冲积河流推移质输沙最优河道形态影响因素理论分析

为从理论上确定水沙动力、阻力和边界条件对冲积河流推移质输沙最优河道形态和最小比降的影响,基于 水力半径分割方法将河床整体糙率划分为河岸糙率和河底糙率;采用河道形态自动调整变分方法,以等腰梯形为 河道过水断面,推导推移质输沙率与河道形态的关系,分析河岸与河底相对糙率、河岸坡角、流量、输沙率、中值 粒径和河底糙率对最优河道形态和最小比降的影响。结果表明：最优河道形态和最小比降随河岸与河底相对糙 率的增大而减小,随河岸坡角的增大而增大。流量或者河底糙率的增加将使最小比降减小,同时造成最优河道形 态趋向窄深。输沙率或者中值粒径的增加将使最小比降增大,但两者对最优河道形态演变的影响不同,输沙率增 大将使最优河道形态向宽浅发展,而中值粒径增加将使最优河道形态向窄深发展。     

清水冲刷不连续宽级配床面阻力特性及输沙规律试验研究(Ⅰ)——床面阻力特性

不连续宽级配床沙在天然河道中广泛存在,作为非均匀沙的特殊类型,其床面阻力与一般意义上的非均匀床面相比具有不同的特性。本文通过水槽试验对不连续宽级配床面阻力特性进行了探讨,引入峰度系数表征粗糙床面床沙粒径的非均匀性,将不连续宽级配床面与连续宽级配床面统一起来,根据试验数据拟合得到不连续宽级配床面阻力系数表达式,具有较好的精度。     

山区河流河床形态对推移质输沙率影响的试验研究

为探索山区卵砾石河流推移质运动受水流条件和河床形态的影响规律,开展了大比降浅水流动条件下卵砾石输移的室内水槽试验,获得了两组泥沙组成的19个流量条件下的水流、泥沙及河床三维地形场数据。结合室内水槽试验及文献中的天然河流输沙观测数据,分析了不同水沙输移阶段水流阻力、河床形态与推移质运动之间的关系。试验结果表明:河床阻力系数随着河床形态强度参数增大而增大,形态阻力与河床形态强度参数相关性更强。在泥沙补给充分阶段,推移质输沙率与床面阻力、形态阻力及河床形态强度参数均呈正相关关系;在泥沙补给不充分的水流冲刷阶段,推移质输沙率随河床形态强度参数增大而减小。     

含植物河道等效床面阻力试验研究

植物广泛存在于滩地和河槽中,可有效改善水环境,但同时也增加了水流阻力。通常采用不同材料的棍状物或仿生植物模拟实际植物进行试验研究,将植物阻力附加于床面上与原床面阻力一起构成等效床面阻力,因模拟实际植物的不相似导致含植物河道等效床面阻力的研究不够完善。本文提出了对实际植物分区施加实际流速条件进行试验的思路,即按河道现场调研的植物密度布置,沿横向和垂向对河道横断面分区,对实际植物区域施加实际流速条件,试验研究分区水体中的植物阻力,最后换算得到表征等效床面阻力的等效床面糙率。以独流减河上游河道为对象,选用乔木、灌木和芦苇三种典型植物,考虑河道横断面不同分区的流速条件进行了试验,结果表明,当遭遇100年一遇洪水时,乔木种植区域的等效床面糙率为0.060～0.066,灌木种植区域的等效床面糙率为0.083～0.099,芦苇种植区域的等效床面糙率为0.698～0.989。研究成果可为防洪计算和水环境治理提供理论支持。     

砂质河床与砾石河床的河型判别研究

砂质河床与砾石河床在水力学特征与泥沙运动特征方面都有较大差异，由此导致了河型特征的差异。本研究以世界上近200条河流的资料为基础，在建立同时适用于砂质与砾石河床河型判别统一关系方面进行了尝试。以水流切力、河流功率以及无量纲切力Sd/D50来表示水流强度，而以宽深比和无量纲河宽来间接反映河岸约束性，从而在一定程度上克服了河岸约束性难以定量表达的困难。研究发现，上述水流强度变量和河岸约束性变量的组合关系，在具有不同河型的砂质与砾石河床之间表现出较大的差异，从而实现了对砂质河床与砾石河床河型的定量判别，得到了一系列的沙质与砾石河床河型的判别关系。     

