Bedload sediment transport was estimated by the SEDTRANS96 model based on three-day hydrodynamics data obtained off the Dongfang coast in the Beibu Gulf during Typhoon Ketsana in September 2009. Bed- forms on the sea ...Bedload sediment transport was estimated by the SEDTRANS96 model based on three-day hydrodynamics data obtained off the Dongfang coast in the Beibu Gulf during Typhoon Ketsana in September 2009. Bed- forms on the sea floor off the Dongfang coast and internal structures of a typical dune were interpreted to evaluate storm influences on individual dunes and the dune field. Results indicated that flow forcings and related bedload transport were both strengthened significantly due to Typhoon Ketsana. The measurements and modeling results, which mainly included three different stages, presented noticeable phasic variation. The three stages were dominated by tidal current （Period I）, tidal current combined with wind-induced waves （Period II）, and swells combined with tidal current and seaward flows （Period III）. This phasic varia- tion could be a common trait of hydrodynamics due to typhoons moving westwardly to the south of Hainan Island and Beibu Gulf in South China Sea. Results indicated that the maximum bedioad transport rate for every burst in Period III was almost 100 times larger than that in Period I and was ten times larger than that in Period II. However, the short-term increase in bedload transport induced by storms like Ketsana did not change the long-term evolution of dune morphology. Evidence was given by the internal structures of a typical dune, which revealed renewed modification under subsequent moderate conditions after storm ero- sion. Instead, storms may influence at different scales and regional allocation of sand dunes in some large areas because changes of the sea floor in large scales can hardly be recovered. More surveys during and after storm passage are also needed to document the level of positive contribution to forward migration.展开更多
The paper presents an investigation of injection effects on the bedload transport rate. According to dimensional analysis, two dimensionless groups, an Einstein＇s parameter group and a modified densimetric Froude num...The paper presents an investigation of injection effects on the bedload transport rate. According to dimensional analysis, two dimensionless groups, an Einstein＇s parameter group and a modified densimetric Froude number group, were chosen to examine how injection affects the bedload transport rate. Experimental studies were conducted in an open-channel flume with an upward seepage zone. The sediment particles used for the test were 0.9 mm in diameter. The experimental results show that an increase in the injection velocity causes a reduction in the shear velocity excess, which is defined as the difference between the shear and critical shear velocities, leading to a reduction in the bedload transport rate. The equation for predicting the bedload transport rate in the presence of upward seepage was derived empirically. The proposed prediction method is suitable for engineering practice, since it only requires the undisturbed flow condition, properties of sediment particles, and the injection velocity.展开更多
Mountain rivers are characterized by wide grain size distributions and complex bed surface structures,which significantly affect bedload transport.Owing to the lack of a clear understanding of the quantitative influen...Mountain rivers are characterized by wide grain size distributions and complex bed surface structures,which significantly affect bedload transport.Owing to the lack of a clear understanding of the quantitative influence of the bed surface structure on the bedload transport rate,existing methods for estimating the bedload transport rate in mountain rivers produce large errors.Based on theoretical analysis andflume experiments,this study reveals the influence of bed surface structure on nonuniform bedload transport and proposes a method for estimating bedload transport rate considering the quantitative influence of bed surface structure.Thefindings of the present study provide theoretical methodological support for predicting the sediment transport and bed evolution in mountain rivers.展开更多
Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been develo...Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of： （1） an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, （2） two submerged load cells 0.7 m apart, （3） a pressure sensor and, （4） an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute （DPRI） of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells, Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.展开更多
