Linear Proportional Weirs

The profile equation of the weir with a parabolic bottom is analytically obtained for the condition of the discharge varying linearly with the head. The conditions of the discharge and slope continuities across the profile furnish the result in the form of an integral equation of the Abel type. The solution is obtained in a simple form. Experiments are conducted on a weir plate, with the profile of a proportional weir with a parabolic bottom cut out of a 1/4-in. plate and fixed at the end of a rectangular channel 5.2 m long, 40 cm wide, and 62 cm deep. The experimental results confirm the linearity existing between the discharge and the head, which is measured above an analytically fixed datum line. For the benefit of the designer, a table giving coordinates of the profile in a convenient nondimensional form is also included. The variation of the coefficient of discharge and its recommended value in this case are described in the paper.