geometry and physical properties of the socorro new mexico magma bodies analysis of multichannel seismic reflection profiles gathered by the consortium for continental reflection profiling cocorp constrains the geometry and material properties of a proposed magma body located within the rio grande rift a new spectral ratio method is used to find the reflectivities of the proposed midcrustal intrusion large and spatially variable reflectivities support the interpretation of the reflector as an intrusive molten magma complex modeling of the reflectivity suggests that in one location the intrusion took the form of several thin 30 to 40 m thick layers seismic wave attenuation within the rift s midcrust is low

compositional variation and the origin of deep crustal reflections abstract identifying the sources of crustal reflections is essential for deriving more geological information from deep crustal reflection profiles theoretical and model studies help place constraints on the role of compositional variation in producing deep crustal reflections analysis of laboratory derived velocities and densities of rock types typical for the continental crust indicates that reflection coefficients are generally small but significantly 17 of the possible reflection coefficients have magnitudes between 0 1 and 0 2 comparison between reflection coefficients derived from well logs and reflections observed in associated seismic profiles indicates that constructive interference associated with geological layering is at least as important as the magnitude of the reflection coefficients for producing detectable reflections constructive interference can increase reflection amplitude by two to three times but is limited to a relatively narrow range of layer thickness for a typical 10 40 hz seismic wavelet and typical crustal velocities of about 6 km s constructive interference occurs for layer thickness ranging between about 35 and 80 m layers thinner than 35 m interfere destructively if reflections result from compositional variation seismic models of hypothetical and observed geologic relations provide analogs for interpreting complex reflection patterns observed in deep crustal reflection profiles such models show reflection patterns similar to those observed in the reflection profiles the models indicate that the reflections could originate in the complexly deformed and intruded terranes that are common in the crystalline crust and it may not be necessary to appeal to unobserved phenomena such as special lamellae or fluid filled fractures to explain the reflections

deconvolution technique to separate signal from noise in gravel bedload velocity data a deconvolution procedure is presented to estimate the probability density function of bedload transport velocity from noisy stationary data collected using the bottom tracking feature of acoustic doppler current profilers adcps the procedure involves the optimization of a computational summation of random variables for the instrument noise assumed to be gaussian with zero mean and the spatially averaged bedload velocity within the insonified area of each acoustic beam v the procedure was tested on two adcp time series measured in two different gravel bed rivers fraser river and norrish creek models generated using either a semitheoretical compound poisson gamma distribution or an empirical gamma distribution for v were similar and did not differ significantly from the distribution of the original data optimized distributions for v were highly positively skewed the instrument noise was comparable to instrument noise for adcp water velocity measurements i e an order of magnitude greater t

bed load grain velocities and sediment transport rates theoretical consideration of the dynamics of bed load sediment transport leads to expressions for bed grain velocity and sediment transport rate as respectively ub a u u c and ib a tan u u c 0 c agreeing in form with many previous analyses the grain velocity equation agrees well with all experimentally determined velocities of single grains moving over fixed rough beds if a is allowed to vary with bed roughness and saltation height values of u c for such overriding grains are substantially less than normally accepted values the sediment transport rate equation predicts plane bed experimental data well over five orders of magnitude of ib values of a tan increase significantly from lower to upper stage plane beds due to an increase in a with suspended sediment concentration but also due to a decrease in tan with increasing transport stage and grain size as predicted by bagnold

resistance to overland flow due to bed load transport on plane mobile beds during bed load transport by overland ow momentum is transferred from the ow to the bed via grain collisions resulting in a decrease in ow velocity and an increase in ow resistance herein termed bed load transport resistance in overland ow on mobile plane beds total ow resistance f consists of grain resistance fg and bed load transport resistance fbt in order to identify and evaluate the relative importance of the factors controlling fbt 38 ume experiments were performed on slopes of 2 7 and 5 5 using sediment with median diameters of 0 74 and 1 16 mm all ows were supercritical and turbulent this study is an extension of a recent study by gao and abrahams earth surface processes and landforms 2004 vol 29 pp 423 435 these authors found that fbt is controlled by three factors sediment concentration c dimensionless sediment diameter d and relative submergence h d where h is ow depth d is median sediment diameter however a new dimensional analysis identi es two additional factors froude number f and slope s multiple regression analyses reveal 1 that these ve factors together explain 97 per cent of the variance of fbt and 2 that s controls fbt entirely through c the variable c is therefore redundant and a new functional equation relating fbt to d h d s and f is developed this equation may be used to predict fbt an advantage of this equation is that it may be used to predict fbt without measuring bed load transport rate copyright 2004 john wiley sons ltd

