An Experimental Study on Trench Weir With Flat Bars Under Free Flow Condition

Abstract

Trench weirs constructed across streams and rivers have been utilized for generations of hydropower due to their simplicity, cost-effectiveness, and minimal disruption to natural water courses. This type of weir consists of rack bars to control the deposition of sediments and floating debris. This article presents the investigations of the effects of different parameters, particularly the spacing of rack bars, specific energy of flow in the approach channel, velocity head, and porosity of rack bars on the discharging ability of trench weirs. Due to their greater flexural rigidity, flat bars are chosen in the current investigation from a structural perspective. The experiment was carried out in an open channel taking different combinations of bed slope, rack slope, and spacing of flat rack bars while testing under free flow conditions and having a pre-defined discharge in the approach channel. In addition, the discharge characteristics and coefficient of discharge (C_d) of the trench weir have been examined with varying clear spacing of rack bars, specific energy of approach flow, velocity head, and porosity of rack bars. The findings indicate that, in free flow conditions, C_d decreased as the porosity, clear spacing of rack bars, and specific energy of the approach flow increased. Further, during the analysis of experimental data, it was observed that C_d does not show any systematic pattern with velocity head. Thus, this study provides valuable insights on trench weir performance and the variables affecting discharge characteristics of trench weirs.