Pocket Safety Guide for Dams and Impoundments

80 Pages·2016·8.66 MB·English

Pocket Safety Guide for
Dams and Impoundments
FEMA P-911 / October 2016
FEMA
This document has been developed from the FEMA P-911 Pocket Safety Guide for Dams and

Impoundments developed by the U.S. Forest Service (USFS) and

Federal Emergency Management Agency (FEMA).

It was revised in cooperation with 6 agencies of the Department of the Interior

(Bureau of Indian Affairs, Bureau of Land Management, Bureau of Reclamation, National Park Service,

Office of Surface Mining, Reclamation and Enforcement and US Fish and Wildlife Service) as part of the

Department of the Interior’s Enterprise Architecture Project “Reduce Dam Safety Risk”.

Further review was provided by the National Dam Safety Review Board and the

Association of State Dam Safety Officials
Pocket Safety Guide for Dams and Impoundments
October 2016
The Federal Emergency Management Agency (FEMA) has developed
this information for the guidance of its employees, its contractors, and
its cooperating Federal and State agencies and is not responsible
for the interpretation or use of this information by anyone except
its own employees. The use of trade, firm, or corporation names in
this document is for the information and convenience of the reader
and does not constitute an endorsement by FEMA of any product or
service to the exclusion of others that may be suitable. FEMA prohibits
discrimination in all its programs and activities on the basis of race,
color, national origin, age, disability, and where applicable, sex, marital
status, familial status, parental status, religion, sexual orientation,
genetic information, political beliefs, reprisal, or because all or part of
an individual’s income is derived from any public assistance program.
(Not all prohibited bases apply to all programs.) FEMA is an equal
opportunity provider and employer.
Lily Lake Dam, Rocky Mountain National Park, Colorado.
Photograph by Kevin Gagner.
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Acknowledgements
○ Martin McCann, U.S. Department of Agriculture, Forest Service,
FEMA would like to thank the following people and organizations for Southern Region
assistance in developing and reviewing this guide:
○ Sue Peterson, U.S. Department of Agriculture, Forest Service,
● Developing the original guide: Eastern Region

○ James Scott Groenier, Project Leader for the USDA Forest Service
○ Steve Romero, U.S. Department of Agriculture, Forest Service,
Pocket Safety Guide for Dams and Impoundments, January 2012,
Pacific Southwest Region
assisted by the following individuals and organizations:
○ Charles Showers, U.S. Department of Agriculture, Forest Service,
○ Terri Anderson, U.S. Department of Agriculture, Forest Service,
Missoula Technology and Development Center
Bitterroot National Forest

○ Lori Spragens, Association of State Dam Safety Officials
○ Brad Campbell, U.S. Department of Agriculture, Forest Service,

Boise National Forest
○ Nate Tatum, U.S. Department of the Interior, National Park Service
○ James Demby, U.S. Department of Homeland Security, Federal
○ Association of State Dam Safety Officials
Emergency Management Agency, National Dam Safety Program

○ U.S. Department of Agriculture, U.S. Forest Service
○ Cliff Denning, U.S. Department of Agriculture, Forest Service,

Eastern Region
○ U.S. Department of Homeland Security, Federal Emergency
Management Agency, National Dam Safety Program
○ Brad Iarossi, U.S. Department of the Interior, U.S. Fish and

Wildlife Service
○ U.S. Department of the Interior, U.S. Fish and Wildlife Service
● Revising the guide:
● Figures 1, 2, 14, and 15: Ed Jenne,
● Members of the 2013 – 2014 U.S. Department of the Interior Missoula, Montana
Reduce Dam Safety Risk team:
● Figures 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39,
○ Mark Baker, National Park Service
41, 43, 45, 47, 53, and 55 were adapted from the
○ Jessica Bush, Bureau of Land Management 1986 FEMA publication “Dam Safety: An Owner’s
Guidance Manual,” developed by the Colorado
○ Scott Goss, Bureau of Indian Affairs
Division of Disaster Emergency Services
○ Dave Hibbs, U.S. Fish and Wildlife Service
○ Stacy Johnson, Bureau of Reclamation
○ Stefanie Self, Office of Surface Mining,
Reclamation and Enforcement
○ Jade Soddell, Bureau of Reclamation
○ Jay Stateler, Bureau of Reclamation
○ Mike Vail, Bureau of Indian Affairs
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Contents Sinkholes..........................................................................................................24

Slide, Slump or Slip.........................................................................................26

