Bed Deformation Research Articles

Numerical Investigation of a Flash Flood Process that Occurred in Zhongdu River, Sichuan, China

In 2018, a flash flood occurred in the Zhongdu river, which lies in Yibin, Sichuan province of China. The flood caused many casualties and significant damage to people living nearby. Due to the difficulty in predicting where and when flash floods will happen, it is nearly impossible to set up monitors in advance to detect the floods in detail. Field investigations are usually carried out to study the flood propagation and disaster-causing mechanism after the flood’s happening. The field studies take the relic left by the flash flood to deduce the peak level, peak discharge, bed erosion, etc. and further revel the mechanism between water and sediment transport during the flash flood This kind of relic-based study will generate bigger errors in regions with great bed deformation. In this study, we come up with numerical simulations to investigate the flash flood that happened in the Zhongdu river. The simulations are based on two-dimensional shallow water models coupled with sediment transport and bed deformation models. Based on the real water level and discharge profile measured by a hydrometric station nearby, the numerical simulation reproduced the flash flood in the valley. The results show the flood coverage, water level variation, and velocity distribution during the flood. The simulation offers great help in studying the damage-causing process. Furthermore, simulations without considering sediment transport are also carried out to study the impact of bed erosion and sedimentation. The study proved that, without considering bed deformation, the flood may be greatly underestimated, and the sediment lying in the valley has great impact on flood power.

Experiments on Longitudinal and Transverse Bedload Transport in Sine-Generated Meandering Channels

Bedload grains in consecutive meandering bends either move longitudinally or across the channel centerline. This study traces and quantifies the grains’ movement in two laboratorial sine-generated channels, i.e., one with deflection angle θ0 = 30° and the other 110°. The grains originally paved along the channels are uniform in size with D = 1 mm and are dyed in various colors, according to their initial location. The experiments recorded the changes in the flow patterns, bed deformation, and the gain-loss distribution of the colored grains in the pool-bar complexes. We observed the formation of two types of erosion zones during the process of the bed deformation, i.e., Zone 1 in the foreside of the point bars and Zone 2 near the concave bank downstream of the bend apexes. Most grains eroded from Zone 1 are observed moving longitudinally as opposed to crossing the channel centerline. Contrastingly, the dominant moving direction of the grains eroded from Zone 2 changes from the longitudinal direction to the transversal one as the bed topography evolves. Besides, most building material of the point bars comes from the upstream bends, although low- and highly curved channels behave differently.

Preparation and Mechanical Properties of Polyurethane Material for Railway Ballast

ABSTRACTThe elastic solidification of track bed is a new track structure improvement technology between the traditional gravel track bed and the ballast less track monolithic track bed. It can effectively solve the main technical problems of heavy haul railway transportation, such as large impact force of wheel rail, serious deformation of track bed and frequent maintenance etc. In this paper, combined with the characteristics of polyurethane properties affected by its chemical composition, a solidified ballast polyurethane material suitable for heavy haul railway was developed by adding diluents and other materials. Physical property test and mechanical triaxial test were carried out to assess the influence of diluent content on the hardening effect of ballast; the physical process and mechanical properties of different proportion materials were analyzed. The experimental results show that adding appropriate amount of diluent into polyurethane material can effectively improve the integrity of ballast bed, increase the strength, reduce the deformation, and prolong the service life of ballast track bed.

A Numerical Study on Impacts of Sediment Erosion/Deposition on Debris Flow Propagation

Debris flows tend to erode sediment from or deposit sediment on the bed, which changes their volume and, thus, in turn, affects their rheological properties. However, previous modeling studies on debris flows mostly ignore sediment erosion/deposition. Here, three models are presented: a debris model without bed deformation, which is similar to traditional models in that it does not consider sediment erosion/deposition but uses the Herschel–Bulkley formulation to describe the non-Newtonian nature; a debris model with bed deformation, which is better improved than the traditional model in that it considers sediment erosion/deposition; and a turbidity current model, which is further simplified from the debris model with bed deformation by ignoring the non-Newtonian nature. These models, formulated in the same modeling framework, are solved by a shock-capturing finite volume method. These models were firstly validated against three laboratory experiments, which indicated that the debris models with and without bed deformation with reasonably well-specified parameters can give satisfactory agreements with the measurements, whereas the turbidity current model overestimated the experimental result due to its lack of yield stress and dynamic viscosity. Moreover, a hypothetical field application was used to explain the difference between a turbidity current and debris flows with and without bed deformation. It was shown that debris flows and turbidity currents are capable of impacting the bed significantly. However, turbidity currents have thinner tails, less shear stress, and form horizontal deposits on the bed, while debris flows have a thicker tail, high shear stress, and form vertical deposits on the bed. Finally, sensitivity analyses were carried out to study the impact of sediment size, bed slope, concentration, and porosity on the deformation of the bed after debris flow where they all showed a positive correlation.

