double averaging concept for rough bed open channel and overland flows theoretical background the goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum passive substances and suspended sediments the averaging theorems the double averaged in time and in space fluid momentum equation and advection diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough bed flows experimental design and data interpretation are discussed the suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility change in roughness density in space and time and particle settling effects for the case of suspended sediments we show that the form of the double averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling we also show that the suggested methodology offers better definitions for hydraulic characteristics variables and parameters such as flow uniformity flow two dimensionality and bed shear stress

spatially averaged open channel flow over rough bed in this paper it is suggested that the double averaged in temporal and in spatial domains momentum equations should be used as a natural basis for the hydraulics of rough bed open channel flows especially with small relative submergence the relationships for the vertical distribution of the total stress for the simplest case of 2d steady uniform spatially averaged flow over a rough bed with flat free surface are derived these relationships explicitly include the form induced stresses and form drag as components of the total stress using this approach we define three types of rough bed flows 1 flow with high relative submergence 2 flow with small relative submergence and 3 flow over a partially inundated rough bed the relationships for the double averaged velocity distribution and hydraulic resistance for all three flow types are derived and compared with measurements where possible the double averaged turbulent and form induced intensities and stresses for the case of regular spherical segment type roughness show the dominant role of the double averaged turbulence stresses and form drag in momentum transfer in the near bed region

flow adjustment and interior flow associated with a rectangular porous obstruction the flow at the leading edge and in the interior of a rectangular porous obstruction is described through experiments and scaling the porous obstruction consists of an emergent rectangular array of cylinders in shallow flow a configuration that mimics aquatic vegetation the main features of the flow depend upon the non dimensional canopy flow blockage which is a function of the obstruction width and porosity for the ranges of canopy flow blockage tested in this paper the fluid decelerates upstream of the obstruction over a length scale proportional to the array width for high flow blockage the interior adjustment length within the porous obstruction is set by the array width for low flow blockage the array s frontal area per unit volume sets the interior adjustment length downstream of the adjustment regions the interior velocity is governed by a balance between the lateral divergence of the turbulent stress and canopy drag or by a balance between the pressure gradient and canopy drag depending on the lateral penetration into the array of kelvin helmholtz kh vortices which is set by the non dimensional canopy flow blockage for a porous obstruction with two stream parallel edges the kh vortex streets along the two edges are in communication across the width of the array a phenomenon that results in cross array vortex organization which significantly enhances the vortex strength and creates significant lateral transport within the porous obstruction

applying the mixing layer analogy for flow resistance evaluation in gravel bed streams abstract previous studies show that the flow velocity profile is s shaped for low submergence flows in gravel bed streams as a consequence the power or logarithmic flow resistance equations cannot be theoretically deduced for a low submergence flow in this study the mixing layer analogy in an accurate and innovative way is applied to express the flow resistance in gravel bed streams laboratory experiments over 12 uniform gravel bed runs the relative submerged height ranging from 2 6 to 4 6 are used to determine the physical rationality and accuracy of the analogy that statistical flow turbulent properties are closer to typical values in the mixing layer than in the surface layer the key parameters of shear strength ls applied by an incomplete self similarity analysis for the dimensionless groups and difference coefficient cu defined as the ratio of velocity at the reference level to shear velocity deduced by the simplified darcy forchheimer brinkman equation are expressed and tested using experimental data the new approach is further underpinned by using 104 field measured reaches located in 40 different natural streams which adds to the more widely ranged field data with the relative submerged height ranging from 0 9 to 20 the analysis shows that the flow layer subdivisions theoretical approach based on the multivariable mixing layer analogy and optimized katul law characterized by the lowest root mean square error relative error and closest 1 nash sutcliffe index has potential in future research

depth averaged drag coefficient for modeling flow through suspended canopies aquatic suspended canopies are porous obstacles that extend down from the free surface but have a gap between the canopy and bed examples of suspended canopies include those formed by aquaculture structures or floating vegetation the major difference between suspended canopies and the more common submerged canopies which are located on the bottom boundary is the influence of the bottom boundary layer beneath the suspended canopy data from laboratory experiments are presented which explore aspects of the flow through and beneath suspended canopies constructed from rigid cylinders the experiments using both acoustic doppler and two dimensional 2d particle tracking velocimetry give details of the flow structure that may be divided vertically into a bottom boundary layer a canopy shear layer and an internal canopy layer the experimental data show that the penetration of the shear layer into the canopy is limited by the distance between the canopy and bottom boundary layer peaks in velocity spectra indicate an interaction between the bottom boundary and canopy shear layer an analytical model is also developed that can be used to calculate a drag coefficient that includes the effect of both canopy drag and bed friction this drag coefficient is suitable for use in 2d depth averaged hydrodynamic modeling the model also allows the average velocity within and beneath the canopy to be calculated and is used to investigate the effect of canopy density and thickness on both total drag and bottom friction

crystal chemical characterization of tourmalines from the english lake district electron microprobe analyses and mossbauer spectroscopy electron microprobe analyses empa and mossbauer spectra ms have been acquired for natural tourmalines sampled near crummock water and haweswater english lake district in the former the dravite schorl series is prevalent whereas in the latter the dravite species is dominant all tourmaline samples presently studied are chemically disordered the compositional and ms data give an insight into the thermal and fluid evolution experienced by the tourmalinite rocks the tourmalines from crummock water crystallized in a closed low f o 2 environment under the influence of a magmatic fluid the tourmalines from haweswater are of hydrothermal origin and were formed under low variable t and low f o 2 conditions from a fluid of constant composition

