History

The combined generation capacity of all four units is 28.5 megawatts, with a combined flow of 8670 cubic feet per second. Minidoka Dam was originally designed and constructed without a powerplant and was completed in 1907. The powerplant (and three pumping plants) was added later (1909-1910) to allow water to be delivered to lands which could not be fed by gravity irrigation. The concrete buttress section of the dam forms the upstream structure of the original powerplant. The powerplant could only use a fraction of the water that passed through the dam, so Unit 6 was added in 1927 to allow commercial sales of power in excess of project needs. Unit 7 was added in 1942 to help feed the public`s growing thirst for electric power. In September 1995, the five original units were retired and Units 6 and 7 were rebuilt. Units 8 and 9 were added in 1997 at Minidoka Dam with the building of the Minidoka Replacement (now Allen E. Inman) Powerplant. The original powerplant building continues to house units 6 and 7.

The Secretary of the Department of the Interior authorized the Minidoka Project on April 23, 1904. The Upper Snake River storage was authorized by a finding of feasibility by the Secretary of the Interior and approved by the President on September 20, 1935.

Natural flow of the Snake River and some of its tributaries and water stored in the reservoirs at Jackson Lake, Grassy Lake, Island Park, American Falls, and Lake Walcott are delivered at numerous diversion points to irrigation districts, American Falls Reservoir District, and Warren Act contractors. Much of the power developed on the project is used for pumping water to lands lying above the gravity canals and for pumping drainage water.

Plan

Minidoka Powerplant was originally authorized and constructed to provide power for pumping water to high bench lands on the south side of the Snake River. Since that time, two generating units have been added and the energy in excess of project needs is marketed by the BPA. Water delivery to the high bench lands has enabled the transformation of 48,000 acres of high sagebrush desert into productive farmland. The economy of the local communities heavily depends on agriculture Minidoka Powerplant and Dam is a combined diversion, storage, and power structure located just south of Minidoka, Idaho. A key structure in the initial development of the project, the zoned earthfill dam is 86 feet high. The reservoir, Lake Walcott, has an active storage capacity of 95,200 acre-feet. During the irrigation season, water is diverted at the dam into a canal on each side of the river. The original powerplant was constructed upon the concrete buttress section of the dam, located at the right end of the rockfill section. The original generator Units 1-5 have been retired. Units 6 and 7 have been refurbished and continue to operate. At full head and flow Unit 6 provides 3 megawatts, and Unit 7 provides 5.5 megawatts of power. Construction was completed in 1997 at the Allen E. Inman Powerplant. Intended to replace the retired units (1-5) and utilize more of the excess flows previously spilled, this powerplant houses two 10-megawatt horizontal shaft Kaplan Units. The combined generation capacity of all four units is 28.5 megawatts, with a combined flow of 8670 cubic feet per second. Minidoka Dam was originally designed and constructed without a powerplant and was completed in 1907. The powerplant (and three pumping plants) was added later (1909-1910) to allow water to be delivered to lands which could not be fed by gravity irrigation. The concrete buttress section of the dam forms the upstream structure of the original powerplant. The powerplant could only use a fraction of the water that passed through the dam, so Unit 6 was added in 1927 to allow commercial sales of power in excess of project needs. Unit 7 was added in 1942 to help feed the public`s growing thirst for electric power. In September 1995, the five original units were retired and Units 6 and 7 were rebuilt. Units 8 and 9 were added in 1997 at Minidoka Dam with the building of the Minidoka Replacement (now Allen E. Inman) Powerplant. The original powerplant building continues to house units 6 and 7. Full automation and remote control was completed in 2000. Control is carried out from the Black Canyon Control Center near Emmett, Idaho. Long-term plans include installation of some automated gates to control spillway flows and repair or replacement of concrete spillway. The spillway at Minidoka Dam consists of a radial gate structure and 300 6-foot long stoplog bays which each contain 11 stoplog boards. The structure is one-half mile long. Long-term summertime spilling over the dam has created a blue ribbon trout fishery in the area below this spillway. Minimum flows are guaranteed to this area, even if power production must be curtailed to provide them. Because the Inman Powerplant encroached on 1.6 acres of existing wetland, a new controlled flow 5-acre wetland was developed as mitigation for this loss. Waste materials from excavation of the new powerhouse were used to build the core of the dikes for the wetland. Construction of the new complex was carefully conducted so as not to disturb the endangered Utah Valvata snails in the river below the site. The original Minidoka Powerplant is listed on the National Register of Historic places. Structural changes and maintenance must be conducted so as not to change the historic nature of the facility. Western Electricity Coordinating Council, Northwest Power Pool Area Bonneville Power Administration Conventional Above Ground, two powerplants at site Francis - Units 6 and 7, Kaplan Units 8 and 9. (Francis Propeller - Units 1 to 5 were retired in Sept. 1995.) 6,000 kW 27,700 kW 1909 98 years 112,594,220 kWh 2007 47 ft

General