sediment motion and velocity in a glacier fed stream current understanding of coarse sediment transport e g threshold for motion travel length and virtual velocity in mountain rivers is still quite limited and even less is known about glacial streams however the hydrological characteristics of these systems strong daily discharge fluctuations high water turbidity pose challenges to the use of tracers to monitor bed sediment dynamics as tagged clasts are usually located after bedload events when flow stage has receded e g by means of portable antennas in the case of passive integrated transponders pit the use of stationary antennas still scarcely in use worldwide to detect pit tagged particles has potential advantages in glacier fed streams if water discharge is monitored continuously a stationary antenna provides real time data on the actual discharge at the moment of tracer particles passage this study focuses on incipient motion and virtual velocity of bed particles measured by a stationary antennas system in a steep mountain channel saldur river drainage area 18 6 km2 italian alps where significant daily discharge fluctuations and bedload transport occur as a result of a nivo glacial regime four stationary antennas were installed 50 m apart in the study reach a total of 629 pit tagged clasts were inserted in the studied reach between 2011 and 2014 ranging in size from 35 mm to 580 mm with an overall recovery rate of around 44 critical discharge for sediment entrainment was obtained by detecting the movement of tracers placed immediately upstream of antennas virtual velocity was derived by knowing distances between the antennas and travel time of tracers results on initiation of motion show that the relationship between the size of transported tracers and the discharge measured at the time clasts were passing the stationary antenna is very weak the influence of antecedent flows on incipient motion was thus investigated by dividing the highest discharge recorded between each pit deployment and the subsequent entrainment by the actual critical discharge at the time of movement ratio qmax qc results show that approximately 50 of tracers moved at qmax qc 1 2 and that 73 of tracers moved at qmax qc 1 5 therefore about 30 of tracers had to previously experience a discharge substantially greater than the one that actually mobilized them also coarser particles moved at higher qmax qc ratios suggesting that higher antecedent flows may be needed to destabilize bed clustering results on the virtual velocity of the pit tagged clasts employed in the field show that the virtual velocity turned out to be highly variable ranging from 101 to 10 5 m min 1 and weakly related to either particle size or flow discharge however virtual velocity was well correlated with the highest flow discharge experienced by each tracer normalized by a percentile of the flow duration curve this evidence further stresses the importance of flow history on sediment entrainment and transport finally the pros and cons of the deployed monitoring technology are discussed

an experimental investigation of mechanisms involved in bed load sheet production and migration 1 field measurements indicate that in gravel bed rivers bed load may not be a one to one response to shear stress but may instead fluctuate a great deal over time for a given flow condition both in flume and field experiments these fluctuations were often associated with migration of low relief bed forms called bed load sheets whereas several studies have described bed load sheets as a consequence of grain sorting little is known about the mechanisms responsible for their production and migration these were investigated in flume experiments a set of 20 experiments was conducted under constant feeding rate conditions with mixtures of different uniform sediments and for slopes varying from 0 8 to 9 except for runs performed in high flow conditions we observed periodic bed load sheet production and migration associated with fluctuations of bed slope bed state bed fining and paving and bed load observations allowed us to conclude that bed load sheets resulted from very efficient vertical and longitudinal grain sorting that produced periodic local bed aggradation and erosion clearly observed in the upstream section of the flume fractional transport rates were measured in one run combined with the results of experiments previously conducted by authors with uniform sediments this experiment showed that the highest peak solid discharges were essentially caused by the much greater mobility of the coarser gravels when transported within bed load sheets a scenario is proposed for the mechanisms involved in bed load sheet production and migration

effective shear stress of graded sediments 1 a meta analysis of fractional mobilization data from 14 sets of experiments totaling 103 different mixed sand and gravel beds and flow conditions has been carried out in order to identify an expression for effective shear stress here defined as the component of bed shear stress that is directly involved in transporting each grain size fraction in graded sediment in doing so we test the assumption that excess stress should be defined solely in terms of a critical stress rather than effective stress which exhibits sensitivity to the flow stage in contrast to the approach which evaluates the size distribution effects on motion threshold by comparing inferred transport rates an alternative approach is utilized which is based on the skill of reproducing the measured mobilized particle size distribution a simple equation is developed for mobilization of sediment mixtures based on a well established transport law and employing a classical hiding function approach to the problem of mitigating the bias toward mobilizing fine material in the mixture we use inverse methods to find the optimal form of the hiding function which provides the best fit with the data we find that the hiding function is indeed sensitive to the flow and bed composition on this basis a simple deterministic equation is proposed for fraction specific effective stress which outperforms the next best existing formula based on critical stress by 34 on aggregate

comment on effects of hydraulic roughness on surface textures of gravel bed rivers and effects of sediment supply on surface textures of gravel bed rivers by john m buffington and david r montgomery

normal and anomalous diffusion of gravel tracer particles in rivers received 12 december 2008 revised 16 november 2009 accepted 10 december 2009 published 4 may 2010 1 one way to study the mechanism of gravel bed load transport is to seed the bed with marked gravel tracer particles within a chosen patch and to follow the pattern of migration and dispersal of particles from this patch in this study we invoke the probabilistic exner equation for sediment conservation of bed gravel formulated in terms of the difference between the rate of entrainment of gravel into motion and the rate of deposition from motion assuming an active layer formulation stochasticity in particle motion is introduced by considering the step length distance traveled by a particle once entrained until it is deposited as a random variable for step lengths with a relatively thin e g exponential tail the above formulation leads to the standard advection diffusion equation for tracer dispersal however the complexity of rivers characterized by a broad distribution of particle sizes and extreme flood events can give rise to a heavy tailed distribution of step lengths this consideration leads to an anomalous advection diffusion equation involving fractional derivatives by identifying the probabilistic exner equation as a forward kolmogorov equation for the location of a randomly selected tracer particle a stochastic model describing the temporal evolution of the relative concentrations is developed the normal and anomalous advection diffusion equations are revealed as its long time asymptotic solution sample numerical results illustrate the large differences that can arise in predicted tracer concentrations under the normal and anomalous diffusion models they highlight the need for intensive data collection efforts to aid the selection of the appropriate model in real rivers

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

experimental study of incipient motion in mixed size sediment transport rates of five sediments were measured in a laboratory flume three of these sediments had the same mean size the same size distribution shape and different values of grain size distribution standard deviation the critical shear stress for incipient motion of the individual size fractions within these sediments was estimated as that shear stress that produced a small dimensionless transport rate the sorting of the sediment mixture had little effect on the critical shear stress of individual fractions once the median size d50 of the mixture and a fraction s relative size di d50 are accounted for our data combined with previously published data show a remarkably consistent relation between the critical shear stress of individual fractions and the fraction s relative grain size despite a broad variation in the available data of mixture sorting grain size distribution shape mean grain size and grain shape all fractions in a size mixture begin moving at close to the same value of bed shear stress during steady state transport conditions this result is apparently true for transport systems where the transport rates of individual fractions are determined solely by the flow and bed sediment recirculating systems as well as for systems where the fractional transport rates are imposed on the system feed systems this equivalence in initial motion results is important because natural transporting systems often show attributes of both types of behavior in an unknown combination

tephra fallout hazard assessment for a plinian eruption scenario at volcan de colima mexico abstract volcanic ash fallout associated with renewal of explosive activity at colima represents a serious threat to the surrounding urbanized area here we assess the tephra fallout hazard associated with a plinian eruption scenario the eruptive history of volcan de colima shows that plinian eruptions occur approximately every 100 years and the last eruption the 1913 represents the largest historic eruption of this volcano we used the last eruption as a reference to discuss volcanic hazard and risk scenarios connected with ash fallout tephra fallout deposits are modeled using hazmap a model based on a semi analytical solution of the advection diffusion sedimentation equation for volcanic particles based on a statistical study of wind profiles at colima region we first reconstructed ash loading maps and then computed ground load probability maps for different seasons the obtained results show that a plinian eruptive scenario at volcan de colima could seriously damage more than 10 small towns and ranches and potentially affect big cities located at tens of kilometers from the eruptive center the probability maps obtained are aimed to give support to the risk mitigation strategies

experimental study of the transport of mixed sand and gravel we measured a wide range of transport rates for five different sand gravel mixtures in a laboratory flume each mixture used the same gravel and sand was added to produce mixtures containing 6 15 21 27 and 34 sand control of other variables allows us to isolate the effect of bed sand content on transport as sand content increases gravel transport rates increase by orders of magnitude even though the proportion of gravel in the bed decreases the increase in gravel transport rate is most rapid over the range of bed sand content between 15 and 27 the increase in transport rate is larger than predicted using standard scaling relations between transport rate and grain size indicating that models of transport and sorting and predictions of stream channel response to sand inputs need to be revised to account for the influence of sand content bed surface grain size was measured at the end of each run surface grain size varied with sand content but showed little or no coarsening with flow strength and transport rate this casts doubt on the idea that armor layers form at small flows and weaken or vanish with increasing flow and transport rate

