Glossary
Do bypass, spill, spillbay, tail race, forebay, etc., have you confused?
Here’s a quick glossary.
attraction: Water flows designed to draw fish toward ladders or
other bypass systems.
bypass system, bypass channel: A structure in a dam that
provides a route for fish to move through or around the dam without going
through the turbine units. The bypass channel is the part of a system that
includes a conduit built into the dam to pass fish.
drawdown: Releasing water from a hydroelectric project to lower
the reservoir elevation. Drawdowns are used for energy production or to
create additional space in the reservoir to hold back floodwaters; to reduce the
cross-sectional area of the reservoir, increasing the current to aid downstream
fish passage; and to expose normally submerged structures for maintenance.
fish guidance efficiency (FGE): The percentage of fish moving
toward a dam’s turbine units that are diverted away by a fish guidance device,
such as a submersible traveling screen.
fish ladder: A series of ascending pools, similar to a
staircase, that enables fish to migrate up the river past dams. Also
called a fishway.
fish passage efficiency: The percentage of fish passing a dam
but avoiding the turbine units.
fish sampling facility: A facility at a dam where some portion
of the fish moving past the dam are collected periodically for research
purposes.
fish trapping or collection facility: A facility where juvenile
fish are captured to be transported down the river (around the dams) or adult
fish are culled to be taken to a hatchery.
forebay: The part of a dam’s reservoir that is immediately
upstream of the powerhouse.
gatewell: The slot on the upstream face of a concrete dam where
hydraulic gates are stored when not used to close the turbine intakes.
(The gatewell also typically houses the fish screening device.)
generating capacity: The maximum power that a power plant, such
as a hydroelectric dam, can produce under specific conditions.
hydraulic capacity: The maximum amount of water that can go
through the powerhouse at a project.
intake: The entrance to a turbine unit at a hydroelectric dam.
lock: A chamber with watertight gates at each end used to lift
or lower watercraft between the downstream tailrace water level and the upstream
reservoir level.
mainstem: The main channel of the river in a river basin, as
opposed to the streams and smaller rivers that feed into it. In the fish
and wildlife program, mainstem refers to the Columbia and Snake rivers.
mid-Columbia: The section of the Columbia River below Chief
Joseph Dam and above the river’s junction with the Snake River.
Mid-Columbia Settlement Agreement: A process initiated by the Federal
Energy Regulatory Commission, at the request of
state and federal fishery agencies and Indian tribes, dealing with protection of
migrating salmonids. FERC approved the first agreement among those parties
and the
Mid-Columbia PUDs in 1980.
penstock: The pipe leading from the water intake to the
hydraulic turbine.
powerhouse: That part of a hydroelectric dam where the
turbine-generators are housed and where power is produced by the action of the
water on the turbine blades.
pumped storage: A hydroelectric project designed to store
electrical energy on a short-term basis. A pumped storage project is
typically used to store electricity during nighttime periods of low demand for
use during daily peak demand periods.
river miles: Miles calculated from the mouth of the river or,
for upstream tributaries, from the confluence with the main river.
run-of-the-river dams: Hydroelectric dams without large
reservoirs and, therefore, with only a limited capacity for water storage.
This means they also have limited control of their outflow and power generation.
sluiceway: A channel designed to collect ice and trash in the
river (e.g., logs) before they get into the turbine units and cause damage.
spill, spillbay: Releasing water out the spillbays rather than
through the turbine units. The spillbay is the dam’s safety valve.
Without it, excess water can damage the dam’s structure or overflow the
dam. Dams without bypass systems spill water laden with fish to carry them
away from turbines.
storage dam: A dam with a large reservoir that can hold water
over from the annual high-water season to the following low-water season.
Of the major Columbia River Basin dams, the Grand Coulee, Brownlee, Dworshak,
Hungry Horse, Libby, Round Butte, and Boundary dams are storage dams.
submersible traveling screen (STS): A rotating screen, designed
to fit into a dam’s turbine intake to divert fish up into bypass channels.
tailrace: The canal or channel that carries water away from the
dam.
tailwater: The water surface immediately downstream from a dam.
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