Why would someone want to build a dam?

 

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Water is one of our most precious resources; our lives depend on it. Throughout the history of humankind, people have built dams to maximize use of this vital resource.  

Dams provide a life-sustaining resource to people in all regions of the United States. They are an extremely important part of this nation&#;s infrastructure&#;equal in importance to bridges, roads, airports, and other major elements of the infrastructure. They can serve several functions at once, including water supply for domestic, agricultural, industrial, and community use; flood control; recreation; and clean, renewable energy through hydropower.

As populations have grown and moved to arid or flood-prone locations, the need for dams has increased.

Potential Benefits of Dams

Renewable, clean energy: According to the U.S. Department of Energy, in , hydropower accounted for more than 7% of U.S. electricity generation and nearly 37% of U.S. renewable electricity generation.

Flood control: Dams built with the assistance of the Natural Resources Conservation Service provide an estimated $1.7 billion in annual benefits in reduced flooding and erosion damage, recreation, water supplies, and wildlife habitat. Dams owned and operated by the Tennessee Valley Authority produce electricity and prevent an average of about $280 million in flood damage each year.

Water storage: Dams create reservoirs that supply water for a multitude of uses, including fire control, irrigation, recreation, domestic and industrial water supply, and more.

Irrigation: Ten percent of American cropland is irrigated using water stored behind dams.

Navigation: U.S. Army Corps of Engineers navigation projects in the U.S. serve 41 states, maintain 12,000 miles of channels, carry 15% of U.S. freight carried by inland waterways, operate 275 locks, and maintain 926 harbors.

Recreation: Dams provide prime recreational facilities throughout the U.S. Ten percent of the U.S. population visits at least one U.S. Army Corps of Engineers facility each year.

The purpose of a dam is to impound (store) water, wastewater or liquid borne materials for any of several reasons, such as flood control, human water supply, irrigation, livestock water supply, energy generation, containment of mine tailings, recreation, or pollution control. Many dams fulfill a combination of the above functions.

Manmade dams may be classified according to the type of construction material used, the methods used in construction, the slope or cross-section of the dam, the way the dam resists the forces of the water pressure behind it, the means used for controlling seepage and, occasionally, according to the purpose of the dam.

The materials used for construction of dams include earth, rock, tailings from mining or milling, concrete, masonry, steel, timber, miscellaneous materials (such as plastic or rubber) and any combination of these materials.

Types of Dams

Embankment Dam

Forces Acting on an Embankment Dam

Gravity Dam

Forces Acting on a Concrete Gravity Dam

Buttress Dam

Forces Acting on a Buttress Dam

Arch Dam

Forces Acting on an Arch Dam

Types of Dams

Embankment Dams: Embankment dams are the most common type of dam in use today. Materials used for embankment dams include natural soil or rock, or waste materials obtained from mining or milling operations. An embankment dam is termed an &#;earthfill&#; or &#;rockfill&#; dam depending on whether it is comprised of compacted earth or mostly compacted or dumped rock. The ability of an embankment dam to resist the reservoir water pressure is primarily a result of the mass weight, type and strength of the materials from which the dam is made.                   

Concrete Dams: Concrete dams may be categorized according to the designs used to resist the stress due to reservoir water pressure. Three common types of concrete dams are: gravity, buttress and arch.

Gravity: Concrete gravity dams are the most common form of concrete dam. The mass weight of concrete and friction resist the reservoir water pressure. Gravity dams are constructed of vertical blocks of concrete with flexible seals in the joints between the blocks.

Buttress: A buttress dam is a specific type of gravity dam in which the large mass of concrete is reduced, and the forces are diverted to the dam foundation through vertical or sloping buttresses.

Arch: Concrete arch dams are typically rather thin in cross-section. The reservoir water forces acting on an arch dam are carried laterally into the abutments.The shape of the arch may resemble a segment of a circle or an ellipse, and the arch may be curved in the vertical plane as well. Such dams are usually constructed of a series of thin vertical blocks that are keyed together; barriers to stop water from flowing are provided between blocks. Variations of arch dams include multi-arch dams in which more than one curved section is used, and arch-gravity dams which combine some features of the two types of dams.