Non-dispersive impact technology for powder flow characterization

This study developed a tester where the powder flow was characterized using a low sample mass (2 g) and impact instead of dispersion mechanism to mitigate test space constraint. An impact chamber was established where the test powder bed of seven lactose grades was weight-impacted to produce impact crater and ejecta, and imaged quantitatively to determine crater profiling signature (crater depth), regional topography (ejecta roughness), Otsu threshold (bed continuity) and edge segmentation (bed deformation). The Hausner ratio (HR) and Carr’s index (CI) values of lactose, and their powder dispersion distance and surface area characteristics evaluated by gas-pressurized dispersibility test were examined as reference method. The crater signature profiling and regional topography were correlated to HR, CI, dispersive distance and surface area. A poorer powder flow was characterized by higher values of crater signature profiling, regional topography, HR, CI, and lower dispersive distance and surface area. The crater signature profiling and regional topography values were higher with smaller and rougher lactose particles that were cohesive. The powder impact flow is a viable non-dispersive approach to characterize powder flowability using a small sample mass and test space.

Installation and adaptive management of T-shaped and L-shaped spur dikes to control bed deformation and diversify physical environment in rivers

This study concerns a method to install spur dikes in the Yodo River, for the purpose of bed deformation control and diversification of physical conditions around the spur dikes. The effects on the physical conditions around the installed spur dikes are evaluated, based on numerical analysis and field survey. The numerical analysis results show that, by installing spur dikes with a focus on hydraulic conditions of not forming sand bars, sediment deposition is suppressed in the main channel. The field survey results demonstrate that sediment deposition in the channel is also suppressed. By installing the spur dikes, some physical conditions around the installed spur dikes can be diversified. By installing spur dikes using large movable sandbags and changing their height after several years, it is possible to maintain the effect of the spur dike installation and diverse bed material conditions for a long period as adaptive management. (For example, by changing the height of the spur dikes 0.3 m lower, bed degradation is produced up to 0.5 m downstream of the spur dikes.) As a result, spur dike in case 8 (shape(c), height 0.7 m from average water level) is better for the present. After several years, changing the height of the spur dikes would be better.

On steady alternate bars forced by a localized asymmetric drag distribution in erodible channels

Studying the effect of different in-stream fluvial turbines siting on river morphodynamics allowed us to witness the onset of a time-averaged, large-scale, alternate distortion of bed elevations, which could not be exclusively related to the turbine rotor blockage. The longitudinal profiles of this two-dimensional bathymetric perturbation resemble those of steady fluvial bars. In this contribution we generalize the problem addressing a spatially impulsive, asymmetric distribution of drag force in the channel cross-section. This is experimentally investigated through the deployment of differently sized grids perpendicular to the flow, and analytically explored as a finite perturbation of an open channel flow over an erodible sediment layer, as described by a coupled flow–sediment shallow water equation. The steady solutions of this fluvial morphodynamic problem, physically represented by alternate bars scaling with the channel width, highlight the importance of the resonant conditions in defining the spatial extent of the bed deformation. The equations further suggest that in very shallow flows any asymmetric obstruction may lead to an upstream propagation of the steady bars, consistent with previous studies on the effects of channel curvature. In broad terms, this study provides the preliminary framework to control the onset of river meandering through imposed finite perturbations of the cross-section. In a more applied sense, it provides a tool to predict non-local scour–deposition patterns associated with the deployment of energy converters or other flow obstructions.

