River Bed Evolution Research Articles

Engineering Regulation of the Weird Branches in a Branching Estuary and its Mechanics: Using the North Branch of the Yangtze Estuary as an Example

Weird horizontal shapes of branches, in large branching estuaries, often cause significant flood risks and environment-related problems. People usually resort to engineering methods to improve the horizontal shape of the weird branches and solve related issues. The responses of the riverbed evolution of a branching estuary to anthropogenic activity are complicated because of complex estuarine hydrodynamics and sediment transports, especially when the project locates specially (e.g., at estuary outlets). The North Branch of the Yangtze Estuary has a narrow upper reach which is almost orthogonal to the South Branch and has a trumpet-shaped lower reach with a wide outlet. The weird horizontal shape of the North Branch brings significant flood risks to cities along this branch, the shrinkage of its entrance, and other problems. In this study, a regulation of the North Branch, which is launched at Guyuan Sand (GYS) just outside the exit of the North Branch, is taken as an example. The GYS regulation aims to improve the weird horizontal shape of the North Branch by building new layouts of outlets, by which people decrease the flood risk of the surrounding cities. The GYS regulation is studied using a 2D numerical model. The riverbed evolution of the Yangtze Estuary in a typical hydrological year is simulated, while the water/sediment fluxes at cross-sections of branches in the estuary during a spring/neap tide are quantitatively calculated. It is found that the regulation changes the rotational flows near the shore, and further reshapes the estuarine circulations of mass inside the outlets, especially exchanges of water/sediment between different branches. The regulation directly changes the riverbed evolution at the outlet of the North Branch, and meanwhile has significant indirect influences on the riverbed evolution of the entrance of the North Branch. The varying riverbed evolution at the entrance of the North Branch and the varying water/sediment fluxes, under different designs of regulations, are related and analyzed. An essential improvement for the weird horizontal shape of the North Branch by an engineering method is shown to be possible, while the regulation mechanism of the engineering method and the response of estuarine riverbed evolution to the regulation are clarified. This study provides a new insight for improving estuarine branches with weird horizontal shapes, by reshaping the tidal processes and the accompanying sediment transports in a branching estuary.

Tidal dynamic response to riverbed evolution in the Yangtze River Estuary

Since 1958, there have been significant changes in the Yangtze River estuary. Due to extensive reclamation and construction of ports and channels, the water area has drastically decreased, resulting in corresponding changes in hydrodynamics and riverbeds at the mouth of the river. According to the analysis of measured topographic data and Delft3D-FLOW model for seven typical historical periods since 1958 at the Yangtze River Estuary, this study investigates the characteristics of riverbed evolution and tidal flow dynamics. From 1958 to 2019, driven by strong human activities, the total area of the Yangtze River Estuary decreased from 2084 km2 to 1403 km2, with a decrease of 32.7%, while the total volume of the corresponding river channel changed slightly and remained stable. Compared with 1958, the volume of the Yangtze River Estuary in 2019 only increased by 345 million m3, with an increase of about 4.1%. The tidal dynamic change of the Yangtze Estuary is closely related to the riverbed evolution of each reach, which not only shapes the estuary landform, but also is affected by the riverbed evolution. Tidal level, tidal range and water area change are closely related. With the decrease of water area in the Yangtze River Estuary, tidal range tends to increase. Tidal prism change is closely related to channel volume. In the past 60 years, the tidal volume at the mouth of the Yangtze River has decreased by 8%. The research findings will provide technical support for enhancing flood control and tide resistance measures at the Yangtze River Estuary, as well as formulating comprehensive management plans for estuaries, contributing to the protection and sustainable development of the Yangtze River Estuary.

