994)
Badgers may be discouraged from inhabiting an area if 
high-intensity lights are installed and used at night.
6.7.6 North American Badger Control Through 
Repellents (University of Nebraska, 1994)
No repellents are registered for badger control.
6.7.7 North American Badger Control Through 
Shooting (University of Nebraska, 1994)
Shooting can be an effective method of controlling small 
populations of badgers. Early morning, late evening, and 
after dark are the best times for hunting. Where legal, 
spotlights can be an effective tool for hunting at night. Dam 
owners should contact their state wildlife agency regarding 
hunting regulations and restrictions. 
6.8 Nutria Management Methods
6.8.1 Nutria Control Through Habitat Modification 
(University of Nebraska, 1994; USDA, 1991)
Nutria can be discouraged from inhabiting an area by eliminating 
brush, trees, thickets, and weeds, which provide food 
and cover. Cleared vegetation should be burned or removed. 
In certain situations, water level manipulation may be 
another damage control option. Dropping water levels in 

the summer and raising water levels in the winter will 
cause stress to nutria populations and may encourage them 
to relocate. The viability of this option is dependent upon 
reservoir useage (e.g., water spray, recreation, etc.) and 
owner willingness. In addition, lowering the water level has 
not yet been proven effective by researchers, but it is a tool 
to consider as part of a comprehensive nutria management 
strategy. 
6.8.2 Nutria Control Through Trapping 
(University of Nebraska, 1994)
Trapping is a very effective method of controlling nutria. 
Leghold traps are most commonly used. Most trappers 
prefer double longspring traps (No. 11 or 2), but the No. 1 
 coilspring, No. 3 double longspring, and soft-catch fox 
traps are also effective. Traps should be set just under the 
water where an active nutria trail enters the reservoir. The 
trap should be staked to the ground just off to the side of 
the trail and covered with leaves or other debris. To increase 
effectiveness, traps should be baited with chunks of apples, 
carrots, sweet potatoes, or watermelon rinds. In deep water, 
a drowning set should be used. If a nutria is captured alive 
in shallow water, then it should be disposed of humanely. 
Single- or double-door live traps may be used to capture 
nutria. The cage should be at least 9 x 9 x 32 inches in size. 
Place the trap along active trails and bait with sweet potatoes 
or carrots. Captured nutria should be humanely destroyed.
Conibear traps (No. 220-2, 160-2, and 330-2) are also 
commonly used to reduce nutria populations. These traps 
should be set on trails, at den entrances, in culverts, or in 
narrow waterways. They should not be used in areas frequented 
by children, domestic pets, or desirable wildlife 
species. 
Snaring is another option for capturing nutria. Snaring 
involves setting a steel-cable loop in an animals path to 
capture it by the neck, body, or leg. Snares constructed with 
3/32-inch flexible stainless steel wire or galvanized aircraft 
cable are suitable for catching nutria. They should be set 
along trails, travel routes, feeding lanes, or bank slides. 
Dam owners should contact their state wildlife agency regarding 
trapping regulations.
6.8.3 Nutria Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are registered for nutria control.
6.8.4 Nutria Control Through Toxicants 
(University of Nebraska, 1994)
Zinc phosphide is the only toxicant registered for nutria 
control. It is a Restricted Use Pesticide that must be purchased 
and applied by a certified pesticide applicator. The 
zinc phosphide is mixed with bait, such as apples, carrots, 
or sweet potatoes, and then the bait is placed in waterways, 
ponds, and ditches where permanent standing water and 
recent signs of nutria activity are found. Do not place bait 
directly in the water, but rather on floating rafts (anchored 
to the bottom or tied to the shore as depicted on figure 
6-4), small islands, floating logs, or exposed tree stumps. 
Ground baiting is not recommended because humans and 
nontarget animals may be exposed to the toxicant. 
Prebaiting increases the effectiveness of this control method. 
Apply corn oil to chunks of apples, carrots, or sweet potatoes 
and place the prebait at the designated baiting station. 
The station should be prebaited for several nights. Observe 
the station to ensure that nutria, rather than nontarget 
animals, are taking the bait. Once the nutria are accustomed 
to eating the prebait, the zinc-phosphide treated bait can 
be applied. The toxic bait should be applied until no more 
bait is being taken. Dead nutria that have been exposed to 
zinc phosphide should be collected and disposed of by deep 
burial or burning to prevent zinc phosphide exposure to 
domestic and wild scavengers. 
6.8.5 Nutria Control Through Frightening 
(University of Nebraska, 1994)
Harassment may temporarily deter nutria from inhabiting 
an area. Loud noises and high-pressure water sprays have 
worked in some cases. As a long-term control method, however, 
frightening is not an effective or practical option. 
6.8.6 Nutria Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for nutria control. 

6.8.7 Nutria Control Through Shooting 
(University of Nebraska, 1994)
Shooting is an effective method of controlling nutria. This 
method is most effective at night with a spotlight, although 
it should be noted that this technique is not legal in all 
states. Shooting can be effective when carried out at bait 
stations, from boats, or from the bank. Dam owners should 
contact their state wildlife agency for information on hunting 
regulations and restrictions.
6.9 Prairie Dog Management Methods
Because other animals frequently inhabit prairie dog towns, 
including the Federally protected burrowing owl and black-
footed ferret, dam owners need to be particularly cautious 
when taking action to control prairie dogs. In regions and 
habitats where burrowing owls and black-footed ferrets are 
known to live, dam owners should coordinate with their 
state wildlife agency and the USFWS to determine whether 
either of these species is present; field surveys by qualified 
biologists may be required. Burrows that have feathers or 
white droppings at the mouth probably contain burrowing 
owls. Black-footed ferrets are secretive animals, and since it 
can be very difficult to verify their existence in a particular 
burrow system, it is best to contact the USFWS and the state 
wildlife agency for guidance on completing a black-footed 
ferret survey (University of Nebraska, 1994). If either of 
these species is present, the dam owner must contact the 
USFWS and their state wildlife agency for management 
guidance.
It is also important to remember that the Utah prairie dog, 
one of the four prairie dog species found in the United 
States, is listed as a Federally threatened species and is therefore 
subject to the provisions of the Endangered Species Act. 
As the name implies, the Utah prairie dog is found only 
in Utah. Dam owners in Utah who suspect that they have 
a prairie dog problem should contact the USFWS and the 
Utah Division of Wildlife Resources for species identification 
and management guidance.
6.9.1 Prairie Dog Control Through Habitat 
Modification (University of Nebraska, 1994)
Installation of visual barriers may discourage prairie dogs 
from inhabiting an area. Prairie dogs prefer areas of low 
vegetation to provide a clear view of their surroundings and 
to improve their ability to detect predators. Objects such 
as fences or hay bales that are strategically placed to block 
prairie dog views may reduce suitability of the habitat. 
6.9.2 Prairie Dog Control Through 
Trapping (USDA, 1991)
Trapping may be used to control prairie dogs, but it is quite 
labor intensive and therefore only practical for removing 
small populations. Cage traps for live capture, Conibear 
traps (No. 110), and leg-hold traps are often used. Cage 
traps are most effective in early spring. They should be baited 
with oats flavored with corn or anise oil. Dam owners 
should consult with their state wildlife agency for guidance 
on releasing captured prairie dogs. Conibear and leg-hold 
traps should be set in burrow entrances. They do not require 
bait. Dam owners should consult with their state wildlife 
agency regarding specific trapping regulations.
6.9.3 Prairie Dog Control Through Fumigants 
(University of Nebraska, 1994)
Fumigants can be used to control prairie dogs in some situations, 
however this method is often costly, time-consuming, 
and particularly hazardous to other wildlife. Fumigation 
is most effective as a follow-up to toxic baits. It should 
not be used in burrows where nontarget species are thought 
to be present. 
Aluminum phosphide is a registered fumigant for control of 
burrowing rodents, including prairie dogs. It is a Restricted 
Use Pesticide and therefore must be purchased and apIn 
certain areas, legal 
hunting with a shotgun 
or small caliber rifle 
has reduced nutria 
populations by 80%.
Aluminum phosphide 
can reduce prairie 
dog populations by 
85% to 95%.