study of structural disorder in natural tourmalines by infrared spectroscopy abstract fourier transformation infrared ftir spectroscopy in the range 2000 10000 cm 1 was used to examine tourmalines from metarhyolites near majjur within the gadag schist belt and are compared with those from known compositions from quartz vein from gold mineralised area ftir spectra in this region are comprised of fundamental and combinational vibrational modes of hydroxyl ions delineating their structural environment in these samples three fundamental vibrations observed at 3730 3720 3637 3627 and 3550 3500 cm 1 and combination modes at 4529 4454 4356 and 4238 cm 1 and the electron probe analysis indicate that the tourmalines could be classified in to dravite schrol series however additional shoulder mode observed around 3490 cm 1 in tourmaline from gadag schist belt indicates structural disorder

improved parameterization of seagrass blade dynamics and wave attenuation based on numerical and laboratory experiments seagrass blade dynamics were explored through numerical and laboratory experiments in order to improve parameterization of wave attenuation by submerged aquatic vegetation in the presence of a background current in the numerical model a single blade was modeled as a series of rigid plates attached by torsion springs for the laboratory model strips of low density polyethylene were placed in a recirculating wave flume a new form of the keulegan carpenter number based on the horizontal excursion of the blade tip was found to be an excellent predictor of drag coefficient an algebraic model for predicting wave attenuation was developed based on the following observations during the portion of the wave period when the fluid velocities are highest the blade motion is almost completely arrested and the vast majority of the turbulence production occurs during this time turbulence production when the blade is pronated is accurately predicted by the maximum fluid velocity over the wave period the relative contribution to the total turbulence production over the wave period is determined by the relative strength of the waves and the current therefore using a simple algebraic fit the total depth integrated time averaged turbulence production can be accurately predicted by two flow parameters the maximum fluid velocity over the wave period and a non dimensional number that compares the wave and current velocities by fitting the algebraic model to data from a particular site it can be used to efficiently estimate wave attenuation and drag coefficient in seagrass exposed to waves with a background current

extreme winds and waves in the aftermath of a neoproterozoic glaciation the most severe excursions in the earth s climatic history are thought to be associated with proterozoic glaciations according to the snowball earth hypothesis the marinoan glaciation which ended about 635 million years ago involved global or nearly global ice cover at the termination of this glacial period rapid melting of continental ice sheets must have caused a large rise in sea level here we show that sediments deposited during this sea level rise contain remarkable structures that we interpret as giant wave ripples these structures occur at homologous stratigraphic levels in australia brazil canada namibia and svalbard our hydrodynamic analysis of these structures suggests maximum wave periods of 21 to 30 seconds significantly longer than those typical for today s oceans the reconstructed wave conditions could only have been generated under sustained high wind velocities exceeding 20 metres per second in fetch unlimited ocean basins we propose that these extraordinary wind and wave conditions were characteristic of the climatic transit and provide observational targets for atmospheric circulation models

sediment transport and shear stress partitioning in a vegetated flow vegetation is a common feature in natural coastal and riverine water ways interacting with both the water flow and sediment transport however the physical processes governing these interactions are still poorly understood which makes it difficult to predict sediment transport and morphodynamics in a vegetated environment we performed a simple experiment to study how sediment transport responds to the presence of flexible single blade vegetation and how this response is influenced by the vegetation density we found that the skin friction and sediment transport are reduced in a plant patch and that this effect is larger for denser vegetation we then evaluated several methods to calculate the skin friction in a vegetated flow which is the key to sediment transport prediction among these the inversion of bed load transport formulas and the einstein and banks 1950 methods appeared to produce the most reasonable values of the skin friction finally we suggest using the parameter which is the ratio of the skin friction computed by these methods to the total bed shear stress to make more realistic sediment transport predictions in morphodynamic models

geometrical and mechanical properties of four species of northern european brown macroalgae abstract aquatic vegetation interacts with the flow by posing an obstruction and in return experiences drag and is reconfigured by acting forces it is suggested that plant buoyancy and stiffness affect these bio physical interactions and hence should be considered when including vegetation in physical and numerical hydrodynamic models however data on these parameters is either lacking for many species or existing information is insufficient to model flexible aquatic vegetation correctly previous studies have focused on plant stems but did not take plant foliage into account the present study extends the existing knowledge base by providing data for four northern european brown macroalgae and also provides a comparison between the mechanical properties of stem and blade tissue for these species specimens of alaria esculenta laminaria digitata fucus serratus and fucus vesiculosus were collected from a small tidal inlet in norway other than f serratus the macroalgae were positively buoyant and all stems showed bending moduli in agreement with previous studies with respect to their order of magnitude only l digitata exhibited a significant difference between bending moduli for stems and blades and also between the tip and the base of the blades however there were differences in flexural rigidities product of bending modulus and second moment of cross sectional area of both stems and blades and the tip and the base of blades of all but f serratus this highlights the important influence of cross sectional area and cross sectional shape on stiffness

geometry prediction for wave generated bedforms published data on wave generated bedform geometry from field and laboratory measurements are re evaluated in terms of relative fluid orbit diameter at the bed and a wave period parameter d 8t2 laboratory bedform data shows a strong dependence on these parameters however for very small values of the period parameter typically field data there is evidence that bedform length depends only on sediment grain size the disappearance of sediment bedforms at high fluid velocities apparently occurs through a decrease in bedform height improved methods for the prediction of bedform geometry under waves are provided in graphical form and computer code

