combined visual and quantitative techniques in the study of natural turbulent flows an important difficulty in understanding turbulence in natural flows is that one does not see what is being measured by devices recording velocity fluctuations this study shows how visualization of turbulent structures can be effectively implemented in natural river flows in order to match turbulent flow structures with their velocity signatures flow visualization is combined with high frequency 20 hz velocity measurements from electromagnetic current meters two fluvial environments are examined in a river confluence where the difference in turbidity provides a natural tracer very strong negative velocity fluctuations for the streamwise component are concomitant with an upwelling motion a video recording made from a bridge of the passage of turbulent structures delineated by turbid and clear water allowed us to relate the marked fluctuations in velocity to eddies of a duration of 1 2 s in the mixing layer in a gravel bed river we have examined patterns of eddy shedding in the lee of a pebble cluster these patterns were highlighted by dye milk injected in the separation zone downstream black and white images were obtained from an underwater lens linked to a video camera recorder we observed a complex dynamic characterized by two dominant patterns of eddy shedding one with a clear motion of eddies toward the water surface and another with a downward expansion toward the bed of the structures this pattern is related to the passage of intermittent wedges of low speed fluid separated by wedges of fast moving fluid

turbulence structure over two dimensional bed forms implications for sediment transport turbulence measurements from the flow over two dimensional fixed dune shapes are presented along with analysis and discussion of the ramifications of the observations for transport of sediment as bed load over bed forms the spatial structure of the local transport rate determines the shape and stability of bed forms such as ripples and dunes and the transport of sediment is a highly nonlinear process that is profoundly affected by the statistics of the temporal fluctuations in the near bed flow field the measurements presented herein show strong spatial evolution of the joint probability distribution of the streamwise and bednormal fluctuating velocity components unlike measurements in uniform boundary layers these distributions and the higher moments of the velocity do not scale with the local shear velocity indicating that it is probably inappropriate to use the shear stress to characterize the sediment flux this conclusion is supported by observations of sediment flux over a dune

measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravel maps are presented of the spatial distribution of two dimensional bedload transport velocity vectors bedload velocity data were collected using the bottom tracking feature of an acoustic doppler current pro ler adcp in both a gravel bed reach and a sand bed reach of fraser river british columbia block averaged bedload velocity vectors and bedload velocity vectors interpolated onto a uniform grid revealed coherent patterns in the bedload velocity distribution concurrent helley smith bedload sampling in the sand bed reach corroborated the trends observed in the bedload velocity map contemporaneous 2d vector maps of near bed water velocity velocity in bins centered between 25 cm and 50 cm from the bottom and depth averaged water velocity were also generated from the adcp data using a vector correlation coef cient which is independent of the choice of coordinate system the bedload velocity distribution was signi cantly correlated to the near bed and depth averaged water velocity distributions the bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress published in 2004 by john wiley sons ltd

theoretical analysis of wing dike impact on river flood stages the question of whether wing dikes bank perpendicular river training structures or groynes cause higher flood levels has been debated in the united states for many years some researchers point to empirical data that show large stage increases which are associated with wing dike construction whereas other researchers have suggested that such increases are contrary to engineering theory in a recent report the u s government accountability office usgao presented this question as a priority to be resolved by engineers and scientists as a first step to better understand the connection between navigation structures and flood levels on the middle mississippi river mmr a simplified theoretical analysis is presented to test the assertion made in the usgao report and elsewhere that such increases are contrary to hydraulic theory this analysis predicts that wing dike construction may lead to water level lowering for in bank flows and to water level increases for out of bank flood flows this confirms that in principle wing dikes may have contributed to the observed flood water level trends in the mmr more detailed follow up studies are required to accurately quantify the impact of wing dikes on flood levels doi 10 1061 asce hy 1943 7900 0000698 2013 american society of civil engineers

on the correspondence between morphological and hydrodynamical patterns of groyne fields this paper examines a variety of recirculation flow patterns that develop in the groyne fields on rivers a comprehensive data set was obtained from flume experiments at delft university of technology and field measurements performed on the elbe river in germany the analysis focuses on patterns of velocity scour and deposition and corresponding change of riverbed morphology the results show that velocity patterns in the groyne fields depend mainly on the aspect ratio between groyne length and length of groyne field when the aspect ratio is greater than 0 5 a one gyre pattern of recirculation develops while at groyne fields with aspect ratios less than 0 5 a two gyre recirculation pattern emerges the spatial distribution of fine sediment deposition between the groynes coincides with the locations of gyres moreover the thickness of the fine sediment layer decreases toward the gyre margins where recirculation velocities are greatest although the total concentration of suspended sediment in the river does not change considerably as the flow moves through the groyne field the biological and gravimetrical composition of the suspended material changes substantially within the groyne field these changes are due to preferential deposition of coarse mineral particles and the replacement of those minerals with finer organic material copyright 2002 john wiley sons ltd