sampling techniques for gravel sized sediments the methods commonly used for sampling the coarser surface layers of gravel bed streams are reviewed it is found that while an areal sample is biased toward the coarser grains compared with a volumetric sample of the same material the conversion formula suggested by a voidless cube model overcompensates for this effect a modified version of the cube model that accounts for porosity is proposed the modified cube model and tests conducted with areal sampling using wax indicate that area by weight analyses can be converted successfully to the equivalent bulk sieve analyses the average depth of the wax samples ranged from d65 d91 increasing with median grain size the equivalence of the grid by number and bulk sieve analyses is reaffirmed

grain size and topographical differences between static and mobile armour layers a series of laboratory flume experiments under conditions of sediment starvation zero sediment feeding and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers the experiments were carried out in an 8 m long flume using a bimodal grain size mixture d50 6 2 mm and a range of shear stresses ranging from 4 0 to 8 6 n m 2 the results confirm that a static armour layer is coarser than a mobile one and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength an analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges the topography of mobile armour layers created by rising discharges differed they exhibited a greater roughness length scale and were less organized despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation also the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges these differences were mainly due to the transport of the coarser fraction of bed sediments which diminished to zero over the static armour because of being hidden within the bed whereas in the mobile armour the coarser particles protruded into the flow and were actively transported increasing the vertical roughness length scale overall the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness detailed elevation models of exposed surfaces of gravel bed rivers are required to provide critical insight on the sediment availability and sedimentation processes copyright 2011 john wiley sons ltd

effects of check dams on bed load transport and steep slope stream morphodynamics abstract check dams are transversal structures built across morphologically active streams in mountainous regions these structures have been used widely in torrent hazard mitigation for over 150 years thousands of them are regularly maintained by stream managers and torrent control services the stabilization role of these structures is well known i e they durably constrain the stream bed through the creation of vertical and planar fixed points what is not yet clear is to what extent check dams influence bed load transport how do peak solid discharge or flood transported volume change when check dams are added to a reach to address these questions long lasting small scale experiments were conducted in a 4 8 m long flume with either one three or no structures the results show that the addition of structures creates independent compartments in the bed level which have a strong influence on bed surface armouring and stream morphodynamics the consequence is that instantaneous transport intensities are unchanged but peak solid discharge occur more often and for shorter duration this results in the same total transported volume over the long term but reduced volume for a single transport event it reaffirms the observation of pioneering authors of the mid 19th and early 20th century who conceptualized the possible sediment transport regulation function of check dams in addition to stabilizing the stream bed check dams influence bed load transport through a buffering effect releasing frequently and in small doses what in their absence would be transported abruptly en masse during rare extreme events

structural properties of mobile armors formed at different flow strengths in gravel bed rivers differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume the temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size microtopography and bed organization at both grain and mesoscales measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds structured mobile armors formed quickly in each experiment at the grain scale 1 45 mm 9 ds50 17 mm where ds50 is the median surface particle size surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor particles comprising the armor also became flow aligned and developed imbrication at a larger scale 100 200 mm the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations metrics of mobile armor structure showed remarkable consistency over prolonged periods of near constant transport demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure bed structuring was least developed in the experiments conducted at the lowest flow strength however little difference was observed in the structural metrics of the mobile armors generated at higher flows although the range of transport rates studied was limited the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low 0 03 where is the dimensionless shear stress

downstream fining in a rapidly aggrading gravel bed river downstream changes in particle size that occur in the waipaoa river a 104 km long gravel bed river in which rapid aggradation in the historic post 1800 period was triggered by the conversion of native forest to pasture are summarized in this paper the textural data presented are unique for a field situation not only because of the spatial resolution and extent of the sampling program but also because they provide information about the pattern of fining at different points in time they are supported by equally comprehensive topographic survey data from which local rates of aggradation can be derived despite variability induced by lateral sediment inputs there is an essentially continuous pattern of fining along the entire length of the river fining occurs in both the fine and coarse size fractions of the bed material the highest rates of fining occur in the larger percentiles of the subsurface bed material and in the surface bed material downstream fining in the waipaoa river appears to be a response to changes in flow hydraulics that are regulated by the concave configuration of the long profile the fining gradient developed rapidly in 45 years it does not appear to be influenced by the rate of aggradation nor the overall rate of sediment supply to the channel system because in the short term aggradation has a negligible impact on the inherited form of the long profile

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

alluvial morphodynamics of low slope bedrock reaches transporting nonuniform bed material research on bedrock rivers primarily focused on bedrock incision and to the best of our knowledge morphodynamic models have not yet considered the variability of sediment grain size and the prese

vertical gradational variability of fines deposited in a gravel framework vertical gradational structures develop as sand infiltrates into static gravel beds understanding the vertical distribution of interstitial sand deposits will improve predictions of ecological suitability and hyporheic hydrodynamics a series of flume experiments was performed to investigate fine infiltration processes four sand distributions were introduced into flows over gravel beds after each experiment bed cores were extracted and analysed in vertical layers to examine the gradational trends with depth vertical trends of fine content were highly sensitive to the relative grain size distributions of the gravel bed and the introduced sand for experiments with d15gravel d85sand ratios 15 4 and larger unimpeded static percolation was observed where sand filled the voids relatively uniformly from the bottom of the gravel layer to the top experiments with ratios 10 6 and smaller bridged sand clogged a thin layer of gravel pores near the bed surface precluding subsequent infiltration interstitial sand deposits fined with depth of penetration for all experiments which was the result of three distinct but overlapping processes i granular sorting as particles fell through the substrate smaller material preferentially passed through the voids deeper into the gravel ii bed load sorting size segregation occurs in the wake of the leading bed form as smaller particles saltate further and settle first iii hydraulic sorting smaller sand was transported preferentially as suspended load filling the deep voids of the furthest flume positions downstream finally when the experiments that formed a bridge layer were replicated with higher bed shear stresses less interstitial sand deposition was observed higher shear stresses transported coarse particles downstream more efficiently causing bridge layers to form earlier and allowing less time for suspended load to settle into the deeper substrate pores before the pathways were closed

experimental study of the coarse surface development effect on the bimodal bed load transport under unsteady flow conditions abstractgravel bed rivers display a surface layer that is coarser than the substrate lining below this armored surface the armored layer that is developed under certain flow conditions may be attributed as water worked sediment bed both the threshold of incipient motion and the bed load transport are affected by the presence of this layer in this study the coarse surface development and its effect on the sediment transport were investigated experimentally in a rectangular flume four antecedent flow rates were combined with an input hydrograph without sediment feeding the reference shear stress of individual fractions and the grain size distribution were determined after the development of the coarse surface due to the antecedent flow then a triangular shaped hydrograph was generated for both the intact surface and the coarse surface cases it was seen that the maximum bed load transport values obtained in unsteady flow experiments were highly dependent on the coarse surface formed by the anteceden

upstream sediment input effects on experimental dune trough scour in sediment mixtures 1 understanding causes of dune irregularity especially dune trough scour is important for the modeling of vertical sorting of sediment mixtures in morphological models of rivers with sediment mixtures sediment in dunes is generally sorted in a fining upward manner which affects the sediment transport composition depending on the scour depth distribution of the dunes why dunes become more irregular and develop deep scour holes in some conditions is only partially understood moreover there is a feedback between vertical sorting and dune irregularity in gravelly sands erosion resistant coarse layers may form that decrease or inhibit dune trough scour the causes of dune irregularity and the feedback by coarse sediment layers are explored in experiments and are demonstrated to be related partly to the upstream sediment boundary condition determined by the experimental setup sediment feeding or recirculating sediment recirculation flumes promote fining of the transported sediment and formation of a less or immobile gravel lag layer in the dune troughs sediment feed flumes may force the transported sediment at the flume entry to be equal to the bed sediment equal mobility condition and hence allow no lag layer formation experiments show that the dune trough scour in recirculation is less deep than in feed flumes and the vertical sorting and transport sediment composition are different the experiments also indicate that dune irregularity in feed flumes is related to dimensionless shear stress similarly as in uniform sediments interpretation of experiments of dune dynamics in sediment mixtures should therefore account for differences in the upstream sediment supply condition more in general it is hypothesized that the upstream sediment supply condition resembling either recirculation or feed flumes in rivers may affect dune and vertical sorting dynamics

the effect of hydrographs on bed load transport and bed sediment spatial arrangement 1 field measurements of sediment transport in gravel bed rivers often reveal hysteretic effects due to differences in sediment availability between the rising and falling limbs of a flood hydrograph however only a small number of flume studies have analyzed the dynamics of sediment transport during hydrographs three types of stepped hydrographs with contrasting durations and magnitudes are simulated here under sediment recirculation conditions bed load transport rate and grain size have been measured continuously the dynamic behavior of the surface armor layer has been explored by analyzing digital photographs and laser scanner surveys of the bed surface taken during hydrographs the results indicate that sediment transport during the falling limb was lower than during the rising limb in all of the three types of hydrographs this reduction is more evident for the low magnitude hydrographs the grain size of the bed remained virtually constant throughout the hydrographs but the grain size of transported sediments exhibited a counterclockwise hysteresis also a significant increase in the reference shear stress for sediment entrainment was measured during the falling limb of hydrographs additionally a detailed analysis of partial transport dynamics of the bed surface sediments reveals a reduction in sediment mobility during the falling limb of the hydrographs the difference in sediment entrainment and transport before and after the peak of the hydrographs appears to be caused by a change in the organization of the surface sediments an analysis of detailed laser scan bed surveys reveals a phase of bed restructuring lower vertical roughness clast rearrangement during the falling limb of hydrographs consequently changes in the degree of organization and complexity of the bed surface are likely the cause of the reduced mobility of sediments and thus of the reduced sediment transport rate during the falling limb of the hydrographs

