A dam is a barrier built across a water course to hold back or control the water flow. Some dams divert the flow of river water into a pipeline, canal, or channel. Others raise the level of inland waterways to make them navigable by ships and barges. Many dams harness the energy of falling water to generate electric power. Dams also hold water for drinking and crop irrigation, and provide flood control.
A beaver dam is an example of a small dam. It is made by using sticks and mud to slow down the flow of a stream or a river. This causes water to pool behind the jam of sticks and mud which results in a new pond being built.
Large dams are more complex to build and take a lot of work, power, time and money. A dam can be made of concrete, rocks, wood or earth. An example of a large dam is the Glen Canyon Dam in Arizona. It is about 700 feet tall and is made of concrete.
The most important load that a dam must support is the water behind it. The water pushes on the dam, creating water pressure. Water pressure increases with the depth of the water.
In greater depths, there is more water "piled up," which causes the pressure to be greater at the bottom than at the surface. A dam's design must enable it to withstand greater pressure at the bottom than at the top. As a result, many dams are built in a triangular shape. The wide bottom withstands the great load of the water deep below the surface, while the thinner top of the dam need not use unnecessarily costly materials.
Classification of dams
According to their functions, dams serve three main purposes: storage, diversion, or detention.
Theyare constructed to impound water in periods of surplus supply for use in periods of deficiency. Many small dams impound the spring runoff for later use in dry summers. Storage dams may also provide a water supply, or improved habitat for fish and wildlife. They may store water for hydroelectric power generation, irrigation or for a flood control project
The specific purpose of a storage dam influences its design and determines the amount of reservoir needed. Where multiple purposes are involved e.g. both power and irrigation, reservoir allocation is usually made for each separate use. The volume of storage establishes the height and width of the dam.
They provide sufficient pressure for pushing water into ditches, canals, or other conveyance systems. Such shorter dams are used for irrigation, and for diversion from a stream to a distant storage reservoir.
They minimize the effect of sudden floods and trap sediment.
They carry water discharge over their crests, and are made of materials that will not be eroded by such discharges. Non-overflow dams are designed not to be overtopped, and may include earth and rock in their structure. Often the two types are combined to form a composite structure.
To prevent a dam from being overtopped, spillway structures carry off excess water. In earthfill dams, essential spillways are built as separate structures, often a shaft or tunnel adjacent to the dam. With concrete gravity dams, the downstream side of the structure acts as the spillway.
Dam structure and design
The development of modern construction equipment has made massive earthfill dams economical. The Rogun and Nurek dams in Tajikistan, the world's highest, are earthfill structures. Canada's Syncrude Tailings, which will be the world's most massive, is also an earthfill structure.
Earthfill dams typically have a water-impermeable clay core, and a water cut-off wall from their base to bedrock to prevent underground seepage. During construction, the stream or river must be diverted either through the dam-site by means of a conduit, or around it by means of a tunnel.
Earthfill dams require supplementary structures as spillways for discharging water from behind the dam. If sufficient spillway capacity is not provided, an earthfill dam may be damaged or even destroyed by the erosive water flowing over its crest. Unless special precautions are taken, such dams are also subject to serious damage or even failure, due to water seepage.
Embankment or rockfill dams
The rockfill dam uses rock instead of earth to provide stability. It has an impervious, watertight membrane, usually an upstream facing of impervious soil, concrete paving, or steel plates; or it may have a thin interior core of impervious soil.
Rockfill embankment dams and zoned-embankment dams are the most common embankment dams. Rockfill embankment dams have a mound of loose rock covered with a waterproof layer on the upstream side. The waterproof layer may be made of concrete, flat stone panels, or other impervious materials. Zoned-embankment dams include an impervious core surrounded by a mound of material that water can penetrate. The supporting mound is usually made of loose rock or earth. The core might be built from concrete, steel, clay, or any impervious materials.