laboratory measurement of bottom shear stress on a movable bed a shear plate was developed to obtain direct measurements of bottom shear stress under nonbreaking surface gravity waves on a movable sand bed the experiments were conducted under regular wave conditions in a large wave tank where time histories of bottom shear stress and surface elevation were obtained from a shear plate and wave gauges measurements were made at scales approaching those encountered in the field these data were obtained under steep vortex ripples where form drag dominated over skin friction for all data presented wave friction factors were calculated from measurements and were compared with existing theories as well as with previous laboratory studies values of the wave friction factor obtained using the shear plate exhibited reasonable agreement with existing theory close agreement between values of the wave friction factor obtained from the shear plate and those measured by previous studies demonstrates that use of a shear plate is a reliable additional method for the measurement of bottom shear stress over a movable bed in the laboratory

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

trace elements in tourmalines from massive sulfides deposits and tourmalinites geochemical controls and exploration applications trace element contents of tourmalines from massive sulfide deposits and tourmalinites have been determined in situ by proton microprobe 390 analyses were acquired from 32 polished thin sections concentrations of trace elements in the tourmalines vary widely from 40 to 3 770 ppm mn 4 to 1 800 ppm ni 2 to 1 430 ppm cu 9 to 4 160 ppm zn 3 to 305 ppm ga 6 to 1 345 ppm sr 10 to 745 ppm sn 49 to 510 ppm ba and 3 to 4 115 ppm pb individual grains and growth zones are relatively homogeneous suggesting that these trace elements are contained within the crystal structure of the tourmaline and are not present in inclusions the highest base metal contents are in ore related tourmaline samples from kidd creek ontario broken hill australia and sazare japan tourmaline data from these and many other massive sulfide deposits cluster by sample and display broadly linear trends on zn vs fe plots suggesting chemical control by temperature and hydrothermal and or metamorphic fluid mineral equilibria significant ni occurs only in samples from the kidd creek cu zn pb ag deposit which is associated with a large footwall ultramafic body an overall antithetic relationship between zn and ni probably reflects fluid source controls mn is correlated with fe in tourmalines from barren associations and possibly in some tourmalines associated with sulfide vein deposits sn increases systematically with fe content irrespective of association the highest values are found in schorls from granites other trace elements are generally uncorrelated with major element concentrations e g sr ca base metal proportions in the tourmalines show systematic patterns on ternary cu pb zn diagrams that correlate well with the major commodity metals in the associated massive sulfide deposits for example data for tourmalines from cu zn deposits e g ming mine newfoundland fall mainly on the cu zn join whereas those from pb zn deposits e g broken hill australia plot on the pb zn join no data fall on the cu pb join consistent with the lack of this metal association in massive sulfide deposits the systematic relationship between base metal proportions in the tourmalines and the metallogeny of the host massive sulfide deposits indicates that the analyzed tourmalines retain a strong chemical signature of their original hydrothermal formation in spite of variable metamorphic recrystallization such trace element patterns in massive sulfide tourmalines may be useful in mineral exploration specifically for the evaluation of tourmaline concentrations in rocks soils and stream sediments

large scale 3 d experiments of wave and current interaction with real vegetation part 2 experimental analysis abstract this paper assesses the influence of different flow and vegetation parameters on the wave attenuation provided by two contrasting salt marsh species puccinellia maritima and spartina anglica different water depths and wave parameters height and period are considered for both regular and irregular waves with and without an underlying uniform current coming from different directions the study of the submergence ratio h h v influence shows that wave damping coefficient rapidly decreases as the plant submergence ratio increases the high nonlinearities found in the wave current interaction lead to different wave damping patterns in comparison to wave only conditions a smaller wave damping is found for waves and current acting in the same direction and an increase in the wave damping rate is obtained for waves and current flowing in the opposite direction these wave and current tests allow for the studying of the energy dissipation produced by the vegetation increasing our knowledge about flow and plant interaction in estuarine conditions the biomechanical properties of the two real salt marshes used in the experiments are also evaluated and related to wave damping revealing a higher attenuation for stiffer vegetation both the vegetation density and the biomass strongly influence wave damping higher density and biomass values lead to higher attenuation rates for both species

wind flow and sedimentation in artificial vegetation field and wind tunnel experiments abstract the flow dynamics within and immediately above an artificial plastic vegetation canopy are measured in the field and wind tunnel artificial plants created from wooden dowels and cable zip ties were arranged in a variety of arrays on pegboards where plant cover or lateral cover could be accurately controlled plant covers examined ranged from 12 to 60 wind velocity profiles and the bedforms incipient dunes that developed within and beyond the vegetation in a few hours were measured the results indicate that flow deceleration and drag increases within the canopy as plant density increases in general there is a marked reduction and inflection in velocity at the canopy top and a second major inflection in the velocity profiles occurs immediately below the base of the four arrays equal or 23 density tall vegetation allows flow to sweep under the canopy and local high speed maxima flows may develop leading to minimal sedimentation in those canopies but deposition downwind beyond the canopies short vegetation where the leaves fill the canopy close to the ground display significantly greater drag and rapid rates of sand deposition flow velocities above the canopy increase as plant cover or density increases due to flow compression and acceleration bedform development is strongly correlated with plant cover density or lateral cover and short plants such that shorter length higher bedforms develop in higher density and or shorter plants the relationship between plant cover density or lateral cover and within canopy velocity is non linear and a new tentative flow regime is proposed canopy flow which may occur between wake interference flow and skimming flow this study further confirms that plant density plays a defining role in determining bedform and dune morphology the results also apply to flow in semi arid grasslands

