American Falls Dam


The American Falls Dam is a concrete gravity-type
dam A dam is a barrier that stops or restricts the flow of surface water An example of surface water is Lake Kinney. Surface water is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tas ...

located near the town of
American Falls The American Falls is the second-largest of the three waterfall A waterfall is a point in a or where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where drops over the edge of a tabular or . Water ...
Idaho Idaho () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper in ...

, on
river mile A river mile is a measure of distance in miles The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and US customary unit United States customary units (U.S. customary ...
714.7 of the
Snake River The Snake River is a major river of the greater Pacific Northwest The Pacific Northwest (PNW) is a geographic region in western bounded by its coastal waters of the to the west and, loosely, by the to the east. Though no official bounda ...

Snake River
. The dam and reservoir are a part of the
Minidoka Project The Minidoka Project is a series of public works by the U.S. Bureau of Reclamation to control the flow of the Snake River in Wyoming and Idaho, supplying irrigation water to farmlands in Idaho. One of the oldest Bureau of Reclamation projects in th ...
on the
Snake River Plain image:Snake River view near Twin Falls, Idaho.jpg, The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges, gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geology, geologic feature ...

Snake River Plain
and are used primarily for flood control, irrigation, and recreation. When the original dam was built by the
Bureau of Reclamation The United States Bureau of Reclamation (USBR), and formerly the United States Reclamation Service, is a List of United States federal agencies, federal agency under the U.S. Department of the Interior, which oversees water resource manage ...
, the residents of American Falls were forced to relocate three-quarters of their town to make room for the reservoir. A second dam was completed in 1978 and the original structure was demolished. Although the dam itself is located in Power County, its reservoir also stretches northeastward into both Bingham County and Bannock County.


lava Lava is magma Magma () is the molten or semi-molten natural material from which all s are formed. Magma is found beneath the surface of the , and evidence of has also been discovered on other and some s. Besides molten rock, magma may al ...

dam created a broad shallow lake in the area of the
Raft River The Raft River is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed May 4, 2011 tributary of the Snake River located in northern Utah and southern Idaho in the United States. It is part ...
during the late
Pliocene The Pliocene ( ; also Pleiocene) epoch (geology), Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

s (called the Raft Formation) lie beneath most of the present-day American Falls Reservoir. At other times the Snake River was dammed completely by
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extr ...

extruded Extrusion is a process used to create objects of a fixed cross-sectional Cross-sectional data, or a cross section of a study population, in statistics and econometrics is a type of data set, data collected by observing many subjects (such as in ...
from vents. One lava dam a few miles downstream from the present American Falls Dam formed a reservoir in which more than of sediments (clay, silt, and sand) were deposited. This series of basalt flows and original sediments were covered by the new lake bed sediments and are named the Snake River Group and the American Falls Lake Beds. These events occurred up until the late
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally ...
, less than one million years ago. The Snake River has continued to
erode Erode () is a city in the Indian state of Tamil Nadu. The seventh largest urban agglomeration in the state, after Chennai, Coimbatore, Madurai, Tiruchirapalli, Tiruppur and Salem, Tamil Nadu, Salem. It is also the administrative headquarters of ...

channel Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austr ...
in the basalt and modify the lake bed sediments until the present time.


The dam at American Falls is on the Snake River Plain at an elevation of 4357/1328 (ft/m).[ USGS Place names] The topography in the immediate vicinity of the river is gently rolling, with differences in elevation of less than . The original falls occur where the river
channel Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austr ...
narrows to about 600 ft (180 m) and Waterfall, cascades about in several 6–10 ft. drops over highly jointed basalt. The final drop is about a plunge.



The city of American Falls was first platted in the early 1880s. It was named for the waterfall on the Snake River near the settlement. During the last part of the 19th century, privately financed irrigation canals were created to sustain the emerging agriculture industry in southern Idaho and other parts of the west. The Carey act (1894) paved the way for private investment in irrigation projects. By 1895, the American Falls irrigation project came before the Idaho State Land Board. In 1902 the Newlands Reclamation Act, National Reclamation Act was signed into law and federal funds from the sale of public lands became available to create and maintain irrigation projects in the Western United States. The first power plant was built in 1902 on the falls and was acquired by the Idaho Power Company in 1916.Idaho Power – American Falls
Damming the rivers became the preferred method for harnessing the abundant water of the western rivers. The reservoirs could then provide year-round downstream irrigation via canals, even during traditional low water times. The use of eminent domain by the government to appropriate the original townsite in 1923 resulted in several lawsuits. One in particular, ''BROWN v. U S, 263 U.S. 78 (1923) '' allowed that the property valuation should include the value of the streets and improvements which would need to be replaced in the substitute site.


The first dam at American Falls was begun in 1925 by the Bureau of Reclamation and was completed in 1927. The river was temporarily impounded while the new concrete structure was put in place. The Oregon Short Line Railroad bridge over the river had to be raised to allow for crossing the new reservoir. This dam was designed by Frank A. Banks.


The existing dam is the second structure to be called the American Falls Dam. Core samples taken in the early 1960s of the concrete of the original structure revealed deterioration resulting in impaired durability and strength caused by a chemical reaction between components of the concrete. The solution was to replace the original dam with a second dam built downstream in 1978. Replacement of the original dam was authorized by a congressional act of December 28, 1973 (87 Stat. 904, Public Law 93-206). In 1976, the Idaho Power Company built the dam's current power plant which consists of three Electric generator, generators with a capacity to produce 112,420 kilowatts (112 MW) of hydroelectricity. In 1976, the upstream Teton Dam failed during filling, causing spring snowmelt to race downstream into the Teton River (Idaho), Teton River, a tributary of the Snake, demolishing several towns along its path. In an attempt to contain this flood, water was released from American Falls Dam as quickly as possible. If the dam were to fail, the other Snake River dams would experience a flood they were not designed to cope with, although the lower Columbia River dams would most likely survive. The American Falls reservoir filled, but its level did not even rise to its spillway crest. When the second dam was planned, members of the Shoshone and Bannock (tribe), Bannock communities opposed expansion as it would further flood the lands of the Fort Hall Bottoms. Native Americans have inhabited this region for at least 10,000 years and the area is an important resource for them. Many scientists were opposed as well because of the loss of natural habitat and access to fossil records of the Bottoms.

See also

*List of dams in the Columbia River watershed


External links

American Falls Dam at US Bureau of ReclamationData from American Falls Dam (downstream) from the Teton Dam Failure
{{authority control Dams in Idaho Hydroelectric power plants in Idaho Reservoirs in Idaho Buildings and structures in Power County, Idaho Dams on the Snake River Lakes of Power County, Idaho Minidoka Project Idaho Power dams United States Bureau of Reclamation dams Dams completed in 1978 Energy infrastructure completed in 1978