Bed Sediment Characteristics in the Paraná and Paraguay Rivers

ABSTRACT

This paper presents a granulometric characterization of the Paraná and Paraguay rivers bed sediments. Samples obtained along 2,900 km of the thalweg of those rivers form the basis of this study. The main results and other features of the study are as follows: a) the bed sediment of both rivers is composed mainly of medium to fine well-sorted sands, with sizes in the Paraná slightly higher than those in the Paraguay river; b) the variations of mean diameters for both rivers are well correlated with the energy slopes. The correlation coefficient in the Paraguay river increases notably if the discharge and width/depth relationship variations along the channel are included in the regression; and, c) the origin of the transported sands could be related to the geologic characteristics of the Paraná river basin. An explanation is also suggested for the different bed sediment texture found in the Paraná de las Palmas and Paraná Guazú rivers in the lower delta. The explanation is based on the geomorphic processes that built that region of the Paraná river.     

Simulation of Runoff and Suspended Sediment Transport Rate in a Basin with Multiple Watersheds

Accurate runoff and suspended sediment transport rate models are critical for watershed management. In this study, a physiographic soil erosion–deposition (PSED) model is used in conjunction with GIS, to simulate the runoff and sediment transport process during storm events in a multi-watershed basin. This PSED model is verified using three typhoon events and 33 storm events in Cho-Shui River Basin, located in central Taiwan. Cho-Shui River Basin has 11 sub-watersheds displaying a variety of hydrologic and physiographic conditions as well as high concentrations of suspended sediment in river flow and a steep average channel bed slope of 2%. The results show the capability, applicability, and accuracy of the PSED model for multi-watershed basins.     

Avulsions in a Simulated Large Lowland Braided River

The understanding of the complicated braiding mechanisms in braided rivers is closely related to avulsions. They control the channel generation, migration and disappearance in large lowland braided rivers, and are considered to be the key factor that keeps the river maintaining a dynamic braided pattern. However, their occurring processes and mechanisms are still not well understood due to the lack of detailed measurements with sufficient temporal and spatial data covering multiple bifurcations. In the present study, a numerical model based on the physical process of hydrodynamics and sediment transport is used to simulate the suspended sediment transport and river channel evolution in braided rivers. The model predicted braiding processes are comparable to those observed in nature. Efforts are made to investigate the morphological processes that are key for river braiding. Three types of avulsions observed in natural rivers have been identified in the model predicted river and their evolution processes and controlling factors are examined based on the predicted flow velocity, sediment concentration, bed elevation and sediment size distribution. It was found that, a curving channel bend is the key factor in introducing a constriction avulsion, while the choking avulsion and apex avulsion are controlled by the water surface slope and bed elevation. They are mostly affected by the upstream channel pattern changes.     

黄河口泥沙输运三维数值模拟Ⅱ--河口双导堤工程应用

黄河口双导堤工程是继国家“八五”攻关项目:“延长清水沟流路行水年限”完成后提出的黄河口治理的重大工程设想。本文利用河口海岸三维数学模型(HEM-3D)对黄河口双导堤工程实施后河口高、中流量条件及低流量与东北风组合条件下的河口泥沙输送过程进行了数值计算。对比不同方案下的计算结果发现,当河口流量控制在1 500m3/s以上时,泥沙可以经由河口双导堤顺畅入海,在潮流作用下向导堤两侧输送,这对疏通河口拦门沙并进一步稳定黄河入海流路能够起到积极的作用。在低流量与东北大风的组合条件下,河口泥沙难以通过双导堤顺畅入海,大部分的泥沙可能会在导堤内部淤积。因此,在目前形势下如何通过水库调度保证充足的入海径流量是工程实施前需要深入研究的重要问题。     

Estimating Sediment Budget at a River Basin Scale Using a Process-Based Distributed Modelling Approach

The paper presents a process-based distributed modelling approach for estimating sediment budget at a river basin scale with partitions of suspended and bed loads by simulating sediment loads and their interactions. In this approach, a river basin is represented by hillslopes and a network of channels. Hillslopes are divided into an array of homogeneous grid cells for modelling surface runoff and suspended sediments. Channels are defined by incorporating flow hydraulic properties into the respective hillslope grids as sub-grid attributes for modelling both suspended and bed loads. Suspended sediment transport is modelled using one dimensional kinematic wave approximation of Saint-Venant’s principles of conservation of mass and momentum. Transport capacity of runoff or streamflow is used to set the limit of suspended sediment transport rate. Bed load in channels is estimated based on the instantaneous water and hydraulic parameters. Fractional interchange between suspended load and bed load is then back calculated. The performance of the model was evaluated through a case study application in a large river basin in Japan. The model satisfactorily calculated the sediment transport and total sediment budget in the basin. The simulated bed load was found to be reasonable and consistent with the water flow and suspended sediment flux. The results showed the bed load can be expressed as a linear function of the suspended load. The fractions of different sediment loads also exhibit linear relationships with water discharge for the rising and recession limbs of the flood hydrographs. The case study has demonstrated that the process-based distributed modelling approach can efficiently describe the basin-scale sediment budgets with due consideration of the suspended and bed loads and their interactions in the hillslopes and channels.     

