A
dam is a barrier that
impound water or
underground streams. Dams generally serve the primary purpose of
retaining water, while other structures such as
floodgates or
levees (also
known as
dikes) are used to
manage or prevent water flow into specific land regions.
Hydropower and
pumped-storage
hydroelectricity are often used in conjunction with dams to
provide clean electricity for millions of consumers.
History
The word
dam can be traced back to
Middle English, and before that, from
Middle Dutch, as seen in the names of
many old cities.
Most early dam building took place in
Mesopotamia and the
Middle East.
Dams were used to control the water level,
for Mesopotamia's weather affected the Tigris and Euphrates rivers, and could be quite
unpredictable.
The
earliest known dam is situated in Jawa, Jordan, 100 km
northeast of the capital Amman. This
gravity dam featured a 9 m high and 1 m wide stone wall, supported
by a 50 m wide earth rampart. The structure is dated to 3000 BC.
The
Ancient Egyptian Sadd Al-Kafara at
Wadi Al-Garawi, located about 25 kilometers south of Cairo, was 102 m
long at its base and 87 m wide. The structure was built
around 2800 or 2600 B.C. as a
diversion
dam for flood control, but was destroyed by heavy rain during
construction or shortly afterwards.
The Romans
were also great dam builders, with many examples such as the three
dams at Subiaco on the river Anio in
Italy. Many large dams also survive at Mérida in Spain.
The oldest
surviving and standing dam in the world is believed to be the
Quatinah barrage in modern-day Syria. The
dam is assumed to date back to the reign of the Egyptian Pharaoh
Sethi (1319–1304 BC), and was enlarged in the
Roman period and between 1934-38.
It still supplies the city of Homs with
water.
Eflatun
Pınar is a Hittite dam and spring temple near Konya,
Turkey. It's thought to the time of the Hittite empire
between the 15th and 13 century BC.
The
Kallanai is a massive dam of unhewn
stone, over 300 meters long, 4.5 meters high and 20 meters (60 ft)
wide, across the main stream of the
Kaveri
river in India. The basic structure dates to the 2nd century AD.
The purpose of the dam was to divert the waters of the Kaveri
across the fertile Delta region for irrigation via canals.
Du Jiang
Yan is the oldest surviving irrigation system in China
that included a dam that directed waterflow. It was finished
in 251 B.C.
A large earthen dam, made by the Prime Minister of Chu , Sunshu Ao,
flooded a valley in modern-day northern Anhui province
that created an enormous irrigation
reservoir (62 miles in circumference), a reservoir that is still
present today.
In
Iran, bridge dams were used to provide hydropower through water
wheels, which often powered water-raising mechanisms.
The first
was built in Dezful, which could
raise 50 cubits of water for the water supply to all houses in the town.
Also
diversion dams were
known.
Donald Routledge Hill
(1996), "Engineering", p. 759, in
Milling
dams were introduced which the
Muslim engineers called the
Pul-i-Bulaiti.
The first was built at Shustar on the River
Karun, Iran, and many of
these were later built in other parts of the Islamic world. Water was conducted from
the back of the dam through a large pipe to drive a water wheel and
watermill. In the 10th century,
Al-Muqaddasi described several dams in Persia.
He
reported that one in Ahwaz was more
than 3,000 feet long, and that and it had many water-wheels raising
the water into aqueducts through which it
flowed into reservoirs of the city.
Another one, the
Band-i-Amir dam, provided irrigation for
300 villages.
In the
Netherlands, a low-lying country, dams were often
applied to block rivers in order to regulate the water level and to
prevent the sea from entering the marsh lands. Such dams
often marked the beginning of a town or city because it was easy to
cross the river at such a place, and often gave rise to the
respective place's names in Dutch.
For instance the Dutch capital Amsterdam (old name Amstelredam) started with a dam
through the river Amstel in the late 12th
century, and Rotterdam started with a dam through the river
Rotte, a minor tributary of the Nieuwe Maas. The central square of Amsterdam, covering
the original place of the 800 year old dam, still carries the name
Dam
Square or simply the Dam.
Types of dams
Dams can be formed by human agency, natural causes, or even by the
intervention of wildlife such as
beavers.
Man-made dams are typically classified according to their size
(height), intended purpose or structure.
By size
International standards define
large dams as higher than
15-20 meters and
major dams as over 150-250 meters in
height.
The
tallest dam in the world is the 300-meter-high Nurek Dam in Tajikistan.
