Hydraulic Downpull on Ice Harbor Powerhouse Gate

Results of a hydraulic model study show the relative importance of certain geometric factors, initial discharge, and closure speed on the hydraulic downpull on a high-head leaf gate used for emergency closure of a powerhouse intake. When the initial discharge is large (design condition), the downpull on the top and bottom beams is the major part of the maximum downpull on the gate, and the shape of the gate bottom has a marked influence on the magnitude of the downpull. Proper design of the gate slot headwall minimizes the downpull on the top seal of the gate. Variation of the gate closure speed within the normal operation range of 7.6 fpm to 11.9 fpm has a negligible effect on the downpull, but the maximum downpull on the moving gate during closure is only 74% to 79% of that on the gate at fixed openings. The downpull data for the top and bottom beams (eight bottom shapes) and the discharge ratings (three initial discharges) are generalized for use in the design of similar gates.