a simple effective medium model for water saturation in porous rocks a general equation for water saturation is derived from effective medium theory a simpler low frequency equation is also derived both equations are directly solvable for water saturation the model should be applicable to any granular water wet formation additional relationships are derived specifically for application to shaly sandstones but the model should be applicable to a wide range of rock types water conductivities and tool frequencies in the derivation hydrocarbons are included in the matrix component of the equation and the combined matrix elements are treated as resistors in parallel the low frequency equation is compared to various approaches to calculation of water saturation such as dual water waxman smits and bussian the general equation is compared to three component effective medium porosity index and complex refractive index models crim the model is proven to work on experimental data under a wide range of frequencies and water conductivities it is recommended that

measured and simulated flow near a submerged spur dike to improve knowledge of the flow and scour processes associated with spur dikes three dimensional flow velocities were measured at 2 592 points using an acoustic doppler velocimeter over a fixed flat bed with a trapezoidal shaped submerged spur dike in a laboratory flume general velocity distribution and detailed near field flow structures were revealed by the measurements and numerical simulations performed using a free surface turbulent flow model with a k e closure scheme the three dimensional flow separation characterized in this study was found to yield forces on the bed that were significantly different from nonsubmerged vertical obstructions that have been measured in other studies values of bed shear stress derived from both measured and simulated values were similar but indicated that local scour would be initiated in one rather than in the two locations of initial local scour measured in previous experiments with a similar flow

acoustic measurement of river discharge this paper presents a new moving boat method for rapidly measuring river discharge using an acoustic doppler current profiler adcp the method uses an adcp to measure current profiles and boat velocity along transects across a river measurements from the river elbe near hamburg germany are presented to illustrate the method and its associated uncertainties an adcp measures profiles of current velocity relative to the boat and the velocity of the boat relative to the bottom the discharge calculation depends only on these data and it is not necessary to know either compass heading or the actual location of the boat furthermore the transect can be an arbitrary curve as long as it starts near one side of the river and ends near the other uncertainty in discharge from random errors biases and missed data near the surface bottom and sides of the river is investigated missed data near the surface and bottom are the largest source of error unless the data are corrected by assuming model profiles

an investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel 1 conditions corresponding to the initiation of the erosion and deposition process 1 the present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start flat bed of the scouring process large eddy simulation les is performed at a relatively low channel reynolds number re 18 000 in the range where most flume studies with clear water scour conditions are conducted similar to these studies the incoming flow is fully turbulent and contains realistic turbulence fluctuations visualization experiments are conducted to better understand the nature of the interactions between the dominant coherent structures playing a role in the erosion process it is found that the structure of the horseshoe vortex hv system at the base of the spur dike changes considerably in time and in vertical sections perpendicular to the trajectory defined by the axis of the main necklace vortex however its intensity is the largest at vertical sections situated around the tip of the spur dike it is in this region that the core of the main necklace vortex oscillates aperiodically between two preferred modes in one of them zero flow mode the necklace vortex is closer to the spur dike and more compact and the near bed jet flow beneath it is weak in the other one back flow mode a strong near bed jet flow convects the primary necklace vortex away from the spur dike and its core is more elongated and less compact this explains the large amplification by about 1 order of magnitude compared to the surrounding turbulent flow of the turbulent kinetic energy and pressure fluctuations inside the hv system in the region situated around the tip of the spur dike and the double peak distribution of the turbulent kinetic energy past the spur dike in the legs of the necklace vortex the intensity of the bimodal oscillations decreases such that they are not observed in spanwise sections situated at more than one channel depth behind the spur dike it is found that the legs of the horseshoe vortices can interact at times with the vortex tubes shed in the detached shear layer dsl and with the tip of the spur dike these events typically result in a significant change in the coherence of the hv system the largest bed shear stress values in the mean flow are present in the strong acceleration region near the tip of the spur dike but high bed shear stress values are also observed beneath the upstream part of the dsl the bed shear stress fluctuations around the local mean values can be very high especially in the region situated beneath the upstream part of the dsl at random times some of the vortices shed in the dsl merge or interact with eddies from the recirculation region this leads to an increase in their strength and to a large increase of the bed shear stress along their path

hydraulic validation of two dimensional simulations of braided river flow with spatially continuous adcp data 1 gravel bed braided rivers are characterized by shallow branching flow across low relief complex and mobile bed topography these conditions present a major challenge for the application of higher dimensional hydraulic models the predictions of which are nevertheless vital to inform flood risk and ecosystem management this paper demonstrates how high resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers specifically we detail applications of the shallow water model delft3d to the rees river new zealand at two nested scales a 300 m braid bar unit and a 2 5 km reach in each case terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy dense observations of depth and velocity acquired from a mobile acoustic doppler current profiler adcp along with low altitude aerial photography were then used to create a data rich framework for model calibration and testing at a range of discharges calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity h through comparison of predictions with distributed hydraulic data results revealed strong sensitivity to h which influenced cross channel velocity and localization of high shear zones the high resolution bed topography partially accounts for form resistance and the recovered roughness was found to scale by 1 2 1 4 d84 grain diameter model performance was good for a range of flows with minimal bias and tight error distributions suggesting that acceptable predictions can be achieved with spatially uniform roughness and h

