EP 1110-2-13
28 Jun 96
Reservoir surface area
Sill
The area covered by a reservoir when filled to a
A submerged structure across a river to control the
specified level.
water level upstream. The crest of a spillway. A
horizontal gate seating, made of wood, stone,
concrete, or metal at the invert of any opening or gap
Riprap
A layer of large uncoursed stone, precast blocks, bags
in a structure; hence, the expressions "gate sill" and
of cement, or other suitable material, generally placed
"stoplog sill."
on the upstream slopes of an embankment or along a
watercourse as protection against wave action,
Slope
erosion, or scour. Riprap is usually placed by
Inclination from the horizontal. Sometimes referred
dumping or other mechanical methods and in some
to as batter when measured from vertical.
cases is hand placed. It consists of pieces of relatively
large size as distinguished from a gravel blanket.
Sluice
An opening for releasing water from below the static
head elevation.
Risk
The relationship between the consequences resulting
from an adverse event and its probability of
Spillway
occurrence.
A structure over or through which flow is discharged
from a reservoir. If the rate of flow is controlled by
mechanical means such as gates, it is considered a
Risk assessment
As applied to dam safety, the process of identifying
controlled spillway. If the geometry of the spillway is
the likelihood and consequences of dam failure to
the only control, it is considered an uncontrolled
provide the basis for informed decisions on a course
spillway.
of action.
Spillway, auxiliary
Any secondary spillway which is designed to be
Rock anchor
A steel rod or cable placed in a hole drilled in rock,
operated very infrequently and possibly in
held in position by grout, mechanical means, or both.
anticipation of some degree of structural damage or
In principle, the same as a rock bolt, but usually the
erosion to the spillway during operation.
rock anchor is more than 4 meters long.
Spillway, primary (or service)
A spillway designed to provide continuous or
Rock bolt
A steel rod placed in a hole drilled in rock, held in
frequent releases from a reservoir without significant
position by grout, mechanical means, or both. A rock
damage to either the dam or its appurtenant structures.
bolt can be pretensioned.
Runup
Spillway Design Flood (SDF)
The vertical distance above the setup that the rush of
See Flood, Inflow Design.
water reaches when a wave breaks on the dam
embankment.
Spillway channel
An open channel or closed conduit conveying water
from the spillway inlet downstream.
Seepage
The interstitial movement of water that may take
place through a dam, its foundation, or its abutments.
Spillway chute
A steeply sloping spillway channel that conveys dis-
charges at supercritical velocities.
Significant wave height
The average height of the one-third highest waves of
a given wave group.
Spillway crest
B-11
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