Living with Dams

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Living with Dams: Extreme Rainfall Events | 2015 | 21
It is a fact, extreme rainfall events happen and may
happen more often. These rainfall events can potentially
happen at any dam, large or small. Meteorologists can
predict how intense these storms will be and engineers
can design dams to safely withstand them. These types
of events stress not only the dam’s spillways and outlets
but almost every feature of the dam as well.
Responsible dam owners and their engineers know
and actively apply the proper design, maintenance
and operation standards for their dams. These industry
standards represent the best hydrologic, engineering
and risk management practices available. They have
been developed through years of research, experience
and standard of care dictated in our courts of law, and
have been consistently accepted by our society.
It is the responsibility of all policy-makers, dam safety
officials and dam owners to recognize the risk associated
with dams and the consequences of their potential
failure and apply the proper standards of care. These
standards cannot be ignored without being negligent
and incurring additional liability.
The 100-year flood (the flood that has a 1 percent-annual-
chance of being equaled or exceeded) mapped on FEMA’s
Flood Insurance Rate Maps is intended for insurance,
floodplain management, and planning efforts and is not
intended to be a safety standard. In your community, you
have a 26 percent chance of experiencing a 100-Year flood
magnitude during the life of a 30-year mortgage. You have a 4
percent chance of experiencing a fire during the same period
of time. Dam failure flood inundation areas may far exceed
the 1 percent flood zones (100-year flood) mapped by FEMA.
Floods greater than a 100-year flood can and do happen, as
seen in the Midwest, which received two 500-year floods in a
15-year period (1993 and 2008). Dam failure floods are almost
always more violent than the normal stream, river or coastal
flood.
What is the 100-Year Flood?
KnowThis
Resources
Association of State Dam
Safety Officials
Dam Safety Action
National Dam Safety Program
National Inventory of Dams
Dams by Owner Type
Primary
Owner Type Number of Dams
Private 56,541
Local Govt 15,938
State 6,435
Federal 3,808
Public Utility 1,686
Not Listed 2,951
Dams by Primary Purpose
Recreation – 34%
Flood Control – 16%
Fire Protection, Stock or Small Fish - 15%
Irrigation – 9%
Water Supply – 8%
Other – 7%
Unknown – 4%
Hydroelectric – 3%
Fish andWildlife Pond – 2%
Data taken from the 2013 National Inventory of Dams.