高含沙水流二维数值模拟

一定条件下的高含沙水流具有非牛顿体特性，在天然多沙河流中由于地形分布等因素的影响。流动强度差异较大，往往呈现非牛顿体和牛顿体两种不同的流动特性，本文通过引进水流在不同流动状态下的特征，通过数值实验计算对模型进行了初步检验，计算结果与实际观测到的一些现象定性上完全吻合。     

小流域综合治理在水土保持中的特殊作用及发展途径

小流域综合治理在水土保持工作中的主要作用是 :提高土地生产力 ,使土地结构趋于合理 ,具有明显的拦沙效果 ,减轻水旱灾害等 .根据中国的具体情况 ,提出了几条对策 ,包括搞好农田基本建设 ,发展林果业 ,搞好植被建设和水土保持产业化 ,全方位综合治理等 ,以达到生态效益、经济效益、社会效益的互相统一 .     

河流水文学若干研究领域的回顾与展望

就 2 1世纪的产汇流理论、流域定量地貌、河流洪水、河流泥沙、河流热状况与冰情、河流资源利用、河流水质与河流生态环境等河流水文学主要研究领域的发展前景作了初步的展望 :要进一步揭示不同气候和下垫面条件下的产汇流规律 ,研制预测功能强的流域水文模型 ,发展和应用数字流域 ,深入揭示复杂条件下的洪水运动规律 ,提出高精度的分析计算方法 ;水流动力学与泥沙动力学相耦合的产沙计算方法将得到实际应用 ,河流输沙机理将进一步被揭示 ;继续探索河冰形成及河流冰情变化的热力学和水力学机理 ,完善冰凌数学模型 ,进一步揭示河流水流挟带污染物质的运动机理 ,完善水质模型 ,提高计算精度 ;要采用多学科综合的手段 ,深入探讨人类活动对河流生态系统的影响     

Digital Yellow River Model

Soil erosion is one of the key concerns in land use management for the Loess Plateau of the Yellow River, where serious soil loss is the root cause of environmental and ecological degradation of the basin. In this paper, a physically-based, distributed-parameter, and continuous erosion prediction model at the river basin scale was developed with the aim of assisting in developing better land use management strategies. The framework, the major supporting techniques, and the typical erosion processes are described. The physical processes of sediment yield and transport in the Loess Plateau are divided into three sub-processes, including the runoff and sediment yield on hillslopes, gravitational erosion in gullies, and hyperconcentrated flow routing in channels. For each sub-process, a physically-based simulation model was developed and embedded into the whole model system. The model system was applied to simulate the runoff and sediment yield in several typical years in the coarse sediment source area of the Loess Plateau, and the simulated results were in reasonably good agreement with the measured values.     

A new model for predicting bed evolution in estuarine area and its application in yellow river delta

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-e...     

不同条件下矩形沙坑影响的数值模拟对比研究

应用有限体积法建立了河道平面二维水流泥沙数学模型并将模型应用于典型河段的计算,验证了模型的计算精度.设置了不同来水来沙条件和沙坑几何边界条件,将本模型应用于几种工况的理想矩形河道中矩形沙坑影响模拟研究,计算表明采砂对河道的正常演变产生影响,影响结果与离沙坑的距离、沙坑的深度和面积大小以及来水来沙情况等因素有关.初步分析了在采沙规划中可控制采沙影响后果的措施.     

The role of wind-wave related processes in redistributing river-derived terrigenous sediments in Lake Turkana: A modelling study

A complete annual cycle of the dynamics of fine-grained sediment supplied by the Omo and smaller rivers is simulated for Lake Turkana, one of the world’s large lakes, with the hydrodynamic, wave and sediment transport model Delft3D. The model is forced with river liquid and solid discharge and wind data in order to simulate cohesive sediment transport and resuspension. It simulates stratification due to salinity, wave generation and dissipation, and sediment advection and resuspension by waves and currents, with multiple cohesive sediment fractions. A comparison of the simulation results with remotely-sensed imagery and with available in-situ sediment deposition rates validates the model. By devising simulation scenarios in which certain processes were switched on or off, we investigated the contribution of waves, wind-induced surface and bottom currents, salinity-induced stratification and river jet, in resuspending and transporting fine sediments in the lake basin. With only the wind or river influence, most of the sediment deposition occurs in the first 10 km off the Omo River mouth and at a depth < 10 m. When waves are switched on, increased bed shear stresses resuspend most of the fine sediments, that are then deposited further and deeper in the first 30 km, in water depths > 30 m. This study sheds new light on sediment transport in Lake Turkana and in great lakes in general, favouring the view that wind-waves can be the main agent that transports sediment away from river mouths and to deeper areas, as opposed to river-plume or gravity-driven transport.     