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

laboratory flume experiments with the swiss plate geophone bed load monitoring system 1 impulse counts and particle size identification we performed systematic flume experiments using natural bed load particles to quantify the effect of different parameters on the signal registered by the swiss plate geophone a bed load surrogate monitoring system it was observed that the number of impulses computed from the raw signal clearly depends on bed particle size mean flow velocity bed roughness and to a minor extent on particle shape the centroid frequency of the signal resulting from the collision of a bed load particle against the geophone plate was found to be inversely related to particle size but to be less sensitive to variations in mean flow velocity and bed roughness than the signal amplitude which is also related to particle size combining frequency and amplitude information resulted in a more robust identification of the transported particles size over a wide range of sizes than using amplitude information alone

magma in layering at the moho of the basin and range of nevada layering at the moho as determined from seismic reflection data is a commonly observed phenomenon in the basin and range for which we propose a porous flow melt model analysis of seismic reflection data from the 1986 passcal nevada experiment indicates that the moho in the nevada basin and range is layered and has unusually high reflectivity this reflectivity is difficult to explain in terms of a velocity contrast caused by different rock types and in fact a lower velocity of less than 6 5 km s suggests the presence of partially molten material at the moho in a zone containing 20 to 25 of low velocity layers to explain the seismic observations we have developed a viscous porous flow model for basaltic melt ascent such a model produces systematic variations in volumetric melt flow with depth and close correspondence between seismic interpretation and modeling of partial melt ascent this suggests that such layering involving viscous porous flow of partial melt is a plausible explanation of the layering of the moho in the basin and range and may have more general application

seamount abundances and distributions in the southeast pacific abstract sea beam bathymetry was recorded for 17 277 km of ship track in the southeast pacific and has been analyzed for seamount population characteristics all the ship tracks are over the pacific plate and most fall along 7 lines parallel to the east pacific rise between 7 s and 22 s the lines fall into three age categories one line is over 0 5 2 ma crust three are over 5 10 ma crust and three are over 30 40 ma crust seamount locations were recorded diameters were manually estimated and heights were measured if the swath crossed the seamount center over 382 features were counted along the entire ship track with heights ranging from 50 m to over 2500 m with sampling most consistent at heights between 100 m and 1000 m height to radius ratios vary considerably suggesting that seamount shapes do not scale to a single parameter the observed variety of morphological forms demonstrates that there is a wide range of seamount shapes for small features the distribution of sizes for the population was approximated by exponential dependence and by power law dependence using methods developed by smith and jordan 17 the power law distribution overestimates abundances at the smallest size ranges and both distributions fail to predict abundances of large seamounts determined from wide beam data 17 size distributions were also determined for seamounts in each seafloor age category almost all small seamounts appear to be produced on crust younger than 0 5 2 ma while the number of larger seamounts increases to 5 10 ma for all size ranges observed here the number of seamounts at 5 10 ma and at 30 40 ma is roughly identical these observations suggest that most small seamounts are formed on very young thin lithosphere that permits the passage of small volumes of magma small volumes would cool in older thicker lithosphere before reaching the surface although larger magma bodies might not numerous small sources of melt must exist near the ridge crest to supply the small seamounts probably trapped remnants of the large scale upwelling

a ray parameter intercept time spectral ratio method for seismic reflectivity analysis a method is proposed for obtaining reflectivity magnitudes from seismic record sections that are densely sampled in the horizontal dimension the technique consists of finding the spectral ratio of subcritical target to postcritical reference reflection amplitudes the method s novelty is that both target and reference amplitude spectra are estimated from slant also known as ray parameter intercept time p tau or velocity stacks of the record sections the source level is directly determined because the reference amplitude is totally reflected source level estimation does not require knowledge of the impedance structure of the reference reflector the technique functions well for reflections having low s n ratios little or no lateralcontinuity poor near surface velocity control and steep dips application of the method to the consortium for continental reflection profiling cocorp survey in the rio grande rift supports the interpretation that its large amplitude midcrustal reflection is a magma body

