Erosion Coefficient Research Articles

Differential rock uplift along the northeastern margin of the Tibetan Plateau inferred from bedrock channel longitudinal profiles

Bedrock channel profile analysis is a robust reconnaissance tool for examining the rates and patterns of deformation in active orogens. Here, steepness and concavity indices were extracted from bedrock channels draining the northern Qilian Mountains based on the universal shear stress incision model. The profile analysis reveals a systematic spatial distribution of steepness and concavity indices. The average steepness index for channels draining the western part is approximately 1.6 times higher than that for the eastern part. Through empirical calibration of erosion coefficient K, the influence of channel width, rock strength, discharge and sediment flux are identified, and an approximately 1.1–1.2 times difference in K values is found between the west and east under the hypothesis that lithologic resistance and sediment flux have no contribution. Correlating profile analyses with parameter calibration, an approximate 2–3 times increase in the rock uplift rate is found from the eastern part to the western part of the orogen. The integration of this study with previous work in the eastern part of the mountains indicates that cross-strike (2–4 times) and along-strike (2–3 times) differential rock uplift both exist in the northeastern margin of the Tibetan Plateau. In addition, the abnormal values of concavity are apparently associated with the channels transecting large thrust fault zones. Thus, the shortening deformation may play a dominant role in controlling the differential rock uplift through folding and thrusting of the northeast-directed thrust faults across the northeastern margin of the Tibetan Plateau.

Trees within trees II: Nested fragmentations

Poursuivant l’idee de (Electron. J. Probab. 23 (2018)) ou les processus de coalescence emboites sont etudies, nous etendons ici la definition des processus de fragmentation markoviens homogenes aux processus de fragmentation a valeurs dans les partitions emboitees, c’est-a-dire les paires de partitions $(\zeta,\xi )$ telles que $\zeta$ soit plus fine que $\xi$. Comme dans le contexte classique (dit univarie), sous des hypotheses d’echangeabilite et de branchement, nous caracterisons la mesure de saut des processus de fragmentation emboites en termes de coefficients d’erosion et de mesures de dislocation. Les sauts d’une fragmentation emboitee peuvent etre de plusieurs natures differentes : nous distinguons trois formes d’erosions et deux formes de dislocations, l’une d’elles etant specifique au contexte des partitions emboitees et etant generee par un processus de pots de peinture bivarie.

Coupled modeling of bank retreat processes in the Upper Jingjiang Reach, China

AbstractBank retreat processes in the Upper Jingjiang Reach (UJR) have attracted much attention in recent years due to a high occurrence frequency, and these processes can be influenced significantly by the near‐bank fluvial erosion and variations in river stage and groundwater level. A coupled model was thus proposed in this study, integrating the module of bank‐toe deformation with the modules of groundwater level change and bank stability analysis. The proposed model was validated through comparisons between the calculated and measured bank erosion volumes and bank profiles at four typical sections in the UJR, with relatively close agreement being obtained. Multiple tests were conducted to investigate the model performance. These results show that: (i) a more rapid drawdown of river stage resulted in a more significantly delayed response of groundwater level to river stage, indicating that the bank may suffer a higher pore water pressure at the same river stage during the rapid drawdown period; (ii) a larger bank erosion volume was predicted, with the delayed response of groundwater level being considered. In addition, initial groundwater level may take a great impact on bank erosion simulations, especially for the banks with relatively lower soil permeability and shear strength); (iii) based on the adopted method of bank stability analysis, the occurrence of the first failure may greatly influence the sequential failures, and thus the total number and volume of bank failure; (iv) the calculated bank erosion volume was most sensitive to a change in the critical shear stress, especially to its decrease, when the erodibility coefficient was determined by an empirical function of the critical shear stress. © 2018 John Wiley & Sons, Ltd.

