Hydropower

Corps Hydro PlantsNon-Federal Plantsat Corps Dams

US Army Corps of Engineers

T he U.S. Army Corps of Engineers is the largestowner/operator of hydroelectric powerplants in the United

States and one of the largest in the world. The 75 Corpsplants have a total installed capacity of 20,474 megawatts andproduce nearly 100 billion kilowatt-hours a year. This isnearly a third of the nation’s total hydropower output: enoughenergy to serve about ten million households, or roughly tencities the size of Seattle, WA.

Hydropower is one of the products of developing rivers formultiple purposes. Over the years, Congress has directed theCorps to build water resource projects to serve public needssuch as flood control, watersupply, and navigation. Wherefeasible, hydropower has alsobeen included.

The earliest hydropower plantsat Corps projects wereconstructed at navigation damsas joint efforts with electricutility companies. The utilitiesbuilt the powerplants and theCorps usually built the

navigation locks. Later, Congress authorized the Corps toconstruct its own powerplants at dams being built for floodcontrol, navigation, and other purposes. Most of these projectswere placed in service during the decades following WorldWar II. In the late 1970s, emphasis shifted back to allowingnonfederal hydropower development at Corps projects. Morethan 90 of these retrofits have now been completed, bymunicipalities, electric utilities, and independent powerproducers.

The Corps is working hard to keepits powerplants operating at peakefficiency and reliability. State-of-the-art equipment is used wheneverpossible to replace aging turbines,generators, and control systems.

DEFINITIONS:

kilowatt-hour: unit for measuring electric energy; atypical home uses about 900 kilowatt hours per month.Megawatt (one-thousand kilowatts): unit of electricalpower, is used for measuring rate of producing orconsuming electric energy; a megawatt is equal to1340 horsepower.

T he average American home uses about 10,500 kilowatt-hours of electric energy every year. Hydropower is an

important source of that energy. It provides electricity tolight our homes and to run our appliances, televisions,computers, and many labor-saving devices. Just asimportant is the electricity provided to our schools,hospitals, stores, offices, farms, and factories.

There are many ways to generate electricity, but hydropowerhas some characteristics that make it especially valuable tothe community:

• It’s renewable. Hydropower is thenation’s most productive source ofrenewable energy. The earth’shydrologic cycle provides acontinual supply of water fromrainfall and snowmelt. In addition,hydroelectric energy saves scarce,non-renewable fossil fuels.

• It’s efficient. Hydropower plantsconvert about 90 percent of the energy in falling waterinto electric energy. This is much more efficient thanfossil-fueled powerplants, which lose more than half ofthe energy content of their fuel as waste heat and gases.

• It’s clean. Hydropower plants emit none of thewaste gases, like carbon dioxide, that contributeto air pollution, acid rain, and global warning.They don’t cause noise pollution. No trucks,trains, barges, or pipelines are needed to bringfuel to the powerplant site.

• It’s reliable. Hydropower plant machinery is relativelysimple and runs at slow speeds. This makes it reliable anddurable.

• It’s flexible. Hydropower units can start quickly andadjust rapidly to changes in demand for electricity. Thismakes them valuable for meeting peak loads and forserving as reserve capacity to protect power systemreliability and stability.

Corps dams with hydropower plants also serve other purposes,such as navigation, flood damage reduction, water supply,recreation, irrigation, and low augmentation.

US Army Corps of Engineers

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BRINGING ELECTRICITY TO FARMS.

As late as the 1940ʼs, many farms still did not haveelectricity. The 1036 Rural Electrification Act helpedfarmers organize electric cooperatives to bring powerto their farms and communities. These co-ops andother publicly owned utilities were given first priority topower from Corps hydro plants. This power helpedbring rural electrification to reality.

The Hydrologic Cycle

Water moves constantly through a vast global cycle. It (a)evaporates from the land, lakes, streams, and oceans,

(b) forms clouds, (c) precipitates as rain or snow; and then (d)flows back to the ocean. The energy of this water cycle, whichis driven by the sun, is tapped most efficiently withhydropower.

Generating Electricity

Hydropower plants capture the energy of falling water togenerate electricity. A dam impounds water to form a

reservoir and raises the water level to create head. Head is thevertical distance the water falls as it passes through the dam(i.e. the difference in water level between the reservoir and theriver below the powerplant). The water is directed throughpenstocks to turbines, which drive generators to produceelectric power.

