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Armel Unit
Photo of Bonny Dam and Reservoir
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Parent Program/Project
Pick Sloan Missouri Basin Program
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Armel Unit Project History (pdf - 52 KB) (pdf)
General Description| Plan| Development| Benefits


General Description

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.

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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.

Facility Descriptions

Bonny Dam

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.

Operating Agencies

Bonny Dam and Reservoir are operated and maintained by the Bureau of Reclamation. The reservoir water surface and reservoir lands upstream of the dam are administered by the Division of Parks and Outdoor Recreation of the Colorado Department of Natural Resources.

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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. Reclamation is currently working with the State of Colorado to evaluate alternative uses for the developed water supply.


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. 

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Recreation, Fish & Wildlife

Bonny Dam and Reservoir are on the South Fork of the Republican River near Hale, Colorado just west of the Kansas border in Yuma County. An oasis on the plains, Bonny Lake State Park offers a welcomed change from the rolling prairie and grasslands that surround the park. Nestled in the broad valley of the South Fork of the Republican River, at an elevation of 3,700 feet, Bonny Lake State Park has colorful vistas in the fall and a variety of yearround recreational opportunities. Enjoy camping, hunting, hiking, picnicking and wildlife viewing at Bonny Lake State Park. Fishing is wellknown and excellent on this 1,900 surfaceacre reservoir. Walleye, northern pike and a variety of bass are just some of the fish that inhabit the reservoir. With seasonably warm waters, dependable winds and sandy beaches, Bonny Lake State Park is the perfect destination for swimmers, waterskiers and windsurfers. The recreational facilities are managed by the Colorado Division of Parks and Outdoor Recreation, and wildlife areas are managed by the Colorado Division of Wildlife.

For specific information on Bonny Reservoir click on the name below.

Bonny Reservoir

Flood Control

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. Bonny Reservoir has an exclusive flood control capacity of 128,820 acre-feet and a surcharge capacity of 178,230 acre-feet for a total flood capacity of 307,050 acre-feet. As of 1998, Bonny Reservoir had prevented $2,241.0 million in flood damages.

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Last updated: Apr 04, 2013