Salinity effects on the erosion behaviour of MX-80 bentonite: A modelling approach

Abstract The erosion behaviour of bentonites is influenced by the ions concentration to which they are exposed, which could lead to link the erodibility of bentonite to salinity. However, changes in salinity produce further changes in bentonite hydration and swelling that are not always considered. The aim of this work is to apply a numerical model to inspect the influence of salinity in the erosion behaviour of MX-80 bentonite, analysing the effect of swelling on erosion. To this end, a coupled hydro-chemo-mechanical and erosion model, which considers the expansive behaviour of bentonite as a function of salinity, and a hydro-mechanical model with a salinity-dependent erodibility coefficient are used to simulate pinhole erosion laboratory tests with saline waters. The results of the simulations illustrate that the influence of ion species concentration in the erosion behaviour of bentonites does not need a change in erodibility to be reproduced. On the contrary, they show that hydro-chemo-mechanical effects, and especially the changes that salinity induces in the swelling behaviour of bentonite, play a key role in erosion. Taking them into account leads to a more consistent formulation approach that can explain the observed behaviour, and, for that reason, such an approach is strongly recommended to analyse bentonite erosion processes.

Effect of source-varying input data on erosion potential model performance

This paper examines the performance of the Erosion Potential Method (EPM or Gavrilović) and the model response to input data variations caused by choosing different sources of information for the same parameter. The research presented addresses the input data uncertainty via an analysis of the two model input parameters (the soil protection coefficient and the soil erodibility coefficient). The parameter uncertainty analysis is performed following two different approaches: uncertainty analyses of both the selected sample size and the entire population are conducted for an erosion assessment case study of the Dubračina River catchment, Croatia. The analysis indicated that, when changing the data source, significant changes in the model outcome values can occur (up to 47% for this case study). Future method modifications should consider the mitigation of these two parameters by potentially making structural changes in the model and therefore moderating the effect.

Influence of Seepage Flows on the Erodibility of Fluidized Silty Sediments: Parameterization and Mechanisms

AbstractThe influence of seabed fluidization on the erosion of cohesive sediment has been well recognized, however, quantitative parameterization works are rather difficult and remain poorly understood. Therefore, case studies are still needed to achieve better results even locally. Silty seabed in the Yellow River Delta (YRD) has been exposed to frequent fluidization and serious erosion. The present paper attempts to advance the research progress on the influence of fluidization on erosion using an annular flume and the YRD silts as a case study. Erosion coefficients are found to increase from 8.27 × 10−5 to 5.44 × 10−4 , corresponding to fluidization degrees from 0.03 to 0.96. Erodibility may increase by 6–7 times when the bottom sediments are fluidized. The significant influence is successfully parameterized into the erosion coefficient of the linear erosion formulation. Both direction and magnitude of the seepage flows dominate the erodibility of fluidized silts. Infiltration inhibits while upward seepage enhances entrainment of fluidized sediments, specifically via (a) loss of the original cohesive force between soil particles, (b) uplifting seepage forces acting onto the sediments at the water‐seabed interface, which partially offset the particle gravity, and (c) seepage pumping of fines from the interior to the surface, which enlarges the surface Shield parameter.

Modeled Postglacial Landscape Evolution at the Southern Margin of the Laurentide Ice Sheet: Hydrological Connection of Uplands Controls the Pace and Style of Fluvial Network Expansion

AbstractLandscapes of the U.S. Central Lowland were repeatedly affected by the Laurentide Ice Sheet. Glacial processes diminished relief and disrupted drainage networks. Deep valleys carved by meltwater were disconnected from the surrounding uplands. The upland area lacking surface water connection to the drainage network is referred to as noncontributing area (NCA). Decreasing fractions of NCA on older surfaces suggest that NCA becomes drained over time. We propose that the integration could occur via (1) capture of NCA as channels propagate into the upland or (2) subsurface or intermittent surface connection of NCA to external drainage networks providing increased discharge to promote channel incision. We refer the two cases as “disconnected” and “connected” since the crucial difference between them is the hydrological connection of the upland to external drainage. We investigate the differences in evolution and morphology of channel networks in low‐relief landscapes under disconnected and connected regimes using numerical simulations. We observe substantially faster rates of erosion and integration of the channel network in the connected case. The connected case also creates longer, more sinuous channels than the disconnected case. Sensitivity tests indicate that hillslope diffusivity has little influence on the evolution and morphology. The fluvial erosion coefficient has significant impact on the rate of evolution, and it influences the morphology to a lesser extent. Our results and a qualitative comparison with landscapes of the glaciated U.S. Central Lowland suggest that connection of NCAs is a potential control on the evolution and morphology of postglacial landscapes.

