Wissota Hydro Plant Automatic Spillway Gate Studies Phase II

Northern States Power Company (NSP) is examining various alternatives to modify the automatic spillway gates at the Wissota Hydro Plant on the Chippewa River at Chippewa Falls, Wisconsin. The gates are called "stauwerke" gates. The main purpose of the study is to assure that the automatic spillway gates operate properly during a probable-maximum-flood (PMF) as required by the Federal Energy Regulatory Commission (FERC) and the Department of Natural Resources (DNR). The position of the gates must be controllable so that they can be fully lowered or raised with Lake Wissota at its normal elevation of 898.0 ft. The gates must go down for the design flood which currently is the PMF. The spillway has 13 automatic gates, each 64 feet, wide in the configuration shown in Fig. 1. NSP conducted field tests on Gate 1 at the south end of the spillway on April 15, 1988, in which the gate was pulled down to 7.2 ft. It was not possible to test the prototype gates from 7.2 ft down to the fully lowered position of 10.8 ft. During the tests, pulldown forces, piezometric pressures, and water surface profiles were measured. The results of the field tests down to 7.2 ft were correlated with a physical hydraulic model at the St. Anthony Falls Hydraulic Laboratory. These studies are summarized in a previous project report* by the Laboratory. As reported in these studies, good correlation was observed between the field tests and the model tests. The model studies were expanded to include gate positions down to 10.8 ft (the full-down position of the gate), and the results were extrapolated to the prototype. It was concluded from the calculated gate hinge moments that the gates would probably not remain in the full-down position at the higher discharges without additional force being applied.