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The Hyrum Project in Northern Utah includes as its principal construction features Hyrum Dam, Dike, Reservoir, and Spillway, Hyrum Feeder Canal, Hyrum-Mendon Canal, Wellsville Canal, Wellsville Canal Pumping Plant, and appurtenant structures. The system stores and diverts water from the Little Bear River to furnish supplemental water supplies to 6,800 acres of privately owned and cultivated project lands.
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Storage for the project is provided by Hyrum Reservoir, which stores the runoff of Little Bear River. Water for the irrigation system is diverted from the outlet works of Hyrum Dam. Three canals, Hyrum Feeder Canal, Hyrum-Mendon Canal, and Wellsville Canal, divert from this point. The Hyrum Feeder Canal extends north for about 1.3 miles and discharges into a lateral of the Hyrum Irrigation Co. The 14 mile long Hyrum-Mendon Canal crosses the Little Bear River Flood Plain in an inverted siphon and delivers water to lands on the southwest side of Cache Valley. The 5.4 mile long Wellsville Canal also crosses the Little Bear River Flood Plain in an inverted siphon. This canal receives its water from the Wellsville Pumping Plant and supplies water to lands on the southwest side of the valley which lie about 70 feet above those watered by the Hyrum-Mendon Canal. Water is made available to approximately 2,000 acres of project lands upstream of the reservoir by exchange.
Hyrum Dam and Reservoir are located on the Little Bear River just south of Hyrum City. The dam is a rolled earth and rockfill structure containing 352,000 cubic yards of earthfill, 62,000 cubic yards of rockfill, and 13,000 cubic yards of riprap and gravel blanket, for a total of about 430,000 cubic yards of material. The construction period was 1934 to 1935. The date of closure (first storage) was April 1, 1935, and the first water was made available in July 1935. The dam has a maximum base width of 600 feet, a maximum structural height of 116 feet, a hydraulic height of 82 feet (from the streambed to the maximum water surface elevation), a crest width of 35 feet, a crest length of 540 feet, and a crest elevation of 4,680 feet. The maximum water surface elevation of this reservoir is 4,672.0 feet (top of the spillway radial gates). The dam is located near the southwest corner of Hyrum City and creates a reservoir with a total capacity of 18,685 acre-feet, and a surface area of 480 acres. The maximum capacity of the outlet works is 300 cubic feet per second (cfs) at a water surface elevation of 4,666.0 feet. Water flows from the reservoir through the outlet works in a concrete lined pressure tunnel, located in the right abutment, controlled by two sets of 33 inch square high pressure slide gates in the gate chamber. Two steel pipes continue to the outlet well.
Prior to the construction of Hyrum Dam, a diversion dam diverted water from the Little Bear River into the East Field Canal. This canal does not receive project water because its primary water right is the water coming down the river. The outlet works has a capacity of 300 cfs, of which 113 cfs can be delivered through the Hyrum Feeder, Wellsville, and Hyrum-Mendon Canals for irrigation. In an emergency drawdown, the full 300 cfs flow could be returned to the Little Bear River.
Hyrum Dike, a rolled earthfill structure, has a crest length of about 900 feet, a crest elevation of 4,683 feet, and a structural height of 15 feet. The dike contains the northwest part of the reservoir and is between the Hyrum State Park and the Hyrum Dam Spillway, both of which are located northeast of Hyrum Dam.
The spillway consists of an inlet channel, an inlet transition, a gate controlled open channel with two bridge piers, a chute transition, a concrete chute with 1:1 side slopes on the walls, a stilling basin, and an outlet channel. The inlet transition is located approximately 900 feet northeast of the right abutment of the dam and at the west end of the dike. The effective length of the spillway is 1,108 feet. The crest elevation is 4,660 feet, and flow is controlled by three, 16 by 12 foot radial gates, with a discharge capacity of 6,000 cfs.
The project is operated and maintained by the South Cache Water Users Association.
Although fur trappers visited Cache Valley frequently from 1824 to 1856, actual settlement of lands now included in the Hyrum Project commenced in September 1856, when `Maughan`s Fort` was built at the site of the present city of Wellsville. From that time through the early 1860`s, settlement of the valley was rapid and communities were located on several streams where water could readily and cheaply be conveyed to the land.
The Reclamation Service investigated irrigation possibilities for the Hyrum Project area during 1902-1904. After this early study, interest lagged until 1922 when the Department of Agriculture made a report on the land and water resources of the valley. This report revived the interest of the community in irrigation and on March 21, 1923, representatives of the Cache Valley Water Users Association petitioned the Utah Water Storage Commission for assistance in developing a plan for using the water resources of the valley. Funds were subsequently allotted for investigation of the water resources of Cache Valley. Investigation continued at intervals until 1932, when a report by the Bureau of Reclamation formed the basis for project construction.
The project was initiated under the provisions of the National Industrial Recovery Act of 1933 (48 Stat. 195), and an allotment of funds for construction was made on August 19, 1933. The President approved the project on November 6, 1935, under the terms of Section 4, Act of June 25, 1910 (36 Stat. 835), and Subsection B of Section 4, act of December 5, 1924 (43 Stat. 701).
Construction of the project began on March 26, 1934. The first delivery of water was made available in July of 1935.
During 1977, rehabilitation work was completed. The Wellsville Canal steel discharge line of the pumping plant was replaced by a 24 inch diameter reinforced concrete pipe buried in the same location. Rehabilitation of the Hyrum-Mendon Canal consisted of removing five steel flumes and replacing them with 42 inch diameter reinforced concrete pipe siphons.
Major rehabilitation work initiated in 1990 was completed in 1995. The work included repair of concrete structures at Hyrum Dam, modifying and extending (raising) the outlet works intake structure, renovating the spillway gates, the outlet works pipes and penstock, the pump-turbine unit and gate control units. Also 2,430 feet of Hyrum Feeder Canal was placed in 24 inch diameter Polyvinyl Chloride (Plastic) pipeline. Earth lining was placed in 11,000 feet of the Hyrum-Mendon Canal and 1,000 feet of the Wellsville Canal. A Hyrum-Mendon Canal steel flume was removed and replaced by an earthfill section of canal.
Irrigation of project lands has greatly increased their productivity and has improved the general economy of the community. Alfalfa, wheat, barley, and pasture are the principal crops in the area. A large proportion of the farms are small and are owned by part-time farmers.
Although there is no specific reservoir capacity assigned for flood control, the Hyrum Project has provided an accumulated $96,000 in flood control benefits from 1950 to 1999.