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Ririe Project History (28 KB) (pdf)
General Description| Plan| Development| Benefits

General Description

The Ririe Project was constructed to impound and control the waters of Willow Creek, a Snake River tributary in eastern Idaho, for flood control, irrigation, and recreation. Significant fish and wildlife protection measures also are included. Major features include Ririe Dam and Lake, and Ririe Outlet Channel.

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Ririe Lake, formed by construction of Ririe Dam, serves a principal purpose of flood control on the lower reaches of Willow and Sand Creeks. Out of a total reservoir capacity of 100,500 acre-feet, 10,000 acre-feet is dead and inactive space, 80,500 acre-feet serves both flood control and irrigation, and the top 10,000 acre-feet is held exclusively for emergency flood control operations.

Ririe Dam

Ririe Dam is located on Willow Creek, a minor tributary of the Snake River, in Bonneville County of eastern Idaho. The dam is 15 miles northeast of the city of Idaho Falls and about 4 miles southeast of the town of Ririe. Constructed by the Corps of Engineers, the dam is an earth and rockfill structure, 253 feet high and 1,070 feet long. The reservoir impounded by the dam has a total capacity of 100,500 acre-feet (active 90,500 acre-feet).

Floodway or Outlet Channel

The floodway or outlet channel is a structure to control the water flow in Willow Creek below the dam, especially that section flowing through Idaho Falls and the area northeast of the city. Also controlled is Sand Creek as it flows east and southeast of Idaho Falls. Required releases of 1,900 cubic feet per second from Ririe Lake can be carried adequately in the natural channel to the point where the stream divides into Willow and Sand Creeks. The floodway bypass begins on Willow Creek just downstream from the point where Sand Creek branches from Willow Creek and extends directly west 7.8 miles to enter the larger natural channel of the Snake River 4.5 miles north of Idaho Falls. The bypass is gated at the Willow Creek intake to control initial inflow. The north bank of the channel was constructed at ground level to permit surface inflow of floodwaters along its course. Sand Creek can adequately carry 1,000 cubic feet per second and the floodway bypass channel was designed to carry 900 cubic feet per second, thereby providing the required additional capacity to control water flows.

Operating Agencies

The authorizing act through House Document No. 562 provided for the Bureau of Reclamation to operate and maintain the project. Formal transfer of the project from the Corps of Engineers to the Bureau of Reclamation was consummated by a memorandum of agreement effective October 14, 1976.

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Since 1911, at least eight spring floods and nine winter floods have caused considerable damage in the Willow Creek and Sand Creek floodplains. The largest known floods were those of 1917 and 1962. The 1917 flood was a spring snowmelt flood augmented by rainfall peaking at 4,200 cubic feet per second in Willow Creek near Ririe. Some 3,000 acres of land were inundated for 2 to 3 weeks. The 1962 flood was a winter rain flood augmented by frozen ground and snowmelt, peaking at 5,080 cubic feet per second in Willow Creek above its confluence with Sand Creek. About 54,000 acres were inundated for 2 to 3 days. Flows above 2,000 cubic feet per second that occur about 3.5 miles below the present damsite cause flooding conditions


The review report on `Columbia River and Tributaries,` dated June 1949, prepared by the Corps of Engineers and printed as House Document 531, 81st Congress, 2nd session, summarized field studies for storage and channel works on Willow Creek and indicated that flood control works were not economically feasible at that time. The Upper Snake River Basin report of 1961, prepared jointly by the Corps of Engineers and the Bureau of Reclamation, indicated that Ririe Dam and Reservoir warranted early construction. Interim Report No. 3, dated March 1962 and prepared by the Corps, presented additional information on structures and costs, economic analysis, and operating procedures. This report included a brief summary of the February 1962 flood, with comments on the control of such a flood by storage at the Ririe site.


Construction of Ririe Dam and Reservoir was authorized by the Flood Control Act of October 23, 1962 (76 Stat. 1193, Public Law 87-874). House Document No. 562 served as the basis for that authorization. Project purposes are irrigation, flood control, and recreation.