Bimodal Bed Load Transport Characteristics under the Influence of Mixture Ratio

The transport of a non-uniform bed load in a river is a complicated process and has enormous implications on the sediment flux and anomalous riverbed evolution. To investigate the transport characteristics of the non-uniform bed load and the related particle interactions, a real-time monitoring system of the bed load transport was developed to determine the instant transport rate and grain composition of the bed load. Doppler Velocimetry was used to synchronously measure the fluctuating velocity in high frequency. A total of 211 cases of flume experiments were conducted, focusing on non-uniform sediment with a bimodal pattern. The experimental results indicate that the random fluctuation of the bed load transport amount closely depends on the flow-intensity fluctuation caused by the turbulence burst near the bed. When the value of the flow-fluctuation peak is bigger than 2.5 σ, the coarse sands tend to incipient motion in high probability but are mostly fine sand transport when the peak is less than 1.5 σ. The transport rate of fine particles remains continuous throughout the process, while that of coarse particles is intermittent because the incipient motion mechanism of bed load sands mainly follows three modes. If the difference in diameter between the coarse and fine particles is large, the transport of coarse particles may undergo supernormal transport because of the effect of the fine particles on the coarse particles. The bed load flux of total, fine, and coarse sand present different trends with changes in the bed material composition, in which the transport rate of coarse sands and total bed load sands presents a humped curve in terms of the mixture ratio, and the optimal corresponding mixture ratio ηc is about 3:7. The optimal mixture ratio is not fixed, and it depends on the grain composition and size differential of bed material. With a proper mixture ratio, the transport rate of a non-uniform bed load is higher than the uniform bed load of related size. These findings might provide valuable support for predicting bed load transport and bed evolution in rivers.

Forest Litter Features in Floodplain Forest of the “Bolshaya Kokshaga” Reserve

The studies, carried out in the floodplain ecotopes of the Bolshaya Kokshaga reserve (Russia, the Republic of Mari El) are relevant due to the need to understand the patterns of formation of the forest litter properties, which are a sensitive integral indicator of the biogeocenoses conditions. The work has been carried out on 20 test plots located in different parts of the floodplain in areas with a point bar type of river bed evolution, and, in addition to the main physicochemical parameters, the weight of the litter, its fractional composition and seasonal dynamics, as well as carbon reserves in it, were estimated. It was established that the weight of the litter on the studies sites decreased during the growing season from 20 to 33% of its value at the end of May. The main loss of its mass was observed in the first half of summer. The variability of the litter’s physicochemical parameters, especially its acidity, the degree of base saturation, the exchangeable calcium content, as well as the content of mobile phosphorus and potassium compounds, was found to be tied mainly to the features of the ecotopes, and their seasonal changes turned out to be statistically insignificant. It was determined that the greatest differences between the ecotopes were in the litter mass and the carbon stock in it. The mobile potassium and exchangeable calcium content were the highest in the litter of biotopes from the central part of the floodplain, and the content of ash and mobile phosphorus was the highest in the near-river zone. The ecotopes differed least of all in terms of the litter acidity and the degree of base saturation. It was shown that the carbon mass and stock in the litter of floodplain forests were significantly lower than in watershed stands, which was explained by its partial removal during floods, having the strongest effect in near-river ecotopes. The litter from the floodplain ecotopes, compared to the watershed ecotopes, also had significantly lower values of acidity, ash content, the sum of exchangeable bases, and the mobile potassium content. They surpassed the litter of lichen and mossy pine forests only in the mobile phosphorus content.

Flow Structure and Short-Term Riverbed Evolution in Curved Flumes

River bending is the major effect responsible for bed topography and bank changes. In this study, fluid velocity (measured by a three-dimensional Doppler advanced point current meter) and bed topographical data have been collected in 40 sections of an experimental model. The whole flume was composed of an organic glass bend, upstream and downstream water tanks, two transition straight sections, a circulation pump, and a connection pipeline. Each section has been found to be characterized by a primary circulation and a small reverse circulation, with some sections even presenting three more or more circulation structures. The minimum circulation intensity has been detected in proximity to the top of the curved channel, while a region with small longitudinal velocity has been observed near the concave bank of each bend, corresponding to the flat bed formed after a short period of scouring. The maximum sediment deposition and scour depth in the presence of a uniform distribution of living flexible vegetation within 10 cm of the flume wall have been found to be smaller than those observed in the tests conducted without vegetation.