D-jump in rough sloping channels at low Froude numbers

Hydraulic jump is a phenomenon which usually occurs in rivers and in correspondence with hydraulic structures. It is characterized by a rapid transition from a super- to sub-critical flow conditions, involving a huge energy dissipation. For its characteristics and its relevance in hydraulics, it has been studied since the early years of the last century. Nevertheless, many features still require a further investigation, e.g., scale effects, air entrainment process, effect of bed roughness on conjugate depths, etc. In particular, in the last few decades, the analysis of the main geometric parameters has been further developed. Nevertheless, no studies dealing with D-jump occurring on a rough sloping channel are present in literature. Therefore, the present paper reports the results of experimental investigations, which allowed to develop a semi-theoretical approach in order to evaluate the D-jump conjugate depth in a wide range of channel bed geometric and boundary configurations.     

Flow Resistance in Lowland Rivers Impacted by Distributed Aquatic Vegetation

Water Resources Management - This study addressed a research concern that employing a fixed value for the bed roughness coefficient in lowland rivers (mostly sand-bed rivers) is deemed practically...     

TURBULENT FLOWS AROUND SAND DUNES IN ALLUVIAL RIVERS

The sand dunes are typical bed forms of natural alluvial rivers.In this article,a vertical 2-D Reynolds stress model is established for the simulation of turbulent flows around sand dunes,and water-sand boundary conditions are set with particular attention.By numerical simulations,the following conclusions can be drawn.(1) The flow resistance in rivers with sand dunes could be divided into the sand-grain resistance and the sand dune resistance,and the sand-grain resistance coefficient mainly depends on Reyn...     

动床床面阻力公式的比较研究

选择了21个有代表性的冲积河流动床床面阻力公式，利用近10000组水槽和天然河道实测资料，全面客观地比较了这些公式在已知单宽流量、能坡和泥沙粒径时，计算水深的精度。对水槽资料和天然河道资料分别给出了各公式的计算精度，可供有关泥沙研究人员参考。其中Peterson和Peterson公式是其中精度最高的公式。     

DETERMINATION OF RESISTANCE TO FLOW IN ICECOVERED CHANNELS USING SEMI-LOGARITHMIC VELOCITY DISTRIBUTION

1.INTRODUCTIONTheformationoficecoveronflowingwatergreatlyaltersflowcharacteristics,resultinginthechangeofvelocitydistributionandtheincreaseofflowdepthincomparisonwithfreesurfaceflowwiththesamedischargeduetotheincreasedresistancecausedbyanadditionalsolidboundary.Fromengineeringpointofview,estimationofconveyingcapacityofice--coveredstreams,orcalculationofwatersurfaceprofilealongriverreachwithicecoverisveryoftenrequiredinrivermanagementinvolvingtheoperationofreservoirswhenreleasesbaseduponthe…     

Longitudinal variations of hydraulic characteristics of overland flow with different roughness简

The evolution of the overland flow velocity along the distance downslope on smooth and granular beds in different cases is investigated by means of the electrolyte tracer via flume experiments.The results demonstrate that a non-uniform flow regime and a uniform flow regime exist in the development process of the overland flow.Owing to the different attributes of beds’roughness,the position of those zones with different flow regimes varies correspondingly:(1)the overland flow on granular beds enters into the uniform regime much sooner,additionally,the roll waves tend to appear because of the presence of the proper flow resistance imparted by the roughness(coarse sands),and large slopes(20o and 25o)which makes the flow velocities and depths to undulate spatially.Furthermore,the flow resistance of the overland flows with different roughness elements,that is the non-sands,the fine sands and the coarse sands,is calculated.A quadratic interpolation method of the third order accuracy is employed in the calculation of the longitudinal flow resistance.The results show that it is rational to use the bed slope to approximate the hydraulic energy slope over a relative small roughness(the present roughness),however on the other hand,if the mean flow velocities and depths rather than the local parameters are used to calculate the flow resistance,a considerable error will be induced within the non-uniform regime of the overland flows,including the acceleration zone and the roll-wave zone.     

