Fontenelle Dam facts for kids
Quick facts for kids Fontenelle Dam |
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| Location | Lincoln and Sweetwater counties, Wyoming, USA |
| Coordinates | 42°01′42.4″N 110°03′37.9″W / 42.028444°N 110.060528°W |
| Construction began | 1961 |
| Opening date | 1964 |
| Operator(s) | U.S. Bureau of Reclamation |
| Dam and spillways | |
| Type of dam | Zoned earthfill |
| Impounds | Green River |
| Height | 139 feet (42 m) |
| Length | 5,421 feet (1,652 m) |
| Dam volume | 5,265,000 cu yd (4,025,000 m3) |
| Spillway type | Gated spillway |
| Spillway capacity | 20,200 cu ft/s (570 m3/s) |
| Reservoir | |
| Creates | Fontenelle Reservoir |
| Total capacity | 345,360 acre-feet (0.42600 km3) |
| Catchment area | 4,156 sq mi (10,760 km2) |
| Power station | |
| Hydraulic head | 121 ft (37 m) |
| Turbines | 1 x 10 MW Francis-type |
| Installed capacity | 10 MW |
The Fontenelle Dam is a large dam built on the Green River in southwestern Wyoming. It was constructed between 1961 and 1964. This dam is 139-foot (42 m) tall and is made of earth and rock, a type called a "zoned earthfill" dam.
The dam creates the Fontenelle Reservoir, which can hold a huge amount of water – about 345,360-acre-foot (0.42600 km3). The Fontenelle Dam and its reservoir are key parts of the Seedskadee Project. The U.S. Bureau of Reclamation manages the reservoir. Its main job is to store water for the larger Colorado River Storage Project.
In 1965, the dam had a serious problem when a leak appeared on its right side. Water had to be released quickly, which caused flooding downstream. Luckily, the dam was repaired successfully. However, in 1983, experts rated the dam as "poor" because water kept leaking. This led to another emergency where the reservoir had to be emptied. To fix this, a special concrete wall was built inside the dam to stop the leaks.
Contents
Why Fontenelle Dam Was Built
At first, the Fontenelle Dam was planned to store water for farming. But in 1962, work was paused to study how to water crops in high-altitude areas. Because of these studies, many of the original farming plans for the project were canceled.
The main reason for the dam changed. It became important for Wyoming to keep its water rights in the Colorado River basin. This meant holding onto water that would otherwise flow downstream to other states. The dam also helps produce electricity, which is a secondary benefit.
One reason the farming plans were put on hold was the discovery of trona in the area. Trona is a valuable mineral used to make glass and other products. Mining trona was more profitable than farming, so those lands were removed from the project. This made the irrigation part of the project less practical.
How the Dam Was Built
Plans for developing the upper Green River basin started way back in 1946. More detailed reports for the Seedskadee Project came out in 1950 and 1953. Finally, in 1956, the U.S. Congress approved the Colorado River Storage Project, which included the Seedskadee Project.
Initial plans were finished in 1959. In 1961, the plans were updated to make the Fontenelle Reservoir even bigger. This larger size made it possible to add a power plant to generate electricity. Work on the farming parts of the project stopped in 1962.
The dam was designed with very large outlet works. These are tunnels that can release a lot of water quickly. They could release 18,000 cu ft/s (510 m3/s) of water. This was almost as much as the spillway, which is the main overflow channel, could handle (20,200 cu ft/s (570 m3/s)). The large outlet works were chosen because it was cheaper to make them bigger than to make the spillway bigger.
Construction of the Fontenelle Dam began with building a community for the workers. This base camp, called Fontenelle, started in 1961 with prefabricated houses. The main contract for building the dam was given out on June 13, 1961, to Foley Brothers, Inc. and Holland Construction Company. Work on the dam itself started on June 30, costing $7.9 million.
