Spillway for Little Goose Dam, Snake River, Washington, Hydraulic Model Investigation.

The spillway for Little Goose Dam, designed to pass discharges up to 850,000 cfs (2125 cfs per ft of crest), was studied in a 1:42.47-scale, 3-bay, sectional model and a 1:100-scale general model to investigate the performance of various elements of the structure and to determine flow conditions in the tailrace. Maximum velocities that fluctuated between 5 and 12 fps along the north embankment upstream from the spillway were indicated by the spillway model. Tests indicated that the stilling basin of original design was not satisfactory. An acceptable stilling basin was developed in the model, but unusual artesian flow at the site would have required a costly drainage system to protect the basin slab against uplift. Sixteen roller bucket plans were investigated in efforts to eliminate the basin slab and drainage system. A modified Angostura-type bucket, with simpler teeth and shorter apron, was adopted.