Sedimentation always leads to loss of reservoir storage. This is an important issue for reservoir management, particularly for reservoirs on the Yellow River. As a result of sedimentation, sandbars are frequently found at the mouth of tributaries in reservoirs. The evolution of a tributary mouth sandbar, including its formation and scouring, plays a key role in reservoir sedimentation. However, there are few effective numerical models reported in previous studies for tributary mouth sandbar evolution in reservoirs. In this study, we propose two modules for evolution processes of mouth sandbars: one for intrusion and sedimentation and the other for scouring process. Both modules coupled turbidity current, open‐channel flow, and flow exchanges between the main stream and tributaries. Field measurements and laboratory experiments with different set‐ups were used to test the capabilities of the two proposed modules. By coupling formation and scouring modules with a 2D morphodynamic model in reservoirs, we successfully built a novel numerical model to simulate the evolution processes of tributary mouth sandbars in reservoirs. A field‐scale application of the coupled model was undertaken to simulate evolution of tributary mouth sandbars in the Xiaolangdi Reservoir, Yellow River. The results indicate that the numerical model in this study is more practical than previous models and could provide great support for optimizing reservoir operation in other systems.

In the heavily silt-laden river, density current belongs to an excellent method for flushing the input sediment without water level drawn down. Heavily silt-laden fluid mud in reservoir comes from heavily silt-laden density current. Density current comes into being in the reservoir and may reach the front of the dam with certain flood duration in addition. And the flood also needs to meet a certain sediment concentration and discharge. That makes water and sediment input need to provide density current with energy to overcome the energy loss during the forming process. For example, in a density current creeping process, the current energy shortage often can unsuccessfully reach the front of the Xiaolangdi dam, the stop makes a muddy pond before the dam. Another situation occurs during the density current flushing process. When the input flood ends without subsequent enough energy retention, the foremost density current creeps slowly and suspends before the dam. In these two cases, the muddy layer along the vertical section in front of the reservoir dam will be called fluid mud in this paper. On the basis of understanding the mixing characteristics of hyper-concentrated flow settlement characteristics, viscoelastic and Bingham fluid in the Yellow River, under the flume experiments combined with theoretical analysis method, the formula which concludes high sediment rheological properties of mud and sediment particle size, the volume ratio of sediment concentration, is established and fluid mud layer theoretical analysis had been carried out and flume experiments had been combined to carry out about the effect between density currents and fluid mud. It is found that the difference between the fluid mud with the Bingham shear stress and the flow shear stress due to different sediment concentration, which can divide the movement regime into 2 types, named invasive and interface. The heterogeneous density flow of different sediment does not only affect the muddy water thickness and blending extent, but also determine the movement regime of the head. The flow discharge mainly affects the muddy water thickness and the velocity of the density current. The density of fluid mud increased from fast to slow with the time lasting, which is formed due to settlement. Through the theoretical deduction, the critical judgment parameter of the fluid mud layer incipient motion is obtained. The calculation formula which concluded volumetric sediment concentration, slope and density current thickness is proposed based on the experiments. Obviously, timely opening the desilting tunnel or with the help of the subsequent flood, this will enable the fluid mud incipient motion and flushing out of the reservoir to achieve the purpose of efficient sediment transport. With the adhesion of the fine sediment mud layer in group settlement mechanism and process, conditions on follow-up density current occurrence, and fluid mud layer motion possibility, and its interaction are the basis and key technology of efficient way flushing sediment out of the reservoir in the heavily silt-laden river. The research results can enrich the contents of river sediment dynamics and provide technical reference for the operation and planning of sediment-laden river reservoir

Density currents with low sediment concentration are muddy and consist of a large number of fine granular particles. The extremely small settling velocity of the granules leads to adverse water environment, and immense difficulties in water diversion and water treatment in mountainous and plateau areas. This is a cause of concern for society in general, and design departments in particular. In this work, we have used the upper and lower reaches of the Niulan River, a tributary of the Jinsha River, as prototypes, and studied the formation and movement of currents with low sediment concentration and density using a generalized flume test. In addition, we have explored the variations in the characteristics of the head velocity and sediment concentration along the flow path. The results reveal a gradual decrease of the head velocity and sediment concentration along the flow path. For the same amount of discharge, the head velocity of the middle and bottom layers of the current increases with an increase in the sediment concentration. The top layer exhibits a higher head velocity compared to the middle and bottom layers for the same amount of discharge and sediment concentration. The middle layer exhibits the smallest velocity head, while the velocity head of the bottom layer has an intermediate value. These results can serve as a guide for test simulations of physical models of reservoirs.

