Selective Withdrawal System, Libby Dam, Kootenai River, Montana. Hydraulic Model Investigation.
ARMY ENGINEER DIV NORTH PACIFIC BONNEVILLE OREG DIV HYDRAULIC LAB
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Three hydraulic models were used to study elements of the multibulkhead selective withdrawal structure. Overall flow conditions and the effects of withdrawal from a stratified reservoir were investigated in a 150-scale model. Flow conditions were studied in greater detail and modifications were developed in a 120-scale model of one penstock intake and 1.5 bays of the adjacent withdrawal structure. A 15-scale model was used to measure opening torque and discharge at a typical 3- by 6-ft bulkhead pressure relief panel. The initial withdrawal structure was not satisfactory for the design maximum discharge of 5,800 cfs per unit and desired minimum bulkhead submergence of 10 ft. The maximum discharge for good flow conditions with 10-ft submergence was about 1,000 cfs. Vortices formed inside the structure when the pool was above elev 2435 24 ft below normal full pool. In the final design, the pier nose profile above elev 2390 and the bulkhead storage area were revised, and slots for 4-ft-high floating skimmers were placed at upstream edges of the bulkhead slots. The skimmers improved flow conditions in intermediate bays and were required to prevent vortex formation in end bays of each intake. Maximum head losses were 0.8 ft across a skimmer, 1.1 ft across a skimmer and trashrack, and 3.9 ft through the withdrawal structure. Densities, simulated temperatures, velocities, and interface profiles for an unstratified reservoir and for five conditions of stratification were studied. Torque and discharge data for a typical pressure relief panel were measured for panel openings of 20 to 90 degrees and head differentials of 0.20 to 15.23 ft. The panel opened to the 90-degree position under a differential head of 1.42 ft. Author
- Civil Engineering