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Instantaneous sediment transport formula for sheet flow beneath asymmetric wave and current

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Journal of Hydrodynamics 2022年第4期34卷 712-724页

作者： Xin-yu Hu Zhong-hua Weng Xin Chen Hai-fei Liu The Key Laboratory of Water and sediment Sciences of Ministry of Education School of EnvironmentBeijing Normal UniversityBeijing100875China Pearl River Water Resources Research Institute Pearl River Water Resources CommissionGuangzhou 510611China College of Water Resources and Civil Engineering China Agricultural UniversityBeijing 100083China

An instantaneous formula is obtained for the sheet flow transport beneath the wave and the current by a product integration of the concentration and velocity profiles over the mobile seabed. The formula involves: (1) The product of the erosion depth and the free stream velocity, which can be reduced to the Shields parameter of power 3/2 in accordance with the classical formulae. (2) The ratio of the wave boundary layer thickness to the erosion depth. The formula incorporates the effects of the acceleration and the phase lag on the erosion depth, the asymmetric wave boundary layer and the wave-current interaction. The validation of the formula is made by the data obtained from the oscillatory tunnels covering a wide range of wave-current and sediment conditions. The instantaneous sediment transport rate is compared with the power function of the velocity with different exponents. The formula consists of a wave force part and a current force part and their relative importance depends on the wave shapes. The present formula gives very good results for the net sediment transport as compared to several existing steady and unsteady formulae. The net sediment transport rates are affected by not only the acceleration, the phase lag and the wave-current interaction, but also the asymmetric boundary layer development.

关键词： Boundary layer thickness erosion depth instantaneous formula sediment transport rate wave and current

sediment transport in pure acceleration-skewed oscillatory sheet flow

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Journal of Hydrodynamics 2018年第6期30卷 1045-1054页

作者： Xin Chen Fu-jun Wang Gen-fa Chen Liu-chao Qiu College of Water Resources and Civil Engineering China Agricultural University Beijing Engineering Research Center of Safety and Energy Saving Technology for Water Supply Network System China Agricultural University China Institute of Water Resources and Hydropower Research

In the present study, an analytical concept model is built, using a two-phase model for the sediment transport in a pure acceleration-skewed oscillatory sheet flow. The analytical model is based on the asymmetric wave theory, the irregular boundary layer theory and the exponential concentration distribution theory, to be used for analyzing the phase lag and the boundary layer development related to the acceleration skewness. The two-phase model is applied for the calculations of the instantaneous erosion depth, the sediment flux, the boundary layer thickness and the sediment transport rate, as well as the differences between the positive acceleration stage and the negative acceleration stage caused by the acceleration skewness, as very important in the net current and sediment transport. The effects of the sediment diameter and the phase lag are explained by a comparison with the instantaneous type empirical formula, as is closely related to the acceleration skewness. With the analytical concept model and the two-phase model, the generation of the net sediment transport in the pure acceleration-skewed flows is clearly explained. The phase lag effect is important for the instantaneous sediment transport in the pure acceleration-skewed flow, whereas the boundary layer development difference between the positive acceleration stage and the negative acceleration stage plays a major role in the determination of the net sediment transport.

关键词： Acceleration skewness analytical concept model boundary layer thickness two-phase model sediment transport rate

sediment generation and soil mound denudation in areas of high-density tree throw along a river valley in the Jura Mountains, Switzerland

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Journal of Mountain Science 2021年第2期18卷 377-391页

作者： Philip GREENWOOD Jan BAUER Nikolaus J KUHN Physical Geography&Environmental Change Research Group Department of Environmental SciencesUniversity of BaselKlingelbergstrasse 27Basel-4056Switzerland

A preliminary field-based investigation was undertaken in a small(<10 km^(2))river valley located in the mountainous Jura region of northwest *** aims of the work were to assess sediment generation and annual sediment... 详细信息

A preliminary field-based investigation was undertaken in a small(sediment generation and annual sediment transport rates by tree throw on forested hillslopes,and to document surface hydrology characteristics on four fresh soil mounds associated with recent tree throws over a 24-day monitoring *** the soil mounds,average sediment recovery ranged from 7.7-28.2 g(dry weight),equivalent to a suspended sediment concentration of 145.2-327.8 g L^(-1),and runoff coefficients ranged from 1.0%-4.2%.Based on a soil bulk density value of 1,044 kg m^(-3),upslope runoff generation areas were denuded by an average 0.14 mm by the end of the 24-day monitoring period,representing an erosion rate equivalent to 2.1 mm yr^(-1).A ca.50 cm high soil mound could therefore feasibly persist for around 200-250 *** tree throw work,the dimensions of 215 individual tree throws were measured and their locations mapped in 12 separate locations along the river valley representing a cumulative area equivalent to 5.3 ha(***,43 per ha).Tree throws generated a total of 20.1 m^(3) of fine-sediment(sediment transport rate of 2.7×10^(-5) m^(3) m^(-1) yr^(-1).Exploring the relationship with wind on fall direction,65.5%of tree throws(143)generally fell in a downslope direction irrespective of hillslope aspect on which they were *** infers that individual storms may not have been responsible for the majority of tree throws,but instead,could be associated with root *** the high density of tree throws and their relative maturity(average age 41 years),we hypothesise that once tr