Because the purpose of a dam is to retain water effectively and safely, the water retention ability of a dam is of prime importance. Water may pass from the reservoir to the downstream side of a dam by any of the following:

• Passing through the main spillway or outlet works
• Passing over an auxiliary spillway
• Overtopping the dam
• Seepage through the abutments
• Seepage under the dam

Overtopping of an embankment dam is very undesirable because the embankment materials may be eroded away (See Video Example). Additionally, only a small number of concrete dams have been designed to be overtopped. Water normally passes through the main spillway or outlet works; it should pass over an auxiliary spillway only during periods of high reservoir levels and high water inflow. All embankment and most concrete dams have some seepage. However, it is important to control the seepage to prevent internal erosion and instability. Proper dam construction, and maintenance and monitoring of seepage provide this control.

Release of Water

Intentional release of water is confined to water releases through outlet works and spillways. A dam typically has a principal or mechanical spillway and a drawdown facility. Additionally, some dams are equipped with auxiliary spillways to manage extreme floods.

Outlet Works: In addition to spillways that ensure that the reservoir does not overtop the dam, outlet works may be provided so that water can be drawn continuously, or as needed, from the reservoir. They also provide a way to draw down the reservoir for repair or safety concerns. Water withdrawn may be discharged into the river below the dam, run through generators to provide hydroelectric power, or used for irrigation. Dam outlets usually consist of pipes, box culverts or tunnels with intake inverts near minimum reservoir level. Such outlets are provided with gates or valves to regulate the flow rate.

Spillways: The most common type of spillway is an ungated concrete chute. This chute may be located over the dam or through the abutment. To permit maximum use of storage volume, movable gates are sometimes installed above the crest to control discharge. Many smaller dams have a pipe and riser spillway, used to carry most flows, and a vegetated earth or rockcut spillway through an abutment to carry infrequent high flood flows. In dams such as those on the Mississippi River, flood discharges are of such magnitude that the spillway occupies the entire width of the dam and the overall structure appears as a succession of vertical piers supporting movable gates. High arch-type dams in rock canyons usually have downstream faces too steep for an overflow spillway. In Hoover Dam on the Colorado River, for example, a shaft spillway is used. In shaft spillways, a vertical shaft upstream from the dam drains water from the reservoir when the water level becomes high enough to enter the shaft or riser; the vertical shaft connects to a horizontal conduit through the dam or abutment into the river below.

The National Inventory of Dams (NID) has catalogued the more than 90,000 dams on America's waterways according to their hazard classification. Hazard classification is determined by the extent of damage a failure would cause downstream, with high-hazard potential dams resulting in loss of life and significant-hazard potential indicating a failure would not necessarily cause a loss of life, but could result in significant economic losses. As you can see on this map from the NID, there are numerous dams across America and ensuring their safety is a critical goal.

Safety is key to the effectiveness of a dam. Dam failures can be devastating for the dam owners, to the dam&#;s intended purpose and, especially, for downstream populations and property. Property damage can range in the thousands to billions of dollars. No price can be put on the lives that have been lost and could be lost in the future due to dam failure. Failures know no state boundaries&#;inundation from a dam failure could affect several states and large populations.

Early in this century, as many dams failed due to lack of proper engineering and maintenance, it was recognized that some form of regulation was needed. One of the earliest state programs was enacted in California in the s. Federal agencies, such as the Corps of Engineers and the Department of Interior, Bureau of Reclamation built many dams during the early part of the twentieth century and established safety standards during this time. Slowly, other states began regulatory programs. But it was not until the string of significant dam failures in the s that awareness was raised to a new level among the states and the federal government.

