Discharge Coefficient of a Spillway with a Riser Perforated by Rectangular Orifices

Perforated riser principal spillways are widely used in check dams, and rectangular orifices are the preferred orifice geometry for risers constructed of brick. However, there is little research based on risers perforated with rectangular orifices. This paper discusses the discharge coefficient of such a structure, based on the experimental data and data collected from literature, during which an estimation of the discharge equations for a riser perforated with circular orifices was made. First, an existing equation for a riser with circular orifices is selected based on the coefficient of determination (R2) index and the Nash-Sutcliffe efficiency (NSE) index. Then, an equation for the discharge coefficient of a riser perforated with rectangular orifices is proposed (R2=0.95, NSE=0.91) considering the factors of the diameter of the riser pipe, the width of the rectangular orifice, and the head over the centerline of the orifice. This work is expected to provide a reference for the design and investigation of a perforated riser principal spillway.