The impact of blockage on the performance of canal coverage structures

Abstract

Despite the benefits of canal coverage structures, they may turn out to be a significant reason of decreasing canals conveyance efficiency if they are subject to blockage. The difficulty of removing wastes from closed canals further exaggerates the problem. This study investigates the effects of blockage in canal coverage structures, focusing on various cross-sectional shapes and blockage ratios. Seven coverage cross-section shapes, namely the square box, pipe, pipe arch, ellipse, arch, conspan arch, and rectangular box, were studied in combination with 10 different Froude numbers and 10 different blockage ratios. An experimental setup was used in the study along with the HEC-RAS 1D numerical model, which was evaluated through a series of comparative tests.The study demonstrated that blockage in a canal coverage structure and its extent significantly impairs the structure’s hydraulic performance, leading to an increased head loss ratio and a reduced velocity ratio. The extent of this reduction varied with different coverage shapes, and the sensitivity to blockage was found to be the highest in the square box section, followed by the pipe section at the same design Froude number.A crucial threshold was identified at a blockage ratio of 30% where the performance of coverage structures started to decline sharply, indicating a key maintenance point. Among the shapes studied, the pipe arch had the best performance in terms of head loss reduction, while a rectangular box with a height to width ratio of 2:3 was found to be a close second. Considering the construction complexities associated with the pipe arch, the rectangular box is recommended as the most practical and efficient option for canal coverage structure design. The findings from this study provide valuable insights for engineers and decision-makers involved in canal management and infrastructure planning.