Due to vegetation drag and vegetation-generated turbulence,bedload transport in vegetated channels is more complicated than that in nonvegetated channels.It is challenging to obtain accurate predictions of bedload tra...Due to vegetation drag and vegetation-generated turbulence,bedload transport in vegetated channels is more complicated than that in nonvegetated channels.It is challenging to obtain accurate predictions of bedload transport in vegetated channels.Previous studies generally used rigid circular cylinders to simulate vegetation,and the impact of plant morphology on bedload transport was typically ignored;these methods deviate from natural scenarios,resulting in prediction errors in transport rates of more than an order of magnitude.This study measured bedload transport rates inside P.australis,A.calamus and T.latifolia canopies and in arrays of rigid cylinders for comparison.The impact of plant morphology on bedload transport in vegetated channels was examined.Inside the canopies of natural morphology,the primary factor driving bedload transport is the near-bed turbulent kinetic energy(TKE),which consists of both bed-generated and vegetation-generated turbulence.A method was proposed to predict the near-bed TKE inside canopies with natural morphology.For the same solid volume fraction of plants,the transport rate inside canopies with a natural morphology is greater than or equal to that within an array of rigid cylinders,depending on the plant shape.This finding indicates that plant morphology has a significant impact on transport rates in vegetated regions and cannot be ignored,which is typical in practice.Four classic bedload transport equations(the Meyer-Peter-Müller,Einstein,Engelund and Dou equations),which are suitable for bare channels(no vegetation),were modified in terms of the near-bed TKE.The predicted near-bed TKE was inserted into these four equations to predict the transport rate in canopies with natural morphology.A comparison of the predictions indicated that the Meyer-Peter-Müller equation had the highest accuracy in predicting the transport rate in vegetated landscapes.展开更多
推移质运动规律对河床演变具有重要影响,是河流动力学研究的重点和难点。本文开展中低水流条件下的推移质平衡输沙试验,将灰度相减方法和深度学习方法相结合,旨在提出一种优化的推移质运动颗粒识别算法,并在此基础上应用粒子跟踪测速技...推移质运动规律对河床演变具有重要影响,是河流动力学研究的重点和难点。本文开展中低水流条件下的推移质平衡输沙试验,将灰度相减方法和深度学习方法相结合,旨在提出一种优化的推移质运动颗粒识别算法,并在此基础上应用粒子跟踪测速技术(PTV)和卡尔曼滤波算法计算推移质颗粒运动轨迹,从而建立紊流相干结构与颗粒运动强度关系。为清晰捕捉运动距离较小颗粒,对YOLOv5(you only look once)目标检测模型网络结构进行卷积块改进、增加注意力机制和优化损失函数处理,以增强其在推移质颗粒识别任务中对极小目标的检测能力。结果表明:1)灰度相减方法可识别运动距离较大的颗粒,改进YOLOv5模型则能够更好识别运动距离较小的颗粒,通过合并优化两种方法,在本文设置的试验工况下可更准确识别推移质运动颗粒和运动轨迹;2)中低水流强度条件下,推移质泥沙颗粒运动强度受紊流相干结构影响沿水槽横向方向呈现间隔条带结构,并且随着水流强度增加,条带结构逐渐由密集变得稀疏,其宽度也由窄转宽,当水流强度继续增大时紊动掺混剧烈,条带结构遭到破坏逐渐消失;3)总体看来:泥沙颗粒运动多集中在水槽中间区域,边壁处运动较少,沙条带结构呈现中间宽两边窄的空间分布特征,表明条带结构是受紊流大尺度相干结构的影响而形成,而非二次流结构。展开更多
As an important type of emerging pollutants, ecological toxicity and risk of artificial musks are increasingly concerned. Thus, single and joint toxic effects of 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8- hexamethylcyclopenta...As an important type of emerging pollutants, ecological toxicity and risk of artificial musks are increasingly concerned. Thus, single and joint toxic effects of 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8- hexamethylcyclopenta-gamma-2-benzopyran （HHCB） as one of the most widely applied artificial musks and cadmium （Cd） as an toxic metal on zebrafish （Danio rerio） were investigated by the exposure of zebrafish to various concentrations of HHCB or/and Cd in feculent water containing bedloads. The results indicated that the joint effect of HHCB and Cd changed during different exposure times within 120 h. The index of the antioxidant enzyme system including superoxide dismutase （SOD） and perox- idase （POD）, and malondialdehyde （MDA） were sensitive and induced in the zebrafish stressed by Cd, and content of soluble protein （SP） was sensitive to HHCB and could be used as a biomarker for HHCB. Joint effects on antioxidant enzymes depended more on the effect of single Cd in the first one or two days. However, in the rest exposure days, the effect of HHCB began to dominate in the joint effect during the exposure process.展开更多