storage conditions and magma processes triggering the 1818 ce plinian eruption of volcan de colima abstract volcan de colima has an eruptive history punctuated with explosive plinian eruptions followed by long periods of effusive events both of the best documented plinian eruptions which occurred in 1818 ce and 1913 ce emitted andesitic magma 58 wt sio 2 that contains pl opx cpx amph fe ti oxides ap resorbed ol whereas effusive magmas from the 1819 1868 and 1962 2015 periods are particularly scarce in amphibole and are slightly more silicic 59 61 wt sio 2 pumice from the 1818 and 1913 deposits contain three groups of amphibole with different abundance texture and composition composition is the most distinctive between them the first group consists of crystals with high al iv 1 84 2 32 the second group of amphiboles is less abundant in al iv 1 45 1 76 and the third has low al iv 1 29 1 39 in contrast amphibole from two colima prehistoric lavas can only be grouped as medium al iv 1 45 1 76 a set of hydrothermal experiments were carried out using a 1818 natural sample to investigate amphibole compositional variability with changes in pressure and temperature two groups of amphibole found in the plinian deposits can be reproduced experimentally between 875 and 900 c and 150 200 mpa another type of amphibole could not be equilibrated in the 1818 explosive colima magma and their origin can be attributed to mixing with more mafic magmas we found that amphibole abundance is greater in explosive events and that mafic inherited amphiboles can only be found in colima plinian deposits when the influx of mafic magma is large or frequent enough and they mix with more silicic colima magma then explosive events are more likely if mafic melts cannot mix with the resident magmas or just pond and heat the reservoir regardless of location in the plumbing system then magmas can decompress more slowly and amphibole will have time to completely react out

effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics abstractexperimental sediment transport and river morphologic studies in laboratory flumes can use two sediment supply methods an imposed feed at the upstream end or a recirculation of sediment f

understanding heavy mineral enrichment using a three dimensional numerical model layered deposits of relatively light and heavy minerals can be found in many aquatic environments quantification of the physical processes which lead to the fine scale layering of these deposits is often limited with flumes or in situ field experiments therefore the following research questions were addressed i how can selective grain entrainment be numerically simulated and quantified ii how does a mixed bed turn into a fully layered bed and iii is there any relation between heavy mineral content and bed stability herein a three dimensional numerical model was used as an alternative measurement to study the fine scale process of density segregation during transport the three dimensional model simulates particle transport in water by combining a turbulence resolving large eddy simulation with a discrete element model prescribing the motion of individual grains the granular bed of 0 004 m in height consisted of 200 000 spherical particles d50 500 m five suites of experiments were designed in which the concentration ratio of heavy 5000 kg m to light particles i e 2560 kg m was increased from 6 15 35 60 to 80 all beds were tested for 10 s at a predefined flow speed of 0 3 m s analysis of the particle behaviour in the interior of the beds showed that the lighter particles segregated from the heavy particles with increasing time the latter accumulated at the bottom of the domain forming a layer whereas the lighter particles were transported over the layer forming sweeps particles below the heavy particle layers indicated that the layer was able to armour the particles below consequentially enrichment of heavy minerals in a layer is controlled by the segregation of a heavy mineral fraction from the light counterpart which enhances current understanding of heavy mineral placer formation this article is protected by copyright all rights reserved

controls of strength and rate of downstream fining above a river base level we report sensitivity tests on a numerical model of the development of downstream fining by size selective transport and deposition above a base level in a gravelbed river with no lateral inputs of water or sediment strong fining requires deposition mainly to the surface otherwise its amount and streamwise distribution are not highly sensitive to any single factor but vary somewhat with hiding factor excess shear stress and bed sorting low initial concavity inhibits fining but different higher concavities generate fairly similar fining profiles lower sediment supply leads to a coarser bed with less fining but there is no simple relationship between fining and aggradation rate the rate of development of fining is sensitive to all these factors but is always rapid initially followed by a far slower approach towards final equilibrium surface grain size adjustment is potentially an important degree of freedom in river response to any environmental change or human impact which causes overloading

the decrease in shear stress and increase in transport rates subsequent to an increase in sand supply to a gravel bed channel abstract it is generally accepted that a gravel bed river will aggrade if the supply of sediment to the river is increased in a series of flume experiments using constant discharge and gravel feed rate sand feed rates were increased to 6 1 times that of gravel the slope of the bed decreased with increasing sand supply indicating that the increased sediment load could be transported at the same rate due to a decrease in shear stresses these results extend previous experiments to a wider range of boundary conditions a recent surface transport model is used to predict the changes in bed composition and transport using the same sediment supply composition and feed rates as in the laboratory experiments this model reasonably predicts a decrease in the reference shear stresses of the sand and gravel fractions as the sand supply is increased an increase in sand supply can increase the mobility of gravel fractions in the stream bed which can lead to bed degradation and preferential evacuation of these sediments from the river

experimental study of the response of a gravel streambed to increased sediment supply if increased sediment supply to a river channel exceeds its transport capacity deposition necessarily occurs as the bed adjusts to accommodate the increased supply both the mean and spatial patterns in bed elevation and grain size may change and an ability to understand their relative importance is needed to predict bed response we report on an experiment in a field scale flume in which sediment supply is increased to a gravel bed with alternate bars sediment was recirculated in the experiments but augmented in two steps after which the bed was allowed to reach a new steady state the transport rate at the end of the experiment was three times larger than at the start high resolution sediment flux and topographic measurements grain size derived from photographs and hydrodynamic modeling allow us to document the topographic and textural response of the bed to increased sediment supply the spatial patterns of bed topography and texture were forced by the flume setup and the initial and final steady states included long stationary alternate bars with associated grain size sorting the transient bed contained several scales of shorter wavelength migrating bedforms superimposed on and temporarily replacing the stationary alternate bars bed topography and textural patterns adjusted to increased sediment supply over different timescales bed slope and mean stress increased directly with sediment supply rate to produce a new transport steady state in a time about 2 5 times the minimum needed to deposit the required sediment wedge indicating a trap efficiency of about 40 for the aggrading wedge adjustments in local topography and sorting primarily in the form of smaller migrating bars continued for a period approximately equal to that required to initially reach transport steady state copyright 2013 john wiley sons ltd

unequal mobility of gravel and sand in weakly bimodal river sediments bed load was trapped during flood events over a 20 month period at the lower end of the allt dubhaig a small river in scotland with rapid downstream fining of gravel bed material on a slowly aggrading concave long profile the channel bed near the trap is predominantly gravel with a secondary sand mode total transport in each event depended mainly on peak shear stress rather than duration over a threshold bed load was mainly sand in smaller events bimodal in intermediate events and mainly gravel in the biggest floods mean and maximum grain diameter both increased with peak shear stress but in different ways analysis of fractional transport rates and maximum grain size in relation to peak shear stress suggests that gravel transport is slightly size selective but sand transport is close to equal mobility the slight selectivity in gravel transport is consistent with previous field studies of near equilibrium unimodal beds and supports assumptions made in the numerical model of hoey and ferguson 1994 which successfully simulates the observed amount of downstream fining over the 2 5 km upstream of the bed load trap

