a network scale intermediate complexity model for simulating channel evolution over years to decades abstract excessive river erosion and sedimentation threatens critical infrastructure degrades aquatic habitat and impairs water quality tools for predicting the magnitude of erosion sedimentation and channel evolution processes are needed for effective mitigation and management we present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale the model uses modified versions of bagnold s sediment transport equation to simulate bed erosion and aggradation as well as a simplified bank stability and toe erosion model bstem to simulate bank erosion processes the model is mechanistic and intermediate complexity accounting for the dominant channel evolution processes while limiting data requirements we apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution the model was also tested on two field data sets below parker dam on the lower colorado river and the north fork toutle river nftr which responded dramatically to the 1980 eruption of mount st helens it accurately predicts observed channel incision and bed material coarsening on the colorado river as well as observations for the upstream 18 km of the nftr watershed the model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower nftr where the channel migrated across a wide valley bottom rem is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance

provenance discrimination of surface sediments using rare earth elements in the yalu river estuary china rare earth elements ree are important tracers with which to explore sediment provenance this study analyzed the distribution features of ree in surface sediments of the yalu river estuary and determined their provenance estuarine systems of small rivers such as the yalu river are suitable target areas to understand sediment transport and transfer processes the fractional characteristics of ree distribution plots la yb ucc eu and ce anomalies la yb ree dendrograms and discriminant functions can all be used for provenance discrimination of the surface sediments in the yalu river estuary all these indicate that ree can be one of the most important tools for the study of the coupling mechanism between the watershed and coast either as a provenance tracer or as a signal of environmental change the results from this study show that the middle and upper reaches of the yalu river do not directly supply sediments to the estuarine delta the western branch transported most material before the construction of the shuifeng reservoir in 1941 and these sediments have diffused to other sections via re suspension the dayang river directly supplies sediments to the coasts of the northern yellow sea which is transported toward land under the action of tidal currents or storm surges these findings also reveal that anthropogenic activities have halted yalu river estuarine delta preservation and dominated regional landform development in the last 100 years

simulating bank erosion over an extended natural sinuous river reach using a universal slope stability algorithm coupled with a morphodynamic model meandering river channels are often associated with cohesive banks yet only a few river modelling packages include geotechnical and plant effects existing packages are solely compatible with single threaded channels require a specific mesh structure derive lateral migration rates from hydraulic properties determine stability based on friction angle rely on nonphysical assumptions to describe cutoffs or exclude floodplain processes and vegetation in this paper we evaluate the accuracy of a new geotechnical module that was developed and coupled with telemac mascaret to address these limitations innovatively the newly developed module relies on a fully configurable universal genetic algorithm with tournament selection that permits it 1 to assess geotechnical stability along potentially unstable slope profiles intersecting liquid solid boundaries and 2 to predict the shape and extent of slump blocks while considering mechanical plant effects bank hydrology and the hydrostatic pressure caused by flow the profiles of unstable banks are altered while ensuring mass conservation importantly the new stability module is independent of mesh structure and can operate efficiently along multithreaded channels cutoffs and islands data collected along a 1 5 km long reach of the semialluvial medway creek canada over a period of 3 5 years are used to evaluate the capacity of the coupled model to accurately predict bank retreat in meandering river channels and to evaluate the extent to which the new model can be applied to a natural river reach located in a complex environment our results indicate that key geotechnical parameters can indeed be adjusted to fit observations even with a minimal calibration effort and that the model correctly identifies the location of the most severely eroded bank regions the combined use of genetic and spatial analysis algorithms in particular for the evaluation of geotechnical stability independently of the hydrodynamic mesh permits the consideration of biophysical conditions for an extended river reach with complex bank geometries with only a minor increase in run time further improvements with respect to plant representation could assist scientists in better understanding channel floodplain interactions and in evaluating channel designs in river management projects

stability of composite river banks the stability of a river bank depends on the balance of forces motive and resistive associated with the most critical mechanism of failure many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size geometry and structure of the bank the engineering properties of the bank material the hydraulics of flow in the adjacent channel and climatic conditions rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt clay bank erosion occurs by fluvial entrainment of material from the lower cohesionless bank at a much higher rate than material from the upper cohesive bank this leads to undermining that produces cantilevers of cohesive material upper bank retreat takes place predominantly by the failure of these cantilevers three mechanisms of failure have been identified shear beam and tensile failure the stability of a cantilever may be analysed using static equilibrium and beam theory and dimensionless charts for cantilever stability constructed application of the charts requires only a few simple measurements of cantilever geometry and soil properties in this analysis the effects of cracks and fissures in the soil must be taken into account these cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface following mechanical failure blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue hence the rate of bank retreat is fluvially controlled even though the mechanism of failure of the upper bank is not directly fluvial in nature this cycle of bank erosion undermining cantilever failure and fluvial scour of the toe operates over several flood events and has important implications for river engineering channel changes and the movement of sediment through fluvial systems

