found on this site:
built dams across the Tennessee Valley in the 1930s and ’40s.
Who Started TVA, and Why?
If you were carried back in
time to 1933, you might not recognize most areas in the
Tennessee Valley, the region that runs through seven southeastern
states and surrounds the Tennessee River.
At that time, the region was in
pretty bad shape compared with the rest of the United States. It was
dangerous to travel on major stretches of the Tennessee River. Many
of the people who lived in the Valley had no electricity and were barely
getting by. Farmers were suffering because the soil where they grew
their crops was poor and worn out.
To make matters worse, the
entire country was in the middle of a huge economic slump known today as
the Great Depression, which meant that a lot of people had no jobs.
Many families in the Tennessee Valley region were unable to buy or grow
enough food to stay healthy.
When our 32nd president,
Franklin Delano Roosevelt, entered office in 1933, he wanted to help the
people of the Tennessee Valley become more prosperous, healthy, and
productive. In order to do this, President Roosevelt signed the
Tennessee Valley Authority Act on May 18, 1933.
This act of Congress created
the Tennessee Valley Authority (TVA), a federal corporation. The new
agency was asked to tackle important problems facing the Valley, such as
flooding, providing electricity to homes and businesses, and replanting
forests. Other TVA responsibilities written in the act included
improving travel on the Tennessee River and helping develop the region's
business and farming.
President Roosevelt signs the TVA Act on May 18, 1933. The
president is surrounded by members of Congress from the TVA
region. At his left shoulder is Senator George Norris of
Nebraska, the man for whom Norris Dam is named. Senator Norris
was a strong supporter of TVA.
Today, TVA has certainly lived
up to President Roosevelt's hopes. TVA is the largest public power
company in the United States. The agency also carefully runs the
nation's fifth-largest river system in order to reduce flood damage,
make rivers easier to travel, provide recreation, and protect water
quality. The Tennessee Valley is now a great place for families to live
People build dams to control
water—to make sure the right amount is at the right place at the right
River water rises behind dams,
forming artificial lakes called reservoirs. The stored water can be used
to generate electricity or to supply water for homes and industries, for
irrigation, or for navigation. Reservoirs also are good places to fish
How are dams built?
Engineers use models and
computers to figure out how much water a dam will have to support and
how big and strong it must be. Then they can decide what sort of dam to
There are four main types of
Embankment dams are the most common type in the United States. They
are massive structures made of earth and rock that rely on their
heavy weight to resist the force of the water. A layer of clay or
concrete may be used to stop leaks through gaps in the rocks. TVA’s
Cedar Creek Dam is an embankment dam.
dams are concrete dams that also hold back the water entirely by
their own weight. Usually the side of the dam that faces the
oncoming water is straight. Most gravity dams are expensive to build
because they require so much concrete. TVA’s
Norris Dam is a gravity dam.
dams have a series of supports, or buttresses, that brace the dam on
the downstream side. Buttress dams may be flat or curved. Most are
made of reinforced concrete. There are no buttress dams in the TVA
are good for narrow, rocky locations. Their curved shape holds back
the water in the reservoir. Arch dams are thin and require less
material than any other type of dam. There are no arch dams in the
Read more information about all
dams in the TVA system.
...what a cofferdam is?
Click here for the answer
Do dams ever break?
If a dam is
well designed, it will be strong enough to hold back the water behind
it, whatever happens. But tragic accidents still occur, often caused by
the unimaginable power of natural forces such as earthquakes,
landslides, or floods.
The worst dam disaster happened
over a century ago. A huge dam in Philadelphia burst in 1889, killing
it like to dangle from a rope hundreds of feet in the air with
nothing but deep water far below? Just ask one of the guys who
regularly rappel down the face of TVA dams during safety
inspections. Divers and remotely operated machines also are used
to check for problems below the water line.
More recently, in 1976, the
Teton Dam in Idaho broke as the reservoir behind it was being filled for
the first time. Fourteen people were killed. The Teton Dam disaster
resulted in new government rules to ensure that dams are safe.
Dam safety at TVA
Every TVA dam
is checked regularly to make sure it that it is safe and the equipment
used to operate it is working properly.
Because many of these dams were
built in the 1930s, TVA has had to do a lot of work on them to make sure
that they meet modern safety regulations. These ensure that TVA’s dams
can stand up to the biggest flood or earthquake that we would ever
expect to see in the Tennessee Valley.
power, or hydroelectricity, is generated by the force of falling water.
(Hydro comes from the Greek word for water.) It’s one of the
cleanest sources of energy, and it’s also the most reliable and costs
the least. That means that TVA’s
hydroelectric power plants are able provide electricity at a
reasonable cost to families, schools, farms, factories, and businesses.
How does hydroelectric
Water is needed to
hydroelectric power-generating unit. The water is held behind a dam,
forming an artificial lake, or reservoir. The force of the water being
released from the reservoir through the dam spins the blades of a giant
turbine. The turbine is connected to the generator that makes
electricity as it spins. After passing through the turbine, the water
flows back into the river on the other side of the dam.
