The Fort Peck Dam is the highest of six major
dams along the
Missouri River, located in northeast
Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...
in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
, near
Glasgow
Glasgow ( ; sco, Glesca or ; gd, Glaschu ) is the most populous city in Scotland and the fourth-most populous city in the United Kingdom, as well as being the 27th largest city by population in Europe. In 2020, it had an estimated popu ...
, and adjacent to the community of
Fort Peck. At in length and over in height, it is the largest
hydraulically filled dam in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
, and creates
Fort Peck Lake
Fort Peck Lake, or Lake Fort Peck, is a major reservoir in Montana, formed by the Fort Peck Dam on the Missouri River. The lake lies in the eastern prairie region of Montana approximately east of Great Falls and north of Billings, reaching i ...
, the fifth largest artificial lake in the U.S., more than long, deep, and it has a shoreline which is longer than the state of California's coastline. It lies within the
Charles M. Russell National Wildlife Refuge
The Charles M. Russell National Wildlife Refuge (abbreviated as the CMR NWR) is a National Wildlife Refuge in the U.S. state of Montana on the Missouri River. The refuge surrounds Fort Peck Reservoir and is in size.U.S. Fish and Wildlife Servi ...
. The dam and the lake are owned and operated by the
U.S. Army Corps of Engineers
, colors =
, anniversaries = 16 June (Organization Day)
, battles =
, battles_label = Wars
, website =
, commander1 = ...
and exist for the purposes of hydroelectric power generation, flood control, and water quality management.
The dam presently has a
nameplate capacity of 185.25
megawatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s, divided among 5 generating units (which in turn are divided between the
Western and
Eastern grids). Three units in powerhouse number one, completed in 1951, have a capacity of 105 MW. Completed in 1961, the two remaining generating units in powerhouse number 2, have a nameplate capacity of 80 MW.
The lake has a maximum operating pool elevation of above mean sea level and a normal operating pool elevation of above mean sea level. The lake level fluctuates over time based on a number of factors. During the first week of February 2007, the reservoir set a record low elevation of above mean sea level, nearly lower than the previous record low set in 1991. In June 2011, in response to the
2011 Missouri River Floods
The 2011 Missouri River floods was a flooding event on the Missouri River in the United States.The flooding was triggered by record snowfall in Rocky Mountains of Montana and Wyoming along with near-record spring rainfall in central and easte ...
, the dam was releasing almost , which greatly exceeded its previous record release of set in 1975.
Background
Fort Peck was a major project of the
Public Works Administration
The Public Works Administration (PWA), part of the New Deal of 1933, was a large-scale public works construction agency in the United States headed by Secretary of the Interior Harold L. Ickes. It was created by the National Industrial Reco ...
, part of the
New Deal
The New Deal was a series of programs, public work projects, financial reforms, and regulations enacted by President Franklin D. Roosevelt in the United States between 1933 and 1939. Major federal programs agencies included the Civilian Con ...
. Construction of Fort Peck Dam started in 1933, and at its peak in July 1936 employed 10,546 workers. The dam, named for a 19th-century trading post, was completed in 1940, and began generating electricity in July 1943. The town of
Fort Peck, Montana
Fort Peck is a town in Valley County, Montana, United States. The population was 239 at the 2020 census.
History
The name Fort Peck is associated with Col. Campbell K. Peck, the partner of Elias H. Durfee in the Leavenworth, Kansas trading firm ...
, "the government town," was built for Army Corps of Engineers personnel and men in "positions of responsibility" and their families during the dam's construction. Many of the facilities that supported the dam's workers are still used today, such as the recreation center and the
Fort Peck Theater
The Fort Peck Theatre was built as a temporary structure in 1934 in Fort Peck, Montana to serve as a movie theatre. It is also known as the Fort Peck Summer Theatre. The theater was designed in a pseudo-Swiss-chalet style as an amenity for the ...
. In addition to Fort Peck, other towns sprang up to house the workers. Among these were Wheeler and McCone City as well as more than a dozen others. Many of the homes were later moved to farms and towns around Montana.
Fort Peck Dam is one of six Missouri River
Main stem
In hydrology, a mainstem (or trunk) is "the primary downstream segment of a river, as contrasted to its tributaries". Water enters the mainstem from the river's drainage basin, the land area through which the mainstem and its tributaries flow. ...
dams operated by the U.S. Army Corps of Engineers,
Omaha District. The dams downstream of Fort Peck Dam are:
Garrison Dam (near
Riverdale, North Dakota
Riverdale is a town in McLean County, North Dakota, United States. The population was 223 at the 2020 census.
Riverdale was the largest of the construction camps that sprang up in 1946 to house workers building the Garrison Dam just to the wes ...
),
Oahe Dam (near
Pierre, South Dakota),
Big Bend Dam (near
Fort Thompson, South Dakota),
Fort Randall Dam (near
Pickstown, South Dakota), and
Gavins Point Dam (near
Yankton, South Dakota
Yankton is a city in and the county seat of Yankton County, South Dakota, United States.
The population was 15,411 at the 2020 census, and it is the principal city of the Yankton Micropolitan Statistical Area, which includes the entirety of Y ...