sediment loads and sources in heavily modified irish catchments a move towards informed management strategies abstract implementation of the eu water framework directive 2000 60 ec has forced regulatory authorities to take an integrated view of the link between water quality and catchment management in northern ireland concern over progressive habitat degradation of one of the province s prime salmon rivers the river bush provided the stimulus for a sediment monitoring programme the aims of this study were to quantify instream sediment loads and to identify sources of fine sediment feeding into the river channel this information would then be used to justify changes in the way the catchment s resources were managed sediment loads were assessed at four sampling stations on the river bush system over a one year period between 18 07 02 and 24 07 03 using sediment collection tubes and pit type traps these ranged between 0 196 and 4 98 t yr 1 for bed load and 1 70 and 102 t yr 1 for suspended load a combination of desktop studies erosion potential mapping monitoring visual observations bank erosion magnitude and yield and analytical work sediment fingerprinting was then applied in order to elucidate links between catchment sediment erosion and downstream sediment delivery bank erosion was highest in regions of the catchment with the least cohesive bank materials during high flow conditions livestock poaching and peak flows caused damage to banks at a localised scale and led to selective patches of bare land being susceptible to further erosion augmenting the sediment load approximately 2 of the annual suspended sediment and 60 of the annual bed load drainage maintenance work 60 and 30 forest clearfell 1 and 2 and ploughed land 37 and 8 also contributed to the annual suspended sediment and bed load respectively nine key actions were suggested in order to improve habitat quality in relation to sediment supply in the river bush these included wetland restoration prohibiting drainage maintenance work strategies to control conifer plantation felling reducing bare ground livestock access restrictions construction site management macrophyte clearance employment of a river warden and systematic dissemination of project recommendations to the general public to generate community involvement it was essential that these actions were both cost effective and practical in order to maximise catchment stakeholder uptake

effects of riparian vegetation on stream bank subaerial processes in southwestern virginia usa riparian vegetation is frequently used for stream bank stabilization but the effects of vegetation on subaerial processes have not been quantified subaerial processes such as soil desiccation and freeze thaw cycling are climate related phenomena that deliver soil directly to the stream and make the banks more vulnerable to fluvial erosion by reducing soil strength this study compares the impact of woody and herbaceous vegetation on subaerial processes by examining soil temperature and moisture regimes in vegetated stream banks soil temperature and water tension were measured at six paired field sites in southwestern virginia usa for one year results showed that stream banks with herbaceous vegetation had higher soil temperatures and a greater diurnal temperature range during the summer compared to forested stream banks daily average summer soil water tension was 13 to 57 per cent higher under herbaceous vegetation than under woody vegetation probably due to evapotranspiration from the shallow herbaceous root system on the bank in contrast to summer conditions the deciduous forest buffers provided little protection for stream banks during the winter the forested stream banks experienced diurnal temperature ranges two to three times greater than stream banks under dense herbaceous cover and underwent as many as eight times the number of freeze thaw cycles during the winter the stream banks under the deciduous forests were exposed to solar heating and night time cooling which increased the diurnal soil temperature range and the occurrence of freeze thaw cycling study results also indicated that freeze thaw cycling and soil desiccation were greater on the upper stream bank due to thermal and moisture regulation of the lower bank by the stream therefore subaerial erosion and soil weakening may be greater on the upper stream banks additional research is needed on the influence of subaerial processes on both subaerial and fluvial erosion copyright 2006 john wiley sons ltd

stability of streambanks formed in partially saturated soils and effects of negative pore water pressures the sieve river italy abstract streambanks of alluvial channels are usually composed of loose materials which are unsaturated in ambient conditions unsaturated soils are subject to negative pore water pressures which cause an apparent cohesion the latter is the main factor in allowing the stability of near vertical banks even during moderate in bank flow events the apparent cohesion can be strongly reduced as the material approaches full saturation therefore during the drawdown phase as the confining pressure of the water in the channel disappears a bank failure is likely to occur channel bed level lowering along the sieve river central italy has caused widespread bank instability a geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils in order to obtain relations between bank angle and height in limit equilibrium conditions a stability chart was obtained with curves for different apparent cohesion values and a stability analysis was performed taking into account the effects of flow events in order to investigate the pore pressure effects a series of piezo tensiometers were installed in a streambank of the sieve river data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall evapotranspiration and water stage variations a planar failure with a tension crack occurred in the upper cohesive part of the bank during december 1996 the safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material safety factor variations through time are therefore shown as a function of seasonal variations in matric suction

modelling of the retreat process of composite riverbank in the jingjiang reach using the improved bstem bank retreat in the jingjiang reach is closely related not only to the near bank intensity of fluvial erosion but also to the composition and mechanical properties of bank soils therefore it is necessary to correctly simulate bank retreat to determine the characteristics of fluvial processes in the jingjiang reach the current version of bstem 5 4 was improved to predict riverbank retreat by inputting a dynamic water table and calculating the approximation of the distribution of dynamic pore water pressure in the soil near the river bank face and considering the depositional form of the failed blocks which is assumedly based on a triangular distribution with the slope approximately equalling the stable submerged bank slope and half of collapsed volume deposited in the bank toe region the degrees of riverbank stability at jing34 were calculated using the improved bstem the results indicate the following trends i the degrees of riverbank stability were high during the dry season and the rising stage which led to minimal bank failure and ii the stability degrees were low during the flood season and the recession stage with the events of bank collapse occurring frequently which belonged to a stage of intensive bank erosion considering the effects of bank toe erosion water table lag and the depositional form of the collapsed bank soil the bank retreat process was simulated at the right riverbank of jing34 the model predicted results exhibit close agreement with the measured data including the total bank retreat width and the collapsed bank profile a sensitivity analysis was conducted to determine the quantitative effects of toe erosion and water table lag on the degree of bank stability the calculated results for toe erosion indicate that the amount of toe erosion was largest during the flood season which was a primary reason for bank failure the influence of water table lag on the degree of stability demonstrates that water table lag was an important cause of bank failure during the recession stage

