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Dispersion features of pollutants in a compound channel with vegetated floodplains

Journal of Hydrodynamics 2022年第6期34卷 1095-1105页

作者： Yan-fang Zhao Jing-jing Fan Wei-jie Wang Han-qing Zhao Fei Dong Zhen Han Shi-yan Wang School of Water Conservancy and Hydroelectric Power Hebei University of EngineeringHandan056038China State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin China Institute of Water Resources and Hydropower ResearchBeijing100038China China Three Gorges Corporation Wuhan430010China National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety Nanjing210024China

The planting of the vegetation on the floodplain helps the ecological restoration,which is the main form of the river’s ecological corridor.Therefore,the current research of the river dynamics focuses on the water movement under a compound channel with the vegetated floodplains.Two simulated vegetation species are selected in this paper for the flume simulation experiments of the floodplain vegetation,and the compound channel is divided into three subregions in the transverse direction.The Navier-Stokes equation and the eddy viscosity theory are applied to obtain the transverse distribution of the depth-averaged velocity and the results agree well with the experimental data.This paper proposes a new method based on the analytical solution of the flow velocity distribution to calculate the average flow velocity in each section.Calculation results can effectively simulate the average flow velocity of the measured sections.The description of the pollutant transport processes in a moving stream requires a refined determination of the dispersion coefficients in the compound channel.The process of the pollutant concentrations in each zone and the reasons for their occurrence are elucidated on the basis of the experimental results.Simultaneously,the measured values of the longitudinal dispersion coefficients are obtained by the“routing procedure,”and a two-zone model of the pollutant dispersion is constructed on the basis of the hydrodynamic study.The prediction method for the longitudinal dispersion coefficients is also presented.Applying the predicted and measured section average flow velocities to the two-zone model to predict the longitudinal dispersion coefficient,and the average relative errors are only 4.17%,7.15%,respectively.This result indicates that the two-zone model can effectively predict the longitudinal dispersion coefficients.The calculation methods for the longitudinal dispersion coefficients from—various studies are compared.The results reveal that the predicted values of these calculation methods are

关键词： compound channel floodplain vegetation velocity distribution pollutant transport dispersion coefficient

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Flow structure at the downstream of a one-line riparian emergent tree along the floodplain edge in a compound open-channel flow

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Journal of Hydrodynamics 2018年第3期30卷 470-480页

作者： Ayse Yuksel Ozan Civil Engineering Department Engineering Faculty Adnan Menderes University

This study focuses on the effects of one-line emergent natural tree（Cupressus Macrocarpa） planted at the edge of the floodplain in a compound open-channel flow. The flow velocity and water level are measured and used to analyze the flow structure. The time averaged and depth-averaged streamwise velocity distributions with root mean square（rms） and time series of streamwise velocity distrbution are analyzed. The velocity distribution considerably changes along the compound channel. The streamwise velocity distribution fits with logarithmic distribution in the non-vegetated case, but for vegetated cases, the streamwise velocity distribution shows S shaped profile at the 1/3 part of floodplain（/3）B_f and main channel（/3）B_m close to the boundary between floodplain and main channel. Additionally, it is obtained that the presence of tree line increases turbulence intensity over the compound open-channel. Moreover, an oscillation period is obtained in the flow caused by tree line by analyzing time series of the streamwise velocity distribution. The oscillation is present everywhere in the floodplain and present at almost/3 B_m part of the main channel which is close to the junction between floodplain and main channel.

关键词： Floodplain natural vegetation open channel flow compound channel velocity profile

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Behavior of near-field dilution of thermal buoyant jet discharged horizontally in compound open-channel

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Applied Mathematics and Mechanics(English Edition) 2008年第2期29卷 263-271页

作者：槐文信肖庆华曾玉红杨中华钱忠东 State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University

The RNG κ-ε model considering the buoyancy effect, which is solved by the hybrid finite analytic method, is used to simulate the mixture of the horizontal round thermal buoyant jet in compound open channel flow. The mixing features near the spout and flowing characteristic of the secondary currents are studied by numerical simulation. Meanwhile, （1） the distribution of the measured isovels for stream-wise velocity, （2） secondary currents, （3） the distribution of the measured isovels for temperature of typical cross-section near the spout, were obtained by the three-dimensional Micro ADV and the temperature measuring device. Compared with experimental data, the RNG κ-ε model based on buoyancy effect can preferably simulate the jet which performs the bifurcation phenomenon, jet reattachment （Conada effect） and beach secondary currents phenomenon with the effect of ambient flow, buoyancy, and secondary currents of compound section and so on.