State Regulation Today

Today, every state except Alabama has a dam safety regulatory program. State governments have regulatory responsibility for 70% of the approximately 90,000 dams within the National Inventory of Dams. These programs vary in authority but, typically, the program activities include:

• Safety evaluations of existing dams
• Review of plans and specifications for dam construction and major repair work
• Periodic inspections of construction work on new and existing dams
• Review and approval of emergency action plans

Federal Regulation Today

There are several federal government agencies involved with dam safety. Together, these federal agencies are responsible for five percent of the dams in the U.S. They construct, own and operate, regulate or provide technical assistance and research for dams. Included in this list are the Departments of Agriculture, Defense, Energy, Interior, Labor and State (International Boundary and Water Commission), the Federal Energy Regulatory Commission, Nuclear Regulatory Commission and the Tennessee Valley Authority. The Federal Emergency Management Agency administers the National Dam Safety Program, a program established by law in to coordinate the federal effort through the Interagency Committee on Dam Safety, to assist state dam safety programs through financial grants, and to provide research funding and coordination of technology transfer.

Federal Agencies

Federal agency representatives make up about 16% of the ASDSO membership. About 14% of dams in the USA are owned or regulated by federal agencies.

The Federal Emergency Management Agency (FEMA), part of the Department of Homeland Security, does not own or regulate dams itself but administers the National Dam Safety Program, which coordinates all federal dam safety programs and assists states in improving their dam safety regulatory programs. The Office of Infrastructure Protection, also within the Department of Homeland Security, leads a coordinated national program to reduce risks to the nation's critical infrastructure, including dams, posed by acts of terrorism.

Federal agencies involved with dam safety, either as owners and/or regulators, include the following:

U.S. Department of Agriculture

• Natural Resources Conservation Service
• Agriculture Research Service

Department of Defense

• Army Corps of Engineers
• Engineer Research and Development Center
• Hydrologic Engineering Center (HEC)

Department of the Interior

• Bureau of Indian Affairs
• Bureau of Land Management
• Bureau of Reclamation
• Fish & Wildlife Service
• National Park Service
• Office of Surface Mining

Federal Energy Regulatory Commission

Mine Safety and Health Administration

International Boundary and Water Commission (U.S. Section)

Nuclear Regulatory Commission

Tennessee Valley Authority

Together the agencies listed above make up the Interagency Committee on Dam Safety (ICODS), overseen by FEMA as head of the National Dam Safety Program.

Other federal agencies that stay involved with ASDSO and the dam safety community are the National Oceanic and Atmospheric Association (NOAA), National Weather Service and the U.S. Geological Survey.

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Note that not all lessons and activities will exist under a unit, and instead may exist as "standalone" curriculum.

Units serve as guides to a particular content or subject area. Nested under units are lessons (in purple) and hands-on activities (in blue).

Summary

Students are introduced to the concept of a dam and its potential benefits, which include water supply, electricity generation, flood control, recreation and irrigation. This lesson begins an ongoing classroom scenario in which student engineering teams working for the Splash Engineering firm design dams for a fictitious client, Thirsty County.

This engineering curriculum aligns to Next Generation Science Standards ( NGSS ).

The Hoover Dam on the Colorado River.copyright

Copyright © US Bureau of Reclamation http://www.usbr.gov/lc/hooverdam/images/D001a.jpg

The company is the world’s best dam construction companies supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

Engineering Connection

Human-made dams are important in our modern life. Civil engineers and city planners compare the benefits, cost and environmental impacts to determine whether a community could benefit from a dam.

Learning Objectives

After this lesson, students should be able to:

• Interpret and evaluate data to formulate conclusions.
• Understand the needs for and impacts of dams and reservoirs.
• Describe how the use of technology provides essentials and luxuries for everyday living.

Introduction/Motivation

Where does your water come from? Mountains, rivers, reservoirs? What is a reservoir? A reservoir is a human-made lake created by building a dam. Why do we need dams? When you turn on a faucet at home, where does that water come from? Why is there always water coming out? There is always a supply of water because we hold water in reservoirs. To do this, we must build dams.