comparison of linear and nonlinear models for cohesive sediment detachment rill erosion hole erosion test and streambank erosion studies abstractcohesive sediment detachment is typically modeled for channels levees spillways earthen dams and internal erosion by using a linear excess shear stress approach however mechanistic nonlinear detachment models such as the wilson model have recently been proposed in the literature questions exist as to the appropriateness of nonlinear relationships between applied shear stress and the erosion rate therefore the objective of this research was to test the appropriateness of linear and nonlinear detachment models for cohesive sediment detachment using three data sets 1 rill erodibility studies across a limited range of applied shear stress 0 9 21 4 pa 2 hole erosion tests hets across a wide range of applied shear stress 12 6 62 0 pa and 3 streambank erodibility as quantified by jet erosion tests jets for the linear excess shear stress equation and the nonlinear wilson model across a small range of shear stress 1 4 pa the wilson model was also incorporated into the bank st

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

an alternative method for interpreting jet erosion test jet data part 2 application this paper reports the results of jet tester experiments on soil samples of uniform properties which allow quantitative application of the new theory proposed in part 1 of these publications this theory explores the possibly that a more adequate indicator of soil erodibility may be obtained by using the mass and so volume of soil eroded by the jet and the depth of scour penetration rather than by using penetration depth alone as assumed in the commonly used data interpretation method it is shown that scour geometry can be well described using a generalized form of the gaussian function defined by its standard deviation and maximum depth using a published expression for jet kinetic energy flux the new theory divides this flux into that used to erode soil and the remainder which is dissipated in a variety of ways jet experiments on a specially prepared uniform soil sample are reported which provide the key to determining the spatial variability in the profile resistance to erosion offered by field soils this resistance is expressed in the work required to erode unit mass of soil denoted as j in j kg the paper also gives results obtained on the profile variation in j for jet tests carried out at riverine sites on the upper brisbane river queensland australia as expected in most natural soil profiles the results show an increase in j with depth in the profile the soil resistance j is compared to the traditional interpretation of soil erodibility kd the graphical comparison of these two indicators illustrates the inverse type of relationship between them which is expected from their respective definitions but this relationship is associated with significant scatter possible reasons for this scatter are given together with comments on jet tester experience in a wide variety of soil types copyright 2017 john wiley sons ltd

seepage erosion in layered stream bank material current stream restoration practices often require anthropogenic manipulation of natural field soils to reconstruct stream banks in the absence of stabilizing vegetation for this study researchers conducted laboratory experiments on reconstructed non vegetated stream banks with layered soils experiencing seepage the objective of the study was to determine the effect of seepage pore water pressure and bank geometry on erosion and bank stability of layered streambanks the experimental design consisted of an intermediate size soil lysimeter packed with a sandy clay loam top soil and an underlying fine sand layer at three bank slopes 90 45 and 26 shallow groundwater flow and seepage resulted in bank failure of geometrically stable banks pop out failures liquid deformation and piping were all observed failure mechanisms in the underlying sand material dependent on the bank angle groundwater seepage processes created small scale failures of the underlying sand leading to larger scale failures of the overlying sandy clay loam the underlying sand layer eroded according to the initial bank angle and change in overburden loading the overlying loam layer failed along linear failure planes the gradually sloped bank i e 26 slope failed faster hypothesized to be due to less confining pressure and greater vertical seepage forces researchers analyzed the laboratory experiments using the bank stability and toe erosion model version 4 1 the model calculated an accurate shear surface angle similar to the failure angle observed in the lysimeter tests the model predicted failure only for the undercut 90 bank slope and indicated stable conditions for the other geometries steeper initial bank slopes and undercut banks decreased the bank factor of safety the observed failure mechanisms and measured saturation data indicated an interaction between overburden pressure seepage forces and bank slope on bank stability future bank stability modeling would benefit by incorporating lateral seepage erosion and soil liquefaction prediction calculations copyright 2009 john wiley sons ltd

