Some Design Aspects of a Divided Gate Tower

The procedures adopted for the design of the power plant intakes for the Portage Mountain Development are described. Considerations leading to the selection of the type of intakes are listed. Three of the ten intakes planned are to be 250 ft below full supply level and for these intakes there is sufficient distance between the intake tunnels and the gate towers to cause the towers to act as surge chambers. Prediction of the surge behavior is complicated by the partition of the towers into two independent shafts and the fact that the inertial forces in the towers are greater than in the intake conduit for high reservoir levels. As the intake gates seal on the upstream side, the orifice at the base of the gate tower has to be large enough so that for emergency closure of the operating gate the tower can drain without vapor pressure occurring downstream from the gate. An existing model of one of the seven high-level intakes was modified to represent the low-level structures and tests were conducted to study the surge behavior following wicket or operating gate operation. Surges were measured by means of a buoyancy gage which records changes in the buoyant force on a partially submerged cylinder. Comparison of theoretical and model predicted surge behavior shows good agreement.