Intended purposes include providing water for
irrigation to town or city
water supply, improving navigation, creating a
reservoir of water to supply industrial uses, generating
hydroelectric power, creating recreation
areas or
habitat for fish and
wildlife, retaining wet season flow to minimise downstream
flood risk and containing
effluent from industrial sites such as
mines or factories. Some dams can also serve as
pedestrian or vehicular bridges across the river as well. When used
in conjunction with intermittent power sources such as wind or
solar, the reservoir can serve as pumped water storage to
facilitate base load dampening in the power grid. Few dams serve
all of these purposes but some multi-purpose dams serve more than
one.
A
saddle dam is an auxiliary dam constructed to confine
the reservoir created by a primary dam either to permit a higher
water elevation and storage or to limit the extent of a reservoir
for increased efficiency. An auxiliary dam is constructed in a low
spot or
saddle through which the reservoir would otherwise
escape. On occasion, a reservoir is contained by a similar
structure called a
dike to
prevent inundation of nearby land. Dikes are commonly used for
reclamation of arable land from a shallow lake. This is
similar to a
levee, which is a wall or
embankment built along a river or stream to protect adjacent land
from
flooding.
An
overflow dam is designed to be over topped. A
weir is a type of small overflow dam that are often
used within a river channel to create an impoundment lake for water
abstraction purposes and which can also be used for flow
measurement.
A
check dam is a small dam
designed to reduce flow velocity and control
soil erosion. Conversely, a
wing dam is a structure that only partly
restricts a waterway, creating a faster channel that resists the
accumulation of sediment.
A
dry dam is a dam designed to
control flooding. It normally holds back no water and allows the
channel to flow freely, except during periods of intense flow that
would otherwise cause flooding downstream.
A
diversionary dam is a
structure designed to divert all or a portion of the flow of a
river from its natural course.
By structure
Based on structure and material used, dams are classified as
timber dams,
arch-gravity dams,
embankment dams or
masonry dams, with several subtypes.
Masonry dams
Arch dams
In the arch dam, stability is obtained by a combination of arch and
gravity action. If the upstream face is vertical the entire weight
of the dam must be carried to the foundation by gravity, while the
distribution of the normal
hydrostatic pressure
between vertical
cantilever and arch
action will depend upon the
stiffness of
the dam in a vertical and horizontal direction. When the upstream
face is sloped the distribution is more complicated. The
normal component of the weight of the arch
ring may be taken by the arch action, while the normal hydrostatic
pressure will be distributed as described above. For this type of
dam, firm reliable supports at the abutments (either
buttress or
canyon side wall)
are more important. The most desirable place for an arch dam is a
narrow canyon with steep side walls composed of sound rock.The
safety of an arch dam is dependent on the strength of the side wall
abutments, hence not only should the arch be well seated on the
side walls but also the character of the rock should be carefully
inspected.
Two types of single-arch dams are in use, namely the constant-angle
and the constant-radius dam. The constant-radius type employs the
same face radius at all elevations of the dam, which means that as
the channel grows narrower towards the bottom of the dam the
central angle subtended by the face of the dam becomes smaller.
Jones Falls Dam, in Canada, is a
constant radius dam. In a constant-angle dam, also known as a
variable radius dam, this subtended angle is kept a constant and
the variation in distance between the abutments at various levels
are taken care of by varying the radii. Constant-radius dams are
much less common than constant-angle dams.
Parker Dam is a constant-angle arch dam.
A similar type is the double-curvature or thin-shell dam. Wildhorse
Dam near Mountain City, Nevada in the United States is an example
of the type. This method of construction minimizes the amount of
concrete necessary for construction but transmits large loads to
the foundation and abutments. The appearance is similar to a
single-arch dam but with a distinct vertical curvature to it as
well lending it the vague appearance of a concave lens as viewed
from downstream.
The
multiple-arch dam consists of a number of single-arch dams with
concrete buttresses as the supporting abutments, as for example the
Daniel-Johnson Dam, Québec, Canada. The multiple-arch dam does
not require as many buttresses as the hollow gravity type, but
requires good rock foundation because the buttress loads are
heavy.