plied by a certified pesticide applicator. Aluminum phosphide 
comes in tablet form. One tablet should be inserted 
into each burrow and then the burrow entrance should be 
tightly plugged with soil. When used correctly, aluminum 
phosphide typically provides an 85% to 95% reduction in 
prairie dog populations. The legal application of aluminum 
phosphide may vary from state to state so dam owners 
should consult with their state wildlife agency or state pesticide 
registration board before implementing this control 
method.
Gas cartridges may also be used to control prairie dogs. Gas 
cartridges are General Use Pesticides that can usually be 
purchased at local farm supply stores or pesticide dealers. 
When ignited, a gas cartridge will produce carbon monoxide, 
carbon dioxide, and other gases that are toxic to the 
prairie dog. The cartridge should be lit before it is placed in 
the burrow. Once it has been inserted, the burrow should 
be immediately plugged with soil. Gas cartridges should be 
used with caution and in accordance with the directions on 
the label. When used correctly, gas cartridges can provide a 
95% reduction in prairie dog populations. 
Dam owners should consult with their state wildlife agency 
for information on state and local regulations regarding gas 
cartridges and the use of fumigants.
6.9.4 Prairie Dog Control Through Toxicants 
(University of Nebraska, 1994)
Baiting with a toxicant is generally the most economical 
and effective method of controlling prairie dogs. Zinc phosphide 
bait is currently the only registered and legal toxicant 
available for prairie dog control. It is available in 2% zinc 
phosphide-treated grain bait and pellet formulations. It is a 
Restricted Use Pesticide, which means that it is only available 
for sale to and use by certified pesticide applicators. 
Zinc phosphide baits can be applied from July 1 through 
January 31, though it is best to apply the baits in late summer 
and fall when prairie dogs are most active and there is 
no green forage available. 
A prebait must be applied to the burrows before the toxic 
bait. The prairie dogs will become accustomed to eating the 
non-toxic grains, which will increase the effectiveness of 
the toxic bait. The prebait and the toxic bait may be applied 
by hand or by a mechanical bait dispenser attached to an 
all-terrain vehicle, motorcycle, or horse. 
6.9.5 Prairie Dog Control Through Frightening 
(University of Nebraska, 1994)
Frightening is not an effective method of control for prairie 
dogs. 
6.9.6 Prairie Dog Control Though Repellents 
(University of Nebraska, 1994)
No repellents are Federally registered for prairie dog control.
6.9.7 Prairie Dog Control Through Shooting 
(University of Nebraska, 1994)
Continuous shooting of prairie dogs can remove about 65% 
of the population annually, but it is generally not a practical 
or cost-effective method of control. Shooting is most effective 
in spring because it can disrupt breeding. Dam owners 
should consult with their state wildlife agency regarding 
specific hunting regulations and requirements.
6.10 Ground Squirrel Management Methods
The northern Idaho ground squirrel, one of 23 ground 
squirrel species in the United States, is Federally listed as a 
threatened species and is therefore subject to the provisions 
of the Endangered Species Act. The northern Idaho ground 
squirrel is found in limited distribution in the northwest. 
Dam owners in that region who experience problems with 
ground squirrels should contact the USFWS and their state 
wildlife agency for species identification and management 
guidance.
Zinc phosphide can be 
75% to 85% successful 
in controlling prairie dogs 
when used correctly. 
Gas cartridges can provide 
a 95% reduction in 
prairie dog populations.

6.10.1 Ground Squirrel Control Through 
Habitat Modification (USDA, 1991)
Routine weed control and vegetative management may limit 
some ground squirrel damage, but the effectiveness of this 
method is usually limited.
6.10.2 Ground Squirrel Control Through Trapping 
(University of Nebraska, 1994)
Trapping is a labor-intensive control method, and therefore 
it is generally only useful for removing small populations 
of ground squirrels. Jaw traps (No. 1 or No. 0), box or cage 
traps, and Conibear traps (No. 110 or No. 110-2) may be 
used (refer to Figure 6-1). Generally, one trap is needed for 
every 10 to 15 squirrels present. Traps should be set on trails 
or near burrow entrances. Box or cage traps require bait, 
such as fruit, vegetables, peanut butter, or grain; baiting is 
not necessary with jaw traps or Conibear traps. Dam owners 
should contact their state wildlife agency for information 
on state and local trapping regulations. 
6.10.3 Ground Squirrel Control Through Fumigants 
(University of Nebraska, 1994)
Aluminum phosphide and gas cartridges are both registered 
fumigants for ground squirrel control. Fumigants work best 
for light squirrel infestations limited to a few acres. This 
method is most effective in the spring, when ground squirrels 
have just emerged from hibernation. 
Aluminum phosphide is a Restricted Use Pesticide that 
comes in tablet form. This fumigant can only be purchased 
and applied by a certified pesticide applicator. One tablet 
should be placed in each burrow entrance and then the 
burrow should be plugged with soil to form an air-tight 
seal. The legal application of aluminum phosphide may vary 
from state to state so dam owners should consult with their 
state wildlife agency or state pesticide registration board 
before implementing this control method.
Gas cartridges are General Use Pesticides that can usually be 
purchased at local farm supply stores or pesticide dealers. 
When ignited, a gas cartridge will produce carbon monoxide, 
carbon dioxide, and other gases that are toxic to ground 
squirrels. The cartridge should be lit before it is placed in 
the burrow. Once it has been inserted, the burrow should 
be immediately plugged with soil. Gas cartridges should be 
used with caution and in accordance with the directions on 
the label. Dam owners should consult with their state wildlife 
agency for information on state and local regulations 
regarding gas cartridges and the use of fumigants.
6.10.4 Ground Squirrel Control Through Toxicants 
(University of Nebraska, 1994)
Zinc phosphide and two anticoagulants, chlorophacinone 
and diphacinone, are currently registered for ground squirrel 
control. 
Zinc phosphide is a Restricted Use Pesticide, which means 
that it can only be purchased and applied by a certified 
pesticide applicator. It is a single-dose toxicant delivered on 
oat baits. The ground squirrels should be exposed to an untreated 
prebait several days before using the toxic grain. Bait 
can be delivered by hand or mechanically dispensed. 
Chlorophacinone and diphacinone are two anticoagulant 
baits that are registered in some states under various trade 
names. A continuous supply of bait must be applied for 4 to 
9 days for the toxicant to be effective. The bait is usually delivered 
in a bait box, which can be made of rubber tires or 
metal, plastic, or wood containers. The commonly used PVC 
Inverted-T anticoagulant bait station consists of 4-inch sections 
of plastic irrigation pipe formed into an inverted T 
configuration (Figure 6-12). Dam owners should contact 
The New Mexico and 
Nebraska Dam Safety 
Offices have set up roosts 
in the dam environment 
to support raptors such 
as red-tailed hawks to 
provide predator control 
of small rodents.
When used correctly, zinc 
phosphide can result in an 
85% to 95% reduction in 
ground squirrel population. 

their state wildlife agency for information on anticoagulants 
that may be available for use.
All products should be used as directed. Dam owners should 
consult with their state wildlife agency regarding legality of 
toxicant use in their state.
6.10.5 Ground Squirrel Control Through Frightening 
(University of Nebraska, 1994)
Frightening is not an effective method of control for 
ground squirrels.
6.10.6 Ground Squirrel Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for ground squirrel control.
6.10.7 Ground Squirrel Control Through Shooting 
(University of Nebraska, 1994)
Shooting may be used to remove small populations of 
ground squirrels, although it is an expensive and time-consuming 
method of control. Dam owners should consult 
with their state wildlife agency regarding specific hunting 
regulations and requirements
6.11 Armadillo Management Methods
6.11.1 Armadillo Control Through Habitat 
Modification (University of Nebraska, 1994)
It is possible to discourage armadillos from burrowing in an 
earthen dam by implementing the following habitat mitigation 
techniques:
Remove brush or other cover to reduce the amount of 
suitable habitat.
Apply soil insecticides to remove insects and other invertebrates 
that make up the majority of the armadillos diet. 
6.11.2 Armadillo Control Through Trapping 
(University of Nebraska, 1994)
Trapping can be an effective method of managing armadillos. 
Live or box traps (10 x 12 x 32-inch), such as the 
Havahart or Tomahawk, work best. A traps effectiveness can 
be enhanced by adding wings (1 x 4-inch or 1 x 6-inch 
boards about 6 feet long) to funnel the animal into the trap 
(Figure 6-13). The best locations to set traps are along pathways 
to burrows and along fences or other barriers where 
armadillos may travel. Conibear (No. 220) or leghold 
traps (No. 1 or 2) may also be used (refer to Figure 6-1). 
These types of traps should be placed at the entrance of a 
burrow.
24 to 30
45
12 to 15
PVC (4) T 
4
Figure 6-12. The PVC Inverted-T bait station delivers 
anticoagulant bait to ground squirrels. 
Figure 6-13. The effectiveness of cage traps can be enhanced 
by adding wings to funnel the armadillo into the trap.

6.11.3 Armadillo Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are Federally registered for armadillo control. 
However, there are some fumigants that are effective and 
that may be legal in certain states. Dam owners should consult 
their state wildlife agency regarding fumigants that may 
be legal in their area.
6.11.4 Armadillo Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are registered for armadillo control.
6.11.5 Armadillo Control Through Frightening
Frightening is not an effective method of armadillo control.
6.11.6 Armadillo Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for armadillo control.
6.11.7 Armadillo Control Through Shooting 
(University of Nebraska, 1994)
Shooting is an effective method of controlling armadillos. 
The best time to shoot is during twilight hours or at 
night when armadillos are most active. Dam owners should 
consult with their state wildlife agency regarding specific 
hunting regulations and requirements. 
6.12 Livestock (Cow, Sheep, Horse, Pig, and 
Wild Pig) Management Methods
6.12.1 Livestock Control Through Habitat 
Modification (USDA, 1991)
Providing a water source away from the earthen dam may 
help reduce livestock damage near the dam, since livestock 
are often at the dam in search of drinking water.
6.12.2 Livestock Control Through Trapping (USDA, 
1991; University of Nebraska, 1994)
Trapping is quite effective for wild pigs. Stationary corral-
type traps and box traps are commonly used (Figure 6-14). 
They are most effective in summer when acorns and other 
steel fence post
spring
18
6
48
2 x 4 mesh welded 
wire (12 gauge)
48
96
front
side
2 x 4 x 24 wood
36 x 48 x 3/4 plywood
36 x 2 x 4 mesh welded wire
4 6 strap hinges
2 12 screen door springs
8 6 steel fence posts
4 lbs 16-penny nails
1 lbs 12-penny nails
2 lbs 1 1/2 staples
1 100 12-gauge wire
Figure 6-14. Stationary hog trap.

