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.     

Analysis of Bed Load Equations and River Bed Level Variations Using Basin-Scale Process-Based Modelling Approach

Bed load transport is a key process in maintaining the dynamically stable channel geometry for restoring the form and function of river ecosystems. Bed load consists of relatively large sediment particles that are moved along the streambed by rolling, sliding or saltation. Currently, various empirical correlations are used to estimate bed load transport rates since no single procedure, whether theoretical or empirical, has yet to be universally accepted as completely satisfactory in this aspect. Bed load particles are primarily sourced from river bed materials or banks. The amount of bed load and its spatial distribution contributes significantly to river bed level changes. Hillslope sediment contribution, mostly available to the river in the form of suspended load, also plays an important role in river bed level changes. This study aims to analyse different bed load equations and the resultant computations of river bed level variations using a process-based sediment dynamic model. Analyses have revealed that different bed load equations were mainly deduced from the concept of relating bed shear stresses to their critical values which are highly factored by the slope gradient, water discharge and particle sizes. In this study, river bed level variations are calculated by estimating total surplus or deficit sediment loads (suspended loads and bed loads) in a channel section. This paper describes the application of different widely used bed load equations, and evaluation of their various parameters and relative performances for a case study area (Abukuma River Basin, Japan) using a basin-scale process-based modelling approach. Relative performances of river bed level simulations obtained by using different bed load equations are also presented. This paper elaborates on the modelling approaches for river bed load and bed level simulations. Although verifications were not done due to unavailability of field data for bed load, qualitative evaluations were conducted vis-à-vis field data on flow and suspended sediment loads as well as the bed loads presented in different past studies.     

浅析水利水电工程沉沙池泥沙沉降计算方法

本文对沙早水电工程沉沙池设计中最常用的泥沙沉降计算方法，准静水沉降法和一度流超饱和输沙法，从公式结构上进行了一定的分析研究，结果表明，在一定条件下，准静水沉降法之计算公式是一度流超饱和输沙法（不考虑水流挟沙能力）的一种近似表达式，可用来估算沉沙池内含沙量变化。     

柳河流域输沙能力探讨

分析了柳河各个河段及支流含沙量、输沙能力、径流等情况,掌握流域内水土流失状况的分布,探讨流域内的变化规律,为柳河流域的综合治理提供科学依据。     

河口泥沙研究的进展

作者通过大量的文献调研，评述了国内外学者在河口泥沙运动的基本理论、数值模型等方面的研究工作和成果，结合近年来作者关于河口水流结构、盐淡水混合以及泥沙输运的研究工作，提出加强对河口泥沙非恒定运动过程、河口最大浑浊带形成机理及其与河口拦门沙演化关系研究的必要性，并指出河口泥沙运动与河口地区湿地演变和浮游生物生长环境的关系是当前河口泥沙运动研究的两大热点。     

多组分流元模型在稀性泥石流堆积分选特征研究中的应用

基于结构两相流模型和PIC数值计算方法，本文探讨了稀性泥石流堆积过程中的泥沙分选特征。文中的模型可以模拟阵性泥沙流的非稳定特性，通过将传统的Euler和Lagrangian方法结合泥沙流运动的整个过程都能够采用多组分流元模型进行很好的描述。该模型也能够合理描述泥沙分选过程中伴随的冲淤过程。文中采用2～5°的坡度，固相颗粒被分为三组粒径不同的组分。研究表明，泥石流的垂向和横向分选都不明显，但是纵向分严为明显。河槽坡度和泥石流的密度是影响泥石流分选过程的两个关键因素。泥沙输移能力越大，颗粒分选越不明显，对泥石流分选特性的定量预测有助于深入了解泥石流的沉积机理和泥石流灾害的防治。     

水库三角洲河道输沙之研究

水库进口附近三角洲河道之水流系近似均匀流，并非真正之均匀流。三角洲河道动床之自我调整作用，因水库水位之回水影响，其输沙特性有异于明渠均匀流，传统上，将明渠均匀流平衡条件之下输沙公式应用于估算的三角洲河道之输沙能力，似有其不稳定性。本研究进行一系列水流区输沙试验，并纳入文献「１０」Ｈｏｔｃｈｋｉｓｓ之试验数据一并分析。     

重金属污染物动态吸附试验及数学模拟

本文采用泥沙动力学中Ｒｏｕｓｅ等人用来研究泥沙浓度沿垂线分布的装置。对泥沙吸附重金属污染物进行了动态模拟。试验分有底泥和无底泥两种情况。研究中发现在Ｒｏｕｓｅ装置的水力、泥沙条件下泥沙吸附重金属污染物达到平衡状态需要６小时以上，由极坐标下的重金属迁移转化数学模型方程，在本文具体试验条件下进行数值求解，计算结果和试验结果合良好，说明数学模型是正确合理的试验是可靠的。计算时依据室内静态试验结果，对动态     