sand ripples under sea waves part 2 finite amplitude development in the present paper the authors formulate a theory to predict the time development of sand ripples characterised by small but finite amplitude under the action of surface gravity waves the theory is based on a weakly nonlinear stability analysis of a flat sandy bottom subject to viscous oscillatory flow the parameters of the problem namely the reynolds number of the flow and the reynolds and froude numbers of sediments are assumed to fall within a neighbourhood of the critical conditions determined in blondeaux 1990 the analysis can predict the actual ripple height wavelength and profile when flow separation is absent i e for the case of rolling grain ripples assuming sleath s 1984 criterion for separation the values of the relevant parameters at which transition from rolling grain ripples to vortex ripples occurs are predicted a comparison between theoretical findings and experimental data supports the validity of the present theory

subelement form drag parameterization in rough bed flows spatial averaging of the reynolds averaged navier stokes equations gives the double averaged navier stokes equations for which boundary drag appears naturally and explicitly in momentum conservation equations increasing use of the double averaged equations e g for relating flows to three dimensional bed roughness for evaluation of profiles of flow stresses and velocities in ecologically significant regions below roughness tops and for modeling purposes requires parameterization of boundary drag at subelement scales based on seven flows over repeated square rib roughness and ten flows over repeated fixed simulated sand waves with measured velocities and bed pressures expressions for form drag coefficient cd f elevation below roughness top relative roughness submergence roughness steepness are obtained for each of the two dimensional roughness types using these equations form drag variation with elevation below roughness tops can be calculated using either the double average of the square

the limited growth of vegetated shear layers 1 in contrast to free shear layers which grow continuously downstream shear layers generated by submerged vegetation grow only to a finite thickness because these shear layers are characterized by coherent vortex structures and rapid vertical mixing their thickness controls exchange between the vegetation and the overlying water experiments conducted in a laboratory flume show that the growth of these obstructed shear layers is arrested once the production of shear layer scale turbulent kinetic energy ske is balanced by dissipation of ske within the canopy this equilibrium condition along with a mixing length closure scheme was used in a one dimensional numerical model to predict the mean velocity profiles of the experimental shear layers the agreement between model and experiment is very good but field application of the model is limited by a lack of description of the drag coefficient in a submerged canopy

waving plants and turbulent eddies new large eddy simulations of flow over a flexible plant canopy by dupont et al j fluid mech 2010 this issue vol 652 pp 5 44 have produced apparently paradoxical results work over the last three decades had suggested that turbulent eddies could lock onto to the waving frequency of uniform cereal canopies their new simulations contradict this view although a resolution may lie in the essentially three dimensional nature of the instability process that generates the dominant eddies above plant canopies

plant patch hydrodynamics in streams mean flow turbulence and drag forces 1 this paper investigates the effects of a finite size vegetation patch on flow turbulence variations in drag forces experienced by individual plants within the patch and flow drag interrelations the experiments were conducted in a 32 m long laboratory flume with a 2 8 m long artificial patch the plants were arranged to form a staggered pattern and three flow scenarios were tested velocities were recorded with an acoustic doppler velocimeter whereas specifically designed devices were used to simultaneously measure the drag forces acting on nine plants within the patch for all studied cases the results show zones of increased turbulent energy close to the leading edge and along the patch canopy top where turbulence shear production is enhanced zones of negative reynolds stresses u w are found inside the patch and they reflect the influence of plant morphology which affects the shape of the longitudinal velocity profile and associated turbulent fluxes modifications to the power spectral densities of velocity by the plants indicate the emergence of two plant induced mechanisms of energy production which are most likely related to the wake turbulence and shear layer turbulence drag fluctuations appear to be correlated with the velocity field with this correlation being especially profound at the highest studied flow rate the data suggest that the highlighted correlation stems from flow plant interactions at the top of the vegetation canopy likely due to the presence of large three dimensional coherent structures

cohesionless fine sediment bed forms in shallow flows bed form data from laboratory experiments using cohesionless fine silica solids in shallow water flows are analyzed to find dimensionless relationships for geometry and friction factor with increasing flow discharge over a stationary flat bed the bed form sequence is primary ripples barchanoid and linguoid ripples secondary ripples ripples on dunes for silt grades only and a moving flat bed the primaries develop from the incipient transport stress otherwise called the primary threshold by extrapolating dimensionless bedform length and height data to this threshold it is shown that the geometry is proportional to the depth of the viscous sublayer thickness the secondaries develop from a secondary threshold which is an approximate constant stress condition at which incipient suspension also begins the ripples on dune form is associated with a tertiary threshold for which the dimensionless stress ratio iy n iy dc n is about 20 and the moving flat bed form occurs at a transition threshold for which iy n iy dc n appears to be a natural constant at about 15 a single friction factor curve is demonstrated for all these data

