Embankment Dams

1. Download the data file Dams.docx from the Course Resources folder of the Start Here section. Also, you can download the same file from here too if that is easier for you, then save the document as EmbankmentDams.
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3. Apply the Heading 1 Quick Style to the following paragraphs: History, Overview, Aswan Dam, Dams of the Missouri River, Largest Embankment Dam: Itapu Dam, and Problems.
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19. On page 1, in the first paragraph under the History heading, using Insert Citation control / Add New Source first, select the highlighted text [citation], and then insert the following citation:
Type of Source: Book
Author: R.L. Warren
Title: Dam Building Deconstructed
Year: 2003
City: Boston

Publisher: Anston Press
20. On page 2, in the first paragraph under the Aswan Dam heading, using Insert Citation control / Add New Source first, select the highlighted text [citation] with the following citation:
Type of Source: Web Site

Name of web page: Modern Dams
Name of Web Site: The Science of Building
Year: 2014
Month Accessed: June
Day Accessed: 4

URL: building.org/dams/modern.html
21. On page 4, replace the highlighted text [citation] with a citation to Dam Building Deconstructed by R.L. Warren.
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23. Using Insert Citation control create the following source without inserting a citation to it:
Type of Source: Book
Author: Mark Crawford
Title: Dams on the Missouri
Year: 2001
City: New York
Publisher: Messier Publishing
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Embankment Dams History

Historically, dams have been embankment dams. Farmers would pile up soil to collect a pool of water to water their crops. One of the earliest recorded dams was an embankment dam built in Egypt constructed around 1800 B.C. It was 70 feet high, and 300 feet thick at the base [citation]. The middle of the dam was composed of clay, and cut stone was on both sides of this. The reservoir it created was known as Lake Moeris.

Until 1900, either embankment dams or dams built of cut stone fitted with hydraulic cement were commonly built. Then in the early part of the twentieth century, the United States Department of Reclamation took giant steps in the design of dams and the material used to build them; specifically, they started using concrete and reinforced concrete instead of cut stone. The Hoover and the Grand Coulee Dams were built during this time period. These new breeds of dams, although impressive, required enormous amounts of concrete and a huge labor force. These two factors drove up the cost significantly.

In the middle of the twentieth century, embankment dams became a more attractive option due to the availability of better earth-moving equipment, allowing dam builders to use fewer people to move very large amounts of material. Because of this and because embankment dams use more local materials, agencies such as the Department of Reclamation took a fresh look at embankment dams.

Overview

From outer space, the pyramids of Egypt, the Great Wall of China, and dams are the only visible traces of man’s handiwork on planet Earth. Water and power are key elements in any modern society. Dams provide both. Embankment dams, when properly designed and built, hold back the same amount of water for less cost than other types of dams.

Types of Dams

Dams are built in a variety of shapes and sizes. One of the most famous, the Hoover Dam, is a gravity arch dam. Gravity arch dams are a good choice when there are solid rock abutments on either side with which to anchor the dam. Gravity arch dams are also preferable when a dam must be taller than it is wide. Another famous dam is the Grand Coulee Dam, which is a concrete gravity buttress dam. This type of dam is a good choice when the dam must be very high. However, a disadvantage to both gravity arch dams and concrete buttress gravity dams are that millions of yards of concrete are needed to construct the dams.

Embankment dams may be less glamorous than gravity arch dams or concrete gravity buttress dam, but they get the job done. An embankment dam can hold back just as much water as a gravity arch dam or a concrete buttress gravity dam. Embankment dams, the most common type of dams in the world, can be any size and are built with local materials, such as rock, clay, gravel, and sand. Concrete is only used in strategic spots such as the spillways, locks, gatehouses and fish ladders. Embankment dams can be built when there is no solid bedrock to anchor the dam to, and some settlement of the dam during construction is allowable, unlike a massive concrete dam.

Aswan Dam

The Aswan High Dam, a classic example of an embankment dam, is located in Egypt. There have been many dams in the Aswan area, but in 1952, the Egyptian president Nassar pledged to control his country’s annual flood and to provide electric power and irrigation. The plans for the dam were drawn up by the British, but due to Cold War politics, the British withdrew and the Russians lent technical engineering personnel and paid for the dam at an estimated cost of $1 billion. The Aswan Dam created the fourth largest reservoir in the world. This dam is 360 feet high, 12,562 feet long, and 57,940,000 cubic yards of material was used in construction [citation].

The construction of the Aswan Dam provided many challenges to the dam builders. Perhaps the biggest challenge was that under the river bed, bedrock was over 600 feet down, and the material between the river bed and the bedrock was all layers of sand. The engineers were worried that if they placed the dam on top of the sand, the water would run under it. They came up with the answer of an alluvial grout curtain.

They drilled parallel rows of drill holes every 1.5 meters down to the bedrock, and then filled these holes with pressurized grout. Above this grout curtain they layered packed sand, gravel, dirt, and rubble. This solution prevented seepage under the dam. The impermeable layer in the dam, above the grout curtain, is a clay core. Six large tunnels were laid before the building of the dam was started. These tunnels transfer water from the front to the rear of the dam to 12 generators that provide 2.1 million kilowatts of electric power.

