Experience with Prototype Energy Dissipators

A large number of replies from 200 questionnaires, distributed to obtain all the information possible on experience with prototype stilling devices at dams, indicated that no damage or unsatisfactory experience had been encountered. For one project, Tenkiller Ferry Dam in Oklahoma, a gated saddle spillway is located on a narrow sandstone ridge at the right side of the valley. The small ogee crest is followed by a flat concrete chute approximately 108 ft long. After construction in 1952, joints and bedding planes in the excavated sandstone exit channel opened because of seasonal temperature changes and the freezing and thawing process. During the 1957 flood, approximately 10,000 cfs were released for 6 days. The water supplied force and lubrication to separate some of the blocks of sandstone, 45 ft to 65 ft high, in the massive rock toward the base of the ridge. These blocks slid on the bottom of a horizontal shale seam 6 in. thick. Remedial action was to extend the concrete chute down the slope in 1960-1961.