The Boysen Unit of the Pick-Sloan Missouri Basin Program, on the Wind River about 20 miles south of Thermopolis, Wyoming, consists of Boysen Dam, Reservoir, and Powerplant. Boysen Dam impounds the waters of Wind River, providing regulation of the streamflows for power generation, irrigation, flood control, sediment retention, fish propagation, and recreation development.
Settlement in the vicinity of the Boysen Unit began about 1850; the first known irrigation works were constructed in the 1860`s along the Popo Agie River near Lander, Wyoming. During the next 15 years, settlements became more extensive, and irrigation works were constructed by private organizations and individuals in the areas where diversions were available. Irrigation continued as a private endeavor until about 1920, when opportunities for low-cost diversions were practically exhausted.
In 1908, a concrete dam was constructed across the Wind River about 1.5 miles downstream from the present site of Boysen Dam, primarily for power purposes. A flood in 1923 raised the water surface in the reservoir and inundated several miles of railroad tracks. A portion of the dam was blasted away to reduce the reservoir area and forestall future flooding. Repairs to the dam were never undertaken, and generation of power ceased in the early 1930's. The dam was removed in 1948 to improve the tail-water conditions for the Boysen Power Plant.
Investigations of the area were made by the Bureau of Reclamation in 1904 and again in 1916-17. In 1939, the Corps of Engineers made additional studies of the Bighorn River, recommending construction of a dam at the site of the old dam. In 1941, the Bureau of Reclamation resumed investigations and studies, and a report was published in 1942. The Boysen Unit was included in the Missouri River Basin program, as outlined in Senate Document 191. The report recommended construction of a dam about 1.5 miles upstream from the old site, where relocation costs would be more reasonable.
Authorized by the Flood Control Act of December 22, 1944, Public Law 534, which approved the general comprehensive plan set forth in Senate Document 191, as revised and coordinated by Senate Document 247, 78th Congress, 2d session.
Construction began on Boysen Dam and Powerplant and relocation of the CB&Q Railroad on September 19, 1947, and was completed December 11, 1952.
The unit is operated by the Bureau of Reclamation.
The Boysen Unit provides irrigation water through storage for lands below and above the reservoir. No direct irrigation is made from the unit.
Hydroelectric power is tied into the transmission lines to Alcova, Thermopolis, and Pilot Butte-Thermopolis.
Boysen Reservoir has a joint use capacity of 144,229 acre-feet, an exclusive flood control capacity of 150,623 acre-feet, and a surcharge capacity of 520,679 acre-feet for a total flood capacity of 892,296 acre-feet and has been effective in reducing flood damage to property. Total damages reduced by the reservoir since construction totaled about $75.0 million by the end of 1998.
Boysen Reservoir, on the Wind River about 20 miles upstream from Thermopolis, Wyoming, quickly became popular for camping, fishing, boating, and sightseeing. Fishing season is open year round with a State fishing license. Fish species available include trout, walleye, perch, and ling. Other activities include wildlife watching, big game hunting in season with a State license, rock-hounding, and horseback riding. The narrow gorge in the Owl Creek range is an additional attraction.
Irrigation was not included as an integral part of the Boysen Unit. However, Boysen Reservoir is essential to irrigation in the Wind River Basin above the reservoir and the Bighorn Basin below the reservoir. Releases from Boysen Reservoir supply water for 7,441 acres on the Hanover-Bluff Unit, and 2,380 acres within the Lucerne area of the Owl Creek Unit. Another 41,000 acres of privately owned land below Boysen Dam are provided supplemental water by contract. Low-season streamflow, which formerly had to satisfy prior rights downstream of Boysen Reservoir, has been made available to upstream irrigation by exchange of an equal amount of stored water released from Boysen Reservoir. Storage contracts for irrigation of about 20,000 acres of land above Boysen are held by private irrigation entities.
Power generated at the 15,000-kilowatt Boysen Powerplant is fed into the Western Division, Pick-Sloan Missouri Basin Program transmission facilities for use within that division. In addition, floods are controlled, the river loses its silt load, municipal water supplies are augmented, fish and wildlife habitats are improved, and recreation possibilities are expanded.
Boysen Dam and Power Plant
Boysen Dam is zoned earthfill structure having a structural height of 220 feet. An overflow, weir-type spillway controlled by radial gates is located on the right abutment and discharges immediately upstream and to the left of the power plant.
Design discharge through the spillway is 20,000 cubic feet per second at an elevation of 4722.0 ft. Boysen Reservoir has a total controlled storage capacity of 802,000 acre-feet at a water surface elevation of 4725.0 ft.
The outlet works are on the right abutment of the dam. Discharge is through a 66-inch-diameter steel pipe located above the power penstock and a 57-inch-diameter steel pipe joined to the 10-foot-diameter power penstock serving Unit 1 in the power house.
The power plant has an installed capacity of 15,000 kilowatts developed by two 7,500-kilowatt units operating under an average head of 99 feet. Each unit is served by a 10-foot-diameter steel penstock joined to a common 15-foot-diameter steel penstock immediately upstream from the power plant. The 15-foot-diameter penstock leading from the intake structure to the units was located to utilize the bore of an existing railroad tunnel made available through relocation of the CB&Q Railroad.
Other features of the construction activity were the relocation of 13.5 miles of the railroad track, which required a tunnel 1.25 miles long, seven bridges, two sidings, and other construction features. The unit is operated by the Bureau of Reclamation.