coarse sediment particle motion under highly asymmetrical waves with implications for swash zone sediment transport abstract hydrodynamics and sediment transport in the swash zone are unique and very complex phenomena acquiring a robust model for predicting sediment motion in the swash zone requires in depth insight about the behavior of sediment particles in highly asymmetric and turbulent waves that continuingly uprush the beach face and retrieve in backwashes in order to consider a physical system of the coarse particle motion in the swash zone with a reduced number of external parameters and capture some of the realism of the situation the experiments are conducted in rather simple conditions to provide some information about the particle responses in terms of jump length against asymmetric waves to be implicated for the swash zone the results show that despite reduction of many external parameters jump length is still a highly skewed stochastic parameter the probability distribution of jump length is quite wide large variance and skewed different from that of saltation length in steady unidirectional flow in which the distribution is close to normal considering integral of excess energy of an arbitrary single wave over its duration as a rational and meaningful representative of flow condition the average jump length j l incremental trends reduces in the higher energy condition resulting in a linear trend in logarithmic scale the j l s due to higher turbulent kinetic energy follow similar trend of less turbulent flow conditions

evaluation of the saltation process of bed materials by video imaging under altered bed roughness the purpose of this paper is to examine the nature of particle saltation and movement over the beds of fixed roughness from flume experiments a series of experiments are carried out to study the saltation of individual sand particles of different sizes over rough beds under different flow conditions a 3 d acoustic doppler velocimeter is used to record the fluid velocity components subsequently under different flow conditions the images of released sand particles are recorded using high speed video imaging technique systematic analysis is made with regard to the forces acting on the grains and the variation of their magnitudes along the saltation trajectories of the grains relations between the saltation parameters flow intensity and bed roughness are developed the distributions of the angle of orientations during a single saltation follows almost a gaussian distribution the shape of the gaussian distribution depends on the particle size and bed roughness particle collisions with rough beds and the resulting coefficients of restitution are also discussed a theoretical framework is developed to compute the mean particle velocity considering the spin in the energy balance equation results of the detailed analysis using the imaging technique are much better than in previously reported studies copyright 2013 john wiley sons ltd

active megadetachment beneath the western united states geodetic data interpreted in light of seismic imaging seismicity xenolith studies and the late quaternary geologic history of the northern great basin suggest that a subcontinental scale extensional detachment is localized near the moho to first order seismic yielding in the upper crust at any given latitude in this region occurs via an m7 earthquake every 100 years here we develop the hypothesis that since 1996 the region has undergone a cycle of strain accumulation and release similar to slow slip events observed on subduction megathrusts but yielding occurred on a subhorizontal surface 5 10 times larger in the slip direction and at temperatures 800 c net slip was variable ranging from 5 to 10 mm over most of the region strain energy with moment magnitude equivalent to an m7 earthquake was released along this megadetachment primarily between 2000 0 and 2005 5 slip initiated in late 1998 to mid 1999 in northeastern nevada and is best expressed in late 2003 during a magma injection event at moho depth beneath the sierra nevada accompanied by more rapid eastward relative displacement across the entire region the event ended in the east at 2004 0 and in the remainder of the network at about 2005 5 strain energy thus appears to have been transmitted from the cordilleran interior toward the plate boundary from high gravitational potential to low via yielding on the megadetachment the size and kinematic function of the proposed structure in light of various proxies for lithospheric thickness imply that the subcrustal lithosphere beneath nevada is a strong thin plate even though it resides in a high heat flow tectonic regime a strong lowermost crust and upper mantle is consistent with patterns of postseismic relaxation in the southern great basin deformation microstructures and low water content in dunite xenoliths in young lavas in central nevada and high temperature microstructures in analog surface exposures of deformed lower crust large scale decoupling between crust and upper mantle is consistent with the broad distribution of strain in the upper crust versus the more localized distribution in the subcrustal lithosphere as inferred by such proxies as low p wave velocity and mafic magmatism

