2015 National Dam Safety Program Technical Seminar No. 22:
Dam Breach Modeling
and Consequence Assessment
Overview of Failure Modes
Jay N. Stateler
Embankment
Dams
Riprap
Slope
Protection
Earthfill
Foundation Soil
Riprap
Slope
Protection
Earthfill Zones
Toe
Drain
Filters
Foundation Soil
Grout Curtain
Foundation Rock
Potential
Failure Mode
• Seepage through
dam
• Erodes earthfill
• Carries earthfill
downstream
• Eventually
breaches dam
Riprap
Slope
Protection
Earthfill
Foundation Soil
Riprap
Slope
Protection
Earthfill Zones
Toe
Drain
Filters
Foundation Soil
Grout Curtain
Foundation Rock
Hadlock Pond
New York
Constructed: 1896
Modified: 2004-2005
Failed: July 2, 2005
Seepage Failure
0 Fatalities
Baldwin Hills Dam
Los Angeles, California
Constructed: 1947-1951
Failed: December 11, 1963
Seepage Failure
5 Fatalities
San Francisco Dam
New Mexico
Constructed: 1960’s
Failed: May 24, 2003
Flood – Seepage Failure
No Fatalities
Delhi Dam, Iowa
Constructed: 1929
Failed: July 24, 2010
Flood – Some overtopping,
but failed due to seepage
0 Fatalities
Potential
Failure Mode
• Seepage through
dam
• Erodes earthfill
• Carries earthfill
downstream
• Eventually
breaches dam
• Filter lets water
through, but not
earthfill carried by
seepage
• Stops failure mode
development
Riprap
Slope
Protection
Earthfill
Foundation Soil
Riprap
Slope
Protection
Earthfill Zones
Toe
Drain
Filters
Foundation Soil
Grout Curtain
Foundation Rock
Potential
Failure Mode
• Seepage through
foundation soil
• Erodes soil
• Carries soil to a
downstream exit
point
• Eventually creates
a dam breach
Riprap
Slope
Protection
Earthfill
Foundation Soil
Riprap
Slope
Protection
Earthfill Zones
Toe
Drain
Filters
Foundation Soil
Grout Curtain
Foundation Rock
Arthur V. Watkins Dam
Constructed: 1958-1964
Nearly Failed: November, 2006
Seepage
20 feet high
Foundation soil
deposits in South
Drain
Potential
Failure Mode
Riprap
Slope
Protection
Earthfill
• Seepage through
foundation soil
• Cutoff trench, grout
curtain, cutoff wall,
etc. limit seepage
through foundation
• Downstream filters
and toe drain collect
(and filter seepage)
• Potential for failure
mode development
is reduced
Foundation Soil
Riprap
Slope
Protection
Earthfill Zones
Toe
Drain
Filters
Cutoff Trench
Grout Curtain
Foundation Soil
Foundation Rock
Into Coarse Layers in Foundation Soil
Potential
Failure Mode
• Seepage carries
earthfill into
foundation
• Erodes earthfill
• Carries earthfill
downstream
• Eventually breaches
dam
Into Joints, Openings, Etc. in Foundation Rock
Teton Dam, Idaho
Constructed: 1975
Failed: June 5, 1976
Seepage Failure –
During first filling
11 Fatalities
Quail Creek Dike
Constructed: 1984
First Filling: 1985
Failed: January 1, 1989
Seepage Failure –
During first filling
No Fatalities
Into Coarse Layers in Foundation Soil
Potential
Failure Mode
• Seepage carries
earthfill into
foundation
• Filter protects against
earthfill being carried
by seepage into
foundation soil
• Foundation treatment
seals openings in rock
– no seepage into rock
Filter
Protection
Into Joints, Openings, Etc. in Foundation Rock
Foundation Treatment
(slush grouting, dental
concrete, etc.)
Potential
Failure Mode
• Seepage along
conduits through dam
embankment
• Erodes earthfill
• Carries earthfill
downstream
• Breaches dam
Filter material
needs to be
completely wrapped
around the conduit –
stops development
of the failure mode
Lawn Lake Dam
Colorado
Constructed: 1903
Failed: July 15, 1982
Seepage
3 Fatalities
Isabel Myron Dam
Colorado
Constructed: Unknown
Failed: 1978
Wind  Tree Toppling
 Overtopping (?)
 or Seepage (?)