Why else do we build dams? (Take suggestions; write answers on the board.) Dams are important because they provide water for domestic, industry and irrigation purposes. Dams often also provide hydroelectric power production and river navigation. Domestic use includes everyday activities such as water for drinking, cooking, bathing, washing, and lawn and garden watering. Dams and their reservoirs provide recreation areas for fishing and boating. They help people by reducing or preventing floods. Students can learn more about why dams are built with the associated activity How Much Water Do You Use? During times of excess water flow, dams store water in the reservoir; then they release water during times of low flow, when natural flows are inadequate to meet water demand. When engineers design and maintain dams, they consider all these purposes.Bagnell Dam on the Osage River in Missouri.copyright

Copyright © Microsoft Corporation, One Microsoft Way, Redmond, WA - USA. All rights reserved.

For the next several lessons, you are going to be civil engineers working for the company Splash Engineering. Your main client is the government (also known as a "municipality") of Thirsty County. The government of Thirsty County has been receiving complaints from its residents over the last decade. The main problems include:

• Not enough water for people during the summer droughts.
• Farmers have trouble growing food without enough irrigation water.
• During drought periods, the Birdseye River is not deep enough for ships to cross to bring valuable goods to Thirsty County.
• Flash floods ruin houses and stores.
• Air pollution from a nearby coal-fired power plant makes people sick.

The Thirsty County government has hired the Splash Engineering firm (your class) to study the needs of the community and develop a solution that addresses those needs.

Lesson Background and Concepts for Teachers

A dam is built to control water through placement of a blockage of earth, rock and/or concrete across a stream or river. Dams are usually constructed to store water in a reservoir, which is then used for a variety of applications such as irrigation and municipal water supplies. Reservoir water can also be directed to flow through hydraulic turbines, producing electric power for use in homes and industries. Hydroelectric power is considered a renewable source of energy because the reservoir water that is used to generate electricity is continuously replenished. A dam using locks and canals, such as the series of locks on the Panama Canal, enables navigation through a human-made water route that must overcome elevation differences.

The disadvantages of dams include the resulting flooding of large areas of land (destroying flora and fauna), altering the physical characteristics of the river below the dam (also affecting flora and fauna), impeding fish migration, and killing large numbers of fish that pass through hydroelectric turbines. In recent years, engineers and scientists have begun to manage reservoirs and their releases to be less harmful to aquatic and terrestrial wildlife and plants, as well as humans residing below the dam&#;a method of water resource management called adaptive management.

Associated Activities

• How Much Water Do You Use? - Students explore one of the main reasons why dams are built&#;to satisfy everyday domestic water use. Students track their own water use during one week, and from that data estimate a community's residential water needs from a potential regional dam.

Lesson Closure

Dams can be useful for a variety of reasons. What are some purposes for which we create dams? (Answers: To supply water for irrigation, municipal water, flood control, hydroelectric power generation, river navigation.) What might be negative effects from a dam? (Answers: Upstream flooding that destroys animals, plants, ecosystems and private property; downstream alteration of terrain, ecosystems, plants and wildlife; impeding fish migration, killing fish that pass through turbines, etc.)

In the case of our imaginary Thirsty County, why should the municipality consider building new dams? (Answers: To provide enough water for people and farmers during the summer, to allow boats to cross Birdseye River year round, to help control flash floods, to produce electricity without air pollution.)

Vocabulary/Definitions

adaptive management: The operation of dams and reservoirs to benefit not only human needs, but also the needs of the aquatic and terrestrial ecosystems impacted by the dam.

dam: A barrier to obstruct the flow of water, especially one made of earth, rock, masonry and/or concrete, built across a stream or river.

engineer: A person who applies her/his understanding of science and mathematics to creating things for the benefit of humanity and our world.

hydroelectric power: Renewable energy generated by water flowing through turbines.

migration: To periodically move from one region or climate to another, as by wildlife such as birds and fish.

municipality: A political unit, such as a county, city, town or village, incorporated for local self-government.

reservoir: An artificial lake where water is collected and stored behind a dam.

turbine: A machine that converts the kinetic energy of falling water (or any moving fluid, including steam, gases or air) into electrical energy by connecting a generator to a rotating shaft that is spun by water pressure pushing blades, buckets or paddles.

