Discharging capacity of rectangular side weirs in straight open channels

A side weir is a hydraulic control structure used in irrigation and drainage systems and combined sewer systems. A comprehensive laboratory study, including 843 tests for the discharge coefficient of a sharp-crested rectangular side weir in a straight channel, was conducted in a large physical model under subcritical flow conditions. The discharge coefficient is a function of the upstream Froude number, the ratios of weir length to channel width, weir length to flow depth, and weir height to flow depth. An equation was developed considering all dimensional parameters for discharge coefficient of the sharp-crested rectangular side weir. The average error of the proposed equation is 4.54%. The present study data were compared with ten different discharge coefficient equations developed by several researchers. The study also presents water surface profile and surface velocity streamlines.

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► L/bL/b and L/h1L/h1 should not be ignored in equations determining the discharge coefficient of the side weir.
► The discharge coefficient increases with increasing dimensionless weir length.
► For L/b=0.3L/b=0.3 and 0.5, when the Froude number increases, CdCd values decrease. However, the variation of CdCd with F1F1 shows an increasing tendency when L/b=3L/b=3.
► An equation predicting the discharge coefficient of rectangular sharp-crested side weirs was developed.
► The proposed equation was shown to be reliable for the subcritical flow conditions.