flow in bedrock canyons a survey along the fraser canyon in canada reveals complex flow dynamics involving velocity inversions and upwelling which suggests ways to improve flow and bedrock incision modelling canyons carved into the bedrock in areas of actively uplifting terrain are important for our understanding of the link between tectonics climate and topography fluid flow and sediment transport are processes associated with canyon bedrock incision in models but to date there are no field observations of the flow structure in bedrock canyons that can be used to test the model components that represent fluid flow this paper describes a survey along the fraser canyon in canada that provides detailed measurements of flow in a narrow bedrock canyon the data reveal a more complex flow structure than currently assumed in flow models implying that a revision in our understanding of bedrock canyon incision is required bedrock erosion in rivers sets the pace of landscape evolution influences the evolution of orogens and determines the size shape and relief of mountains1 2 a variety of models link fluid flow and sediment transport processes to bedrock incision in canyons the model components that represent sediment transport processes are increasingly well developed3 4 5 in contrast the model components being used to represent fluid flow are largely untested because there are no observations of the flow structure in bedrock canyons here we present a 524 kilometre continuous centreline acoustic doppler current profiler survey of the fraser canyon in western canada which includes 42 individual bedrock canyons our observations of three dimensional flow structure reveal that as water enters the canyons a high velocity core follows the bed surface causing a velocity inversion high velocities near the bed and low velocities at the surface the plunging water then upwells along the canyon walls resulting in counter rotating along stream coherent flow structures that diverge near the bed the resulting flow structure promotes deep scour in the bedrock channel floor and undercutting of the canyon walls this provides a mechanism for channel widening and ensures that the base of the walls is swept clear of the debris that is often deposited there keeping the walls nearly vertical these observations reveal that the flow structure in bedrock canyons is more complex than assumed in the models presently used fluid flow models that capture the essence of the three dimensional flow field using simple phenomenological rules that are computationally tractable are required to capture the dynamic coupling between flow bedrock erosion and solid earth dynamics

comparing different methods of bed shear stress estimates in simple and complex flow fields bed shear stress is a fundamental variable in river studies to link ow conditions to sediment transport it is however dif cult to estimate this variable accurately particularly in complex ow elds this study compares shear stress estimated from the log pro le drag reynolds and turbulent kinetic energy tke approaches in a laboratory ume in a simple boundary layer over plexiglas and over sand and in a complex ow eld around de ectors results show that in a simple boundary layer the log pro le estimate is always the highest over plexiglas the tke estimate was the second largest with a value 30 per cent less than the log estimate however over sand the tke estimate did not show the expected increase in shear stress in a simple boundary layer the reynolds shear stress seems the most appropriate method particularly the extrapolated value at the bed obtained from a turbulent pro le in a complex ow eld around de ectors the tke method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent uctuations close to the de ectors it is suggested that when single point measurements are used to estimate shear stress the instrument should be positioned close to 0 1 of the ow depth which corresponds to the peak value height in pro les of reynolds and tke shear stress copyright 2004 john wiley sons ltd

calibration of a 3d hydrodynamic meandering river model using fully spatially distributed 3d adcp velocity data abstractthis study used fully spatially distributed three dimensional 3d velocity data for the improved calibration of a 3d hydrodynamic model the conventional calibration methods do not account

effects of groyne layout on the flow in groyne fields laboratory experiments this research is aimed at finding efficient alternative designs in the physical economical and ecological sense for the standard groynes as they are found in the large rivers of europe in order to test the effects of various groyne shapes on the flow in a groyne field experiments were performed in a physical model of a schematized river reach geometrically scaled 1 40 four different types of schematized groynes were tested all arranged in an array of five identical groyne fields i e standard reference groynes groynes with a head having a gentle slope and extending into the main channel permeable groynes consisting of pile rows and hybrid groynes consisting of a lowered impermeable groyne with a pile row on top flow velocities were measured using particle tracking velocimetry the design of the experiment was such that the cross sectional area blocked by the groyne was the same in all cases depending on the groyne head shape and the extent of submergence variations in the intensity of vortex shedding and recirculation in the groyne field were observed the experimental data are used to understand the physical processes like vortex formation and detachment near the groyne head it is demonstrated that the turbulence properties near and downstream of the groyne can be manipulated by changing the permeability and slope of the groyne head it is also observed that for submerged conditions the flow becomes complex and locally dominated by three dimensional effects which will make it difficult to predict by applying depth average numerical models or by three dimensional models with a coarse resolution in the vertical direction

morphology and flow fields of three dimensional dunes rio parana argentina results from simultaneous multibeam echo sounding and acoustic doppler current profiling 1 most past studies of river dune dynamics have concentrated on two dimensional 2 d bed forms with constant heights and straight crest lines transverse to the flow and their associated turbulent flow structure this morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels where dune form is predominantly three dimensional for example studies over 2 d forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology this paper details a field study of a swath of 3 d dunes in the rio parana argentina a large 0 35 km wide 1 2 km long area of dunes was surveyed using a multibeam echo sounder mbes that provided high resolution 3 d detail of the river bed simultaneous with the mbes survey 3 d flow information was obtained with an acoustic doppler current profiler adcp revealing a complicated pattern of dune morphology and associated flow structure within the swath dune three dimensionality appears intimately connected to the morphology of the upstream dune with changes in crest line curvature and crest line bifurcations junctions significantly influencing the downstream dune form dunes with lobe or saddle shaped crest lines were found to have larger more structured regions of vertical velocity with smaller separation zones than more 2 d straight crested dunes these results represent the first integrated study of 3 d dune form and mean flow structure from the field and show several similarities to recent laboratory models of flow over 3 d dunes

