Publication: A study on the effect of spur dike Design on sandbar retention ratio in Open channel.
No Thumbnail Available
Date
2025-05
Authors
Li, Baihao
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
In urban settings, large concrete drainage channels often experience water stagnation and waste accumulation during dry seasons. As a nature-based solution, the spur dike and the sandbar offer multiple ecological and hydraulic benefits. By locally narrowing the channel width, the spur dike increases water depth and flow velocity, thereby reducing stagnant water. Additionally, the sandbar contributes to water quality improvement and provides habitats for plants, animals, and microorganisms, promoting ecological restoration. A low-profile spur dike can effectively trap sediment to form a sandbar while also preventing its erosion, without impeding flow during high-discharge events.This study integrates scaled physical modeling with numerical simulations to validate the scouring processes of sandbars between spur dikes in non-movable bed condition. The non-movable bed simulates the conditions of a concrete-lined drainage channel. The results confirm that the numerical approach accurately replicates the erosion and deposition dynamics. Based on this validation, the study further investigates the influence of five key aspects: spur dike length, interval, angle, shape, and arrangement, on the sandbar retention ratio. Previous literature has examined the effects of spur dike shape and angle on the riverbed in the context of mobile bed conditions. In contrast, this study shows that under subcritical flow conditions with unsubmerged spur dikes on a non-movable bed, the T-shaped spur dike and the one oriented perpendicular or slightly inclined upstream to the flow provide the most effective sandbar protection. This is similar to the findings in previous literature. Regarding the other aspects that have been less studied, the findings indicate that a longer spur dike, a wider interval, and a depression arrangement all contribute to higher sandbar retention ratio. It is important to note that while a longer spur dike may increase scouring in movable beds, it enhances sandbar protection in non movable condition. However, excessive length may lead to raised upstream water levels and should be addressed carefully in practical applications.In conclusion, under subcritical flow and non-submerged, non-mobile bed conditions, a sandbar with a larger initial volume, an upstream-facing spur dike that diffuses incoming flow, and the presence of a low-velocity buffer zone (such as in the case of the depression arrangement), are all beneficial for sandbar preservation. The design of the spur dike should be adapted to site-specific conditions to fully utilize the ecological and hydraulic functions of sandbars in environmental restoration.