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Arrowrock Dam Outlet Works Rehabilitation, INT-FES 01-12

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Bureau of Reclamation, Interior.


Notice of Availability of Final Environmental Impact Statement.


Pursuant to section 102(2)(C) of the National Environmental Policy Act of 1969, as amended, the Department of the Interior, Bureau of Reclamation (Reclamation) has prepared a final environmental impact statement (Final EIS) to examine the impacts of alternatives to rehabilitate the outlet works at Arrowrock Dam. The Bureau of Reclamation proposes to remove 10 lower level Ensign valves and replace them with clamshell gates. Two action alternatives were identified that differed only in the timing of reservoir drawdown, and the elevation of Arrowrock Reservoir and Lucky Peak Lake in the third construction season. The preferred alternative requires a Start Printed Page 14933longer period of drawdown of Arrowrock Reservoir, but both Arrowrock Reservoir and Lucky Peak Lake would remain at a higher elevation than with the other action alternative. Based upon comments received on the Draft EIS concerning impacts to water quality and bull trout, the preferred alternative was modified so that the probability of use of the sluice gates was reduced to approximately 15%. The No Action Alternative is also evaluated. The No Action Alternative is defined as the most likely future without the proposed project, and includes actions that would be required for an intensive maintenance program if the Ensign valves were not replaced.


Comments may be addressed to Mr. John Tiedeman, Bureau of Reclamation, 1150 N. Curtis Road, Suite 100, Boise ID 83706-1234.

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Mr. John Tiedeman, (208) 378-5034.

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Arrowrock Dam and Reservoir, completed in 1915, were constructed by the Bureau of Reclamation (Reclamation). The dam is located on the main stem Boise River about 17 river miles upstream from the city of Boise. Anderson Ranch Dam and Reservoir, located on the South Fork Boise River and generally east of Arrowrock Dam, were completed by Reclamation in 1950. Lucky Peak Dam and Lake, located to the southwest and about 11 river miles downstream of Arrowrock Dam, were completed by the U.S. Army Corps of Engineers (Corps) in 1957. Reclamation and the Corps operate the three storage dams in a coordinated method for irrigation water supply (Reclamation markets the water supply in Lucky Peak Lake for irrigation), flood control, recreation, and fish and wildlife.

Reclamation began considering modification of Arrowrock Dam outlet works in 1982; some conceptual designs for replacement of some of the Ensign valves were developed in 1983. Over several years, various possible designs were identified and evaluated, and in 1987 a conceptual design using clamshell gates was developed. Increasing maintenance problems resulted in the current effort to identify and evaluate solutions to the maintenance problems associated with the now 85-year old Ensign valves. The scope of this study was limited to valve replacement to retain and improve operational flexibility of Arrowrock Dam and Reservoir. Environmental effects of the action and No Action alternatives were analyzed for the stream reaches and reservoirs upstream and downstream from Arrowrock Dam and Reservoir. Potential environmental effects are generally limited to those associated with construction and the reservoir drawdowns necessary for maintenance and replacement of the lower outlets. One of the major concerns is about impacts to bull trout which are found in Arrowrock Reservoir and upstream; bull trout were listed as a threatened species in June, 1998.

Reclamation's scoping process included numerous meetings with state and Federal agencies, local groups, and interested individuals. Notices of intent to prepare an EIS and to hold public scoping meetings were published and two public scoping meetings were held on November 20, 1998. Public comments received during scoping were considered in the development of alternatives. Following release of the Draft EIS, two Public Hearings were held on December 12, 2000. Based upon comments received concerning water quality and impacts to bull trout during the Draft EIS review period, the preferred alternative was modified by reducing the probability of use of the sluice gates to15%.

The Final EIS is available for viewing on the internet at:​project/​arrowrock/​arrowrock.shtml

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Dated: March 9, 2001.

Kenneth R Pedde,

ActingRegional Director, Pacific Northwest Region.

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[FR Doc. 01-6308 Filed 3-13-01; 8:45 am]