Sandbar development would stop the water and sediment exchange between main river and tributary and even influence the normal reservoir opeartion. From the surveyed data of reservoir built many years ago, it shows that when there is a bar in tributary mouth, the tributary volume below the bar will become nullification during the period of flood control or water and sediment regulation of reservoir. There are more tributaries in Xiaolangdi reservoir than the others that it occupies 41.3% of the total initial volume of tributary volume. Obviously, the effective use of tributary volume has been important influenced by comprehensive utilization efficiency of reservoir scheduling, such as flood control, sedimentation reduction and comprehensive utilization. Results of Xiaolangdi Reservoir mobile-bed physical model experiments show that tributary is equivalent to lateral extension of river bed, the tributary intrusion deposition process have strongly relations with the factors, such as original topography, river bed deposition shape and its regime, process with input discharge and input sediment, and method of reservoir regulation. The variation trends of main river and tributary terrain forecasted by model test are basically in accordance with field surveyed data. The results could be used for research, design, and forecasting of reservoirs in sediment-laden river.

Retrogressive erosion is a special phenomenon of fluvial processes, where the channel scour develops from downstream to upstream. Retrogressive erosion occurs due to the rapid reduction in water level, which is closely related to the engineering controlling conditions, water and sediment conditions, scouring time and duration, and initial reservoir conditions. Various impacts of destruction degree of a sandbar in a tributary on the retrogressive erosion in the main stream have been investigated. By use of a physical model for the Xiaolangdi Reservoir, which was constructed based on the similarity laws of sediment-laden physical reservoir model, four tests were conducted to investigate the effect of retrogressive erosion due to lower the pond water level quickly. On the constrain of different sandbars evolved in the tributary of Zhenshui, different flow processes and quantities from the interior tributary caused different sediment processes and quantities of the main stem channel below the branch. Restoration efficiencies of reservoir storage capacity for test 1 to test 4 was 11.6%, 6.8%, 12.2% and 6.6%, respectively. More water quantity would be released from the tributary for a severer sandbar destruction degree, which led to a higher restoration efficiency of reservoir storage capacity due to a larger volume of channel scour. In addition, a lower base level of erosion could produce the similar effects. When the volume of reservoir deposition reached 4.2×109m3, the scour effect of retrogressive erosion by lowering the pool level would be better than the case with the volume of reservoir deposition of 3.2×109m3. The results show that the calculated results are in close agreement with the experimental data. The formula for calculating the daily volume of retrogressive erosion has been improved, which was originally proposed by Tsinghua University and Northwest Institute of Hydraulic Science of China. The resulted from the improved formula indicate that a larger water volume released from the tributary could cause a higher amount of channel scour in the main-stem channel below the branch, and the calculations would be in close agreement with the measurements. These results can be used in comparing various schemes of water and sediment regulation of the reservoir in a sediment-laden river. Those enrich the subject content.

The paper was intended to a) determine the best deposition morphology with respect to optimization of released flow and sediment processes, good use of storage within the tributaries and reducing rate of deposition;b) establish the rules for reservoir regulation to maintain the form for long?term and;c) assess the effects of the regulation upon the sedimentation in the reservoir and the downstream reaches. The results from the numerical and physical models with a 20 a feeding processes show that compared with the reference scheme, the optimal scheme will reduce sedimentation in the Xiaolangdi Reservoir by 1.02-1.27 billion m3 , and increase the sediment load into the sea by 0.67 billion t, so yielding better performance in expanding the period for sediment trapping and increasing the sediment load into the sea.

Fluid layer is close to the sediment hyperconcentrated water between it and the upper body of water has obvious interface, it has great mobility. Foreign fluid research began in the 1950s, Inglis and allen (1957) at the time of the thames estuary sediment movement in great britain for the first time using a fluid mud; Then the fluid were found in the gironde estuary in france, the mississippi of the united states,Thailand weinan estuaries and other coastal estuary muddy; Migniot (1968) and dutch engineering consulting association (1968) were also used cremede vase and sling mud other names; Kirby and parker (1983) for a definition of the fluid mud;Parker and hooper (1994) has an alternative fluid with high concentration of water in the sediment layer. Domestic fluid research began in the 1960s, which was first discovered in tianjin new harbor back silting studysubsequently found in lianyun port,Shanghai port,and Yellow river estuary, Yangtze river estuary and other mucky ports estuaries;In recent years the three gorges reservoir, Xiaolangdi reservoir have also found that the presence of fluid mud. Fluid is widely present in the estary,gulf,inland waterways,lakes and reservoirs; It is closely related to port and waterway silting,sailing depth use,reservoir sediment density current and water pollution problem;Thus causing a large number of researchers on the causes fluid mud,defining and motion characteristics,and aspects of research and exploration,We made a series of scientific research. But being limited field data and experimental conditions, At home and abroad in recent years it has been little progress in their research.

