ِِdischarge coefficient in oblique side weirs

side weirs are flow diversion devices that are widely used in irrigation, drainage and urban sewage systems. the present study focuses on the investigation of the effect of oblique side weirs on the discharge coefficient of a side weir under subcritical flow condition in rectangular channels. in this study 106 laboratory tests were conducted and the results were analyzed to find out the influence of non-dimensional parameters on the discharge coefficient of the weirs. the angles of side weirs varied from 0 to 17.5 degrees in six steps, three heights (5, 10 and 15 centimeters) and three lengths (100, 80 and 40 centimeters). two descriptions of the discharge coefficient (traditional side weir coefficients, cd, and de-marchi, cm), along with different discharges and related parameters were used. according to the results, cd is more sensitive to b1/b2 (ratio of channel bottom widths), whereby cm is sensitive to l/b1 (ratio of side weir length to bottom width). the correction formula for estimating the oblique side weir discharge coefficient with a traditional shape shows that a 17.5 degree angle with side wall causes 40 percent change in the discharge coefficient.