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport α and tracking changes in grain size of bed sediment β to predict changes in sediment transport it is essential to know whether transport is regulated mainly by changes in flow or by changes in grain size of sediment on the bed in flows where changes in suspended sediment transport are regulated purely by changes in flow grain size of bed sediment is constant increases in flow strength cause increases in both concentration and grain size of sediment in suspension because stronger flows are able to suspend more sediment and coarser grains under this constraint of constant grain size of bed sediment concentration and median diameter of suspended sediment are positively correlated in contrast where transport is regulated purely by changes in grain size of sediment on the bed concentration and median diameter of suspended sediment are negatively correlated because increasing the median diameter of the bed sediment causes the concentration to decrease while causing the median grain size in suspension to increase where both flow strength and grain size on the bed are free to vary the relation between concentration and grain size in suspension can be used to quantify the importance of grain size regulation relative to flow regulation of sediment transport a measure defined as to predict sediment transport in systems that are regulated dominantly by changes in grain size on the bed it is more useful to measure sediment input events or changes in grain size on the bed than to measure changes in flow more commonly grain size of bed sediment may be secondary to flow in regulating transport but may nevertheless be important the relative coarseness of bed sediment can be measured directly or like can be calculated from measurements of concentration and grain size of suspended sediment

model experiments on mobile paved gravel bed streams laboratory experiments which model streams with poorly sorted gravel beds at reduced scale reveal that pavement is a mobile bed phenomenon it acts to decrease the inherent difference in mobility between large and small grains by overrepresenting the percentage of large grains exposed to the flow pavement can coexist with the motion of all available grain sizes because motion is sporadic so that at any given time only a small percentage of surface grains are actually in motion particles in the immediate subpavement are only occasionally moved and deeper particles are hardly ever moved the experiments were conducted at constant discharges they provide accurate quantitative models of two field streams in that they obey the same bedload law as field data both sediment feed and recirculating configurations were utilized the only systematic difference between the two is in the behavior of the finer grains

vertical sorting in bed forms flume experiments with a natural and a trimodal sediment mixture two sets of flume experiments were conducted to examine grain size selective transport and vertical sorting in conditions with migrating bed forms and bed load transport in the two sets of experiments we used a sediment mixture from the river rhine and a trimodal mixture respectively the vertical sorting profiles showed a downward coarsening trend within the bed forms and in some experiments an essentially immobile coarse bed layer formed underneath the migrating bed forms three mechanisms contribute to the formation of such a coarse bed layer 1 the avalanching process at the lee face 2 conditions of partial transport in which a relatively large amount of coarse material does not participate in the transport process and 3 the winnowing of fines from the trough surface and subsurface the experiments show that vertical sorting fluxes not only occur through net degradation or aggradation but also through the migration of bed forms and through the variability in trough elevations this is contradictory to the way vertical sorting processes are modeled in most existing sediment continuity models for nonuniform sediment the present study is therefore also a plea for modifying existing sediment continuity models to account for vertical sorting processes other than through net aggradation or degradation

understanding eruptive style variations at calc alkaline volcanoes the 1913 eruption of fuego de colima volcano mexico the 1913 sub plinian eruption of fuego de colima volcano mexico occurred after almost 100 years of effusive and minor vulcanian explosive activity which modulated dome growth and destruction dome extrusion persisted from 1869 to 1913 the transition to explosive eruption started on 17 january 1913 and it progressed in three phases 1 opening with the generation of block and ash flows 2 vent clearing with strong explosions that destroyed the summit dome and decompressed the magmatic system and 3 sustained column sub plinian fallout with final collapse producing pyroclastic density currents because of this succession of events the 1913 activity represents an excellent case study for investigating the eruptive style changes at calc alkaline volcanoes we investigated the conditions that led to eruptive style transition from effusive dome growth to explosive the final sub plinian fallout through steady state numerical simulations using subsurface data and independently inferred from volcanological data mass discharge rates as constraints results show good matches for hybrid geometrical settings of the shallow conduit feeding system i e dyke developing into a shallower cylindrical conduit and the magma chamber top at 6 km of depth the fragmentation level was shallower than 2 km as inferred from the lithics contained in the sub plinian fall deposits of phase 3 the most likely solution is represented by a dyke having major axis between 200 and 2000 m and the minor axis of 40 m the dyke cylinder transition was set at a depth of 500 m with a cylinder diameter of 40 m it emerges that at least two main mechanisms may be responsible for the effusive to explosive transition that led to the phase 3 of the 1913 eruption i an increase in magma chamber overpressure magmatic triggering or ii decrease of lithostatic stress acting on the volcano non magmatic triggering the former implies arrival into the magma chamber of a batch of fresh magma which can have volume between 10 and 200 106 m3 depending on the values of magma and host rock compressibility the latter requires decompression induced emptying of at least the equivalent of 1000 m of the magma column to produce the necessary unloading of the conduit feeding system a sudden jerk in the lateral spreading of the fuego de colima cone would be a reliable mechanism for decompressing the upper conduit and driving fragmentation processes over a time period of few hours the results are not conclusive on an internal magma chamber overpressure external lowering of lithostatic load or mixed internal and external trigger of the observed eruptive style transition this work highlights how different processes can have non linear cascade effects on close to equilibrium volcanic systems like fuego de colima volcano

evolution of coarse gravel bed forms field measurements at flood stage field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the north fork toutle river washington sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in december 1989 and january 1990 with concurrent bed load sampling and continuous velocity measurements mean diameter of bed load was about 3 cm flow depths were 1 4 2 4 m and bed shear stresses were 2 5 times the critical stress of mean bed load diameter as computed from the depth slope product these records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed coarse gravel dunes height 20 cm length 6 15 m evolved more than 24 hours after peak stage primarily by accretion as inferred from bed form changes revealed in dual sonar records dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours smaller dunes wavelength 1 3 m transitional from bed load sheets migrated on the backs of the large dunes the superposed dunes finally became indistinguishable from the large dunes which diminished in height by increasing the mean level of troughs gravel deposition occurred at the observation point in conjunction with migration of gravel dunes the direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits

a graded stream response relation for bed load dominated streams 1 the relation between equilibrium stream channel morphology and three independent governing variables discharge sediment supply and valley slope is investigated using a stream table the experiments are based on a generic physical model of a laterally active gravel bed stream and directed by a recently published rational regime model while a variety of channel adjustments are possible the primary adjustment observed was in the channel slope other adjustments such as surface armor composition and cross sectional shape were minor in comparison the equilibrium slope is well predicted by a linear function of sediment concentration which is bounded by two thresholds one associated with the minimum stream power necessary to deform the bed and the other associated with the maximum sediment feed that can be transported by the available flow the results suggest that the system tends to move toward the minimum slope capable of transporting the sediment supply in the process increasing the flow resistance for the system whether or not a minimum slope or a maximum system scale flow resistance is reached cannot be determined given the available data but there appears to be a unique slope or at least a limited range of slopes for which a stable alluvial channel morphology can be established for a given sediment concentration the implications of this behavior are evaluated for the theoretical basis of the extremal hypothesis used to close the formulation of a rational regime model

fingerprinting suspended sediment sources in the catchment of the river ouse yorkshire uk statistically verified composite fingerprints and a multivariate mixing model have been employed to establish the main sources of the suspended sediment transported through the lower non tidal reaches of the river ouse and one of its main tributaries the river wharfe during the period 1994 1997 in the case of the suspended sediment samples collected from the river ouse the load weighted mean contributions from uncultivated topsoil cultivated topsoil and channel bank sources were estimated to be c 25 38 and 37 respectively while for the river wharfe these sources contributed c 70 4 and 23 respectively c 4 was derived from woodland topsoil suspended sediment samples collected during higher flows evidenced a greater contribution from channel banks than samples collected during lower flows source materials were also differentiated according to the three main geological source areas carboniferous permian and triassic and jurassic and their load weighted mean contributions were estimated to be c 24 41 and 35 for the river ouse and c 91 9 and 0 there are no jurassic rocks in this catchment for the river wharfe respectively when suspended sediment samples from tributary streams were used to characterize each geological source area the equivalent results for the river ouse were c 30 46 and 24 considering the three main tributaries that contribute to the river ouse the load weighted mean contributions from the rivers swale ure and nidd were estimated to be 82 15 and 3 respectively these values have been compared with estimates of the relative magnitude of the annual suspended sediment loads of these three rivers for the years 1995 and 1996 derived from continuous monitoring of discharge and turbidity differences between the two sets of results are ascribed to the different periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hydrograph and thus the degree to which the available samples are representative of the overall suspended sediment flux although a number of limitations must be recognized the fingerprinting approach to source ascription is seen as providing valuable information regarding suspended sediment sources in the study catchments copyright 1999 john wiley sons ltd

sediment feed and recirculating flumes fundamental difference two standard modes of laboratory sediment transport flume operation are sediment feed and recirculating in the case of uniform sediment the final equilibriums achieved in the two modes are equivalent and independent of initial conditions even though the specified flow and sediment constraints differ when the sediment consists of a mixture of sizes however this symmetry breaks down in a sediment feed flume both the feed rate and size distribution are specified by the user and must be identical to those of the bed load at final equilibrium the final state thus becomes independent of initial conditions in a recirculating flume however the equilibrium size distribution of neither the bed load nor the bed surface material can be specified in advance as a result the final state depends on the initial conditions and can include the possibility of partial transport the equilibriums themselves are equivalent in that they obey the same laws of flow and sediment transport their ia priori n predictability however differs due to the difference in governing constraints when fractional transport is scaled by the bulk size distribution the two flume modes may produce very different transport relations even for the same sediment a consistent approach requires that the transport be scaled by the size distribution of the bed surface