hydrodynamics of flow through double layer rigid vegetation vegetation in riparian environment varies in size from grass to shrubs to trees a double layer approach with an array of short and tall acrylic dowels is employed here to simulate such an environment the focus of the present work is to study the response of the flow as it travels through a double layer arrangement for a variety of conditions for this purpose instantaneous measurements of velocity were collected using a one dimensional laser doppler velocimeter at multiple locations to create velocity and turbulence intensity profiles the results indicate that velocity is nearly constant within the short and tall dowel array and increases significantly at the top of the arrays the velocity profile behind a dowel is characterized by multiple inflection points and velocity spikes near the bed especially for locations directly behind a tall dowel where a bulge in the velocity at the top of the short dowel array is present followed by a significant drop in velocity the region immediately behind a tall dowel where the highest turbulence intensities are found is very unstable especially at the dowel boundaries where significant mass and momentum exchange occurs the better known case of submerged single layer flow is included for comparison

flow characteristics in the interfacial shear layer between a fluid and a granular bed 1 the shear layer that forms at the interface between a fluid in motion and a granular bed is shown to be tractable in the most general case including the occurrence of flow separation from the grains which appears to be the most common situation the phenomenon of separation produces fundamental leading order effects especially in relation to the mean flow between grains and also in the generation of a disturbed ensemble averaged flow which previous formulations were unable to detect in this respect we argue that some known results pertaining to the jet regime recently introduced by the authors can be directly extended outside that regime in particular the mean force that bed grains exert on the fluid which appears to be generally applicable provided only that separation occurs furthermore the maximum pressure disturbances as well as the velocity disturbances at the outer edge of the shear layer can be evaluated just as in the jet regime this extension permits very general estimates of the main forces and the thickness of the shear layer above and beneath the bed surface in particular the forces on the grains are shown to exhibit a spectrum we present very simple expressions for the mean force as well as for the maximum force which are compared with existing observations on sediment motion initiation under oscillatory flow showing an excellent agreement

flow structure in canopy models dominated by progressive waves summary laboratory experiments were carried out to study the flow structure both inside and above different canopy models which were dominated by progressive waves a set of experimental conditions were considered in a laboratory flume three vegetation models submerged rigid submerged flexible and emergent rigid three plant densities 128 640 and 1280 stems m 2 and three wave frequencies f 0 8 1 and 1 4 hz the progressive waves followed the second order stokes theory in the intermediate depth range the observations revealed that submerged and emergent rigid vegetation models modified the wave induced velocities i e both mean current and wave velocity the submerged rigid vegetation model for plant densities higher than 640 plants m 2 and wave frequency higher than 1 hz acted akin to a false floor confining the mean current to above the plant bed a penetration depth around 2 cm below the top of submerged rigid vegetation was found for the other runs the vertical profile of mean current did not present changes with respect to runs without plants the emergent rigid vegetation model reversed the direction of the induced mean current with the highest velocity corresponding to the highest plant density in contrast the submerged flexible vegetation model had a weak effect on the mean current with the vertical velocity profile similar to that found in experiments without vegetation the wave velocities inside the vegetation for the densest submerged rigid vegetation were found to be reduced by 20 when compared to the wave velocities without vegetation while in emergent rigid vegetation this reduction was of 45

analytical solutions of velocity profile in flow through submerged vegetation with variable frontal width abstract flow within vegetation is one of the main driving forces for material exchange and energy transfer in wetland systems impacted by vegetation the flow velocity profile illustrates distortions to the classic logarithmic velocity profile and has attracted much attention among researchers different from analytical models of velocity distribution in literature which is mainly suitable for vegetation with uniform frontal width this paper establishes new analytical solutions of the velocity profile for vegetation such as shrub and sedge that have a variable frontal width in the vertical direction a new shape function is proposed under these conditions in which the frontal width exhibits a gradual increase in the vertical direction from bottom up in the vegetation along with different closure models for eddy viscosity in the vegetation layer and surface layer analytical solutions of the velocity profile are derived from the momentum equations good agreement between calculated and measured data shows our analytical model is effective in predicting velocity profiles

modeling flow in coral communities with and without waves a synthesis of porous media and canopy flow approaches both canopy flow and porous media theories have been developed independent of one another to predict flow through submerged porous structures these approaches are very similar albeit with some key differences in how canopy resistance forces are parameterized canopy models provide a means of parameterizing the shear stresses that occur at the top of the canopy whereas porous media models can often provide a simpler and more tractable way of parameterizing turbulent form drag based on simple morphological metrics and empirical relationships already in the hydrology literature we developed a set of equations combining aspects of both models and applied this hybridized model to predict the flow structure within an experimental canopy formed by the branching coral porites compressa using model parameter values obtained from the literature results from the model predictions agreed well with direct measurements of flow speed and flow forces derived from particle image velocimetry under conditions of both unidirectional and wave driven oscillatory flow

laboratory measurements of flow and turbulence in discontinuous distributions of ligulate seagrass turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies the reliability of velocity measurements obtained using an acoustic doppler velocimeter within the canopy was shown using specifically designed experiments in relatively fast flow mean velocity 5 5 cm s 1 the mean flow profile was logarithmic above the canopy had an inflection point near its top and uniformly low values within it within the gap a recirculation cell formed reynolds stress maxima were approximately coincident with the mean flow inflection point quadrant analysis revealed an ejection dominated upper layer a sweep dominated region around the top of the canopy and within the gap and no dominant quadrant within the canopy in slower flow mean velocity 1 7 cm s 1 the plants were quasiemergent and the flow fields more uniform sweeps similarly dominated the region near the top of the canopy and within the gap in both flows autocorrelation of longitudinal velocity fluctuations showed a lagrangian time scale maximum at the downstream end of the gap

