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Coupled 2D Hydrodynamic and Sediment Transport Modeling of Megaflood due to Glacier Dam-break in Altai Mountains,Southern Siberia

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Journal of Mountain Science 2014年第6期11卷 1442-1453页

作者： HUANG Wei CAO Zhi-xian Paul CARLING gareth pender State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Institute for Infrastructure and Environment Heriot-Watt University School of Geography University of Southampton

One of the largest known megafloods on earth resulted from a glacier dam-break,which occurred during the Late Quaternary in the Altai Mountains in Southern *** modeling is one of the viable approaches to enhancing the understanding of the flood *** computational domain of this flood is over 9460 km2 and about 3.784 × 106 cells are involved as a 50 m × 50 m mesh is used,which necessitates a computationally efficient *** the Open MP(Open Multiprocessing) technique is adopted to parallelize the code of a coupled 2D hydrodynamic and sediment transport *** is shown that the computational efficiency is enhanced by over 80% due to the *** floods over both fixed and mobile beds are well reproduced with specified discharge hydrographs at the dam ***,backwater effects during the flood are resolved at the bifurcation between the Chuja and Katun ***,the computed maximum stage and thalweg are physically consistent with the field data of the bars and *** effects of sediment transport and morphological evolution on the flood are *** analyses indicate that the impact of the peak discharge is significant,whilst those of the Manningroughness,medium sediment size and shape of the inlet discharge hydrograph are marginal.

关键词： Glacier dam-break flood Well-balanced 2D hydrodynamic and sediment transport model Open MP parallelization

Numerical Analysis of Adaptation-to-capacity Length for Fluvial Sediment Transport

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Journal of Mountain Science 2014年第6期11卷 1491-1498页

作者： LI Zhi-jing CAO Zhi-xian gareth pender HU Peng State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University School of the Built Environment Heriot-Watt University Department of Ocean Science and Engineering Zhejiang University

Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological ***,it remains poorly understood if the adaptation to capacity could be fulfilled instantly in response to differing inflow discharges and sediment supplies,and thus if the calculation of morphological changes in rivers based on the assumed capacity status is fully *** we present a numerical investigation on this *** distance required for sediment transport to adapt to capacity(i.e.,adaptation-to-capacity length) of both bed load and suspended sediment transport is computationally studied using a coupled shallow water hydrodynamic model,in line with varied inlet sediment *** is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or *** cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse ***,the adaptation-to-capacity length of bed load sediment is limited to tens of times of the flow depth,whilst that of suspended sediment increases substantially with decreasing Rouse number and can be up to hundreds of times of the flow *** present finding concurs that bed load sediment transport can adapt to capacity much more rapidly than suspended sediment transport,and it facilitates a quantitative criterion on which the applicability of bed load or suspended sediment transport capacity for natural rivers can be readily assessed.

关键词： Sediment transport Sediment transport capacity Mathematical river modeling Bed load Suspended load

Non-capacity transport of non-uniform bed load sediment in alluvial rivers

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Journal of Mountain Science 2016年第3期13卷 377-396页

作者： CAO Zhi-xian HU Peng pender gareth LIU Huai-han State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Wuhan 430072 China Institute for Infrastructure and Environment Heriot-Watt University Edinburgh EH14 4AS UK Ocean College Zhejiang University Hangzhou 316021 China Changjiang Waterway Bureau Wuhan 430010 China

Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.

关键词： Fluvial process Sediment transport Bed deformation Non-uniform bed load Capacity transport

Numerical modelling of riverbed grain size stratigraphic evolution

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International Journal of Sediment Research 2014年第3期29卷 329-343页

作者： Peng HU Zhi-xian CAO gareth pender Huai-han LIU Ocean College Zhejiang University State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Institute for Infrastructure and Environment Heriot-Watt University Institute for Infrastructure and Environment Heriot-Watt University State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Yangtze Waterway Planning Design and Research Institute

