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Ainsworth Unit
Photo of Merritt Dam and Reservoir
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Pick Sloan Missouri Basin Program
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Ainsworth Unit Project - 33 KB (pdf)
General Description| Plan| Development| Benefits
General Description

The Ainsworth Unit of the Pick-Sloan Missouri Basin Program is located in North-central Nebraska. The storage facilities are on the Snake River approximately 14 miles upstream from its confluence with the Niobrara River, in Cherry County southwest of Valentine. The irrigable lands extend 22 miles from west to east and 14 miles from north to south, beginning near Johnstown and continuing eastward to a point near Long Pine, all in Brown and Rock Counties.

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The unit provides a full water supply for the irrigation of 34,540 acres of land in the Ainsworth Irrigation District. Project facilities include Merritt Dam and Reservoir, the Ainsworth Canal, a system of laterals, and surface and subsurface drains. Although essentially a single-purpose irrigation development, additional benefits accrue from recreation, fish and wildlife, and water quality control.

The water supply for the unit comes from the Snake River and is stored in Merritt Reservoir for timely release into the Ainsworth Canal, by which it is conveyed to project lands for irrigation. The Snake River originates in the Sandhills region of Nebraska, an area characterized by highly permeable sands and many closed basins. Precipitation falling into these basins seeps into the ground or ponds temporarily, and feeds the streams with a large, steady baseflow. Because of the underground flow, the total drainage area contribution to the Snake River above Merritt Dam is about 600 square miles. Of this, only 83 square miles contribute surface runoff. Average annual runoff was 184,600 acre-feet for the period 1947-1962. Average annual irrigation diversion requirement to provide a full supply for the 33,960 irrigable acres is 102,000 acre-feet.

Facility Descriptions
Merritt Dam and Reservoir

Merritt Dam has a structural height of 126 feet and a crest length of 3,222 feet. The zoned earthfill embankment consists of 1,548,000 cubic yards of material. It is the first Bureau of Reclamation earthfill dam to use soil cement instead of the traditional rock riprap to protect the upstream face.

The morning-glory ungated spillway protects the dam from damage by floods. It consists of a concrete intake structure, concrete conduit, concrete chute and stilling basin, and outlet channel. The spillway has a capacity of 2,080 cubic feet per second at water surface elevation 2949.8 feet.

A branched outlet works in the dam provides for diverting water to the Ainsworth Canal or for controlling releases to the Snake River through the stilling basin.

The canal outlet works consist of a 78-inch-diameter steel pipe, a concrete control house with two 4- foot-square high-pressure gates, a stilling basin, a wave suppressor, a gage house, and a Parshall flume.

The river outlet works consist of a concrete intake structure, a concrete conduit, a gate chamber for one 5- by 6-foot high-pressure gate, an access shaft and access house, a 54-inch-diameter steel pipe, a control house for two 2.75-foot-square high-pressure gates, and a stilling basin.

Merritt Reservoir has a total capacity of 74,486 acre-feet at elevation 2946.0, an active conservation capacity of 67,686 acre-feet between elevations 2896.0 ft and 2946.0 ft, and a surface area of 3,222 acres at elevation 2946.0 ft.

Ainsworth Canal and Distribution System

The Ainsworth Canal originates at the Merritt Dam outlet works and extends eastward through the Sandhills to the project lands. The canal is concrete lined for its entire length to minimize seepage losses in the sandy soils it traverses, is 52.9 miles long, and has an initial capacity of 580 cubic feet per second.

The lateral system which delivers the water to the project lands has a total length of 169.7 miles and the initial capacities range from 530 to 4 cubic feet per second. Five miles of surface water disposal drains and several disposal ponding areas have been constructed. Other surface water disposal and subsurface drainage facilities will be constructed as necessary.

Operating Agencies

Merritt Dam and Reservoir, the Ainsworth Canal, and the laterals and drains are operated and maintained by the Ainsworth Irrigation District. The Nebraska Game and Parks Commission administers the recreation and fish and wildlife aspects of the reservoir.

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Settlement of the territory was slow until 1860-1870, when the Homestead Act of 1862, the demobilization of Civil War veterans, the establishment of military posts on the frontier, and the completion in 1867 of a transcontinental railway running through Nebraska combined to stimulate settlement. By 1890, nearly all of the irrigable lands in the Ainsworth Unit area had been homesteaded.

Early interest in the possibilities of irrigation development in the Ainsworth area is evidenced by the recording of applications for water rights in 1880`s along the Niobrara River and its tributaries. Many of the developments were unsuccessful or did not materialize, mainly because of the inability of the farmers to finance the construction and maintenance.


The Bureau of Reclamation began a comprehensive investigation of the land and water resources of the Niobrara River Basin in 1946 after local residents attended a public hearing at Valentine, Nebraska to present evidence and discuss possibilities of developments for irrigation, power generation, flood control, and other functions associated with water resource development. At this hearing, the people of the basin appealed to the Federal Government for assistance in investigating the opportunities for future development. A basin report dated June 1953 recommended that four units - Mirage Flats Extension, Lavaca Flats, O`Neill (excluding the proposed Long Pine and Meadville Powerplants), and the Ainsworth Unit - be considered for development. Both engineering and economic reasons prompted the selection of the Ainsworth Unit for early construction.


The Ainsworth Unit was authorized as an integral part of the Missouri River Basin Project on August 21, 1954, by Presidential approval of Public Law 612, 83d Congress, 2d session (68 Stat. 757).


Construction of Merritt Dam and Reservoir began in August 1961, and storage of water was started in February 1964. Construction of the dam was completed in May 1964, and the dam and reservoir were transferred from construction to operation and maintenance status on March 10, 1965.

Construction of the irrigation distribution system began in April 1962, was completed in June 1966, and was transferred to operation and maintenance status on September 1, 1966.

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The local economy had been almost entirely dependent on dryland agriculture. After development of the unit, the predominant type of farming became a livestock-general crop pattern in which the major income is derived from livestock and its products. The principal crops being irrigated are feed grains, alfalfa, and small grains.

Recreation, Fish & Wildlife

A facility of the Ainsworth Unit, Sandhills Division, Pick-Sloan Missouri Basin Project, the dam is operated by the Ainsworth Irrigation District. The Game and Parks Commission administers the water surface and adjacent lands for recreation and wildlife purposes. The reservoir has 44 miles of shoreline; 74,486 acre feet of storage, and a surface area of 2,906 acres. It irrigates approximately 34,539 acres of Nebraska farmland.

For campers, primitive ovemight facilities are available at all the areas on this scenic reservoir, along with drinking water and vault toilets. Merritt Dam Trading Post, the area concession, is located at the east end of the dam and offers fee camping with water and electrical hookups. A trailer dump station for recreational vehicles is provided adjacent to the Main Area.

Although Merritt is remote, the locale boasts several other attractions. McKelvie National Forest lies immediately to the north, with its thousands of acres of grassy sandhills and grouse hunting. Other attractions include the nearby Valentine National Wildlife Refuge, the beautiful Snake River Falls, the Valentine State Fish Hatchery, and Fort Niobrara Wildlife Refuge.

For specific information about Merritt Reservoir click on the name below.

Merritt Reservoir
Flood Control

Keith Sebelius Reservoir protects the valley downstream against flash floods which have damaged or destroyed towns, crops, livestock, bridges, railroads, and other property in the past. To the extent practicable, floodwater is stored in the reservoir for future releases for irrigation and municipal water use. As of 1998, Keith Sebelius Reservoir has prevented $3.4 million in flood damages.

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Last updated: Apr 04, 2013