Embankment dams hold back water by the force of gravity acting upon their mass. Embankment dams require more material because loose rock and earth are less dense than concrete. Engineers often choose to build them if the materials are readily available. Our Tarbela Dam contains more than 126 million cubic metres earth and rock. This amounts to more than 15 times the volume of concrete used in the Grand Coulee Dam.
Gravity dams hold back water only by the sheer force of their weight pushing downward. To do this, gravity dams must consist of a mass so heavy that the reservoir water cannot push the dam downstream or tip it over. They are much thicker at the base than the top. As water becomes deeper, it exerts more horizontal pressure on the dam. Gravity dams are relatively thin near the surface of the reservoir, where the water pressure is light. A thick base enables the dam to withstand more intense water pressure at the bottom of the reservoir.
Most gravity dams are made from concrete, a mixture of port land cement, water, and aggregates. Concrete is well suited for dam construction. A concrete gravity dam uses a triangular cross-section and steep upstream face. Its shape differs from that of the earthfill or rockfill dam in that its inward, water-facing side is perpendicular to the water surface; in profile, the dam forms a right-angled triangle.
The Grand Coulee Dam contains nearly 8 million cubic metres concrete. It is one of the most massive structures ever built, standing 168 metre high and 1,592 metre long.
Concrete arch dams are built in narrow, steep-walled canyons. The canyon walls take up the thrust exerted by the arch and the pressure of the water. Such dams can be extraordinarily thin. Vaiont Dam is 265 metres high, but only 22.7 metres thick at its base. In comparison, Hoover Dam is 221 metres high and 201 metres thick at its base and has a partial arch effect.
Glen Canyon Dam, which spans the Colorado River in Arizona, is the highest arch dam in the United States. It is 216 metres high and 475 metres long but contains less than four million cubic metres of concrete. Arch dams can be less expensive to build than gravity dams..
A buttress dam consists of a face supported by several buttresses on the downstream side. Buttress dams are made of concrete reinforced with steel. Buttresses are typically spaced across the dam site every 6 to 30 metre, depending upon the size and design of the dam. Buttress dams are sometimes called hollow dams because the buttresses do not form a solid wall stretching across a river valley.
Buttress dams require less concrete than gravity dams, but are not necessarily less expensive to build. Costs associated with the complex work of forming the buttresses or multiple arches may offset the savings in construction materials. Buttress dams may be desirable, however, in locations with foundations that would not easily support the massive size and weight of gravity dams.
Ha on April 24, 2017:
"Dam" that was a good page!
DE LUCKY on April 14, 2015:
I learned a lot in this page and it is a good idea that dams are introduced
Basheer Ahmad Mukhtar Ahmad Guru on April 22, 2012:
Its very usefull paper for introduction of dams.
I learned a lote from this page.
fantactic page. but imporoving of this page please insert pictures
Basheer Ahmad Mukhtar Ahmad
From: Pakistan chack No : 750/GB Kamali
muhammad faizan on March 17, 2012:
it is a very very very very.............................................. nice page it helped me soooooooooo much making my assignment THANK YOU SO MUCH:)
jaya on February 24, 2012:
it is a very good presentation.i love it,it's very useful for me and it helped for my science club exchibition. THANK YOU.
Bolaji abubakar on February 02, 2012:
It is a very good presentation, i love it am proud to be a civil engineer. Am more expose to different types of dam.
Gbadamosi Rukayat on February 02, 2012:
It help me a lot during d course of studing in hydraulics structure.l want u 2 put more emphasis on their method of construction.thank u very much ur effort
mhalappa khandekar on January 23, 2012:
nic info thanks
bettzy on January 22, 2012:
i got my research done because of this
kh on January 18, 2012:
nice dam inforamtion, thanks a lot
VEMOPIRE on January 09, 2012:
.....................THESE MUCH BE OF GOOD IF EACH TYPES OF DAMS ARE HAVING DRAWING AND THE LABEL OF EACH IMPORTANT PARTS!!!(^_^)............................
ankit on January 03, 2012:
hey can anybody tell me, what can be the different materials used for construction of dam????(e.g= i heard of rubber dam, what is the rubber dam????)
