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05 - DEFINITIONS
30. Spillway Design Flood (SDF). The selected inflow design flood (hydrograph) based
on the hazard-potential classification and administrative classification of the dam. The SDF is
the recommended spillway design flood (table 1), unless an exception has been approved by the
Regional Director of Engineering.
Table 1
RECOMMENDED SPILLWAY DESIGN FLOOD
Hazard potential
Size class
Spillway design flood
High
A
B
C
D
PMF
PMF
1/2 PMF to PMF
100 yr. to 1/2 PMF
Moderate
A
B
C
PMF
1/2 PMF to PMF
100 yr. to 1/2 PMF
Low
A
B
C
1/2 PMF to PMF
100 yr. to 1/2 PMF
50 yr. to 100 yr.
Emergency spillways for all dams will be designed at least a 100-year recurrence event with no
freeboard.
This criteria is established to reduce the potential for resource damage. Even a small dam can
cause considerable watershed damage when it fails. The cost of an earth spillway designed for
the 100-year, no-freeboard flood will normally be little more than the cost of a spillway designed
for the 25- or 50-year flood with a reasonable freeboard.
In cases where the resource damage potential will not justify the additional expense, obtain
approval for a smaller design flood from the Regional Engineer. The approval will be based
upon a request fully documenting the cost estimates and risk of resource damage (exhibit 1).
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Exhibit 1
CALCULATED RISK DIAGRAM 1/
1000
|
|
|
|
|
7
|
15
|
30
|
70
800
600
500
400
300
200
150
100
75
50
25
10
5
2
1
1
2
5
10
20
DESIRED LIFETIME, Td (Years)
1 After U.S. Weather Bureau TP 40
50
100
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08 - REFERENCES.
The listed publications are not all inclusive, but they are representative of Federal agency and
other publications available relative to water storage and transmission structures.
1. Federal Guidelines for Dam Safety. These guidelines outline good management
practices for dam safety for all Federal agencies responsible for the planning, design,
construction, operation, or regulation of dams. They are not intended as standards for
technology of dams. The basic principles of the guidelines apply to all dams. Reasonable
judgments need to be made in their application commensurate with each dam's size, complexity,
and hazards. The information in the guidelines is subject to change as the state of the science
develops.
2. Engineering Foundations Conference Proceeding published by the American Society
of Civil Engineers:
a. Inspection, Maintenance and Rehabilitation of Old Dams, 1973.
b. Foundations For Dams, 1974.
c. Safety of Small Dams, 1974.
d. Responsibility and Liability of Public and Private Interest on Dams, 1975.
e. The Evaluation of Dam Safety, 1976.
3. Joint ASCE/USCOLD publications, published by the American Society of Civil
Engineers:
a. Arch Dams Embankment Dams & Concrete Gravity Dams, 1967.
b. Lessons From Dam Incidents, USA, 1975.
4. BUREAU OF RECLAMATION
a. Earth Manual, Second Edition, 1974
b. Ground Water Manual, First Edition, 1977.
c. Design of Gravity Dams, First Edition, 1976.
d. Design of Arch Dams, First Edition, 1977.
e. Design of Small Dams, Second Edition, 1973.
f. Manual for Safety Evaluation of Existing Dams, Preliminary, 1977.
g. Design of Small Canal Structures, First Edition, 1974.
h. Safety Evaluation of Existing Dams (SEED) Manual, 1980.
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5. CORPS OF ENGINEERS
a. Engineering Manuals (EM):
EM 1110-2-1602 Hydraulic Design of Reservoir Outlet Structures
-1603 Hydraulic Design of Spillways
-1902 Stability of Earth & Rockfill Dams
-1908 Instrumentation of Earth and Rockfill Dams
-1911 Construction Control for Earth and Rockfill Dams
-2200 Gravity Dam Design
-2300 Earth and Rockfill Dams General Design and Construction
Considerations
-1601 Hydraulic Design of Flood ControlChannels
b. Engineering Reports (ER):
ER 1110-2-1450 Hydrologic Frequency Estimates
-1806 Earthquake Design and Analysis for Corps of Engineers Dams
6. Soil Conservation Service, National Engineering Handbooks.
7. Technical Publication, National Weather Service.
8. Forest Service
a. "Guide for Safety Evaluation and Periodic Inspection of Existing Dams (EM7570-1)," 1980, U.S. Forest Service and Soil Conservation Service. Although this
book is out of print and will not be reprinted, any copies presently in circulation may
be used. The information is still valid.
b. "Operation and Maintenance Inspection for Dams (EM-7570-2)," 1981, USDA
Forest Service. Although this book is out of print and will not be reprinted, any
copies presently in circulation may be used. The information is still valid.
9. GENERAL
a. Seepage, Drainage, and Flow Nets, Cedergreen, 1977, Wiley.
b. Embankment - Dam Engineering, Casagrande, 1973, Wiley-Interscience.
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c. Earth and Earth-Rock Dams, Sherard, Woodward, Gizienski and Clevenger, 1963,
Wiley.
d. Handbook of Hydraulics, King and Brater, Fifth Edition, 1963, McGraw-Hill.
e. Open-Channel Hydraulics, Chow, 1959, McGraw-Hill.
f. Fundamentals of Earthquake Engineering, Newmark and Rozenbleuth, 1971,
Prentice-Hall.
g. "Glossary of Geology and Related Sciences," American Geological Institute.
h. Standards of the American Society for Testing and Materials, as cited.
i. Standards of the American Water Works Association, as cited.
j. "Subsurface Exploration and Sampling of Soils for Civil Engineering Purposes,"
Hvorslev, Engineering Foundation, New York, New York.
k. Standards of the American Concrete Institute, as cited.
l. Standards of United States of America Standards Association.
The technical principles, practices, and guidelines for existing dams follow those established for
the planning, design, and construction of new structures.
Users should refer to FSM 2710, 2720, and 2780 for additional information on structures under
special-use authorization, and to FSM 2770 for those licensed by the Federal Energy Regulatory
Commission.
These references and others, if appropriate, should be available and kept current in each
engineering office where work of the nature described in this handbook is performed.