preferred natural foods are not available. Traps should be 
baited with grains, fruits, or vegetables. The traps may be 
placed anywhere that wild pigs concentrate.
6.12.3 Livestock Control Through 
Fumigants (USDA, 1991)
Fumigants are not suitable for livestock control.
6.12.4 Livestock Control Through 
Toxicants (USDA, 1991) 
Toxicants are not suitable for livestock control.
6.12.5 Livestock Control Through 
Frightening (USDA, 1991)
Frightening devices such as animated scarecrows or firecrackers 
may temporarily deter livestock from inhabiting an 
area, but these techniques generally do not provide a long-
term solution to livestock damage. 
6.12.6 Livestock Control Through 
Repellents (USDA, 1991)
Repellents are not suitable for livestock control.
6.12.7 Livestock Control Through 
Shooting (USDA, 1991)
Shooting may be an effective method of removing a small 
population of nuisance livestock; however, hunting is generally 
only permitted for wild animals such as pigs. Dam 
owners should contact their state wildlife agency regarding 
hunting regulations and restrictions. 
6.13 Crayfish Management Methods
6.13.1 Crayfish Control Through Habitat Modification 
(Virginia Cooperative Extension, 2001a).
Damage may be prevented by stocking the reservoir with 
natural enemies of crayfish, such as trout, bass, catfish, and 
large bluegills. These species will eat the crayfish, which 
will reduce the overall crayfish population and decrease the 
number of burrows. 
6.13.2 Crayfish Control Through Trapping 
(University of Nebraska, 1994)
Wire cage traps baited with fish or meat can be used to 
catch crayfish. 
6.13.3 Crayfish Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are Federally registered for crayfish control. 
6.13.4 Crayfish Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are Federally registered for crayfish control. 
Some states, however, have regulations that allow application 
of certain insecticides for crayfish burrow treatment. 
Dam owners should consult with their state wildlife agency 
regarding the legality of toxicants in their state. 
6.13.5 Crayfish Control Through Frightening
Frightening is not an effective method of controlling crayfish.
6.13.6 Crayfish Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for crayfish control.
6.13.7 Crayfish Control Through Shooting
Shooting is not a suitable method of controlling crayfish.
6.14 Coyote Management Methods
6.14.1 Coyote Control Through Habitat 
Modification (USDA, 1991)
Proper vegetative management (mowing and brush removal) 
and rodent control will often discourage coyotes from 
digging in earthen dams. 
6.14.2 Coyote Control Through Trapping 
(University of Nebraska, 1994)
Steel leg-hold traps (No. 3 and 4) are often used for coyote 
removal. Effective use of these traps for coyote control 
generally requires a great deal of experience and training. 

Dam owners should contact their state wildlife agency for 
guidance on trapping nuisance coyotes. 
Snaring is another method of removing coyotes. Snaring 
involves setting a steel-cable loop in an animals path to 
capture it by the neck, body, or leg. Snares are light-weight, 
compact, easy to set, low-cost, and they offer a high degree 
of human safety. In one study, they were proven to 
be more effective than leg-hold traps for coyote control. 
Snares are usually made of a 2.5- to 10-foot long piece of 
galvanized aircraft cable with a slide lock that forms a loop. 
Snares should be set along known coyote trails. They must 
be attached to a solid object so that the captured animal 
cannot escape. Snares should not be set where they could 
capture pets or livestock. Snares are not legal in all states so 
dam owners should consult with their state wildlife agency 
before choosing this control method. Once caught, coyotes 
should be humanely destroyed.
6.14.3 Coyote Control Through Fumigants 
(University of Nebraska, 1994)
Gas cartridges are the only registered fumigant for coyote 
control. Gas cartridges are General Use Pesticides that can 
usually be purchased at local farm supply stores or pesticide 
dealers. When ignited and placed in the den, a gas cartridge 
will produce carbon monoxide, carbon dioxide, and other 
gases that are toxic to the coyote. Gas cartridges should be 
used with caution and in accordance with the directions 
on the label. Dam owners should consult with their state 
wildlife agency regarding state and local regulations on gas 
cartridges and the use of fumigants.
6.14.4 Coyote Control Through Toxicants 
(University of Nebraska, 1994)
The only toxicant registered for coyote control is sodium 
cyanide used in an M-44 ejector device. The M-44 is a 
spring-activated device that expels a sodium cyanide capsule 
into the animals mouth. The M-44 device should be 
set along the sides of trails or paths used by coyotes. This 
control method is most effective during cooler months. The 
M-44 sodium cyanide device is classified as a Restricted Use 
Pesticide and may only be used by USDA Animal Damage 
Control personnel and, in some states, certified pesticide 
applicators. The M-44 is not registered for use in all states so 
dam owners must consult their state wildlife agency before 
implementing this control measure. 
6.14.5 Coyote Control Through 
Frightening (USDA, 1991)
Several types of frightening devices are available for coyote 
control, but these devices were designed for livestock protection 
and are not practical for protection of earthen dams.
6.14.6 Coyote Control Through Repellents 
(University of Nebraska, 1994)
No repellents have proven effective for coyote control.
6.14.7 Coyote Control Through 
Shooting (USDA, 1991)
Coyote hunting is often an effective method of control for 
livestock protection, but it is generally not practical for 
protecting earthen dams. If a dam owner decides to pursue 
this method of control, they must contact the state wildlife 
agency for information on hunting regulations. 
6.15 Mole and Vole Management Methods
6.15.1 Mole and Vole Control Through 
Habitat Modification (University of 
Nebraska, 1994; USDA, 1991)
It is possible to discourage moles from burrowing in an 
earthen dam by implementing the following habitat modification 
techniques:
Compact the soil with a roller to reduce soil moisture. 
This will reduce the habitats attractiveness to moles.
Apply insecticides to reduce food supply. Legal insecticides 
may vary by state so dam owners should contact 
their state wildlife agency for specific guidance. 
6.15.2 Mole and Vole Control Through Trapping 
(University of Nebraska, 1994) 
Trapping is the most effective method of reducing mole 
populations. Several traps are specifically designed for 
moles, including the Victor mole trap, Out O Sight, and 
Nash (choker loop) mole trap. If used properly, any of these 
traps can be effective. Traps should be set in the surface runway 
where there is evidence of recent mole activity.
Trapping is generally not an effective method of reducing 
large vole populations because of prohibitive time and 

labor costs. Mouse snap traps may be used for control of a 
few individual voles. Traps should be set perpendicular to a 
runway with the trigger end in the runway. Voles are easiest 
to trap in the fall and late winter. 
6.15.3 Mole and Vole Control Through Fumigants 
(University of Nebraska, 1994)
Both aluminum phosphide and gas cartridges are Federally 
registered for mole control. Aluminum phosphide is 
a Restricted Use Pesticide that comes in tablet form. One 
tablet should be placed in each burrow entrance and then 
the burrow should be plugged with soil to form an air-tight 
seal. The legal application of aluminum phosphide may vary 
from state to state so dam owners should consult with their 
state wildlife agency or state pesticide registration board 
before implementing this control method.
Gas cartridges are General Use Pesticides that can usually be 
purchased at local farm supply stores or pesticide dealers. 
When ignited, a gas cartridge will produce carbon monoxide, 
carbon dioxide, and other toxic gases. The cartridge 
should be lit before it is placed in the burrow. Once it has 
been inserted, the burrow should be immediately plugged 
with soil. Gas cartridges should be used with caution and 
in accordance with the directions on the label. Dam owners 
should consult with their state wildlife agency for information 
on state and local regulations regarding gas cartridges 
and the use of fumigants.
Fumigants are generally not effective for vole control. The 
vole burrow system is so complex and shallow that the 
fumigant easily escapes to the surface.
6.15.4 Mole and Vole Control Through Toxicants 
(University of Nebraska, 1994)
Strychnine alkaloid and chlorophacinone are both Federally 
registered for mole control. Strychnine alkaloid is a Restricted 
Use Pesticide that can only be purchased and applied by 
a certified pesticide applicator. However, since moles do not 
normally consume grain, strychnine alkaloid grain baits are 
seldom effective. Chlorophacinone is commercially available 
in pellet form under the name Orco Mole Bait. Researchers 
have found that this is a highly effective and easy to apply 
mole control technique. Dam owners should be aware, 
though, that two or more successive treatments are often 
required. If a dam owner chooses either of these methods 
of control, they should contact the state wildlife agency 
regarding the legality of toxicant use in their state.
Zinc phosphide is often used for vole control. Zinc phosphide 
is a single-dose toxicant available in pellet or grain 
bait formulas. Pellets or grain bait can be delivered to burrows 
by hand or mechanically dispensed. Zinc phosphide is 
a Restricted Use Pesticide, which must be purchased and applied 
by a certified pesticide applicator. Anticoagulant baits 
can also be used to reduce vole populations. Anticoagulants 
generally require several feedings and can take anywhere 
from 5 to 15 days to be effective. Bait can be delivered by 
hand, mechanically dispensed, or placed in various types 
of bait containers. Registration for anticoagulants varies by 
state.
All products should be used as directed. Dam owners should 
consult with their state wildlife agency regarding legality of 
toxicant use in their state.
6.15.5 Mole and Vole Control Through Frightening 
(University of Nebraska, 1994)
Frightening is not an effective method of control for moles 
or voles.
6.15.6 Mole and Vole Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for mole control.
Several repellents using thiram or capsaicin as the active 
ingredient are registered for vole control, but there is no 
evidence that these repellents are actually effective. Dam 
owners should contact their state wildlife agency or pesticide 
regulatory agency for information on available repellents 
in their state. 
6.15.7 Mole and Vole Control Through Shooting 
(University of Nebraska, 1994)
Shooting is not an effective method of control for moles or 
voles.
6.16 River Otter Management Methods
6.16.1 River Otter Control Through Habitat 
Modification (University of Nebraska, 1994)
Habitat modification is generally not an effective method 
of control for river otters. Otters often share their environment 
with beavers, whose burrowing activity is detrimental 
to the earthen dam environment. Otters will often live in 