The yellow river-bed evolution a statistical proof of the mountain-river-desert conjecture

When the Yellow River flows through the Hetao Plain in Inner Mongolia, north China, it forms a mountain-river-desert system with the Yin Mountains on one side and the Hobq desert on the other side. In this mountain-river-desert system, a dense growth of green grass is formed in the area fronting the river and with the mountains at the back, however, on the opposite the river, the area has an inherent trend to lost moisture, which might cause desertification. This study verifies this theoretical conjecture by analyzing the Yellow Riverbed change from 2014 to 2021. The seven year change showed the river is the inherent boundary between the grassland and the dessert, and it was nothing to do with the river banks? past earth surfaces.

Theoretical Model and Solution of Dynamic Evolution in Initial Stage of Lacustrine Delta

Sediment is carried by flows into lake during the formation of lacustrine deltas. The subsequent movement of sediment-laden flow is maintained by the initial momentum at the early stage of delta growth. A theoretical model of the plane jet boundary layer in the initial stage of a lacustrine delta, including the consideration of gravity action on the slope and bottom friction, was established according to characteristics of this process, and a similarity solution method was used to solve the model. A coefficient ε was introduced that describes the characteristics of sediment-laden flow spreading along a straight line and its value is given. The theoretical expression of morphological characteristics of the initial stage was derived based on the general mathematical model of river bed evolution, and the erosion and deposition patterns were quantitatively analyzed. It was verified through experimental data that the theoretical model can be solved accurately and, can satisfactorily describe the trend in erosion and deposition and morphological characteristics of the initial stage of a delta.

Variation of dominant discharge along the riverbed based on numerical and deep-learning models: A case study in the Middle Huaihe River, China

River morphology plays an important role in water environment and resources. The dominant discharge (QD) is a crucial indicator for understanding river morphology and bed evolution under the impact of various interacting processes. At present, the identification of QD mainly depends on the analysis of a large number of hydrological data derived from measuring stations, leading to difficulty in obtaining detailed QD distributions along the study reach.In this paper, QD is approximately expressed as the bed-steadying discharge (QS) which is based on major factors of water level and sediment-carrying capacity. Subsequently, an integrated model combining a numerical fluid-flow and sediment model with a deep-learning algorithm is applied to analyze the changing process of the QS. The flow and sediment transport processes are simulated by the calibrated mathematical model, which are then adopted as the input sequences for the long short-term memory (LSTM) module. The verification results of the established LSTM model show robustness and accuracy in predicting the flow and sediment transport processes under multi-stage incoming flow and sediment conditions. Furthermore, the proposed integrated model is applied to identify the detailed process of QS in the Middle Huaihe River. Results show that the changing process of QS along the study reach is characterized by a particular trend of “increase-decrease-rapid increase” due to natural changes and human activities. Additionally, the QS agrees well with QD at the hydrological station, showing that QS can be applied as an approximation for QD along the study reach. By analyzing longitudinal and transverse profiles, the rationality of using QS as obtained by the newly presented model is demonstrated. Its temporal variation is also consistent with the cross-sectional changes for the specified stations.

Concerning the Stream Turbidity During the Laying of the Underwater Crossing of the Main Pipeline Across the River Lena

The stream turbidity significantly changes during the river bed evolution. It depends on the sediment storage, which is affected by the bottom dredging works, the construction of underwater crossings of main pipelines, bridge crossings, and others.In the present paper, we consider the change in the stream turbidity during the laying of the underwater crossings of the main pipelines (ML) across the river Lena. A significant increase in the water turbidity and the discharge of suspended sediment has been detected during the construction of linear structures intended for transporting the energy resources. The river bed erosion in the trench area is one of the factors of the decrease in the service life of the underwater crossing of ML when the siphon is trench laid across a water channel. When the bottom is scoured, and the siphon of the underwater pipeline is denuded, significant hydrodynamic loads not specified by the project are added to the operational loads. Torsional, bending, and overturning moments, as well as the phenomena of hydro-abrasive erosive wear, develop [1]. They lead to fatigue failure of individual sections of the underwater pipeline on the base metal and welded joints. It is crucial to conduct further studies to assess the deterioration degree of the ecological state of the river Lena.