colorado river sediment transport 2 systematic bed elevation and grain size effects of sand supply limitation the colorado river in marble and grand canyons displays evidence of annual supply limitation with respect to sand both prior to topping et al this issue and after the closure of glen canyon dam in 1963 systematic changes in bed elevation and systematic coupled changes in suspended sand concentration and grain size result from this supply limitation during floods sand supply limitation either causes or modifies a lag between the time of maximum discharge and the time of either maximum or minimum depending on reach geometry bed elevation if at a cross section where the bed aggrades with increasing flow the maximum bed elevation is observed to lead the peak or the receding limb of a flood then this observed response of the bed is due to sand supply limitation sand supply limitation also leads to the systematic evolution of sand grain size both on the bed and in suspension in the colorado river sand input during a tributary flood travels down the colorado river as an elongating sediment wave with the finest sizes because of their lower settling velocities traveling the fastest as the fine front of a sediment wave arrives at a given location the bed fines and suspended sand concentrations increase in response to the enhanced upstream supply of finer sand then as the front of the sediment wave passes that location the bed is winnowed and suspended sand concentrations decrease in response to the depletion of the upstream supply of finer sand the grain size effects of depletion of the upstream sand supply are most obvious during periods of higher dam releases e g the 1996 flood experiment and the 1997 test flow because of substantial changes in the grain size distribution of the bed stable relationships between the discharge of water and sand transport rates i e stable sand rating curves are precluded sand budgets in a supply limited river like the colorado river can only be constructed through inclusion of the physical processes that couple changes in bed sediment grain size to changes in sand transport rates in some rivers the upstream supply of sediment is in equi librium with the upstream supply of water whereas in others the upstream supply of sediment is decoupled either com pletely or partially from the upstream supply of water in the first type of river changes in sediment transport are controlled by changes in the discharge of water whereas in the second and perhaps more common type of river changes in sedi ment transport are also coupled to changes in sediment grain size in this paper we investigate the systematic changes in bed elevation sediment transport and sediment grain size that occur in response to changes in the upstream supply of sand in a river with an intermittent limited supply of sand specifically the colorado river in marble and grand canyons figure 1 to develop an intuitive understanding of the linkage be tween sediment grain size and the upstream supply of sediment in a river it is informative to first examine sediment transport

effects of sediment supply on surface textures of gravel bed rivers using previously published data from flume studies we test a new approach for quantifying the effects of sediment supply i e bed material supply on surface grain size of equilibrium gravel channels textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size d9 50 we find that surface median grain size d50 varies inversely with sediment supply rate and systematically approaches the competent value d9 at low equilibrium transport rates furthermore equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes d9 and d50 consequently we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size while the approach appears promising we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions

evolution of a sediment wave in an experimental channel the routing of bed material through channels is poorly understood we approach the problem by observing and modeling the fate of a low amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave the wave essentially dispersed upstream and downstream without translation although there was inconclusive evidence of translation late in the experiment when the wave was only 10 20 grain diameters high alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume celerity or transport rate sediment that overpassed migrating bars was apparently responsible for dispersion of the wave the evolution of the wave was well predicted by a one dimensional model that contains no adjusted empirical constants numerical experiments demonstrate however that the theory does not predict sediment waves that migrate long distances downstream such waves can only be explained by the following processes not represented by the theory selective bed load transport spatial variations in bar and other form roughness the mechanics of mobile armor and perhaps other mechanisms

eyewitness stratigraphy chemistry and eruptive dynamics of the 1913 plinian eruption of volcan de colima mexico abstract based on the stratigraphic record of the deposits analysis of previous works historic archives and eyewitness accounts the 1913 eruption of volcan de colima was reconstructed the eruption started in 17 january and peaked in 20 january 1913 it occurred in three main phases 1 an opening phase with the generation of merapi type pyroclastic flows units f1 f2 f3 and a pyroclastic surge s1 2 a vent clearing phase with strong explosions that produced vulcanian soufriere type pyroclastic flows f4 and a pyroclastic surge s2 which destroyed the summit dome decompressing the magma system and 3 a plinian phase with the establishment of a 23 km high column dispersing a fallout c1 to the ne followed by the collapse of the column that generated a pyroclastic surge s3 and 15 km long pumice rich pyroclastic flows f5 after the eruption remobilization of the pyroclastic material generated lahars in main gullies around the crater fallout c1 blanketed an area of 191 318 km2 covering the cities of guzman guadalajara and saltillo coahuila located at 725 km from the source it had a volume of 1 4 km3 0 57 km3 dre dense rock equivalent the total volume of pyroclastic flow and surge deposits was 0 26 km3 0 07 km3 dre giving a total volume of the eruption of 1 66 km3 0 64 km3 dre the plinian column lasted 4 6 h with a total mass of 1 5 1012 kg and a mass eruption rate of 9 02 107 kg s the column height and the ejected magma volume indicate that the 1913 eruption had a vei 5 being the largest event in the historical record of colima volcano juvenile scoria and pumice consisted of pl opx cpx hbl accessory titanomagnetite ap and ol with reaction rims chemistry of juvenile scoria and pumice samples is andesitic very homogeneous 58 3 0 5 wt sio2 and similar to the 1818 juvenile products 58 9 0 2 wt sio2 the presence of banded scoria olivine phenocrysts with reaction rims and trace element variations strongly suggest that the 1913 eruption was caused by a magma mixing event

channel degradation and slope adjustment in steep streams controlled through bed sills general parallel and rotational degradation and the effect of bed sills are investigated with the aid of historical field data and laboratory experiments the case under consideration is a system of two tributaries and a main river in northeast spain characterized by its short length steepness and ephemeral nature the comparison of bed profiles since 1962 revealed an incision greater than 5 5 m the main causes of degradation are thought to be channelization width reduction and urban growth the equilibrium slopes with and without sills were obtained in 111 live bed flume tests it is demonstrated that the bed slope is milder with sills than without sills under the same flow and sediment rates the equations for the calculation of equilibrium slopes scaled to prototype are applied to the case study with good agreement copyright 2008 john wiley and sons ltd

bed load transport of mixed size sediment fractional transport rates bed forms and the development of a coarse bed surface layer fractional transport rates bed surface texture and bed configuration were measured after a mixed size sediment had reached an equilibrium transport state for seven different flow strengths in a recirculating laboratory flume fractional transport rates were also measured at the beginning of each run when the bed was well mixed and planar the start up observations allow us to describe the variation of fractional transport rates with bed shear stress for a constant bed surface texture and bed configuration the start up and equilibrium observations together allow for the first time an unambiguous description of the mutual adjustment among the transport the bed configuration and the bed surface as the transport system moves toward equilibrium we find that a substantial interaction exists among the transport bed surface and bed configuration bed forms and a coarse surface layer coexist over a range of bed shear stress under some flow conditions the size and shape of the bed forms are controlled by the presence of the coarse surface layer at higher flows the coarse surface layer is eliminated by scour in the lee of the bed forms if the bed surface is defined as that over which the bed forms move a coherent relation between the bed surface texture and the transport grain size distribution may be defined at equilibrium the transport rates of all fractions were not equally mobile defined as identical transport and bed grain size distributions although equal mobility was approached for runs in which the bed shear stress was more than twice that for initial motion of the mixture under some flow conditions the transport was observed to adjust away from equal mobility as the bed adjusted from a well mixed start up condition to an equilibrium state development of a partial static armor wherein some individual grains become essentially immobile even though other grains in the same fraction remain in transport is suggested to explain these adjustments between the transport and bed surface grain size distributions constraints on equilibrium mixed size sediment transport are defined the special conditions for which equal mobility must hold and the relevance to natural conditions of flume results and the equal mobility concept are discussed

geomorphology and endangered fish habitats of the upper colorado river 2 linking sediment transport to habitat maintenance alluvial reaches of the colorado river near grand junction colorado provide important habitat for the endangered colorado squawfish this paper examines recent changes in the geomorphology of the colorado river and addresses the question of what can be done to improve existing fish habitats observations of channel change during periods of above average runoff from 1993 through 1995 indicate minor scour and fill of the main channel but more significant scour and enlargement of side channel and backwater habitats and flushing of fine sediment from the bed modeled relations between discharge and dimensionless shear stress indicate that the threshold of bed load transport 0 03 occurs at about half the bank full discharge these flows are exceeded about 26 days per year on average the bank full discharge produces an average of 0 047 and is exceeded about 8 days per year the width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of 1 5 times greater than the critical shear stress the effective discharge is slightly less than the bank full discharge and approximately 80 of the total sediment load is carried by the highest 10 of all discharges

experiments on bar formation in a straight flume 2 graded sediment laboratory experiments have been carried out in a large laboratory flume using a strongly bimodal sediment mixture in a range of flow conditions such that the initially flat bed of the flume became unstable enhancing the development of alternate bars in order to elucidate the effect of grain sorting the present experiments are compared with a previous set of experiments performed in the same flume under similar hydraulic conditions but using a nearly uniform sand with a mean geometric grain diameter equal to that characterizing present experiments the comparison suggests that sediment heterogeneity may appreciably affect bed form characteristics the development of smallscale ripples and mesoscale dunes sediment waves tended to be inhibited thus allowing a decrease in flow resistance owing to the bimodal character of the adopted mixture at low values of the bed shear stress a condition of partial transport was attained for which only the finer grained portion of the mixture was observed to move while the coarsergrained fractions remained essentially immobile throughout the experimental run however complete mobilization of all size fractions was observed to occur in runs carried out at higher slopes i e at higher bed shear stress in order to generate an alternate bar pattern selective transport of individual grain size fractions coupled with the characteristic bar topography pattern led to an intense longitudinal sorting which accreted the coarser particles on bar crests furthermore bar migration caused through scour and fill a significant vertical sorting as a consequence of these sorting processes and in accordance with previous experimental observations bar height turns out to be invariably damped with respect to uniform sediment experiments the trend exhibited by the wavelengths is less clear and suggests that in the present experiments sorting effects do not enhance the clear shortening of bar wavelengths typically observed in other series of flume experiments carried out with weakly bimodal mixtures

