Fontenelle Dam
Encyclopedia
Fontenelle Dam was built between 1961 and 1964 on the Green River
in southwestern Wyoming
. The 139 feet (42.4 m) high zoned earthfill dam impounds the 345360 acre.ft Fontenelle Reservoir
. The dam and reservoir are the central features of the Seedskadee Project
of the U.S. Bureau of Reclamation, which manages the Fontenelle impoundment primarily as a storage reservoir for the Colorado River Storage Project
. The dam suffered a significant failure in 1965, when the dam's right abutment developed a leak. Emergency releases from the dam flooded downstream properties, but repairs to the dam were successful. However, in 1983 the dam was rated "poor" under Safety Evaluation of Existing Dams (SEED) criteria, due to continuing seepage, leading to an emergency drawdown. A concrete diaphragm wall was built through the core of the dam to stop leakage.
basin, retaining water that would otherwise go downstream to states in the lower Colorado basin. The dam provides power generation as a secondary feature. One motivation for the deferral of irrigation activities was the discovery of trona
in the southern portion of the proposed irrigated region. As the extraction of trona was a higher-value activity, the removal of those lands from the project made the irrigation project nonviable.
The first element of construction at Fontenelle Dam was the building of the Fortenelle community, the base camp for construction, with work starting in 1961 to build prefabricated relocatable houses for dam workers. The construction contract for the dam was awarded on June 13, 1961 to Folley Brothers, Inc. and the Holland Construction Company of St. Paul, Minnesota, with construction starting on June 30, at a cost of $7.9 million. The surface of the bedrock at the dam's base was found to be fragmented, so the cut-off trench intended to preclude water infiltrating under the dam, was deepened by 6 feet (1.8 m). The exposed rock was not prepared or smoothed with concrete. The foundation grouting required an unusually large amount of material to fill cracks in the upper 65 feet (19.8 m), with additional grouting required at the right abutment and outlet works. Work on the dam was completed by the end on 1963, with final completion on April 24, 1964. Work on the powerplant started in 1963, with completion in 1965.
bulldozed from the nearby dam surface into the hole. The hole was 30 feet (9.1 m) deep, with the bottom 11 feet (3.4 m) below the level of the reservoir, with only 45 feet (13.7 m) of dam structure remaining between the sinkhole and the downstream face. Further collapse could have created a breach in the dam, leading to total failure. Leakage did not increase during the incident. The emergency release of water flooded areas along the Green River downstream, damaging ranches and homes. The unusually large outlet works allowed the reservoir to be drawn down by as much as 4 feet (1.2 m) per day, a measure not available eleven years later at Teton Dam
.
The reservoir was drawn down further during the remainder of the year, and work began on repairs to the embankment, along with an intensive program of pressure-grouting at the abutment and down the centerline of the dam embankment. Work continued through 1966, with a complete replacement of the right abutment embankment. The reservoir was partly refilled in the spring of 1967 to check the efficacy of the grouting work, which consumed 200000 cubic feet (5,663.4 m³) of grout. Water was released through the power penstock with the turbine and generator removed while the outlet works were repaired. 23 observation wells were drilled at this time. The reservoir was fully refilled in the summer of 1968. Subsequent evaluations described failure as "narrowly averted." The near-failure was not widely reported, but did cause organizations other than the USBR to change their design and construction practices for embankment dams. The Bureau of Reclamation concluded that water used in mixing concrete was contaminated with trona. The sodium carbonate
in the trona accelerated setting of the grout in the original grout curtain, leaving it weak and fissured.
s into the reservoir, clogging the outlet works. The reservoir partially filled, preventing flooding in the town of Green River
, but creating anxiety about possible failure of the dam, which was retaining fifty feet of water, rising at times five feet in a day. An environmental assessment of the repair program noted that the only alternative was an intentional and permanent breaching of the center section of the dam, leaving local industries without water. The test section of wall was completed, and a full-length wall was considered, but the completed section appeared to have solved the leakage problem.
Green River (Utah)
The Green River, located in the western United States, is the chief tributary of the Colorado River. The watershed of the river, known as the Green River Basin, covers parts of Wyoming, Utah, and Colorado. The Green River is long, beginning in the Wind River Mountains of Wyoming and flowing...
in southwestern Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
. The 139 feet (42.4 m) high zoned earthfill dam impounds the 345360 acre.ft Fontenelle Reservoir
Fontenelle Reservoir
Fontenelle Reservoir is an artificial reservoir located in southwest Wyoming. It lies almost entirely within Lincoln County, although the east end of the Fontenelle Dam and a tiny portion of the reservoir are actually in northwestern Sweetwater County. Impounded by Fontenelle Dam, the reservoir...
