Evaluating Manning's Roughness Coefficient for Flows with Equilibrium and Non-equilibrium Sediment Transport

IF 1 Q4 ENGINEERING, CIVIL
Miskar Maini
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Abstract

One of the challenges in using Manning’s equation lies in accurately determining Manning’s roughness coefficient, especially due to sediment transport. The condition of sediment transport within a specific section of a river can be in equilibrium, meaning that the amount of sediment entering and exiting the segment is balanced or it can be in non-equilibrium, where there is an imbalance between the sediment entering and leaving the segment. Experiments were carried out in the laboratory to simulate both transport conditions, one involving sediment feeding (equilibrium condition) and the other without sediment feeding (non-equilibrium condition). A total of 180 mean velocity profiles were measured using an acoustic doppler velocimeter (ADV) in fixed and movable bed flows. The present experiment was combined with theoretical approaches to evaluate Manning’s coefficient in open channels under sediment transport-flow conditions and reach conclusive results. The shape of the velocity profile, u/U, for flows over a movable bed with sediment feeding is “slender” compared to those without sediment feeding. The presence of sediment transport affects the shape of the velocity profile, especially in the inner region, influencing Manning's roughness coefficient. This coefficient can be determined from two-point velocity measurements at z/H = 0.1 and 0.2 for fixed and movable bed flows with and without sediment feeding, respectively. On average, sediment feeding increases the coefficient by 19% compared to the non-sediment feeding case. KEYWORDS: Manning’s roughness coefficient, Velocity profile, Equilibrium and non-equilibrium, Sediment transport, Open-channel flow
评估具有平衡和非平衡沉积物迁移的水流的曼宁粗糙度系数
使用曼宁方程的难点之一在于准确确定曼宁粗糙度系数,尤其是由于泥沙输运造成的粗糙度系数。河流特定河段内的泥沙输运条件可能处于平衡状态,即进入和流出该河段的泥沙量是平衡的;也可能处于非平衡状态,即进入和流出该河段的泥沙量不平衡。在实验室中进行了模拟这两种输运条件的实验,一种是有沉积物馈入的条件(平衡条件),另一种是没有沉积物馈入的条件(非平衡条件)。使用声学多普勒测速仪(ADV)在固定床和活动床水流中总共测量了 180 个平均流速剖面。本实验结合理论方法对泥沙输运-流动条件下明渠的曼宁系数进行了评估,并得出了结论性结果。与没有泥沙馈入的水流相比,有泥沙馈入的活动床水流速度曲线 u/U 的形状是 "细长 "的。泥沙输运会影响速度剖面的形状,尤其是在内部区域,从而影响曼宁粗糙度系数。该系数可通过分别在 z/H = 0.1 和 0.2 处对有泥沙馈入和无泥沙馈入的固定床流和活动床流进行两点速度测量来确定。与无泥沙馈入的情况相比,泥沙馈入平均增加了 19% 的系数。关键词: 曼宁粗糙度系数、流速剖面、平衡与非平衡、泥沙输运、明渠水流
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来源期刊
CiteScore
2.10
自引率
27.30%
发文量
0
期刊介绍: I am very pleased and honored to be appointed as an Editor-in-Chief of the Jordan Journal of Civil Engineering which enjoys an excellent reputation, both locally and internationally. Since development is the essence of life, I hope to continue developing this distinguished Journal, building on the effort of all the Editors-in-Chief and Editorial Board Members as well as Advisory Boards of the Journal since its establishment about a decade ago. I will do my best to focus on publishing high quality diverse articles and move forward in the indexing issue of the Journal.
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