rare earth element abundances in hydrothermal fluids from the manus basin papua new guinea indicators of sub seafloor hydrothermal processes in back arc basins abstract rare earth element ree concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the manus back arc basin vienna woods pacmanus desmos and susu knolls vent areas sampled vent fluids show a wide range of absolute ree concentrations and chondrite normalized reen distribution patterns lan smn 0 6 11 lan ybn 0 6 71 eu n eu n 1 55 reen distribution patterns in different vent fluids range from light ree enriched to mid and heavy ree enriched to flat and have a range of positive eu anomalies this heterogeneity contrasts markedly with relatively uniform reen distribution patterns of mid ocean ridge hydrothermal fluids in manus basin fluids aqueous ree compositions do not inherit directly or show a clear relationship with the ree compositions of primary crustal rocks with which hydrothermal fluids interact these results suggest that the rees are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of rees in submarine hydrothermal fluids in contrast differences in aqueous ree compositions are consistently correlated with differences in fluid ph and ligand chloride fluoride and sulfate concentrations our results suggest that the rees can be used as an indicator of the type of magmatic acid volatile i e presence of hf so2 degassing in submarine hydrothermal systems additional fluid data suggest that near seafloor mixing between high temperature hydrothermal fluid and locally entrained seawater at many vent areas in the manus basin causes anhydrite precipitation anhydrite effectively incorporates ree and likely affects measured fluid ree concentrations but does not affect their relative distributions

influence of seepage undercutting on the stability of root reinforced streambanks several mechanisms contribute to streambank failure including fluvial toe undercutting reduced soil shear strength by increased soil pore water pressure and seepage erosion recent research has suggested that seepage erosion of noncohesive soil layers undercutting the banks may play an equivalent role in streambank failure to increased soil pore water pressure however this past research has primarily been limited to laboratory studies of non vegetated banks the objective of this research was to utilize the bank stability and toe erosion model bstem in order to determine the importance of seepage undercutting relative to bank shear strength bank angle soil pore water pressure and root reinforcement the bstem simulated two streambanks little topashaw creek and goodwin creek in northern mississippi simulations included three bank angles 70 to 90 four pore water pressure distributions unsaturated two partially saturated cases and fully saturated six distances of undercutting 0 to 40 cm and 13 different vegetation conditions root cohesions from 0 0 to 15 0 kpa a relative sensitivity analysis suggested that bstem was approximately three to four times more sensitive to water table position than root cohesion or depth of seepage undercutting seepage undercutting becomes a prominent bank failure mechanism on unsaturated to partially saturated streambanks with root reinforcement even with undercutting distances as small as 20 cm consideration of seepage undercutting is less important under conditions of partially to fully saturated soil pore water conditions the distance at which instability by undercutting became equivalent to instability by increased soil pore water pressure decreased as root reinforcement increased with values typically ranging between 20 and 40 cm at little topashaw creek and between 20 and 55 cm at goodwin creek this research depicts the baseline conditions at which seepage undercutting of vegetated streambanks needs to be considered for bank stability analyses copyright 2008 john wiley sons ltd

exposed tree root analysis as a dendrogeomorphic approach to estimating bank retreat at the south river virginia abstract we use a biometric approach based on anatomical changes in the wood of exposed tree roots to quantify riverbank erosion along south river virginia a site where commonly applied techniques for determining bank erosion rates are either not appropriate because of the required spatial scale of analysis i e erosion pins traditional surveys lidar analysis or have failed to detect obvious erosion i e photogrammetric techniques we sampled 73 exposed roots from 22 study reaches and identified the year of exposure macroscopically 2 to 20 times magnification and microscopically 20 to 100 times magnification comparing the estimated erosion rates between levels of magnification and to those obtained with photogrammetric techniques we found no statistical differences between the results of macroscopic and microscopic analyses t test 0 01 but encountered difficulty in identifying the year of root exhumation in some samples when comparing exposed root analysis to photogrammetric techniques the results indicate that the exposed root approach is a feasible and effective method for estimating annual to decadal scale bank erosion in addition to producing erosion rates statistically indistinguishable from photogrammetric techniques at sites with erosion rates large enough for detection using historical aerial photographs regression analysis and t test 0 01 exposed root analysis was able to estimate erosion rates at sites where photogrammetric techniques failed we also identify deciduous species well suited for this approach fraxinus pennsylvanica and others that prove more problematic e g acer negundo celtis occidentalis acer saccharinum this study is significant because it describes a robust tool that provides insights into annual to decadal scale erosion where other commonly applied techniques may not be appropriate or easily applied

bank undercutting and tension failure by groundwater seepage predicting failure mechanisms groundwater seepage can lead to the erosion and failure of streambanks and hillslopes two groundwater instability mechanisms include i tension failure due to the seepage force exceeding the soil shear strength or ii undercutting by seepage erosion and eventual mass failure previous research on these mechanisms has been limited to non cohesive and low cohesion soils this study utilized a constant head seepage soil box packed with more cohesive 6 and 15 clay sandy loam soils at prescribed bulk densities 1 30 to 1 70 mg m 3 and with a bank angle of 90 to investigate the controls on failure mechanisms due to seepage forces a dimensionless seepage mechanism sm number was derived and evaluated based on the ratio of resistive cohesion forces to the driving forces leading to instability including seepage gradients with an assumed steady state seepage angle tension failures and undercutting were both observed dependent primarily on the saturated hydraulic conductivity effective cohesion and seepage gradient also shapes of seepage undercuts for these more cohesive soils were wider and less deep compared to undercuts in sand and loamy sand soils direct shear tests were used to quantify the geotechnical properties of the soils packed at the various bulk densities the sm number reasonably predicted the seepage failure mechanism tension failure versus undercutting based on the geotechnical properties and assumed steady state seepage gradients of the physical scale laboratory experiments with some uncertainty due to measurement of geotechnical parameters assumed seepage gradient direction and the expected width of the failure block it is hypothesized that the sm number can be used to evaluate seepage failure mechanisms when a streambank or hillslope experiences steady state seepage forces when prevalent seepage gradient forces should be considered when analyzing bank stability and therefore should be incorporated into commonly used stability models copyright 2013 john wiley sons ltd

