Characterizations of flow over stepped spillways with steps having transverse slopes

Abstract

The top and downstream face of the embankment dams must be protected from overtopping damages happen due to extreme floods. This can be achieved by providing one of the overtopping protection systems. The most common overtopping protection systems are those which have stepped fashion. This type of protection systems consists of a series of continues steps mostly made of concrete. In this study, the effects of the transverse slope of steps on flow properties over the overtopping protection systems were explored experimentally. Steps with transverse slopes are those which have inclinations from one spillway wall towards the other spillway wall in a zigzag way. To achieve the goals of the study, three physical models, stepped spillways, were made of wood and tested in a prismatic flume. The width, depth, and length of the wooden models were 0.6 m, 0.96 m and 1.92 m respectively. Sixteen steps (with three different transverse slopes ranging from zero to 5.7°) were cut into the surface of the models from the crest to the toe. The models were then tested under various flow rates ranging from 0.003 to 0.05 m3/s. The results showed that the models with steps having transverse slope had higher energy dissipation capability compared to the model with steps having zero transverse slopes (flat steps); up to 14% higher. In addition, for the models with steps having the transverse slope, the onset of the skimming flow occurred at higher ratios of critical depth (yc) to step height (h); greater than 1.37. However, the distances of the inception points from the first step brink (inception point locations) were reduced by half, on average, for the model with steps having a transverse slope of 5.7°.