Gravity dams
In a gravity dam, stability is secured by making it of such a size
and shape that it will resist overturning, sliding and crushing at
the toe. The dam will not overturn provided that the
moment around the turning point, caused by
the
water pressure is smaller than
the moment caused by the weight of the dam. This is the case if the
resultant force of water pressure
and weight falls within the base of the dam. However, in order to
prevent
tensile stress at the
upstream face and excessive
compressive stress at the downstream
face, the dam cross section is usually designed so that the
resultant falls within the middle at all elevations of the cross
section (the
core). For this type of dam,
impervious foundations with high
bearing strength are
essential.
When situated on a suitable site, gravity dams can prove to be a
better alternative to other types of dams. When built on a
carefully studied foundation, the gravity dam probably represents
the best developed example of dam building. Since the fear of
flood is a strong motivator in many regions,
gravity dams are being built in some instances where an arch dam
would have been more economical.
Gravity dams are classified as "solid" or "hollow". This is called
"Zoning". The core of the dam is zoned depending on the
availability of locally available materials, foundation conditions
and the material attributes. The solid form is the more widely used
of the two, though the hollow dam is frequently more economical to
construct. Gravity dams can also be classified as "overflow"
(spillway) and "non-overflow."
Grand Coulee Dam is a solid gravity dam and Itaipu Dam is a hollow gravity dam. A gravity dam can
be combined with an arch dam, an
arch-gravity dam, for areas with massive
amounts of water flow but less material available for a purely
gravity dam.
Embankment dams
Embankment dams are made from
compacted earth, and have two main types,
rock-fill and earth-fill dams. Embankment dams rely on their weight
to hold back the force of water, like the gravity dams made from
concrete.Recently there have been some interesting developments in
the production of a composite core fill for smaller embankments by
a British company, (The Instant Barrage Company). This composite
core fill has certain advantages in that it will not dry out in
long periods of exposure to dry conditions.
Rock-fill dams
Rock-fill dams are embankments of
compacted free-draining granular earth with an impervious zone. The
earth utilized often contains a large percentage of large particles
hence the term
rock-fill. The impervious zone may be on
the upstream face and made of masonry,
concrete, plastic membrane, steel sheet piles,
timber or other material. The impervious zone may also be within
the embankment in which case it is referred to as a
core.
In the instances where clay is utilized as the impervious material
the dam is referred to as a
composite dam. To prevent
internal erosion of clay into the rock fill due to seepage forces,
the core is separated using a filter. Filters are specifically
graded soil designed to prevent the migration of fine grain soil
particles. When suitable material is at hand, transportation is
minimized leading to cost savings during construction. Rock-fill
dams are resistant to damage from
earthquakes. However, inadequate quality control
during construction can lead to poor compaction and sand in the
embankment which can lead to
liquefaction of the rock-fill during
an earthquake. Liquefaction potential can be reduced by keeping
susceptible material from being saturated, and by providing
adequate compaction during construction.
An example of a
rock-fill dam is New
Melones Dam in California.
Earth-fill dams
Earth-fill dams, also called earthen, rolled-earth or simply earth
dams, are constructed as a simple
embankment of well compacted earth. A
homogeneous rolled-earth dam is
entirely constructed of one type of material but may contain a
drain layer to collect
seep water. A
zoned-earth
dam has distinct parts or
zones of dissimilar material,
typically a locally plentiful
shell with a watertight
clay core. Modern zoned-earth embankments
employ filter and drain zones to collect and remove seep water and
preserve the integrity of the downstream shell zone. An outdated
method of zoned earth dam construction utilized a
hydraulic fill to produce a watertight core.
Rolled-earth dams may also employ a watertight facing or
core in the manner of a rock-fill dam. An interesting type of
temporary earth dam occasionally used in high latitudes is the
frozen-core dam, in which a coolant is circulated through
pipes inside the dam to maintain a watertight region of
permafrost within it.
Tarbela Dam also Know Tora Bela Dam (Pashto) is a large dam on
the Indus
River in Pakistan. It is located about 50 km (31 mi) northwest
of Islamabad, and a height of 485 ft (148 m) above the river bed
and a reservoir size of 95 sq mi (250 km2) makes it the largest
earth filled dam in the world. The principal element of the project
is an embankment 9,000 feet (2743 meters) long with a maximum
height of 465 feet (143 meters). The total volume of earth and rock
used for the project is approximately 200 million cubic yards
(152.8 million cu. Meters) which makes it the largest man made
structure in the world , except for the Great Chinese Wall which
consumed somewhat more material.
Because earthen dams can be constructed from materials found
on-site or nearby, they can be very cost-effective in regions where
the cost of producing or bringing in concrete would be
prohibitive.
