power industry. Both small and large hydroelectric power developments were
instrumental in the early expansion of the electric power industry.

Hydroelectric power comes from flowing water winter and spring runoff from mountain
streams and clear lakes. Water, when it is falling by the force of gravity, can be used to turn
turbines and generators that produce electricity.

Hydroelectric power is important to our Nation. Growing populations and modern technologies
require vast amounts of electricity for creating, building, and expanding. In the 1920's,
hydroelectric plants supplied as much as 40 percent of the electric energy produced. Although
the amount of energy produced by this means has steadily increased, the amount produced by
other types of powerplants has increased at a faster rate and hydroelectric power presently
supplies about 10 percent of the electrical generating capacity of the United States.
Hydropower is an essential contributor in the national power grid because of its ability to
respond quickly to rapidly varying loads or system disturbances, which base load plants with
steam systems powered by combustion or nuclear processes cannot accommodate.

Reclamation=s 58 powerplants throughout the Western United States produce an average of 42
billion kWh (kilowatt-hours) per year, enough to meet the residential needs of more than 14
million people. This is the electrical energy equivalent of about 72 million barrels of oil.
Hydroelectric powerplants are the most efficient means of producing electric energy. The
efficiency of today's hydroelectric plant is about 90 percent. Hydroelectric plants do not create
air pollution, the fuel--falling water--is not consumed, projects have long lives relative to other
forms of energy generation, and hydroelectric generators respond quickly to changing system
conditions. These favorable characteristics continue to make hydroelectric projects attractive
sources of electric power.

HOW HYDROPOWER WORKS

Hydroelectric power comes from water at work, water in motion. It can be seen as a form of
solar energy, as the sun powers the hydrologic cycle which gives the earth its water. In the
hydrologic cycle, atmospheric water reaches the earth=s surface as precipitation. Some of this
water evaporates, but much of it either percolates into the soil or becomes surface runoff. Water
from rain and melting snow eventually reaches ponds, lakes, reservoirs, or oceans where
evaporation is constantly occurring.


Moisture percolating into the soil may become ground water (subsurface water), some of which
also enters water bodies through springs or underground streams. Ground water may move
upward through soil during dry periods and may return to the atmosphere by evaporation.

Water vapor passes into the atmosphere by evaporation then circulates, condenses into clouds,
and some returns to earth as precipitation. Thus, the water cycle is complete. Nature ensures
that water is a renewable resource.

Generating Power

In nature, energy cannot be created or destroyed, but its form can change. In generating
electricity, no new energy is created. Actually one form of energy is converted to another form.

To generate electricity, water must be in motion. This is kinetic (moving) energy. When
flowing water turns blades in a turbine, the form is changed to mechanical (machine) energy.
The turbine turns the generator rotor which then converts this mechanical energy into another
energy form -- electricity. Since water is the initial source of energy, we call this hydroelectric
power or hydropower for short.

At facilities called hydroelectric powerplants, hydropower is generated. Some powerplants are
located on rivers, streams, and canals, but for a reliable water supply, dams are needed. Dams
store water for later release for such purposes as irrigation, domestic and industrial use, and
power generation. The reservoir acts much like a battery, storing water to be released as needed
to generate power.


The dam creates a Ahead@ or height from which water flows. A pipe (penstock) carries the water
from the reservoir to the turbine. The fast-moving water pushes the turbine blades, something
like a pinwheel in the wind. The waters force on the turbine blades turns the rotor, the moving
part of the electric generator. When coils of wire on the rotor sweep past the generator=s
stationary coil (stator), electricity is produced.

This concept was discovered by Michael Faraday in 1831 when he found that electricity could be
generated by rotating magnets within copper coils.

When the water has completed its task, it flows on unchanged to serve other needs.

Transmitting Power

Once the electricity is produced, it must be delivered to where it is needed -- our homes, schools,
offices, factories, etc. Dams are often in remote locations and power must be transmitted over
some distance to its users.
Vast networks of transmission lines and facilities are used to bring electricity to us in a form we
can use. All the electricity made at a powerplant comes first through transformers which raise
the voltage so it can travel long distances through powerlines. (Voltage is the pressure that
forces an electric current through a wire.) At local substations, transformers reduce the voltage
so electricity can be divided up and directed throughout an area.

Transformers on poles (or buried underground, in some neighborhoods) further reduce the
electric power to the right voltage for appliances and use in the home. When electricity gets to
our homes, we buy it by the kilowatt-hour, and a meter measures how much we use.




While hydroelectric powerplants are one source of electricity, other sources include powerplants
that burn fossil fuels or split atoms to create steam which in turn is used to generate power. Gas-
turbine, solar, geothermal, and wind-powered systems are other sources. All these powerplants
may use the same system of transmission lines and stations in an area to bring power to you. By
use of this Apower grid, electricity can be interchanged among several utility systems to meet
varying demands. So the electricity lighting your reading lamp now may be from a hydroelectric
powerplant, a wind generator, a nuclear facility, or a coal, gas, or oil-fired powerplant or a
combination of these.


The area where you live and its energy resources are prime factors in determining what kind of
power you use. For example, in Washington State hydroelectric powerplants provided
approximately 80 percent of the electrical power during 2002. In contrast, in Ohio during the
same year, almost 87 percent of the electrical power came from coal-fired powerplants due to the
area=s ample supply of coal.

Electrical utilities range from large systems serving broad regional areas to small power
companies serving individual communities. Most electric utilities are investor-owned (private)
power companies. Others are owned by towns, cities, and rural electric associations. Surplus
power produced at facilities owned by the Federal Government is marketed to preference power
customers (A customer given preference by law in the purchase of federally generated electrical
energy which is generally an entity which is nonprofit and publicly financed.) by the Department
of Energy through its power marketing administrations.


How Power is Computed

Before a hydroelectric power site is developed, engineers compute how much power can be
produced when the facility is complete. The actual output of energy at a dam is determined by
the volume of water released (discharge) and the vertical distance the water falls (head). So, a
given amount of water falling a given distance will produce a certain amount of energy. The
head and the discharge at the power site and the desired rotational speed of the generator
determine the type of turbine to be used.

The head produces a pressure (water pressure), and the greater the head, the greater the pressure
to drive turbines. This pressure is measured in pounds of force (pounds per square inch). More
head or faster flowing water means more power. To find the theoretical horsepower (the measure of mechanical energy) from a specific site, this
formula is used:


THP = (Q x H)/8.8


where: THP = theoretical horsepower
Q = flow rate in cubic feet per second (cfs)
H = head in feet
8.8 = a constant

A more complicated formula is used to refine the calculations of this available power. The
formula takes into account losses in the amount of head due to friction in the penstock and other
variations due to the efficiency levels of mechanical devices used to harness the power.

To find how much electrical power we can expect, we must convert the mechanical measure
(horsepower) into electrical terms (watts). One horsepower is equal to 746 watts (U.S. measure).

Turbines

While there are only two basic types of
turbines (impulse and reaction), there are
many variations. The specific type of
turbine to be used in a powerplant is not
selected until all operational studies and
cost estimates are complete. The turbine
selected depends largely on the site