Dam, History Dams, Construction, Buttress, Embankment, Gravity, Aswan, Edwards, Folsom, Grand Coulee, high, vital statistics, Reservoir, Capacity, Purpose, Materials. Engineers, Flood Control, Columbian Basin Project, Hoover, Hydroelectric, Concrete, Gravity, South Fork, Three Gorges Dam, Diversionary, Timber, Embankment, Rockfill, Masonry, Eder, Arch, Steel, Coffer, Beaver, Spillway, Teton Failure, Pablo, Outlet, Tunnelling, Power PLant, Road Tunnel Lyaskovo, Environment Planning, Stress, Soil Behaviour, parameters, impervious core, FEM, Mechanism,

Overview

Grand Coulee Dam is a large hydroelectric dam located on the Columbia river in Central Washington. Made from 12 million cubic yards of concrete, Grand Coulee Dam is the largest concrete structure in the United States and the third largest hydroelectric facility in the world. Sharing the river with 10 other U.S. dams, Grand Coulee is the first dam encountered on the Columbia after the river enters the U.S from Canada. Lake Roosevelt, the reservoir created by the dam, contains 9 million acre-feet of water and streches over 150 miles back to the border.

Grand Coulee Dam fills three primary rolls. First, with its 24 generators providing up to 6.5 million kilowatts of power, it is a major provider of electrical power to the Northwest. Secondly, water pumped from behind the dam provides irrigation for over half a million acres of the Columbia basin from Coulee City in the north to Pasco, WA in the south. Finally, by strictly regulating the Columbia's highly variable flow rate, the dam provides much needed flood control to the river basin.

History

Grand Coulee Dam and the Columbia Basin Project are managed by the U.S. Bureau of Reclamation, an agency of the Department of the Interior. The Bureau was established by congress in 1902 and was tasked with boosting development in the West by developing water storage and irrigation networks west of the 100th meridian. The Bureau took a tentative interest in providing Central Washington with irrigation water pumped from the Columbia as early as 1904. For one reason or another this idea was not followed up for several years.

The idea for damming the Columbia below the Grand Coulee was first proposed by Ephrata attorney William M. Clapp in the spring of 1917. The idea gained rapid support from the citizens of Ephrata and the surrounding area. Eventually the state government took an interest in the project as well.

Preliminary feasibility studies were carried out in the 1920s. Initially the primary purpose of the dam was to provide irrigation water. Although the dam idea had a great deal of local support there were other irrigation proposals in the works. In particular, a plan to build a long canal to carry water down from the Pend Oreille river in Northern Idaho was under serious consideration.

A final report favoring the construction of the dam was produced by the Corp of Engineers in late 1931 and presented to the 73d Congress of the United States as House Document #103. This was supplemented in January of 1932 by a report from the Bureau of Reclamation outlining the details of a dam-based irrigation project.

$377,000 was comitted to the project by the State of Washington in 1933. This was followed soon afterward by a promise from president Franklin D. Roosevelt to provide initial funds to the tune of 63 million dollars to begin work on the dam as a project under the Public Works Administration.

Not wanting to back up water into Canada, it was decided that the Canadian border would be the ultimate limiting factor as to how high the dam could be built. However, at the time there was a surplus of electric power in the Northwest and no major increase predicted for the foreseeable future. For this reason the original proposal called for a LOW dam. This dam would be 200 feet lower than the maximum height allowed by the Canadian border restriction. It would provide irrigation and flood control with the possibility of a reduced amount of power generation. However, it was decided to design the structure in such a way that it could be raised to its full height providing a corresponding increase in generation capacity if the need ever presented itself.

Initial excavation of the dam site began in December of 1933 with work toward improving the local infrastructure proceeding in parallel. On August 30, 1935 congress authorized the construction of the full high dam and no low dam version was ever completed. By 1941 the main dam was essentially finished with construction of the powerhouses and pumping plant underway.

Ironically, because of the Second World War and the importance of the Northwest's aluminum industry to that effort, the production of electricty became the overriding priority for the dam. Irrigation was deferred until later. During the war six Grand Coulee generators were brought on line as well as two generators borrowed from the yet to be completed Shasta dam.

After the war an emphasis was put back on irrigation. Construction was resumed on the pumping plant in 1946. By 1951 the plant and its six 65,000 horsepower pumps were ready for operation. The first water was delivered to the Banks Lake equalizing reservoir above the dam that same year. The first year only 66,000 acres were irrigated. Since then this figure has steadily increased as more canals, siphons, reservoirs and auxilary pumping plants have been added to the project.

In 1973 the pumping plant was extended to the south and two of six 67,500 horsepower pump-generator units were installed. Unlike the existing six pumps, these pump-generators can be reversed during periods of high power demands and operated as generators. In their generation mode each unit can produce 50,000 kW of electrical power. The remaining four pump/generator units were installed and operating by late 1983.

Dam

Jump to: navigation, search

This article discusses structures for water impoundment. For other meanings, see dam (disambiguation).

Scrivener Dam, in Canberra, Australia, was engineered to withstand a once-in-5000-years flood

A dam is a barrier across flowing water that obstructs, directs or retards the flow, often creating a reservoir, lake or impoundment. In Australian and South African English, the word "dam" can also refer to the reservoir rather than the structure. Most dams have a section called a spillway or weir over which or through which it is intended that water will flow either intermittently or continuously.