Asphalt-concrete core
A third type of embankment dam is built with
asphalt concrete core. The majority of such
dams are built with rock and/or gravel as the main fill material.
Almost 100 dams of this design have now been built worldwide since
the first such dam was completed in 1962. All asphalt-concrete core
dams built so far have an excellent performance record. The type of
asphalt used is a
viscoelastic-
plastic material that can adjust to the movements
and deformations imposed on the embankment as a whole, and to
settlements in the foundation. The flexible properties of the
asphalt make such dams especially suited in
earthquake regions.
Cofferdams
A
cofferdam is a (usually temporary)
barrier constructed to exclude water from an area that is normally
submerged. Made commonly of wood,
concrete
or
steel sheet
piling,
cofferdams are used to allow construction on the
foundation of permanent dams,
bridges, and similar structures. When the project is completed, the
cofferdam may be demolished or removed. See also
causeway and
retaining
wall. Common uses for cofferdams include construction and
repair of off shore oil platforms. In such cases the cofferdam is
fabricated from sheet steel and welded into place under water. Air
is pumped into the space, displacing the water allowing a dry work
environment below the surface. Upon completion the cofferdam is
usually deconstructed unless the area requires continuous
maintenance.
Timber dams
Timber dams were widely used in the early
part of the industrial revolution and in frontier areas due to ease
and speed of construction. Rarely built in modern times by humans
because of relatively short lifespan and limited height to which
they can be built, timber dams must be kept constantly wet in order
to maintain their water retention properties and limit
deterioration by rot, similar to a barrel. The locations where
timber dams are most economical to build are those where timber is
plentiful,
cement is costly or difficult to
transport, and either a low head diversion dam is required or
longevity is not an issue. Timber dams were once numerous,
especially in the North American west, but most have failed, been
hidden under earth embankments or been replaced with entirely new
structures. Two common variations of timber dams were the
crib and the
plank.
Timber crib dams were erected of heavy timbers or dressed
logs in the manner of a log house and the interior filled with
earth or rubble. The heavy crib structure supported the dam's face
and the weight of the water.
Splash dams
were timber crib dams used to help float
logs downstream in the late 19th and early 20th
centuries.
Timber plank dams were more elegant structures that
employed a variety of construction methods utilizing heavy timbers
to support a water retaining arrangement of planks.
Very few timber dams are still in use. Timber, in the form of
sticks, branches and withes, is the basic material used by
beavers, often with the addition of mud or
stones.
Steel dams
Red Ridge steel dam, b.
A
steel dam is a type of dam briefly
experimented with in around the turn of the 19th-20th Century which
uses steel plating (at an angle) and load bearing beams as the
structure. Intended as permanent structures, steel dams were an
(arguably failed) experiment to determine if a construction
technique could be devised that was cheaper than masonry, concrete
or earthworks, but sturdier than timber crib dams.
Beaver dams
Beavers create dams primarily out of mud and sticks to flood a
particular habitable area. By flooding a parcel of land, beavers
can navigate below or near the surface and remain relatively well
hidden or protected from predators. The flooded region also allows
beavers access to food, especially during the winter.
Construction elements
Power generation plant
As of 2005, hydroelectric power, mostly from dams, supplies some
19% of the world's electricity, and over 63% of
renewable energy.
Much of this is
generated by large dams, although China uses small
scale hydro generation on a wide scale and is responsible for about
50% of world use of this type of power.
Most hydroelectric power comes from the
potential energy of dammed water driving a
water turbine and
generator; to boost the power
generation capabilities of a dam, the water may be run through a
large pipe called a
penstock before the
turbine. A variant on this simple model uses
pumped storage
hydroelectricity to produce electricity to match periods of
high and low demand, by moving water between
reservoirs at different elevations. At
times of low electrical demand, excess generation capacity is used
to pump water into the higher reservoir. When there is higher
demand, water is released back into the lower reservoir through a
turbine.
Hydroelectric dam in cross
section.
Spillways
A
spillway is a section of a dam designed to pass water
from the upstream side of a dam to the downstream side. Many
spillways have
floodgates designed to
control the flow through the spillway. Types of spillway include: A
service spillway or
primary spillway passes
normal flow. An
auxiliary spillway releases flow in excess
of the capacity of the service spillway. An
emergency
spillway is designed for extreme conditions, such as a serious
malfunction of the service spillway. A
fuse plug spillway is a low embankment
designed to be over topped and washed away in the event of a large
flood. Fusegate elements are independent free-standing block set
side by side on the spillway which work without any remote control.