TVA uses water to make
electricity at 29 hydroelectric dams and one pumped-storage power plant
Raccoon Mountain near Chattanooga, Tennessee). Together these plants
produced about 13.9 million megawatt hours of electricity in 2004,
enough electricity to power nearly one million homes for a year.
How TVA Stops Floods
The best time
to stop a flood is before it starts, right? That’s exactly what TVA
tries to do.
TVA uses 35 dams to reduce
flood damage by holding back the water from heavy rains in reservoirs.
These “flood-storage” reservoirs (usually located on “tributary
rivers”—rivers that run into the main Tennessee River) do most of the
work in controlling floods.
TVA, flooding plagued the Tennessee Valley in late winter and
Big storms — the ones that can
cause flooding — are most likely to hit the Tennessee Valley in the
winter and early spring. So, to make room for this water in the
flood-storage reservoirs, TVA lowers their water levels by January 1
each year. The water in tributary reservoirs can rise and fall as much
as 60 feet per year.
When a storm hits, TVA holds
the water back by closing the gates of the dams in areas where it is
raining. When the rain stops and the danger of downstream flooding is
over, TVA lets the water out at a gradual rate to get ready for the next
As you might expect given how
much it rains, there were lots of floods in the Tennessee Valley before
TVA dams were built. These floods washed away the topsoil, causing
problems for farmers. Even worse, hundreds of people died and thousands
more lost their homes and farms. The city of Chattanooga, Tennessee,
would flood about once a year.
Click here to find out why.
Today, TVA’s system of dams and
reservoirs prevents about $224 million in flood damage along the
Tennessee, Ohio, and Mississippi Rivers every year.
Dams and Water Quality
When people build a dam on a
river, it changes the water quality. Some of these changes are good, but
others can cause problems.
At dams that produce
hydroelectric power, these problems can really affect the fish and other
animals that live in the “tailwater” area. That’s the stretch of river
on the downstream side of the dam, where the water comes out when
electricity is being produced.
Keeping water in the riverbed
When water is flowing through
the dam to make electricity, there is plenty of water in the tailwater
area. But when the equipment that makes the electricity is shut off, the
riverbed can dry out, sometimes for several miles below the dam, which
is bad news for fish—as you can imagine!
at South Holston Dam keeps water in the riverbed and adds oxygen
to it so that fish and other aquatic animals and plants can
In 1991 TVA decided to do
something about this problem. At some dams, TVA built small dams, called
“weirs,” which hold back some of the water when electricity is being
generated, then slowly empty when generation stops.
At other dams, TVA turns the
equipment used to make electricity on and off throughout the day to make
sure that there is always enough water flowing through the dam to keep
the tailwater area from drying out.
...what fish need, besides water, to stay alive?
Click here for the answer
What is stratification?
Oxygen is another big problem
in the tailwater area below some dams, especially dams that form very
deep reservoirs. That’s because the water used to spin the turbines at
these dams comes from the lower part of the upstream reservoir. This
water usually doesn’t have much oxygen in it during late summer and
autumn because of a natural process called “stratification.”
Maybe you’ve never heard this
word before, but if you’ve ever jumped into a reservoir on a hot summer
day, you’ve probably felt the effects of stratification. The deeper you
go, the colder the water feels; then you pop back up to the warmer
surface water that’s been heated by the sun’s rays.
Because of the difference in
temperature, the surface water and the bottom water of deep reservoirs
don’t mix, so the bottom water becomes trapped. It doesn’t have any
contact with the air, which means there’s no way to replace the oxygen
that is used up as plants die, settle to the bottom, and decay. By late
summer or fall, sometimes there’s no oxygen in the water near bottom at
You’ve probably figured out the
problem already: when this low-oxygen water passes through the dam in
the process of producing electricity, it affects the amount of oxygen in
the tailwater area and the health of the animals that live there.
These pumps at Douglas Dam operate like big fans
to help push water that’s higher in oxygen down to the bottom.
TVA tackled this problem at the
same time it decided to do something to keep the riverbed from drying
out. The solution involved a lot of research. TVA installed different
kinds of equipment at 16 dams to add oxygen to the water—from huge fans
that push the oxygen-rich surface water down to the reservoir bottom to
hoses that hang just above the reservoir bottom with holes that create
millions of tiny bubbles as oxygen is pumped into the hoses from a tank
on the land.
Want to know more? Read about
tailwater improvements on the TVA Web site.
Ancient fish return
A fish that first appeared in
Valley waters more than 350 million years ago, before the dinosaurs, is
making a comeback, thanks to better water quality below TVA dams and
other clean water improvements.
Hundreds of young lake sturgeon
have already been released into the French Broad River below TVA’s
Douglas Dam as part of a 10-year restoration effort.
Lake sturgeon once thrived
throughout the Tennessee River system until water pollution, overfishing,
and changes in habitat resulted in near-extinction.
These fascinating fish usually
live 50 to 100 years. The largest lake sturgeon ever recorded weighed
310 pounds and was a little over eight feet long.
Sturgeon photo by Todd Stailey
TVA Reservoirs and
Use this map to link to detailed information on
all of TVA’s facilities.
Point to a colored dot on the map to see the TVA site name.
