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Conconully Dam
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Okanogan Project History (57 KB) (pdf)
General Description| Plan| Development| Benefits

General Description

Project facilities include Conconully Dam and Reservoir, Salmon Lake Dam and Conconully Lake, Salmon Creek Diversion Dam, and canals and laterals to serve some 5,000 acres of irrigable lands along the Okanogan River in the vicinity of Okanogan, Washington.

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Plan

Water is stored in Conconully Lake, a natural lake in which additional storage was developed by the construction of Salmon Lake Dam and a feeder canal diverting water from Salmon Creek, and in Conconully Reservoir, formed by the construction of Conconully Dam on Salmon Creek. Both reservoirs are near the town of Conconully, about 17 miles northwest of Okanogan. Water released from the reservoirs is conveyed through the channel of Salmon Creek for about 12 miles to the diversion dam and main canal heading. Two pumping plants provide a supplemental water supply during water-short years. Shell Rock Point Pumping Plant lifts water from the Okanogan River, and Duck Lake Pumping Plant lifts water from Duck Lake.

Facility Descriptions

Salmon Lake Dam

Salmon Lake Dam is an earthfill structure 54 feet high, and has a volume of 195,000 cubic yards. The total active reservoir capacity of Conconully Lake is 15,700 acre-feet (active 10,500 acre-feet). The spillway is a siphon type with a capacity of 400 cubic feet per second. The outlet works is a conduit controlled by two gates. A small diversion headwords structure on Salmon Creek diverts the flow into the reservoir through a short feeder canal.

In July 1998, a reservoir operating restriction to elevation 2314 feet was imposed on Conconully Lake as an interim risk reduction measure pending structural modifications to address seismic safety concerns. This reduces the active reservoir capacity to 7,400 acre-feet.

Concully Dam

Conconully Dam is a hydraulic earthfill structure that when completed in 1910, was 70 feet high, and contained 359,000 cubic yards of fill. In 1920, the dam was raised 2.5 feet. Total capacity of the reservoir is 13,000 acre-feet (active 13,000 acre-feet). During 1968-69, the crest of the dam was repaired with new embankment materials and riprap. The old open-chute concrete spillway that had an inadequate capacity of 6,000 cubic feet per second was replaced with a concrete-baffled apron spillway that has a capacity of 11,580 cubic feet per second.

Salmon Creek Diversion Dam

About 12 miles downstream from Conconully Dam is the concrete diversion weir, 6 feet high, and 140 feet across the crest, with a 300 cubic-foot-per-second overflow capacity. The dam diverts Salmon Creek releases to the Main Canal, which is 2 miles long and has a capacity of 100 cubic feet per second which conveys water to the High Line and Low Line Canals.

Shell Rock Point Pumping Plant

The Shell Rock Point Pumping Plant was built on the Okanogan River in 1977-1978 to replace two smaller pumping plants. The new plant has four pumps, each with a capacity of 8.3 cubic feet per second against a total head of 620 feet that discharge into the High Line Canal. Each drive motor is rated at 800 horsepower.

Operating Agencies

Operation and maintenance of the irrigation system was assumed by the Okanogan Irrigation District on December 31, 1928.

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Development

History

In 1886, the lands west of the Okanogan River were separated from the Colville Indian Reservation and thrown open to settlement. Settlers soon began to arrive and commenced irrigating forage crops for winter stock feed.

In 1897, because of the popularity of irrigation and the increasing demand for water from Salmon Creek, or Salmon River as it was shown on early maps, the Conconully Reservoir Company was organized to manage storage of some 1,500 acre-feet of water in Salmon Lake. By 1902, about 1,500 acres of land with water-right appropriations of 57 cubic feet per second from the Salmon River had been developed.

Investigations

In 1902, a preliminary investigation was undertaken by the Reclamation Service (now Bureau of Reclamation). The investigations were continued in 1903 and eventually the project was declared infeasible. In the first investigation, five reservoir sites were considered: the present Conconully and Salmon Lakes, the Scotch Coulee, and Green and Brown Lakes. In 1904, investigations of feasibility were again undertaken, and in December 1905 the project was declared feasible. Immediately following this declaration, the Okanogan Water Users Association was formed, representing some 10,000 acres. The name of the Association was later changed to Okanogan Irrigation District.

Authorization

The construction of the Okanogan Project was authorized by the Secretary of the Interior on December 2, 1905, under authority of the Reclamation Project Act of 1902. Shell Rock Point Pumping Plant was built under authority of the Emergency Drought Act of April 7, 1977, (91 Stat. 36, Public Law 95-18). The purpose of the project is irrigation.

Construction

Conconully Dam was built during 1907-1910, increased in height in 1920, and a new spillway completed in 1969; Salmon Lake Dam, 1919-1921; Salmon Creek Diversion Dam, 1906; North Fork Salmon Creek Diversion Dam, originally completed in 1920, but rebuilt in 1948; Main, High Line, and Low Line Canals, 1911-1917; Shell Rock Point Pumping Plant, 1977-1978.

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Benefits

Irrigation

Full development of the project depended on reliable irrigation facilities. Although apples always have been the principal crop, other fruits, hay, and forage crops also are grown.

Recreation

Both Conconully Reservoir and Conconully Lake are located in an area of steep-sided hills that have open forests of coniferous and deciduous trees. Conconully Reservoir is the smaller of the two reservoirs in the area; it has 5 miles of shoreline. Four roads provide good access. There are three campgrounds but the reservoir area is used predominantly by picnickers. The reservoir offers good fishing for trout and perch. Washington State Parks and Recreation Commission administers recreation at Conconully Reservoir.

Conconully Lake has 8 miles of shoreline and is served by one access road. There are two campgrounds on the lake, and two concessions provide lodging and rental boats. There is excellent trout fishing. Some of the upper reservoir area lies within the boundaries of the Okanogan National Forest which administers recreation for that portion. Recreation administration of the remaining reservoir area is by the Okanogan Irrigation District.

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Last updated: May 11, 2011