The incipient motion of bedload is due to the interaction between the flow and sediment.It is stochastically correlated with the flow structure,the sediment gradation and the arrangement of grains on the bed surface.T...The incipient motion of bedload is due to the interaction between the flow and sediment.It is stochastically correlated with the flow structure,the sediment gradation and the arrangement of grains on the bed surface.The random position of the sediment on bed can be represented by a hiding factor or an exposure degree.Based on the numerical simulation of the disturbed flow in the interstice of grains,the influence of the two-way exposure degree(the vertical exposure degree and the longitudinal exposure degree) on the coarse grain incipient motion was investigated in this work.Results show that the exposure degree varies with the position of the sediment on the bed,which influences the flow structure around the particle and the incipient motion.In this paper,the major research achievements on this phenomenon include:Firstly,a mathematical model is established for the rolling-pattern incipient motion of the coarse grain under a critical state of moment balance.The influence of the partial disturbed flow is considered.Secondly,the two-way relative-exposure-degree probability distribution functions are developed to reflect the influence of the disturbed flow and the random arrangement of sediments.Thirdly,a formula to calculate the incipient velocity is presented based on the above results,which considers the impact of the two-way exposure degree of sediment particles.展开更多
This paper studies the flow structure and the bedload transport regime in backwater flows, to provide a theoretical support for solving the sediment transport and bed scour problems in rivers or reservoirs with backwa...This paper studies the flow structure and the bedload transport regime in backwater flows, to provide a theoretical support for solving the sediment transport and bed scour problems in rivers or reservoirs with backwater. The bedload transport rates under different conditions are analyzed first on the basis of theoretical analysis, measurement comparison and flume experiment, and it is pointed out that the existing formulas for the bedload transport rate are not applicable for the bedload transport rate in backwater flows. Next, the flow structure in a non-uniform flow is observed by flume experiments, and by introducing the backwater degree index, the quantitative relation between the relative bed shear stress and the backwater degree is obtained. Finally, the formula for the bedload transport rate applicable for the reservoir channel segment with backwater flows is obtained through measurements and flume experiments.展开更多
A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10,...A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10, 2003. The bed shear stress and bedload transport rates, in response to wave-current interactions, are calculated, which in- dicate that wind waves enhance the bottom shear stress and bedload transport rates. At the station for measurements, bedload transport was directed to seaward, with a sediment discharge of 30—150 kg·m?1 per tidal cycle. The surficial sediment samples were collected from a grid with 10 m spatial intervals over a rectangle 2×104 m2 experimental area, near the MIDAS-400 during the spring tide of July 4, 2003, and the neap tide of July 9, 2003. In addition, leveling survey was undertaken to obtain the detailed topog- raphy of the sampling area. Grain-size trend analysis of the sediment samples shows that the bedload transport patterns are complex, mainly controlled by the hydrodynamics and local geomorphology (e.g. tidal creeks) over the intertidal flats. Furthermore, the grain-size trends pattern during the neap tide rather than during the spring tide is consistent with the cal- culated bedload transport, and the grain-size trend vectors for the spring tide are larger than those forthe neap tide, indicating that the sampling thickness of surficial sediment during the neap tide may contain the information on the geomorphological evolution (or sediment deposition/erosion) from the spring to the neap tide.展开更多
Fast water can cause extraordinary bedload transport.Of the record floods considered here,the Jul.26,2022 urban flash flood on the upper River des Peres,St.Louis,Missouri provides particularly well-constrained data on...Fast water can cause extraordinary bedload transport.Of the record floods considered here,the Jul.26,2022 urban flash flood on the upper River des Peres,St.Louis,Missouri provides particularly well-constrained data on flow conditions associated with large block movement.Field measurements and a detailed lidar survey show that concrete slabs as large as 3.0×2.5×0.33 m^(3)were moved from the open channel to reside 215 to 450 m inside a 6.5 m-diameter drainage tunnel,some to become part of a 10-m long imbricated pile.Peak flows of 160 m^(3)/s were recorded at a gauging station located only 1.6 km upstream of the tunnel entrance,which provides a good estimate of 4.2 m/s for the peak flow velocity in the tunnel.Available observational data and a new theoretical analysis show that the radius of large boulders that can be moved by flowing water is directly proportional to the velocity head.展开更多