One-dimensional morphodynamic model for a tail reach of the Yellow River estuary

A one-dimensional morphodynamic model was improved to study the unsteady flow and sediment transport processes in a tail reach of the Yellow River estuary (YRE). In this model, the modified equations for flow hydrodynamics take the effects of sediment concentration and bed evolution into consideration. The improved model was validated using measurements in the tail reach of the YRE for the years 2003 and 2015, and the model showing an excellent data fit for discharge, water level, suspended sediment concentration and the cumulative volume of channel evolution. The effect of different cross-sectional spacings was also studied using the model results in the tail reach, with various numerical tests of the 2015 flood event conducted. It was found that an appropriate cross-sectional distance of less than 3.14 km should be adopted when simulating the process of bed deformation. Moreover, the interaction between runoff and tide in 2015 was studied on the basis of the simulated water levels and an empirical relation for the location of tidal limit was established. The results show that the tidal limit in 2015 was 15.84 km downstream of Xihekou.

The variation of load diffusion and ballast bed deformation with loading condition: an experiment study

ABSTRACT Ballast bed deformation is significantly influenced by its internal stress state. However, investigations concerning ballast bed deformation focus mainly on the deformation behaviour under various external loading conditions or ballast states, where the influence of load diffusion variation has rarely been considered directly. In this work, a full-scale model test was established to obtain simultaneously the external deformation and the internal stress of ballast bed, with respect to various loading conditions (equivalent axle load 14–30 t, 3–6 Hz). The results show that both average stress and stress ratio on ballast increase with loading magnitude. Meanwhile, a larger proportion of vertical load concentrates within the sleeper projection area. Accordingly, the plastic (elastic) deformation is more (less) sensitive to the load variation at larger wheel–rail load. Besides, the dynamic stiffness increases gradually with loading amplitude while showing a small drop as loading frequency increases.

Coupled modeling of bed deformation and stability analysis on a typical vulnerable zone on the Ningxia reach of the Yellow River during flood season

AbstractThe Ningxia reach of the Yellow River (NRYR) is wide and shallow, and instability and damages are likely to occur at its vulnerable zone. In this study, based on the one‐dimensional hydro‐sediment dynamics, two‐dimensional hydro‐sediment dynamics and vulnerable zone stability analysis model, a coupled model was established to analyze the scouring risk of the vulnerable zones in the NRYR during flood season. Considering the morphological change of bank slope at the vulnerable zones caused by flow erosion, the seepage stability of a typical spur dyke and protection embankment under the water level fluctuation conditions was analyzed. To fully reflect the coupled scouring effect of flow and sediment, the water flow scouring intensity index α is proposed. A significant increase of water flow scouring intensity index α will result in bank toe scouring, while its significant decrease will lead to silting of the bank toe. The probability of instability failure of the bank for the spur dyke slope is greater during the flood recession period. Compared with the influence of the change of river water level in the flood season, the slip stability of the bank slope is more sensitive to the change of bank toe erosion.

Not all Icequakes are Created Equal: Basal Icequakes Suggest Diverse Bed Deformation Mechanisms at Rutford Ice Stream, West Antarctica

AbstractMicroseismicity, induced by the sliding of a glacier over its bed, can be used to characterize frictional properties of the ice‐bed interface, which are a key parameter controlling ice stream flow. We use naturally occurring seismicity to monitor spatiotemporally varying bed properties at Rutford Ice Stream, West Antarctica. We locate 230,000 micro‐earthquakes with local magnitudes from −2.0 to −0.3 using 90 days of recordings from a 35‐station seismic network located ∼40 km upstream of the grounding line. Events exclusively occur near the ice‐bed interface and indicate predominantly flow‐parallel stick‐slip. They mostly lie within a region of interpreted stiff till and along the likely stiffer part of mega‐scale glacial lineations. Within these regions, micro‐earthquakes occur in spatially (<100 m radius) and temporally (mostly 1–5 days activity) restricted event‐clusters (up to 4,000 events), which exhibit an increase, followed by a decrease, in event magnitude with time. This may indicate event triggering once activity is initiated. Although ocean tides modulate the surface ice flow velocity, we observe little periodic variation in overall event frequency over time and conclude that water content, bed topography and stiffness are the major factors controlling microseismicity. Based on variable rupture mechanisms and spatiotemporal characteristics, we suggest the event‐clusters relate to three end‐member types of bed deformation: (1) continuous creation and seismogenic destruction of small‐scale bed‐roughness, (2) ploughed clasts, and (3) flow‐oblique deformation during landform formation or along bedrock outcrops. This indicates that multiple processes, simultaneously active during glacial sliding, can accommodate stick‐slip behavior and that the bed continuously reorganizes.