关键词： turbulence model compound channel buoyant jets hybrid finite analytic method secondary currents

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Two dimensional analytical solution for a partially vegetated compound channel flow

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Applied Mathematics and Mechanics(English Edition) 2008年第8期29卷 1077-1084页

作者：槐文信徐治钢杨中华曾玉红 State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072P.R.China

The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.

关键词： compound channel depth-averaged velocity drag force eddy viscosity model analytical solution vegetation

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Two-dimensional analytical solution for compound channel flows with vegetated floodplains

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Applied Mathematics and Mechanics(English Edition) 2009年第9期30卷 1121-1130页

作者：槐文信高敏曾玉红李丹 State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University

This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.

关键词： compound channel vegetation drag force secondary currents

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Investigating the Effect of Relative Width on Momentum Transfer between Main channel and Floodplain in Rough Rectangular compound channel Sunder Varius Relative Depth Condition

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Open Journal of Geology 2016年第4期6卷 225-231页

作者： Shima Bahadori Mehdi Behdarvandi Askar Master’s Student Department of Offshore Structures Faculty of Marine EngineeringKhorramshahr University of Marine Science and Technology Khorramshahr Iran Assistant Professor Department of Offshore Structures Faculty of Marine EngineeringKhorramshahr University of Marine Science and Technology Khorramshahr Iran

compound section is referred to a section the surface of which is made of several sub-sections with different flow characteristics. The difference in the hydraulic and geometry characteristics causes a complexity in flow hydraulic and creates an interaction between the main channel and floodplains, resulting in an apparent shear stress and a transverse momentum transfer. The amount of such a stress plays an important role in many river engineering measures [1]. Due to the flow complexity, the common approximate analytical methods are not enough to identify the flow profile. The FLOW3D Software with its great features in three-dimensional analysis of flow field is used as a tool to investigate the shear stress in a direct symmetrical compound rectangular channel. After the simulation of models, it is found that an increase in the relative width and relative depth parameters decreases the percentage of apparent shear stress and an increase in the relative roughness causes it to be increased [2].

关键词： compound channel Momentum Transfer Relative Roughness Relative Depth Relative Width

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Temporal evolution of scour at bridge abutments in compound channels

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International Journal of Sediment Research 2022年第5期37卷 662-674页

作者： Yifan Yang Bruce W.Melville Xiaozhou Xiong Lu Wang School of Engineering The University of Waikato Risland New Zealand Department of Civil and Environmental Engineering The University of Auckland State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resource and Hydropower Sichuan University

Bridge abutment-induced sediment scour in compound river channels is time-sensitive during floods, and, thus, estimating the scour rate has significance in design. In the current study, large-scale laboratory experiments were done to examine the influence of multiple factors on scour evolution,including channel geometry, bed mobility(clear-water or live-bed), and lateral(embankment intrusion) and vertical(deck submergence) flow contractions. A new method is applied for scour measurement and determination of characteristic scour trends. Results show that the nondimensional time scale is related to flow intensity and may peak before reaching the clear-water scour threshold; the corresponding equations also are derived. It is found that the use of scour countermeasures has a significant impact on the scour rate, and the existing equations for unprotected abutments have limitations. Under clear-water conditions, the scour rate is closely related to the overall flow contraction, which can be better reflected by the ratio of the approaching unit discharge to that at the bridge section. Specifically, the effect of vertical flow contraction on scour rate is more dominant than other factors. Two scour rate curves are derived to suit different structural and flow contraction types for clear-water scour. In contrast, the live-bed scour rate data are generally consistent and fall in a narrow band, showing less dependence on other factors. Finally, a new design approach is established to estimate the time scale and scour rate using the new equations proposed in this paper.