variability of fluvial erodibility parameters for streambanks on a watershed scale abstract typically the erosion rate of cohesive soils is modeled using the excess shear stress equation which includes two soil parameters the erodibility coefficient k d and the critical shear stress c alternatively a mechanistic detachment rate model the wilson model was recently developed to predict the erosion rate of cohesive soils also based on two soil parameters b 0 and b 1 the wilson model is proposed as advantageous in terms of being a more mechanistic fundamentally based erosion equation the objective of this research was to derive the excess shear stress model parameters k d and c from field jet erosion tests jets on numerous streambanks across the illinois river watershed in oklahoma to investigate i erodibility parameter variability or uniformity at a river basin scale ii correlations between the derived parameters and soil texture iii influence of solution technique on the estimated erodibility parameters and iv the applicability of predictive relationships between k d and c the second objective was to demonstrate the applicability of the mechanistic wilson model using field jet data and to investigate correlations between the excess shear stress model parameters k d and c and the wilson model parameters b 0 and b 1 erodibility parameters for streambanks of varying soil texture were measured using a miniature version of the jet device mini jet data from the jets were used to derive the erodibility parameters using a blaisdell and scour depth approach soil samples were acquired at locations of the jets to quantify particle size distribution average particle size d 50 and bulk density no significant relationships existed between k d or c and bulk density d 50 percent clay silt or sand or percent clay silt existing empirical relationships should be used with caution considering the variability between the results observed in this research and previous relationships proposed in the literature strong correlations were observed between b 0 and k d r 2 0 62 to 0 89 and between b 1 and c r 2 0 31 to 0 96 therefore the wilson model parameters closely resemble the empirical excess shear stress parameters

sources of ree in sediment cores from the rainbow vent site 36 14 n mar a geochemical investigation was carried out on two sediment cores collected at 2 and 5 km from the rainbow hydrothermal vent site bulk sediment compositions indicate that these cores record clear enrichments in fe cu mn v p and as from hydrothermal plume fallout cave et al 2002 cave r r german c r thomson j nesbitt r w 2002 fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge geochim cosmochim acta 66 11 1905 1923 sequential dissolution of the bulk sediments has been used to discriminate between a leach biogenic and oxy hydroxide component and a residual phase detrital and sulphide sulphate fractions major element data al fe ti mn mg ca si and index reveal that the hydrothermal input as recorded in the leach phase is much stronger than apparent from bulk sediment analyses alone ree patterns for the leach phase record contributions from both biogenic carbonate mimicking seawater ree patterns and hydrothermal oxy hydroxides with the latter exhibiting positive eu anomalies hydrothermal derived and negative ce anomalies seawater derived based on major element and ree data the residue contains contributions from aeolian dust input local morb material and a hydrothermal component ternary ree mixing calculations indicate that most of the ree within the residual fraction 80 is derived from hydrothermal material while detrital contributions to the ree budget as deep sea clay and volcanic debris are

effects of riparian plant roots on the unconsolidated bank stability of meandering channels in the tarim river china abstract meandering channels with highly sinuous and distorted bends have developed along the middle and lower reaches of the tarim river in northwestern china riverbanks composed of unconsolidated materials have much lower bank strengths and are susceptible to fluvial erosion and bank collapse particularly under high flow conditions thus the formation and development of meander bends in such environments appear unintuitive it is logical to speculate that riparian plant roots in unconsolidated banks have significant effects on bank stability and bend development in the absence of cohesive sediments but this has not been verified to determine the influence of root cohesion on the bank stability of meandering channels in the tarim river in situ measurements and sampling of roots from locally dominant riparian vegetation i e populus euphratica pe tamarix ramosissima tr and phragmites australis pa were conducted on the meandering bends to obtain root parameters including diameter and root area ratio the radius of curvature of local bends corresponding to sampling sites was also calculated using remote sensing imagery we used the bank stability and toe erosion model bstem to quantitatively estimate the effects of different root conditions on channel bank strength the results confirmed that roots and sand root composites provide effective reinforcement to unconsolidated banks control the bank erosion and hence enhance bank stability however the effects were highly variable under different root conditions pa roots generally improved bank strength more than those of pe or tr with pa pe and tr improving bank strength by 88 2 73 2 and 63 6 respectively riparian vegetation in this extremely arid and unconsolidated sediment environment therefore appears to be a prerequisite for sustaining the meandering channel

