Artificial aeration of stepped spillways by crest piers and flares for the mitigation of cavitation damage

Abstract

Stepped spillways are one of the oldest spillway designs dating back to 500 B.C. With technical advances in Roller Compacted Concrete (RCC) construction, the stepped spillway has become increasingly popular over recent decades. However, the use of this spillway is limited to a maximum safe unit discharge of 25 m2/s due to the risk of cavitation. In order to increase the discharge capacity on stepped spillways, various crest pier designs were introduced for flow aeration, thereby reducing the risk of cavitation damage. These pier designs were investigated on two physical models, constructed on a scale of 1:15 and 1:50, both with a standard ogee crest profile which transit to a stepped spillway chute. Air concentration was recorded along the pseudo-bottom, while pressures were measured at the step riser. The results of the 1:15 scale model indicated that the implementation of a short bullnose pier increased the safe unit discharge capacity to 30 rm/s. The innovative Flaring Gate Pier design, which was adapted on existing spillways in China, with reported design prototype unit discharges exceeding 200 m2/s, was investigated on the 1:50 scale model. Based on the experimental results of the current study, the safe unit discharge capacity (i.e. a discharge satisfying the relevant criteria defined for this study) was increased to 50 m2/s with an X-shape Flare Gate Pier (FGP) on the spillway crest.