Exploring Proper Spacing Threshold of Non-Submerged Spur Dikes with Ipsilateral Layout

Zhenghua Gu,Xiaomeng Cao,Qiaoya Gu,Wei-Zhen Lu

doi:10.3390/w12010172

Abstract

Concerning the clustering of spur dikes on river systems, the spacing thresholds of twin spur dikes are important parameters to influence the estimations on the impact scales of spur dike groups and the overall responses of river systems. In this study, both numerical investigations and experimental measurements are proceeded to quantify the influence of the spacing threshold of non-submerged twin spur dikes with ipsilateral and orthogonal layout in a straight rectangular channel. Through dimensional analysis, three normalized indices, i.e., Froude number Fr, ratios of channel width to dike length B/b, and ratios of channel width to water depth B/h are identified as the main influencing factors of the relative spacing threshold Sc/b, i.e., dike spacing threshold to dike length. The simulation results indicate that the similarity of mean velocity along the water depth nearby the tips of twin spur dikes is determined by the criterion of the spacing threshold of non-submerged twin spur dikes with ipsilateral and orthogonal layout in straight rectangular channel. The results also show that: Fr plays the least impact among the three influencing factors; with the fixed values of Fr and B/h, the relative threshold Sc/b sharply increases first and then decreases slightly as B/b factor increases, with which the relationship presents approximately convex quadratic function; while both Fr and B/b are fixing, the Sc/b changes oppositely, i.e., slightly increasing first and then sharply decreasing as B/h increases, which, again presents a convex quadratic function. Hence, the normalized empirical formula of spacing threshold can be deduced by multivariate regressions and verified by the corresponding measurements in good agreements. Such empirical formula further suggests that the reasonable spacing threshold ranges from 24b to 130b, which is wider than the recovery area scales found in literature. The outputs of this study provide foundation for the characterization of impact scales of spur dike groups.

Highlights

Rivers relate to human being’s living and development significantly and, are depicted as the cradle of human civilization
Unlike previous on reasonable spacing, which to improve the training quantitatively analyze the researches spacing threshold of non-submerged twinaimed spur dikes with ipsilateral and effects of small-scale spur dike group on the local segment of river researches system [8,24,25], this study aims orthogonal layout in straight rectangular channel
In order to classify “impact scale of spur dikes”, we proposed the concept of spacing threshold of non-submerged twin spur dikes with equal skew angle and ipsilateral layout in straight prism channel before [2], that is, the minimum spacing for maintaining the similarity of lateral distributions of magnitude velocity V at the cross-sections of twin spur dikes

Summary

Introduction

Rivers relate to human being’s living and development significantly and, are depicted as the cradle of human civilization. Water 2020, 12, 172; doi:10.3390/w12010172 www.mdpi.com/journal/water main flow, bank and acquiring land resource [7,8,9,10,11,12]. Spite of different water depth,protecting changing river the direction of bed, mainand flow, protecting river bank and bed, In and acquiring land types [8,13], the spur dikes present simple structure and multiple functions, which can be regarded as resource [7,8,9,10,11,12]. In spite of different types [8,13], the spur dikes present simple structure and the simplification ofwhich many river works [12,14]

Objectives

Methods

Conclusion