Discharge characteristics of chimney weir under free-flow conditions

The assumption of a constant coefficient of discharge in the linear head-discharge relationship of a chimney weir is reinvestigated. Based on dimensional analysis and subsequent experiments conducted with three different chimney weirs at various crest heights and channel widths, it is found that the coefficient of discharge in the linear relationship is not a constant, but is found to vary with the ratio of head to altitude, h/d; half-vertex angle in the form of w/d, w being the half crest width; h/(h+P), P being the crest height; and the channel width contraction ratio, w/C, C being the channel width. A linear regression equation correlating the coefficient of discharge with the above variables is proposed that, along with the linear head-discharge relationship, provides an accurate prediction of free-flow discharge. CE Database keywords: Free flow; Weirs; Discharge coefficients.