Cowlitz Falls Sluice Gates: Modification and Testing of a Jammed Gate

The Cowlitz Falls Hydroelectric Project. located in southwestern Washington State on the Cowlitz River. has two 3.6 x4.8 m (12 ft wide by 16 ft high) low-level sluice gates that jammed when first placed into service in May 1994. These two upstreamsealing gates operating under 28 m (92 ft) of head were derailed by large, nearly periodic, hydrodynamic loading that occurs as the gates are being withdrawn from the conduit. Most surprisingly. the loading does not disappear even when the gates are fully raised within the gate well with the gate lip about 0.6 m (2 ft) above the conduit ceiling. A number of modifications were made to prevent excessive motion of the gates. including installation of a pressing system to keep the gate firmly against the downstream rails, installation of side guides to prevent sideways motion of the gate. and changes to the gate control logic to support the pressing system. Since the sluice gates are located in a spillway bay, tests had to be run with and without the spillway in service to demonstrate that the sluice gates could operate satisfactorily under all operating conditions. Results of the tests showed that the forces induced on the gate in the rough zone of operation were nearly periodic and persisted even with the gate fully raised. The periodic characteristic of the forces induced on the gate disappeared and the amplitude of the fluctuating forces decreased significantly if the spillway gate was operated simultaneously with the sluice gates fully open. The periodic characteristic of the forces induced on the gate appears to be caused by cavitation in the vortices shed from the shear-layer under the gate and gate slot coupled with the gate slot geometry. A discussion of the tests, the possible mechanisms for the periodic loading and an evaluation of the serviceability of the modified gate are presented in the paper. 1. Chief Hydraulic Engineer, Bechtel Corporation. San Francisco, CA 94119 2. Supervising Mechanical Engineer, Bechtel Civtl Corporation, San Francisco, Ca 94119