water saturations in a wilcox shaly reservoir sandstone fordoche field point coupee parish louisiana abstract a new model has been derived for calculation of water saturation in shaly reservoir sandstones the model is based on effective medium theory emt and has been used successfully on a wide range of clayey low resistivity reservoirs a further independent test of saturations calculated by the model was made for a deep wilcox shaly reservoir at a depth of 13 176 ft 4016 m in fordoche field the reservoir w8 has a low average resistivity of about 2 5 ohm m and an estimated 18 clay as compared to an average resistivity of 1 5 ohm m in an underlying wet sandstone w 10 of similar clay content for the reservoir calculated water saturations are in the range of 35 to 50 increasing downward and suggest that the shaly sandstone should produce water free oil other shaly sand models generally give water saturations in excess of 50 for the reservoir water saturations calculated by the emt model agree well with other parameters for sandstones reported production core analysis and synthetic capillary pressures the reservoir w8 had an initial potential of 213 bbl of oil per day confirming water free oil production which could have been predicted by the emt model

modulation of outer bank erosion by slump blocks disentangling the protective and destructive role of failed material on the three dimensional flow structure the three dimensional flow field near the banks of alluvial channels is the primary factor controlling rates of bank erosion although submerged slump blocks and associated large scale bank roughness elements have both previously been proposed to divert flow away from the bank direct observations of the interaction between eroded bank material and the 3 d flow field are lacking here we use observations from multibeam echo sounding terrestrial laser scanning and acoustic doppler current profiling to quantify for the first time the influence of submerged slump blocks on the near bank flow field in contrast to previous research emphasizing their influence on flow diversion away from the bank we show that slump blocks may also deflect flow onto the bank thereby increasing local shear stresses and rates of erosion we use our measurements to propose a conceptual model for how submerged slump blocks interact with the flow field to modulate bank erosion

geometry of scour holes associated with 90 spur dikes the stable pools formed by spur dikes can be a significant factor for improving aquatic habitat in unstable degraded streams prediction of the volume and geometry of the scour hole associated with a spur dike yields information that is valuable for assessing the potential benefit to the aquatic habitat volumes of the scour hole in the vicinity of model spur dikes were measured in a laboratory flume under clear water overtopping flows spur dike length flow depth and shear velocity ratio were varied in the experiments and found to significantly influence the volume of the scour hole for overtopping flows the ratio of the flow depth to the spur dike height was found to be an important control on the geometry of the resulting scour hole at higher flow depth to spur dike height ratios the location of the maximum depth of scour changed from the upstream point of the dike toward the channel bank and caused a secondary scour zone to form downstream of the spur dike a preliminary technique is proposed to predict the volume of scour for spur dikes perpendicular to the bank

a grain conductivity approach to shaly sandstones the effects of clay conduction on the electrical behavior of shaly sandstones at low frequencies are analyzed by considering self similar mixtures of conductive grains as representative of these porous rocks an essential step in this model is the representation of the surface conductivities of the clay platelets by an equivalent volume conductivity based on their pattern of occurrence the clays are treated either as a continuous coating over the sand grains or as individual detrital grains mixed with a nonconductive mineral matrix in the first case the solids are modeled as layered conductive particles taken as spheres to a first approximation in the second case we generalize from the results of a three component self similar mixture of spherical particles for linear approximations the models are described by expressions quite similar to the frequently used waxman smits and dual water equations but dependent upon the clay type concentration and its distribution in the rock the models are written in terms of geometric parameters readily available from well log measurements the derived analytical expressions are successfully applied to describe a set of available experimental core and geophysical log data the results clearly demonstrate the applicability of the equations to well log interpretation as a practical procedure for computing formation factors and shaliness of argillaceous sandstones

north american continental margin records of the paleocene eocene thermal maximum implications for global carbon and hydrological cycling the impacts of the paleocene eocene thermal maximum petm 55 ma one of the most rapid and extreme warming events in earth history are well characterized in open marine and terrestrial environments but are less so on continental margins a major carbon sink here we present stable isotope carbonate content organic matter content and c n ratio records through the petm from new outcrop sections in california and from cores previously drilled on the new jersey margin foraminifer 18o data suggest that midlatitude shelves warmed by a similar magnitude as the open ocean 5 c 8 c while the carbon isotope excursion cie recorded both in carbonate and organic matter 13c records is slightly larger 3 3 4 5 than documented in open ocean records sediment accumulation rates increase dramatically during the cie in marked contrast to the open ocean sites in parallel mass accumulation rates of both organic and inorganic carbon also increased by an order of magnitude the estimated total mass of accumulated carbon in excess of pre cie rates suggests that continental margins at least along north america became carbon sinks during the cie mainly because of weathering feedbacks and rising sea level this result is significant because it implies that the negative feedback role of carbon burial on continental margins was greater than previously recognized