河流水冰沙耦合模型研究Ⅰ：原理和方法

河流水沙研究一般忽略冬季河冰对泥沙输运、河床侵蚀和岸滩崩塌的影响,但北方河流如黄河等冬季冰期的防凌减灾和河道的演变均不能忽略河冰过程,亟需研究河冰全过程影响下的水冰沙耦合作用机理。本文首先总结了河冰水力学的理论发展,针对北方河流建立了二维水冰沙耦合数学模型,包括二维水沙数值模块、河冰动力学模块和岸滩侵蚀模块,并介绍了该耦合模型的求解步骤和方法。研究表明:通过三个模块间的信息传递和数据反馈,该数学模型具备模拟冰塞冰坝等极端工况下的水流变化、河冰堆积和释放、泥沙运动、河床冲淤和岸滩侵蚀等过程的能力。该模型将水沙理论和河冰理论结合起来,可用于北方河流全季节与河冰生消全过程的水冰沙耦合过程模拟,为北方河流管理提供了有力工具。     

日本大井河河床变动的数值模拟

利用一维的泥沙数值模型研究了位于日本中部的大井河河床变动情况.在传输模块中考虑了床沙的非均质特性.1981至1996年实测的流量和泥沙数据被用于确定模型参数.为了控制下游河道的淤积,针对不同的挖沙范围和大坝的有无对大井河泥沙传输进行了30年的预测.根据计算结果提出了下游河道和河口的整治方案.     

Development and application of 2-D mobile-bed model with bedrock river evolution mechanism

Steep slope and severe bed change are the characteristics of mountain rivers. These characteristics often cause the bed armour layer flushed away, make the bedrock exposed, and then increase the channel incision. Most mobile-bed models of past few decades aimed at the sediment transport of alluvial channel. In this paper, a bedrock river evolution mechanism is proposed, and included in a 2-D mobile-bed model, called the explicit finite analytic model (EFA). The EFA model can consider both incision and deposition over the bedrock, by combining a new stream power type of bedrock erosion rate formula with the flow and sediment transport modules. An uplifted reach of Taan River, Taiwan, caused by the Chi–Chi earthquake occurred in 1999 is chosen as the study site. Rapid bedrock incision since the uplift provides a rare chance to explore its mechanism and evolution process. The field and numerical results show that the proposed model has the capability of simulating morphological changes for bedrock rivers.     

The Yellow River: Managing the Unmanageable

Abstract

Hydrosolidarity in the Yellow River is a complex and difficult task, especially as this river has sediment problems that are unique in the world. The balancing of discharge needed for sediment management, relative to that needed for augmentation of water supply within and outside the basin, and for conservation of threatened ecosystems downstream presents a series of compromises that must rank as amongst the most challenging in basin-wide management of major world rivers. Until such time as south-to-north diversions are in place, the Yellow River is the only major water supply to the North China Plain, where water scarcity is now estimated to be some 40 km³ annually, representing 70 percent of the flow of the Yellow River. The hydrological management of Yellow River erosion involves three major factors: erosion and sediment transport, flooding, and river desiccation in the downstream reaches. This paper outlines several major development projects in the Yellow River basin that are attempting to achieve hydrosolidarity while, at the same time, providing needed water supplies to water-scarce parts of the basin.     

