Hydraulic Model Investigation. Libby Dam, Kootenai River, Montana. Hydraulic Model Investigations

摘要

Libby Dam, located on the Kootenai River 17 miles upstream from the town of Libby, Montana, rises about 422 feet above bedrock and includes a spillway with two 48-foot-wide bays, three 10- by 17-foot regulating sluices, and a powerhouse for eight 105-megawatt generators. At maximum pool, spillway capacity will be 145,000 cfs and regulating sluice capacity will be 61,000 cfs. The 116- by 300-foot stilling basin is designed for a maximum spillway flow of 50,00 cfs. Two separate 1:50-scale models were used to study the spillway, regulating sluices, stilling basin, outlet channel, diversion, and proposals to reduce nitrogen levels downstream from the project. Alternative designs for bellmouthed intakes of the regulating slucies were studied in a 1:20-scale model. The model tests showed that the original spillway abutments, center pier, sluice intakes, spillway chute, and stilling basin should be revised. Satisfactory designs for these elements were developed. Deflectors, flip buckets, and combinations of the two failed to produce flow conditions that would reduce nitrogen levels downstream from the stilling basin for the expected range of sluice discharges during the first years of project operation. Sizes of rock needed to protect the banks and runout area below the stilling basin, discharge required to clean the basin of debris, bank outlines for an excavated exit channel, diversion procedures to use during second and third construction stages, and debris deflectors for legs of a temporary trestle were determined. (Author)