Acknowledgements..............................................................................................ii
Transverse Cracking........................................................................................28

Contents..............................................................................................................iv
Longitudinal Cracking.......................................................................................30

Introduction...........................................................................................................1
Rodent Activity and Animal Impact...................................................................32

Responsibilities and Liability.................................................................................2
Trees or Obscuring Vegetation.........................................................................34

Embankment Dam Diagram.................................................................................3
Surface Erosion................................................................................................36

Noteworthy Observations at an Embankment Dam............................................4
Deteriorated or Missing Riprap.........................................................................38

Concrete Gravity Dam Diagram...........................................................................5
Livestock and Cattle Traffic..............................................................................40

Concrete Arch Dam Diagram...............................................................................7
Low Area in the Crest of a Dam.......................................................................42

Concrete Buttress Dam Diagram.........................................................................9
Failure of Concrete or Rock Outfall (Energy Dissipation) Structures...............44

Concrete Masonry Dam....................................................................................11
Outlet Releases Eroding the Toe of the Dam .................................................46

Noteworthy Observations at a Concrete Dam..................................................12
Concrete or Masonry Dam Problems..................................................................48

Outlet Structures................................................................................................13
Cracking, Opening/Closing or Offsets at Joints, or
Gate Valve........................................................................................................13
Apparent Deformations...................................................................................48

Drop Inlet Riser.................................................................................................14
Deterioration of Structural Materials..................................................................50

Spillway Overview.............................................................................................15
Spillway Problems...............................................................................................52

Embankment Dam Problems.............................................................................16
Excessive Vegetation or Debris in the Spillway Channel or Around
Excessive Quantity and/or Muddy Seepage Water Exiting the Inlet...........................................................................................................52

From a Point.............................................................................................16
Erosion of Unlined Spillway Channels..............................................................54

Seepage Water Exiting From a Point Adjacent to the Outlet Pipe...................18
Resources.......................................................................................................... 56

Seepage Water Exiting as a Boil Downstream of the Dam.............................20 Web Sites........................................................................................................... 57

Seepage Water Exiting at the Abutment Contact.............................................22
Useful Terms.......................................................................................................58
Introduction Hazard potential classification—A system that
categorizes dams according to the degree of adverse
This “Pocket Safety Guide for Dams and incremental consequences from their failure or misoperation
that does not reflect in any way on their current condition (their
Impoundments” was developed for dam owners,
safety, structural integrity, or flood routing capacity), and that
inspectors and other people as a quick reference
includes the following categories:
when assessing dams and impoundments. For
in-depth discussion, please refer to the technical • High hazard potential—loss of one or more human life
manuals and guides available from FEMA at: is probable
http://www.fema.gov/technical-manuals-and-guides.
• Significant hazard potential—no probable loss of
human life but possible economic loss, environmental
Dam—Any artificial barrier of at least a minimum size,
damage, disruption of lifeline facilities, or other impacts
including appurtenant works, that impounds or diverts water
or liquid-borne solids on a temporary or long-term basis (for a
• Low hazard potential—no probable loss of human life
full definition see FEMA 93). The information contained in this
and low economic and/or environmental losses (typically
document is also applicable to impoundments.
limited to the property of the dam owner).
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Various Federal and State agencies may have different Owners can be fiscally and criminally liable for any failure
definitions for the dams over which they have jurisdiction. of a dam and all damages resulting from its failure. Any
Please refer to your agency or State dam regulatory uncontrolled release of the reservoir resulting from a dam
requirements for direction. failure or uncontrolled release can have a devastating effect
on persons, property, and the environment.
Responsibilities and Liability
This guide is designed for a wide audience. The
The owner is responsible for the operation and recommended action taken by individuals will be determined
maintenance of a safe dam. Maintaining a safe dam is a by their expertise with dam maintenance. Inexperienced
key element in preventing failure and limiting the liability individuals should photograph suspected problem(s) and
that an owner could face. The extent of an owner’s liability report them promptly to the dam owner or operator.
varies from State to State and depends on statutes and
case law precedents. Federally owned and regulated dams When you become aware of any unusual conditions that
are subject to the laws, regulations and guidelines of the seem critical or dangerous to a dam, report them immediately
owner agency. to the appropriate Federal or State agency official.
Embankment

Dam Diagram

Figure 1 – Typical
dam diagram
showing common
terms.
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Noteworthy
Observations
at an
Embankment
Dam
Figure 2.