EP 1110-2-13
28 Jun 96
Fetch
Flood, Inflow Design (IDF)
The straight line distance across a body of water
The flood used in the design of a dam and its
subject to wind forces. The fetch is one of the factors
appurtenant works particularly for sizing the spillway
used in calculating wave heights in a reservoir.
and outlet works, and for determining maximum
temporary storage and height of dam requirements.
Filter (filter zone)
One or more layers of granular material graded
Flood, Probable Maximum (PMF)
(either naturally or by selection) so as to allow
The most severe flood that is considered reasonably
seepage through or within the layers while preventing
possible at a site as a result of meteorologic and
the migration of material from adjacent zones.
hydrologic conditions.
Flashboards
Floodplain
Structural members of timber, concrete, or steel
An area adjoining a body of water or natural stream
placed in channels or on the crest of a spillway to
that has been or may be covered by floodwater.
raise the reservoir water level but that may be quickly
removed in the event of a flood.
Freeboard
Vertical distance between the design water level and
the top of dam.
Flip bucket
An energy dissipator located at the downstream end
of a spillway and shaped so that water flowing at a
Full pool
high velocity is deflected upwards in a trajectory
The reservoir level that would be attained when the
away from the foundation of the spillway.
reservoir is fully utilized for all project purposes,
including flood control.
Flood
A temporary rise in water levels resulting in
Gallery
inundation of areas not normally covered by water.
A passageway in the body of a dam used for
May be expressed in terms of probability of
inspection, foundation grouting, and/or drainage.
exceedance per year such as one percent chance flood
or expressed as a fraction of the probable maximum
Gantry crane
flood or other reference flood.
A fixed or traveling bent-supported crane for
handling heavy equipment.
Flood routing
A process of determining progressively over time the
Gate
amplitude of a floodwave as it moves past a dam or
A movable, watertight barrier for the control of water
downstream to successive points along a river or
in a waterway.
stream.
a.
Bascule gate. See flap gate.
Flood, antecedent
A flood or series of floods assumed to occur prior to
b. Bulkhead gate. A gate used either for
the occurrence of an inflow design flood.
temporary closure of a channel or conduit before
dewatering it for inspection or maintenance or for
closure against flowing water when the head
Flood, base safety standard (BSS)
The inflow design flood where there is no significant
difference is small, e.g., for diversion tunnel closure.
increase in adverse consequences from dam failure
c.
Crest gate (spillway gate). A gate on the
compared to non-failure adverse consequences.
crest of a spillway to control the discharge or
reservoir water level.
Flood, Safety Evaluation (SEF)
The largest flood for which the safety of a dam and
d. Drum gate. A type of spillway gate
appurtenant structure is to be evaluated.
consisting of a long hollow drum. The drum may be
B-7
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