关键词： Abutment scour Temporal evolution compound channel Time scale Scour rate

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Temporal variations of sediment and morphological characteristics at a large confluence accounting for the effects of floodplain submergence

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International Journal of Sediment Research 2022年第5期37卷 619-638页

作者： Kun Li Hongwu Tang Saiyu Yuan Lei Xu Yang Xiao Carlo Gualtieri State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University Yangtze Institute for Conservation and Development Department of Structures for Engineering and Architecture University of Napoli Federico Ⅱ

The large confluence between the Yangtze River and the outflow channel of Poyang Lake is receiving attention due to its importance in flood control and ecological protection in the Yangtze River basin.There is a large floodplain along the outflow channel of Poyang Lake, which is submerged during high flow and dry during low flow. The effects of the submergence of this floodplain on sediment and morphological characteristics at this large confluence have not been known. Hence, a field investigation was done in March 2019(relatively high flow, Survey 3) to complement the previous field studies done in August(high flow, Survey 1) and December 2018(low flow, Survey 2) to identify the temporal variations of sediment and morphological characteristics considering the submergence of this large floodplain. The predominant sediment transport modes were wash load for Poyang Lake and confluence particles and mixed bedload/suspended load for the Yangtze River particles. The sediment transport processes were largely affected by both the secondary flows and the water density contrast between the tributaries with a lock-exchange sediment rich, denser flow moving across the inclined mixing interface in Surveys 1 and 2. The sediment flux across the mixing interface was weakened in Survey 3 when the density contrast was very small. The stagnation zone near the confluence apex had a low sediment concentration and played a role in preventing the sediment flux exchange between the two flows, and its size, and, thus, its importance as a barrier to sediment mixing were related to the submergence of the floodplain. The bed morphology with the local scour holes at the confluence was largely affected by the large-size helical cells, and this kind of effect was weakened as the secondary flows got restricted in Survey 3. The current results expand the database and knowledge on the sediment transport and morphological features of large river confluences.

关键词： River confluence Yangtze river Poyang lake compound channel Sediment transport Morphodynamics

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A simple method for estimating bed shear stress in smooth and vegetated compound channels

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Journal of Hydrodynamics 2016年第3期28卷 497-505页

作者：单钰淇刘超罗懋康杨克君 College of Mathematics Sichuan University State Key Laboratory of Hydraulics and Mountain River Engineering and College of Water Resource and Hydropower Sichuan University

Instead of a large number of measurements of the streamwise velocity, a simple method is proposed to estimate the bed shear stress in smooth and vegetated compound channels, based on the Darcy-Weisbach equation. This method contains a dimension- less parameter Ai, to represent the relationship between the bed shear stress and the velocity close to the channel bed （Ub）, which is determined in each divided domain. This method is verified in two smooth compound channels with different geometries, and in one compound channel with emergent floodplain vegetation. The comparison of predicted and measured bed shear stresses indicates the good predictive capability of this method, particularly in the mixing region. This method is further discussed for a channel with submerged vegetation. Once the values of Ai in the main channel and the floodplain are determined, this method is a practical tool

关键词： predictive method bed shear stress compound channel vegetation

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Shear stress distribution prediction in symmetric compound channels using data mining and machine learning models

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Frontiers of Structural and Civil Engineering 2020年第5期14卷 1097-1109页

作者： Zohreh SHEIKH KHOZANI Khabat KHOSRAVI Mohammadamin TORABI Amir MOSAVI Bahram REZAEI Timon RABCZUK Institute of Structural Mechanics Bauhaus Universität-WeimarWeimar D-99423Germany Department of Watershed Management Engineering Faculty of Natural ResourcesSari Agricultural Science and Natural Resources UniversitySari 48181Iran Department of Civil and Environmental Engineering Idaho State UniversityPocatelloID 83209USA School of the Built Environment Oxford Brookes UniversityOxford OX30BPUK Kando Kalman Faculty of Electrical Engineering Obuda UniversityBudapest 1034Hungary Department of Civil Engineering Bu-Ali Sina UniversityHamedan 65178Iran

Shear stress distribution prediction in open channels is of utmost importance in hydraulic structural engineering as it directly affects the design of stable channels.In this study,at first,a series of experimental tests were conducted to assess the shear stress distribution in prismatic compound channels.The shear stress values around the whole wetted perimeter were measured in the compound channel with different floodplain widths also in different flow depths in subcritical and supercritical conditions.A set of,data mining and machine learning algorithms including Random Forest(RF),M5P,Random Committee,KStar and Additive Regression implemented on attained data to predict the shear stress distribution in the compound channel.Results indicated among these five models;RF method indicated the most precise results with the highest R2 value of 0.9.Finally,the most powerful data mining method which studied in this research compared with two well-known analytical models of Shiono and Knight method(SKM)and Shannon method to acquire the proposed model functioning in predicting the shear stress distribution.The results showed that the RF model has the best prediction performance compared to SKM and Shannon models.

关键词： compound channel machine learning SKM model shear stress distribution data mining models

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