new 3 d flow interpolation method on moving adcp data 1 a simple but accurate interpolation procedure for obtaining the three dimensional distribution of three component velocity data from moving acoustic doppler current profiler adcp observation data is proposed for understanding actual flow structure within a river with complex bathymetry the three dimensional mean velocity field provides a basic picture of the flow for obtaining the three dimensional distribution of three component velocity data in this work anisotropic gridding was introduced in order to remove the random component of measured velocity data caused by the turbulence of the flow and measurement error a continuity correction based on the pressure equation was used to reduce both random and systematic errors the accuracy of the developed method was evaluated using three dimensional flow simulation data from a detached eddy simulation des by using the procedure developed the complex flow structure surrounding the spur dikes section in the uji river was successfully visualized and explored the proposed method shows superiorities in both accuracy and consistency for the interpolated velocity field as compared to the kriging and inverse distance weighted idw methods

electrical properties of partially saturated sandstones novel computational approach with hydrogeophysical applications 1 electric and electromagnetic geophysical tools are suitable methods for investigating moisture content transport and storage properties of the subsoil with noninvasive surveys interpretation of field data is still based on empirical or semiempirical equations which must be calibrated with complex time consuming laboratory measurements in this paper we develop pore scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters grain size distribution and porosity we compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions we compare the simulated results with experimental data from sherwood sandstone uk and discuss the effect of these assumptions on the effective conductivity simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data we also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements

direct numerical simulation of bedload transport using a local dynamic boundary condition temporally and spatially averaged models of bedload transport are inadequate to describe the highly variable nature of particle motion at low transport stages the primary sources of this variability are the resisting forces to downstream motion resulting from the geometrical relation pocket friction angle of a bed grain to the grains that it rests upon variability of the near bed turbulent velocity field and the local modification of this velocity field by upstream protruding grains a model of bedload transport is presented that captures these sources of variability by directly integrating the equations of motion of each particle of a simulated mixed grain size sediment bed experimental data from the velocity field downstream and below the tops of upstream protruding grains are presented from these data an empirical relation for the velocity modification resulting from upstream grains is provided to the bedload model the temporal variability of near bed turbulence is provided by a measured near bed time series of velocity over a gravel bed the distribution of pocket friction angles results as a consequence of directly calculating the initiation and cessation of motion of each particle as a result of the combination of fluid forcing and interaction with other particles calculations of bedload flux in a uniform boundary and simulated pocket friction angles agree favourably with previous studies

an effective medium algorithm for calculating water saturations at any salinity or frequency an algorithmic approach is used to mix the conductivities and geometric factors of the disperse components the rock and hydrocarbon particles with the host conductivity formation water the theoretical basis for the algorithm is the hanai bruggeman hb equation which itself incorporates only one disperse component the new approach the incremental model accommodates geometric factors such as sand and shale porosity exponents saturation exponent and also accommodates the associated grain conductivities its advantage over previous methods is that it works at any water salinity or tool frequency while allowing saturation and porosity exponents to have values other than 1 5 the algorithm is general and is written to accommodate simultaneous mixing of up to three disperse components and the formation water but it can be extended to accommodate any number of disperse components in its application to shaley sands hydrocarbon and sand elements are set to zero conductivity at low frequency but they can be nonzero for calculating saturations at higher frequencies the reason for this is that hydrocarbon and sand conductivities are real and very close to zero at low frequencies but at high frequencies the dielectric constants become significant making the complex conductivities nonzero the incremental model compared well with the waxman smits model on multiple water conductivity saturation data from two published experimental data sets the model is adaptable to other rock conductivity problems such as vuggy porosity vuggy water saturation and clay coated sand grains the potential exists for the algorithm to be part of a comprehensive computer program for calculating rock conductivities and saturations using many different combinations of rock fabrics and compositions

analysis of the time averaged properties of sediment motion in a local scour process 1 we examined the kinematics of sediment particles in the proximity of a vertical plate attached to the side wall of a pressurized duct the laboratory phenomenon investigated was archetypal of local scour near bridge abutments in covered rivers we conducted a clear water scour experiment where we measured the temporal evolution of the local erosion depth the latter was found to follow a logarithmic trend the concentration and velocity of the moving particles were measured on the basis of digital movies taken at various evolution stages of the process the spatial pattern of the sediment motion showed that the action of the principal vortex system becomes progressively more evident with the general lowering of the sediment transport intensity detected as the scour hole increases in time furthermore the phenomenology of local sediment transport was analyzed key findings of the research include 1 the time averaged values of the sediment transport rate are linked with those of concentration and velocity through relationships which are almost invariant regardless of the experimental time and of the location within the scour hole 2 intermittency and irregularity of the sediment fluxes increase as their mean intensity decreases 3 the relative weight of the temporal fluctuations of concentration and velocity in the time mean sediment transport activity is significant throughout the entire process potential implications of the present results for the modeling of local scour processes in pressurized flow conditions are discussed the considerations made are likely to have analogous applicability to local scour with a free surface since the large scale evolutions of the erosion depth in the two conditions may not be greatly different given the qualitative analogy of the present findings with earlier ones obtained for one dimensional bed load it is suggested that similar considerations may hold also for the small scale modeling of a wider class of sediment transport processes