基金A CAS(Chinese Academy of Sciences)and CNOOC(China National Offshore Oil Corporation)collaborative research project
文摘Bedload sediment transport was estimated by the SEDTRANS96 model based on three-day hydrodynamics data obtained off the Dongfang coast in the Beibu Gulf during Typhoon Ketsana in September 2009. Bed- forms on the sea floor off the Dongfang coast and internal structures of a typical dune were interpreted to evaluate storm influences on individual dunes and the dune field. Results indicated that flow forcings and related bedload transport were both strengthened significantly due to Typhoon Ketsana. The measurements and modeling results, which mainly included three different stages, presented noticeable phasic variation. The three stages were dominated by tidal current （Period I）, tidal current combined with wind-induced waves （Period II）, and swells combined with tidal current and seaward flows （Period III）. This phasic varia- tion could be a common trait of hydrodynamics due to typhoons moving westwardly to the south of Hainan Island and Beibu Gulf in South China Sea. Results indicated that the maximum bedioad transport rate for every burst in Period III was almost 100 times larger than that in Period I and was ten times larger than that in Period II. However, the short-term increase in bedload transport induced by storms like Ketsana did not change the long-term evolution of dune morphology. Evidence was given by the internal structures of a typical dune, which revealed renewed modification under subsequent moderate conditions after storm ero- sion. Instead, storms may influence at different scales and regional allocation of sand dunes in some large areas because changes of the sea floor in large scales can hardly be recovered. More surveys during and after storm passage are also needed to document the level of positive contribution to forward migration.
文摘The paper presents an investigation of injection effects on the bedload transport rate. According to dimensional analysis, two dimensionless groups, an Einstein＇s parameter group and a modified densimetric Froude number group, were chosen to examine how injection affects the bedload transport rate. Experimental studies were conducted in an open-channel flume with an upward seepage zone. The sediment particles used for the test were 0.9 mm in diameter. The experimental results show that an increase in the injection velocity causes a reduction in the shear velocity excess, which is defined as the difference between the shear and critical shear velocities, leading to a reduction in the bedload transport rate. The equation for predicting the bedload transport rate in the presence of upward seepage was derived empirically. The proposed prediction method is suitable for engineering practice, since it only requires the undisturbed flow condition, properties of sediment particles, and the injection velocity.
基金National Natural Science Foundation of China,Grant/Award Number:U2040219Sichuan Science and Technology Program,Grant/Award Number:2023NSFSC1989Fok Ying Tung Education Foundation,Grant/Award Number:171067。
文摘Mountain rivers are characterized by wide grain size distributions and complex bed surface structures,which significantly affect bedload transport.Owing to the lack of a clear understanding of the quantitative influence of the bed surface structure on the bedload transport rate,existing methods for estimating the bedload transport rate in mountain rivers produce large errors.Based on theoretical analysis andflume experiments,this study reveals the influence of bed surface structure on nonuniform bedload transport and proposes a method for estimating bedload transport rate considering the quantitative influence of bed surface structure.Thefindings of the present study provide theoretical methodological support for predicting the sediment transport and bed evolution in mountain rivers.
基金supported in part by the Research Budget from the Research and Development Center,Nippon Koei Co.,Ltd
文摘Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of： （1） an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, （2） two submerged load cells 0.7 m apart, （3） a pressure sensor and, （4） an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute （DPRI） of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells, Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFE0128200)the National Natural Science Foundation of China(Grant Nos.52379072,52022063)the Fundamental Research Project of China Yangtze Power Co.,Ltd.(Grant No.2423020045).
