Hydraulic Analysis of a Combined Rectangular Sharp-Crested Weir with a Below-Rectangular Gate

Irrigation systems often incorporate composite hydraulic structures, consisting of two key components: a weir, responsible for managing the overflow regime, and a gate, which regulates the underflow regime. Both components are crucial for flow control, measurement, and diversion, playing a vital role in governing the hydraulic behavior of open channels or rivers with precision and reliability. This study examined the flow dynamics through a combined rectangular sharp-crested weir with a below rectangular gate used as a control structure. The experiment tested three different weir sill breadths (Bn) of 3, 5, and 7 cm, and three gate breadths (Bg) of 3, 5, and 7 cm. These dimensions were used in various combinations, including scenarios where either the weir or the gate was absent (Bg = 0 or Bn = 0). The results revealed that the discharge through the combined weir and the below gate system was significantly influenced by the geometric characteristics of the weir and the below gate, i.e. Bg and Bn, and the hydraulic characteristics as their heads, hg and hn. Empirical equations were derived to calculate the combined structure coefficient of discharge (Cd) for the given experimental data. The findings and analyses are limited to the specific range of parameters tested in this study.