beaver burrows and dens and do not often dig their own 
dens. Before mitigating for the river otter, evaluate whether 
the damaging actions are caused by beaver so that the appropriate 
species is managed and proper preventive actions 
are implemented (as discussed in Chapters 4.0 and 5.0 of 
this manual).
6.16.2 River Otter Control Through Trapping 
(University of Nebraska, 1994)
Both Conibear (No. 220 and 330) and leghold (modified 
No. 1  soft-catch and No. 11 double coilspring) traps have 
been successfully used to catch river otters. Traps should 
be placed underwater along river otter trails or on pull-
outs where otters leave the water. Leghold traps can also be 
used out of the water along trails and peninsula crossings. 
River otter trapping is illegal in many states so dam owners 
should contact their state wildlife agency before initiating a 
trapping program. 
6.16.3 River Otter Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are registered for river otter control.
6.16.4 River Otter Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are registered for river otter control.
6.16.5 River Otter Control Through Frightening 
(University of Nebraska, 1994)
Frightening has not proven to be an effective method of 
river otter control.
6.16.6 River Otter Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for river otter control.
6.16.7 River Otter Control Through Shooting 
(University of Nebraska, 1994)
Shooting is generally only effective for removing small 
populations of river otters. Dam owners should contact their 
state wildlife agency for information on hunting regulations 
and requirements. 
6.17 Gopher Tortoise Management Methods
The gopher tortoise is a Federally listed threatened species 
and therefore subject to the provisions of the Endangered 
Species Act. The historic range of the gopher tortoise 
includes Alabama, Florida, Georgia, Louisiana, Mississippi, 
and South Carolina. Dam owners in those states who suspect 
that they have a gopher tortoise problem should contact 
the USFWS and their state wildlife agency for management 
guidance.
6.17.1 Gopher Tortoise Control Through Habitat 
Modification (University of Nebraska, 1994)
Habitat modification is generally not an effective method of 
gopher tortoise control.
6.17.2 Gopher Tortoise Control Through Trapping
Since the gopher tortoise is Federally listed as a threatened 
species, dam owners should contact the USFWS or their 
state wildlife agency for management guidance. 
6.17.3 Gopher Tortoise Control Through Fumigants 
(University of Nebraska, 1994)
No fumigants are registered for gopher tortoise control.
6.17.4 Gopher Tortoise Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are registered for gopher tortoise control.
6.17.5 Gopher Tortoise Control Through Frightening
Frightening has not proven to be an effective method of 
gopher tortoise control and would be prohibited under the 
Endangered Species Act.
6.17.6 Gopher Tortoise Control Through Repellents 
(University of Nebraska, 1994)
No repellents are registered for gopher tortoise control.
6.17.7 Gopher Tortoise Control Through Shooting 
(University of Nebraska, 1994)
Gopher tortoises are protected under the Endangered Species 
Act and therefore, cannot be shot. Dam owners should 

contact the USFWS or their state wildlife agency for management 
guidance. 
6.18 Red Fox and Gray Fox Management Methods
6.18.1 Red Fox and Gray Fox Control 
Through Habitat Modification
Proper vegetative management (mowing and brush removal) 
and rodent control will often discourage foxes from 
digging in earthen dams by reducing their primary food 
source.
6.18.2 Red Fox and Gray Fox Control Through 
Trapping (University of Nebraska, 1994)
Trapping is a very effective method of controlling foxes, 
however it requires a great deal of expertise and training. 
Steel leg-hold traps (No. 1 , 1 , and 2 doublespring coil 
traps; and No. 2 and 3 double longspring trap) are suitable 
for both red and gray foxes. Cage traps may be used for juvenile 
red foxes. Traps set along trails, at entrances to fields, 
and near bait carcasses are most effective. 
Snares may also be used to capture foxes. Snaring involves 
setting a steel-cable loop in an animals path to capture it by 
the neck, body, or leg. Snares should be made from 1/16-
inch, 5/64-inch or 3/32-inch cable to capture red or gray 
foxes. The snare should have a 6-inch loop that is placed 10 
to 12 inches off the ground. Snares should be set on trails 
or in crawl holes that are frequented by foxes. 
Traps and snares are not legal in all states. Dam owners 
should contact their state wildlife agency for specific information 
on trapping regulations.
6.18.3 Red Fox and Gray Fox Control Through 
Fumigants (University of Nebraska, 1994)
Gas cartridges are the only registered fumigant for red and 
gray fox control. Gas cartridges are General Use Pesticides 
that can usually be purchased at local farm supply stores or 
pesticide dealers. When ignited and place in the den, a gas 
cartridge will produce carbon monoxide, carbon dioxide, 
and other gases that are toxic to the fox. Gas cartridges 
should be used with caution and in accordance with the 
directions on the label. Dam owners should consult with 
their state wildlife agency for information on state and local 
regulations regarding gas cartridges and the use of fumigants.
6.18.4 Red Fox and Gray Fox Control Through 
Toxicants (University of Nebraska, 1994)
The only toxicant registered for red and gray fox control is 
sodium cyanide used in an M-44 ejector device. The M-44 
is a spring-activated device that expels a sodium cyanide 
capsule into the animals mouth. It should be set along trails 
and at crossings regularly used by foxes. This is a Restricted 
Use Pesticide and may only be used by USDA Animal Damage 
Control personnel and, in some states, certified pesticide 
applicators. The M-44 is not registered in all states so 
dam owners must consult their state wildlife agency before 
implementing this control measure.
6.18.5 Red Fox and Gray Fox Control Through 
Frightening (University of Nebraska, 1994)
Noise-making devices such as radios, amplifiers, or propane 
exploders may temporarily deter foxes from inhabiting an 
area, but they do not provide a long-term solution.
6.18.6 Red Fox and Gray Fox Control Through 
Repellents (University of Nebraska, 1994)
No repellants are registered for red or gray fox control. 
6.18.7 Red Fox and Gray Fox Control 
Through Shooting
Shooting is another method of managing both red and gray 
foxes. Hunting regulations and seasons vary by state. Dam 
owners should contact their state wildlife agency for specific 
information on hunting foxes.
6.19 Canada Goose Management Methods
6.19.1 Canada Goose Control Through Habitat 
Modification (Virginia Cooperative Extension, 
2001b; University of Nebraska, 1994)
The following habitat modification techniques can be 
implemented to reduce Canada goose damage:
Minimize the amount of forage plants that exists near the 
water body by mowing or hand removal.
Construct a wire grid of stainless steel spring wire or 
monofilament line above the surface of the water. This 
will prevent Canada geese and other waterfowl from using 
the water and discourage them from nesting in that 

area. The individual lines should be staked to the ground 
about 12 inches above the waters surface. 
6.19.2 Canada Goose Control Through Trapping 
(University of Nebraska, 1994; Virginia 
Cooperative Extension, 2001b)
Live trapping may be effective for small populations of 
Canada geese. Several types of traps are effective including 
walk-in funnel traps, rocket or cannon nets, and spring-
powered nets. A federal permit is required before trapping 
may be initiated. In addition, all relevant state and federal 
agencies must agree on what will happen to the geese after 
capture. Dam owners should contact the USFWS and their 
state wildlife agency for guidance.
Walk-in funnel traps are most effective in late June or early 
July. These types of traps can be constructed using poultry 
wire, woven wire fencing, steel fence posts, and netting 
(Figure 6-15). The trap should be set immediately next to 
the affected waterbody and then the geese should be herded 
into the trap. The herders must surround the geese on three 
sides, forcing them into the trap. Once the geese are secured 
in the trap, they may be transported to a designated location.
Net traps may also be used to capture Canada geese. Rocket 
or cannon nets with 2- to 2.5-inch mesh work well for 
large geese. The net should be placed at a location near the 
water and a second site should be repetitively baited with 
corn or other suitable bait until the bait is well accepted. 
Once the geese are trained to feed at the bait site, the area 
should be re-baited in preparation for capture. When the 
geese are concentrated at the site, the rocket or cannon 
net should be fired at the location so the birds are trapped 
underneath. The Canada geese can then be transported to a 
designated location. Spring-powered nets work in a similar 
fashion, though they are smaller than standard rocket or 
cannon nets. The net is triggered mechanically or electronically, 
and because it does not create as much noise as the 
rocket or cannon net, it may be more effective even though 
it is smaller. 
A final method of capturing Canada geese is through the 
use of an immobilizing agent, Alpha-chloralose. Alpha-chloralose 
is a non-lethal chemical that is applied to bait and 
then fed to the geese. Approximately 20 to 90 minutes after 
ingestion, the geese will be unable to fly or escape and can 
be captured by hand. Alpha-chloralose may only be used 
by USDA Animal Damage Control (ADC) staff or biologists 
of other certified state or federal wildlife management 
agencies. Dam owners should contact USDA ADC staff, the 
USFWS, or their state wildlife agency for more information 
about this option 
6.19.3 Canada Goose Control Through Fumigants
Fumigants are not a practical method of control for Canada 
geese. 
6.19.4 Canada Goose Control Through Toxicants 
(University of Nebraska, 1994)
No toxicants are registered for Canada goose control.
6.19.5 Canada Goose Control Through Frightening 
(Virginia Cooperative Extension, 2001b)
Auditory and visual scare devices may be used to deter 
Canada geese from inhabiting an area. Auditory scare devices 
make loud noises that will frighten geese away. Commonly 
used devices include propane cannons, pyrotechnics, 
and pre-recorded tapes of Canada goose distress calls. Visual 
scare devices installed on or around an earthen dam are also 
effective. They are usually inexpensive and easy to install, 
but they work best in conjunction with another deterrent. 
Holding pen
5 welded 
turkey-wire
15 to 20 square
Install steel fence 
posts as needed 
for support
Trap wings 
3 chicken wire 
50 to 100 long
Space steel fence posts every
20 to 30 along wings 
as needed for support
Funnel opening 75 to 100
Figure 6-15. Canada goose funnel trap.