Click for more information.
Point to a name on the list to see the site location on the map.
Click for more information.
What TVA Does
Have you ever wondered what TVA
does? The answer is — many different things.
headquarters in Knoxville, Tennessee
TVA is the largest public power
company in the United States. It’s called “public” because it’s owned by
the U.S. government, unlike most companies that are owned by individual
people or investors. Through its many
plants that make electricity, TVA supplies power to about 8.8
million people in the southeastern United States.
In addition to producing power
for many Americans, TVA also manages the nation’s fifth-largest river
system. The Tennessee River flows 652 miles from east Tennessee down
into Alabama and back up into Kentucky, where it joins the Ohio River.
All along the Tennessee River, TVA employees work to reduce the dangers
of flooding, make it possible for boats to travel safely, and keep the
In the 41,000-square-mile area
drained by the Tennessee River, TVA also operates some of the country’s
recreation areas. Although TVA was first set up in 1933 as an agency
supported by Americans’ tax dollars, today it runs all of its programs
and pays its employees with the money it earns by making and selling
So, the next time you turn on a
computer, drink from the school water fountain, or go fishing on a TVA
reservoir, you will know what part TVA plays in helping everybody in the
Valley lead a better life.
How TVA dams and locks make
Quick! Name some ways TVA dams
benefit people in the Tennessee Valley.
Flood damage reduction, power
production, recreation—those are the ones that come to mind first.
But “promoting navigation” was
actually the very first purpose mentioned in the TVA Act of 1933, which
spelled out exactly how the new agency was to manage the river.
Navigation has been important to the welfare of the Valley ever since.
it weren’t for those barges moving up and down the river, we would be
paying more for all kinds of products. Anything made from materials
shipped in large quantities—grain, stone and gravel, iron and steel,
lumber, coal, and chemicals, for example—would cost more. Why? Because
they’d have to be shipped by rail or truck, which would cost over $550
million a year more than moving them by barge.
One barge can carry as much
stuff as 60 trucks, so there’d be a lot more 18-wheelers on the road,
too. Using barges helps keep our highways safer and reduces fuel use,
air pollution, and the number of tires going to landfills.
A river highway
TVA built nine dams along the
main Tennessee River to create a 652-mile long river highway. TVA
operates these dams to make sure the water all along the way is at least
11 feet deep—enough to float even the heaviest barge.
Before these dams were built,
the water was too shallow for barges to travel very far up the Tennessee
River. In fact, in dry years, you could cross the river near Muscle
Shoals, Alabama, without even getting your feet wet—if you didn’t slip
off the rocks!
The main-river dams form a
“staircase” of quiet, pooled water and controlled current along the
entire length of the Tennessee River. But how do boats get around the
Every dam has a lock—a canal
for raising and lowering boats—which allows boats to pass around the dam
and to deal with the difference in elevation between Knoxville,
Tennessee, and Paducah, Kentucky. Paducah is 513 feet lower than
How does a lock work?
lot like an elevator—only slower! When a barge or other boat enters the
lock, the gates close and the water level inside the lock is raised to
the upstream level or lowered to the downstream level, depending on
which way the boat is moving.
The locks are filled and
emptied by gravity—no pumps are used. If the boat is going downstream,
the water level in the lock is lowered by opening the downstream valves
so the water can drain out. If the boat is moving upstream, the
downstream valves are closed and the upstream valves are opened. This
allows water from the upstream side to flow into the lock, filling the
chamber to the upstream water level.
In about 45 minutes, when the
water level inside the lock is equal to the level of the next reservoir,
gates at the other end of the lock are opened and the boat can continue
on its way.
You can see a little movie of
how a lock works here.
Protecting Wildlife Habitats
is in charge of 293,000 acres of public land and 11,000 miles of
shoreline. It has set aside more than 181,000 acres of that land to
preserve a home for wildlife and to protect and study animals, birds,
TVA has been working to protect
wildlife for years. In 1976 TVA started the
Natural Heritage Project. With help from the Nature Conservancy,
TVA’s wildlife specialists make careful studies of the plants and
animals that are at risk of
becoming extinct. Then biologists create plans that will help
protect wild areas.
Here are some other examples of
how TVA wotks to benefit wildlife:
• Every year TVA studies the
number and health of fish in the reservoirs during its
spring sportfish survey.
• TVA helps
count and protect bald eagles, America’s national symbol.
Scouts from St. Jude Pack 3111 planted butterfly and hummingbird
gardens at TVA’s Raccoon Mountain Pumped Storage Plant near
Chattanooga. The Scouts also check nesting boxes of migratory
birds once a week during the breeding season as part of a
national monitoring effort.
“Aquatic life” means fish and
other creatures that live in the water. TVA helps protect
habitat for aquatic life in a number of ways.
TVA Natural Areas
TVA has set up a network of
Natural Areas along the Tennessee River and its tributaries. They are
designed to protect rare animals and plants and the natural communities
where they live. By setting these areas aside, TVA is better able to
limit activities that could put these animals and plants in danger. Some
of the TVA Natural Areas are open to the public for hiking, wildlife
observation, and nature appreciation