An Examination of Dam Failures
vs.
the Age of Dams
Patrick Regan
FERC
One Simple Question
Does 50 years of, apparently,
successful operation assure
continued safe operation?
Swift 2 Dam
Swift 2 Dam
Taum Sauk
Taum Sauk
Database Facts and Figures
•
•
•
•
•
Total entries
# where age can be determined
# of countries
Earliest construction date
Oldest dam incident/failure
4283
1158
84
1550
286
# of Incidents vs. Age All Dams
Distribution of Incidents by Age
300
250
200
150
100
Age Range
0
>1
0
-9
5
91
-8
5
81
-7
5
71
-6
5
61
-5
5
51
-4
5
41
-3
5
31
-2
5
21
11
-1
5
50
0
<6
# of Incidents
400
350
Camara Dam
Camara Dam
2 Years Old
IVEX Dam
IVEX Dam
152 Years Old
% of Incidents that Occur at an Age Greater Than
All Dams that Survive their 1st Five Years
100%
90%
• To answer the question as to does 50 years
70% of “successful” operation means we don’t
60%
need to worry about a dam any more, the
50%
data
suggests
that
>50%
of
incidents
of
40%
dams that survived their first 5 years occur
30%
20% after the dam is 50 years old.
80%
10%
Age
>95
>90
>85
>80
>75
>70
>65
>60
>55
>50
>45
>40
>35
>30
>25
>20
>15
>10
>5
0%
% of Incidents That Occur At An Age Greater Than
By Type of Dam
100%
How are Incidents for Different
Types of Dams Distributed?
90%
80%
70%
Earthfill
60%
Rockfill
50%
Gravity
Arch
40%
All
30%
20%
10%
Age
>9
5
>8
5
>7
5
>6
5
>5
5
>4
5
>3
5
>2
5
>1
5
>5
0%
% of Incidents
that Occur at an
AgeDifferent
Greater Than
How
are Incidents
for
by Failure Mode
1st 5 Years
of Operation after
FailureAfter
Modes
Distributed
100%
1st 5 years
Flooding
Seepage
Age
>9
5
>8
5
>7
5
>6
5
>5
5
>4
5
>3
5
>2
5
Structural
>1
5
>5
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
# of Incidents by Type of Dam vs. Decade Built
Dams that Survived 1st 5 Years of Operation
How are Incidents Distributed by
the Era of Dam Construction?
60
50
Buttress
40
Crib
30
Rockfill
20
Multiple Arch
10
Gravity Concrete
Gravity Masonry
0
Time Period
89
-1
9
79
19
80
-1
9
69
19
70
-1
9
59
19
60
-1
9
49
19
50
-1
9
39
19
40
-1
9
29
19
30
-1
9
19
19
20
-1
9
09
19
10
-1
9
99
00
-1
8
19
18
50
<1
8
50
Earthfill
Arch
Other
Earth Dam Seepage Incidents % of Incidents
Beyond a Given Year by Era of Construction
(Data Beyond 45 Years of Age Removed)
60%
How are Incidents Distributed by
the Era of Dam Construction?
50%
40%
<1900
30%
1900-1949
1950-1975
20%
10%
0%
>5
>10
>15
>20
>25
Age
>30
>35
>40
>45
Some Data on Older Dams
• 46 Incidents in Database with Age >100
• Failure Modes
– % due to flooding (not PMF)
– % due to structural issues
– % due to seepage/piping
• Oldest Piping/Seepage Incident
– 152 years old (10th oldest)
• Oldest Flood Related Incident
– 286 years (oldest event)
49%
31%
20%
What Contributes to Older Incidents?
• Exposure
– Floods
– Earthquakes
• Aging
– Piping
– ASR
– Settlement
• Changed Conditions
–
–
–
–
Changed Operating Basis
Loss of Knowledge
Modifications that have unforeseen consequences
Changed conditions in vicinity of dam
Merwin Gate Nuts
What’s Causing
Flood Related Failures?
• Gates not working
–
–
–
–
–
Stuck in place
Operators fail
Power fails
Debris plugging
SCADA errors
• Spillways failing
– Overtopping of chute walls
– Cavitation, backcutting, stagnation pressure, etc.
• Human Factors
– Can you get there? Will it work?
Noppikoski Dam
• Noppikoski Dam was a central core rockfill
dam.
• The dam was remotely operated from a
location 30 miles away.
• The two spillway openings were controlled
by steel stoplogs that were raised by using a
hoist located on a moveable trolley.
Noppikoski Dam
• In September, 1985 a major storm occurred
in central Sweden.
• During the initial phase of the flooding the
stoplogs had been removed from the
spillway bays. However, due to a lessening
of the storm the left spillway stoplogs had
been replaced and one stoplog was placed in
the right bay and left hooked to the hoist.
Noppikoski Dam
• On September 6th, a Friday, the storm
increased in intensity. An operator was
dispatched to the site from his home.
• When the operator was about half way to
the dam, he is informed that the road had
been cutoff due to overflowing creeks.
• His remaining trip had just changed from 30
miles to 55 miles on lesser roads.
Noppikoski Dam
• When the operator arrived at the dam, it was
raining very hard and, he could not raise the
remaining stoplog in the right bay because it
had become stuck. This effectively took the
hoist out of service.
• A similar problem had occurred previously
but was believed to have been fixed.
• A crane company was contacted in case the
hoist was the problem.
Noppikoski Dam
• The crane company was delayed in
dispatching the crane because the call came
in late on a Friday evening and they had
trouble finding an operator.
• Additional plant staff were dispatched to
Noppikoski Dam to help try and raise the
stoplogs.
Noppikoski Dam
• In case there weren’t enough problems;
– The telephone lines to the dam went down
– An upstream dam was in danger of overtopping
and the spill into Noppikoski was increased
– The power station was in danger of being
inundated and was shut down thereby losing the
plant’s discharge capacity
– The mobile crane could not reach the dam,
stopping a couple of hundred meters short due
to the road being cutoff by a stream
Noppikoski Dam
• Operators tried to raise the embankment
sections along the sides of the spillway with
no success and the dam overtopped and
failed.
• Luckily, the downstream residents had been
warned and there were no fatalities.
Noppikoski Dam
Can you get there?
Will it work?
Noppikoski Dam
Afterthoughts
After the failure the operator presented a paper describing the
factors that contributed to the failure. In conclusion he stated:
“In my opinion, the important question of
how to adapt the plants – with the exception
of augmented discharge functions – to
practical operation, in view of the
complications of the kind previously listed,
has not been considered or documented to
the same extent.”
What Can We Do?
• Learn from the past
– Case History Workshops
– Database of Dam Safety Incidents
• Utilize Risk Assessment
– Can help assess issues beyond the scope of
traditional analyses
– Consider non-traditional failure modes
• Evolve our Guidelines into Best Practices
that continuously capture the state-of-practice
“We are made wise not by the recollection
of our past, but by the responsibility for
our future.”
George Bernard Shaw