Sensitivity analysis of longitudinal debris accumulation length on the hydraulic performance of trash screens in open channels

Trash screens are essential components in open channels for debris capture and the protection of downstream hydraulic structures. However, debris accumulation can significantly alter flow conditions and reduce conveyance efficiency. While previous research has primarily quantified blockage based on the cross-sectional area, the longitudinal length of accumulation a common real-world phenomenon has received limited attention and has not been investigated independently. This study investigates the impact of debris accumulation length upstream of trash screens on water surface profiles and downstream velocity distributions through a controlled sensitivity analysis, in which the blockage area was maintained constant while only the accumulation length was varied. A total of 75 laboratory experiments were conducted in a trapezoidal flume under subcritical flow conditions (Fr o = 0.065–0.115). Four accumulation lengths (19%, 38%, 64%, and 77% of the water top width) were tested while maintaining a constant blockage area. Water surface profiles were measured upstream and downstream of the screen, and vertical velocity profiles were recorded just downstream. The results demonstrate that increased accumulation length leads to a substantial rise in upstream water levels; specifically, the afflux increased by up to six times as the length progressed from 19 to 77%. Furthermore, longer accumulation lengths significantly reduced hydraulic efficiency and attenuated the downstream jet velocity due to increased upstream energy dissipation. Finally, empirical equations were developed using dimensional analysis and nonlinear regression to predict upstream heading-up and downstream velocity using only two readily measurable variables (Tacc% and Fr o ). The findings suggest that debris accumulation length should be considered a key factor in the design, operation, and maintenance of trash screens in open channels.