River bed evolution processes under conditions of floodplain overgrowing with trees and shrubs vegetation

The article presents the investigation of the influence of tree and shrub vegetation on the discharge capacity of a river bed during high water. It was traced, that the calculating methods for roughness code and floodplain throughput capacity are good enough in case of a simple form of a river lengthwise section, but they do not work in case of meandering channels and in case of overgrown floodplain with vegetation: calculating errors significantly exceed the permissible ones. The method for eliminating the adverse effects of vegetation is proposed. The studies use the field observations results of the processes of vegetation influence on erosion effect and the sediment deposits. The field of observation is located in the middle part of the Volga-Akhtubinskaya floodplain (Kharabalinsky district). Space images (Yandex maps, Sputnik) of this area are used to improve the results of investigation. To correct the calculations in each specific case, it is necessary to carry out additional field hydrological studies. These studies will undoubtedly be much cheaper than the reconstruction costs of the hydraulic systems, and the costs of eliminating the accident results. Based on the research results, a simple and low-cost method for eliminating the impact of vegetation is proposed.

Assessing long-term evolution of the fine sediment budget in the Iffezheim reservoir: temporal upscaling of numerical simulations

ABSTRACT Since the construction of a weir at Iffezheim (Rhine-km 334) in 1977, a continuous deposition of sediments in the weir channel has been observed. The aim of this paper’s underlying investigations was to assess the long-term riverbed evolution of the Iffezheim reservoir in terms of deposition and erosion. The computational fluid dynamic model SSIIM-3D was applied to simulate the morphological changes in the weir channel. To reduce the computation time of long-term simulation (e.g. several decades), a reduced complexity approach called ‘classification of the boundary conditions for discharges (Q) and suspended sediment concentrations (SSC)’ was developed and applied to the Iffezheim reservoir. The basic idea of the approach was to replace instationary simulations by a precalculated series of simulations with stationary boundary conditions. For doing so, daily volume changes were precalculated by combining representative discharge and suspended sediment concentration regimes. To determine the results of the instationary simulation, the number of days in each bin of Q and SSC was counted, multiplied with the precalculated result and added up. The amount of the volume change in the reservoir for a certain period could then be obtained by adding up the calculated daily volume changes. The results of this method showed an acceptable agreement with measurements for long-term periods (years) and for short-term periods (months) with remarkably shortened computation times compared to the instationary simulations (of 97%).

Analysis of Riverbed Evolution of the Waigaoqiao Branch Channel of the Yangtze Estuary in Flood Period Under New Water and Sediment Conditions

With the change of sediment conditions in the Yangtze River Estuary, the river regime evolution pattern has entered a new stage. The overall trend has changed from siltation to erosion, and the impact of the evolution trend of overall river regime on local river regime needs to be further studied. Based on the hydrological and topographic data of flood season in 2020, this paper analyzes the riverbed change of Waigaoqiao branch channel during flood period under new water and sediment conditions. The river bed evolution law and causes of scouring and silting are analyzed statistically. Result shows that the water depth of branch channel decreases with the influence of channel dredging and river regime change in South Harbour under new water and sediment condition. During the flood period of 2020, the Waigaoqiao branch channel generally presents a continuous silting situation, mainly located in the front of Waigaoqiao Wharf (phase IV). The increase of sediment concentration caused by the flood and the scouring of shoal along the upstream of the branch channel are the main reasons for the silting of the branch channel. Based on the actual needs of waterway operation and maintenance, this paper puts forward relevant countermeasures and suggestions according to the analysis results.