p sv conversions of teleseismic waves beneath the chyulu hills volcanic field kenya observations of p sv converted waves provide new insights on the structure of the lithosphere beneath the chyulu hills a quaternary volcanic field on the se shoulder of the kenya rift east africa a 3d teleseismic delay time tomography and a seismic refraction model revealed a zone of reduced p wave velocity 3 5 extending from the lower crust into the uppermost mantle limited to about 70 km depth in this paper waveform and particle motion analyses are used to identify p sv conversions in teleseismic recordings and to search for lateral variations of seismic discontinuities data from 9 teleseisms contain clear sv phases within the first 8 seconds of the p coda the depth of the generating interfaces is determined with a local velocity depth function based on the seismic refraction model our results show that there are no lateral depth variations of the conrad 19 21 km and moho 43 45 km discontinuities indicating no large scale modification of the crustal structure through the magmatic processes in the time window between the sv arrivals from the conrad and moho discontinuities additional sv energy is observed at some stations but its origin cannot be located

erodibility of cohesive streambeds in the loess area of the midwestern usa excess stress parameters critical shear stress c and erodibility coefficient k d for degrading channels in the loess areas of the midwestern usa are presented based on in situ jet testing measurements critical shear stress and k d are used to define the erosion resistance of the streambed the jet testing apparatus applies hydraulic stresses to the bed and the resulting scour due to the impinging jet is related to the excess stress parameters streams tested were primarily silt bedded in texture with low densities which is typical of loess soils results indicate that there is a wide variation in the erosion resistance of streambeds spanning six orders of magnitude for c and four orders of magnitude for k d erosion resistance was observed to vary within a streambed from streambed to streambed and from region to region an example of the diversity of materials within a river system is the yalobusha river basin in mississippi the median value of c for the two primary bed materials naheola and porters creek clay formations was 1 31 and 256 pa respectively streambeds composed of the naheola formation are readily eroded over the entire range of shear stresses whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the porters creek clay formation therefore assessing material resistance and location is essential in classifying and modelling streambed erosion processes of these streams

evaluation of the bank stability and toe erosion model bstem for predicting lateral retreat on composite streambanks abstract streambank erosion is known to be a major source of sediment in streams and rivers the bank stability and toe erosion model bstem was developed in order to predict streambank retreat due to both fluvial erosion and geotechnical failure however few if any model evaluations using long term streambank retreat data have been performed the objectives of this research were to 1 monitor long term composite streambank retreat during a hydraulically active period on a rapidly migrating stream 2 evaluate bstem s ability to predict the measured streambank retreat and 3 assess the importance of accurate geotechnical fluvial erosion and near bank pore water pressure properties the barren fork creek in northeastern oklahoma laterally eroded 7 8 to 20 9 m along a 100 m length of stream between april and october 2009 based on regular bank location surveys the most significant lateral retreat occurred in mid to late may and september due to a series of storm events and not necessarily the most extreme events observed during the monitoring period bstem version 5 2 was not originally programmed to run multiple hydrographs iteratively so a subroutine was written that automatically input the temporal sequence of stream stage and to lag the water table in the near bank ground water depending on user settings eight bstem simulations of the barren fork creek streambank were performed using combinations of the following input data with and without a water table lag default bstem geotechnical parameters moderate silt loam versus laboratory measured geotechnical parameters based on direct shear tests on saturated soil samples and default bstem fluvial erosion parameters versus field measured fluvial erosion parameters from submerged jet tests using default bstem input values underestimated the actual erosion that occurred lagging the water table predicted more geotechnical failures resulting in greater streambank retreat using measured fluvial and geotechnical parameters and a water table lag also under predicted retreat approximately 3 3 m but did predict the appropriate timing of streambank collapses the under prediction of retreat was hypothesized to be due to over predicting the critical shear stress of the non cohesive gravel under predicting the erodibility of the non cohesive gravel and or under predicting the imposed shear stress acting on the streambank current research improving our understanding of shear stress distributions streambank pore water pressure dynamics and methods for estimating excess shear stress parameters for noncohesive soils will be critical for improving bstem and other streambank stability models

coupled simulations of fluvial erosion and mass wasting for cohesive river banks the erosion of sediment from riverbanks affects a range of physical and ecological issues bank retreat often involves combinations of fluvial erosion and mass wasting and in recent years bank retreat models have been developed that combine hydraulic erosion and limit equilibrium stability models in related work finite element seepage analyses have also been used to account for the influence of pore water pressure in controlling the onset of masswasting this paper builds on these previous studies by developing a simulation modeling approach in which the hydraulic erosion finite element seepage and limit equilibrium stability models are for the first time fully coupled application of the model is demonstrated by undertaking simulations of a single flow event at a single study site for scenarios where i there is no fluvial erosion and the bank geometry profile remains constant throughout ii there is no fluvial erosion but the bank profile is deformed by simulated mass wasting and iii the bank profile is allowed to freely deform in response to both simulated fluvial erosion and mass wasting the results are limited in scope to the specific conditions encountered at the study site but they nevertheless demonstrate the significant role that fluvial erosion plays in steepening the bank profile or creating overhangs thereby triggering mass wasting however feedbacks between the various processes also lead to unexpected outcomes specifically fluvial erosion also affects bank stability indirectly as deformation of the bank profile alters the hydraulic gradients driving infiltration into the bank thereby modulating the evolution of the pore water pressure field consequently the frequency magnitude and mode of bank erosion events in the fully coupled scenario differ from the two scenarios in which not all the relevant bank process interactions are included