processing and inversion of refraction and wide angle reflection data from the 1986 nevada passcal experiment we derive averaged one dimensional velocity models for the crust beneath the basin and range in western nevada by inverting p composites extracted from slant stacks of refraction and wide angle reflection data a combination of high cut filtering in the frequency domain with coherency filtering in the p domain has proved effective in smoothing severe static shifts due to lateral heterogeneities and suppressing artifacts due to spatial aliasing we supplement the low frequency information provided by the refraction records with higher frequency arrivals picked from the normal incidence and wide angle reflection sections generalized least squares inversion of data from eight shots for p and s wave velocity structure beneath two perpendicular profiles yields consistent estimates for total crustal thickness p wave 30 31 km s wave 30 32 km and average crustal velocity 6 2 km s 3 4 3 5 km s average poisson s ratio beneath the n s profile is 0 27 0 28 p wave velocities near the base of the crust 7 4 0 3 km s are estimated by inverting precritical reflections from the moho standard errors in depth for these models range from 1 to 3 km extremal depth bounds in general are about twice as large uncertainties in velocity estimated from resolving kernels range from 0 1 to 0 3 km s estimates of poisson1s ratio as a function of depth are characterized by large standard errors reflecting the poor resolution of shear wave velocities the combination of low average p and s wave velocities with a high average poisson s ratio in the upper half of the crust however is consistent with the presence of fluid filled cracks these results highlight the need for three component recording to better resolve shear wave velocity structure

the seismic reflection character of the continental mohorovicic discontinuity the continental mohorovicic discontinuity is most often interpreted as a step function velocity boundary however on deep crustal seismic reflection profiles reflections at depths where refraction data places the moho have laminated character and are laterally discontinuous these observations on continental reflection data point to a model of the moho that has thin layered rather than block structure previous workers who have synthetically generated seismic responses from various crust mantle boundary models have shown that thin layered models of alternating high and low velocity generate responses that best emulate observed moho arrivals geologic interpretations of the thin layering include relatively undeformed metasediments cumulate layering tectonic banding and lenses of partial melt to obtain more direct geologic evidence a synthetic seismogram is generated from geologic cross sections of the ivrea verbano zone an exposed section through the lower crust and upper mantle the synthetic shows laminations similar to those observed on reflection data without more direct evidence no single geologic interpretation of the moho is reasonable indeed the moho may be a laterally variable boundary its composition and structure dependent upon the geologic history of the overlying crust

implications of the saltation abrasion bedrock incision model for steady state river longitudinal profile relief and concavity the saltation abrasion model predicts rates of river incision into bedrock as an explicit function of sediment supply grain size boundary shear stress and rock strength here we use this experimentally calibrated model to explore the controls on river longitudinal profile concavity and relief for the simple but illustrative case of steady state topography over a wide range of rock uplift rates we find a characteristic downstream trend in which upstream reaches are close to the threshold of sediment motion with large extents of bedrock exposure in the channel bed while downstream reaches have higher excess shear stresses and lesser extents of bedrock exposure profile concavity is most sensitive to spatial gradients in runoff and the rate of downstream sediment fining concavity is also sensitive to the supply rate of coarse sediment which varies with rock uplift rate and with the fraction of the total sediment load in the bedload size class variations in rock strength have little influence on profile concavity profile relief is most sensitive to grain size and amount of runoff rock uplift rate and rock strength influence relief most strongly for high rates of rock uplift analysis of potential covariation of grain size with rock uplift rate and rock strength suggests that the influence of these variables on profile form could occur in large part through their influence on grain size similarly covariation between grain size and the fraction of sediment load in the bedload size class provides another indirect avenue for rock uplift and strength to influence profile form copyright 2008 john wiley sons ltd

moho reflectivity patterns a comparison of canadian lithoprobe transects abstract the complex nature of the continental moho may be strongly influenced by the tectonic and magmatic history of the lithosphere observations of moho variability from near vertical incidence seismic reflection surveys suggest that it may be possible to correlate moho reflectivity and lithospheric evolution as an initial step in attempting to determine such correlations we qualitatively compare seismic reflection data from canadian lithoprobe transects that sample regions of exceptionally diverse age and tectonic history the seven selected datasets were collected using consistent acquisition parameters facilitating effective and meaningful comparisons among transects the moho reflections exhibit considerable variability however in virtually all recent transects a distinct moho is observed even in regions where lower crust is considered to have stabilized in the early proterozoic or archean this suggests not only that relationships between moho reflectivity and tectonics can be extended into the archean but that tectonic age is poorly correlated with moho reflectivity the qualitative comparisons do not clearly link a specific tectonic process with a distinctive reflection pattern however well defined moho reflections are associated with lower crustal deformational processes including compression transpression and extension this indicates that ductile shear and the rheologies of the lower crust moho transition and upper mantle play important roles in influencing reflective character indistinct moho reflectivity may be associated with regions that have experienced little ductile deformation or with processes that have disrupted reflective laminations however the majority of incoherent moho reflections appear related to signal degradation associated with data acquisition the study demonstrates that the qualitative characteristics of moho reflectivity are difficult to correlate with tectonic history and thus use as an interpretive tool isolating quantitative reflection characteristics of the moho from distortions imposed by the overlying crust is a challenging problem but appears necessary to further understanding of the crust mantle transition