0 Fatalities (believed)
Slope Instability
Potential
Dam overtopping in a flood
Failure Mode • The capacity of the spillway(s) is
Embankment
Dams
exceeded by flood flows
• Water flows over the dam crest
• The overtopping flow erodes the
dam embankment
• Dam breaches
Auxiliary
spillway
Rainbow Dam
Michigan
Failed: 1986
Flood - Overtopping
Erosion Begins
Dam is Breached
Ka Loko Dam
Hawaii
Constructed: 1890
Failed: March 14, 2006
Flood – Overtopping
7 Fatalities
Brazil
Failed: 1980’s
Flood – Overtopping
Spillway gates not opened
Noppikoski Dam, Sweden
Constructed: Not known
Failed: September 6, 1985
Flood – Overtopping – Could not
remove stoplogs in time
0 Fatalities
El Guapo Dam
Venezuela
Failed: December 16, 1999
Spillway
failure in
a flood
event
Potential
Failure Mode
Earthquake causes strength loss in
foundation soil leads to instability
and failure by dam overtopping
The dam slides in the
downstream direction on
the weak layer
The liquefied soil is
more like a fluid –
has little shear
strength
Foundation soil that is saturated
and loose (not very dense)
Earthquake shaking causes
it to lose strength (liquefy)
Embankment Dams – Earthquake-Related Failure
Potential
Failure Mode
Earthquake causes strength loss in
foundation soil leads to instability
and failure by dam overtopping
Dam failure occurs
almost immediately after
the earthquake
Embankment Dams – Earthquake-Related Failure
Sheffield Dam
California
Constructed: 1917
Failed: June 29, 1925
Earthquake – Liquefaction
No Fatalities
Lower San Fernando
(Van Norman) Dam
Los Angeles, California
Constructed: 1912, Raised 1921
Nearly Failed: February 9, 1971
Earthquake
No Fatalities
Potential
Failure Mode
Earthquake-caused cracks and/or
damage that leads to seepagerelated dam failure
• Mostly rock, rather
Major Types of Dams than soil
• Thin impervious core
• Potential failure
• Embankment
modes and monitoring
• Rockfill
are similar to
– Central Core
embankment dams
– Impervious Upstream Face • Filter protection for
the core is key
• Concrete
– Gravity
– Arch
– Buttress
• Masonry
• Composite
Filtering
Transition
Zones
Impervious
Earthfill
Core
Rock
Rock
Rockfill Dam
Impervious
Upstream
Face
Could be:
Geomembrane
Concrete
Asphalt
Steel
Clay
Rock
Should be free draining
Settlement of rockfill and/or earthquake shaking
could cause damage to the upstream face and
leakage
– If the rockfill is free-draining (as it should be), this
would not be an issue (except for the lost water)
– If the rockfill is not free-draining, then water
pressure buildup could cause slope instability and
dam failure
Rockfill Dam
Impervious
Upstream
Face
Could be:
Geomembrane
Concrete
Asphalt
Steel
Clay
Rock
Should be free draining
• Overtopping flow in a flood could result in
erosion at the downstream slope and toe area
• Competent rockfill and foundation material
should not suffer much damage, but significant
erosion could occur in poorer materials
• Erosion  Oversteepened slope  Slope
Failure
Rockfill Dam
Impervious
Upstream
Face
Could be:
Geomembrane
Concrete
Asphalt
Steel
Clay
Rock
Should be free draining
Taum Sauk Dam, Missouri
Constructed: 1962
Failed: December 14, 2005
Overtopping – operational
issues
0 Fatalities
Key Issue for all Concrete Dam Types:
Foundation Support of Structure
• Loads on the dam ultimately are transferred and carried
by the foundation (and abutments for arch dams)
• Problems with foundation support have been the cause
of the majority of concrete dam failures
Bayless (Austin) Dam
Pennsylvania
Constructed: 1909
Failed: September 30, 1911
Failed by Sliding in Flood
78 Fatalities
St. Francis Dam
California
Constructed: 1926
Failed: March 12, 1928
Sliding of Abutment
in First Filling
~450 Fatalities
St. Francis Dam
California
Constructed: 1926
Failed: March 12, 1928
Sliding of Abutment
in First Filling
~450 Fatalities
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
By: J. David Rogers, Professor of
Geological Engineering, Missouri
University of Science and Technology
Malpasset Dam
France
Constructed: 1959
Failed: December 2, 1959
Abutment Movement
in First Filling
421 Fatalities
Camara Dam
Brazil
Constructed: 2002
Failed: June 2004
Foundation Movement
in Essentially First Filling
5-25 Fatalities
Gibson Dam
Montana 1964 dam overtopping
Overtopping flow could erode foundation material
Gibson Dam
Montana 1964 dam overtopping
Overtopping flow could erode foundation material
To protect against
a future possibly
larger flood event
Overtopping protection
provided after the event
Cascade Dam
Colorado
Failed: July 15, 1982
Overtopping due to failure of
upstream Lawn Lake Dam
2 Fatalities
Lawn Lake Dam
Colorado
Constructed: 1903
Failed: July 15, 1982
Seepage
3 Fatalities
Masonry
Dams
Most potential
failure modes
similar to
concrete gravity
dams
Good foundation
support is
crucial
Castlewood Dam, Colorado
Constructed: 1890
Failed: August 3, 1933
Failed in Flood – Erosion at toe of dam
7 Fatalities
Leakage
May, 1990
Virginia Kendall Dam, Ohio
Constructed: 1930’s
Overtopped: July 21, 2003
Did not fail
Delhi Dam, Iowa
Constructed: 1929
Failed: July 24, 2010
Flood – Overtopping, but failed due to seepage
0 Fatalities
Frozen Lake Dam
Washington
Constructed: 1930
Failed: Hopefully Never
A. Embankment Dam
Seepage Failure
Unconstrained
Development
B. Embankment Dam
Seepage Failure
Constrained
Development
Sudden
Failure
Sudden
Failure
Large Flow
Large Flow
Large Dam
Failure Flood?
Not Sudden Failure
Very Large Flow
C. Embankment Dam
Overtopping in Flood
E. Embankment Dam
Earthquake
Delayed
Failure
D. Concrete Dam
All Failure Types
Sudden Failure?
Maybe
(Limited Warning Time)
No Water
Released
Not Sudden
Failure
F. Embankment Dam
Earthquake
Immediate Failure
Sudden Failure
Large Flow
Maybe No
Water Released
Sudden Failure