The Armel Unit, formerly called the St. Francis Unit, of the Pick-Sloan Missouri Basin Program is in eastern Colorado on the South Fork of the Republican River. The principal feature of the unit is Bonny Dam and Reservoir which serves as an important flood control feature and provides benefits for recreation and fish and wildlife conservation and enhancement. Originally, irrigation was to have been a part of the multiple-purpose benefits included in the unit plan; however, investigations have shown that an economically feasible plan for Federal development could not be formulated within the 24,000 acre upland area considered for irrigation.
In the early 1880`s, settlers moved into this region and established claims under the Homestead, Timer Claim, and Preemption Acts. Prior to this time, only a few scattered ranches were located in the area, although cattle were often trailed through from Texas to the Platte River, where they were shipped east by rail.
Recurring droughts throughout the Great Plains and in the Republican River watershed in particular, have stimulated considerable interest in irrigation possibilities in this area during the past 80 years or more. Several attempts were made to irrigate directly from the stream, and a number of canals were built as early as 1889. Most of the projects failed because of destructive floods, sandy soil, lack of water supply, or financial difficulties.
Investigations of the Armel Unit on the South Fork of the Republican River were initiated in 1939. These investigations resulted in Bonny Dam and Reservoir being included in Senate Document No. 191. The plan called for construction of the multiple-purpose dam and reservoir as the major feature of the unit.
Subsequent to initiation of investigations for irrigation, Public Law 88-442, August 14, 1964, was enacted which required reauthorization of the irrigation portion of the unit. Accordingly, in December 1969 investigations of the irrigation phase were initiated. The results of these investigations disclosed that an economically feasible plan for Federal development could not be formulated within the 24,000-acre upland area previously investigated.
The unit was authorized by the Flood Control Acts of December 22, 1944, and July 24, 1946.
Construction of Bonny Dam began December 8, 1948, and was completed May 4, 1951.
Bonny Dam and Reservoir are operated and maintained by the Bureau of Reclamation. The reservoir water surface and reservoir lands upstream from the dam are administered by the Division of Parks and Outdoor Recreation of the Colorado Department of Natural Resources.
Bonny Dam provides a high degree of flood control in the upper reaches of the Republican River and, together with other dams and reservoirs downstream, furnishes effective control of floods in the Republican River Basin.
Recreation and Fish and Wildlife
The reservoir and surrounding lands, set aside for that purpose, serve as a center for outdoor, water-oriented recreational activities for the immediate locale as well as more distant areas. Recreational use includes picnicking, camping, swimming, water skiing, boating, fishing, and hunting. The reservoir is stocked with fish, and the State of Colorado operates a fish hatchery and manages the surrounding lands for conservation and enhancement of wildlife resources.
The primary purpose of Bonny Dam is the protection of the lower South Fork of the Republican River Valley from recurring floods originating upstream of Hale, Colorado. The estimated frequency and magnitude of floods occurring upstream of Bonny Dam, which can be wholly or partially controlled, make this dam and reservoir one of the most important flood-control features in the Republican River Basin upstream of the Corps of Engineers' Harlan County Dam. The unit also provides regulation of the existing water supply to Hale Ditch, which serves 750 acres, 400 of which are owned by the State of Colorado. The State operates a fish hatchery and wildlife habitat area on these lands. The reservoir and surrounding lands provide excellent recreation opportunities and fish and wildlife conservation.
Bonny Dam is a modified homogeneous earthfill structure rising 158 feet above foundation. It contains 8,853,000 cubic yards of embankment material.
The spillway is an uncontrolled concrete-lined chute in the left abutment with a sluiceway at the center and below the spillway crest partially controlled by a 16.5- by 10.75-foot fixed-wheel gate. The maximum capacity of the spillway is 73,300 cubic feet per second. The sluiceway was designed to discharge 10,000 cubic feet per second from the reservoir at elevation 3710.0 ft.
The outlet works, extending through the dam near the left abutment, is a 56-inch-diameter steel pipe designed to provide releases into the stream for downstream purposes. A 40-inch-diameter branch pipe was installed for future use. A 32-inch-diameter branch, constructed across the downstream face of the dam, serves the 750 acres of non-project land south of the river. The Hale Ditch outlet pipe, which is an integral part of the Bonny Dam outlet works, has been modified to permit regulatory releases during the winter months. This enhances fish spawning in the spring and affords excellent hunting conditions in the fall.
Bonny Reservoir has 170,160 acre-feet of total capacity below the crest of the spillway at elevation 3710.0 ft.
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