. The dam and reservoir are the central features of the Seedskadee Project
Seedskadee Project
The Seedskadee Project is a water resources development project of the U.S. Bureau of Reclamation. The project focuses on the upper Green River in western Wyoming, storing the river's waters in Fontenelle Reservoir. The project is associated with the Colorado River Storage Project, retaining the...
of the U.S. Bureau of Reclamation, which manages the Fontenelle impoundment primarily as a storage reservoir for the Colorado River Storage Project
Colorado River Storage Project
The Colorado River Storage Project is a United States Bureau of Reclamation project designed to oversee the development of the upper Colorado River basin...
. The dam suffered a significant failure in 1965, when the dam's right abutment developed a leak. Emergency releases from the dam flooded downstream properties, but repairs to the dam were successful. However, in 1983 the dam was rated "poor" under Safety Evaluation of Existing Dams (SEED) criteria, due to continuing seepage, leading to an emergency drawdown. A concrete diaphragm wall was built through the core of the dam to stop leakage.
Use
Initially conceived as a storage reservoir for irrigation water, the project was suspended for a time in 1962 to pursue a study high-altitude irrigation methods. The results of the studies caused the cancellation of many irrigation features for the project. The primary project rationale evolved to support Wyoming water rights in the Colorado RiverColorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...
basin, retaining water that would otherwise go downstream to states in the lower Colorado basin. The dam provides power generation as a secondary feature. One motivation for the deferral of irrigation activities was the discovery of trona
Trona
Trona ; Na3•2H2O is an evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has replaced the Solvay process used in most of the rest of the world for sodium carbonate production.- Etymology :The word "trona" comes to English by way of either...
in the southern portion of the proposed irrigated region. As the extraction of trona was a higher-value activity, the removal of those lands from the project made the irrigation project nonviable.
Construction
Development of the upper Green River basin was included in a 1946 Bureau of Reclamation report on the Colorado River basin. A 1950 supplementary report dealt with details of the proposed Seedskadee Project, followed by another addendum in 1953. The Colorado River Storage Project, including the Seedskadee Project, was authorized by Congress in 1956. Initial planning was completed in 1959, and amended in 1961 to increase the capacity of Fontenelle Reservoir to 345400 acre.ft, making the construction of a powerplant feasible. Work was stopped on irrigation infrastructure in 1962. The dam featured unusually large outlet works, capable of discharging 18000 ft3/s (compared with a spillway capacity of 20200 ft3/s) because the outlet works could be increased in size at lower cost than the spillway.The first element of construction at Fontenelle Dam was the building of the Fortenelle community, the base camp for construction, with work starting in 1961 to build prefabricated relocatable houses for dam workers. The construction contract for the dam was awarded on June 13, 1961 to Folley Brothers, Inc. and the Holland Construction Company of St. Paul, Minnesota, with construction starting on June 30, at a cost of $7.9 million. The surface of the bedrock at the dam's base was found to be fragmented, so the cut-off trench intended to preclude water infiltrating under the dam, was deepened by 6 feet (1.8 m). The exposed rock was not prepared or smoothed with concrete. The foundation grouting required an unusually large amount of material to fill cracks in the upper 65 feet (19.8 m), with additional grouting required at the right abutment and outlet works. Work on the dam was completed by the end on 1963, with final completion on April 24, 1964. Work on the powerplant started in 1963, with completion in 1965.
Partial failure
Problems with the embankment became apparent in May 1964, when part of the backfill slid into the stilling basin downstream, attributed to too-fast lowering of the reservoir level. When the reservoir had filled to 10% of capacity, seepage became apparent at the dam's base, with further seepage observed about 4000 feet (1,219.2 m) below the dam from shale outcroppings. In July 1965 another slide occurred in the area of the stilling basin. A significant leak appeared on September 3, 1965 at the west abutment, starting as a wet spot that grew with time. The weakened downstream face lost 10000 cubic yards (7,645.5 m³) of material that slid into the stilling basin, accompanied by continuing water flow, a condition known as "hydraulic piping." Work began the next day to lower the reservoir, with a 24-hour watch on the dam. The wet spot became a waterspout, flowing at a rate of between 10 and 12 million gallons per day. On September 6 a 15 feet (4.6 m) by 20 feet (6.1 m) sinkhole developed on the upstream face of the dam's crest, which workers immediately filled with riprapRiprap
Riprap — also known as rip rap, rubble, shot rock or rock armour or "Rip-rap" — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.It is made from a variety of rock types, commonly granite or...
