[Federal Register: October 20, 1998 (Volume 63, Number 202)]
[Notices]               
[Page 56047]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr20oc98-116]

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DEPARTMENT OF THE INTERIOR

Bureau of Reclamation

 
Arrowrock Dam Outlet Works Rehabilitation, Boise, ID

AGENCY: Bureau of Reclamation, Interior.

ACTION: Notice of intent to prepare an environmental impact statement.

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SUMMARY: Pursuant to the National Environmental Policy Act (NEPA) of 
1969, as amended, the Bureau of Reclamation (Reclamation) intends to 
prepare an environmental impact statement (EIS) for the proposed 
rehabilitation of the outlet works at Arrowrock Dam on the Boise River 
near Boise, Idaho. The purpose of the proposed rehabilitation is to 
reduce the maintenance requirements of the existing outlet works, which 
are past their useful life, while meeting the operational needs of the 
dam for irrigation and flood control. The current proposal is to remove 
some of the existing outlet works and install 10 clamshell gates. This 
work will require operational changes during construction, including 
prolonged drawdown of Arrowrock Reservoir.

FOR FURTHER INFORMATION CONTACT:
Mr. Steve Dunn, telephone (208) 334-9844.

ADDRESSES: Bureau of Reclamation, Snake River Area Office, 214 Broadway 
Avenue, Boise, Idaho 83702.

SUPPLEMENTARY INFORMATION: Arrowrock Dam is located on the Boise River, 
about 13 miles east of Boise, Idaho. Reclamation completed construction 
of the dam in 1915, and at that time it was the highest dam in the 
world. The downstream face of the dam was resurfaced and the height was 
increased by 5 feet in 1937.
    Arrowrock Dam is one of three instream storage dams on the Boise 
River. Anderson Ranch Dam is located upstream of Arrowrock Dam on the 
South Fork Boise River, and Lucky Peak Dam, constructed by the U.S. 
Army Corps of Engineers, is located on the Boise River downstream of 
Arrowrock and impounds water up against Arrowrock Dam when full. 
Arrowrock Reservoir is operated for irrigation and flood control in 
combination with Anderson Ranch and Lucky Peak Reservoirs. In general, 
water is stored in Arrowrock Reservoir during the winter and spring 
according to predicted runoff and flood control requirements. Beginning 
in April water is released for irrigation from Arrowrock and Anderson 
Ranch Dams until early September when Lucky Peak Reservoir is drafted 
to meet irrigation demands. Lucky Peak water elevation is kept high 
through most of the summer for recreation.
    The ensign valves controlling releases from Arrowrock Dam are the 
original valves installed in 1915. These valves have reached the end of 
their useful life, resulting in complex operational and maintenance 
concerns. Most of the valves have been damaged through prolonged use, 
and there is an increasing need for frequent inspection and repair. 
Three of the 10 ensign valves in the lower bank are no longer usable.
    In order to ensure against malfunctioning valves, inspection and 
maintenance should be performed about every 5 years, which requires the 
reservoir level to be below the outlets. Under normal operations the 
upper row of ensign valves are out of the water by the end of summer 
and easily accessed. However, in order to dewater the lower bank of 
valves, the sluice gates must be used. There is some concern about use 
of the sluice gates since they too are over 80 years old and are in 
need of repair. If one of the sluice gates were to stick open, 
uncontrolled releases from Arrowrock would occur which could empty the 
reservoir.
    The existing ensign valves also limit Arrowrock Dam's operational 
flexibility. The lower bank of ensign valves cannot be used under high 
water pressure when the reservoir is full. This reduces the dam's 
capability to release water for flood control operations in years with 
high runoff.
    Reclamation has developed a proposal to replace the 10 lower ensign 
valves with ``clamshell gates.'' The clamshell gates would allow 
releases at any reservoir level, providing more operational 
flexibility. The remaining upper row of 10 ensign valves and the sluice 
gates could be abandoned which would significantly reduce maintenance. 
The clamshell gates would be designed to allow inspection and 
maintenance without dewatering.
    Reclamation has studied several other engineering alternatives to 
the proposal which involve different configurations of outlet control 
structures and rehabilitating the existing outlet works. Reclamation 
will also study operational alternatives to be implemented during the 
construction phase. Other alternatives to the proposal may be developed 
through the public scoping process. It is expected that the presence of 
threatened bull trout in Arrowrock Reservoir and the requirements of 
the Endangered Species Act may also influence the range of 
alternatives. All reasonable alternatives which meet the purpose and 
need for the project will be evaluated in the EIS.
    Federal, state and local agencies, tribes, and the general public 
are invited to participate in the EIS process. Scoping meetings to 
obtain input about concerns and issues associated with this proposal 
will be held but are not yet scheduled. Notification of meeting dates 
will be provided in a Federal Register notice, as well as through local 
media.
    Anyone interested in more information concerning the EIS or who has 
information that may be useful in identifying significant environmental 
issues, should contact Mr. Dunn at the telephone number or address 
indicated above.

    Dated: October 14, 1998.
Steven R. Clark,
Acting Regional Director, Pacific Northwest Region.
[FR Doc. 98-28031 Filed 10-19-98; 8:45 am]
BILLING CODE 4310-94-M