基于典型次洪泥沙动力学过程的岔巴沟流域水沙关系分析

为准确把握岔巴沟流域径流泥沙变化趋势并分析其原因,以岔巴沟流域1970—2016年98场洪水输沙过程为研究对象,通过分析不同年代次洪输沙量,阐明了次洪水输沙动力学过程。结果表明:岔巴沟流域近50 a来次洪输沙滞回曲线模式主要表现为顺时针型、逆时针型、8字型、复杂型4种,4种模式中逆时针型所占比例和次洪输沙量最大,顺时针型所占比例最小,但平均洪峰流量和平均输沙峰值最高,复杂型洪水平均持续时间最长。不同年代次洪输沙频率表现为1980—1989年间洪水输沙滞回曲线以逆时针型为主,其次为复杂型洪水,2006年以来逆时针型和复杂型洪水数量大幅减少,8字型洪水数量增多; 出现这种现象可能是由于岔巴沟流域自20世纪70年代以来开展小流域综合治理,各种水土保持措施在1970—1989年间产生较强的作用,但2000年后,由于长期使用后产生淤满和损坏等状况,效力逐渐降低,对岔巴沟流域整体的水沙输移模式产生影响。     

放射性同位素示踪在泥沙研究中的应用

介绍了放射性同位素作为示踪物应用在泥沙运动研究中的情况，特别是国外广泛使用的同位素，如^113In铟，^198Au金，^51Cr铬^192Ir铱，^46Sc钪，^110Ag银等及其示踪的物理形式，和在悬移质、推移质研究对同位素颗粒大小的选择，描述了如何准备放射性同位素物质以及注入、示踪和数据收集等等。另外还介绍了在印度Madras港开展放射性同位素示踪疏浚泥沙运动研究的实例。最后，分析评述了国内利用放射性同位素示踪研究的进展情况。     

Sediment transport under dry weather conditions in a small sewer system

Increased knowledge of the processes which govern the transport of solids in sewers is necessary in order to develop more reliable and applicable sediment transport models for sewer systems. Proper validation of these are essential. For that purpose thorough field measurements are imperative. This paper renders initial results obtained in an ongoing case study of a Danish combined sewer system in Frejlev, a small town southwest of Aalborg, Denmark. Field data are presented concerning estimation of the sediment transport during dry weather. Finally, considerations on how to approach numerical modelling is made based on numerical simulations using MOUSE TRAP (DHI 1993).     

泥沙源区沟道输沙能力的计算方法

小流域沟道是泥沙进入江河的初级通道，在洪水流量较大时，沟道挟沙力强，其输沙量往往接近断面以上流域侵蚀量，进入江河的沙量取决于流域内的补给沙量，但在洪水流量较小时，沟道水流挟沙力下降，其输沙量小于断面以上流域侵蚀量，进入江河的沙量取决于各级沟道的挟沙能力。黄土地区小流域沟道纵坡陡，固体物质补给又十分丰富，虽然沟道尺度不大，但水流含沙量却很高，已有各种基于低含沙水流的挟沙公式不能表达沟道中高含沙水流的输沙特性。作者通过分析及试验研究，求得在输沙平衡条件下水流泥沙因子间的关系，提出小流域沟道挟沙力公式，经初步验证结果满意，这为估算分析不同条件下流域输沙量提供依据，也对水土保持规划有一定的指导意义。     

长江流域泥沙输移与概算

泥沙概算是一种通过研究泥沙在流域不同位置和一定时期内的时空分布，从而揭示河流水沙平衡状态的方法。本文通过分析提出了长江泥沙概算方法，探讨长江流域产沙、输沙和泥沙沉积三者的关系。在此基础上，通过流域侵蚀、沉积物和悬移质泥沙粒径级配的对比分析，计算得出每年从长江上游侵蚀下来的泥沙中，粒径大于0．5mm的近12亿t泥沙几乎都沉积在长江流域上游的沟谷和支流中，粒径在0．05-0．5mm范围内的4．92亿t泥沙有3．13亿t沉积在上游沟谷和支流中，而粒径小于0．05mm的5．36亿t泥沙也有2．02亿t沉积在这些区域。当长江上游（宜昌站）和汉江总输沙量超过2．86亿t时，长江中下游将发生淤积，总输沙量超过5亿t时的淤积量超过1亿t；当宜昌输沙量超过1亿t时，洞庭湖区将发生淤积。文章还根据长江干流、部分支流和通江湖泊的水沙关系，建立水沙动态图，研究分析了长江水沙在时空上的分布特点。     

Combination of Runoff Simulation with Sediment Modeling in Rivers and Its Application in the Lower Yellow River

Abstract

Previous research on runoff show flow and sediment movement in rivers, and river bed variations are usually separated. This paper, from the point of view of the basin as a whole system, presents an integrated approach by combining runoff simulation with numerical model of sediment transport in rivers to simulate the whole processes of hydrological variables and flow-caused bed variations from the very upper part of the basin to the river mouth. To accomplish this purpose, BTOPMC, a rainfall-runoff model, and NUSTM-1D, a well-developed numerical model for sediment transport and river bed variations, are selected to form a combined model. The application of the proposed model to the lower Yellow River shows that it can properly simulate rainfall-caused runoff, the change of suspended sediment concentration along the river, and river bed variation.     