Among traditional depth-averaged models for predicting turbidity currents,it is difficult to take into account the influence of flow and sediment conditions at the plunge point and the gradient of free water surface. Therefore,a one-dimensional unsteady turbidity current model for reservoirs with irregular cross-sections is proposed,and a two-step calculation mode of alternating the calculations of turbidity current and open channel flow is adopted in this model. The proposed calculation mode can dynamically determine the location of the upstream boundary for the turbidity current simulations using the plunge criterion,and can also connect the reach transported in the pattern of open channel flow and the reach transported in the pattern of turbidity current. Three processes of flow movement,sediment transport and bed evolution in a reservoir are solved by a fully coupled approach,with a TVD(Total Variation Diminishing) version of the MUSCL-Hancock scheme being used in this solution. Turbidity current movements in two laboratory experiments were simulated under different setups,including an instantaneous fixed-volume release and a constant-flux input,with the effect of free surface gradient on the model predictions being investigated. The calculations indicate that the proposed model can satisfactorily predict the thickness and sediment concentration of turbidity currents and their propagation processes,which can be used as a tool for the sediment management in reservoirs.

针对传统的深度平均异重流模型在实际应用中获取上游边界条件的困难,提出了两步计算模式下的水库明流与异重流耦合模型.浑水明流段与异重流段交替运算,利用潜入点弗汝德数与体积比含沙量的关系作为判别条件确定异重流段的上游边界位置与相应水沙条件,在设置下游边界条件时使用极限吸出高度公式计算出流流量.采用该模型计算了三门峡水库两次异重流的形成、发展与消退全过程.模型预测的异重流潜入位置与观测结果一致,对库区内3个监测断面的异重流到达时间做出了较为准确的预测.计算的清浑水层交界面高程和含沙量过程与实测结果相符,模拟结果反映出浑水水库发生时异重流排沙效率降低的现象.因此该模型可用于水库异重流过程模拟和排沙方案设计.

By October 2010, the mainstream delta vertex of Xiaolangdi Reservoir had moved up to cross section HH12 which is 18.75km to dam, and the amount of sediment reached 2.823 billion m3. The re?sults show that under the same amount of sediment and water storage,compared with cone deposition mor?phology, the backwater length of delta deposition morphology is obviously shorter and the water lever be?fore dam is obviously lower. The delta deposition morphology is obviously superior to cone deposition mor?phology in the aspects of trapping the coarse sand,discharging the fine sand,and reducing deposition and optimizing the process of outlet water and sediment,and so on. The delta deposition morphology is benefi?cial to shape density current, and the sediment ejection effect of density current is superior to backwater free flow. Physical model tests of Xiaolangdi Reservoir show that when channel suffers from retrogressive erosion and water level drops, the unconsolidated deposits in saturation state on both bank beaches will lost stability and slump into the channel and the storage capacity may recovery under the combined action of gravity and seepage water pressure. Therefore,in the current process of reservoir operation,retrogressive erosion can be shaped in river reach before dam and delta continent surface by controlling water level of inflow floods,so as to delay the transformation from delta deposition morphology into cone deposition mor?phology as long as possible.

The flat form of the Xiaolangdi Reservoir area is wide upstream and narrow downstream, the river valley of the upper part is 200 similar to 400 m wide and the lower part is 800 m to 1,400 m wide. There is a reach with 4 km long named "Balihutong" which has 26 similar to 30 km distance from the dam, whose width is 200 m to 300 in. There are more than 10 larger branches such as Dayu River, Meiyao River, Zhenshui River, Shijing River, Dongyang River, Dajiao River, Xiyang River, Yuli River, Yanxi River, Boqing River and so on, which converge at the reservoir. They are all concentrated in the lower reservoir area which has a rugged topography. This article has researched the modes of density current converse intruding tributary through the prototype and physical model data of Xiaolangdi Reservoir. Also the changes of the sediment transport character and the silt configuration of tributary density current has been resolved. Both Formula Han Qiwei and Formula Qin Wenkai on the backflow length to tributaries have been calculated and validated as examples.

Based on the experimental data obtained from an undistorted,moveable-bed model for studying bedload,three methods for determining bedload grain size distribution including the statistic-theory method,maximum-diameter method and average-diameter method are compared from the view points of model and prototype respectively.The results show that from the view point of model the accuracy of statistic-theory method is low at small or large flow discharge,and the other two methods give satisfactory results at various discharges.From the view point of prototype the grain size calculated with statistic-theory method is larger than the experimental data at small discharge and is smaller at large discharge.The calculated result obtained from the maximum-diameter method is smaller than experimental result at large discharge.Whereas,the calculation results always agree well with experimental data when average diameter method is used.

