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Title: Spillway Modifications for Chief Joseph Dam, Columbia River, Washington : Hydraulic Model Investigation
Authors: United States. Army. Corps of Engineers. North Pacific Division. Hydraulic Laboratory.
Keywords: Hydraulic models
Stilling basins
Design and construction
Columbia River
Chief Joseph Dam (Wash.)
Publisher: United States. Army. Corps of Engineers. Seattle District.
Abstract: Spillway modifications were required in plans to increase power production by raising the level of the forebay pool and adding generating units. Pool was to be raised 10 ft initially and later an additional 14 ft. Effect of heads on the crest 1.33 to 1.70 times the design head was studied initially in a 1:42.47-scale model of Lower Granite spillway. Pressures on the spillway were satisfactory with gated flows but indicated cavitation with free flow. Surging occurred in the bays during gated flow. Preliminary studies indicated surging could be controlled by modifications. A modified Chief Joseph spillway with the existing crest, 36-ft-wide bays, and higher gates was studied with heads as high as 1.65 times the design head in a 1:43.35-scale, 4-bay sectional model. Pressures on the spillway and the stilling basin baffles were satisfactory with all free and gated flows. The existing stilling basin was adequate with the higher-head flows. Surging in the gated bays was controlled with vertical suppressors attached to the side of the piers. A flow deflector on the spillway just below tailwater was developed to divert the nappe of discharges as large as the 10-year flood along the surface of the tailwater in the stilling basin to reduce the amount of air forced into solution. Large quantities of dissolved air, often called nitrogen supersaturation, can be harmful to fish. Wave deflectors attached to the downstream edge of the piers of the end bays were developed to reduce spray created by the flow deflector. In a 1:72-scale comprehensive model of the project, flow conditions with the modified spillway without a flow deflector were satisfactory. The spillway also functioned satisfactorily with a flow deflector when the spill was regulated to avoid surging in the stilling basin. If surging was permitted, high long-period waves occurred along the powerhouse and on the south bank at Foster Creek. Existing riprap on the north bank of the tailrace was adequate with the high head flows.
Description: Technical Report
Rights: Approved for Public Release; Distribution is Unlimited
Size: 92 pages / 23.89 MB
Types of Materials: PDF/A
Appears in Collections:Technical Reports

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