RESOURCES

Glossary of Terms

Arch dam
ideal for narrow, rocky locations. They are curved and the natural shape of the arch holds back the water in the reservoir. They are thin and typically use less material to construct than other types of dams.
Buttress dam
a gravity dam that is watertight on the upstream face and may be flat or curved with a series of supports or braces on the downstream side. Usually made of reinforced concrete.
Cofferdam
a temporary dam built to divert a river around a construction site sot he dam can be built on dry ground
Concrete
a mixture of water, sand, small stones and cement
Downstream face
the side of a dam that is not against the water
Drawdown
the release of water from a reservoir for power generation, flood control, irrigation or other water management activity.
Earth dams
the most common made of earth and rock, ( more than 50% of the total volume is formed from compacted fine-grain material obtained from a borrow area, excavation area) they rely on their weight to resist the force of the water. They have a dense waterproof core at the base to prevent water from seeping through.
Embankment dam
a dam structure constructed of fill material, usually earth or rock, placed with sloping sides and usually with a length greater than its height.
Energy
the ability to work ( exert force over a distance) Energy is measured in calories, joules, KWH, BTUs, MW-hours and average MWs
Fishway/Fish ladder
a device made up of a series of stepped pools, similar to a staircase, that enables adult fish to migrate up the river past dams.
Flume
a narrow gorge, usually with a stream flowing through it, - an open artificial channel or chute carrying stream of water, as for furnishing power, conveying logs or as a measuring device
Forebay
the part of a dam’s reservoir that is immediately upstream from the powerhouse
Full pool
the maximum level of a reservoir under its established normal operating range.
Gas supersaturation
the overabundance of gases in turbulent water, such as the base of a dam spillway. Can cause fatal condition in fish similar to the bends.
Generation
act or process of producing electric energy from other forms of energy. Also refers to the amount of electric energy so produced.
Generator
a machine that changes water power, steam power or other kinds of mechanical energy into electricity
Gravity dam
massive structures that resist the thrust of the water entirely by their own weight. Are expensive to build because they are made of concrete
Hydraulic head
the vertical distance between the surface of the reservoir and the surface of the river immediately downstream from the dam
Hydroelectricity ( hydroelectric power)
the production of electric power through use of the gravitational force of falling water.
Impoundment
a body of water formed behind a dam
Kilowatt (KW)
the electrical unit of power which equals 1,000 watts or 1.341 horsepower.
Kilowatt-hour (kWh)
a basic unit of electrical energy that equals one kilowatt of power applied for one hour
Load
the amount of electric power or energy delivered or required at any specified point or points on a system.
Load shaping
the adjustment of storage releases so that generation and load are continuously in balance.
Low-head dam
a dam at which the water in the reservoir is not high above the turbine units.
MAF - million acre feet
the equivalent volume of water that will cover an area of one million acres to a depth of one foot. One MAF equals 1,000 KAF (thousand acre feet)
Megawatts (MW)
a megawatt is one million watts or one thousand kilowatts, a measure of electrical power or generating capacity. A megawatt will typically server about 1000 people.
Outflow
The water that is released from a project during the specified period.
Penstock
The pipe leading from the water intake to the hydraulic turbine.
Powerhouse
A primary part of a hydroelectric dam where the turbines and generators are housed and where power is produced by falling water rotating turbine blades.
Reservoir
A body of water collected and stored in an artificial lake behind a dam.
Run-of-river dams
Hydroelectric generating plants that operate based only on available inflow and a limited amount of short-term storage (daily/weekly pondage).
Spill
Releasing water through the spillway rather than through the turbine units.
Spillway
an overflow channel that allows dam operators to release lake water when it gets high enough to threaten the safety of a dam "The channel or passageway around or over a dam through which excess water is released or "spilled" past the dam without going through the turbines. A spillway is a safety valve for a dam and, as such, must be capable of discharging major floods without damaging the dam, while maintaining the reservoir level below some predetermined maximum level."
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
Tailrace
The canal or channel that carries water away from the dam
Turbine
A mechanism in a dam that rotates with the force of water and produces electricity.
Watt
A measure of the rate at which energy is produced, exchanged, or consumed.
Weir (dam)
A dam in a river to stop and raise the water, for the purpose of conducting it to a mill, forming a fishpond, or the like. When uncontrolled, the weir is termed a fixed-crest weir. Other types of weirs include broad-crested, sharp-crested, drowned, and submerged.