A coupled 1-D/2-D model for simulating river sediment transport and bed evolution

AbstractThe paper details the method to couple a 1-D hydro-sedimentary model to a 2-D hydro-sedimentary model in order to represent the hydrodynamics and morphological processes during a flood event along a river. Tested on two field cases, the coupled model is stable even in the case of generalized overflow over the riverbanks or of levee breaching. For lateral coupling, the coupled model allows saving computational time compared to a full 2-D model and to provide valuable results concerning the flooding features as well as the evolution of the bed topography. However, despite a similar simplified representation of the sediment features in the 1-D and 2-D models, some discrepancies appear in the case of upstream/downstream coupling along a cross section perpendicular to the flow direction because the assumption of homogeneous velocity and concentration is not valid for estimating sediment transport. Further research is necessary to be able to define a suitable distribution of the sediments on the 1-D side of the boundary between the two models.

Accumulation phenomena in fluvial processes and the corresponding stochastic model

Accumulation occurs widely in fluvial processes. Accurately accounting for the effects of previous water and sediment conditions on accumulation is essential for studying riverbed evolution. In this study, to reveal the physical mechanisms of accumulation, various geometric observations of both the upstream and downstream reaches of dams on several typical fluvial channels were analyzed. The changes in water and sediment conditions were defined as external disturbances. Assuming that the probability of an external disturbance conforms to a Poisson distribution, and that the response intensity induced by an individual disturbance decays exponentially over time, a mathematical description of the accumulation of internal responses to external disturbances is given. Furthermore, a corresponding theoretical model for simulating the spatiotemporal readjustments of characteristic river variables is proposed based on stochastic theory. The proposed models are then applied to investigate spatiotemporal readjustment in the upper and lower reaches of dams following their construction. The results indicate that temporally, the vertical, lateral, and overall readjustment rates of the reaches are relatively fast in the early period following dam construction but then decrease rapidly over time. Accumulated riverbed degradation, channel width, and sedimentation continuously increase until a new dynamic equilibrium is reached. These phenomena reflect the representative accumulation characteristics of fluvial processes. Spatially, the erosion intensities in downstream reaches decrease nonlinearly along the channel until eventually diminishing. The unbalanced spatial distribution of erosion intensity arises from the system response characterized by propagation in space but decay over time, which is characteristic of accumulation phenomena after disturbances. The results of the developed model show that the spatiotemporal readjustments of the studied cross-sections and channel reaches can be accurately described by the unified theoretical formula derived herein. The model predictions show good agreement with observed field data with determination coefficients of 0.92, 0.93, 0.76, and 0.95 for vertical, lateral, longitudinal, and overall readjustments, respectively. The proposed theoretical models account for both the accumulation characteristics of fluvial processes and their spatial distributions. In demonstrating the proposed approach, this study provides a theoretical basis and new calculation method for quantitatively describing the spatiotemporal readjustments of non-equilibrium fluvial channels following external disturbances.

Scour Characteristics of the Underwater Crossing of Trunk Gas Pipeline Across the River Lena