single parameter model of vegetated aquatic flows coupled flows through and over permeable layers occur in a variety of natural phenomena including turbulent flows over submerged vegetation in this work we employ a two domain approach to model flow through and over submerged canopies the model amenable of a closed form solution couples the log law and the darcy brinkman equation and is characterized by a novel representation of the drag force which does not rely on a parametrization through an unknown drag coefficient this approach limits to one i e the obstruction permeability the number of free parameters analytical expressions for the average velocity profile through and above the canopies volumetric flow rate penetration length and canopy shear layer parameter are obtained in terms of the canopy layer effective permeability the model suggests that appropriately rescaled velocities in the canopy and surface layers follow two different scaling laws the analytical predictions match with the experimental data collected by ghisalberti and nepf 2004 and nepf et al 2007

a vortex based model of velocity and shear stress in a partially vegetated shallow channel 1 this paper presents a method for predicting the distributions of velocity and shear stress in shallow channels with a boundary of emergent vegetation experiments in a laboratory channel with model vegetation show that the velocity profile exhibits a distinct two layer structure consisting of a rapidly varying shear layer across the vegetation interface and a more gradual boundary layer in the main channel in addition coherent vortices are observed which span both layers and are the dominant contributors to lateral momentum fluxes from these observations we propose a model for the vortex induced exchange and find expressions for the width of momentum penetration into the vegetation the velocity and shear stress at the vegetation edge and the width of the boundary layer in the main channel these variables along with a momentum balance in the main channel comprise a modeling framework which accurately reproduces the observed velocity and shear stress distributions the predictions for the velocity and shear stress can provide a basis for modeling flood conveyance overbank sediment transport and scalar residence time in the vegetated layer

spectra of ocean bottom seismic noise in the 0 01 10 hz range summary in 1988 short term duration 18 hr each ocean bottom seismic noise recordings were made in the frequency range of 0 01 10 hz at the depth of 900 1400 m in the atlantic ocean there were two study areas in the canary upwelling and on the reikjanes ridge the spectral curves obtained for these two areas show the existence of a minimum in the frequency range of 0 05 0 10hz i e in the period range of 10 20 s together with a maximum reflecting the domain of storm microseisms 0 1 1 hz we recommend the use of this minimum for regular recording of strong remote earthquakes and especially for surface wave dispersion studies to obtain velocity sections of the oceanic crust and upper mantle

significance of tourmaline rich rocks in the north range group of the cuyuna iron range east central minnesota concentrations of tourmaline in early proterozoic metasedimentary rocks of the cuyuna iron range east central minnesota provide a basis for redefinition of the evolutionary history of the area manganiferous iron ore forms beds within the early proterozoic trommald formation between thick bedded granular iron formation having shallow water alepositional attributes and thin bedded nongranular iron formation having deeper water attributes these manganese rich units were previously assumed to be sedimentary in origin however a reevaluation of drill core and mine samples from the cuyuna north range has identified strata bound tourmaline and tourmalinite which has led to a rethinking of genetic models for the geology of the north range we interpret the tourmaline rich rocks of the area to be a product of submarine hydrothermal solutions flowing along and beneath the sediment seawater interface this model for the depositional environment of the tourmaline is supported by previously reported mineral assemblages within the trommald formation that comprise aegirine barium feldspar manganese silicates carbonates and oxides and sr rich barite veins in many places tourmaline rich metasedimentary rocks and tourmalinites are associated locally with strata bound sulfide deposits at those localities the tourmaline rich strata are thought to be lateral equivalents of exhalative sulfide zones or genetically related subsea floor replacements on the basis of the occurrence of the tourmaline rich rocks and tourmalinites and on the associated minerals we suggest that there is a previously unrecognized potential for sediment hosted sulfide deposits in the cuyuna north range

highest natural bed forms 1 fluid flow interacts with sedimentary beds forming waves of different kinds which are of considerable practical importance since they influence significantly the near bed flow both over and below the bed sediment transport and wave height attenuation we focus here on steep bed forms capable of producing flow separation in this case the large scale vorticity generated in the phenomenon of separation rules the process of friction which appears to be practically unaffected by sediment motion under the crests of the bed forms the mean shear force due to friction is balanced by the force that bed forms exert on the flow via pressure which can be calculated from the work of gimenez curto and corniero 2002 bed forms grow until they have a height such that friction at their troughs is negligible thus ceasing the motion of fluid and sediment this condition leads to a very simple expression for the limiting steepness which compares favorably with existing observations on bed form geometry under steady open channel flow as well as under oscillatory flow

sand ripples under sea waves part 1 ripple formation in the present paper we formulate a predictive theory of the formation of sand ripples under sea waves the theory is based on a linear stability analysis of a flat sandy bottom subject to a viscous oscillatory flow the conditions for decay or amplification of a bottom perturbation are determined along with the wavelength of the most unstable component as a function of the reynolds number of the flow and of the froude and reynolds numbers of the sediments a comparison between theoretical findings and experimental data supports the validity of the present theory an analytical solution for viscous oscillatory flow over a small amplitude wavy bottom is determined for arbitrary values of the ratio r between the amplitude of fluid displacement and the wavelength of bottom waviness previous works by lyne 1971 and sleath 1976 who considered small or large values of r are thus extended