利用河流平衡理论检验推移质输沙函数的应用性

推移质输沙函数多根据试验资料建立,在实际应用中往往会给出相去甚远的预测,对河流平衡形态影响显著。本研究利用河流平衡理论检验推移质输移通式Φ=cb(τ0*-τ*c)β中各参数对河道平衡形态的影响,式中Φ为无量纲推移质输沙强度,τ0*为无量纲水流平均剪切应力,cb、τ*c和β为输沙参数,分别代表输沙系数、无量纲水流临界剪切力和输沙指数。引入河道过水断面的宽度与平均水深的比值作为表征断面形态的无量纲参数,基于变分原理的图形分析结果表明,输沙通式中指数β的选取是影响平衡河道形态的重要因素。结合长江中游监利河段河道形态实际观测数据,对比分析已有推移质输沙函数对河道平衡形态的定量影响,结果表明β=5/3时河流平衡理论具有很好的实际应用性。     

Analysis of dynamic wave model for flood routing in natural rivers

Flooding is a common natural disaster that causes enormous economic, social, and human losses. Of various flood routing methods, the dynamic wave model is one of the best approaches for the prediction of the characteristics of floods during their propagations in natural rivers because all of the terms of the momentum equation are considered in the model. However, no significant research has been conducted on how the model sensitivity affects the accuracy of the downstream hydrograph. In this study, a comprehensive analysis of the input parameters of the dynamic wave model was performed through field applications in natural rivers and routing experiments in artificial channels using the graphical multi-parametric sensitivity analysis (GMPSA). The results indicate that the effects of input parameter errors on the output results are more significant in special situations, such as lower values of Manning’s roughness coefficient and/or a steeper bed slope on the characteristics of a design hydrograph, larger values of the skewness factor and/or time to peak on the channel characteristics, larger values of Manning’s roughness coefficient and/or the bed slope on the space step, and lower values of Manning’s roughness coefficient and/or a steeper bed slope on the time step and weighting factor.     

河岸与河底相对粗糙度对河道平衡形态的影响研究

边界条件对河流地貌形态具有重要影响,基于河道边界阻力水力半径分割方法,利用变分方法研究河岸与河底相对粗糙度对冲积河流平衡河道形态的影响。结果表明,河岸与河底相对粗糙度对河流达到平衡时的最大输沙率有一定的影响,但对河道平衡形态的影响非常显著。在临界和平均水力几何形态关系式中,随着河岸与河底相对粗糙度的增大,河宽关系式的系数逐渐减小,水深关系式的系数逐渐增大,但控制变量,特别是流量的指数变幅很小。     

考虑浆体黏度的泥石流流速计算方法

泥石流浆体黏度通过影响泥石流内、外部的阻力特征影响泥石流的糙率系数,泥石流糙率系数与浆体黏度之间的关系还没有基于观测数据的定量表述。通过对云南东川蒋家沟泥石流观测资料的分析,研究泥石流糙率系数与浆体黏度之间的关系,并通过回归分析得到考虑浆体黏度的泥石流糙率系数计算公式,最后基于此构建了考虑浆体黏度的泥石流流速计算公式。结果表明,随着泥石流浆体黏度的增加,泥石流糙率系数逐渐增加,浆体黏度在宏观上表现为增阻作用,考虑浆体黏度的泥石流流速计算公式改进了现有公式在计算浆体黏度较高的泥石流流速中的不足。研究结果可为进一步研究浆体黏度对泥石流运动阻力的影响提供参考,也为工程实践中的流速计算和增阻消能设计提供新的思路。     