Whole body sensing dummy of the elderly to evaluate robotic devices for nursing care

ABSTRACT Robotic devices for nursing care are expected to help caregivers work with the elderly. Some robotic devices assist in the physical transfer of the elderly, and these robots come in contact with large surfaces of the human body. The regions of the buttock and the back may be uncomfortable due to the surface material or motions of the robotic devices. Therefore, sensing devices simulating a human body were developed to quantify and evaluate the load of a human body objectively. This simulated buttock consists of simulated bone and soft tissues, which include muscle, fat and skin. These regions have multi-axis force sensors to enable the quantification of the load due to the robotic devices used for nursing care. On measuring the soft exterior, it was found that the stiffness of the buttock dummy was similar to the human buttock. The comfort of a robotic bed was measured using the simulated buttock, and it was found that the shear force increased due to the deformation of the robotic bed. Thus, it was proven that the simulated buttock was capable of measuring the load of the human body when being used with robotic devices for nursing care.

Three-decadal erosion and deposition of channel bed in the Lower Atchafalaya River, the largest distributary of the Mississippi River

Many world's large rivers have experienced significant sediment reduction in the past century. However, channel aggradation near the mouth of these rivers may be still occurring or even accelerating, as evidenced by a recent study on the Lowermost Mississippi River. This study aims to investigate whether such a trend exists near the mouth of another large lowland alluvial river, the Atchafalaya River, which enters the Gulf of Mexico via two outlets — the natural mainstem and a man-made straight channel that is shorter and has a much greater slope. The overarching hypothesis is that, despite the reduction in riverine sediment delivery, lowland alluvial rivers such as the Lower Atchafalaya River in their backwater zone aggrade. We collected bathymetric survey records in 1977 and 2006 to analyze riverbed deformation. We utilized stage records at several gauging stations to determine the change in the hydraulic head over time. Geospatial techniques were used to develop channel bed Digital Elevation Models which were used to identify deformation of the 174-km channel bed of the Lower Atchafalaya River. We found a cumulative erosion of 6.34×107m3 and a cumulative deposition of 8.79×107m3, resulting in a net deposition of 2.45×107m3 during the study period. While much of the river including the man-made channel was in a degrading state, the last 35km of the river's natural mainstem experienced substantial aggradation. On average, riverbed elevation of the Lower Atchafalaya decreased by 1.47m in the upper 98km, but increased by 0.96m in the final 35km of the river's mainstem to the Gulf of Mexico. The channel erosion in the upstream reach will likely continue with the river discharge projected to increase, and the channel deposition in the downstream mainstem may accelerate because of sea-level rise.

Deformation mechanisms and kinematics of a soft sedimentary bed beneath the Scandinavian Ice Sheet, north-central Poland, revealed by magnetic fabrics

Characterising deformable substrates of modern and past ice sheets is a key factor in understanding ice mass behaviour and dynamics. This is challenging when field-scale signatures of deformation in soft sedimentary beds are weakly developed or absent. To overcome these difficulties, in this study, we combine micro- and macroscale studies and quantitative analyses to decipher the nature of subglacial sediment deformation under a Pleistocene fast-flowing (streaming) ice sheet. We investigated a complex sedimentary succession at Nieszawa in north-central Poland. A multi-proxy approach involving till micromorphology in thin sections, ripple-cross lamination orientation, till fabric, clast microfabric and the anisotropy of magnetic susceptibility (AMS) data in a closely sampled vertical profile throughout the fluvial sand and till was used to reveal subglacial bed deformation mechanisms and kinematics. This records subglacial deformation of the sedimentary succession at Nieszawa under low basal shear stresses, where simple shear was the dominant bed deformation mechanism. Intergranular advection, decoupling at the ice-bed interface related to high subglacial water pressure, clast ploughing, and basal sliding also took place. The main finding of this study is that AMS reveals the shear strain development and ice flow direction in the structurally and texturally complex deposits under weak coupling conditions at the ice-bed interface beneath a fast flowing/streaming ice sheet, where strain and kinematic indicators other than AMS fabrics are vague or absent.