modeling the effects of bed topography on fluvial bedrock erosion by saltating bed load abrasion by saltation is an important mechanism of fluvial incision into bedrock sklar and dietrich 2004 introduced an abrasion model in which the erosion rate of an approximately planar bed is linearly dependent on the kinetic energy transferred by the vertical velocity of saltating grains however most bedrock floored channels exhibit topographic variations that yield deviations from a planar surface referred to as bed topography observations show that bed topography affects erosion here the saltation abrasion model is extended for a nonplanar bed a several centimeter high bump transverse to the flow is repeated every 50 cm the kinetic energy of grain impacts is calculated in two ways 1 impact velocity normal to bed topography and 2 vertical impact velocity by comparing the latter case with the planar model it is possible to isolate the effects of topography on the interception of saltation trajectories incorporating bed topography changes erosion in three ways first erosion is 10 to 1000 times faster depending upon transport stage and grain size enhanced erosion results from both the interception of grains by topography and the increased kinetic energy transfer associated with high angle impacts on the stoss side of bumps second erosion increases monotonically with transport stage whereas maximum erosion occurs at low to intermediate transport stage with a planar bed third erosion decreases monotonically with grain size whereas maximum erosion occurs with intermediate sized grains with a planar bed although the model is highly simplified results show that bed topography should be considered when simulating erosion of bedrock

sediment transport by wind toward a general model a general model of eolian sediment transport by both saltation and suspension is developed saltation is analyzed through calculations of single trajectories given initial conditions of liftoff speed angle and spin profiles of particle concentration and mass flux generated by assuming that all trajectories are identical display distinct maxima at the top of the trajectory by incorporating the realistic distribution of trajectories that arises from the stochastic nature of grain impacts with a granular bed the model yields monotonic decreases in particle concentration and mass flux with height in accordance with published empirical data the analysis of suspension as the balance between downward advective flux as a result of the settling of grains and their upward diffusive flux as a result of turbulence results in concentration profiles that fall off as power laws with height also in accordance with empirical data a relation for reference level concentrations is presented for both blowing snow and dust profiles the solutions for saltation and suspension are combined to yield mass flux profiles for the entire range of grain sizes in the bed the saltation layer emerges naturally as that region where the total flux of saltating grains exceeds that of suspended grains the model points clearly to the need for further research on the stochastic grain bed interactions which control both the probability distribution of liftoff velocities in saltation and the production of fine particles in suspension

the moho in the northern basin and range province nevada along the cocorp 40 n seismic reflection transect cocorp seismic reflection profiles across nevada at about 40 n image a prominent essentially continuous band of reflectors at a two way traveltime of 9 to 11 s the approximate correspondence of this reflection time with estimates of the two way traveltime to the moho in this area provided by seismic refraction data suggests that the prominent reflections are from the moho the relief on these reflectors the reflection moho beneath nevada across a latitudinal transect of

2d process based morphodynamic model for flooding by noncohesive dyke breach abstractinundation models based on the shallow water equations swe have been shown to perform well for a wide variety of situations even at the limit of their theoretical applicability and arguably somewhat beyond one of these situations is the catastrophic event of floods induced by dyke breach and consequent dyke erosion the dyke collapse is often not sudden as assumed by many flood simulations in which the dyke boundary is treated as a dam break the dyke erosion is a gradual and complex process that delays the onset of the flood affecting the hydrograph of the flow to simulate correct temporal passage of a flood it is important to understand the rate at which these dykes collapse in this paper an overtopping flood event combined with dyke erosion is simulated the model is built upon the two dimensional 2d shallow water equations together with sediment flow interactions and incorporates a sediment transport equation the model is solved using a second order godunov type finite volume me

