FLOOD09216

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Glossary of Terms for Dam Safety
• Date: 2/1/1988
• Prepared By: Interagency Committee on Dam Safety
• Floodplain - Doc Type: Educational/Technical/Reference Information

Drawdown. The difference between a water level and a lower water level in a
reservoir within a particular time. Used as a verb, it is the lowering of the
water surface.

Earthquake. A sudden motion or trembling in the earth caused by the abrupt
release of accumulated stress along a fault.

Earthquake, Maximum Credible (MCE). The most severe earthquake that can be
expected to occur at a given site on the basis of geologic and seismological
evidence.

Earthquake, Maximum Design (MDE). A postulated seismic event, specified in
terms of specific bedrock motion parameters at a given site, which is used to
evaluate the seismic resistance of manmade structures or other features at the
site.

Earthquake, Operating Basis (OBE). The earthquake(s) for which the structure
is designed to resist and remain operational. It reflects the level of earth-
quake protection desired for operational or economic reasons and may be deter-
mined on a probabilistic basis considering the regional and local geology and
seismology.

Earthquake, Safety Evaluation (SEE). The earthquake, expressed in terms of
magnitude and closest distance from the dam site or in terms of the character-
istics of the time history of free-field ground motions, for which the safety
of the dam and critical structures associated with the dam are to be evalu-
ated. In many cases, this earthquake will be the maximum credible earthquake
to which the dam will be exposed. However, in other cases where the possible
sources of ground motion are not easily apparent, it may be a motion with pre-
scribed characteristics selected on the basis of a probabilistic assessment of
the ground motions that may occur in the vicinity of the dam. To be con-
sidered safe, it should be demonstrated that the dam can withst~d this level
of earthquake shaking without release of water from the reservoir.

Earthquake, Synthetic. Earthquake time history records developed from mathe-
matical models that use white noise, filtered white noise, and stationary and
nonstationary filtered white noise,or theoretical seismic source models of
failure in the fault zone. (White noise is random energy containing all fre-
quency components in equal proportions. Stationary white noise is random
energy with statistical characteristics that do not vary with time.)

Emergency Action Plan (EAP).
potential for property damage
failure or large flood.

A plan of action to be taken to reduce the
and loss of life in an area affected by a dam

Energy dissipator. A device constructed in a waterway to reduce the kinetic
energy of fast flowing water.

Epicenter. The point on the earth's surface located vertically above the
point of origin of an earthquake.

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