文摘Due to vegetation drag and vegetation-generated turbulence,bedload transport in vegetated channels is more complicated than that in nonvegetated channels.It is challenging to obtain accurate predictions of bedload transport in vegetated channels.Previous studies generally used rigid circular cylinders to simulate vegetation,and the impact of plant morphology on bedload transport was typically ignored;these methods deviate from natural scenarios,resulting in prediction errors in transport rates of more than an order of magnitude.This study measured bedload transport rates inside P.australis,A.calamus and T.latifolia canopies and in arrays of rigid cylinders for comparison.The impact of plant morphology on bedload transport in vegetated channels was examined.Inside the canopies of natural morphology,the primary factor driving bedload transport is the near-bed turbulent kinetic energy(TKE),which consists of both bed-generated and vegetation-generated turbulence.A method was proposed to predict the near-bed TKE inside canopies with natural morphology.For the same solid volume fraction of plants,the transport rate inside canopies with a natural morphology is greater than or equal to that within an array of rigid cylinders,depending on the plant shape.This finding indicates that plant morphology has a significant impact on transport rates in vegetated regions and cannot be ignored,which is typical in practice.Four classic bedload transport equations(the Meyer-Peter-Müller,Einstein,Engelund and Dou equations),which are suitable for bare channels(no vegetation),were modified in terms of the near-bed TKE.The predicted near-bed TKE was inserted into these four equations to predict the transport rate in canopies with natural morphology.A comparison of the predictions indicated that the Meyer-Peter-Müller equation had the highest accuracy in predicting the transport rate in vegetated landscapes.
文摘推移质运动规律对河床演变具有重要影响,是河流动力学研究的重点和难点。本文开展中低水流条件下的推移质平衡输沙试验,将灰度相减方法和深度学习方法相结合,旨在提出一种优化的推移质运动颗粒识别算法,并在此基础上应用粒子跟踪测速技术(PTV)和卡尔曼滤波算法计算推移质颗粒运动轨迹,从而建立紊流相干结构与颗粒运动强度关系。为清晰捕捉运动距离较小颗粒,对YOLOv5(you only look once)目标检测模型网络结构进行卷积块改进、增加注意力机制和优化损失函数处理,以增强其在推移质颗粒识别任务中对极小目标的检测能力。结果表明:1)灰度相减方法可识别运动距离较大的颗粒,改进YOLOv5模型则能够更好识别运动距离较小的颗粒,通过合并优化两种方法,在本文设置的试验工况下可更准确识别推移质运动颗粒和运动轨迹;2)中低水流强度条件下,推移质泥沙颗粒运动强度受紊流相干结构影响沿水槽横向方向呈现间隔条带结构,并且随着水流强度增加,条带结构逐渐由密集变得稀疏,其宽度也由窄转宽,当水流强度继续增大时紊动掺混剧烈,条带结构遭到破坏逐渐消失;3)总体看来:泥沙颗粒运动多集中在水槽中间区域,边壁处运动较少,沙条带结构呈现中间宽两边窄的空间分布特征,表明条带结构是受紊流大尺度相干结构的影响而形成,而非二次流结构。
基金Acknowledgements The authors acknowledge the financial support from the National Natural Science Foundation of China （Grant Nos. 40930739 and 21037002）. The Sino-Russian Joint Research Center on Natural Resources and Eco-Environmental Sciences also gave partial aids in this work.