They allow to increase the normal pool of the dam without
compromising the security of the dam because they are designed to
be gradually evacuated for exceptional events. They work as fixed
weir most of the time allowing overspilling for the common
floods.
The spillway can be gradually
eroded by
water flow, including
cavitation or
turbulence of the water flowing over the
spillway, leading to its failure.
It was the inadequate design of the
spillway which led to the 1889 over-topping of the South Fork
Dam in Johnstown, Pennsylvania, resulting in the infamous Johnstown
Flood (the "great flood of 1889").
Erosion rates are often monitored, and the risk is ordinarily
minimized, by shaping the downstream face of the spillway into a
curve that minimizes turbulent flow, such as an
ogee curve.
Dam creation
Common purposes
Function |
Example |
Power generation |
Hydroelectric power is a
major source of electricity in the world. Many countries have
rivers with adequate water flow, that can be dammed for power
generation purposes. For example, the Itaipu on the
Paraná
River in South America
generates 14 GW and supplied 93% of the energy
consumed by Paraguay and 20% of that consumed by Brazil as of
2005. |
Water supply |
Many urban areas of the world are supplied with water
abstracted from rivers pent up behind low dams or weirs.
Examples
include London - with
water from the River Thames and
Chester with water taken from the River Dee. Other major sources
include deep upland reservoirs contained by high dams across deep
valleys such as the Claerwen series of dams and reservoirs. |
Stabilize water flow /
irrigation |
Dams are often used to control and stabilize water
flow, often for agricultural
purposes and irrigation. Others such as the
Berg Strait dam can help to stabilize or
restore the water levels of inland lakes and seas, in this
case the Aral
Sea. |
Flood prevention |
Dams
such as the Blackwater dam of
Webster, New
Hampshire and the
Delta
Works are created with flood control in mind. |
Land reclamation |
Dams (often called dykes or
levees in this context) are used to prevent
ingress of water to an area that would otherwise be submerged,
allowing its reclamation for human
use. |
Water diversion |
A typically small dam used to divert water for irrigation,
power generation, or other uses, with usually no other function.
Occasionally, they are used to divert water to another drainage or
reservoir to increase flow there and improve water use in that
particular area. See: diversion
dam. |
Recreation and aquatic beauty |
Dams built for any of the above purposes may find themselves
displaced by time of their original uses. Nevertheless the local
community may have come to enjoy the reservoir for recreational and
aesthetic reasons. Often the reservoir will be placid and
surrounded by greenery, and convey to visitors a natural sense of
rest and relaxation. |
Location
One of the best places for building a dam is a narrow part of a
deep
river valley; the
valley sides can then act as natural walls. The primary function of
the dam's structure is to fill the gap in the natural reservoir
line left by the stream channel. The sites are usually those where
the gap becomes a minimum for the required storage capacity. The
most economical arrangement is often a composite structure such as
a
masonry dam flanked by earth embankments.
The current use of the land to be flooded should be
dispensable.
Significant other
engineering and
engineering geology
considerations when building a dam include:
- permeability of the
surrounding rock or soil
- earthquake faults
- landslides and slope stability
- water table
- peak flood flows
- reservoir silting
- environmental
impacts on river fisheries, forests and wildlife (see also
fish ladder)
- impacts on human habitations
- compensation for land being flooded as well as population
resettlement
- removal of toxic materials and buildings from the proposed
reservoir area
Impact assessment
Impact is assessed in several ways: the benefits to human society
arising from the dam (agriculture, water, damage prevention and
power), harm or benefits to nature and wildlife (especially fish
and
rare species), impact on the
geology of an area - whether the change to water flow and levels
will increase or decrease stability, and the disruption to human
lives (relocation, loss of
archeological or cultural matters
underwater).
Environmental impact
Wood and garbage accumulated because
of a dam
Dams affect many ecological aspects of a river. Rivers depend on
the constant disturbance of a certain tolerance.
Dams slow Water
exiting a turbine usually contains very little suspended sediment,
which can lead to scouring of river beds and loss of riverbanks;
for example, the daily cyclic flow variation caused by the Glen Canyon
Dam was a contributor to sand
bar erosion.