Erosion estimation of guide vane end clearance in hydraulic turbines with sediment water flow

The end surface of guide vane or head cover is one of the most serious parts of sediment erosion for high-head hydraulic turbines. In order to investigate the relationship between erosion depth of wall surface and the characteristic parameter of erosion, an estimative method including a simplified flow model and a modificatory erosion calculative function is proposed in this paper. The flow between the end surfaces of guide vane and head cover is simplified as a clearance flow around a circular cylinder with a backward facing step. Erosion characteristic parameter of [Formula: see text] is calculated with the mixture model for multiphase flow and the renormalization group (RNG) k–[Formula: see text] turbulence model under the actual working conditions, based on which, erosion depths of guide vane and head cover end surfaces are estimated with a modification of erosion coefficient K. The estimation results agree well with the actual situation. It is shown that the estimative method is reasonable for erosion prediction of guide vane and can provide a significant reference to determine the optimal maintenance cycle for hydraulic turbine in the future.

Utilization of Water Turbidity Meter Devices in Estimating the Aggregate Stability of Many Artificially Stabilized Soils

This study is designed to utilize portable turbidity meters, usually available in most water analysis laboratories, in developing of a quick Dispersion Ratio test (DR, %) as an index of soil stability. The work includes: first, the use of many stabilizers (Bitumen, Lime and Cement) in the preparation of many artificially stabilized lead contaminated soil; second, the measurements of the scouring depth (SD, in mm), by a “Mini” Jet Erosion Test and then both the critical shear stress (τc, pa) and the erodibility coefficient (kd, cm3/kN.s); and finally, the comparisons between dispersion ratio (DR, %) values of soils, as estimated by a portable turbidity meter first and then by the gravimetric method. The results showed that all stabilizers can markedly improve the stability of soil; either as (SD, τc, and kd) or as (DR, %) and cement was the best. In general, good correlations were found between the turbidity (NTU) and suspended solids (mg/l) of the stabilized soils (R= 0.99, 0.96 and 0.97) for bitumen, lime and cement, respectively. However, the turbidity DR (%) appears to have a higher correlation with both lime (R= -0.98) and bitumen (R= -0.96) and in a lesser extent with cement (R= -0.87); because only 3% cement could sharply reduce DR of the untreated soil from 7.03 to 2.54%, compared with 4.9 and 4.25% for lime and bitumen respectively. Moreover, the turbidity DR (%) seems to be highly correlated with the kd of soils (R= 0.99, 0.96 and 0.90) for cement, bitumen and lime, respectively and cement was a superior in the reduction of both kd and DR (%) even at 3%. The salient conclusion of this work is that the turbidity DR (%) can be easily utilized to be as a successful index of soil stability. Because this method is quick and of results that are highly correlated with the erodibility coefficient (kd), this may suggest and recommend the use of the turbidity meter devices in estimating the stability of artificially stabilized soils and other similar soils.

Prediction of river bank erosion and protection works in a reach of Chenab River, Pakistan

The impacts of floods on river bank erosion are generally significant in the alluvial river reaches. This paper presents the prediction of the river bank erosion along the right bank in the reach of Chenab River (starting from downstream of Marala Barrage) where excessive erosion had been reported. The bank erosion is predicted due to flow/flood events of 2010 by coupling the output from the two-dimensional numerical model to the excess shear stress approach. The predicted bank erosion was compared with the one estimated from Landsat images. The Landsat ETM+ images were processed in the ArcGIS software to assess the external bank erosion. The results show that the excess shear stress approach underpredicts the bank erosion. Therefore, the erodibility coefficient was modified by forcing the best agreement between predicted and estimated (i.e., from Landsat images) bank erosion which was used for further analysis. The results reveal that coupling the output from the numerical model to the excess shear stress approach (by modifying the erodibility coefficient) predicts the river bank erosion with a reasonable level of accuracy, thus helpful to identify the locations for the protection works. The predicted river bank erosion presents good coefficient of determination (R2) of 0.82 when compared with the estimated bank erosion from Landsat images. The findings of the present study will help to implement the river protection works at the identified locations in the selected reach of River Chenab and will also act as a guideline for similar river reaches.