Examples of visual scare devices include strobe lights, scarecrows, 
owl effigies, mylar reflective tape, flags, and balloons. 
Harassment or hazing of Canada geese is generally more 
effective than visual or auditory deterrents, but it can be 
labor intensive and expensive. Examples of common hazing 
programs include use of radio-controlled toys (boats or 
airplanes), trained dogs, or high-power water spray devices. 
These deterrent activities must be persistent and repeated to 
remain effective. 
6.19.6 Canada Goose Control Through Repellents 
(Virginia Cooperative Extension, 2001b)
Methyl anthranilate has been registered as a goose repellant 
under the name ReJeX-iT. This repellant is non-toxic 
and does not harm the geese. Re-JeX-iT is applied directly 
to the grass of an affected area. It may have to be reapplied 
frequently to remain effective. Repellents should always be 
used as directed. 
6.19.7 Canada Goose Control Through Shooting 
(University of Nebraska, 1994)
Hunting is another effective method of reducing Canada 
goose populations. Since Canada geese are listed as migratory 
birds under the Migratory Bird Treaty Act, a federal 
permit is required. In many areas, state permits are also 
required for hunting Canada geese. Dam owners should 
contact the USFWS and their state wildlife agency for specific 
hunting regulations and requirements. 
6.19.8 Other Methods of Canada Goose Control
It is also possible to reduce resident Canada goose populations 
by oiling, shaking, or puncturing their eggs. This requires 
a federal permit; dam owners should contact USFWS 
and their state wildlife agency for more information. 
6.20 American Alligator Management Methods
The American Alligator is Federally listed as a threatened 
species due to similarity of appearance to the federally 
endangered American crocodile. This listing grants the 
American Alligator protection under the Endangered Species 
Act. Dam owners who experience problems with nuisance 
alligators should contact the USFWS and their state wildlife 
agency for management guidance. 
6.20.1 American Alligator Control Through Habitat 
Modification (University of Nebraska, 1994)
Removal of emergent wetland vegetation may reduce alligator 
densities by reducing cover. There are strict laws however, 
regarding human modifications to wetlands so dam 
owners must consult with appropriate state environmental 
agencies before disturbing any wetland vegetation. 
6.20.2 American Alligator Control Through 
Trapping (University of Nebraska, 1994)
Trapping is an effective method of eliminating alligators 
from an area. A baited hook is the simplest and most effective 
method. This involves rigging a large fish hook (12/0 
forged) with bait (e.g., fish, beef, chicken, or nutria) and 
suspending it via rope from a tree or pole about 2 feet 
above the water. When the alligator swallows the bait, the 
hook is lodged in its stomach and the alligator is retrieved 
using the attached rope. This method almost always kills or 
injures the alligator. 
Trip-snare traps and wire box traps may also be used. They 
are not quite as effective as the baited hook, but they do 
not kill or injure the alligator, which then must be relocated. 
Dam owners must contact the USFWS and their state 
wildlife agency for information on trapping regulations, the 
Endangered Species Act, and permit requirements.
6.20.3 American Alligator Control Through 
Fumigants (University of Nebraska, 1994)
No fumigants are registered for alligator control.
6.20.4 American Alligator Control Through 
Toxicants (University of Nebraska, 1994)
No toxicants are registered for alligator control.
6.20.5 American Alligator Control Through 
Frightening (University of Nebraska, 1994)
Under the Endangered Species Act, no actions to harass or 
frighten a protected species are allowed.
6.20.6 American Alligator Control Through 
Repellents (University of Nebraska, 1994)
No repellents are registered for alligator control.

6.20.7 American Alligator Control Through 
Shooting (University of Nebraska, 1994)
Shooting is an effective method of eliminating alligators. 
A sufficiently powerful rifle (.243 caliber or larger) should 
be used for a humane kill. Dam owners must contact the 
USFWS and their state wildlife agency for information on 
hunting regulations, compliance with the Endangered Species 
Act, and permit requirements.
6.21 Ant Management Methods
6.21.1 Ant Control Through Habitat Modification 
(University of Georgia Cooperative 
Extension Service, 2000)
It may be possible to reduce ant populations by physically 
destroying visible ant mounds. This can be accomplished by 
simply knocking down or disturbing mounds with a stick 
or shovel. Another option is to pour very hot (almost boiling) 
water directly on each mound. 
6.21.2 Ant Control Through Trapping
Ant traps are commercially available, but they are not effective 
for large, outdoor ant infestations.
6.21.3 Ant Control Through Fumigants (University 
of Georgia, 1993; University of Georgia 
Cooperative Extension Service, 2000)
Fumigants may help control some type of ant species. 
Earthfire (vaporized resmethrin) and Brom-O-Gas (methyl 
bromide) are two examples of fumigants that have proven 
effective against fire ants. Both are Restricted Use Pesticides 
that must be purchased and applied by a certified pesticide 
applicator. These fumigants may not necessarily be effective 
for all ant species. Dam owners should contact a professional 
pest removal company for information on fumigants that 
may be effective for their particular ant infestation. 
6.21.4 Ant Control Through Toxicants (University of 
Florida Cooperative Extension Service, 2002)
Ants can usually be controlled with baits or chemical treatments. 
Many of these products are available commercially at 
hardware stores, home and garden suppliers, and other retail 
outlets. These treatments come in various forms, including 
granules, liquids, gels, and ready-to-use tamper resistant 
containers. Treatment should be tailored to the type of ant 
species present and the extent of infestation. Dam owners 
should contact their local cooperative extension agency or 
a professional pest control company for assistance. Professional 
pest control companies may also be able to provide 
stronger treatment options if damage is significant and the 
use of commercially available products is not effective. 
6.21.5 Ant Control Through Frightening
Frightening is not an effective or practical method of ant 
control.
6.21.6 Ant Control Through Repellents
Large, outdoor ant infestations cannot be effectively controlled 
through the use of repellents.
6.21.7 Ant Control Through Shooting
Shooting is not a practical method of ant control.
Insecticides can 
contaminate both ground 
and surface waters so 
dam owners need to be 
particularly cautious when 
applying baits or chemical 
treatments near a reservoir. 
Insecticide use must occur 
in accordance with Federal 
law (FIFRA of 1996).
Pouring very hot water 
on each ant mound 
will eliminate about 
60% of mounds. 

97
Chapter 7. Fiscal Considerations For Managing Animal Damage On Earthen Dams
7.0 Fiscal Considerations 
for Managing Animal 
Damage on Earthen Dams
There is no free lunch. Either we make the investments required to keep our 
nations dams safe, or we will pay the price in dam failures.
Martin McCann, consulting professor of civil and environmental engineering at Stanford 
University and director of the National Performance of Dams Program (NPDP). 
Almost everyone in the dam community agrees that the 
funds spent preserving a dams integrity and safe operation 
will almost always be less than those spent repairing 
an unsafe dam or worse, recovering from a dam failure. The 
economics behind this understanding are self-explanatory 
and probably need no quantitative explanation; yet across 
the nation, dams deteriorate from animal intrusion damages 
and dam owners struggle with the financial responsibility 
of repairing their unsafe dams, or removing them altogether 
when the repair costs become too great. Clearly then, the 
economic considerations related to appropriate dam management 
go beyond the economic efficiency and long-term 
benefit of such repairs; the considerations involve acknowledgement 
of animal damages as a problem, human motivation 
factors, and the availability of funding mechanisms at 
the federal and state level.
7.1 Fiscal Considerations for the 
Reluctant Dam Owner
As indicated in the FEMA/ASDSO workshops, inspectors, 
engineers, and regulators can find it difficult to convince 
dam owners that animal burrows and erosion can have 
serious detrimental effects on their dams. Even though dam 
failures are becoming all too commonpartially a product 
of Americas aging damssome dam owners put too much 
confidence in the integrity of their dams, even when visible 
evidence of animal burrows and inappropriate vegetation 
are present on their dams. For these dam owners, animal 
damage management is not likely to become a budget line 
item until an understanding is developed of how adverse 
animal intrusion effects can cascade, resulting in extensive 
repair/replacement costs, as well as the associated liabilities, 
that follow a dam failure. 
7.2 Fiscal Considerations of the Willing Dam Owner
Other dam owners are aware of the dangers inherent to 
animal damages at an earthen dam, but overlook routine 
owner actions that are relatively affordable and can save 
hundreds of thousands of dollars in the long-term, not to 
mention reduce the public safety hazard for those located 
downstream of the dam. Inspections and repair actions are 
indeed overlooked, as documented by the states in the 2003 
surveys and in the 2002 workshop where financial limitations 
by owners is listed as the most common impediment 
to timely and adequate dam upkeep. Considering that over 
50% of the dams in this country are privately owned (AS