EFFECTS OF PILE-GROUP LAYOUTS ON BED DEFORMATION AROUND THE STRUCTURE

Pile-groups are one of the hydraulic structures used for riverbank protection. Controlling the local scour around a pile-group is a desirable attempt for the structural stability. In this study, bed deformations around different pile-groups were investigated experimentally. This research was aimed to depict the effects of pile-group layout parameters on the bed characteristics. The maximum scour depth was well expressed by the modified blockage ratio with an identical trend in all the cases. Increasing the modified blockage ratio resulted in a larger scour and smaller deposition around all types of the pile-groups. Total scour volume in the channel was shown to be almost proportional to the maximum scour depth in all the cases.

A Computational Model for Simulation of Shallow Water Waves by Elastic Deformations in the Topography

We propose a coupled model to simulate shallow water waves induced by elastic deformations in the bed topography. The governing equations consist of the depth-averaged shallow water equations including friction terms for the water freesurface and the well-known second-order elastostatics formulation for the bed deformation. The perturbation on the free-surface is assumed to be caused by a sudden change in the bottom beds. At the interface between the water flow and the bed topography, transfer conditions are implemented. Here, the hydrostatic pressure and friction forces are considered for the elastostatic equations whereas bathymetric forces are accounted for in the shallow water equations. The focus in the present study is on the development of a simple and accurate representation of the interaction between water waves and bed deformations in order to simulate practical shallow water flows without relying on complex partial differential equations with free boundary conditions. The effects of location and magnitude of the deformation on the flow fields and free-surface waves are investigated in details. Numerical simulations are carried out for several test examples on shallow water waves induced by sudden changes in the bed. The proposed computational model has been found to be feasible and satisfactory.

One-dimensional morphodynamic model of channel deformation with the consideration of river regulation works and its application

在冲积河流上，各类河道整治工程的实施一定程度上会影响河床的演变过程.本文通过改进现有的一维水沙数学模型，重点研究护岸及护滩（底）这类限制河床进一步冲刷的整治工程对水沙输移及河床冲淤变形的影响.首先对固定断面的各节点采用特定的代码进行标记，以此区分河漫滩、有或无整治工程的主槽区域.然后对悬沙输移及河床冲淤变形模块进行改进：当断面发生淤积时，其形态调整不受整治工程的影响，淤积量将在整个断面上进行分配；当发生冲刷时，断面形态调整仅发生在未实施工程的位置或者受工程限制但形成了一定厚度淤积层的区域；在实施了整治工程且无法提供沙源的区域，河床冲刷则不会发生.最后长江中游荆江段2016年的模拟结果表明：考虑整治工程情况时，改进模型计算的河道冲刷量偏小且与实测值更为接近；河槽断面形态与实测结果也更为吻合.;A one-dimensional morphodynamic model has been improved to simulate the fluvial processes influenced by large-scale river regulation works, and the focus is paid to investigate the effect of a bank-, shoal- and bed-protection works. In the refined model, different zones of a cross-section are first demarcated by different point codes, including the zones of floodplain and main-channel with or without engineering. Then the modules of sediment transport and bed deformation are modified. When channel deposition occurs, it is not influenced by regulation engineering and the deposition volume will be allocated at a whole cross-section. However, channel scour will only occur at the unprotected bed or the protected bed with a deposition layer newly formed over the previous simulation period; at the protected bed without sediment to be scoured, erosion is not allowed. Then the Jingjiang Reach of the middle Yangtze River was selected as the study reach. Simulated results for the year 2016 show that the channel scours volume calculated using the improved model was smaller and in closer agreement with the measurements that without the consideration of river regulation works. Besides, the variation in channel geometry calculated by the improved model was more consistent with the measured result.