For several decades,quantification of riverbed grain size stratigraphic evolution has been based upon the active layer formulation(ALF),which unfortunately involves considerable *** it is the sediment exchange across the bed surface that directly affects the riverbed stratigraphy,it has been assumed in the ALF that the sediment fraction at the lower interface of the active layer is a linear function of the sediment fraction in the *** it is proposed that the sediment fraction of the sediment exchange flux is used directly in estimating the sediment fraction at the lower surface of the active *** with the size-specific mass conservation for riverbed sediment,the modified approach is referred to as the surface-based formulation(SBF).When incorporated into a coupled non-capacity modelling framework for fluvial processes,the SBF leads to results that agree as well or better than those using ALF with laboratory and field *** is illustrated for typical cases featuring bed aggradation and degradation due to graded bed-load sediment *** experiments on graded sediment transport by unsteady flows are warranted for further testing the modified formulation.

关键词： Bedload Riverbed grain size stratigraphy Active layer formulation Surface-based formulation Numerical modelling

Graded and uniform bed load sediment transport in a degrading channel

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International Journal of Sediment Research 2016年第4期31卷 376-385页

作者： Zhijing Li Zhixian Cao Huaihan Liu gareth pender State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Changjiang River Scientific Research Institute School of the Built Environment Heriot-Watt University Yangtze River Waterway Bureau

Twenty runs of experiments are carried out to investigate non-equilibrium transport of graded and uniform bed load sediment in a degrading ***-sorted gravel and sand are employed to compose four kinds of sediment beds with different gravel/sand contents,i.e.,uniform 100%gravel bed,uniform 100%sand bed,and two graded sediment beds respectively with 53%gravel and 47%sand as well as 22%gravel and 78%*** different sediment beds,the experiments are conducted under the same discharges,thereby allowing for the role of sediment composition in dictating the bed load transport rate to be identified.A new observed dataset is generated concerning the flow,sediment transport and evolution of bed elevation and composition,which can be exploited to underpin developments of mathematical river *** data shows that in a degrading channel,the sand greatly promotes the transport of gravel,whilst the gravel considerably hinders the transport of *** promoting and hindering effects are evaluated by means of impact factors defined based on sediment transport *** impact factors are shown to vary with flow discharge by orders of magnitude,being most pronounced at the lowest *** is characterized that variations in sand or gravel inputs as a result of human activities and climate change may lead to severe morphological changes in degrading channels.

关键词： Sediment transport Bed load Gravel Sand Promoting Hindering

A depth-averaged two-phase model for debris flows over fixed beds

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International Journal of Sediment Research 2018年第4期33卷 462-477页

作者： Ji Li Zhixian Cao Kaiheng Hu gareth pender Qingquan Liu State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Institute of Mountain Hazards and Environment Chinese Academy of Sciences Institute for Infrastructure and Environment.Heriot-Watt University Edinburgh Campus Department of Mechanics Beijing Institute of Technology

A depth-averaged two-phase model is proposed for debris flows over fixed beds, explicitly incorporating interphase and particle-particle interactions, fluid and solid fluctuations and multi grain sizes. A firstorder model based on the kinetic theory of granular flows is employed to determine the stresses due to solid fluctuations, while the turbulent kinetic energy-dissipation rate model is used to determine the stresses from fluid fluctuations. A well-balanced numerical algorithm is applied to solve the governing equations. The present model is benchmarked against USGS experimental debris flows over fixed *** the stresses due to fluid and solid fluctuations and properly estimating the bed shear stresses are shown to be crucial for reproducing the debris flows. Longitudinal particle segregation is resolved, demonstrating coarser sediments around the fronts and finer grains trailing the head. Based on extended modeling exercises, debris flow efficiency is shown to increase with initial volume, which is underpinned by observed datasets.