Contents below:

1 History
2 Types of dams
- 2.1 Diversionary dams
- 2.2 Timber dams
- 2.3 Embankment dams
- 2.4 Masonry dams
- 2.5 Gravity dams
- 2.6 Arch dams
- 2.7 Steel dams
- 2.8 Cofferdams
- 2.9 Beaver dams
3 Spillways
4 Other considerations
5 Examples of failed dams
6 See also
7 External links
8 Notes

History

Some of the first dams were built in Mesopotamia up to 7,000 years ago. These were used to control the water level, for Mesopotamia's weather effected the Tigris and Euphrates rivers and could be quite unpredictable. The earliest recorded dam is believed to have been on the Nile river at Kosheish, where a 15m high masonry structure was built about 2900 B.C. to supply water to capital of Memphis.

Types of dams

The Hoover Dam, a concrete gravity-arch dam in the Black Canyon of the Colorado River

Dams can be formed by human agency, natural causes, or by the intervention of wildlife such as beavers. Man-made dams are typically classified according to their structure, intended purpose or height.

Based on structure and material used, dams are classified as timber dams, embankment dams or masonry dams, with several subtypes.

Intended purposes include providing water for irrigation or 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, flood control and containing effluent from industrial sites such as mines or factories. Few dams serve all of these purposes but some multi-purpose dams serve more than one.

According to height, a large dam is higher than 15 metres and a major dam is over 150 metres in height. Alternatively, a low dam is less than 30 m high; a medium-height dam is between 30 and 100 m high, and a high dam is over 100 m high.

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 overtopped. A weir is a type of small overflow dam that can 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.

Diversionary dams

A diversionary dam is a structure designed to divert all or a portion of the flow of a river from its natural course.
Timber dams

A timber crib dam in Michigan, photographed in 1978.

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 due to 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.

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.

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.

Rock-fill dams

A rockfill dam

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 potentical 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

A Farmer's Dam

Earth-fill dams, also called earthen, rolled-earth or simply earth dams, are constructed 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. Examples of earth-fill dams include Nurek Dam in Tajikistan, the tallest dam in the world, and Oroville Dam, the tallest dam in the United States.

Masonry dams

Masonry dams are of either the gravity or the arch type.

Gravity dams

The Eder dam in Germany, built around 1910.

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, a gravity dam inspires more confidence in the layman than any other type; it has mass that lends an atmosphere of permanence, stability, and safety. When built on a carefully studied foundation with stresses calculated from completely evaluated loads, the gravity dam probably represents the best developed example of the art of dam building. This is significant because the fear of flood is a strong motivator in many regions, and has resulted in gravity dams being built in some instances where an arch dam would have been more economical.

Gravity dams are classified as "solid" or "hollow." 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.

With a height of 285m the tallest gravity dam in the world is the Grande Dixence Dam in Switzerland.

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. 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. See Geotechnical engineering.

Steel dams

Red Ridge steel dam, b. 1905, Michigan

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. Only two examples remain in the US.
Cofferdams

A cofferdam during the construction of locks at the Montgomery Point Lock and Dam.

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 decontructed unless the area requires continuous maintenance.

Beaver dams

Beaver dams are made by beavers and are made out of wood. they are also usually the beaver's home at the same time, becuase they are in a dome shape.
Spillways

Spillway on Llyn Brianne dam, Wales soon after first fill

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.

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 overtopped and washed away in the event of a large flood.

Any cavitation or turbulence of the water flowing over the spillway slowly erodes the dam's wetted surfaces. To minimize that erosion (especially with maximum water elevation at the crest), the downstream face of the spillway is ordinarily made an ogee curve.

It was the inadequate design of the spillway that caused the overtopping of a dam that caused the infamous Johnstown Flood.

Other considerations

The best place 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
peak flood flows
reservoir silting
environmental impacts on river fisheries, forests and wildlife (see 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

The reservoir emptying through the failed Teton Dam

Dam failures are generally catastrophic if the structure is breached or significantly damaged. Routine 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.

Examples of failed dams

Baldwin Hills Reservoir - 1963
Banqiao and Shimantan Dams - 1975
Big Bay Dam, Mississippi - 2004
Buffalo Creek Flood - 1972
Camará Dam - 2004
South Fork Dam - 1889
Kelly Barnes Dam - 1977
Lawn Lake Dam - 1982
Malpasset, Côte d'Azur, France - 1959
Opuha Dam - 1997
Shakidor Dam - 2005
St. Francis Dam, Los Angeles, California - 1928
Taum Sauk reservoir - 2005
Teton Dam - 1976
Tous Dam, Valencia, Spain - 1982
Vajont Dam - 1961
Val di Stava Dam Collapse - 1985

2/4	Dam Construction History of Dams	3/4
	Welcome Brian's compendium website on Dam Construction and the History of Dams Important words found on this site. Dam, History Dams, Construction, Buttress, Embankment, Gravity, Aswan, Edwards, Folsom, Grand Coulee, high, vital statistics, Reservoir, Capacity, Purpose, Materials. Engineers, Flood Control, Columbian Basin Project, Hoover, Hydroelectric, Concrete, Gravity, South Fork, Three Gorges Dam, Diversionary, Timber, Embankment, Rockfill, Masonry, Eder, Arch, Steel, Coffer, Beaver, Spillway, Teton Failure, Pablo, Outlet, Tunnelling, Power PLant, Road Tunnel Lyaskovo, Environment Planning, Stress, Soil Behaviour, parameters, impervious core, FEM, and Mechanism. Important words found on this site. You can find this site again by typing in the Google search engine the unique word " 1smaD " which is OR " Dams1 " backwards. or "1noitcurtsnoCmaD " which is OR " DamConstruction1 " backwards. Article Word Count 26,868