FLOOD10353

• County: Larimer
• Community: Fort Collins
• Stream Name: Big Thompson River
• Basin: South Platte
• Title: Twenty Years Later, What We Have Learned Since the Big Thompson Flood - Proceedings of a Meeting Held in Fort Collins - July 13-15, 1996
• Date: 7/13/1996
• Floodplain - Doc Type: Educational/Technical/Reference Information

41

these

to help answer

are evaluated

U.S

the world and the

Graham

Data from
questions

~

r
t

u.s. Dam Failure History

to dam failure has diminished with
were a large number of dam

History shows that loss of life due
time. In the late 1800s and early 1900s, there
failures that caused considerable loss of life

~

The largest U.S. loss of life from a dam break occurred in May 1889,
when the 72-foot-high South Fork Dam near Johnstown, Pennsylvania, failed.
A flood caused the 36-year-old dam to overtop. Warnings were meager, and
the widespread flooding that was already occurring in Johnstown before the
dam failure prevented evacuation of the community. In some dam failures,
buildings are damaged but not destroyed. In the case of this dam failure,
however, a large number of buildings in Johnstown were washed away. More
than 2,200 people lost their lives in this disaster (U.S. National Park Service,
1977).
Another significant dam failure in the U.S. occurred north of Los
Angeles, California, on March 12, 1928, a few minutes before midnight. The
two-year-old St. Francis Dam, a 188-foot high concrete gravity structure,
failed as a result of a foundation failure at one of the abutments. The death
toll from this dam failure was about 420 people (Outland, 1977).
Table 1 summarizes all dam failures in the United States that resulted in
fatalities during the period 1960-1995. This table expands previously
published information (U.S. Bureau of Reclamation, 1989; Brown and
Graham, 1988). During this 36-year period, about 320 people died as a result
of dam failure. There were about 260 fatalities during the 1970s. During the
1980s, when the number of dams in the U.S. was larger than ever before and
the average dam was continuing to age, there were only seven fatalities. In
the first half of the 1990s, there were 10 fatalities resulting from dam failure.
During the 36-year period from 1960 to 1995, dam failures caused an
average of nine fatalities per year in the United States. During the 16-year
period from 1980 to 1995, dam failures caused less than one fatality per year
in the United States. Some reasons for this reduction from losses in earlier
times include

.

Improved design standards and construction techniques

.

after comple-

of dams during their first few years
dams were constructed during this period

Higher failure rates
tion; fewer

.

were more prone to failure.

Removal or modification of dams that

.