Older dams often lack a
fish ladder,
which keeps many fish from moving up stream to their natural
breeding grounds, causing failure of breeding cycles or blocking of
migration paths. Even the presence of a fish ladder does not always
prevent a reduction in fish reaching the
spawning grounds upstream. In some areas,
young fish ("smolt") are transported downstream by
barge during parts of the year. Turbine and
power-plant designs that have a lower impact upon aquatic life are
an active area of research.
A large dam can cause the loss of entire
ecospheres, including
endangered and
undiscovered species in the area, and the
replacement of the original environment by a new inland lake.
Depending upon the circumstances, a dam can either reduce or
increase the net production of
greenhouse
gases. An
increase can occur if the reservoir
created by the dam itself acts as a source of substantial amounts
of potent
greenhouse gases (
methane and
carbon
dioxide) due to plant material in flooded areas decaying in an
anaerobic environment. A
study for the National Institute for Research in the Amazon found
that Hydroelectric dams release a large pulse of carbon dioxide
from above-water decay of trees left standing in the reservoirs,
especially during the first decade after closing. This elevates the
global warming impact of the dams to levels much higher than would
occur by generating the same power from fossil fuels. According to
the
World Commission on
Dams report (Dams And Development), when the reservoir is
relatively large and no prior clearing of forest in the flooded
area was undertaken, greenhouse gas emissions from the reservoir
could be higher than those of a conventional oil-fired thermal
generation plant.
For instance, In 1990, the impoundment
behind the Balbina
Dam in Brazil(closed in 1987) had over 20 times the
impact on global warming than would generating the same power from
fossil fuels, due to the large area flooded per unit of electricity
generated. A
decrease can occur if the dam
is used in place of traditional power generation, since electricity
produced from hydroelectric generation does not give rise to any
flue gas
emissions from fossil fuel combustion (including
sulfur dioxide,
nitric oxide,
carbon
monoxide, dust, and
mercury
from
coal).
The Tucurui dam in Brazil (closed in 1984) had only 0.4 times the
impact on global warming than would generating the same power from
fossil fuels.
Large lakes formed behind dams have been indicated as contributing
to earthquakes, due to changes in loading and/or the height of the
water table.
Human social impact
The impact on human society is also significant.
For example, the
Three Gorges
Dam on the Yangtze River in China is more than
five times the size of the Hoover Dam (U.S.), and will
create a reservoir 600 km long to be used for hydro-power
generation. Its construction required the loss of over a
million people's homes and their mass relocation, the loss of many
valuable archaeological and cultural sites, as well as significant
ecological change. It is estimated that to date, 40-80 million
people worldwide have been physically displaced from their homes as
a result of dam construction.
Economics
Construction of a
hydroelectric
plant requires a long lead-time for site studies, hydrological
studies, and environmental impact assessment, and are large scale
projects by comparison to traditional power generation based upon
fossil fuels. The number of sites that
can be economically developed for hydroelectric production is
limited; new sites tend to be far from population centers and
usually require extensive
power
transmission lines. Hydroelectric generation can be vulnerable
to major changes in the
climate, including
variation of rainfall, ground and surface
water levels, and glacial melt, causing
additional expenditure for the extra capacity to ensure sufficient
power is available in low water years.
Once completed, if it is well designed and maintained, a
hydroelectric power source is usually comparatively cheap and
reliable. It has no fuel and low escape risk, and as an
alternative energy source it is cheaper
than both nuclear and wind power. It is more easily regulated to
store water as needed and generate high power levels on demand
compared to
wind power, although dams
have life expectancies while
renewable
energies do not.
Dam failure
International special sign for works
and installations containing dangerous forces
Dam failures are generally catastrophic if the structure is
breached or significantly damaged. Routine
deformation monitoring of seepage
from drains in and around larger dams is necessary to anticipate
any problems and permit remedial action to be taken before
structural failure occurs. Most dams incorporate mechanisms to
permit the reservoir to be lowered or even drained in the event of
such problems. Another solution can be rock
grouting - pressure pumping
portland cement slurry
into weak fractured rock.
During an armed conflict, a dam is to be considered as an
"installation containing dangerous forces" due to the massive
impact of a possible destruction on the civilian population and the
environment. As such, it is protected by the rules of
International Humanitarian
Law (IHL) and shall not be made the object of attack if that
may cause severe losses among the civilian population. To
facilitate the identification, a
protective sign consisting of three bright
orange circles placed on the same axis is defined by the rules of
IHL.