haji on December 28, 2011:
I get enough information
ROOPAN on December 18, 2011:
jayant on December 12, 2011:
raman on November 22, 2011:
it's good to have such kind of sites and r very helpful according to ur study point of view
lauren on November 19, 2011:
i think this website should tell me about the structure and force of dams!!!!!!!!!
ame on November 15, 2011:
It's really a good presentation thanks a lot for giving such a good information
7887 on November 10, 2011:
sadat on October 20, 2011:
that was avery good general out line
it wouid be excellent if some details of at least the main dams were added
akash on October 17, 2011:
thanks for giving me the appropriate information
Cristine O. Balgua on October 11, 2011:
very clear answers for my assignment..
and i never forget this...
I LEARN MANY kinds of Dams
Caroline A. Ogada on October 05, 2011:
This is a great paper for my MBA CDM coursework. Thank you very much
erions on September 23, 2011:
we came to know about different types of dams
thisis sailesh kumar on September 19, 2011:
this will helps us to study
Miss Bedford on August 28, 2011:
thanx a lot for the info. It helped a lot in my research on dam construction.
(first year Civil Engineering student. Western Cape, South Africa)
soniika sharma on August 27, 2011:
thanks for providing me good presentation on dams
phattypro on August 02, 2011:
thanks for the info now im going to play wow
lwazi lobi on June 14, 2011:
second yr.. civil engineering student, relevant information for my project....dam construction in limpompo
jeganathan on June 13, 2011:
vignesh on June 13, 2011:
its very informative
eddie f. ibanez on October 20, 2010:
PReN on October 12, 2010:
Provides decent enough information to get an understanding of what each type of dam is. (Johannesburg, South Africa)
ilyas on October 05, 2010:
Ganapati Joshi on September 24, 2010:
Good piece of information.
sathish on September 12, 2010:
you are expressing in a good manner go through an exellent manner
Niyon Lakshan on September 02, 2010:
This helped me a a lot with my assignment in CIVIL ENGINEERING CONSTRUCTION B-HND IN CIVIL ENGINEERING....
Thanks a lot Very Usefull website
Engr M Rahmat ullah Khan on August 27, 2010:
Really very informative, if some basic parameters are also incorporate during design then it will be more helpful
yaras khan on July 19, 2010:
plz give photos with each type of Dam
sukheshwar on July 09, 2010:
osman siddiquie on May 09, 2010:
too gud info for my company
Anna on March 31, 2010:
I would like more advanced and concise information
sunny on September 21, 2009:
helped a lot in my dam project (environmental studies Engineering)
jeevanandan on July 29, 2009:
hafeezrm from Pakistan on April 22, 2009:
I have a faint memory of an incident at the time initial filling of the lake of Tarbela Dam. If my memories are in tact, there were many villages which were not vacated by the residents as they were demanding more compensation. A time came, when the government had to decide whether to let them drown or open a drain tunnel which was only to be used when water level was very low. Eventually, the drain was opened which was ruptured with the thrust of water and it took quite sometime before re-filling was started. (This happened, as far as remembered, before power tunnel house tunnels were tested which cracked the crest of the basin. The concerned engineer, perhaps Italian, committed suicide.)
Is this all true?
Rocket Richard on March 23, 2009:
it really helped with my science homework
sobcee on March 16, 2009:
It's really a good presentation, I agree.
easy boy on January 29, 2009:
thanks a lot 4 giving such a good presentation on dams
Moses on January 23, 2009:
Hey guys, does anyone know anything about any specifications for impermeable clay cores in earthfill dams, especially with the desirability ratings of the soils in as far as expansive clay content (smectite) is concerned?
saranya on November 15, 2008:
provide more information.......about its types with its sketches
Sonia on November 04, 2008:
prove a helpful page for the preparation of my field report on dam.
Jane Mogotsi on September 10, 2008:
I agree with you Mzwa? ;-)
Mzwandile Mbatha on September 09, 2008:
Geat page for my second year civil engineering research on dams..(south africa)