Dam Owners Manual to Animal Intrusion of Earthen Dams
98
DSO, 2003), financial limitations to upkeep pose a daunting 
threat to public safety. 
Still other dam owners know the inherent problems of 
animal damage, and vigilantly conduct inspections, mow 
twice annually, and fill burrows in a timely manner. However, 
some dams because of their size, location, and biological 
attractiveness continue to have animal damage problems 
despite owner vigilance. In these cases, the dam owner pays 
continuously to correct animal damages and routine owner 
actions become an expensive proposition in terms of both 
time and money. 
7.3 Overcoming the Economic Hurdles
The current and persisting economic issues with regard to 
animal damage management at earthen dams is twofold: 
first, reluctant owners need to be educated on the dangers 
of animal damages and motivated by economic examples; 
and second, funding sources for all owners need to be identified 
to assist funding of needed repairs. To begin to address 
the first consideration, a simple estimate of routine dam 
maintenance as it relates to vegetation and animal management 
(one influences the other) is given below: 
As the table indicates, the cost of routinely maintaining a 
dam is estimated at greater than $500.00 dollars per year. 
For many private dam owners, such as businesses and 
citizens, the outlay of these funds, though relatively low, 
is prohibitive. Even those dam owners with substantial 
financial resources are often overwhelmed by the costs of 
dam maintenance and repairs (WaterWebster, 2003). In 
these cases, it is important for dam owners to consider that 
neglect will eventually lead to greater costs on many levels; 
in short, dam owners cant afford to save money when it 
comes to the upkeep of their dams. Economic impacts of a 
failed dam can include:
Liability Costs of Loss of Life and Property Damage. Liability 
may be imposed on a dam owner if maintenance, 
repair, or operations were conducted in an unsafe or 
improper manner. Liability could apply to the dam owner 
as well as the company who possesses the dam and the individual 
who or company which operates and maintains the 
dam. The dam owner must take actions to ensure the dam 
functions properly so that injuries to people or property are 
avoided. This applies to foreseeable conditions or circumstances 
that can be predicted with reasonable certainty. If an 
inspection identifies problems at the dam, then an owner 
should correct them (Pennsylvania DEP, 1995). 
Clean-up Costs. The costs associated with clean-up from a 
dam failure can be tremendous, depending on the size of 
the reservoir and the amount of downstream development. 
Debris removal, sediment clean-up, and reconstruction of 
damaged infrastructure could be required. 
Loss of Dam Infrastructure and Its Revenue. Over 30% of 
the dams in the United States are used primarily for recreation 
(ASDSO, 2003). The benefit of dams to recreational 
income to the community can be in the millions of dollars 
each year, depending on the reservoir size and recreational 
opportunities available. 
Environmental Losses. Many reservoirs provide wildlife 
habitat and associated ecotourism revenue, which generates 
$59 billion annually in the United States. Communities 
often benefit from the wilderness which dams and their 
reservoirs provide. 
Economic Effect on Community. A community that 
depends on the dam for several uses (e.g., flood control, 
irrigation, water supply) will have to locate other facilities 
to serve these purposes should the dam fail or be removed. 
Alternative sources could be costly or may not be available 
as quickly as needed, resulting in an adverse social and economic 
impact on the community. 
In essence, a neglected dam can cause a cascade of adverse 
effects at the community level as well as result in liability issues 
for the dam owner. Attaching a reasonable dollar figure 
to each of the considerations above would illustrate that this 
considerable investment per year in maintenance is like paying 
an insurance premium that covers the dam owner and 
their community. 
Table 7.1
tnemeganaMnoitategeV)raeyrepeciwtgniwom(
*yllaunna0001$ot005$
oteno(noitcepsnIrenwO)raeyrepsemitowtrenwomadroftsocoN;noitcepsnisraey5ot2yreveecnonoitcepsnitsocnacreenignElanoisseforPayb005,7$dna005,3$neewtebsworrublaminagnilliF)worrubrep(
nopugnidneped003$ot001$
tuorg(dohtemriaperdnaezisworrub)ecalperdnaetavacxero.2002,AMEFnidetacidnisa,smadtsomrof*
tahtdnanoitidnocdoognisimadehtsemussaetamitsesihTnoitarepoelbatsydaerlanafopeekpugnidivorpsirenwoeht

Lessons Learned:
Maintenance of animal burrows is critical. Burrows 
should be backfilled and animals removed as soon as 
possible.
Owners should inspect their dams in a regular and thorough 
manner.
Pond levels should be monitored and safety precautions 
such as spillways and freeboard should be factored into 
design.
The second consideration presents the most current and 
widespread dilemma facing the entire dam community. 
Many dam owners conduct inspections and typical maintenance 
as required, but preventive measures and wildlife 
mitigation actions may also be required. It would seem 
that vigilant dam owners would ensure the required actions 
were forthcoming; however, this is not always the case. 
According to the workshop (FEMA, 2001) and the state 
surveys (FEMA, 2003), and as echoed in the document The 
Cost of Rehabilitating Our Nation's Dams (ASDSO, 2003), 
owners of dams in need of repair are often not able to 
finance the required actions due largely to a lack of funding 
mechanisms at the state and federal levels; dams become 
neglected and deteriorate to the point of being hazardous. 
Currently, there are only a handful of states that provide 
financial assistance in the form of loans or grants to repair 
unsafe dams, as presented in Table 7-2.
Animal Burrows Contribute to $5 Million Dam 
Breach 
Wallula, Iowa
The Iowa Beef Processors (IBP) Waste Pond was 
constructed in 1971 to store wastewater from the 
IBP Plant. When full, the pond had a surface area of 
37 acres and a maximum storage capacity of 270 
acre-feet. The pond was located on a natural drainage 
course and was impounded behind a 15-foot-high, 
1000-foot-long earthen dam. State inspections in 
1981 and 1985 discovered that the embankment was 
riddled with animal burrows. It was recommended 
that the burrows be filled and the animals removed 
from the site. Repairs were not made quickly enough, 
and the rapid melting of record snow pack coupled 
with higher than normal pond levels filled the waste 
pond and overtopped a portion of the west end of 
the dam (the dam had no emergency spillway). High 
pond levels allowed water to exit through animal 
burrows that were normally above the pond elevation. 
Uncontrolled leakage and seepage through the 
animal borrows exiting on the downstream face likely 
resulted in erosion that backcut rapidly toward the upstream 
face, eventually breaching the dam.
The estimated cost of the failure was $5 million, 
which included the cost of the five locomotives that 
were derailed downstream, environmental cleanup, 
and repair to the rail line. The cost to construct a new 
facility was several million more dollars.

Similarly, the federal government extends dam rehabilitation 
assistance through only a few programs. The combination 
of existing state and federal assistance does not approach 
the estimated $36.2 billion needed nationwide to support 
needed dam repair and rehabilitation related to wildlife 
damages and other structural integrity issues.
Table 7-2 Summary of State Dam Funding Programs 
etatSepyTdnaemaNmargorPytilibigilEtnuomAtnarG/naoLanozirA)tnargronaol(riapeRmaDotmadsenimretedreenigneetatSycnegreme-non,efilotsuoregnadebtcejorpfotsoCnaoLdnalyraMnaol(ecivreSlatnemnorivnEdnalyraM)ecnatsissagninnalpdnaetavirpdna,seitilitu,seitnuoCdehsilbatseevahtsum;spuorg,ylppusretawroftcirtsidecivresrognigderd,noitamalcerecruoserretawmrotssttesuhcassaM)stnarg(nevigemanoNroriaperrofseitinummoclacoLlavomererahslacol;tcejorpehtfo%57snoitubirtnocdnik-niebnacyesreJweNtsurTretaWnaelCdnanoitarotseRmaDtnargwen;dnufnaolgnivlover(dnuF)smaddenwo-yllapicinumrofdnufetavirp;stnemnrevogfostinulacoLstnacilppa-ocebnacsrenwotcejorpfotsoCnaoL%001otpUstnarGkroYweNtcAdnoBriAnaelC/retaWnaelC)stnarg(
ytefasmadrofseitilapicinuMstcejorp%52htiwtcejorpelbigilefo%57reppac000,003$;hctamlacoltcejorpoihOytirohtuAtnempoleveDretaWoihO)dnufnaolgnivlover(
morfetadnamrednuebtsumrenwORNDOmargorPnaoLytefaSmaDlacoL
stcirtsid,etats,tnemnrevogfostinumargorPtisopeDdekniLytefaSmaDsnoitazinagro/srenwoetavirp
tcejorpfotsoCainavlysnneP)dnufnaolgnivlover(tsevnneP,retawetsawhtiwdetaicossastcejorPretawmrotsro,ylppusretawtcejorpfotsocotpUhatUsnaol(secruoseRretaWfodraoBhatU)stnargrodetadnam;srenwomaddrazahhgiHsriaperretawronoitagirriroftnarg%59-08rofstnargrosnaol;smadylppussrenworehtonisnocsiWmargorPtnarGmaDlapicinuMRND)stnarg(
ekaldnatnemnrevogfostinulacoLstcirtsid000,002$;stnarg05-05mumixam