Assessment

Pre-Lesson Assessment

Brainstorming: Ask students to think of all the different ways in which they use water on an everyday basis. Possible answers include drinking, bathing, cooking, swimming, cleaning, etc. Write these answers on the board and then ask the students to tell you where the water comes from for these activities. Students may answer that water comes from rivers, lakes, and streams, in which case you can start a discussion about the need for dams to store water. Be sure to mention that 33% of American citizens get their water from groundwater sources.

Post-Introduction Assessment

Teaming: After you have introduced the hypothetical Thirsty County scenario, divide the class into engineering teams of 2-3 students each, and ask each team to write a short "proposal" response to the municipality of Thirsty County to address the residents' needs. Proposals should comment on the needs of the residents, some possible solutions (at least a Plan A and Plan B), and benefits/problems associated with each plan proposed. For example, students may write a statement that says their team will "address the residents' needs by designing a dam that provides people with water during summer droughts, protects buildings from flash floods and storms, and produces hydropower as a clean energy alternative to coal-fired power plants." This exercise helps students understand their role as civil engineers working for Splash Engineering firm. Emphasize that engineers must propose multiple plans to the County Board and convince the board members that their design is worth spending taxpayer money. Encourage students to address topics such as water-saving appliances, efficient water use in gardens and landscaping, (both water conservation measures) and not building on land that has a high risk of annual flooding.

Lesson Summary Assessment

Pros and Cons: Ask students to think of all the benefits of building a dam (such as water storage, hydroelectricity, flood mitigation, etc.). Create a list of these benefits on the board. Next, ask students to think of some negative effects of dam construction (such as impeding fish migration, damaging flora and fauna, etc.). Next to the list of benefits, create a list of these negative effects. Ask students: "What should engineers do when their designs have both positive and negative impacts on society?" Do students think this is a common dilemma for engineers? (Answer: All engineering projects have positive and negative effects. The main job of engineers is to develop plans to help address problems people have without creating new problems or making other problems worse. If Thirsty County has no money for schools and people are starving in the streets, spending money on a dam might not be the best engineering solution to the water issues Thirsty County faces.)

Lesson Extension Activities

Plan a field trip to a nearby dam to give students a real-world sense of these (often) gigantic engineering structures. If a field trip is not possible, show students a library video on dams or photographs of the Hoover Dam, located on the border between the states of Arizona and Nevada; see a link in the Additional Multimedia Support section.

Additional Multimedia Support

Show students recent and historic photographs of the well-known Hoover Dam on the US Bureau of Reclamation's Lower Colorado River region website. The photograph gallery provides dam views, power plant, historic views and old post cards. See: http://www.usbr.gov/lc/hooverdam/gallery/picindex.html

As a general introduction to dams, show students a 22-slide overview "virtual tour" of the Shasta Dam in northern California, available at the US Bureau of Reclamation's Mid-Pacific Region page at http://www.usbr.gov/mp/ncao/ and http://www.usbr.gov/mp/ncao/shasta/virtual_tour.pdf

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References

Dictionary.com. Lexico Publishing Group, LLC. Accessed July 8, . (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

Down the Drain: How Much Water Do You Use? . Collaborative Projects, Center for Innovation in Engineering and Science Education (CIESE), Stevens Institute of Technology, Hoboken, NJ. Accessed February 29, . http://www.ciese.org/

United States Society on Dams. Last revised November 14, . USSD. Accessed December 4, . http://www.ussdams.org/

Copyright

© by Regents of the University of Colorado

Contributors

Sara Born; Kristin Field; Denali Lander; Michael Bendewald; Lauren Cooper; Timothy M. Dittrich; Denise W. Carlson

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. ). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: June 12,

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