关键词： Tree throw Hillslope processes sediment generation mechanism sediment transport rate Soil mound Ibach river valley

Time-Dependent sediment transport Subjected to Downward Seepage

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Transactions of Tianjin University 2014年第2期20卷 133-138页

作者：刘小谢赵以明白玉川 State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University Institute for sedimentation on River and Coastal Engineering Tianjin University School of Civil Environmental Engineering Nanyang Technological University

Experiments were conducted using cohesionless sand particles with median diameter of 0.48 mm to investigate the time variation of sediment transport rate under the influence of local downward *** experimental results show that the bedload transport rate in terms of volumetric sediment transport rate per unit width increased rapidly with time in the presence of suction,eventually reaching a peak beyond which it started to *** trend of reduction was significantly reduced beyond 8 400 s after the test *** analytical expression was derived in terms of dimensionless sediment transport rate and dimensionless *** hypothesized relationships were compared with the experimental data,indicating a good agreement with each other.

关键词： time effect suction seepage sediment transport rate

An Investigation of Stochastic Nature of Bed Load Motion in Chuanjiang River

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四川大学学报（工程科学版） 2005年第S1期37卷 112-117页

作者： ZHANG Zhixiang~1 HE Wenshe~(1,2) YANG Kejun~1 (1.State Key Lab.of Hydraulics and Mountain River Eng.,Sichuan Univ.,Chengdu 610065,China 2.China Three Gorges Project Corporation,Yichang 443002,China)

Bed Load Motion and its transport rate is one of the basic issues in river *** this paper, the authors discussed the stochastic nature of bed load motion in Chuanjiang River in *** lies in the upstream reach of Yangtze *** stochastic nature is shown in the following four ***, even though all the conditions are the same,due to the fluctuation of the flow,the bed load discharge and the location and width of sediment transport belts are ***,during the ...

关键词： pebble bed load motion Chuanjiang River stochastic nature sediment transport rate

ON THE THEORIES OF HYDRAULIC GEOMETRY

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International Journal of sediment Research 2003年第3期18卷 196-218页

作者： Vijay P. SINGH Baton Rouge Department of Civil and Environmental Engineering Louisiana State University LA 70803-6405 U.S.A.

Hydraulic geometry is of fundamental importance in planning, design, and management of river engineering and training works. Although some concepts of hydraulic geometry were proposed toward the end of the nineteenth century, the real impetus toward formulating a theory of hydraulic geometry was provided by the work of Leopold and Maddock (1953). A number of theories have since been proposed. Some of the theories are interrelated but others are based on quite different principles. All theories, however, assume that the river flow is steady and uniform and the river tends to attain a state of equilibrium or quasi-equilibrium. The differences are due to the differences in hydraulic mechanisms that the theories employ to explain the attainment of equilibrium by the river.

关键词： Energy Energy dissipation Entropy Equilibrium Extremal hypothesis Flow efficiency Friction factor Froude number sediment transport rate Stream power Tractive force

transport OF GRAVELS WITH DIFFERENT RANGES OF GRAIN SIZES IN A STEEP CHANNEL

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International Journal of sediment Research 2005年第2期20卷 143-155页

作者： Jau-Yau LU,Chih-Chiang SU Prof. Dept.of Civil Engrg. National Chung-Hsing University Taichung Taiwan China Ph.D.student Dept.of Civil Engrg. National Chung-Hsing University Taichung Taiwan China

An understanding of the transport mechanism of gravel-bed rivers is very important for the river management and engineering works. The main objective of this study was to conduct a series of laboratory experiment in a steep flume to investigate the particle segregation and the transport rate of nonuniform gravel. Median sizes of 15 mm and 7.5 mm,and gradation coefficients of 1.5 and 2.0 were selected for the particle size distributions of nonuniform gravel. In addition to the 36 sets of data collected in this study,635 sets of existing data for gravel with both nonuniform and nearly uniform sizes were analyzed. According to the results of the sieve analysis and the related theory,hiding functions for both particle size distributions of this study were derived. An attempt was made to develop an Einstein-type transport relationship for nonuniform gravel using dimensionless parameters with mean size as a representative particle size. A modified Schoklitsch-type sediment transport equation with a critical unit flow discharge was also developed to reasonably predict the transport rate of gravels. In addition,an artificial neural network (ANN) model with a back-propagation network (BPN) algorithm was also applied in this study.

关键词： sediment transport rate Bed load Steep flume Nonuniform gravel Particle gradation Hiding phenomenon Back-propagation network Artificial neural network