EP 1110-2-13
28 Jun 96
a. Dead storage. The storage that lies below
The lowest level at which water can flow over or
through the spillway.
the invert of the lowest outlet and that, therefore,
cannot readily be withdrawn from the reservoir.
Spillway, fuse plug
b. Inactive storage. The storage volume of a
A form of auxiliary spillway consisting of a low
embankment designed to be overtopped and washed
reservoir between the crest of the invert of the lowest
away during an exceptionally large flood.
outlet and the minimum operating level.
c.
Active storage. The volume of the reservoir
Spillway, shaft
A vertical or inclined shaft into which water spills and
that is available for some use such as power
then is conveyed through, under, or around a dam by
generation, irrigation, flood control, or water supply.
means of a conduit or tunnel. If the upper part of the
The bottom elevation is the minimum operating level.
shaft is splayed out and terminates in a circular
d. Live storage. The sum of the active and the
horizontal weir, it is termed a bellmouth or morning
glory spillway.
inactive storage.
e.
Reservoir capacity. The sum of the dead
Stilling basin
A basin constructed to dissipate the energy of rapidly
and live storage of the reservoir.
flowing water, e.g., from a spillway or outlet, and to
protect the riverbed from erosion.
f.
Flood surcharge. The storage volume
between the top of the active storage and the design
water level.
Stoplogs
Large logs, timbers, or steel beams placed on top of
each other with their ends held in guides on each side
Surcharge
of a channel or conduit so as to provide a cheaper or
Any storage above the full pool.
more easily handled means of temporary closure than
a bulkhead gate.
Tailrace
The tunnel, channel, or conduit that conveys the
discharge from the turbine to the river; hence, the
Storage
The retention of water or delay of runoff either by
terms "tailrace tunnel" and "tailrace canal."
planned operation, as in a reservoir, or by temporary
filling of overflow areas, as in the progression of a
Tailwater level
flood wave through a natural stream channel.
The level of water in the tailrace at the nearest free
Definitions of specific types of storage in reservoirs
surface to the turbine or in the discharge channel
are:
immediately downstream of the dam.
Threshold Flood
The flood that fully utilizes the existing dam, i.e., the
flood that just exceeds the design maximum water
surface elevation at the dam.
Thrust block
A massive block of concrete built to withstand a
thrust or pull.
Toe of dam
The junction of the face of a dam with the ground
surface. For concrete dams, see heel.
B-12
Previous Page