Just having water in the river isn’t enough. Agood hydropower site must have enoughstreamflow as well as enough head. Forexample, the Mississippi River hastremendous streamflow, but only a few of itsdams are high enough to provide the headneeded for efficient hydropower development.Dams in the arid West may have plenty ofhead, but not enough streamflow. Where theright combination of streamflow and head exists, theCorps has included powerplants at its dam.

Hydropower ProjectOperation

Corps of Engineers projects withhydropower generating facilities

fall into two categories: storageprojects and run-of-river projects.

Storage projects

Storage projects are usually located inthe headwaters of river basins. Theirpurpose is to more evenly distributethe streamflow they release over the course of theyear. In nature, river flow fluctuates widely. Streamflow istypically high during the rainy season and low in late summerand fall. In semi-arid regions, rivers become nearly dry inautumn. In many of the western river basins, flows remainlow all winter as snow accumulates in the mountains and thenswell with snowmelt in the spring.

Storage reservoirs capture river flow during the high runoffseason and release it during the dry periods. This creates amore dependable year-round flow for generating power.

US Army Corps of Engineers

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Keeping flows higher during the dryseason also benefits other

downstream river uses, likenavigation, fisheries, recreation,water quality, and municipal watersupply. Also capturing part of therunoff during high flow periodshelps reduce flood damagedownstream. In fact, flooddamage reduction is one of the

major purposes of all Corps storageprojects.

Because storage projectsfollow a seasonal pattern ofreleasing water during dryperiods and refilling in thehigh runoff season, waterlevels in the reservoirs behinddams fluctuate. They areusually full in early summer,but once the dry season

begins, there is a gradualdrawdown. Since reservoir

recreation is an important project use,the Corps keeps reservoirs from filling

in the spring or may force thedrawdown to start before or during the recreation season.

Run-of-river projects

The other major type of dam is the run-of-river project. It haslittle or no storage. The most common example of a Corpsrun-of-river project is the navigation lock and dam. Itspurpose is to raise the river level toprovide enough depth for commercialnavigation. Such dams wouldtypically be located on the lowerreaches of a navigable river. Somelock-and-dam projects have a smallamount of storage, called pondage.This is used to regulate powerhouseflow so that most of the generation isproduced in the hours of peak powerdemand. Other lock-and-damprojects have no storage at all. Theypass inflows straight through withoutany regulation.

River basins like the Arkansas,Missouri, Columbia, andCumberland have storage projects inthe headwaters and run-of-riverprojects in the lower reaches. These

projects operate together as a system. During the low flowseason, the storage projects release water to increasedownstream flows, some or all of which are used to increasepower generation at downstream run-of-river projects. Powergeneration is only one of the objectives of these storagereservoirs.Carefulmanagement isrequired toensure that allproject purposesare servedsuccessfully.

US Army Corps of Engineers

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US Army Corps of Engineers

The greatest benefit from the Corps hydropower program isthe abundant low-cost energy the projects contribute to

electric power grids. Because hydroelectric powerplants burnno fuel, operating costs are low and are immune to risingfossil fuel prices. In addition, most of these projects were builtyears ago, when construction costs were low. These factorshelp to make Corps hydropower among the least costlysources of electric power available today.

In most parts of the country,hydropower can carry only aportion of the system powerload. The objective is to usethis limited amount of energyin a way that will keep theoverall cost of electricity to theconsumers as low as possible.The highest-value use ofhydropower is for “peaking” –generating as much energy aspossible in the peak demandhours of the day. This saveshaving to produce this powerat high-cost thermal peakingplants. Not all hydro plants canbe used for peaking, but theirpower output is always used asefficiently as possible withinthe given project operatinglimits.

In years of ample runoff, hydropower plants produce extraenergy. This is used to displace more expensive generation atfossil-fuel powerplants, which further helps to reduceconsumers’ electricity bills.

Corps hydropower pays its own way. The full cost of buildingand operating these plants must be repaid, with interest, infifty years. This includes a share of the dam, reservoir,spillway, and fish ladders costs.

Concern about our Nation’s limited energy resources isgrowing; many wonder if the output of hydropower can beincreased. Four main options are available:

• Installing new high-efficiency turbines to increase energyoutput

• Installing uprated generators or adding more generatingunits to increase the power produced in the peak demandhours

• Upgrading aging equipment at older plants with newer,more reliable components

• Modifying project operation to increase powerplantproductivity

The Corps considers these and other options as well asenvironmental factors in its ongoing program ofpowerplant renovation and upgrading.