). These six mainstem dams impound these Missouri River reservoirs with a total combined water storage capacity of approximately and approximately of water surface area.
Construction
The site chosen was on a stretch of the Missouri River flowing from south to north. The river bed at the site consisted of approximately of
alluvial deposits, varying from coarse, pervious
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...
s and
gravel
Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone.
Gravel is classifi ...
s to impermeable
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
s. Beneath these deposits lay a thick (approximately ) deposit of Bear Paw
shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...
. This shale is classified as a firm shale and contains thin (< layers of
bentonite
Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...
. The topmost layer of soft clay was removed from the alluvium in order to found the dam on the stable sandy deposits beneath, at an elevation of approximately . The remaining deposits consisted of the alluvial materials mentioned above. These deposits had many interconnecting layers of coarse sands and gravels, necessitating the installation of a
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
sheet pile wall down to the firm shale, from the left to the right
abutment
An abutment is the substructure at the ends of a bridge span or dam supporting its superstructure. Single-span bridges have abutments at each end which provide vertical and lateral support for the span, as well as acting as retaining wal ...
.
As designed, the dam extends to an elevation of , for a total height of from the cleared river bed and has a length from the left to the right abutment of approximately . The upstream face was designed with an average slope of one vertical on four horizontal and included three horizontal shelves built into the slope. A flatter (1 on 7.5)
berm
A berm is a level space, shelf, or raised barrier (usually made of compacted soil) separating areas in a vertical way, especially partway up a long slope. It can serve as a terrace road, track, path, a fortification line, a border/ separation ...
was to be placed between stations 30+00 and 75+00 (approximately the center half of the length of the dam).
Since the construction method of
hydraulic fill
Hydraulic fill is a means of selectively emplacing soil or other materials using a stream of water. It is also a term used to describe the materials thus emplaced. Gravity, coupled with velocity control, is used to effect the selected depositi ...
was chosen, four electric dredges were built. Because of the distance of the site from the nearest shoreline, a shipyard was started on the site, affectionately dubbed "The Fort Peck Navy" and "The Biggest Shipyard in Montana" by the workers. These dredges would pump material from nearby
borrow pit
Digging, also referred to as excavation, is the process of using some implement such as claws, hands, manual tools or heavy equipment, to remove material from a solid surface, usually soil, sand or rock on the surface of Earth. Digging is actuall ...
s to the dam site where it was discharged by pipes along the outside edges of the fill. The coarser material settled out quickly, while the fines were carried downhill toward what would eventually become the core of the dam. Samples were taken from all zones regularly to ensure that the material had the gradation and
consolidation characteristics specified by the design.
Dam failure during construction
This process proceeded until elevation of the fill reached approximately , while the reservoir was at an elevation of . At this point, the danger of the core pool overtopping or bursting the shell became greater because the beaches became narrower. For this reason, an extensive alarm system was implemented along the narrower upstream shell. This alarm system could immediately shut off the dredge pumps if a shell breach was detected. Part of this alarm system involved monitoring the elevations of the core pool and the pipelines carrying the dredged fill.
On the morning of September 22, 1938, an inspection by the engineer in charge of construction revealed that the elevation of the pipeline relative to the core pool near station 15+10 (see attached overhead photo) was only when it should have been . A survey crew was dispatched immediately to determine if the fill on which the pipeline was founded was settling or if the pipeline footing itself was settling. Preliminary measurement showed that the pipeline was closer to the pool than expected from station 15+00 to station 17+00. A meeting with the district
engineer
Engineers, as practitioners of engineering, are professionals who Invention, invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considerin ...
and supervisory personnel was scheduled for 1:15 p.m. near the location in question.
At approximately 1:15 p.m. the core pool near station 15+00 began to settle slowly. As its rate of settlement increased, cracks appeared below the crest in the upstream embankment. As the settlement of the pool got larger, portions of the shell began to slide backwards into the core pool area and the majority of the upstream shell began to move into the reservoir,
translating south and rotating slightly about the east abutment. The west end of the slide mass broke away from the dam near station 27+00 and the core pool water rapidly poured out of the breach that was created in the shell. Portions of the core in the still-stable portion of the dam continued to slump into the hole created by the loss of the slide mass. One construction supervisor was backing his car away from the advancing
scarp
Scarp may refer to:
Landforms and geology
* Cliff, a significant vertical, or near vertical, rock exposure
* Escarpment, a steep slope or long rock that occurs from erosion or faulting and separates two relatively level areas of differing elevatio ...
to the west along the beach to avoid the slumping and noted that the small scarp in the core was advancing to the west at a speed equal to his own (approximately 10 mph (16 km/h)).
A pump
barge
Barge nowadays generally refers to a flat-bottomed inland waterway vessel which does not have its own means of mechanical propulsion. The first modern barges were pulled by tugs, but nowadays most are pushed by pusher boats, or other vessels. ...
moored near the dam at the east abutment was swamped by the slide and was lost along with several tractors, loadmasters, and draglines on the slope. Of the 134 men working in the area at the time, 34 were carried into the sliding material. Of these 34, eight were unable to be rescued and lost their lives. Of the eight men, only two bodies were ever recovered, leaving six men permanently entombed in the structure.
