Hydraulics of Nappe Flow Regime above Stepped Chutes and Spillways

Stepped chutes have become a popular method for discharging flood waters. The steps increase significantly the rate of energy dissipation taking place on the spillway face and reduce the size of the required downstream dissipation basin. In this paper, the author reviews the characteristics of nappe flows on stepped chutes. An analogy with drop structures enables the estimation of all the flow parameters along the chute. Calculations of the rate of energy dissipation are developed. The limiting conditions for nappe flow are also detailed. The results indicates that nappe flow regime occurs for small discharges. Also the rate of energy dissipation along stepped channels with nappe flow regime increases with decreasing discharges.

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