three dimensional numerical simulation and analysis of flows around a submerged weir in a channel bendway to improve navigation conditions for barges passing through river channels many submerged weirs sws have been installed along the bendways of many waterways by the u s army corps of engineers this paper presents results from three dimensional numerical simulations that were conducted to study the helical secondary current hsc and the near field flow distribution around one sw the simulated flow fields around a sw in a scale physical model were validated using experimental data the three dimensional flow fields around a sw the influence of the sw on general hsc and the implication of effectiveness of submerged weirs to realign the flow field and improve navigability in bendways were analyzed the numerical simulations indicated that the sw significantly altered the general hsc its presence induced a skewed pressure difference cross its top and a triangular shaped recirculation to the downstream side the over top flow tends to realign toward the inner bank and therefore improves conditions for navigation

what drove sea level fluctuations during the mid cretaceous greenhouse climate the major states in which earth s climate operates i e icehouse greenhouse and hothouse are epochs of tens of millions of years these states set long term boundary conditions that need to be considered for climate and sea level interpretations this paper summarizes the conceptual models for hydrological cycling derived from the characteristics of these three climate states while glacio eustatic forcing of sea level changes under icehouse climate conditions is fairly well understood the drivers of eustatic sea level fluctuations under greenhouse conditions remain enigmatic this lack of understanding may be related to incoherencies in the current ideas about the impact of accelerated hydrological cycling on sea level under greenhouse climate conditions as an example for a greenhouse climate we review evidences that link proxies for climate and sea level for the intensely studied but controversially discussed mid cretaceous sea level history based on sequence stratigraphy and a recently published high precision timescale we demonstrate that the late middle turonian pewsey 13c isotope maximum represents a major transgression not a regression as previously stated which conflicts with the interpretation of a co occurring 18o maximum to reflect a short glacial episode this contradiction can be solved by the concept presented here that dominance of aquifer eustasy characterized sea level forcing during the turonian greenhouse climate despite a possible though contentious sporadic presence of minor ice sheets the effects of temperature and ice volume both lead to a pronounced 18ocarb maximum during glacio eustatic regressions in contrast the opposing effects of temperature and groundwater volume on oxygen isotope fractionation lead to a 18ocarb maximum during aquifer eustatic transgressions we suggest that throughout earth history both aquifer eustatic and glacio eustatic forcing formed a combined sea level response with dominance of aquifer eustasy being typical for the greenhouse climate mode during the icehouse mode aquifer eustasy apparently remains active as a background process but is outpaced by the glacio eustatic effect

comparison of fixed and moving vessel flow measurements with an adp in a large river a comparison of three dimensional flow velocity measurements made with an acoustic doppler profiler adp from fixed and moving vessels at cross sections of the parana river argentina was performed the purpose was to design a rapid and reliable procedure for quantifying the velocity field and related parameters such as bed shear velocity and the identification of secondary circulations in large rivers using an adp the fixed vessel measurements were performed over a period of 10 min at three vertical profiles along two of the sections these data were then compared with the results of ten moving vessel repeat transects made at each of the sections and which intersected the fixed vessel sampling locations using a number of different adp setup configurations from the velocity profiles obtained with both fixed and moving vessel measurements total bed shear velocity values were computed by applying the law of the wall the results indicate there can be significant differences between velocities obtained using the moving vessel method and fixed vessel measurements averaged over 10 min these differences in horizontal velocity can be significantly reduced by averaging five or more moving vessel transects with corresponding shear velocities calculated from five transect averages showing differences ranging between 10 and 15 dependent on the adp configuration location of the at a point vertical velocity profile in relation to large scale bed roughness may also be an influential factor and ideally the bed morphology should be quantified together with the adp derived velocities when using the adp to identify secondary flow cells it was found that although one cross section transect can provide a reasonable overall picture an average of five cross sections is necessary to resolve the finer details of flow the implications for applications that use moving vessel techniques for measurement and analysis of three dimensional flow structures including secondary flows are highlighted

improved flow velocity estimates from moving boat adcp measurements acoustic doppler current profilers adcps are the current standard for flow measurements in large scale open water systems existing techniques to process vessel mounted adcp data assume homogeneous or linearly changing flow between the acoustic beams this assumption is likely to fail but is nevertheless widely applied we introduce a new methodology that abandons the standard assumption of uniform flow in the area between the beams and evaluate the drawbacks of the standard approach the proposed method strongly reduces the extent over which homogeneity is assumed the method is applied to two field sites a mildly curved bend near a junction featuring a typical bend flow and a sharply curved bend that features a more complex sheared flow in both cases differences are found between the proposed method and the conventional method the proposed technique yields different results for secondary flow patterns compared with the conventional method the velocity components estimated with the conventional method can differ over 0 2 m s in regions of strong shear we investigate the number of repeat transects necessary to isolate the mean flow velocity vector from the raw adcp signal discarding the influences of noise positioning and projection errors and turbulence results show that several repeat transects are necessary the minimum number of repeat measurements needed for robust mean velocity estimates is reduced when applying the proposed method