水土保持措施对黄河水沙影响评价模型及效益评价研究

黄河水沙变化研究是黄河水、沙资源合理利用的前提，水土保持措施对水沙影响评价模型及效益评价是黄河治理开发的基础。本文对第三期黄河水土保持科研基金项目第三专题研究成果进行了总结：综合分析了现有水沙评价模型和孤山川流域水沙变化研究成果，探讨了水土保持措施对产流产沙机制的影响，遴选了用于研究的水沙评价模型，并对研究区的水土保持措施对水沙的影响做了定量分析评价。     

宁蒙黄河治理对策

资料分析表明,宁蒙黄河冰凌灾害频繁的被动局面是由于主槽萎缩、卡冰结坝所致;而洪灾与用水安全问题则是河势变化无常和多沙支流突发性洪水淤堵干流形成"沙坝"引起的。为有效恢复宁蒙河段的行洪排沙功能,实现河道减淤、恢复和维持河道中水河槽、保障防洪(凌)安全的宁蒙黄河治理目标,从产沙、输沙、调控机理三个角度出发,分析了各因素对宁蒙黄河河床演变特征的影响。就产沙而言,通过产沙地貌分区、遥感影像分析和流域水系分区相结合的方法确定黄河上游不同沙源区的分布。基于提出的风蚀输沙通量计算方法及风沙入河估算方法,并结合区域风速与植被覆盖率实测数据,发现近30 a风速下降、区域植被覆盖率上升是风沙侵蚀量与入黄风沙量逐渐减少的原因。分析宁蒙河段日均风速、日降雨量和已有侵蚀观测资料,发现宁蒙地区的风水两相侵蚀主要体现为风蚀与水蚀交错存在及其交互促进,风力侵蚀主要发生在3—5月,水力侵蚀则集中在7—9月。现场观测与黄土降雨侵蚀模型试验则表明,重力侵蚀在黄土高原的整个侵蚀过程中占有重要的份额,暴雨形成的径流是黄土遭到侵蚀的主要外营力,也是激发和加剧重力侵蚀发展的重要影响因子。总体来看,宁蒙黄河的流域产沙具有典型的风-水-重力多营力交互特点,在比尺模型与野外观测揭示的流域径流汇集过程、沟道水流与河床自适应以及非平衡输沙机理基础上,构建了复杂地貌形态的小流域产流产沙动力学模型,成功模拟了不同植被特征和分布状况对流域产流产沙的影响,并得出了植被的减水减沙效果与延滞径流洪峰的作用同郁闭度呈正相关关系,陡坡区域植被对径流洪峰的延滞作用大于缓坡区域的结论。就输沙而言,以泥沙起动、推移质输沙与河床均衡调整等基础理论为基础,提出了水沙两相流数值模拟方法与冲积河流全沙运动模型相似条件。数值计算与模型试验表明,龙羊峡、刘家峡水库联合运用改变径流分配是导致宁蒙河道淤积萎缩的主因,协调水沙关系是修复黄河行洪排沙功能的有效途径。并分析确定了宁蒙黄河河道水沙调控阈值和多沙支流入汇口干流防淤堵的流量阈值,即宁蒙黄河临界调控流量为2 000～2 500 m~3/s,临界含沙量5.4～10.5 kg/m~3,调控时间为15～20 d,证实了通过协调水沙关系可修复和维持宁蒙黄河行洪排沙功能;防止多沙支流入汇堵河的黄河流量阈值为2 500 m~3/s,治理淤堵沙坝配合"挖引疏浚"有效冲刷的干流阈值流量为3 000 m~3/s。从各河段模型试验给出的来沙系数阈值沿程减小的变化趋势看,在内蒙古河段现状河床边界条件下,全线冲刷要求的流量至少为2 600 m~3/s,表明黑山峡工程必须预留充足的水沙调控库容。就宏观调控而言,针对流域下垫面条件多样、入黄泥沙沙源众多、河道输沙受水库调度影响显著等特点,以干流水库群为调节器,以径流泥沙为调节对象,采用模块化开发方法集成了风-水-重力侵蚀模型、河道输沙模型、冰情预报模型于水库联调模型上,构建了可进行大范围、高精度的水沙过程模拟预报的宁蒙黄河区域数字流域模型平台,并成功在下河沿—石嘴山河段进行了调试和应用。此外,针对宁蒙黄河河型复杂、凌汛期易卡冰结坝、夏季多沙支流突发性洪水易堵干流形成"沙坝"等河情状况,提出了"水沙调控、支流拦沙、堤外放淤"的处治模式。在稳定性分汊河段、大型支流入汇段、受沙卵石河床组成限制的河段,则指出不宜强行套用微弯型治理方案,而可采用"工程导送(简称为‘导’)、塞支强干(简称为‘塞’)、挖引疏浚(简称为‘挖’)"方针,亦即"导、塞、挖并举"的对策。建设黑山峡水库、南水北调西线工程等是宁蒙河段长远治理的根本对策,通过增加河道内汛期水量和调水调沙,恢复并维持中水河槽,提供防凌库容,才能彻底解决宁蒙河段凌洪灾害,并得出建立黄河上游沙源固定、支流泥沙阻截、干流泥沙输导与堤外淤沙处置的"固-阻-输-置"综合防治体系,是目前可行的治理对策的结论。