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| 1 | Numerical modelling of riverbed grain size stratigraphic evolution显示文摘For several decades,quantification of riverbed grain size stratigraphic evolution has been based upon the active layer formulation(ALF),which unfortunately involves considerable uncertainty.While 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 flow.Here 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 layer.Together 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 observations.This is illustrated for typical cases featuring bed aggradation and degradation due to graded bed-load sediment transport.Systematic experiments on graded sediment transport by unsteady flows are warranted for further testing the modified formulation. | Peng HU Zhi-xian CAO Gareth PENDER Huai-han LIU | 2014 | International Journal of Sediment Research2014，29，3： | 9 |
| 2 | Non-capacity transport of non-uniform bed load sediment in alluvial rivers显示文摘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. | CAO Zhi-xian HU Peng PENDER Gareth LIU Huai-han | 2016 | Journal of Mountain Science2016，13，3： | 7 |
| 3 | Coupled 2D Hydrodynamic and Sediment Transport Modeling of Megaflood due to Glacier Dam-break in Altai Mountains,Southern Siberia显示文摘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 Siberia.Computational modeling is one of the viable approaches to enhancing the understanding of the flood events.The 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 model.Here the Open MP(Open Multiprocessing) technique is adopted to parallelize the code of a coupled 2D hydrodynamic and sediment transport model.It is shown that the computational efficiency is enhanced by over 80% due to the parallelization.The floods over both fixed and mobile beds are well reproduced with specified discharge hydrographs at the dam site.Qualitatively,backwater effects during the flood are resolved at the bifurcation between the Chuja and Katun rivers.Quantitatively,the computed maximum stage and thalweg are physically consistent with the field data of the bars and deposits.The effects of sediment transport and morphological evolution on the flood are considerable.Sensitivity 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. | HUANG Wei CAO Zhi-xian Paul CARLING Gareth PENDER | 2014 | Journal of Mountain Science2014，11，6： | 5 |
| 4 | Well-balanced numerical modelling of non-uniform sediment transport in alluvial rivers显示文摘The last two decades have witnessed the development and application of well-balanced numerical models for shallow flows in natural rivers.However,until now there have been no such models for flows with non-uniform sediment transport.This paper presents a 1D well-balanced model to simulate flows and non-capacity transport of non-uniform sediment in alluvial rivers.The active layer formulation is adopted to resolve the change of bed sediment composition.In 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 equations.The 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 failure.The agreement between the computed results and measured data is encouraging.Compared to a non-well-balanced model,the well-balanced model features improved performance in reproducing stage,velocity and bed deformation.It should find general applications for non-uniform sediment transport modelling in alluvial rivers,especially in mountain areas where the bed topography is mostly irregular. | Honglu Qian Zhixian Cao Gareth Pender Huaihan Liu Peng Hu | 2015 | International Journal of Sediment Research2015，30，2： | 4 |
| 5 | Full 2D Hydrodynamic Modelling of Rainfall-induced Flash Floods显示文摘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. | HUANG Wei CAO Zhi-xian QI Wen-jun Gareth PENDER ZHAO Kai | 2015 | Journal of Mountain Science2015，12，5： | 4 |
| 6 | Coupled flood and sediment transport modelling with adaptive mesh refinement显示文摘Coupled flood and sediment transport modelling in large-scale domains has for long been hindered by the high computational cost.Adaptive mesh refinement is one of the viable ways to solving this problem without degrading the accuracy.This goal can be accomplished through mesh adaptation,e.g.,mesh coarsening and refining based on the dynamic regime of the flow and sediment transport along with bed evolution.However,previous studies in this regard have been limited to cases either without involving sediment transport or featuring flow-sediment-bed decoupling and the assumption of sediment transport capacity,which are not generally justified.Here,a coupled hydrodynamic and non-capacity sediment transport model is developed on adaptive non-uniform rectangular mesh.The proposed model is validated against experimental tests and numerical results based on the fixed meshes.It is demonstrated that the proposed model can properly capture shock waves,resolve the wetting/drying transition and reproduce morphological evolution.Compared with models based on the fixed meshes,the proposed model features great advantage in computational efficiency and holds promise for wide applications. | HUANG Wei CAO ZhiXian PENDER Gareth LIU QingQuan CARLING Paul | 2015 | Science China(Technological Sciences)2015，58，8： | 4 |
