The investigation, under BuRec's Safety of Dams program, is beginning in late August and is to continue into November at Yellotail, part of the government's Pick-Sloan Missouri Basin project.
The examination involves drilling from the crest of the dam in the vicinity of the left abutment. No change in reservoir operations is anticipated, the agency said.
Comprising 1.5 million cubic yards of concrete, the thin-arch dam is 525 feet tall, with a crest length of 1,480 feet. Four 12-foot-diameter penstocks supply four 87,500-horsepower Francis turbines with 62.5-MW generators in a dam toe powerhouse.
Yellowtail was completed in 1966 on the Bighorn River about 45 miles west of Hardin, in south-central Montana. BuRec operates and maintains the multi-purpose dam for irrigation water, flood control, and power generation. (HNN 3/15/06)