In conclusion, the dam community is composed of owners 
in need of education and economic understanding of the 
consequences associated with neglected dams, as well as 
those owners who are diligent in dam upkeep, but perhaps 
unable to fund the necessary repair and preventive actions. 
Even if federal, state, and local agencies can educate the 
reluctant dam owners such that they become vigilant in the 
upkeep of their dams, our nation's dams will likely continue 
to degrade without adequate funding to implement the 
sometimes perpetual animal damage repair and management 
needed.
Table 7-3. Summary of Potential Federal Programs for Dam Management
ycnegAmargorPnoitpircseDsecruoseRlarutaN,ecivreSnoitavresnoCerutlucirgAfotnemtrapeDdehsretaW619.01margorPnoitatilibaheRmorfecnatsissahtiwtliubyllanigirosmadetatilibahertstnargsedivorPmadehtfoefilehtdnetxetsumnoitatilibaheR.smargorPdehsretaWADSUotnevigsiytiroirP.stnemeriuqerytefasdnaecnamrofrepelbacilppateemdna.smaddrazahhgihsecruoseRlarutaN,ecivreSnoitavresnoCerutlucirgAfotnemtrapeDdehsretaW409.01doolFdnanoitcetorPnoitneverPtnemevorpmidehsretawtuoyrracotecnatsissalainhcetdnastnargsedivorPnisecruoserretawdnadnalehtezilitudna,poleved,tcetorptahtstcejorp.sdehsretawllams,sriaffAnaidnIfouaeruBroiretnIehtfotnemtrapeDsmaDfoytefaS560.51sdnaLnaidnInostnemnrevoglabirtnaidnIdezingoceryllaredefotstnemyapceridsedivorPsmadfoytirgetnilarutcurtsehtevorpmiotnoitazinagronaciremAevitaNdna.sdnalnaidnInoycnegremElaredeF,ycnegAtnemeganaMdnalemoHfotnemtrapeDytiruceSretsasiD-erP740.79)MDP(noitagitiMdrazahevitceffe-tsocrofseitinummocdnasetatsotstnargsedivorPdna,margorpnoitagitimevisneherpmocafotraperatahtseitivitcanoitagitim.ytreporpfonoitcurtseddnaegamaddna,efilfossol,seirujniecudertaht:fignidnufMDProfelbigileebyamstcejorpnoitatilibaherdnariapermaDycnegremElaredeF,ycnegAtnemeganaMdnalemoHfotnemtrapeDytiruceSlanoitaN013-701.L.PytiruceSdnaytefaSmaD2002fotcA.smargorpytefasmadetatsotraeyhcaedetnargerasdnuFdnaecnarusnIlaredeF,noitartsinimdAnoitagitiMycnegremElaredeFycnegAtnemeganaMmaDlanoitaN055.38maD(margorPytefaSecnatsissAetatSytefaS)margorPmadetatsot)stnargtcejorpfomrofehtni(raeyhcaedetubirtsiderasdnuF.smargorpytefas
 The project has a high benefit-cost ratio; 
 There is a high risk of dam failure or dam failure would result in 
significant damages; and 
 The project is consistent with State funding priorities. 

Dam Owners Manual to Animal Intrusion of Earthen Dams
102
8.0 References
Association of State Dam Safety Officials. 2001. ASDSO West 
Region Technical Seminar. Plant and Animal Penetrations 
of Earthen Dams. Dr. B. Dan Marks, P.E.; Dr. Bruce 
Tschantz, P.E., and Mr. David K. Woodward, M.S., editors.
Association of State Dam Safety Officials. 2002. A Technical 
Manual on the Effects of Tree and Woody Vegetation 
Root Penetrations on the Safety of Earthen Dams.
Association of State Dam Safety Officials. 2003. The Cost 
of Rehabilitating our Nations Dams: A Methodology, 
Estimate & Proposed Funding Mechanisms.. 
Barnes, Thomas G. 1991. Managing Beaver Problems in 
Kentucky. University of Kentucky College of Agriculture. 
http://www.ca.uky.edu/agc/pubs/for/for50/for50.
htm. Site accessed December 8, 2003.
Benyus, Janine M. 1989. The Field Guide to Wildlife Habitats 
of the Eastern United States. Simon & Schuster Inc.: 
New York, New York.
Colorado State University Cooperative Extension. 2003. 
Managing Pocket Gophers. www.ext.colostate.edu/
pubs/natres/06515.html. Site accessed December 3, 
2003.
Connecticut Department of Environmental Protection. 1999. 
Muskrat. http://dep.state.ct.us/burnatr/wildlife/factshts/
muskrat.htm Site accessed December 12, 2003. 
Enchanted Forest Nature Sanctuary. 2003. Gopher Tortoises. 
http://nbbd.com/godo/ef/gtortoise/ Site accessed 
October 31, 2003. 
Federal Emergency Management Agency. 2000. Report on 
Specialty Workshop #1. Plant and Animal Impacts on 
Earthen Dams. Prepared by the Association of State Dam 
Safety Officials; Lexington, Kentucky.
Federal Emergency Management Agency. 2003. Dam Owners 
Guide to Plant Intrusion of Earthen Dams. Prepared 
by URS Group, Inc.

103
Chapter 8. References
Gopher Tortoise Council. 2001. The Gopher Tortoise: A Species 
in Decline. http://www. gophertortoisecouncil.
org/tortoise.htm. Site visited October 31, 2003; and 
Novermber 4, 2004.
Indiana Department of Natural Resources. 2003. Dam 
Safety: Rodent Control. Fact Sheet 03-14.
Indiana Department of Natural Resources. 2003. Division of 
Water. Indiana Dam Safety Inspection Manual.
Michigan State University Extension. 1998. Aquatic Pest 
Management: A Training Manual for Commercial Pesticide 
Applicators (Category 5). http://www.msue.msu.
edu/msue/imp/modet/morefile/e-2437.pdf. Site accessed 
December 12, 2003. 
New York State Department of Environmental Conservation 
(DEC). 2002. Handout #5 Modifying Sites to Discourage 
Beaver Occupation. http://www.dec.state.ny.us/
website/dfwmr/wildlife/beaver/handout5.htm. Site 
accessed December 8, 2003. 
Niering, William A. 1985. Wetlands. Chanticleer Press, Inc. 
New York.
North Carolina State University. 1994. Beavers. http://www.
ces.nscu.edu/nreos/wild/wildlife/wdc/beavers.html. 
Site accessed December 8, 2003. 
__2003. Wildlife. http://h2osparc.wq.ncsu.edu/wetland/
aqlife/wildlife.html. Site accessed October 31, 2003. 
Ohio Department of Natural Resources (DNR). 1999. Dam 
Safety: Rodent Control. http://www.dnr.state.oh.us/
water/pubs/fs_div/fctsht27.htm. Site accessed November 
11, 2003. 
Peckarsky, Barbara L., Pierre R. Fraissinet, Marjory A. Penton, 
and Don J. Conklin Jr. 1990. Freshwater Macroinvertebrates 
of Northeastern North America. Cornell University 
Press: Ithaca, New York. 
Pehling, Dave. 2003. Principles of Vertebrate Pest Management. 
http://snohomish.wsu.edu/vertchap.htm. Site 
accessed December 10, 2003.
Pennsylvania Department of Environmental Protection 
(DEP). 1995. Liability and Responsibility of Dam Owners. 
3200-FS-DEP-1954. http://www.dep. state.pa.us/
dep/deputate/watermgt/WE/FactSheets/Dam/fs1954.
htm. Site accessed December 8, 2003. 
Porter, Mike. 2003. Beaver Damage Preventable With Appropriate 
Techniques. Noble Foundation. http://www.
noble.org/Ag/Wildlife/BeaverDamagePreventable/ Site 
accessed December 8, 2003. 
Salisbury, David. 1998. $20 Billion Needed to Ensure Safety 
of Nations Dams, Engineer Estimates. Stanford Online 
Report. http://news-service.stanford.edu/news/
march11/damsafety.html. Site accessed November 11, 
2003. 
Smith, Diana. 2003. University of Nebraska. Personal 
Communication with E. Zamensky. URS Corporation. 
October 21. 
__2004. University of Nebraska. Personal Communication 
with E. Zamensky. URS Corporation. Novermber 22.
South Carolina Department of Natural Resources. 2003. 
The Muskrat in South Carolina: Biology, Management 
& Control. www.dnr.state.sc.us/wild/img/muskrat.pdf. 
Site accessed November 21, 2003. 
Texas Wildlife Management Damage Service. 1998. Controlling 
Badger Damage. Publication L-1923. 
U.S. Department of Agriculture. 1991. Prevention and Control 
of Animal Damage to Hydraulic Structures. 
U.S. Fish and Wildlife Service. 2002a. ESA Basics. http://endangered.
fws.gov/pubs/esa%20basics.pdf. Site accessed 
November 3, 2003.
__2002b. Migratory Bird Permits. http://birds.fws.gov/Permits-
Fact-Sheet.pdf. Site accessed November 3, 2003.
U.S. Forest Service. 1994. Animal Damage Management 
Handbook. Pacific Northwest Research Station.
University of Arizona. 1997. Ant Information. http://insected.
arizona.edu/antinfo.htm. Site accessed November 
25, 2003.

University of Florida Cooperative Extension Service. 2002. 
Ants. http://edis.ifas.ufl.edu/BODY_IG080. Site accessed 
November 25, 2003. 
University of Georgia Cooperative Extension Service. 1993. 
Controlling Fire Ants in Urban Areas. Bulletin 1068. 
http://www.ces.uga.edu/pubcd/b1068-w.html. Site 
accessed December 4, 2003.
University of Georgia. 2000. Managing Imported Fire Ants 
in Urban Areas. Bulletin 1191. http://www.ces.uga. 
edu/pubcd/B1191.htm. Site accessed December 4, 
2203.
University of Michigan Museum of Zoology. 2002. Branta 
Canadensis. http://animaldiversity.ummz.umich.
edu/accounts/branta/b._canadensis$narrative.html Site 
accessed November 25, 2003. 
University of Missouri Extension. 1999. Controlling Nuisance: 
Muskrats. Agricultural publication MX0136. 
http://muextension.missouri.edu/explore/miscpubs/
mx0136.htm. Site accessed June 2, 2003. 
University of Nebraska. 1994a. Prevention and Control of 
Wildlife Damage.
__1994b. Animal Damage Management Handbook. General 
Technical Report PNW-GTR-332. 
__2003. Fact Sheet: Managing Canada Goose Damage. 
University of New Hampshire Cooperative Extension. 1997. 
Beavers and Their Control. http://ceinfo.unh.edu/Forestry/
Documents/beavers.pdf. Site accessed December 
12, 2003. 
Virginia Cooperative Extension. 2000. Managing Wildlife 
Damage: Beavers (Castor Canadensis). Publication 
Number 420-202. http://www.ext.vt.edu/pubs/wildlife/
420-202/420-202.html. Site accessed December 8, 
2003. 
Virginia Dam Safety Program. 2003. www.dcr.state.va.us/
sw/damrdnts.htm. Site accessed June 2, 2003.
Virginia Tech. 2001a. The Control of Burrowing Crayfish in 
Ponds. Publication Number 420-253. http://www.ext.
vt.edu/pubs/fisheries/420-253/420-253.html. Site accessed 
November 17, 2003.
__2001b. Managing Wildlife Damage: Canada Goose (Branta 
canadensis). Publication Number 420-203. http://
www.ext.vt.edu/pubs/wildlife/420-203/420-203.
html. Site accessed November 25, 2003. 
Washington State Department of Ecology. 2003. Iowa Beef 
Processors Waste Pond. http://www.ecy.wa.gov/programs/
wr/dams/iowa.html. Site accessed November 
13, 2003.
Water Webster. 2003. Americas Crumbling Infrastructure: 
$36 billion needed to fix nations dams; $10.1 billion 
for most critical structures. http://www.waterwebster.
com/Assn.ofStateDamSafetyOfficialsNov.102003.htm. 
Site accessed December 8, 2003. 
Wilson, Judy M. 2001. Beavers in Connecticut: Their Natural 
History and Management. Connecticut Department of 
Environmental Protection. 
Witmer, Gary W., Rodney D. Sayler, and Michael J. Pipas. 
1995. Repellant Trial to Reduce Reforestation Damage 
by Pocket Gophers, Deer, and Elk. In: Proceedings of the 
Second DWRC Special Symposium: pp. 321-332.

