River bending is the major effect responsible for bed topography and bank changes.In this study,fluid velocity(measured by a three-dimensional Doppler advanced point current meter)and bed topographical data have been ...River bending is the major effect responsible for bed topography and bank changes.In this study,fluid velocity(measured by a three-dimensional Doppler advanced point current meter)and bed topographical data have been collected in 40 sections of an experimental model.The whole flume was composed of an organic glass bend,upstream and downstream water tanks,two transition straight sections,a circulation pump,and a connection pipeline.Each section has been found to be characterized by a primary circulation and a small reverse circulation,with some sections even presenting three more or more circulation structures.The minimum circulation intensity has been detected in proximity to the top of the curved channel,while a region with small longitudinal velocity has been observed near the concave bank of each bend,corresponding to the flat bed formed after a short period of scouring.The maximum sediment deposition and scour depth in the presence of a uniform distribution of living flexible vegetation within 10 cm of the flume wall have been found to be smaller than those observed in the tests conducted without vegetation.展开更多
The Three Gorges Project(TGP)has changed the flow-sediment process in the middle Yangtze River.For navigation purposes,there is an urgent need to study the changes of the river regime over a long-term period and the s...The Three Gorges Project(TGP)has changed the flow-sediment process in the middle Yangtze River.For navigation purposes,there is an urgent need to study the changes of the river regime over a long-term period and the shoal-channel evolution over different seasons since the completion of the TGP.Based on analysis of the measured data and the results of a two-dimensional mathematical model,the changes of the river regime and river bed evolution in the Yaojian reach downstream of the TGP were studied.Results show that a high sediment transport flux helps to keep the main flow in the North Branch,while a low sediment transport flux helps to keep the main flow in the South Branch.Thus,the main branch will not change in the near future because of the low sediment transport load.In this study,the flow-sediment process adjusted by the TGP was restored to the conditions before the TGP,and the river bed evolution under the adjusted and non-adjusted flow-sediment conditions was calculated.After the completion of the TGP,the reservoir storage accelerated the flood recession process and decreased the erosion by 11.9%under the flow-sediment conditions in 2010,and the deposition in the flood season decreased by 56.4%.展开更多
This article discusses the process of sediment transport and proposes a morphological model to predict the bed evolution in estuaries. The hydrodynamic module is based on an existent model-Depth Integrated Velocity An...This article discusses the process of sediment transport and proposes a morphological model to predict the bed evolution in estuaries. The hydrodynamic module is based on an existent model-Depth Integrated Velocity And Solute Transport （DIVAST） and the wetting and drying method is adopted to deal with the moving boundary. Both cohesive sediment and non-cohesive sediment are taken into consideration in the sediment transport module with the capability of simulating the transport of graded sediments under non-equilibrium conditions. The fall velocity of the suspended sediment is modified in the present model due to the high sediment concentration. A 3-layer approach is adopted to simulate the variations of sediment gradations of bed materials. Furthermore, the model is used to simulate the bed evolution in the Yellow River Delta （YRD） from 1992 to 1995. Field data are used to calibrate the parameters. The numerical results show how the morphology was developed in the Yellow River Estuary with a good agreement with the field data.展开更多
In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well asacidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning ...In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well asacidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning andcorrelation analyses of CaCO_3, C / P_2O_5, Fe^(2+) / Fe^(3+), pH and Eh values, taking the Xiaodukou section in theNihewan basin as an example. The CaCO_3, C / P_2O_5 and pH were calculated respectively using the optimalpartitioning method. Thus five cold zones and six warm zones as well as five reduction and six oxidation zoneswere distinguished. Then the inductive method was used to produce four numerical groups: 8.10, 8.3-8.4,8.6-8.7 and 8.9-8,97. The above-mentioned results are respectively based on CaCO_3 content, C/P_2O_5 andpH values. From Fig. 3, Tables 1 and 2 it can be seen that the Nihewan Beds were formed mainly under a re-duction and slightly alkaline environment of cold climate, with pH values of 8.3-8.4. Fig. 3 shows that bed 35is approximately near the boundary between the Brunhes and Matuyama polarity epochs, 0.73 Ma in age; bed26 is roughly near the Jaramillo event (base), 0.97 Ma in age; bed 18 coincides roughly with themagnetostratigraphic boundary of 2.00 Ma (?). Bed 13 may be the Pleistocene-Pliocene boundary, 2.48 Ma inage. Thus geochemical zones Ⅰ, Ⅱ, Ⅲ and Ⅳ include respectively cold zones 1; 2 and 3; 4; and 5.展开更多
A two-dimensional depth-integrated numerical model is refined in this paper to simulate the hydrodynamics, graded sediment transport process and the fate of faecal bacteria in estuarine and coastal waters. The sedimen...A two-dimensional depth-integrated numerical model is refined in this paper to simulate the hydrodynamics, graded sediment transport process and the fate of faecal bacteria in estuarine and coastal waters. The sediment mixture is divided into several fractions according to the grain size. A bed evolution model is adopted to simulate the processes of the bed elevation change and sediment grain size sorting. The faecal bacteria transport equation includes enhanced source and sink terms to represent bacterial kinetic transformation and disappearance or reappearance due to sediment deposition or re-suspension. A novel partition ratio and dynamic decay rates of faecal bacteria are adopted in the numerical model. The model has been applied to the turbid water environment in the Bristol Channel and Severn estuary, UK. The predictions by the present model are compared with field data and those by non-fractionated model.展开更多
A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynol...A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.展开更多
基金supported in part by the Special Fund for Basic Scientific Research Business Expenses of Central Public Welfare Scientific Research Institutes under Grant TKS20210103the Open Fund of Key Laboratory of Ocean Observation Technology,Ministry of Natural Resources of China(2021klootA06).