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

local high slope effects on sediment transport and fluvial bed form dynamics 1 we investigate the morphodynamic evolution of an arbitrarily tilted coarse mobile bed under the action of a free surface water flow the analysis is based on the experimental observations of the evolution of a mobile bed from its initial laterally tilted configuration to the final laterally flat state due to the presence of a lateral component of bed load transport measurements of the bed topography at different times allow one to reconstruct the flattening process the experimental observations are interpreted by means of a three dimensional numerical hydromorphodynamic model employing different relationships linear and nonlinear to evaluate bed load intensity and direction the analysis shows that the inclusion of nonlinear gravitational effects in the description of the bed load leads to a more satisfactory description of the bed evolution this finding opens important issues on how the inclusion of the nonlinear gravitational effects on the bed load can affect the morphodynamic evolution of complex bed topography occurring in natural rivers to investigate this point an application to the evolution of river bars is presented

experimental study on coarse grain saltation dynamics in bedrock channels saltation of bed load particles on bedrock surfaces is important for landscape evolution and bedrock incision in steep landscapes however few studies have investigated saltation in bedrock channels where unlike alluvial channels the bed roughness height and the sediment size may be independent to address this data gap we measured the saltation hop height hop length and velocity of gravel saltating over a planar bed using 80 160 readings from high speed photography and direct measurements two separate dimensional analyses are used one leading to a bed shear stress scaling and another leading to a froude number fr scaling our new saltation data coupled with numerous data from previous studies suggest that both shear stress and fr scaling analyses are valid in characterizing bed load saltation dynamics with bed roughness ranging from smooth to alluvial beds however the fr approach has the advantages that 1 there is no need to estimate a critical shields stress c which alone can vary up to 2 orders of magnitude e g 0 001 0 1 due to changes in relative bed roughness and slope and 2 the fr based scaling fits the saltation data set better in a least squares sense results show that the saltation velocity of bed load is independent of grain density and grain size and is linearly proportional to flow velocity saltation height has a nonlinear dependence on grain size saltation length increases primarily with flow velocity and it is inversely proportional to submerged specific density our results suggest that either c or bed roughness coefficient must be properly estimated to yield accurate results in saltation abrasion models

bed load or suspended load the difference between the sediment transport processes of bed load and suspended load is explained and quantified the mean and fluctuating components of the particle motion are studied by examining both components of the particle s dynamics in open channel flows for sand particles the time required for particles leaving the bed to attain the free fall velocity is shown to be the critical parameter for the saltation suspension distinction an example of the use of the distinction is given

bedload transport resistance in rough open channel flows during bedload movement by saltation streamwise momentum is transferred from the ow to the saltating grains when the grains collide with other grains on the bed or in the ow streamwise momentum is reduced and there is a decrease in streamwise ow velocity and an increase in ow resistance herein termed bedload transport resistance fbt based on experiments in two umes with xed and mobile plane beds and previously published data an equation is developed that may be used to predict fbt for both capacity and non capacity ows the variables in this equation are identi ed by dimensional analysis and the coef cients are determined by non linear regression this equation applies to rough turbulent open channel ows where the relative submergence is between 1 and 20 and the entire sediment load moves by saltation an investigation of the relative magnitudes of fbt and grain resistance fc suggests that where dimensionless shear stress is less than 1 and saltation is the dominant mode of bedload transport fbt fc increases with but never exceeds 1 copyright 2004 john wiley sons ltd

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

average velocity of solitary coarse grain in flows over smooth and rough beds abstracta formula is derived for the prediction of the average velocity of a solitary coarse grain moving over a rigid flat channel bed to verify the theoretical consideration data collected in the present study and reported in the literature 811 sets in total are analyzed for typical bed roughness configurations the results show significant improvements in the prediction of solitary grain velocity for both smooth and rough bed conditions in comparison with other formulas available in the literature from the proposed formula it follows that for rough bed conditions the dimensionless grain velocity depends on the shields number and also the ratio of bed roughness height to the grain diameter the present study is limited to motion of solitary grains but the result obtained implies that bed load transport rate could be also affected by the equivalent bed roughness height even under mobile bed conditions and such effects may become pronounced for nonuniform sediments

two dimensional nonequilibrium noncohesive and cohesive sediment transport model the purpose of this paper is to develop an unsteady 2d depth averaged model for nonuniform sediment transport in alluvial channels in this model the orthogonal curvilinear coordinate system is adopted the transport mechanisms of cohesive and noncohesive sediment are both embedded the suspended load and bed load are treated separately in addition the processes of hydraulic sorting armoring and bed consolidation are also included in the model the implicit two step split operator approach is used to solve the flow governing equations and the coupling approach with iterative method are used to solve the mass conservation equation of suspended sediment mass conservation equation of active layer sediment and global mass conservation equation for bed sediment simultaneously three sets of data including suspension transport degradation and aggradation cases for noncohesive sediment and aggradation degra dation and consolidation cases for cohesive sediment have been demonstrated to show the rationality and accuracy of the model finally the model is applied to evaluate the desilting efficiency for ah gong diann reservoir located in taiwan to show its applicability