The design data of the underwater crossing of the trunk gas pipeline (TGPL), which is an extension of the main gas pipeline of Hatassy GDS-2, for gasification of regions on the eastern side of the river Lena of the Republic of Sakha (Yakutia) are considered. Scours behaviour of the underwater crossing of TGPL across the river Lena is examined taking into account hydromorphological factors. The influence of hydrological and exogenous processes on the state of the underwater passage of Hatassy-Pavlovsk TGPL is shown by the example of the line-II. Changes of the river bottom profiles in the area of TGPL fixed at four discharge section lines, as well as water consumption were analyzed. It is shown that the presence of the underwater gas pipeline significantly affects the nature of the movement of micro- and meso-forms of the river bottom. It has been established that the constantly changing hydrological and hydromorphological processes resulted in sagging of the inverted siphon section in the line-II of the underwater crossing of Hatassy-Pavlovsk TGPL. During the designing and construction of the first line of the underwater gas pipeline across the river Lena, major omissions were committed, the peculiarities of the hydromorphological and hydrologic features of the river bed evolution in the section of the underwater passage of Tabaga-Kangalassy TGPL across the river Lena had not been taken into account. The effects of hydrodynamic and permafrost processes, heaving phenomena on floodplain and shore slope together increase the non-functional loads on the underwater gas pipeline. As a result of these factors, high longitudinal tensile stresses arise, especially in the welded joints of the inverted siphon pipes, and lead to accidents and incidents at the underwater gas pipeline across the river Lena.

Responses of river bed evolution to flow-sediment process changes after Three Gorges Project in middle Yangtze River: A case study of Yaojian reach

The Three Gorges Project (TGP) has changed the flow-sediment process in the middle Yangtze River. For navigation purposes, there is an urgent need to study the changes of the river regime over a long-term period and the shoal-channel evolution over different seasons since the completion of the TGP. Based on analysis of the measured data and the results of a two-dimensional mathematical model, the changes of the river regime and river bed evolution in the Yaojian reach downstream of the TGP were studied. Results show that a high sediment transport flux helps to keep the main flow in the North Branch, while a low sediment transport flux helps to keep the main flow in the South Branch. Thus, the main branch will not change in the near future because of the low sediment transport load. In this study, the flow-sediment process adjusted by the TGP was restored to the conditions before the TGP, and the river bed evolution under the adjusted and non-adjusted flow-sediment conditions was calculated. After the completion of the TGP, the reservoir storage accelerated the flood recession process and decreased the erosion by 11.9% under the flow-sediment conditions in 2010, and the deposition in the flood season decreased by 56.4%.

三角洲初始段射流边界层相似解求解

Sediment is carried by flow to the lake area during the formation process of the initial segment of a delta, which mainly depends on the initial momentum to maintain its own continuous movement. According to the characteristics of this process, the theoretical model for the plane jet boundary layer in the initial segment of the delta was established based on the shallow water equations for muddy water, and the flow field distribution of the initial segment of delta formation was obtained with the similarity solution method. Based on the general mathematical model of river bed evolution, the theoretical expression of the morphological characteristics of the initial segment was derived, and the erosion and deposition of the initial segment were quantitatively analyzed. Through the experimental verification, the theoretical solution can well describe the erosion and deposition trend and morphological characteristics in the early stage of delta formation.