bulldozed from the nearby dam surface into the hole. The hole was 30 feet (9.1 m) deep, with the bottom 11 feet (3.4 m) below the level of the reservoir, with only 45 feet (13.7 m) of dam structure remaining between the sinkhole and the downstream face. Further collapse could have created a breach in the dam, leading to total failure. Leakage did not increase during the incident. The emergency release of water flooded areas along the Green River downstream, damaging ranches and homes. The unusually large outlet works allowed the reservoir to be drawn down by as much as 4 feet (1.2 m) per day, a measure not available eleven years later at Teton Dam
Teton Dam
The Teton Dam was a federally built earthen dam on the Teton River in southeastern Idaho, set between Fremont and Madison counties, USA, which when filling for the first time suffered a catastrophic failure on June 5, 1976. The collapse of the dam resulted in the deaths of 11 peopleand 13,000 head...
.
The reservoir was drawn down further during the remainder of the year, and work began on repairs to the embankment, along with an intensive program of pressure-grouting at the abutment and down the centerline of the dam embankment. Work continued through 1966, with a complete replacement of the right abutment embankment. The reservoir was partly refilled in the spring of 1967 to check the efficacy of the grouting work, which consumed 200000 cubic feet (5,663.4 m³) of grout. Water was released through the power penstock with the turbine and generator removed while the outlet works were repaired. 23 observation wells were drilled at this time. The reservoir was fully refilled in the summer of 1968. Subsequent evaluations described failure as "narrowly averted." The near-failure was not widely reported, but did cause organizations other than the USBR to change their design and construction practices for embankment dams. The Bureau of Reclamation concluded that water used in mixing concrete was contaminated with trona. The sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...
in the trona accelerated setting of the grout in the original grout curtain, leaving it weak and fissured.
Safety evaluation
As a result of the catastrophic failure of the closely similar Teton Dam under much the same circumstances in 1976, the Safety Evaluation of Existing Dams (SEED) program was initiated in the late 1970s and early 1980s. The 1983 report on Fontenelle Dam rated the dam "poor," the second-lowest rating. The report noted increasing seepage, similar in nature to the seepage that caused the 1965 failure. Plans were advanced in 1984 to build a 600 feet (182.9 m) long concrete wall at the east canal outlet works to evaluate its efficacy. However, in May 1985, operators initiated an emergency drawdown of the reservoir after deciding that the dam was "in very serious distress." With the fast drawdown, slumping appeared on the upstream face. The reservoir was entirely drained. In September work began on the trenching of an 840 feet (256 m) test section of 24 inches (61 cm) thick concrete diaphragm wall into the core of the dam, using the "Hydrofraise" system of grout trenching, extending 40 feet (12.2 m) to 50 feet (15.2 m) below the base of the dam into bedrock. The reservoir was to be kept empty in 1986, but heavy spring runoff carried logs and tumbleweedTumbleweed
A tumbleweed is the above-ground part of a plant that, once mature and dry, disengages from the root and tumbles away in the wind. Usually, the tumbleweed is the entire plant apart from the roots, but in a few species it is a flower cluster. The tumbleweed habit is most common in steppe and desert...
s into the reservoir, clogging the outlet works. The reservoir partially filled, preventing flooding in the town of Green River
Green River, Wyoming
Green River is a city in and the county seat of Sweetwater County, Wyoming, United States, in the southwestern part of the state. The population was 11,808 at the 2000 census....
, but creating anxiety about possible failure of the dam, which was retaining fifty feet of water, rising at times five feet in a day. An environmental assessment of the repair program noted that the only alternative was an intentional and permanent breaching of the center section of the dam, leaving local industries without water. The test section of wall was completed, and a full-length wall was considered, but the completed section appeared to have solved the leakage problem.
See also
- Teton DamTeton DamThe Teton Dam was a federally built earthen dam on the Teton River in southeastern Idaho, set between Fremont and Madison counties, USA, which when filling for the first time suffered a catastrophic failure on June 5, 1976. The collapse of the dam resulted in the deaths of 11 peopleand 13,000 head...
, a similar design which failed catastrophically in 1976 under similar circumstances after a leak developed at the dam's abutment when the reservoir was filled.
External links
- Fontenelle Dam at the U.S. Bureau of Reclamation
- Seedskadee Project at the U.S. Bureau of Reclamation
- Fontenelle Powerplant at the U.S. Bureau of Reclamation