Jefferson County - East-West Gateway Coordinating Council

A Regional Overview All-Hazard Mitigation Plan 111
are loss of human life, economic loss including property damage, lifeline disruption and
environmental damage.
While the definition varies from place to place, it generally means if failure of a high-hazard
dam occurs, there probably will be loss of life. I t must be emphasized that this
determination does not mean that these dams are in need of repair--these dams could be
in excellent condition or they could be in poor condition. "High-hazard" just reflects the
dam's potential for doing damage downstream should it fail.
High-hazard potential dams exist in every state and affect the lives of thousands
downstream. The current issue and debate is over the increasing number of these highhazard
structures--not because more high-hazard dams are being built, but that more
development is occurring downstream. Dam and reservoir safety regulators generally have
no control over local zoning issues or developers' property rights. So this issue continues to
worry regulators as the trend persists.
Some dams are considered to have a greater hazard potential than others. There are
approximately 10,000 state-regulated "high-hazard" potential dams in the U.S. "Highhazard"
is a term used by a majority of state dam safety programs and federal agencies as
part of a three-pronged classification system used to determine how hazardous a dam's
failure might be to the downstream area. Historically, dams that failed had some
deficiency, as characterized above, which caused the failure. These dams are typically
termed "unsafe." Currently, there are about 2,000 "unsafe" dams in the U.S. There are
unsafe dams in almost every state. (A majority of states and federal agencies define an
"unsafe" dam as one that has been found to have deficiencies that leave it more susceptible
to failure.)
Hazard Event History
Thousands of people have been injured, many killed, and billions of dollars of property
damaged by dam failures in the United States. Dam failures at Lawrenceton in 1968,
Washington County in 1975, Fredericktown in 1977, and a near failure in Franklin County
underscored the problem of unsafe dams in Missouri in 1978.
Frequency of Occurrence
Table F51 below summarized the frequency of dam failures in Missouri. Four dams failed
in ten years.
TABLE J51 RECENT DAM FAILURES IN MISSOURI
Community Date
Lawrenceton 1968
Washington County 1975
Frederickton 1977
Franklin County (near failure) 1978