Experimental Investigation of Nappe Flow Domain on Stepped Spillways

Document Type : Research Article


1 Research Expert / water research ins Institute

2 Hydro-Environment Department, Water Research Institute

3 Faculty of Civil Engineering, K. N. Toosi University of Technology


Stepped spillways are used to discharge the floods flow entering the reservoirs. Along these spillways, the energy is highly dissipated. It consists of a series of arranged steps along the spillway to ensure a uniform flow depth and velocity. Stepped spillways improve the rate of longitudinal energy dissipation on the spillway. The energy dissipation affects the flow characteristics and the energy dissipaters at downstream. The flow over stepped spillways is divided into three regimes of nappe, transition and skimming flows. So far, limited numbers of studies have been performed on the basis of analytical and empirical information to check the features and complicated nature of nappe flows. Limitations on physical model studies are also important to mention. As a result, few relationships have been suggested to describe nappe flow characteristics over stepped spillways. In this study, a set of experiments were performed on three large-scales hydraulic spillway models of Siahbisheh upper and lower dams and Zhaveh spillway dam. The data cover six spillway slopes and 24 flow rates. Measurements of depth, velocity, and static pressure were made at 40 different cross sections along the chutes. Major effective geometrical and hydraulic parameters on energy dissipation in nappe flow regime over stepped spillways were analyzed, based on present measurements. A relationship was then suggested to calculate the rate of energy dissipation in nappe flow regime. This study showed that the ratio of critical depth to height of spillway is the most important dimensionless parameter in predicting energy dissipation, the increase of which reduces the relative energy dissipation in the nappe flow regime.


Main Subjects

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