shallow water carbonate responses to the paleocene eocene thermal maximum in the tethyan himalaya southern tibet tectonic and climatic implications this study presents a detailed stratigraphic record of the paleocene eocene thermal maximum petm in the gamba area of the tethyan himalaya a carbonate platform succession originally deposited along the southern margin of the eastern tethys ocean the paleocene eocene boundary interval is marked by a negative carbon isotope excursion at the boundary between members 3 and 4 of the zongpu formation the succession is erosionally truncated at this surface which is overlain by an intraformational carbonate conglomerate and only the upper part of the petm interval is preserved foraminiferal assemblages of shallow benthic zone 4 are present below the conglomerate bed but are replaced by assemblages of shallow benthic zone 6 above the conglomerate depositional facies also change across this surface below the disconformity floatstones and packstones containing nummulitid forams record progressive transgression in an open marine environment whereas restricted or lagoonal inner ramp deposits containing alveolina and orbitolites are typical above the disconformity the prominent negative excursion observed in the 13c of whole rock carbonate 1 0 at zongpu 2 4 at zengbudong and organic matter 24 7 at zengbudong is correlated to the characteristic petm carbon isotope excursion this major negative excursion in shallow marine carbonates may have partly resulted from syndepositional alteration of organic matter the erosional unconformity can be constrained to the lower petm interval between 56 and 55 5 ma and is identifiable throughout the tethyan himalaya this widespread disconformity is attributable to tectonic uplift associated with the southward migration of an orogenic wave originated 3 1 ma earlier in the middle paleocene at the first site of india asia continent continent collision a possible eustatic component of the pre petm sea level fall which resulted in the excavation of incised valleys filled during the subsequent sea level rise when the conglomerate bed was deposited remains to be assessed

evaluation of adcp apparent bed load velocity in a large sand bed river moving versus stationary boat conditions detailed mapping of bathymetry and apparent bed load velocity using a boat mounted acoustic doppler current profiler adcp was carried out along a 388 m section of the lower missouri river near columbia missouri sampling transects moving boat were completed at 5 and 20 m spacing along the study section stationary fixed boat measurements were made by maintaining constant boat position over a target point where the position of the boat did not deviate more than 3 m in any direction for each transect and stationary measurement apparent bed load velocity vb was estimated using adcp bottom tracking data and high precision real time kinematic rtk global positioning system gps the principal objectives of this research are to 1 determine whether boat motion introduces a bias in apparent bed load velocity measurements and 2 evaluate the reliability of adcp bed velocity measurements for a range of sediment transport environments results indicate that both high transport v b 0 6 m s and mo

a new concept in modeling the dielectric response of sandstones defining a wetted rock and bulk water system experimental data for the real part of the dielectric constant k of three sandstone samples are considered as a function of the level of water saturation sw in the frequency range 60 khz to 4 mhz existing theoretical models have previously shown poor agreement with k versus sw data for rock samples undoubtedly due to the complexity involved in adequately accounting for geometrical and electrochemical effects in analyzing the data presented here we find a pronounced increase in k in the low saturation region which in all cases can be attributed to the establishment of geometrical and surface effects associated with the rock water interface when this increase in k is accounted for by defining wetted matrix parameters the data show excellent agreement with existing theoretical models

submarine volcanic morphology of the western galapagos based on em300 bathymetry and mr1 side scan sonar 1 a compilation of high resolution em300 multibeam bathymetric and existing mr1 side scan sonar data was used to investigate the volcanic morphology of the flanks of the western galapagos islands the data portray an assortment of constructional volcanic features on the shallow to deep submarine flanks of fernandina isabela and santiago islands including rift zones and groups of cones that are considered to be the primary elements in constructing the archipelagic apron ten submarine rift zones were mapped ranging in length from 5 to 20 km comparable in length to western canary island rift zones but significantly shorter than hawaiian submarine rift zones a detailed analysis of the northwestern fernandina submarine rift including calculated magnetization from a surface towed magnetic study suggests that the most recent volcanism has focused at the shallow end of the rift small submarine volcanic cones with various morphologies e g pointed cratered and occasionally breached are common in the submarine western galapagos both on rift zones and on the island flanks where no rifts are present at depths greater than 3000 m large lava flow fields in regions of low bathymetric relief have been previously identified as a common seafloor feature in the western galapagos by geist et al 2006 however their source s remained enigmatic the new em300 data show that a number of the deep lava flows originate from small cones along the mid lower portion of the nw submarine rift of fernandina suggesting that the deep flows owe their origin at least in part to submarine rift zone volcanism

3 d flow and scour near a submerged wing dike adcp measurements on the missouri river 1 detailed mapping of bathymetry and three dimensional water velocities using a boat mounted single beam sonar and acoustic doppler current profiler adcp was carried out in the vicinity of two submerged wing dikes located in the lower missouri river near columbia missouri during high spring flows the wing dikes become submerged creating a unique combination of vertical flow separation and overtopping plunging flow conditions causing large scale three dimensional turbulent flow structures to form on three different days and for a range of discharges sampling transects at 5 and 20 m spacing were completed covering the area adjacent to and upstream and downstream from two different wing dikes the objectives of this research are to evaluate whether an adcp can identify and measure large scale flow features such as recirculating flow and vortex shedding that develop in the vicinity of a submerged wing dike and whether or not moving boat single transect data are sufficient for resolving complex three dimensional flow fields results indicate that spatial averaging from multiple nearby single transects may be more representative of an inherently complex temporally and spatially variable three dimensional flow field than repeated single transects results also indicate a correspondence between the location of calculated vortex cores resolved from the interpolated three dimensional flow field and the nearby scour holes providing new insight into the connections between vertically oriented coherent structures and local scour with the unique perspective of flow and morphology in a large river