The main
causes of dam failure include spillway design error (South Fork
Dam), geological instability caused by changes to water
levels during filling or poor surveying (Vajont Dam, Malpasset), poor maintenance, especially of outlet pipes
(Lawn Lake
Dam, Val di Stava Dam collapse), extreme rainfall (Shakidor Dam), and human, computer or design
error (Buffalo
Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage
plant).
A notable
case of deliberate dam failure (prior to the above ruling) was the
Royal Air Force 'Dambusters' raid on Germany in World War II
(codenamed "Operation
Chastise"), in which three German dams were selected to be
breached in order to have an impact on German infrastructure and
manufacturing and power capabilities deriving from the Ruhr and Eder rivers. This
raid later became the basis for several films.
Since
2007, the Dutch IJkdijk foundation is developing, with an open innovation model an early warning
system for levee/dike failures. As a part of the development
effort, full scale dikes are destroyed in the IJkdijk fieldlab. The
destruction process is monitored by sensor networks from an
international group of companies and scientific institutions.
Notes
- The American Heritage Dictionary of the English Language,
Fourth Edition
- Source: Tijdschrift voor Nederlandse Taal- en
Letterkunde (Magazine for Dutch Language and
Literature), 1947. The first known appearance of the word
dam stems from 1165. However, there is one village, Obdam,
that is already mentioned in 1120. The word seems to be related to
the Greek word taphos, meaning grave or grave
hill. So the word should be understood as dike from dug
out earth. The names of more than 40 places (with minor
changes) from the Middle Dutch era (1150–1500 CE) such as
Amsterdam (founded
as 'Amstelredam' in the late 12th century) and Rotterdam, also bear testimony to
the use of the word in Middle Dutch at that time.
- Günther Garbrecht: "Wasserspeicher (Talsperren) in der Antike",
Antike Welt, 2nd special edition: Antiker
Wasserbau (1986), pp.51-64 (52)
- S.W. Helms: "Jawa Excavations 1975. Third Preliminary Report",
Levant 1977
- Günther Garbrecht: "Wasserspeicher (Talsperren) in der Antike",
Antike Welt, 2nd special edition: Antiker
Wasserbau (1986), pp.51-64 (52f.)
- Needham, Joseph (1986). Science and Civilization in China:
Volume 4, Part 3. Taipei: Caves Books, Ltd.
- Adam Lucas (2006), Wind, Water, Work: Ancient and Medieval
Milling Technology, p. 62. BRILL, ISBN 9004146490.
- Guinness Book of Records 1997 Pages 108-109 ISBN
0-85112-693-6
- Renewables Global Status Report 2006 Update,
REN21, published
2006, accessed 2007-05-16
- Dam Fact Sheet
- Fearnside, P.M. 1995. hydroelectric dams in the Brazilian
Amazon as sources of 'greenhouse' gases. Environmental Conservation
22(1): 7-19.]
- Hydroelectric power's dirty secret revealed - earth
- 24 February 2005 - New Scientist
- World Commission on Dams Report
See also
External links
- Providence Journal video of the Blackstone River
- International Commission on Large Dams (ICOLD)
- Structurae: Dams and Retaining Structures
- The World's Largest Dams
- Historical Development of Arch Dams : from
Cut-Stone Arches to Modern Concrete Designs, Australian
Civil/Structural Engineering Transactions, CE43 : 39-56, 2002
- Timber Crib Weirs in Queensland, Australia: Some
Heritage Structures with a Solid Operational Record, Royal
Historical Society of Queensland Journal, 18 3: 115-129, 2002
- Dams on Planete-TP
- "Design of Small Dams", US Bureau of Reclamation,
65MB pdf
- "Dam science" Canadian Geographic
- International Rivers
- Dam
Research
- asphaltcoredams.com
- University of Washington Freshwater and Marine
Image Bank Collection
- Bibliography on Water Resources and International
Law Peace Palace Library
- Railway Dams in Australia: Six Historical
Structures, Transactions Newcomen Society, 71 b: 283-304,
1999
- The 75-Miles Dam in Warwick : The World's Oldest
Concrete Arch Dam, Royal Historical Society of Queensland
Journal, 17 2: 65-75
- Application of the Method of Characteristics to the
Dam Break Wave Problem, Journal of Hydraulic Research,
IAHR, 47 1: 41-49 (DOI: 10.3826/jhr.2009.2865).