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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


What is the 100-Year Flood?



Association of State Dam

Safety Officials

Dam Safety Action

National Dam Safety Program safety-program

National Inventory of Dams

Dams by Owner Type


Owner Type Number of Dams



Local Govt






Public Utility


Not Listed


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.