Physical model tests were conducted to forecast the regime of the sediment transport and morphological changes of the Xiaolangdi Reservoir in the early sediment impoundment period.The experimental results show that the sediment transport in the early operation period took the mode of density current;in the main river channel sediment appeared in the form of delta deposition,which moved towards the dam;the deposition also occurred in the branches and gullies,especially when sand bar existed at the junctions due to the sediment-laden flow inversely running from the main river channel to the branches and gullies.When the reservoir water level sharply fell,headward erosion and bank erosion occurred in the main riverbed and the siltation area will be reduced in the branches and gullies. Although the model conditions in the experiments didn't fully agree with those of the prototype in the real case,the general agreement of the data measured in situ with those predicted in model has validated the rationality of experiment.

Based on the concept of ecological velocity and ecological water depth a hydraulic method of determining the necessary discharge for maintaining the specific ecological functions of river,with the hydraulic parameters of river including the wetted perimeter,roughness coefficient and hydraulic gradient taken into account,is proposed.Through this method the problem of calculation for compound river channel can be avoided.The application of the proposed method to determine the ecological water demand in the Xiaochuan river section located at the upper reaches of the Yellow River shows that the result accords with the existing situation of the river.The method is better than the Tennant method.

淄博市是一座经济比较发达的现代化工业城市,但水资源短缺一直是该市可持续发展的重要制约因素。黄河是该市惟一的客水资源,因此“引黄济淄”成为该市解决水问题的重要举措。“引黄济淄”一期工程2001年竣工通水,有效地缓解了淄博市水资源供需矛盾,发挥了显著的经济、社会和环境效益。但随着该市的发展和用水量的增加,现有25万t/d的供水规模将不能满足日益增长的用水需求,迫切需要尽快对“引黄济淄”二期工程进行决策建设。

The paper is intended to show the research results which are obtained by a physical scale model for the Xiaolangdi Reservoir to address the problems involved in the pilot field experiments of regulating flow and sediment with the Xiaolangdi Reservoir conducted in 2002 similar to 2004. With the model experiments, the authors came to master critical technological know - how and have deep understanding of the field experiments, quantified the indices for genesis and moving to the dam heel of density current in the Xiaolangdi reservoir, established critical discharge for eroding the deposits at the tail reach of the reservoir and found out the optimum matching of erosion discharge with erosion duration. The research results provided soundly scientific and technological support for the field experiments, and were proven to have a good agreement with the field data.

The paper is intended to investigate the laws governing the density current and show the application of the laws in Xiaolangdi reservoir on the stem Yellow River. Sediment brought by the feeding flow to the reservoir, which is on the early stage of impoundment, can be only released out of it through density current. Using the data of density current measured in Xiaolangdi reservoir, and referring to the research results obtained in physical models, the authors investigated the basic laws for genesis, movement and sediment releasing of density current, and obtained the critical conditions for sediment release by density current, and formulas for resistance, sediment carrying capacity, travel time, and sediment release of density current. Prior to the field experiments of flow - sediment regulation, which were conducted in 2002 - 2004, the authors applied the results to design regulation schemes for operating Xiaolangdi dam and other dams. Following the schemes, the field experiments were implemented smoothly. The field experiments not only regulated the formed - naturally density current in a proper way, but created density current as wanted and released the sediment by the density current successfully as well, therefore realizing the objectives like sedimentation reduction, optimizing the rebalance between flow and sediment released.

Density flow in Xiaolangdi Reservoir was simulated in corresponding reservoir physical model. The experiment results show that the location of density flow submerged, flow velocity and sediment distribution, muddy flow forming, deposition morphology and amount of main stream and tributaries are accordant with prototype. Further demonstrated it is useful to study density flow similarity scale during physical model design. Falling velocity of muddy flow in the model was faster than in prototype, this only caused sediment discharge duration shorter when bottom outlets discharged small amount of water, and could not influence deposition morphology and amount seriously.

The theoretical frame of a new two-dimensional sediment mathematical model is established on the basis of the resent research achievements about the sediment transport law of the Yellow River. The formulas of sediment carrying capacity of flow, which reflect the features of the Yellow River, are applied to it. The finite element scheme is employed to deduce the discretized equations of the model. Verifications of the model are carried out with the flood occurring on Jinan reach of the Yellow Rive during the flood season in 1976. The calculation results with the model are in good agreement with the measured data. The programs calculating indicates that the Jinanyan's constructing will be of great benefit to Jinan city's flood protecting and water supply.