Model Study of Power Intake Gate of Mossyrock Dam

The action which catapulted one of the penstock service gates at Mossyrock Dam high in the gate shaft from where it fell, rebounded and inflicted severe damage to itself, its embedded steel beam sill and its operating mechanism, when it was used at a small opening to fill the penstock is described. Tests on a 1:26 scale model of the gate and penstock to ascertain how each of five separate forces contributed to the catapulting action and to develop corrective measures are analyzed. The model tests showed that the gate was catapulted up the shaft, perhaps as much as 50 ft., and that major alterations to the gate shaft base, not feasible for the Mossyrock installation, would be required to ensure against the action. Conditions that caused the model gate in early stages of the test program to stop at small openings while descending at slow speeds during simulated emergency closures are examined. Measures taken to assure model-prototype similarity and comparisons of model and prototype test data are presented.