partial transport of a sand gravel sediment grains of a single size within a mixed size bed are entrained over a range of flows within this range some grains exposed on the bed surface are active entrained at least once over the duration of a transport event while the remaining surface grains are immobile a condition we define as partial transport we demonstrate the existence and domain of partial transport using observations of grain entrainment on time series of bed photographs of flume experiments with a widely sorted sand gravel mixture the active proportion of the bed surface increases with bed shear stress 0 at a given 0 90 of the active grains are entrained when the cumulative mass transported exceeds approximately 4 times the active mass on the bed mobilization of grains in a size fraction increases from 10 to 90 over a range of 0 of a factor of 2 the bounds of this range increase with grain size di so that at a given 0 sizes over a range of a factor of 4 are in a state of partial transport fractional transport rates are independent of di for fully mobilized fractions and decrease rapidly with di for partially mobile fractions partial transport is associated with substantial transport rates of finer fully mobile sizes limits both the rate and size distribution of grain exchange with the bed subsurface and may be the dominant transport condition in many gravel bed rivers

a model to predict the evolution of a gravel bed river under an imposed cyclic hydrograph and its application to the trinity river 1 major changes in the morphology of the trinity river in california such as narrowing of the cross section and sedimentation of fine sediment in pools occurred after the closure of a system of dams these changes caused a dramatic reduction in the salmonid population and a resulting decline of the fishery gravel augmentation regulated flood releases and mechanical channel rehabilitation are currently being implemented to help restore the aquatic habitat of the river the present paper describes a tool named the spawning gravel refresher for designing and predicting the effects of gravel augmentation in gravel bed rivers the tool assumes an imposed cycled hydrograph the model is calibrated and applied to the regulated reach of the trinity river in four steps 1 zeroing runs to reproduce conditions of mobile bed equilibrium as best can be estimated for the predam trinity river 2 runs to compare the predictions with the results of previous studies 3 runs at an engineering time scale to reproduce the effects of the dams and 4 runs to design gravel augmentation schemes in the fourth group of runs the combined effects of engineered flood flow releases and gravel augmentation are predicted at an engineering time scale the model indicates that the fraction of fine sediment in the surface layer and in the topmost part of the substrate should decrease when subjected to these two restoration measures with a consequent improvement of the quality of the spawning gravel

contribution of diffuse sources to the sediment and phosphorus budgets in ben chifley catchment australia relative contribution of different diffuse sources to the sediment and phosphorous p budgets in the ben chifley reservoir was estimated using a multivariate mixing model and geochemical indices and tracers the influence of the underlying geology on land use characteristics and the dynamics of sediment and p in the catchment were discussed sediments currently in transport to the reservoir are derived mainly from areas underlain by quaternary alluvium accounting for 33 of the reservoir sediment budget a major portion of the sediments from the quaternary alluvium originates from pasture land which also contributes about 60 of sediment bound p in the reservoir followed by cropland 30 and forest area 10 phosphorus based fertiliser contributes more than 50 of the soil p in pasture and cropland and more than 60 in forest plantation area the remaining p reaching the reservoir originates from natural soils native sources phosphate from both fertiliser and native sources are transported to the water courses and ultimately the reservoir as a consequence of gully stream bank and surface erosion erosion control trapping of fertiliser runoff establishing riparian vegetation and reducing application of p based fertiliser by increasing native pasture cultivation in the risk areas should be considered as management options for controlling the impact of p and sediment in the reservoir

surface based fractional transport rates mobilization thresholds and partial transport of a sand gravel sediment twenty eight coupled observations of flow transport and bed surface grain size distribution were made in a laboratory flume using a wide range of flows and a sediment with a very poorly sorted bimodal grain size distribution these observations permit the transport rates of individual size fractions to be scaled by the proportion of each size immediately available for transport on the bed surface the key to our observations is the use of a sediment in which each size fraction has been painted a different color which permits reliable repeatable and nondestructive measurement of the bed surface grain size distribution from photographs of the bed surface at a given flow the fractional transport rates may be divided into two parts a finer grained portion within which fractional transport rates are a function only of their proportion on the bed surface and total transport rate and a coarser grained portion for which fractional transport rates also depend on the proportion of individual grains within a fraction that remain essentially immobile throughout the experimental run we define the latter condition as one of partial transport and observe that the grain size separating partial and fully mobilized transport consistently increases with flow strength complete mobilization of a size fraction occurs at roughly twice the shear stress necessary for incipient motion of that fraction zones of partial and full mobility are quite distinct when fractional transport rates are scaled by the bed surface grain size distribution although a region of partial transport is evident when these data and other experimental and field observations are scaled by the bulk grain size distribution of the sediment bed critical shear stresses for the incipient motion of individual fractions in our experimental sediment vary over an order of magnitude a result strongly in contrast to many earlier observations but consistent with our observations of incipient motion in sediments with bimodal grain size distributions

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

a model of two phase bedload transport in an oregon coast range stream a descriptive model for bed material routing in small sand and gravel bedded channels with sequences of pools and armoured riffles was developed aspects of the model are demonstrated at flynn creek a 202 ha third order drainage in the oregon coast range assuming that channel geometry sediment transport competence and the availability of sediments for transport are all non uniform in the downstream direction the model described bedload transport as occurring in two phases phase i involves the transport of fine predominantly sand sized bed materials over stable gravel armoured riffles phase ii occurs at higher flows that can entrain riffle armour and transport riffle sediments in addition to phase i sediments phase i bedload transport was sampled during three moderate flow events a power function related phase i bedload transport to water discharge the relationship was consistent between storms and between two successive years phase ii bedload transport sampled during a 1 8 yr return period streamflow event in february 1979 proved non uniform in a downstream direction and unsteady over time at a given stream discharge transport rates closely correlated with the rapid scour and redeposition of the riffle at the bedload sampling cross section transport peaks corresponded to scour and transport decreased greatly during deposition the transport of large 12 5 mm diam bed material increased up to 12 fold during riffle scour

bifurcation modelling in a meandering gravel sand bed river the rhine bifurcation at pannerden forms the major distribution point for water supply in the netherlands distributing not only water and sediment but also flooding risks and navigability its morphological stability has been a concern for centuries we present experiences from more than two decades of numerical morphological modelling of this bifurcation with a gravel sand bed and a meandering planform successive computations have shown the importance of upstream approach conditions the necessity to include physical mechanisms for grain sorting and alluvial roughness and the need to assume a thicker active layer of the river bed than is suggested by laboratory flume experiments using a constant discharge the active layer must be thicker in the model to account for river bed variations due to higher frequency discharge variations that are filtered out in morphological modelling we discuss limitations in calibration and verification but argue that notwithstanding these limitations 2d and 3d morphological models are valuable tools not only for pragmatic applications to engineering problems but also for revealing the limitations of established knowledge and understanding of the relevant physical processes the application of numerical models to the pannerden bifurcation appeared to reveal shortcomings in established model formulations that do not pose particular problems in other cases this application is therefore particularly useful for setting the agenda for further research copyright 2012 john wiley sons ltd

disturbance caused by bed sills on the slopes of steep streams live bed tests on steep bed slopes are run in a laboratory flume to investigate the slope of equilibrium the tests simulate a general degradation until a new equilibrium is reached subsequently different bed sill settings are tested as a countermeasure against degradation evidence is presented that in some cases the bed slope with sills is milder than the one without sills under the same flow and sediment rates this fact implies that the efficiency of the bed sill system to stop degradation decreases as the sills are placed closer together tests are on the verge of sheet flow and friction factors are heavily dependent on sediment transport reaches in uniform and gradually varied flow behave very differently bed profiles are not straight and grain size is linked to this fact other detailed information on testing equipment experimental program time development and local scour in a total number of 111 tests is given