observations of ambient noise and signal coherency on the island of hawaii for teleseismic studies abstract ambient seismic noise conditions at several sites on the island of hawaii have been studied by analyzing noise power spectral density psd and signal to noise ratio snr of teleseisms broadband digital waveform data used in this study were collected during project aloha direct comparison of noise psd and snr of teleseisms simultaneously recorded at stations on hawaii and at station kip on oahu indicates that the stations on hawaii are quieter than station kip on oahu in the frequency band of 0 1 to 1 hz suggesting that the island of hawaii can provide better noise conditions than station kip our interpretation of this observation is that the area and volume of hawaii are much larger than those of oahu and distances to the coast for the stations on hawaii are larger than that for station kip on oahu stronger attenuation and relatively low coherency for teleseismic signals on hawaii in frequencies of 0 4 to 1 2 hz are attributed to the presence of partial melt in the upper mantle teleseismic signal coherency is very low at frequencies above 2 hz for a small array with a radius about 2 km the relatively high coherency of the tangential component is strongly indicative of severe scattering effects caused by the heterogeneity in structure of the active volcanic area

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

vegetated mixing layer around a finite size patch of submerged plants 1 theory and field experiments 1 dynamics of a vegetated mixing layer around a patch of submerged plants was examined theoretically and experimentally in a lowland river theoretical analysis explored analogy with hydrodynamic mixing layers and introduced equations that describe expansion of the layers and alterations in mean flow field experiments provided empirical data for validation of the theory and examination of the effects of population density on the mixing layer dynamics detailed measurements assessed the structure of turbulent flow plant morphology biomechanical properties bending and streamlining due to interaction with the flow the theory was compared with the field experiments and an agreement was concluded it was found that near the upstream edge of the patch the vegetated mixing layer expands similar to the canonical mixing layers although its statistics scale on the velocity differential characteristic for the stabilized part downstream mean momentum flux reduces in magnitude and reverses in direction while turbulence became dominant this was observed to stabilize the velocity differential and increase the mean velocity of the layer that result in its limited growth described by a logarithmic function the population density of vegetation was found to control the flow in dense vegetation the analogy with mixing layers resembled best while in sparse vegetation the flow behaved similar to the boundary layers this theory can be used for quantitative assessment of seasonal effects in natural vegetated rivers because the population density of vegetation varies during the vegetation season the companion paper focuses on the structural properties of turbulence in the vegetated shear layers

influence of permeable beds on hydraulically macro rough flow in this study macro rough flows over beds with different permeability values are simulated using the large eddy simulation and the results are analysed by applying the double averaging da methodology spheres of different sizes and arrangements were used to form the beds which are deemed to be permeable granular beds the influence of bed permeability on the turbulence dynamics and structure is investigated it was observed that the scales of the spanwise vortical structures over more permeable beds are larger than those over less permeable beds this is attributed to large scale spanwise alternate strips of varying reynolds shear stress rss emerging from the surface of macro rough elements for the permeable beds the da stress balance suggests that the time averaged spanwise vortical structure leads to a damping in da rss and an unusual peak of the form induced stress in the main flow in the streamwise direction both large turbulent structures that originate from the kelvin helmholtz type instability and small turbulent structures that are associated with the turbulent transport across the gaps of the roughness elements are more prevalent over highly permeable beds near the bed the relative magnitude of turbulent events shows a transition from a ejections dominating to sweeps dominating zone with vertical distance further several hydrodynamic characteristics normalized by inner scales kinematic viscosity to shear velocity ratio show a greater dependency on permeability reynolds number than those normalized by sediment size the study provides an insight into the mechanism of mass transfer near the fluid particle interface which is vital to benthic and aquatic ecology

turbulence structure in open channel flow with partially covered artificial emergent vegetation abstract an innovative approach was recently proposed to increase water depth and improve navigation in rivers by increasing overall roughness through an adaptive placement of artificial vegetation in this approach a section of the river width is covered with artificial vegetation constructed from an array of dampers that can be added or removed while maintaining sufficient width for navigational purposes the goal of the work here is to explore the mean flow and turbulent momentum transport properties of such flow in a controlled flume setting where the flow rate is steady the vegetation placement is uniform and the froude number is maintained at sub critical conditions the focus is on vegetation induced roughness alterations to the bulk flow statistics as well as the structure of turbulence impacted by the presence of such artificially engineered vegetation the canopy flow experimentally explored here differs from the well studied planar uniform emergent canopy flow because the interface between the vegetation and non vegetation areas occurs along a lateral direction instead of the vertical direction the flume experiments were conducted by partially covering the channel width with emergent artificial vegetation that is flexible and can interact with the flow the quantities studied are the equilibration distance of the flow statistics from the leading vegetation edge as such distance is essential to any engineering design moreover the mean flow and turbulence regimes at several longitudinal sections were analyzed using spectral analysis and conditional sampling to identify the main vortical structures and their contribution to momentum transport spectral analysis demonstrated that the sizes of the dominant vortices can be classified into stem scale small scale and shear scale larger scale vortices as conventional in canonical canopy flows the shear layer formed in the planar direction and its associated coherent vortices are spawned near the edge of the vegetated area in a manner analogous to a plane mixing layer quadrant analysis showed two contributions to the overall shear stress and lateral momentum exchange between the vegetated and non vegetated zone namely ejections and sweeps the measured ejection sweep contributions are short lived but significant to the overall turbulent momentum transport consistent with other canopy flow studies approximately 80 of the turbulent stress contributions at the interface occur within 30 of the time because the flume experiments were conducted at sufficiently high reynolds number and sufficiently low froude number the scalability of the experimental findings here to much larger settings encountered in engineering practice are briefly discussed