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

bright seismic reflections and fluid movement by porous flow in the lower crust abstract the origin of high amplitude lower crustal bright seismic reflections in a phanerozoic area is investigated by modeling a distribution of metamorphic fluid flow through pores as a possible explanation a numerical model of metamorphic fluid flow in a viscous porous medium is developed a model is applied to a tectonically active area such as the basin and range where viscous behavior of the lower crust is suggested calculations show that the characteristic vertical dimension of relative volumetric flow variations corresponds to the thickness of seismic lamellae as determined from reflection frequency spectra for the basin and range this result shows that a dynamic effect which was produced by fluid pressure and viscous matrix resistance could be responsible for the origin of the seismic lamellae in the lower crust in an area of active tectonics

the 1995 7 2 magnitude kobe earthquake and the arima takatsuki tectonic line implications of the seismic risk for central japan abstract along the rokko mountains and awaji island ne sw to ene wsw oriented active faults exist in an en echelon arrangement they constitute a portion of the arima takatsuki tectonic line attl which extends from kyoto through awaji island to the median tectonic line the attl is also correlated to lineaments linking the saddles and steep slopes of gravity bouguer anomalies the main shock of the 1995 magnitude 7 2 m 7 2 kobe earthquake was located at the mid point of the attl the main shock also created a 9 km long rupture on the ground surface along the ne sw nojima fault line in the northern part of awaji island the earthquake aftershocks were distributed over a 40 km long zone along the central segment of the line surface ruptures and cracks accompanying the kobe earthquake were scattered along a 40 km segment centrally located on the attl spatial correlation of the surface ruptures and aftershock distribution on the attl suggests that the kobe earthquake was the result of a 40 km long rupture of the central segment of the attl the average rate of seismic moment release is an important parameter used in evaluating the seismic risk of a fault system the moment release rate averaged over the late quaternary has been evaluated through the average slip rates and the dimensions of constituent faults the average moment release rate for the central portion of the attl has been estimated as 0 0017 0 0063 10 26 dyne cm year 1 evidence of liquefaction and flowage probably associated with the 1596 m 7 5 keicho fushimi earthquake has been identified at several archaeological excavation sites along the attl these observations suggest that the attl was also responsible for the keicho fushimi earthquake which occurred about 400 years ago from the elapsed time since the keicho fushimi earthquake and the average moment release rate the seismic moment accumulated during the interseismic period was calculated for the attl the obtained value amounts to that of the seismic moment released by an earthquake having a magnitude ranging from 6 8 to 7 2 being comparable to that of the kobe earthquake the obtained result is consistent with the view that the kobe earthquake was caused by a rupture of the attl which released almost all the moment accumulated since the previous event

bed load transport i mechanical characteristics this paper deals with the mechanical characteristics of saltation of bed load transport in flowing water experiments have been carried out by means of high speed photography and advanced data processing techniques taking saltation as the mode of bed load transport systematic analysis has been made with regard to the forces acting on grains and the variation of their magnitudes along the saltation trajectories to obtain the kinematic and dynamic properties of these grains moveover the relations between magnitudes of saltation parameters and flow intensity are attained from the measured data some parameters in bagnold s theory of bed load transport are also discussed

absolute reflection coefficients from deep seismic reflections abstract many deep seismic reflection profiles show bright sub horizontal layered reflections in the lower continental crust accurate estimates are obtained for normal incidence reflection coefficients for the brightest of these reflections by using a marine seismic acquisition system that has been calibrated using deep water sea bottom multiples minimum bounds are placed upon these reflection coefficients by assuming minimum losses due to scattering anelastic attenuation and geometric spreading reflection coefficients of around 0 1 are obtained from the layered lower crust and around 0 15 from the moho it is argued that constructive interference between successive reflections from a layered sequence of reflectors is often unimportant consequently these coefficients can be used to place useful limits on the absolute acoustic impedance contrasts present at depth