Computational Fluid Dynamics simulations of the Late Pleistocene Lake Bonneville Flood

At approximately 18.0 ka, pluvial Lake Bonneville reached its maximum level. At its northeastern extent it was impounded by alluvium of the Marsh Creek Fan, which breached at some point north of Red Rock Pass (Idaho), leading to one of the largest floods on Earth. About 5320 km3 of water was discharged into the Snake River drainage and ultimately into the Columbia River. We use a 0D model and a 2D non-linear depth-averaged hydrodynamic model to aid understanding of outflow dynamics, specifically evaluating controls on the amount of water exiting the Lake Bonneville basin exerted by the Red Rock Pass outlet lithology and geometry as well as those imposed by the internal lake geometry of the Bonneville basin. These models are based on field evidence of prominent lake levels, hypsometry and terrain elevations corrected for post-flood isostatic deformation of the lake basin, as well as reconstructions of the topography at the outlet for both the initial and final stages of the flood. Internal flow dynamics in the northern Lake Bonneville basin during the flood were affected by the narrow passages separating the Cache Valley from the main body of Lake Bonneville. This constriction imposed a water-level drop of up to 2.7 m at the time of peak-flow conditions and likely reduced the peak discharge at the lake outlet by about 6%. The modeled peak outlet flow is 0.85·106 m3 s−1. Energy balance calculations give an estimate for the erodibility coefficient for the alluvial Marsh Creek divide of ∼0.005 m y−1 Pa−1.5, at least two orders of magnitude greater than for the underlying bedrock at the outlet. Computing quasi steady-state water flows, water elevations, water currents and shear stresses as a function of the water-level drop in the lake and for the sequential stages of erosion in the outlet gives estimates of the incision rates and an estimate of the outflow hydrograph during the Bonneville Flood: About 18 days would have been required for the outflow to grow from 10% to 100% of its peak value. At the time of peak flow, about 10% of the lake volume would have already exited; eroding about 1 km3 of alluvium from the outlet, and the lake level would have dropped by about 10.6 m.

The role of thermal processes and target evaporation in formation of self-sputtering mode for copper magnetron sputtering

The main focus of the article is the study of function mechanisms of a magnetron sputtering system (MSS) with a heat-insulated metal target in a self-sputtering gasless mode. A distinctive feature of the studied case is that the target evaporation takes place along with its sputtering. The research has been carried out on a copper target sample in molybdenum crucible. It has been found that because of evaporation the MSS can function stably using metal vapors without sputtering gas. The pressure in the chamber is 0.01 Pa. The current-voltage characteristics and spatial distribution of the copper atoms concentration near the target have been determined at the power density from 14 to 72 W/cm2. The minimum power density necessary for a stable gasless self-sputtering mode is 19.4 W/cm2. Herewith the evaporated particles constitute approximately 87% of the total number of copper atoms near the target.It has been found that the erosion coefficients of metal targets at evaporation reach several tens of atoms per ion, which is an order of magnitude higher than the sputtering yield. Due to this, the coatings deposition under self-sputtering conditions takes place without reducing a deposition rate as compared to the case with sputtering gas.