| 7 | Experimental investigations of graded sediment transport under unsteady flow hydrographs显示文摘自然河的隧道能在不稳定的流动条件下面处于沉积运输率经历重要变化,特别在洪水自记水位计事件期间。目前然而,处于分级的沉积运输率有在不稳定的自记水位计流动性质和时间的可变性之间的相互作用的理解的不同缺乏。在当前的学习,一系列参量的实验被进行调查二等级的沉积床的反应到不同不稳定的自记水位计流动条件的一个范围。全部、部分的水流带来的碎石沉积运输率的调查在自记水位计上在运输揭示了强壮的时间的变化,与尺寸依赖者时间落后在山峰流动条件和山峰水流带来的碎石之间观察的效果搬运率。明确地,粗糙的石子在自记水位计的升起的手足期间增加了活动性,也达到他们的山峰水流带来的碎石运输率在以前,或接近山峰流动条件。由对比,更好的等级趋于在自记水位计的后退的手足期间提高了活动性,与在山峰流动条件过去了以后,测量的山峰运输率。测量从的谷物尺寸分布收集了样品也显示了材料在后退的手足期间在升起的手足和 fining 上变粗的水流带来的碎石,当床的相应图象分析大小出现时,作文在自记水位计上显示出仅仅边缘的变化。全部、部分的沉积收益的计算表明测试的 bimodal 沉积混合在测试的所有自记水位计条件上比单峰的混合以显著地更高的率被搬运。这发现显示单峰的沉积床由于中型的石子在单峰的沉积等级介绍的增加的许多内在地是比 bimodal 床更稳定的。在学习建立的参量的依赖在洪水流动自记水位计下面在自然河的隧道以内在分级的沉积运输过程上的床表面和他们的影响为部分内部小粒的效果的改进理解有清楚的含意。 | Le Wang Alan J.S. Cuthbertson Gareth Pender Zhixian Cao | 2015 | International Journal of Sediment Research2015，30，4： | 4 |
| 8 | 明渠挟沙水流双层积分模式的双曲性分析显示文摘将明渠挟沙水流双层积分模式的控制方程系分别作为单一系统和两个降阶的双曲性系统,分析、比较其特征值;结合溃坝挟沙水流和水库挟沙水流等两类典型的强分层挟沙水流,研究其双曲性.分析表明,尽管作为单一系统和两个降阶的系统时,特征值在定量上有差异,但在所涉及的参数域内,双曲性仍然得以保持,并不引发Kelvin-Helmholtz失稳现象.作为应用实例,对水库异重流进行数值模拟研究.结果表明,在所应用的参数范围内,显著增加水库清水泄流量并未导致异重流失稳,且可明显提高排沙比,减少水库泥沙淤积. | 李季 曹志先 PENDER Gareth 刘青泉 | 2015 | 中国科学:物理学、力学、天文学2015，45，10： | 2 |
| 9 | Graded and uniform bed load sediment transport in a degrading channel显示文摘Twenty runs of experiments are carried out to investigate non-equilibrium transport of graded and uniform bed load sediment in a degrading channel.Well-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%sand.For 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 models.The data shows that in a degrading channel,the sand greatly promotes the transport of gravel,whilst the gravel considerably hinders the transport of sand.The promoting and hindering effects are evaluated by means of impact factors defined based on sediment transport rates.The impact factors are shown to vary with flow discharge by orders of magnitude,being most pronounced at the lowest discharge.It 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. | Zhijing Li Zhixian Cao Huaihan Liu Gareth Pender | 2016 | International Journal of Sediment Research2016，31，4： | 2 |
| 10 | Flood hydraulics due to cascade landslide dam failure 显示文摘 | Cao Zhixian Yue Zhiyuan Pender Gareth | 2011 | Journal of Flood risk Management2011，，4： | 1 |
| 11 | Numerical Analysis of Adaptation-to-capacity Length for Fluvial Sediment Transport显示文摘Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,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 justified.Here we present a numerical investigation on this issue.The 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 concentrations.It is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or reduces.For cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse number.Quantitatively,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 depth.The 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. | LI Zhi-jing CAO Zhi-xian Gareth PENDER HU Peng | 2014 | Journal of Mountain Science2014，11，6： | 1 |
| 12 | Numerical modelling of alluvial rivers subject to interactive sediment mining and feeding 显示文摘 | Cao Zhixian Gareth Pender | 2004 | Advances in Water Resources2004，27，5： | 1 |
| 13 | Numerical modelling of alluvial rivers subject to interactive sediment mining and feeding 显示文摘 | Zhixian Cao Gareth Pender | 2004 | Advances in Water Resources v 27 n 5 May2004，，： | 1 |
| 14 | 风沙与水沙运动多重时间尺度与深度积分模式显示文摘针对风沙与水沙动力学研究的共性,提出风沙与水沙运动统一深度积分模式;在此基础上,将水沙运动过程多重时间尺度理论扩展至风沙运动,比较研究风沙与水沙运动向平衡状态调整的时间尺度特征.数值算例与风洞实验结果对比表明,积分平均模型能够基本准确地捕捉风沙运动的输沙率变化等基本特征;风沙与水沙运动的积分时间尺度比较分析表明,风沙运动与水沙运动类似,推移质运动能够很快地调整到平衡状态,而悬移质运动调整到平衡状态则需要相对较长的过程,在湍流悬移质实验和数值模拟研究中应考虑恢复平衡过程的影响. | 李志晶 曹志先 胡鹏 Gareth Pender | 2013 | 力学学报2013，45，2： | 1 |
| 15 | Enhanced bed load sediment transport by unsteady flows in a degrading channel显示文摘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. | Zhijing Li Honglu Qian Zhixian Cao Huaihan Liu Gareth Pender Penghui Hu | 2018 | International Journal of Sediment Research2018，33，3： | 1 |
| 16 | A depth-averaged two-phase model for debris flows over fixed beds显示文摘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 beds.Incorporating 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. | Ji Li Zhixian Cao Kaiheng Hu Gareth Pender Qingquan Liu | 2018 | International Journal of Sediment Research2018，33，4： | 0 |
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