During construction, workers found that the rock at the dam's base was broken. So, they had to dig the cut-off trench, which stops water from seeping under the dam, 6 feet (1.8 m) deeper. They also had to use a lot of grout, a special cement mixture, to fill cracks in the rock, especially on the right side of the dam. The dam was mostly finished by the end of 1963, and fully completed on April 24, 1964. The power plant was built between 1963 and 1965.
When the Dam Almost Failed
Problems with the dam started to show up in May 1964. Part of the dam's backfill slid into the stilling basin, a pool of water downstream. This happened because the reservoir was emptied too quickly. When the reservoir was only 10% full, water started leaking from the dam's base. More leaks were seen about 4,000 feet (1,200 m) below the dam. In July 1965, another slide happened near the stilling basin.
A big leak appeared on September 3, 1965, on the west side of the dam. It started as a wet spot and grew larger. The downstream side of the dam lost 10,000 cubic yards (7,600 m3) of material, which slid into the stilling basin. Water kept flowing out, a problem known as "hydraulic piping."
The next day, workers started to lower the reservoir's water level and kept a 24-hour watch on the dam. The wet spot turned into a waterspout, gushing out between 10 and 12 million gallons of water every day!
On September 6, a sinkhole, about 15-foot (4.6 m) by 20-foot (6.1 m), opened up on the upstream side of the dam's top. Workers quickly filled it with riprap (large rocks) bulldozed from the dam's surface. The hole was 30 feet (9.1 m) deep, with its bottom 11 feet (3.4 m) below the reservoir's water level. Only 45 feet (14 m) of the dam structure remained between the sinkhole and the downstream side. If it had collapsed further, the dam could have completely broken. Luckily, the leakage did not get worse during this time.
The emergency release of water flooded areas along the Green River downstream, damaging farms and homes. The unusually large outlet works of the dam allowed the reservoir to be lowered by as much as 4 feet (1.2 m) per day. This quick action was very important, unlike what happened years later at the Teton Dam.
The reservoir's water level was kept low for the rest of the year. Workers began repairing the dam and injecting a lot of grout into the dam's side and along its center. This work continued through 1966, and the entire right side of the dam was replaced. In the spring of 1967, the reservoir was partly refilled to check if the grouting worked. About 200,000 cubic feet (5,700 m3) of grout was used! Water was released through the power plant's pipe while the turbine was removed and the outlet works were repaired. The reservoir was fully refilled in the summer of 1968.
Experts later said that a complete failure was "narrowly avoided." This near-disaster was not widely known, but it did cause other organizations to change how they designed and built embankment dams. The Bureau of Reclamation believed that water used to mix concrete was contaminated with trona. They thought the chemicals in trona made the grout set too quickly, leaving it weak and cracked.
Checking the Dam's Safety
After the Teton Dam failed in 1976 under similar conditions, a program called Safety Evaluation of Existing Dams (SEED) was started. In 1983, a report on Fontenelle Dam rated it "poor," which is the second-lowest rating. The report noted that water was still leaking, similar to the leaks that caused the 1965 problem.
In 1984, plans were made to build a 600-foot (180 m) long concrete wall at the east canal outlet to see if it would help. However, in May 1985, dam operators decided the dam was in "very serious distress" and started an emergency drawdown of the reservoir. As the water was quickly lowered, the upstream side of the dam began to slump. The reservoir was completely emptied.
In September, work began on a test section of a 840-foot (260 m) long, 24-inch (61 cm) thick concrete wall. This wall was built into the dam's core using a special system called "Hydrofraise." It extended 40 feet (12 m) to 50 feet (15 m) below the dam's base into the bedrock.
The reservoir was supposed to stay empty in 1986. But heavy spring runoff brought logs and tumbleweeds into the reservoir, clogging the outlet works. The reservoir partly filled, which prevented flooding in the town of Green River. However, this also caused worry about the dam possibly failing, as it was holding fifty feet of water, sometimes rising five feet in a single day.
A study of the repair program noted that the only other option was to intentionally break the center of the dam. This would have left local industries without water. The test section of the wall was completed, and it seemed to have solved the leakage problem. A full-length wall was considered, but the completed section proved effective.