105
Appendix A. State Wildlife Agency Contacts
Appendix A
State Wildlife Agency Contacts
Alabama Department of Conservation and Natural Resources
Division of Wildlife and Freshwater Fisheries
64 N. Union Street
Montgomery, Alabama 36130
(334) 242-3469
Alaska Department of Fish and Game
PO Box 25526
Juneau, Alaska 99802-5526
(907) 465-4100
Arizona Game and Fish Department
2221 W. Greenway Road
Phoenix, Arizona 85023-4399
(602) 942-3000
Arkansas Game and Fish Commission
Natural Resources Drive
Little Rock, Arkansas 72205
(501) 223-6359
California Department of Fish and Game
1416 Ninth Street
Sacramento, California 95814
(916) 445-0411
Colorado Department of Natural Resources
Division of Wildlife
6060 Broadway 
Denver, Colorado 80216
(303) 297-1192 
Connecticut Department of Environmental Protection
Bureau of Natural Resources, Wildlife Division
79 Elm Street
Hartford, Connecticut 06106-5127
(860) 424-3011
Delaware Department of Natural Resources and 
Environmental Control
Division of Fish and Wildlife
89 Kings Highway
Dover, Delaware 19901
(302) 739-5297
Florida Fish and Wildlife Conservation Commission
620 South Meridian Street
Tallahassee, Florida 32399-1600
(850) 921-5990 

Dam Owners Manual to Animal Intrusion of Earthen Dams
106
Georgia Department of Natural Resources
Wildlife Resources Division
2070 U.S. Highway 278, S.E.
Social Circle, Georgia 30025
(770) 918-6400
Hawaii Department of Land and Natural Resources
Division of Forestry and Wildlife
1151 Punchbowl Street, Room 325
Honolulu, Hawaii 96813
(808) 587-0166
Idaho Department of Fish and Game
600 S. Walnut, PO Box 25
Boise, Idaho 83707
(208) 334-3700
Illinois Department of Natural Resources
1 Natural Resources Way
Springfield, Illinois 62702-1271
(217) 782-6302
Indiana Department of Natural Resources
Division of Fish and Wildlife
402 W. Washington Street, Room W273 
Indianapolis, Indiana 46204
(317) 232-4080
Iowa Department of Natural Resources
Wildlife Bureau
Henry A. Wallace Building 
502 E. 9th Street
Des Moines, Iowa 50319-0034 
(515) 281-5918 
Kansas Department of Wildlife and Parks
14639 W. 95th
Lenexa, Kansas 66215 
(913) 894-9113
Kentucky Department of Fish and Wildlife
1 Game Farm Road
Frankfort, Kentucky 40601
(800) 858-1549
Louisiana Department of Wildlife and Fisheries
2000 Quail Drive
Baton Rouge, Louisiana.70808
(225) 763-3557
Maine Department of Inland Fisheries and Wildlife
284 State Street
41 State House Station
Augusta, Maine 04333-0041
(207) 287-8000
Maryland Department of Natural Resources
Wildlife and Heritage Service
Tawes State Office Building, E-1 
580 Taylor Avenue 
Annapolis, Maryland 21401
(410) 260-8540 
Massachusetts Department of Fisheries, Wildlife and 
Environmental Law Enforcement
Division of Fisheries & Wildlife
251 Causeway Street, Suite 400
Boston, Massachusetts 02114-2152
(617) 626-1590
Michigan Department of Natural Resources
Wildlife Division
Mason Building, Fourth Floor
PO Box 30444
Lansing, Michigan 48909-7944
(517) 373-1263
Minnesota Department of Natural Resources
500 Lafayette Road
St. Paul, Minnesota 55155-4040
(651) 296-6157
Mississippi Department of Wildlife, Fisheries and Parks
1505 Eastover Drive
Jackson, Mississippi 39211-6374
(601) 432-2400
Missouri Department of Conservation
2901 W. Truman Boulevard
Jefferson City, Missouri 65109
(573) 751-4115
Montana Fish, Wildlife & Parks
1420 East Sixth Avenue
Helena, Montana 59620-0701
(406) 444-2535

Nebraska Game and Parks Commission
2200 North 33rd Street
Lincoln, Nebraska 68503
(402) 471-0641
Nevada Department of Wildlife
1100 Valley Road
Reno, Nevada 89512
(775) 688-1500
New Hampshire Fish and Game Department
Wildlife Division
11 Hazen Drive
Concord, New Hampshire 03301
(603) 271-2461
New Jersey Department of Environmental Protection
Division of Fish and Wildlife
PO Box 400
Trenton, New Jersey 08625-0400
(609) 292-2965
New Mexico Department of Game and Fish
PO Box 25112
Santa Fe, New Mexico 87507
(800) 862-9310
New York State Department of Environmental Conservation
Division of Fish, Wildlife and Marine Resources
625 Broadway
Albany, New York 12233-4750
(518) 402-8919
North Carolina Wildlife Resources Commission
Archdale Building
512 N. Salisbury Street
Raleigh, North Carolina 27604-1188
(919) 733-7191
North Dakota Game and Fish Department
100 N. Bismarck Expressway 
Bismarck, North Dakota 58501-5095
(701) 328-6300
Ohio Department of Natural Resources
Division of Wildlife
1840 Belcher Drive 
Columbus, Ohio 43224-1300
(800) 945-3543
Oklahoma Department of Wildlife Conservation
1801 N. Lincoln
Oklahoma City, Oklahoma 73105
(405) 521-3851
Oregon Department of Fish and Wildlife
3406 Cherry Avenue N.E.
Salem, Oregon 97303-4924
(503) 947-6000
Pennsylvania Game Commission
2001 Elmerton Avenue
Harrisburg, Pennsylvania 17110-9797
(717) 787-4250
Rhode Island Department of Environmental Management
Division of Fish and Wildlife
4808 Tower Hill Road
Wakefield, Rhode Island 02879
(401) 789-3094
South Carolina Department of Natural Resources
Wildlife and Freshwater Fisheries Division
PO Box 167
Columbia, South Carolina 29202
(803) 734-3886
South Dakota Department of Game, Fish, and Parks
Wildlife Division
523 East Capitol Avenue
Pierre, South Dakota 57501-3182
(605) 773-3381
Tennessee Wildlife Resources Agency
Wildlife Division
Ellington Agricultural Center
PO Box 40747
Nashville, Tennessee 37204
(615) 781-6610
Texas Parks and Wildlife Department
4200 Smith School Road
Austin, Texas 78744
(800) 792-1112 
Utah Department of Natural Resources
Division of Wildlife Resources
1594 W. North Temple
Salt Lake City, Utah 84114
(801) 538-4700

Vermont Agency of Natural Resources
Fish and Wildlife Department
103 South Main Street 
Waterbury, Vermont 05671-0501
(802) 241-3700
Virginia Department of Game and Inland Fisheries
4010 West Broad Street
Richmond, Virginia 23230
(804) 367-1000 
Washington Department of Fish and Wildlife
Natural Resources Building 
1111 Washington Street, SE
Olympia, Washington 98501
(360) 902-2200
West Virginia Division of Natural Resources
Wildlife Resources
State Capitol Building 3, Room 812
Charleston, West Virginia 25305
(304) 558-2771
Wisconsin Department of Natural Resources
101 South Webster Street
Madison, Wisconsin 53703
(608) 266-2621
Wyoming Game and Fish Department
5400 Bishop Boulevard
Cheyenne, Wyoming 82006-0001
(307) 777-4600

109
Appendix B. Association of State Dam Safety Officials Contact Information
Appendix B
Association of State Dam Safety 
Officials Contact Information 
Association of State Dam Safety Officials 
450 Old Vine Street, 2nd Floor 
Lexington, KY 40507-1544 
Phone: 859-257-5140 
Fax: 859-323-1958 
E-Mail: info@damsafety.org 
Web: www.damsafety.org
Lori Spragens, Executive Director lspragens@damsafety.org 
Susan Sorrell, Meetings & Membership Director 
sasorrell@damsafety.org 
Sarah Mayfield, Information Specialist smayfield@damsafety.
org 
Maureen Hogle, Administrative Database Specialist 
mhogle@damsafety.org

For information on obtaining a print, CD, or online 
version of this publication or the technical manual go 
to www.fema.gov/fima/damsafe