Geospatial Assessment of the State of the Samara River Floodplain in the Area of Coal Mining in Western Donbas

The discharge of highly mineralized mine waters of the Western Donbass negativelyaffected the Samara Bay area, which is of great fishery importance. Mine water storage pondswere built in deep erosional cuts in the territories of mine fields in the gullies of Kosminnaya,Taranova, Glinyana and Svidovok. The screening of the bottoms was not performed in any pond.The soils that make up the bottom are not aquicludes, which contributes to intensive filtration ofmine waters and pollution of aquifers. Artificial ponds built without waterproofing of bottoms,rock dumps, mine water discharge routes and other sources of pollution are actively involved inthe zone of influence of mine drainage and worsen the quality of drinking water, the reserves ofwhich in the Western Donbass are limited. There is flooding and flooding by groundwater, as wellas increasing (compared to the period before the violations) areas of land temporarily floodedduring floods on rivers in the valleys of the rivers Samara, Velyka Ternivka and such large beamsas Svydovok, Taranova, Kosminna due to subsidence of the earth’s surface. Differences in theconditions of formation of mine waters determine the nature and degree of their impact on theenvironment. The main difficulties making complicated accurate comparison between calculatedand field data in Samara river floodplain are following: a) changes in parameters of mining andpumping rates of water used for local needs; b) hydrological changes including formation ofnew channels, bed deformation; c) transformation of the monitoring network; d) increasing leakagethrough the clayey bottom of the ponds. The main objective is to provide a comprehensivegeo-ecological assessment of the state of the Samara river floodplain in the area of coal miningin the Western Donbass. Multispectral imagery of Sentinel-2 satellite system was used for remoteassessment within the study area. Geomorphologic assessment of the studied area was performedusing Sentinel-1 satellite radar interferometry. Flooding of the territory is observed due to minedrainage and subsidence of the earth’s surface. The risk of salinization of soils under the conditionsof water use from the beam “Glynyana” and from the Samara river is estimated as insignificant,from the beam “Kosminna” ‒ average. The SAR value of mine waters in “Taranova” and“Svydovok” beams corresponds to a high level of salinity. Samara river waters belong to the 3rdclass and are characterized as highly mineralized, sometimes unsuitable for irrigation. Intensivenatural overgrowth of the mine dumps that have passed the stage of mining reclamation has beenrecorded near the “Heroyiv of Space”, “Pavlogradska” and “Samarska” mines. The rate of selfgrowthof the land cover around the mine “Ternovska” and “Blagodatna” is estimated as average.The self-healing levels of the “Ternovska” and “Blagodatna West Donbasska” mines are ratedfrom low to high. The greatest risk of salinization of soils under conditions of use of water forirrigation is possible at a fence from artificial ponds located in Taranov’s and Svidovok’s beams.The conturs of “Verbsky”, “Ternivsky”, “Bogdanovsky” and “Boguslavskiy” piscicultural pondscan be corrected with map of remote sensing of Samara river floodplain geomorphology. The dataobtained can be useful during development of econetwork of promising ecological corridors inthe floodplain part of the Samara River as well..

Slow and intermittent stress relaxation of biomass granular media

In the present work, the relaxation of several wood powders has been investigated in an annular shear cell. It is found that the slow logarithmic relaxation commonly observed for various materials including granular materials is interrupted by large events. Their frequency and amplitude are investigated with respect to particle size and stress-history by measuring stresses and strain. These large events during the relaxation appear to be controlled by the deformation. The coarser the particles are, the bigger is the deformation of the powder bed between two fast relaxation events and during the event.

The development of an interactive database for assessing the ecological and geomorphic state of aquatic ecosystems

The paper discusses the basic principles of using geoinformation technologies to study relief-forming processes and the ecological state of aquatic ecosystems. The object of the study is the territory of the city of Sevastopol within the valleys of the Chernaya, Kacha and Belbek rivers. To conduct environmental monitoring, it is proposed to use field and chemical-analytical methods. According to the data obtained, information and analytical maps with a geodatabase are produced. Creation of an information and analytical map with a database using GIS toolkit makes it possible to identify factors influencing the deformation of the river bed and changes in the ecological state of aquatic ecosystems. The proposed technology for monitoring the study area allows saving data, using them in projects, and supplementing these data as new information becomes available.