bank and near bank processes in an incised channel abstract gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion the interaction of these forces control streambank mechanics hydraulic forces exerted by flowing water on in situ bank toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower bank profiles seepage forces exerted on in situ bank material by groundwater downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength data from a study site on goodwin creek ms usa clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore water pressures negative pore water pressures matric suction have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear a stable bank can be transformed into an unstable bank during periods of prolonged rainfall through 1 increase in soil bulk unit specific weight 2 decrease or complete loss of matric suction and therefore apparent cohesion 3 generation of positive pore water pressures and therefore reduction or loss of frictional strength 4 entrainment of in situ and failed material at the bank toe and 5 loss of confining pressure during recession of stormflow hydrographs relatively small frequent flows during the winter have the ability to erode failed bank materials maintain oversteepened unstable bank surfaces and promote prolonged periods of bank retreat channel migration and high yields of fine grained sediment confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe which steepens the bank for example more than 2 m of bank retreat occurred during the study period at the research site on goodwin creek northern mississippi the loss of matric suction negative pore pressures due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability apparent cohesion friction angle soil bulk unit weight and moisture content were measured in situ matric suction was measured continuously in situ with a series of five pressure transducer tensiometers a bank failure algorithm which combines the mohr coulomb approach for saturated conditions and the fredlund modification for unsaturated conditions was developed for layered cohesive streambanks the resulting equation has been used successfully to investigate the role of matric suction positive pore water pressures and confining pressure for layered streambanks composed of cohesive materials

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

stochastic erosion of composite banks in alluvial river bends the erosion of composite river banks is a complex process involving a number of factors including fluvial erosion seepage erosion and cantilever mass failure to predict the rate of bank erosion with these complexities a stochastic bank erosion model is suitable to define the probability distribution of the controlling variables in this study a bank erosion model in a river bend is developed by coupling several bank erosion processes with an existing hydrodynamic and morphological model the soil erodibility of cohesive bank layers was measured using a submerged jet test apparatus seasonal bank erosion rates for four consecutive years at a bend in the brahmaputra river india were measured by repeated bankline surveys the ability of the model to predict erosion was evaluated in the river bend that displayed active bank erosion in this study different monsoon conditions and the distribution functions of two variables were considered in estimating the stochastic bank erosion rate the probability of the soil erodibility and stochastic stage hydrographs for the nth return period river stage additionally the influences of the deflection angle of the streamflow longitudinal slope of river channel and bed material size on bank erosion rate were also investigated the obtained stochastic erosion predictions were compared with the observed distribution of the annual average bank erosion rate of 45 river bends in the brahmaputra river the developed model appropriately predicted the short term morphological dynamics of sand bed river bends with composite banks copyright 2014 john wiley sons ltd

the hydraulic conductivity structure of gravel dominated vadose zones within alluvial floodplains the floodplains of many gravel bed streams have a general stratigraphy that consists of a layer of topsoil covering gravel dominated subsoil previous research has demonstrated that this stratigraphy can facilitate preferential groundwater flow through focused linear features such as paleochannels or gravelly regions within the vadose zone these areas within the floodplain vadose zone may provide a route for interactions between the floodplain surface and alluvial groundwater effectively extending the hyporheic zone across the floodplain during high stream stage the objective of this research was to assess the structure and scale of texture heterogeneity within the vadose zone within the gravel subsoils of alluvial floodplains using resistivity data combined with hydraulic testing and sediment sampling of the vadose zone point scale and broad scale methodologies in combination can help us understand spatial heterogeneity in hydraulic conductivity without the need for a large number of invasive hydraulic tests the evaluated sites in the ozark region of the united states were selected due to previous investigations indicating that significant high conductivity flow zones existed in a matrix which include almost no clay content data indicated that resistivity corresponded with the fine content in the vadose zone and subsequently corresponds to the saturated hydraulic conductivity statistical analysis of resistivity data and supported by data from the soil sampling and permeameter hydraulic testing identified isolated high flow regions and zones that can be characterized as broad scale high hydraulic conductivity features with potentially significant consequences for the migration of water and solutes and therefore are of biogeochemical and ecological significance

numerical simulation of hydrodynamics and bank erosion in a river bend we present an integrated analysis of bank erosion in a high curvature bend of the gravel bed cecina river central italy our analysis combines a model of fluvial bank erosion with groundwater flow and bank stability analyses to account for the influence of hydraulic erosion on mass failure processes the key novel aspect being that the fluvial erosion model is parameterized using outputs from detailed hydrodynamic simulations the results identify two mechanisms that explain how most bank retreat usually occurs after rather than during flood peaks first in the high curvature bend investigated here the maximum flow velocity core migrates away from the outer bank as flow discharge increases reducing sidewall boundary shear stress and fluvial erosion at peak flow stages second bank failure episodes are triggered by combinations of pore water and hydrostatic confining pressures induced in the period between the drawdown and rising phases of multipeaked flow events