关键词： Debris flow Two-phase model Depth-averaged model Fluctuation kinetic energy Multi grain sizes

Full 2D Hydrodynamic Modelling of Rainfall-induced Flash Floods

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Journal of Mountain Science 2015年第5期12卷 1203-1218页

作者： HUANG Wei CAO Zhi-xian QI Wen-jun gareth pender ZHAO Kai State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Changjiang Waterway Planning Design and Research Institute Office of Shanxi Provincial Flood Defense and Drought Relief Headquarters Institute for Infrastructure and Environment Heriot-Watt University Shanxi Provincial Hydrographic and Water Resources Survey Bureau

Mountain catchments are prone to flash flooding due to heavy rainfall. Enhanced understanding of the generation and evolution processes of flash floods is essential for effective flood risk management. However, traditional distributed hydrological models based on kinematic and diffusion wave approximations ignore certain physical mechanisms of flash floods and thus bear excessive uncertainty. Here a hydrodynamic model is presented for flash floods based on the full two-dimensional shallow water equations incorporating rainfall and infiltration. Laboratory experiments of overland flows were modelled to illustrate the capability of the model. Then the model was applied to resolve two observed flash floods of distinct magnitudes in the Lengkou catchment in Shanxi Province, China. The present model is shown to be able to reproduce the flood flows fairly well compared to the observed data. The spatial distribution of rainfall is shown to be crucial for the modelling of flash floods. Sensitivity analyses of the model parameters reveal that the stage and discharge hydrographs are more sensitive to the Manning roughness and initial water content in the catchment than to the Green-Ampt head. Most notably, as the flash flood augments due to heavier rainfall, the modelling results agree with observed data better, which clearly characterizes the paramount role of rainfall in dictating the floods. From practical perspectives, the proposed model is more appropriate for modelling large flash floods.

关键词： Flash flood Full hydrodynamic model Spatial distribution Rainfall

Well-balanced numerical modelling of non-uniform sediment transport in alluvial rivers

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International Journal of Sediment Research 2015年第2期30卷 117-130页

作者： Honglu Qian Zhixian Cao gareth pender Huaihan Liu Peng Hu State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Institute for Infrastructure and Environment Heriot-Watt University Yangtze River Waterway Bureau School of Ocean Science and Engineering Zhejiang University

The last two decades have witnessed the development and application of well-balanced numerical models for shallow flows in natural ***,until now there have been no such models for flows with non-uniform sediment *** paper presents a 1D well-balanced model to simulate flows and non-capacity transport of non-uniform sediment in alluvial *** active layer formulation is adopted to resolve the change of bed sediment *** the framework of the finite volume Slope Llmiter Centred(SLIC) scheme,a surface gradient method is incorporated to attain well-balanced solutions to the governing *** proposed model is tested against typical cases with irregular topography,including the refilling of dredged trenches,aggradation due to sediment overloading and flood flow due to landslide dam *** agreement between the computed results and measured data is *** to a non-well-balanced model,the well-balanced model features improved performance in reproducing stage,velocity and bed *** should find general applications for non-uniform sediment transport modelling in alluvial rivers,especially in mountain areas where the bed topography is mostly irregular.

关键词： Non-uniform:sediment transport Well-balanced scheme Irregular topography Shallow flow Mathematical river modelling

Enhanced bed load sediment transport by unsteady flows in a degrading channel

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International Journal of Sediment Research 2018年第3期33卷 327-339页

作者： Zhijing Li Honglu Qian Zhixian Cao Huaihan Liu gareth pender Penghui Hu State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University Changjiang River Scientific Research Institute Yangtze River Waterway Bureau School of Energy Geoscience Infrastructure and Society Heriot-Watt University

Laboratory flume experiments were done to investigate bed load sediment transport by both steady and unsteady flows in a degrading channel. The bed, respectively composed of uniform sand, uniform gravel,or sand-gravel mixtures, always undergoes bulk degradation. It is found that both uniform and nonuniform bed load transport is enhanced greatly by unsteady flows as compared to their volumeequivalent steady flows. This enhancement effect is evaluated by means of an enhancement factor, which is shown to be larger with a coarser bed and lower discharges. Also, the fractional transport rates of gravel and sand in non-uniform sand-gravel mixtures are compared with their uniform counterparts under both steady and unsteady flows. The sand is found to be able to greatly promote the transport of gravel, whilst the gravel considerably hinders the transport of sand. Particularly, the promoting and hindering impacts are more pronounced at lower discharges and tend to be weakened by flow unsteadiness.

关键词： Bed load Gravel Sand Unsteady flow Enhancement effect