Estimating Erodibility Parameters for Streambanks with Cohesive Soils Using the Mini Jet Test Device: A Comparison of Field and Computational Methods

The jet test device has been predominantly used for in situ critical shear stress (τc) and erodibility coefficient (kd) measurements of cohesive streambanks/beds using three analytical procedures: the Blaisdell method (BM), the iterative approach (IP), and the scour depth approach (SDP). Existing studies have reported that τc and kd estimates can be influenced by the computational procedure, time intervals for scour-hole depth measurements, and the pressure head selection. This study compared estimates of τc and kd among the three computational procedures using single and multiple pressure settings (SPS, MPS). A new method is introduced applying incrementally increasing pressure heads, hypothesizing depth-averaged erodibility parameters would be generated that better represent bank and fluvial erosion. Estimates of τc applying the MPS-BM procedure were greater by 17% to 100% compared with SPS-BM procedures and kd estimates were lower with less variability (σ = 3.54) compared with other procedures from 126 jet tests among 21 Tennessee stream sites. This finding supports the hypothesis of increasing τc and decreasing kd with greater soil depths into the bank, suggesting the MPS-BM procedure can improve the estimation of τc and kd using the mini-jet test device. Overall, this study demonstrates the need to standardize field and computational procedures.

Experimental study of erosion characteristics of soils in homogeneous embankments

The erosion characteristics of soils in homogeneous embankments is the key problem of dam breach which is directly related to the breach formation and the rate of breaching. The Erosion characteristics of several soils in embankment have been researched. On the basis of the erosion test results, the effects of dry density, net shear stress, sediment detachment exponent on the rate of erosion were analyzed. According to the results the sediment detachment exponent should be calculated based on the erosion velocity and net shear stress. It is not convenient for analysis if the value of sediment detachment exponent was set 1 for cohesive soil or 1.5 for non-cohesive soil. It has an definite logarithmic relationship between erosion coefficient and sediment detachment exponent. The critical shear stress has an significant effect on the rate of erosion of soils. The erosion resistance of soils in embankment dams and the dam safety can be evaluated well by using the sediment detachment exponent.

A New Erosion Model for Wind‐Induced Structural Vibrations

In recent years, computational fluid dynamics (CFD) method has been widely utilized in simulating wind‐induced snow drifting. In the simulating process, the erosion flux is the main controlling factor which can be calculated by the product of erosion coefficient and the differences between the flow stress and threshold stress. The erosion coefficient is often adopted as an empirical constant which is believed not to change with time and space. However, in reality, we do need to consider the influences of snow diameter, density, and wind speed on the erosion coefficient. In this technical note, a function of air density, sow particle density, snow particle radius, and snow particle strength bond is proposed for the erosion coefficient. Based on an experiment study, the effects of these parameters in erosion coefficient is analyzed and discussed. The probability distribution and value range of erosion coefficient are also presented in this technical note. The applicability of this approach is also demonstrated in a numerical study for predicting the snow distributions around a cube structure. The randomness of the structural vibrations is studied with details.

Efekti protiverozionih radova u slivu Palojske reke (Grdelička klisura)

The paper examines the effects of erosion control works performed in the Palojska River Basin, based on a comparative analysis of erosion intensities in 1953 and 2016. Intensive processes of erosion in the basin were reduced by performing technical works in the channel and biological and technical works on the slopes. The effects of the works conducted, accompanied by changes in the land use and socio-demography, are manifested in the reduction of the erosion coefficient from Z = 1.02 (surface excessive erosion) in 1953 to Z = 0.28 (mixed weak erosion) in 2016 and in the reduction of the sediment yield and transport in the basin.

Estimation of riverbank soil erodibility parameters using genetic algorithm

Determination of the erodibility parameters, such as critical shear stress and erodibility coefficient, are necessary before estimating the annual bank erosion (or bank retreat) at river reaches. However, in many cases, the river site is inaccessible making it difficult to assess the soil parameters either by in situ tests or by laboratory experiments. In this study, Genetic Algorithm (GA)-based optimisation technique was used to estimate the erodibility parameters of middle reaches of the Brahmaputra River in India. Two approaches were followed. At first, erodibility parameters were estimated using daily stage records at a selected site. Secondly, based on the annual observed bank erosions (bank retreat) from satellite images, erodibility parameters were estimated in three different river reaches. All these results were compared with that from a previous study using in situ jet tests. Annual bank erosions (bank retreat) were estimated using the median values of the erodibility parameters. The results agree well with the average observed annual bank erosion of these river reaches. In addition, the effects of measurement errors and optimisation algorithms on the parameter estimation were analysed. Sensitivity analysis of the parameters in GA was evaluated and it was found that GA can be utilised in the data-scarce regions to estimate the average erodibility parameters.