INCIPIENT MOTION OF NON-COHESIVE SEDIMENT UNDER ICE COVER - AN EXPERIMENTAL STUDY

Based on a series of experiments under both ice-covered and free surface conditions, the present article discusses the role of flow velocity and critical shear Reynolds number for incipient motion of bed material. The influence of the resistance coefficients of both the underside of the ice cover and the channel bed on the location of the maximum velocity has been discussed. In addition, the impacts of ice and composite resistance coefficients on flow velocity for incipient motion of bed material have been assessed. The diagram describing the critical shear Reynolds number and the dimensionless shear stress for the incipient motion of sediment under ice covered conditions with different under cover resistance coefficient has been established. The effects of grain size on densimetric Froude number for incipient motion of bed material have been investigated. A relationship between the densimetric Froude number for incipient motion of bed material and the median grain size of bed material as well as the roughness coefficient of channel bed and roughness coefficient of ice cover has been established.     

Distribution and Prediction of Boundary Shear in Diverging Compound Channels

Measurement of bed shear stress is always a challenging task for engineers. In river engineering, bed shear is a fundamental variable and is important in estimating flow resistance and sediment transport. In this study, experiments are carried out in diverging compound channel with smooth bed (perspex sheet) and rough bed (Gravel) conditions to determine the effect of roughness. The shear velocity is estimated from universal logarithmic law. The effect of geometry and roughness on Von-Karman constant, eddy viscosity coefficient, friction factor is studied. The mass conservation and momentum conservation equations are used to derive apparent shear forces at interface of main channel and floodplain. A genetic algorithm model is developed to predict percentage of shear force (%Sfp) carried by sub-sections. To perform better with less and unseen data K-Fold cross-validation technique is used. The model is compared with available models in literature and it is observed that developed model gave better predictions with low MAPE.

     

不同布置形态下刚性淹没植被对水流特性的影响

自然河道中植被呈现多种多样的分布状态,为探究不同布置形态下刚性淹没植被对水流特性的影响,利用室内水槽模拟含刚性淹没植被的明渠进行试验研究。结果表明:刚性淹没植被的布置形态对明渠流水流特性影响显著。在本文研究的植被布置形态下的水深、植被阻力系数与植被粗糙系数均增大,表现为交错型布置斑块型布置线性布置;流速与雷诺数均减小,表现为线性布置斑块型布置交错型布置;糙率n随着平均流速与水力半径之积VR的增大而减小。     

汉江丹江口水库下游河床下伏卵石层对河床调整的影响

以二十余年的观测资料为基础，对汉江丹江口水库下游河床过程中下伏卵石层的作用进行了系统的分析。在沙质河床中存在着下伏卵石层的情况下，卵石层的暴是使河床下切受到报制的决定性因素。随着卵石层的暴露，河床糙率将急剧增大，局部河床将不得不采取加大比降的方式进行补偿。     

The effect of a local mesh refinement on hydraulic modelling of river meanders

Large-scale river models are generally discretized by relatively large mesh cells resulting in bathymetry discretization errors and numerical effects. These hydraulic models are generally calibrated by altering the bed roughness to compensate for these errors and effects. Consequently, the calibrated roughness values are mesh-dependent while generally local mesh refinements are executed after model calibration to study the effects of river interventions. This study shows both the errors caused by bathymetry discretization and numerical effects for locally refined meshes. First, schematised river meanders with a flat bed in the transverse flow direction are analysed to isolate the induced numerical effects by the mesh. Afterwards, a case study is considered to verify if similar mesh influences are found in natural river meanders. Curvilinear, triangular and hybrid (combination of curvilinear and triangular cells) meshes are used with different resolutions. The analysis shows that in the schematised river meanders lower depth-averaged flow velocities and larger water depths are simulated with coarser meshes. In the case study, substantial differences in hydrodynamics between the meshes are obtained suggesting that the bathymetry discretization is more influential than the numerical effects. Finally, it was found that triangular meshes, and rivers with narrow meander bends, are most sensitive to mesh resolution. Especially in these cases, it is desirable to refine the mesh at the desired locations before model calibration.