MONITORING AND MANAGEMENT OF HYDROLOGICAL RISKS IN THE RIVER BASINS OF UKRAINE

Background of the study. Due to the increasing intensity and frequency of catastrophic floods occurrence, one of the most important tasks of the water management of Ukraine is to increase the efficiency of the existing system of flood protection due to the implementation of integrated flood risk management methods based on the assessment of flood hazard levels requirements according to Directive 2007/60/EC. The development of scientific and methodological bases for the assessment and mapping of flood hazard and risk levels, as well as the development of integrated flood risk management plans based on them, is an important and urgent task in Ukraine as an associated EU member.
 The purpose of the work is to highlight the main works results, performed at the Institute on the study of patterns of riverbed transformations, the development of strategies for flood risk management and scientific and methodological support of the assessment and mapping of flood hazard and risk, taking into account the nature and the intensity of river bed transformation and exogenous processes in river basins of Ukraine.
 Outline of the main material. Systematic research on flood protection issues and river bed evolution in IWPaLR has been conducted since the middle of the last century.
 The problems of the dynamics of river bed’s evolutions, ensuring the stability of dams, erosion of the tail water of dam, development of active hydraulic structures and their arrangement in river beds, forecasting river bed evolution, runoffs, development study of permissible (nondestructive) flow velocities for alluvial soils, taking into account the phenomenon of self-patching of the river bed, the dynamic equilibrium of the beds, the typing of the beds of mountain rivers, etc., were studied and solved under the natural conditions and in the hydraulic laboratory of the Institute. Based on the results of theoretical and experimental studies of river bed evolution, a number of methodological provisions on the complex regulation of channel deformations and safe passage of high floods were formulated and published a number of regulatory and methodological documents on the calculation and forecasting of river bed transformations, designing of dams and protection structures.
 An important role was given to the issues of regulation and redistribution of floodwater by the system of river reservoirs and replenishment of groundwater reserves.
 The methodological recommendations for sampling of river bed deposits and sediments, on the base of the international ISO standards’ requirements and recommendations of have been developed at the Institute, as well as the method of estimation of the river bed transformation’s dynamics, for the discrete and quantitative assessments of river bed deformations and their intensity.
 The paper also highlights the main results of work on the implementation of the Flood Directive 2007/60/EC in Ukraine, in particular, the development of a Flood Risk Management Strategy in the Ukrainian Carpathian River basins. In the Strategy declared the latest approaches to flood response, which foresee the abandonment of the current paradigm of "flood protection" to favor integrated flood risk management. It defines national mechanisms of strategic management in the field of flood risk reduction, directions of transboundary cooperation, coordination of works within river basins. For the future development of this Strategy, the paper presents the scientific and methodological bases for a comprehensive assessment of the total levels of flood hazard and flood risk and their mapping on a GIS basis.
 Conclusion. In the future, scientific research on integrated flood risk management should focus on the study of patterns of evolution of river bed and development of mathematical models of regulation of channel deformations, improvement of the flood forecasting and prevention methodology based on simulation modeling, as well as the development new management schemes for runoff ‘s regulation.

Extracting the Critical Rooting Length in Plant Uprooting by Flow From Pullout Experiments

AbstractThe growth and establishment of riparian vegetation on river bedforms is of hydrological as well as ecological importance as it helps in enhancing spatial heterogeneity and thus the biodiversity of river corridors. Yet, during floods, flow drag and scouring may reduce the rooting length of plants determining plant mortality via uprooting. In order for uprooting to occur, bed scouring must proceed until the rooting length reaches a critical value and drag forces exceed root residual anchorage. Therefore, the critical rooting length of a plant represents a crucial parameter to estimate the probability of plant removal due to flow erosion. However, difficulties in quantifying such length at the field scale have limited so far the performances of biomorphodynamic models for river bed evolution. In this work, we propose to assess the critical rooting length from controlled plant pullout experiments. To this aim, a free‐body model of the forces acting on a flexible plant in a stream at different erosion stages is developed. At incipient uprooting, we conjecture that the root resistance at the critical rooting length equals that of a plant with equal rooting length when pulled out in static conditions. To illustrate our approach, we validate our model on three different data sets obtained from small‐ and real‐scale plant uprooting experiments. A comparison between modeling and experimental observations reveals that the model provides valid results, despite its deterministic approach. The critical rooting lengths are finally used to assess the probability density function of the time to uprooting via a physically based stochastic model.

Advance of research on the numerical simulation of sediment transport in the Yellow River estuary

The numerical simulation of sediment transport in the Yellow River estuary is an important method to quantitative analyze the problems by water and sediment movement, including sediment deposition and river bed evolution, beach deposition and development, the formation and development of the delta, and so on. Making an intensive study of the problems is useful to study the principles of sediment movement and the evolution law of the estuary bed, and it is also important significance to scientific demonstrate of the estuary sediment deposition, sea water intrusion prevention treatment scheme and solve the problems of engineering. Based on the mathematical modeling of sediment transport and our research work, this paper analyzes the research statement, the unsolved issues and the developed trend of this kind problem, to provide the theoretical reference on more accurate numerical simulation of sediment transport in the Yellow River estuary and the scientific reference on the demonstration and decision of estuarine regulation scheme.