Project construction was performed under the jurisdiction of the Corps of Engineers. Construction of the dam began in January 1970 and was completed in November 1977. Floodway channel work began in June 1975, and was completed in February 1978. Recreation area work was started in May 1977, and was completed in June 1979.

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In 1994, the United States entered into a contract with Mitigation, Inc., which provided that entity with noncontracted irrigation storage and space in Palisades (18,980 acre-feet) and Ririe (80,500 acre-feet) Reservoirs in order to protect existing non-Indian water users from adverse effects that might result from implementation of the 1990 Fort Hall Indian Water Rights Agreement and Fort Hall Indian Water Rights Act of 1990.


Four recreation areas have been developed to meet projected initial demands. Juniper Park, adjacent to the project headquarters visitor center, is the major recreation site. Both overnight camping and day-use facilities are available, including a floating fishing dock and a boat-launching ramp. Blacktail Park, on the lake, includes a swimming area and other day-use facilities. Benchland Park is also on the lake, but is accessible only by boat and has limited day-use facilities. Ririe Lake is stocked annually with rainbow trout and the minimum reservoir pool provides winter habitat for fish survival and growth. A minimum flow of 25 cubic feet per second is maintained downstream in Willow Creek to provide stream fishing habitat. Deer and elk use the area as winter range, so a large area around the south half of Ririe Lake is developed as rangeland for support of these animals during the critical winter months.

The loss of wildlife habitat associated with the construction of Ririe Dam and Teton Dam led to the establishment of the Tex Creek Wildlife Management Area. In 1976 and 1977, the U.S. Army Corps of Engineers and the Bureau of Reclamation purchased 11,000 acres of critical big game winter range in the Tex Creek area just east of Idaho Falls, Idaho. The Idaho Department of Fish and Game eventually assumed additional critical acres. Also, a cooperative agreement with the Bureau of Land Management resulted in the inclusion of 9,600 acres of land, and today, the Tex Creek Wildlife Management Area encompasses more than 28,700 acres. The entire area is managed for wildlife, with emphasis on big game.

Flood Control

Coordinated operation of Ririe Dam and the floodway bypass channel will control the flows in Willow and Sand Creeks to help alleviate flood damages such as those previously experienced in the city of Idaho Falls and on surrounding farmlands. The devastating floods of 1917 and 1962 were created by flows more than double the 2,000-cubic-foot-per-second capacity of Willow Creek. With the present control structures, Willow Creek can be contained at 1,900 cubic feet per second.

Endangered Species Act

In March 2005 the Fish and Wildlife Service (FWS) and National Marine Fisheries Service (NMFS) provided Biological Opinions on Reclamation's Operations and Maintenance of 12 projects and associated facilities in the Snake River Basin above Lower Brownlee Reservoir. If conditions don't change these Opinions should be valid for 30 years.

The FWS determined that Reclamation's proposed actions were not likely to jeopardize the continued existence of ESA listed species in the Snake River basin. The Opinion includes an Incidental Take Statement with Reasonable and Prudent Measures and associated Terms and Conditions to minimize incidental take for bull trout and Utah valvata. The FWS's Opinion contains its conclusions for each species in Chapters 4 through 9, respectively. Reclamation provided a Decision Document in Novemeber of 2005 as well as a Monitoring and Implementation Plan in March of 2006.

NMFS concluded that Reclamation's proposed actions were not likely to jeopardize the continued existence of the 13 salmon and steelhead evolutionarily significant units (ESUs) or adversely modify or destroy critical habitat that is designated for 3 fo the ESUs. A summary of its conclusions is contained in Section 8 of the Biological Opinion. The Opinion includes an Incidental Take Statement with Reasonable and Prudent Measures and associated Terms and Conditions to minimize incidental take.

For more information on the fish and wildlife program, please go to:  http://www.usbr.gov/pn/programs/fish_wild/index.html   

For more information on the Biological Assessment or Biological Opinions, please go to:

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Last updated: Jul 26, 2012