长江流域梯级枢纽泥沙调控关键技术

通过将水沙动力学与水库调度优化理论相结合,围绕长江流域梯级枢纽泥沙调控关键技术开展研究。在改进恢复饱和系数、非均匀沙挟沙力等关键计算模式的基础上,完善并集成长江上游梯级水库群水沙数学模型、长江中下游复杂江湖河网水沙数学模型和典型河段平面二维水沙数学模型,构建了江河湖库水沙输移模拟模块。基于泥沙对防洪、发电、航运和长期使用4个主要目标的影响,构建了长江泥沙优化调控目标函数,进而集成水沙输移模拟模块构建了长江泥沙优化调度模型,并提出了基于预构泥沙信息库、结合BP神经网络的模型求解方法和非劣解集的改进灰靶评价方法。在此基础上,以三峡水库为例,提出了汛期“蓄清排浑”动态运用方案以及长期分阶段泥沙调控策略。     

Estimation of Sediment Yield and Areas of Soil Erosion and Deposition for Watershed Prioritization using GIS and Remote Sensing

A Geographical Information System (GIS) based method is proposed and demonstrated for the identification of sediment source and sink areas and the prediction of sediment yield from watersheds. Data from the Haharo sub-catchment having an area of 565 km² in the Upper Damodar Valley in Jharkhand State in India was taken up for the present study due to availability of gauged data at multiple locations within watershed area. The watershed was discretized into hydrologically homogeneous grid cells to capture the watershed heterogeneity. The cells thus formed were then differentiated into cells of overland flow regions and cells of channel flow regions based on the magnitude of their flow accumulation areas. The gross soil erosion in each cell was calculated using the Universal Soil Loss Equation (USLE). The parameters of the USLE were evaluated using digital elevation model, soil and landuse information on cell basis. The concept of transport limited sediment delivery (TLSD) was formulated and used in ArcGIS for generating the transport capacity maps. An empirical relation is proposed and demonstrated for its usefulness for computation of land vegetation dependent transport capacity factor used in TLSD approach by linking it with normalized difference vegetation index (NDVI) derived from satellite data. Using these maps, the gross soil erosion was routed to the watershed outlet using hydrological drainage paths, for derivation of transport capacity limited sediment outflow maps. These maps depict the amount of sediment rate from a particular grid in spatial domain and the pixel value of the outlet grid indicates the sediment yield at the outlet of the watershed. Up on testing, the proposed method simulated the annual sediment yield with less than ±40% error.     

Numerical modelling: a tool for better constructed wetland design?

There is a need for a simplified computer-based design tool for subsurface flow constructed wetlands (CWs) which is based on process-based numerical models. Parameters of existing design guidelines and rules have been derived from experiments under specific conditions. Therefore designing CWs using these parameters is limited to these conditions (i.e., temperature, wastewater composition, filter material, etc.). Process-based numerical models describe the main processes in CWs in detail. If the design of CWs is based on these models it will be possible to design CWs for a variety of different boundary conditions and therefore the main limitation of existing design guidelines and rules could be overcome. The use of process-based models is currently limited mainly due to their complexity in structure and use. To make numerical modelling a useful and applicable tool for design, a simplified computer-based design tool that does not require special knowledge of numerical modelling is needed. Additionally, simple models for pre- and post-treatments are also required. Besides allowing designs for various boundary conditions, design tools based on process-based models can also predict the dynamic behaviour of the designed system thus showing e.g., the higher robustness of CWs against fluctuating inflows and peak loads compared to other treatment solutions. Such a tool could increase the quality of CW design and the acceptance and use of CW simulation in practice.     

Mathematical model to identify nitrogen variability in large rivers

The river Swale in Yorkshire, northern England has been the subject of many studies concerning water quality. This paper builds on existing data resources and previous 1D river water quality modelling applications at daily resolution (using QUESTOR) to provide a different perspective on understanding pollution, through simulation of the short‐term dynamics of nutrient transport along the river. The two main objectives are (1) building, calibration and evaluation of a detailed mathematical model (Advection‐Dispersion Model: ADModel), for nutrient transport under unsteady flow conditions and (2) the development of methods for estimating key parameters characterizing pollutant transport (velocity, dispersion coefficient and transformation rates) as functions of hydrological parameters and/or seasonality. The study of ammonium and nitrate has highlighted temporal variability in processes, with maximum nitrification and denitrification rates during autumn. Results show that ADModel is able to predict the main trend of measured concentration with reasonable accuracy and accounts for temporal changes in water flow and pollutant load along the river. Prediction accuracy could be improved through more detailed modelling of transformation processes by taking into account the variability of factors for which existing data were insufficient to allow representation. For example, modelling indicates that interactions with bed sediment may provide an additional source of nutrients during high spring flows. Copyright © 2010 John Wiley & Sons, Ltd.