numerical simulation of widening and bed deformation of straight sand bed rivers ii model evaluation in this paper the numerical model presented in the companion paper is tested and applied assessment of model accuracy was based on two approaches first predictions of evolution of a 13 5 km reach of the south fork of the forked deer river in west tennessee were compared to observations over a 24 yr period results suggest that although the model was able to qualitatively predict trends of widening and deepening quantitative predictions were not reliable simulated widths and depths were within 15 of the corresponding observed values but observed change in these parameters at the study sites were also close to these values simulated rates of depth adjustment were within 15 of observed rates but observed rates of channel widening at the study sites were approximately three times those simulated by the model in the second approach the model was used to generate relationships between stable channel width and bank full discharge the model was able to successfully replicate the form of empirically

stage dependent transient storage of phosphorus in alluvial floodplains models for contaminant transport in streams commonly idealize transient storage as a well mixed but immobile system these transient storage models capture rapid near stream hyporheic storage and transport but do not account for large scale stage dependent interaction with the alluvial aquifer the objective of this research was to document transient storage of phosphorus p in coarse gravel alluvium potentially influenced by large scale stage dependent preferential flow pathways pfps long term monitoring was performed at floodplain sites adjacent to the barren fork creek and honey creek in northeastern oklahoma based on results from subsurface electrical resistivity mapping which was correlated to hydraulic conductivity data observation wells were installed both in higher hydraulic conductivity and lower hydraulic conductivity subsoils water levels in the wells were monitored over time and water samples were obtained from the observation wells and the stream to document p concentrations at multiple times during high flow events contour plots indicating direction of flow were developed using water table elevation data contour plots of total p concentrations showed the alluvial aquifer acting as a transient storage zone with p laden stream water heterogeneously entering the aquifer during the passage of a storm pulse and subsequently re entering the stream during baseflow conditions some groundwater in the alluvial floodplains had total p concentrations that mirrored the streams total p concentrations a detailed analysis of p forms indicated that particulate p i e p attached to particulates greater than 0 45 m was a significant portion of the p transport this research suggests the need for more controlled studies on stage dependent transient storage in alluvial systems copyright 2011 john wiley sons ltd

secondary current effects on cohesive river bank erosion 1 the emphasis of this research was placed on the development of a methodology that allows 1 an adequate representation of the distribution of the near bank shear stress s when secondary currents are present and 2 estimation of the critical erosional strength cr and other sediment erodibility parameters for fluvial erosion these two factors combine to form the overarching objective of this investigation which was carried out in union flat creek a stream with pronounced cross sectional irregularities located within the loess region of the palouse basin of washington state united states the study has shown that the presence of the secondary currents increases the magnitude of the depth averaged sidewall shear stress at least by a factor of 2 0 it was also found that the ratio of the maximum to the depth averaged sidewall shear stress is greater than 5 these findings suggest therefore that use of the may be a good approximation of the fluid shear stress magnitude for simple channel geometries but not for natural channels characterized by complex geometries the measured critical erosional strength cr 4 16 pa was comparable with the findings of other laboratory and field studies that also focused on palouse sediments

on slope instability induced by seepage erosion this paper is focused on seepage erosion causing liquefaction processes and rapid slope failures one case history which occurred along an old fluvial terrace in the po plain northern italy is

divergence and flow direction as indicators of subsurface heterogeneity and stage dependent storage in alluvial floodplains assuming homogeneity in alluvial aquifers is convenient but limits our ability to accurately predict stream aquifer interactions research is needed on i identifying the presence of focused as opposed to diffuse groundwater discharge recharge to streams and ii the magnitude and role of large scale bank and transient storage in alluvial floodplains relative to changes in stream stage the objective of this research was to document and quantify the effect of stage dependent aquifer heterogeneity and bank storage relative to changes in stream stage using groundwater flow divergence and direction monitoring was performed in alluvial floodplains adjacent to the barren fork creek and honey creek in northeastern oklahoma based on results from subsurface electrical resistivity mapping observation wells were installed in high and low electrical resistivity subsoils water levels in the wells were recorded real time using pressure transducers august to october 2009 divergence was used to quantify heterogeneity i e variation in hydraulic conductivity porosity and or aquifer thickness and flow direction was used to assess the potential for large scale 100 m bank or transient storage areas of localized heterogeneity appeared to act as divergence zones allowing stream water to quickly enter the groundwater system or as flow convergence zones draining a large groundwater area maximum divergence or convergence occurred with maximum rates of change in flow rates or stream stage flow directions in the groundwater changed considerably between base and high flows suggesting that the floodplains acted as large scale bank storage zones rapidly storing and releasing water during passage of a storm hydrograph during storm events at both sites the average groundwater direction changed by at least 90 from the average groundwater direction during baseflow aquifer heterogeneity in floodplains yields hyporheic flows that are more responsive and spatially and temporally complex than would be expected compared to more common assumptions of homogeneity copyright 2012 john wiley sons ltd