coherence scales of wave induced suspended sand concentration fluctuations multifreqiiency acoustic backscatter measurements made in the nearshore zone are analyzed to determine the correlation structure of the instantaneous suspended sediment concentration field at horizontal separations of 20 cm large amplitude backscatter fluctuations representing suspended sediment concentrations more than a factor of 10 greater than the mean and with vertical coherence scales many times greater than the logarithmic wave boundary layer thickness are shown to be spatially correlated at horizontal separations less than the wave orbital amplitude over successive wave cycles the time lag between the appearance of fluctuations in different acoustic beams is inversely proportional to the fluid velocity showing that the fluctuations in backscatter amplitude contain real information on fluctuations in suspended sediment concentration advected with the fluid it is found that the instantaneous suspended sediment field in shore normal cross section is punctuated by spatially discrete clouds extending well above the logarithmic wave boundary layer the fluctuations appear to be present even in the absence of small scale ripples it is suggested that the sediment clouds may be due to vortex shedding from megaripples other bed forms of intermediate scale or coherent structures in combined wave current flows

evidence of pore and fracture filling gas hydrates from geophysical logs in consolidated rocks of the muli area qinghai tibetan plateau permafrost china

near transducer errors in adcp measurements experimental findings acoustic doppler current profilers adcps are not able to accurately determine velocity near their transducers and near the bed these limitations have restricted the use of adcps to flow depths that are large enough to allow acquisition of few directly measured velocity data that can be subsequently used to accurately estimate vertical velocity profiles and flow discharge in cross sections while the causes that make adcps unable to collect data in the near bed region are relatively well documented the causes of near transducer errors have not yet been fully understood and are only partly documented we present results from an experimental study aimed at characterizing the systematic errors due to the combined effect of acoustic interference and instrument induced flow disturbance near a janus configured adcp the study comprises 1 concurrent measurements with an adcp and an acoustic doppler velocimeter adv under the adcp 2 measurements of the flow disturbance produced by the adcp in the vertical and horizontal planes and 3 adv measurements along the path of the acoustic beams ensonified by the adcp during a measurement results suggest that adcps bias low the velocity profiles with respect to the undisturbed velocity profiles mostly because of the flow disturbance induced by the adcp with acoustic effects playing a secondary role for the range of flows we studied both undisturbed and disturbed profiles exhibit similar shapes when plotted in dimensionless form with the bulk flow velocity and the adcp diameter d as characteristic scales the differences between the undisturbed and the adcp disturbed profiles extend up to a distance of about 1 5d from the adcp except for the profiles measured at locations where the flow depth is close to d for which the boundary layer induced by the adcp interacts with the one induced by the flume bed

linking the spatial distribution of bed load transport to morphological change during high flow events in a shallow braided river this paper provides novel observations linking the connections between spatially distributed bed load transport pathways hydraulic patterns and morphological change in a shallow gravel bed braided river these observations shed light on the mechanics of braiding processes and illustrate the potential to quantify coupled material fluxes using remotely sensed methods the paper focuses upon a 300 m long segment of the rees river new zealand and utilizes spatially dense observations from a mobile acoustic doppler current profiler adcp to map depth velocity and channel topography through a sequence of high flow events apparent bed load velocity is estimated from the bias in adcp bottom tracking and mapped to indicate bed load transport pathways terrestrial laser scanning tls of exposed bar surfaces is fused with the adcp surveys to generate spatially continuous digital elevation models which quantify morphological change through the sequence of events results map spatially distributed bed load pathways that were likely to link zones of erosion and deposition the coherence between the channel thalweg zone of maximum hydraulic forcing and maximum apparent bed load pathways varied this suggests that in places local sediment supply sources exerted a strong control on the distribution of bed load distinct from hydraulic forcing the principal braiding mechanisms observed were channel choking leading to subsequent bifurcation results show the connection between sediment sources pathways and sinks and their influence on channel morphology and flow path directions the methodology of coupling spatially dense adcp surveys with tls has considerable potential to understand connections between processes and morphological change in dynamic fluvial settings

electromagnetic properties of dry and water saturated basalt rock 1 110 ghz this paper reports on the measured electromagnetic properties of dry and water saturated basalt rock over a frequency range of 1 110 ghz tests were conducted in standard waveguides below 12 ghz and with free space systems above 12 ghz the basalt used in this investigation was found to be nonmagnetic measured relative permittivities for the dry basalt varied from approximately 8 19 0 71 at 1 12 ghz to 6 80 0 49 at 110 ghz the porosity of the basalt was determined to be roughly 10 properties of water saturated basalt were also measured at several frequencies and compared to theoretical predictions based on a simple maxwell garnett mixing theory finally the potential of using microwave tomography on basalt rock was examined based on the resulting properties