Recreation: An important benefit of many Corps hydropowerprojects is the recreational use of the lakes created by them.These lakes are now among the most popular recreation sitesin the country. Visitors enjoy a wide variety of water-basedactivities and also make a major contribution to localeconomies.

US Army Corps of Engineers

T he driving force behind the dams and reservoirsconstructed by the Corps has always been to improve our

quality of life. These flood control, navigation, water supply,and hydropower projects were constructed to improve thedeveloped environment of the communities in which most ofus live and work.

Water resource projects can often improve the naturalenvironment as well. For example, increasing flow during drymonths enhances aquatic habitat, while reducing flows inperiods of flood runoff helps prevent damage to vegetationand wildlife habitat along stream banks.

However, dams and reservoirs change the natural riverenvironment. Examples are the loss of open-river environmentwhen a dam is constructed and changes in river ecology thatcome with changes in river flow patterns.

In recent years thepublic has come torealize that we need abalance betweenimproving ourimmediate daily environment and in preserving the naturalenvironment around us. The Corps response is a concertedeffort to mitigate dam and reservoir impacts to make theoperation of these projects more compatible with theenvironment. Three examples illustrate this.

Southeastern States

I n the southeastern states, dissolved oxygen (DO) levelsbelow dams may get so low in the summer that aquatic life

is severely impacted. The Corps is improving DO levels byusing aerating turbines and injecting oxygen directly into thestreamflow.

Missouri River

W hen the six large reservoirs on the Missouri River wereconstructed, the emphasis was on navigation, flood

damage reduction, irrigation, and generation of electric power.Fish and wildlife were also included in the development ofreservoir operating plans. As part of its responsibilities toprovide these multiple project purposes, the Corps continuallyassesses how well operating plans are satisfying basin-widewater needs. One such need has been the improvement ofhabitat for endangered species such as pallid sturgeon, pipingplover, and the threatened interior least tern. This has led to athorough review of the operating plans in order to achieve abetter balance with environmental factors.

Columbia River

C olumbia River salmon may be the biggest environmentalchallenge facing the Corps today. The Corps is working

closely with the fishery agencies, the Tribes, and otherinterests to restore the declining salmon runs. They areworking diligently toward a solution – one that will restorethe fish runs while ensuringthat the projects continue toserve the purpose for whichthey were constructed. In 2008the agencies signed agreementsfor a 10-year commitment tobenefit fish, particularlyColumbia River Basin salmonand steelhead stocks.

Working Together

H ydropower operations at Corps of Engineers projects are ajoint effort between the Corps and the regional offices of

the Department of Energy (DOE). The Corps builds andoperates the projects. The DOE’s four Power MarketingAdministrations (PMAs) market the power and deliver it to localutilities and other users. The PMAs also schedule the power gen-eration to meet their customers’ needs. This requires workingclosely with Corps water managers and powerplant operators toensure that the available power is used most efficiently.

The Corps must also coordinate power operationwith the projects’ other purposes. Flood damagereduction, navigation, recreation, fish and wildlife,water quality, and water supply are some of theneeds that must be considered. This involvesworking hand-in-hand with the many differentgovernment agencies and entities that are affectedby or regulate Corps projects operation, such as thePMAs, U.S. Environmental Protection Agency,National Marine Fisheries Service, U.S. Fish andWildlife Service, etc.

Another pre-eminent government agency is the FederalEnergy Regulatory Commission (FERC) which licenses non-Federal hydropower plants at Corps dams. The Corps workswith the plant owners and FERC to make sure thatpowerplant design and operation are consistent with theprimary purposes of the dams.

Learning More

T o learn more about hydropower in the Corps ofEngineers, visit the following websites:

Value to the Nation: www.CorpsResults.us

Hydroelectric Design Center:https://www.nwp.usace.army.mil/HDC/home.asp

Hydropower Analysis Center: www.nwd-wc.usace.army.mil/PB/welcome.html

©2009 Produced by the U.S. Army Engineer Institute for WaterResources in partnership with the Hydroelectric Design Center andthe Hydropower Analysis Center.

To inquire about this brochure, please contact the IWR publicationsoffice at CEIWR.Publications@usace.army.mil. For the sources ofinformation used in this brochure, visit www.CorpsResults.us.

Bonneville Power Administration (BPA):the Pacific Northwest States

Southeastern Power Administration (SEPA):the Southeastern States

Southwestern Power Administration (SWPA):the South Central States

Western Area Power Administration (WAPA):the remaining Western States