文摘River bending is the major effect responsible for bed topography and bank changes.In this study,fluid velocity(measured by a three-dimensional Doppler advanced point current meter)and bed topographical data have been collected in 40 sections of an experimental model.The whole flume was composed of an organic glass bend,upstream and downstream water tanks,two transition straight sections,a circulation pump,and a connection pipeline.Each section has been found to be characterized by a primary circulation and a small reverse circulation,with some sections even presenting three more or more circulation structures.The minimum circulation intensity has been detected in proximity to the top of the curved channel,while a region with small longitudinal velocity has been observed near the concave bank of each bend,corresponding to the flat bed formed after a short period of scouring.The maximum sediment deposition and scour depth in the presence of a uniform distribution of living flexible vegetation within 10 cm of the flume wall have been found to be smaller than those observed in the tests conducted without vegetation.
基金supported by the National Key Research and Development Program of China(Grants No.2016YFC0402307 and 2016YFC0402103)the National Natural Science Foundation of China(Grant No.51520105014).
文摘The Three Gorges Project(TGP)has changed the flow-sediment process in the middle Yangtze River.For navigation purposes,there is an urgent need to study the changes of the river regime over a long-term period and the shoal-channel evolution over different seasons since the completion of the TGP.Based on analysis of the measured data and the results of a two-dimensional mathematical model,the changes of the river regime and river bed evolution in the Yaojian reach downstream of the TGP were studied.Results show that a high sediment transport flux helps to keep the main flow in the North Branch,while a low sediment transport flux helps to keep the main flow in the South Branch.Thus,the main branch will not change in the near future because of the low sediment transport load.In this study,the flow-sediment process adjusted by the TGP was restored to the conditions before the TGP,and the river bed evolution under the adjusted and non-adjusted flow-sediment conditions was calculated.After the completion of the TGP,the reservoir storage accelerated the flood recession process and decreased the erosion by 11.9%under the flow-sediment conditions in 2010,and the deposition in the flood season decreased by 56.4%.
基金Project supported by the Key Project of National Natural Science Foundation of China(Grant No.51039002)the State Key Laboratory of Hydroscience and Engineering,Tsinghua University(Grant No.2009-TC-2)supported by the Tsinghua University Initiative Scientific Research Program(Grant No.2009THZ07060)
文摘This article discusses the process of sediment transport and proposes a morphological model to predict the bed evolution in estuaries. The hydrodynamic module is based on an existent model-Depth Integrated Velocity And Solute Transport （DIVAST） and the wetting and drying method is adopted to deal with the moving boundary. Both cohesive sediment and non-cohesive sediment are taken into consideration in the sediment transport module with the capability of simulating the transport of graded sediments under non-equilibrium conditions. The fall velocity of the suspended sediment is modified in the present model due to the high sediment concentration. A 3-layer approach is adopted to simulate the variations of sediment gradations of bed materials. Furthermore, the model is used to simulate the bed evolution in the Yellow River Delta （YRD） from 1992 to 1995. Field data are used to calibrate the parameters. The numerical results show how the morphology was developed in the Yellow River Estuary with a good agreement with the field data.
文摘In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well asacidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning andcorrelation analyses of CaCO_3, C / P_2O_5, Fe^(2+) / Fe^(3+), pH and Eh values, taking the Xiaodukou section in theNihewan basin as an example. The CaCO_3, C / P_2O_5 and pH were calculated respectively using the optimalpartitioning method. Thus five cold zones and six warm zones as well as five reduction and six oxidation zoneswere distinguished. Then the inductive method was used to produce four numerical groups: 8.10, 8.3-8.4,8.6-8.7 and 8.9-8,97. The above-mentioned results are respectively based on CaCO_3 content, C/P_2O_5 andpH values. From Fig. 3, Tables 1 and 2 it can be seen that the Nihewan Beds were formed mainly under a re-duction and slightly alkaline environment of cold climate, with pH values of 8.3-8.4. Fig. 3 shows that bed 35is approximately near the boundary between the Brunhes and Matuyama polarity epochs, 0.73 Ma in age; bed26 is roughly near the Jaramillo event (base), 0.97 Ma in age; bed 18 coincides roughly with themagnetostratigraphic boundary of 2.00 Ma (?). Bed 13 may be the Pleistocene-Pliocene boundary, 2.48 Ma inage. Thus geochemical zones Ⅰ, Ⅱ, Ⅲ and Ⅳ include respectively cold zones 1; 2 and 3; 4; and 5.
基金financially supported by the Science Foundation of China University of Petroleum,Beijing(Grant Nos.2462015YQ0213 and 2462017BJB02)
文摘A two-dimensional depth-integrated numerical model is refined in this paper to simulate the hydrodynamics, graded sediment transport process and the fate of faecal bacteria in estuarine and coastal waters. The sediment mixture is divided into several fractions according to the grain size. A bed evolution model is adopted to simulate the processes of the bed elevation change and sediment grain size sorting. The faecal bacteria transport equation includes enhanced source and sink terms to represent bacterial kinetic transformation and disappearance or reappearance due to sediment deposition or re-suspension. A novel partition ratio and dynamic decay rates of faecal bacteria are adopted in the numerical model. The model has been applied to the turbid water environment in the Bristol Channel and Severn estuary, UK. The predictions by the present model are compared with field data and those by non-fractionated model.
基金Supported by the National Natural Science Foundation of China(Nos.51579036,51579030)the Fundamental Research Funds for the Central Universities of China(No.DUT14YQ108)
文摘A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.