Dams on the Missouri River

The lakes behind the Hoover and Glen Canyon Dams, Lake Meade and Lake Powell, are the first and second largest reservoirs by volume in the United States, but the third, fourth, and fifth in volume are the reservoirs behind the six embankment dams on the Missouri River. In the mid-twentieth century, the Department of Reclamation started work on six major dams on the Missouri River. They decided to build embankment dams because there were no classic canyon walls on the Great Plains where a concrete dam could be anchored.

First Dam on the Missouri: Fort Peck

The first dam built on the Missouri was the Fort Peck Dam. This dam was unique because the engineers used the hydraulic fill method instead of the rolled-fill method, which is the usual method for building embankment dams. First, they built the power generation plant and the spillways, and then they filled the river in and piled rock and various other fill material into the river while it was still moving, much like a kid would dam up his neighborhood stream.

The problem with the hydraulic fill method is that an impermeable layer is very hard to install, if it’s even possible at all. While the river is being filled in, the fill is very prone to liquefaction. This problem was demonstrated when part of the Fort Peck Dam slipped 19 feet downstream during construction. To make up for this problem of liquefaction and no impermeable layer, huge amounts of material are added to hold the dam down and to keep it from sliding.

Dams That Followed the Fort Peck Dam

The other dams on the Missouri River—the Garrison, the Gavins Point, the Fort Randall, the Oahe, and the Big Bend Dams—were all built using the rolled-fill method. With the rolled-fill method, the river is first diverted with coffer dams, and then alternating layers of soil and rock are placed and compacted at every level. In the rolled-fill method, the moisture content of the fill is very high as the fill is applied in layers so that it approximates what its moisture content will be upon completion of the dam. Because the river has been diverted, it is much easier to add the impermeable layer.

Largest Embankment Dam: Itaipu Dam

The Itaipu Dam is the most recent and modern embankment dam in the world. It is also the largest power plant in the world. Located on the Parana River between Brazil and Paraguay, the Itaipu is an embankment dam constructed mostly of compacted rock. On the upstream face of the dam, a one-meter thick concrete sheet covers the rock. This thin layer of flexible concrete acts as the impermeable layer for the dam. The final cost of the Itaipu was roughly estimated at 20 million dollars. The builders estimated that if the dam had been made out of all concrete, such as a gravity buttress dam, it would have doubled the cost.

Construction

Large embankment dams are constructed of a variety of materials in alternating layers. Because the materials used are soil and rocks from the surrounding area, and there is no need to bring other materials, such as portland cement and reinforcing steel, to the dam site from great distances, the transportation costs are greatly reduced.
Slope

With embankment dams, water seeps into the dam and under it and tries to lift the dam up. An embankment dam holds back the water purely by its own weight, so it must be heavy enough that it does not slide sideways as the water pushes against it. Therefore, embankment dams are sloped so that they can use gravity to help stop the force of the water as the water pushes against it. This is much like the shore at the ocean’s edge.

Other forces also need to be taken into account when designing an embankment dam, such as ice and wave load on the upstream side, the effects of an earthquake, and the weight that might be on the top of the dam such as bridges, roads, and vehicles.
Most embankment dams are sloped at least at a 3 to 1 ratio or less on both the upstream and downstream sides of the dam to enable them to resist all the forces working against them. On many dams, this ratio is increased to as much as 40 to 1 at the upstream toe, or base, of the dam.

Permeability

Dams need an impermeable layer. In embankment dams, there are two locations for the impermeable layer. The first is in the middle of the dam. This type of impermeable layer is usually clay or bitumen. The second location is on the upstream face of the dam. This is usually accomplished by using a sheet of reinforced concrete with riveted metal. The advantage of putting the impermeable layer here is that it also can resist the wave action of the water.

Problems

The problems with embankment dams, even designed correctly, are erosion and overtopping. The upstream side of an embankment dam is usually faced with rocks to prevent wave action from eroding the structure. The downstream side must be protected from rain that lands on the top of the dam and runs down. Usually, either gravel or vegetation are used to control erosion.

The biggest danger to an embankment dam is when it becomes overtopped. Overtopping is when the level of the water rises higher than the top of the dam. In 1889, the Jonestown Dam in Jonestown, Pennsylvania, was overtopped during a big storm when its spillway became clogged with debris. The dam was overtopped and failed, resulting in a massive wave 37 feet high sweeping down and killing 2,200 people in the town a few miles below the dam [citation]. To avoid the overtopping problem, spillways need to be very carefully designed.

One way to do this is to build a spillway capacity of double that of the highest expected flow into the spillways. It is also very important that a spillway be designed to dissipate the energy of the falling water so that a scour hole that could erode under the dam does not occur. Many times this problem is solved by adding a ski jump shape at the bottom of the spillway to try to get as much air as possible into the water as it falls.

Throughout the centuries, mankind has harnessed water for irrigation, flood control, power, and navigation. The twentieth century saw many massive dams constructed around the world, but when looking for the lowest cost, an embankment dam must be considered as the most economical dam type where conditions permit

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