In the testing and analysis done by the
Corps of Engineers and others to determine the cause of the slide, several
modes of failure were considered. These were: movement along a weak zone in the shale in the abutment, movement along the shale surface, bursting of the shell due to excessive core
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
, and temporary
liquefaction
In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics.
It occurs both naturally and artificially. As an example of th ...
of the shell or foundation sand. Extensive laboratory testing of the shale, both weathered and unweathered indicated strengths leading to a factor of safety greater than one. Also, portions of the weathered shale were found in the slide mass, indicating that the slip surface was located somewhere in the shale, but probably at a shallow depth. The core material turned out to be much stronger than expected (having a
friction angle
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of t ...
of approximately 29 degrees) and was carried out into the slide nearly in a solid mass, making it unlikely that the core was the weak point in the slide. Laboratory testing was done on the shell material and the foundation sand and it was determined that both materials were denser than the critical state for liquefaction. There was no evidence of ground vibration, seismic or otherwise. Some liquefaction may have occurred after the sliding was initiated, but it was unlikely that it caused the slide.
The major weak point in the dam seemed to be the bentonite seams in the Bear Paw shale. Very high water pressures were reported at some points in the shale during the construction. This was likely caused by consolidation due to the overburden of the fill being placed for the dam. The excess
pore pressures could not be relieved due to the low
permeability of the surrounding shale. This resulted in a low effective
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
in the bentonite and a very low
shear strength
In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a materi ...
.
2011 flooding and repairs
According to the ''
Billings Gazette
The ''Billings Gazette'' is a daily newspaper based in Billings, Montana that primarily covers issues in southeast Montana and parts of northern Wyoming. Historically it has been known as the largest newspaper in Montana and is geographically one ...
'', the dam was damaged by "record-high runoff and flooding in 2011." As of March 2013, "more than $42.9 million in repairs to Fort Peck Dam have been approved by the
U.S. Army Corps of Engineers
, colors =
, anniversaries = 16 June (Organization Day)
, battles =
, battles_label = Wars
, website =
, commander1 = ...
."
Representations in art and literature
Fort Peck Dam is probably best known for being the subject of a photograph of the spillway taken by
Margaret Bourke-White while still under construction that was the cover photo of the first issue of
''Life'' magazine on November 23, 1936. Later, the photograph by Bourke-White was used on a United States postage stamp in the "Celebrate the Century" series.
The dam is also center-stage in ''Bucking the Sun'', by the Montana-born writer
Ivan Doig
Ivan Doig (; June 27, 1939 – April 9, 2015) was an American author and novelist, widely known for his sixteen fiction and non-fiction books set mostly in his native Montana, celebrating the landscape and people of the post-war American West.
W ...
, published in 1996. The novel tells the story of the fictional Duff family and their various roles in the mammoth dam project, and in the process describes the working conditions and way of life of the thousands of workers hired to construct the Fort Peck Dam, many of them homesteaders from upriver farms destined to disappear under the waters of the newly formed Fort Peck Lake.
''Fifty Cents an Hour: The Builders and Boomtowns of the Fort Peck Dam'', by Montana author Lois Lonnquist, published in 2006, is an overall history of the Fort Peck dam and spillway construction. Built by the Army Corps of Engineers, PWA Project #30 provided thousands of jobs during the Great Depression. The book includes the history of the boomtowns that sprang up in the area, and the "project people" who lived and worked at Fort Peck during the "dam days."
M.R. Montgomery, Personal History, "Impalpable Dust," ''The New Yorker'', March 27, 1989, p. 94 was written by the son of an engineer who worked at the dam during its construction. After his father's death, the author researched the dam's construction and his father's role in it.
Notes and references
Further reading
*
Doig, Ivan (1996) ''Bucking the Sun'', New York:
Simon & Schuster
Simon & Schuster () is an American publishing company and a subsidiary of Paramount Global. It was founded in New York City on January 2, 1924 by Richard L. Simon and M. Lincoln Schuster. As of 2016, Simon & Schuster was the third largest publi ...
, Inc.
*
Lonnquist, Lois (2006) ''Fifty Cents an Hour: The Builders and Boomtowns of the Fort Peck Dam'', MtSky Press
*Middlebrooks, T. A. (1942), "Fort Peck Slide," Transactions of the American Society of Civil Engineers, 107, 723-764
*"Report on the Slide of a Portion of the Upstream Face of the Fort Peck Dam" (1939), Corps of Engineers, US Army.
External links
U.S. Army Corps of Engineers - Fort Peck ProjectFort Peck Dam, unofficial websiteLife Magazine construction photosFort Peck DamDocumentary produced by ''
PBS''
*
{{National Register of Historic Places
Dams on the Missouri River
Historic Civil Engineering Landmarks
Fort Peck, Montana
United States Army Corps of Engineers dams
Dams completed in 1940
Dams on the National Register of Historic Places in Montana
Earth-filled dams
National Register of Historic Places in McCone County, Montana
Hydroelectric power plants in Montana
Public Works Administration in Montana
1940 establishments in Montana