文摘As an important type of emerging pollutants, ecological toxicity and risk of artificial musks are increasingly concerned. Thus, single and joint toxic effects of 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8- hexamethylcyclopenta-gamma-2-benzopyran （HHCB） as one of the most widely applied artificial musks and cadmium （Cd） as an toxic metal on zebrafish （Danio rerio） were investigated by the exposure of zebrafish to various concentrations of HHCB or/and Cd in feculent water containing bedloads. The results indicated that the joint effect of HHCB and Cd changed during different exposure times within 120 h. The index of the antioxidant enzyme system including superoxide dismutase （SOD） and perox- idase （POD）, and malondialdehyde （MDA） were sensitive and induced in the zebrafish stressed by Cd, and content of soluble protein （SP） was sensitive to HHCB and could be used as a biomarker for HHCB. Joint effects on antioxidant enzymes depended more on the effect of single Cd in the first one or two days. However, in the rest exposure days, the effect of HHCB began to dominate in the joint effect during the exposure process.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51279124,51021004,50979066)
文摘The incipient motion of bedload is due to the interaction between the flow and sediment.It is stochastically correlated with the flow structure,the sediment gradation and the arrangement of grains on the bed surface.The random position of the sediment on bed can be represented by a hiding factor or an exposure degree.Based on the numerical simulation of the disturbed flow in the interstice of grains,the influence of the two-way exposure degree(the vertical exposure degree and the longitudinal exposure degree) on the coarse grain incipient motion was investigated in this work.Results show that the exposure degree varies with the position of the sediment on the bed,which influences the flow structure around the particle and the incipient motion.In this paper,the major research achievements on this phenomenon include:Firstly,a mathematical model is established for the rolling-pattern incipient motion of the coarse grain under a critical state of moment balance.The influence of the partial disturbed flow is considered.Secondly,the two-way relative-exposure-degree probability distribution functions are developed to reflect the influence of the disturbed flow and the random arrangement of sediments.Thirdly,a formula to calculate the incipient velocity is presented based on the above results,which considers the impact of the two-way exposure degree of sediment particles.
基金supported by the National Natural Science Foun-dation of China(Grant Nos.51339001,51479009)
文摘This paper studies the flow structure and the bedload transport regime in backwater flows, to provide a theoretical support for solving the sediment transport and bed scour problems in rivers or reservoirs with backwater. The bedload transport rates under different conditions are analyzed first on the basis of theoretical analysis, measurement comparison and flume experiment, and it is pointed out that the existing formulas for the bedload transport rate are not applicable for the bedload transport rate in backwater flows. Next, the flow structure in a non-uniform flow is observed by flume experiments, and by introducing the backwater degree index, the quantitative relation between the relative bed shear stress and the backwater degree is obtained. Finally, the formula for the bedload transport rate applicable for the reservoir channel segment with backwater flows is obtained through measurements and flume experiments.
基金The study was supported financially by the National Natural Science Foundation of China （Grant Nos. 40206006 and 40231010）.
文摘A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10, 2003. The bed shear stress and bedload transport rates, in response to wave-current interactions, are calculated, which in- dicate that wind waves enhance the bottom shear stress and bedload transport rates. At the station for measurements, bedload transport was directed to seaward, with a sediment discharge of 30—150 kg·m?1 per tidal cycle. The surficial sediment samples were collected from a grid with 10 m spatial intervals over a rectangle 2×104 m2 experimental area, near the MIDAS-400 during the spring tide of July 4, 2003, and the neap tide of July 9, 2003. In addition, leveling survey was undertaken to obtain the detailed topog- raphy of the sampling area. Grain-size trend analysis of the sediment samples shows that the bedload transport patterns are complex, mainly controlled by the hydrodynamics and local geomorphology (e.g. tidal creeks) over the intertidal flats. Furthermore, the grain-size trends pattern during the neap tide rather than during the spring tide is consistent with the cal- culated bedload transport, and the grain-size trend vectors for the spring tide are larger than those forthe neap tide, indicating that the sampling thickness of surficial sediment during the neap tide may contain the information on the geomorphological evolution (or sediment deposition/erosion) from the spring to the neap tide.
文摘Fast water can cause extraordinary bedload transport.Of the record floods considered here,the Jul.26,2022 urban flash flood on the upper River des Peres,St.Louis,Missouri provides particularly well-constrained data on flow conditions associated with large block movement.Field measurements and a detailed lidar survey show that concrete slabs as large as 3.0×2.5×0.33 m^(3)were moved from the open channel to reside 215 to 450 m inside a 6.5 m-diameter drainage tunnel,some to become part of a 10-m long imbricated pile.Peak flows of 160 m^(3)/s were recorded at a gauging station located only 1.6 km upstream of the tunnel entrance,which provides a good estimate of 4.2 m/s for the peak flow velocity in the tunnel.Available observational data and a new theoretical analysis show that the radius of large boulders that can be moved by flowing water is directly proportional to the velocity head.