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

corrigendum to eyewitness stratigraphy chemistry and eruptive dynamics of the 1913 plinian eruption of volcan de colima mexico journal of volcanology and geothermal research 191 2010 149 166 a universidad autonoma de san luis potosi instituto de geologia fac ingenieria av manuel nava no 5 zona universitario 78240 san luis potosi s l p mexico b departamento de vulcanologia instituto de geofisica universidad nacional autonoma de mexico coyoacan d f 04510 mexico c facultad de ciencias universidad de colima bernal diaz del castillo 340 col villas san sebastian c p 28045 mexico d departamento de geologia regional instituto de geologia universidad nacional autonoma de mexico coyoacan d f 04510 mexico e institute de physique du globe de paris paris france f department of geological sciences the university of texas at austin texas 78712 united states g escuela de ciencias de la tierra universidad autonoma de guerrero taxco guerrero mexico

the effects of kinetic sorting on sediment mobility on steep slopes in poorly mobile static armour sorting is usually considered the result of hiding exposure effects we called this effect static sorting in opposition to very efficient grain to grain mechanisms produced by a mobile mixture called kinetic sorting we hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments two long runs were produced with natural poorly sorted sediments and with transport stages of the coarse fraction defined by the ratio between the shear stress and the critical shear stress for transport smaller and higher than 1 respectively both runs produced an efficient transfer downstream of the injected material but with a major difference the first run no kinetic sorting produced permanent armour figuring clusters akin to what has already been observed in similar experiments the second run with kinetic sorting also produced bed armouring but this armour was periodically totally destroyed leading to substantial bed erosion this phenomenon was explained by kinetic sorting the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring the consequence is that fine materials are hidden to the flow during aggradation allowing the slope to attain values much steeper than would have been expected at equilibrium for the mixture however whereas the surface armouring tends to stabilize the bed construction of a layer of fine sediments at the subsurface also contributes to making it very unstable these two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations copyright 2014 john wiley sons ltd

formation and preservation of open framework gravel strata in unidirectional flows open framework gravel ofg in river deposits is important because of its exceptionally high permeability resulting from the lack of sediment in the pore spaces between the gravel grains fluvial ofg occurs as planar strata and cross strata of varying scale and is interbedded with sand and sandy gravel the origin of ofg has been related to 1 proportion of sand available relative to gravel 2 separation of sand from gravel during a specific flow stage and sediment transport rate either high falling or low 3 separation of sand from gravel in bedforms superimposed on the backs of larger bedforms 4 flow separation in the lee of dunes or unit bars laboratory flume experiments were undertaken to test and develop these theories for the origin of ofg bed sediment size distribution sandy gravel with a mean diameter of 1 5 mm was kept constant but flow depth flow velocity and aggradation rate were varied bedforms produced under these flow conditions were bedload sheets dunes and unit bars the fundamental cause of ofg is the sorting of sand from gravel associated with flow separation at the crest of bedforms and further segregation of grain sizes during avalanching on the steep lee side sand in transport near the bed is deposited in the trough of the bedform whereas bed load gravel avalanches down the leeside and overruns the sand in the trough the effectiveness of this sorting mechanism increases as the height of the bedform increases infiltration of sand into the gravel framework is of minor importance in these experiments and occurs mainly in bedform troughs the geometry and proportion of ofg in fluvial deposits are influenced by variation in height of bedforms as they migrate superposition of small bedforms on the backs of larger bedforms aggradation rate and changes in sediment supply if the height of a bedform increases as it migrates downstream so does the amount of ofg changes in the character of ofg on the lee side of unit bars depend on grain size sorting in the superimposed bedforms dunes and bedload sheets thick deposits of cross stratified ofg require high bedforms dunes unit bars and large amounts of aggradation these conditions might be expected to occur during high falling stages in the deeper parts of river channels adjacent to compound bar tails and downstream of confluence scours increase in the amount of sand supplied relative to gravel reduces the development of ofg such increases in sand supply may be related to falling flow stage and or upstream erosion of sandy deposits

evolution of gravel surfaces in a sediment recirculating flume the assumption of the equilibrium state of gravel surfaces in flume experiments under feeding or recirculating conditions is generally justified by three equilibrium criteria based on sediment transport slopes and bed features when these parametersbecome stable an experiment is expected to reach equilibrium this equilibrium state however is based on a one dimensional 1d model the exner equation which may not truly reflect the equilibrium state of the system considering the complex flow and sediment processes in this paper the evolutionary process of a gravel surface is investigated based on a large scale recirculating flume experiment the performances of the three equilibrium criteria are evaluated first and then the evolution of the bed morphology is studied the key findings include the following 1 the sediment transport rate slopes of water and bed surfaces and 1d morphological features reach equilibrium roughly simultaneously 2 two dimensional 2d morphology continually evolves after these characteristics reach equilibrium which is confirmed by the characteristics of the sediment transport process and 3 the results from a numerical simulation suggest that a much longer time is required to reach an equilibrium state our results suggest that sufficient experimental time is required to investigate the equilibrium morphological characteristics of gravel surfaces which is much longer than the equilibrium time reflected by the 1d equilibrium criteria

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

laboratory study on the evolution of gravel bed surfaces in bed armoring processes abstract cluster microforms in bed armoring have important implications for bedload transport in this study two sets of flume experiments were carried out to study the evolution of the cluster microforms in the bed armoring and their influences on the bedload transport dynamically stable armor layers were formed by applying a staged hydrograph on a mobile sediment bed consisted of poorly sorted sand and gravel thus enabling the investigation of the cluster microforms associated with different flow characteristics simulated in these experiments the size and the planimetric positions of the large particles on the bed surface were extracted using photogrammetric technique allowing analysis of surface grain size distribution and particle clustering pattern of the bed the results showed a tendency towards a coarsened and clustered bed surface which is likely responsible for the declining bedload transport rate the cluster microforms evolved with increasing bed shear stress in the following sequence flat bed pebble cluster line cluster heap cluster reticulate structure we found a bed armoring statistics that can partially explain the declining bedload transport rate under constant discharge nonetheless additional parameters are needed to simulate the fluctuation in the bedload transport rate under changing flow conditions

fluvial transport of sand and gravel mixtures with bimodal size distributions abstract initiation of motion and fractional transport rates of sediments with bimodal size distributions were measured in a laboratory channel and in a natural channel transport experiments were conducted with unimodal 100 sand and 100 gravel bed sediments and three bimodal mixtures of the two sediments 10 gravel 90 sand 25 gravel 75 sand and 45 gravel 55 sand in the bimodal sediment beds the critical shear stress for the initiation of motion showed very little change with grain size for the sand sizes but increased with grain size for the gravel sizes for low flow strengths only the sand sizes were in transport while for the highest flow strengths the bed load sediment size distribution approached that of the bed material

influence of the sediment supply texture on morphological adjustments in gravel bed rivers the role played by the texture of the sediment supply on channel bed adjustments in gravel bed rivers is poorly understood to address this issue an experimental campaign has been designed flume experiments lasting 96 h in a 9 m long 0 60 m wide have been performed with different sand gravel mixtures as feed textures the response of the surface texture has been found to be highly dependent on the grain size distribution of the feed when the feed texture included gravel the finest fractions of the sediment supply infiltrate beneath the surface conversely sand remains on the surface when the feed texture lacks gravel this different textural response becomes obscured when water discharge increases further the sediment transport rate approaches the feed rate differently depending on the content of gravel in the feed texture when a small proportion of gravel is part of the feed texture bed load transport rate asymptotically approaches the feed rate however when a significant fraction of gravel is part of the feed grain size distribution bed load transport rate approaches the feed rate by following an oscillatory path these findings have been verified in terms of a one dimensional numerical model this modeling reveals that the higher the differences in mobility among the grain sizes contained in the feed texture the more evident is the nonasymptotic transient trend toward equilibrium

downstream lightening and upward heavying experiments with sediments differing in density sorting and selective transport of particles by material density is important for understanding a wide range of processes including the formation of mineral placers deposition of mine tailings and routing of tracers and contaminants this article describes an experimental study of the transport of mixtures of particles of differing density in a sediment feed flume during the runs a downstream prograding wedge shaped deposit was formed results show two sorting processes i longitudinal sorting characterized by preferential deposition of heavy particles in the upstream part of the deposit downstream lightening and ii vertical sorting with less dense particles preferentially deposited in the lowermost portion of the migrating front upward heavying downstream lightening is the analogue of the well known downstream fining observed in the more studied case of mixtures of heterogeneous size with the same density in both cases the lighter particles are carried further downstream than the heavier particles upward heavying is unexpected when compared with deposits of heterogeneous size and same density particles where the heaviest i e coarsest particles are deposited in the lowermost part of the front the physical mechanism underlying this upward heavying might be related to the physics of gravity driven granular flows the front of the deposit acts like a dense granular flow down an inclined plane in this case the denser particles settle away from the free surface and at the top of the heap while the lighter particles flow to the bottom as the front of the deposit advances this progressively gives rise to an upward heavying pattern the application of classical surface based fractional bedload transport models suggests that equal mobility is not approached in the case of mixtures of particles with uniform size and different densities this study hypothesizes that other mechanics related to the physics of the segregation processes in these systems contribute to these results

transformative geomorphic research using laboratory experimentation abstract laboratory experiments in geomorphology is the theme of the 46th annual binghamton geomorphology symposium bgs while geomorphic research historically has been dominated by field based endeavors laboratory experimentation has emerged as an important methodological approach to study these phenomena employed primarily to address issues related to scale and the analytical treatment of the geomorphic processes geomorphic laboratory experiments can result in transformative research several examples drawn from the fluvial and aeolian research communities are offered as testament to this statement and these select transformative endeavors often share very similar attributes the 46th bgs will focus on eight broad themes within laboratory experimentation and a diverse group of scientists has been assembled to speak authoritatively on these topics featuring several high profile projects worldwide this special issue of the journal geomorphology represents a collection of the papers written in support of this symposium