Relationships between physical‐geochemical soil properties and erodibility of streambanks among different physiographic provinces of Tennessee, USA

AbstractErosion of cohesive soils in fluvial environments is dependent on physical, geochemical and biological properties, which govern inter‐particle attraction forces and control detachment rates from stream beds and banks. Most erosion rate models are based on the excess shear stress equation where the soil erodibility coefficient (kd) is multiplied by the difference between the boundary hydraulic shear stress (τb) and the soil critical shear stress (τc). Both kd and τc are a function of soil properties and must be obtained through in situ field or laboratory testing. Many studies have generated predictive relationships for kd and τc derived from various soil properties. These studies typically were conducted in watersheds within a single physiographic region with a common surficial geology and/or investigated a limited number of soil properties, particularly geochemical properties. With widely reported differences in relationships between τc and soil properties, this study investigated differences in predictive relationships for τc among different physiographic provinces in Tennessee, USA. Erodibility parameters were determined in the field using a mini‐jet test device. Among these provinces, statistically four unique clusters were identified from a dataset of 128 observations and these data clusters were used to develop predictive models for τc to identify dominant properties governing erosion. In these clusters, 16 significant physical and geochemical soil properties were identified for τc prediction. Among these soil properties, water content and passing #200 sieve (percentage soil less than 75 μm) were the dominant controlling parameters to predict τc in addition to clay percentage (< 2 μm), bulk density, and soil pore water chemistry. This study suggests that unique relationships exist for physiographic provinces that are likely due to soil physical‐geochemical processes associated with surficial geology that determine minerology of the cohesive soil. Copyright © 2017 John Wiley & Sons, Ltd.

The influence of diamond blend on the resistance of polyimide films to atomic oxygen

Poly-pyromellitimide and polyamideimide film samples and their modifications obtained with a carbon filler (diamond blend) were irradiated with atomic oxygen flow at an average particle energy of 20 eV. Weight erosion coefficients were calculated for the initial and modified polyimides and a comparative analysis of the resistance of the film samples was carried out. The morphology of the film surface was studied after irradiation with atomic oxygen via scanning electron microscopy. An increase in the percentage of filler in the polymer matrix caused a slight increase in the resistance of the film samples to the effect of atomic oxygen.

Watershed Variability in Streambank Erodibility and Implications for Erosion Prediction

Two fluvial erosion models are commonly used to simulate the erosion rate of cohesive soils: the empirical excess shear stress model and the mechanistic Wilson model. Both models include two soil parameters, the critical shear stress (τc) and the erodibility coefficient (kd) for the excess shear stress model and b0 and b1 for the Wilson model. Jet erosion tests (JETs) allow for in-situ determination of these parameters. JETs were completed at numerous sites along two streams in each the Illinois River and Fort Cobb Reservoir watersheds. The objectives were to use JET results from these streambank tests to investigate variability of erodibility parameters on the watershed scale and investigate longitudinal trends in streambank erodibility. The research also determined the impact of this variability on lateral retreat predicted by a process-based model using both the excess shear stress model and the Wilson model. Parameters derived from JETs were incorporated into a one-dimensional process-based model to simulate bank retreat for one stream in each watershed. Erodibility parameters varied by two to five and one to two orders of magnitude in the Illinois River watershed and Fort Cobb Reservoir watershed, respectively. Less variation was observed in predicted retreat by a process-based model compared to the input erodibility parameters. Uncalibrated erodibility parameters and simplified applied shear stress estimates failed to match observed lateral retreats suggesting the need for model calibration and/or advanced flow modeling.