Investigation of the effect of upstream crest lenght variation and piles usage on main channel on discharge capacity at the labyrinth side weirs

Weirs are hydraulic structures oldest and simplest in terms of usage for centuries used for measuring of discharge and flood control. It has been observed in the literature that there is no discharging in part of the upstream crest length of the side weirs for the high Froude numbers. This causes a decrease in discharge capacity. Thus, the main purpose of this study is to investigation in detail the effect of the upstream crest length variation on the discharge capacity and development of methods for improving the hydraulic performance at the sharp-crested labyrinth side weirs. Experiments have been carried out for triangular labyrinth side weir sections with apex angles of 45°, 90° and 150° for the crest heights of 12, 16, 20 cm with 25, 50 and 75 cm weir opening lengths in straight channel and with bend angle 30° in curved channel. For each crest height, the weir crest length was closed in three steps and readings were taken. However, a series of experiments have been carried out using rectangular and circular piers at the trapezoidal labyrinth sideweir main section for p=16 cm, =16° and L=50 cm. The experiments were made for a discharge of 7-145 L/s and a Froude number of 0.07-0.93. Experiments have been carried out for subcritical flow regime, steady flow and free overflow conditions. The readings for the minimum nap thickness 30 mm were obtained, Froude number and discharge coefficient were calculated and the required graphs were drawn. In this study, De Marchi method is used. As a result of the experimental study, it has been found that the discharge coefficient decreases with decreasing the upstream crest length of the triangular labyrinth side weir in straight channel and with bend angle 30° in curved channel. Also, it has been observed that the discharge coefficient is increased in the tests performed as a result of different arrangements of the piers placed in the trapezoidal labyrinth side weir in the straight channel. Parallel to the differences in the methods applied in the literature review, the labyrinth side weirs in the study, will contribute greatly in terms of the theoretical and empirical basis. Keywords: Straight and Curved Channel, Discharge Coefficient, Labyrinth Side Weir.