bedload abrasion and the in situ fragmentation of bivalve shells the aim of this study was to determine how unio bivalve shells fragment within the channel of the sakmara river southern urals russia the sakmara river has an abundant bivalve population and a highly variable flow regime which at low flow allowed much of the channel bed to be examined a large data set of 1013 shells unio sp was examined and these were shown to have consistent patterns of orientation aspect shell abrasion perforation and fracture the close spatial relationship between areas of shell abrasion shell perforation and shell fracture showed that they form part of a continuum whereby areas of abrasion evolve into perforations and perforations coalesce and enlarge into fractures the mechanism of shell damage proposed is one of abrasion in place whereby the shell remains stationary on the surface of the point bar and is impacted by bedload underpinning this process are the hydrodynamic properties of the bivalve shell with consistency in the orientation and aspect of the valve in a flowing current producing consistency in the distribution of damage on the shell surface valves preferentially lie in a convex up position and orientate in the flow such that the umbo faces upstream the elevated upstream facing umbo region is exposed to particle impact and is the first to be abraded and perforated the vulnerability of the umbo to perforation is greatly increased by the thinness of the shell at the umbo cavity the in situ abrasion process is enhanced by the development of an armoured gravel bed which restricts valve mobility and maintains shells within the abrasion zone at the sediment water interface the in situ abrasion process shows that broken shells are not a reliable indicator of long distance transport the study also raises the issue that tumbling barrel experiments which are generally used to simulate shell abrasion will not replicate the type of directionally focused sand blasting which appears to be the principal cause of shell fragmentation in the sakmara river

a well posed alternative to the hirano active layer model for rivers with mixed size sediment the active layer model hirano 1971 is frequently used for modeling mixed size sediment river morphodynamic processes it assumes that all the dynamics of the bed surface are captured by a homogeneous top layer that interacts with the flow although successful in reproducing a wide range of phenomena it has two problems 1 it may become mathematically ill posed which causes the model to lose its predictive capabilities and 2 it does not capture dispersion of tracer sediment we extend the active layer model by accounting for conservation of the sediment in transport and obtain a new model that overcomes the two problems we analytically assess the model properties and discover an instability mechanism associated with the formation of waves under conditions in which the active layer model is ill posed numerical simulations using the new model show that it is capable of reproducing two laboratory experiments conducted under conditions in which the active layer model is ill posed the new model captures the formation of waves and mixing due to an increase in active layer thickness simulations of tracer dispersion show that the model reproduces reasonably well a laboratory experiment under conditions in which the effect of temporary burial of sediment due to bedforms is negligible simulations of a field experiment illustrate that the model does not capture the effect of temporary burial of sediment by bedforms

numerical modeling of gravel bed river response to meander straightening the coupling between the evolution of bed pavement and long profile 1 artificial meander straightening rectification was conducted in the early 1960s along the sainte marguerite river canada in order to facilitate highway construction along the valley previous studies talbot and lapointe 2002 confirm that vertical reprofiling coupled with pavement coarsening in the degrading reach were the main responses counteracting the disequilibrium in gravel transport rates triggered at rectification of this system numerical simulations using sedrout2 0 a one dimensional hydraulic and sediment transport model and validated against the observed channel response show the important role played by an advancing wave of pavement coarsening down the rectified reach in modulating the bed degradation response simulations extending into the future reveal an asymptotically slowing approach to equilibrium in the middle of the 21st century with a response half time of the order of 10 years in near threshold gravel bed systems like the sainte marguerite river pavement coarsening after rectification buffers the system against extreme degradation most significantly for watershed management this also appears to severely limit the extent of propagation of degradation upstream of the rectification

a physically based bedload transport model developed for 3 d reach scale cellular modelling abstract a bedload transport model is outlined which aims to provide a more physically based description of bed surface and bedload grain size distributions gsds than existing empirical bedload models but is simple enough to be incorporated in a reduced complexity modelling framework one motivation for this is the increasing need for 3 d models of decadal reach scale channel and floodplain evolution for use in river management the computational demands of simulation at these scales mean that the appropriate models are necessarily of the reduced complexity type the bedload model is derived through analysis of sediment beds created using a discrete element model these beds are eroded using a probabilistic entrainment algorithm which predicts the bedload gsd there are two parts to the bedload model the first identifies a functional relationship between the applied shear stress and the fraction of the bed undergoing active transport while the second uses this fraction in conjunction with the surface gsd to produce a bedload gsd the model produces bedload coarsening as shear stress increases from a value of one to a value of five times a reference shear stress this model is tested in a series of numerical experiments applied using a simple cellular model of a straight flume which is run in both recirculation and feed modes in both modes the equilibrium gsds of the bedload and surface are consistent with expected flume behaviour suggesting that the model provides a reasonable reproduction of sediment entrainment transport and sorting

effect of sand supply on transport rates in a gravel bed channel in a series of flume experiments using constant discharge flow depth and gravel feed rate sand feed rates were varied from 0 16 to 6 1 times that of gravel the bed slope decreased with increasing sand supply indicating that the gravel could be transported at the same rate along with increasing amounts of sand at smaller shear stresses prediction of river response to an increase in sediment supply requires prediction of mutual changes in bed composition and transport and therefore a transport model defined in terms of the grain size of the bed surface a recent model provides satisfactory prediction of the experimental observations and indicates the general response of gravel beds to increased sand supply an increase in sand supply may increase the sand content of the river bed and the mobility of gravel fractions which can lead to bed degradation and preferential evacuation of these sediments from the river

linking bed morphology changes of two sediment mixtures to sediment transport predictions in unsteady flows flume experiments were conducted to measure bed morphology adjustments in sand gravel and sand silt sediment mixtures during repeated hydrographs and to link these changes to sediment transport patterns over multiple time scales sediment composition and hydrograph flow magnitude greatly influenced channel morphology which impacted sediment yield hysteresis and transport predictions bed load yields were larger and more variable for the sand silt mixture as gravel in the sand gravel sediment inhibited grain entrainment limited bed form growth and acted to stabilize the bed hysteresis patterns varied due to bed form and surface structure adjustments as well as the stabilizing effect of antecedent low flows using half the data set a dimensionless fractional transport equation was derived based on excess shear stress dimensionless reference shear stresses were estimated in two ways as bulk values from all transport measurements and by applying a separate limb approach in which values were estimated for each limb of each hydrograph for the other half of the data set transport predictions with the separate limb approach were more accurate than those from six existing transport equations and the fractional relationship applied with bulk reference shear stresses thus hydrograph limb dependent dimensionless reference shear stress links changing bed morphology and sediment transport providing a parameter to improve transport predictions during individual flood events and in unsteady flow regimes this approach represents a framework with which to develop site specific transport relationships for varying flow regimes particularly in cases where detailed bed morphology measurements are not feasible and heterogeneous sediment complicates bed structure over time

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

velocity profiles for particles and liquid in open channel flow with suspended sediment experiments were performed to measure the mean velocity and turbulence characteristics in open channel flows with and without suspended sediment alluvial sand of nearly uniform size velocity measurements were obtained by using a newly developed technique the discriminator laser doppler velocimeter dldv which can distinguish both liquid and sediment particle velocities the mean velocity of sediment particles was found to be lower than that of the water while the velocity fluctuations in the water were not changed with the addition of sediment those of the sediment were diminished for the range of concentrations considered the friction velocity and the free surface slope increased with sediment concentration unlike other bulk flow parameters which were practically constant a uniform method of analysis was developed to facilitate data interpretation and comparison between similar studies

the chemical discrimination of clastic sedimentary components abstract the detrital composition of siliciclastic rocks from six localities in the taconic and acadian sections of new york and quebec can be described as mixtures of two or more differentiable sedimentary components a sedimentary component is defined as a mineral or group of minerals that sort independently of other sedimentary constituents because of grain morphology phyllosilicates usually dominate the finer grained component and quartz or mixtures of quartz and feldspar dominate the coarser grained components the chemical composition of a sedimentary component is distinctive and the differentiation of sedimentary components usually results in the concomitant separation of associated elements typical separations include the enrichment of k2o and al2o3 in the finer grained phyllosilicate rich fraction and the enrichment of sio2 and na2o in the coarser grained tectosilicate rich fraction fe2o3 and mgo are also enriched in the fine fraction if they are abundant constituents in the phyllosilicates the chemical composition of the graywackes from north america was compared to the chemical composition of unlithified turbidite sediments from the black sea the chemical variation trends found in the deeply buried sedimentary rocks are similar to the trends found in the suite of slightly buried and unlithified deep sea sediments this indicates that burial alteration does not necessarily result in large scale redistribution of the constituent elements it is possible therefore to use the chemical variations observed in a suite of deeply buried and mineralogically altered sedimentary rock to infer the original clastic assemblage and to help clarify the processes that produced the sediment