observations of amplified roughness from crystal accretion in the sub ice ocean boundary layer ice crystal accretion on the underside of sea ice and ice shelves a signature of pressure induced supercooling has the potential to alter the energy balance in the ocean boundary layer through enhanced hydrodynamic roughness here we present estimates of crystal driven ocean boundary layer roughness in supercooled water beneath sea ice adjacent to the mcmurdo ross ice shelf data were collected from four sites in mcmurdo sound antarctica between 2007 and 2015 and represent a range of ice shelf affected conditions the results show that drag of the rough ice underside in the presence of platelets is 6 30 times larger than typical levels homogeneously applied in ice ocean interaction models the crystal enhanced drag promotes increased entrainment into the boundary layer from the upper ocean which has the potential to affect ice shelf evolution and sea ice growth through enhanced turbulent exchange of heat and momentum

velocity distribution in the roughness layer of rough bed flows several models for the vertical distribution of the double averaged in time and in the plane parallel to the mean bed longitudinal velocity in the flow region between roughness troughs and roughness tops are suggested we found that the same model for velocity distribution may be applicable to a range of flow conditions and roughness types which share some common features the suggested models for velocity distribution in the near bed region are 1 constant velocity 2 exponential velocity distribution and 3 linear velocity distribution the measured velocity distributions may be approximated by a single model or by a combination of models depending on roughness geometry and flow conditions the validity of these models for velocity distribution is supported by laboratory data

first noise and teleseismic recordings on a new ocean bottom seismometer capsule abstract an ocean bottom seismometer capsule designed specifically for the long term monitoring of teleseisms has been designed and tested an efficient triggering algorithm consisting of multiple high pass filters effectively discriminates between locally generated earthquakes and noise and teleseisms during a 1 month deep ocean deployment west of the santa barbara channel a magnitude 5 9 earthquake at a distance of 76 was recorded in addition to a number of regional events in the 300 to 450 km range noise levels were monitored by automatically recording data at intervals vertical noise levels were approximately 20 times greater than those recorded at quiet land sites and horizontal noise levels were about 5 times greater than that the instrument consists of a microprocessor controlled data logging system in three parallel pressure tubes joined by a common baseplate wires between the three tubes are contained within the baseplate there are no external connectors which are exposed to sea water allowing the deployment time to extend to 1 yr data are recorded on two braemar cassette recorders with a capacity of 15 mbits each for a continuous recording time of approximately 43 hr this is adequate for the expected data acquisition rate given the robustness of the triggering algorithm the sensors are mark products l4 c 1 hz seismometers with useful extended low frequency response to about 30 sec periods for earthquake signals the three components are leveled with a mechanical gimbal arrangement the instrument has been successfully deployed 3 times in the santa barbara channel and deep ocean and should prove extremely useful for extending teleseismic studies into the ocean

hydrodynamics of model posidonia oceanica patches in shallow water the hydrodynamics of simulated patches of the mediterranean seagrass posidonia oceanica were studied in laboratory flume experiments in which the height of the pronated canopy was always greater than half the total water depth the effects of variations in speed from 0 08 m s 21 to 0 24 m s 21 and patch configuration on the hydrodynamics were investigated significant speeds penetrated the patches to approximately half their height reducing speed did not change the flow patterns observed except to weaken and blur them flow encountering a single patch formed a turbulent wake at the height of the top of the canopy within this wake the vertical shear stress decreased monotonically downstream but the reynolds stress increased initially and then decayed when a second patch was positioned within the region where reynolds stress increased referred to as the 06 patch the wake center penetrated it causing average turbulent velocities with horizontal components 3 3 times higher and vertical components 4 2 times higher than in the upstream patch when this patch was positioned where the reynolds stress decayed referred to as the 14 patch the wake center rose above it nevertheless the turbulence in the 14 patch had horizontal components 12 higher and vertical components 22 higher on average than in the 06 patch because its upstream end was closer to the reynolds stress maximum thus the ratio of the patch separation to the length of wake in which the reynolds stress increased was identified as central to quantifying the turbulence within the downstream patch the increased turbulence is likely to be important in determining sedimentary and ecological patch characteristics by increasing retention of particulates in suspension and thus reducing depositional rates of for example larvae nutrients and dead organic matter

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

the influence of macrophyte growth typical of eutrophic conditions on river flow velocities and turbulence production the influence of emergent and submerged macrophytes on flow velocity and turbulence production is demonstrated in a 140 m reach of the river blackwater in farnborough hampshire uk macrophyte growth occurs in patches and is dominated by sparganium erectum and sparganium emersum in may 2001 patches of s erectum were already established and occupied 18 of the channel area the flow adjusted to these predominantly lateral patches by being channelled through a narrower cross section the measured velocity profiles showed a logarithmic form with deviations attributable to topographic control the channel bed was the main source of turbulence in september 2001 in stream macrophytes occupied 27 of the channel and overhanging bank vegetation affected 32 of the area overall flow resistance described by manning s n showed a threefold increase that could be attributed to the growth of s emersum in the middle of the channel velocity profiles showed different characteristic forms depending on their position relative to plant stems and leaves the overall velocity field had a three dimensional structure turbulence intensities were generally higher and turbulence profiles tended to mirror the velocity profiles evidence for the generation of coherent eddies was provided by ratios of the root mean square velocities spectral analysis identified deviations from the kolmogorov 5 3 power law and provided statistical evidence for a spectral short cut indicative of additional turbulence production this was most marked for the submerged vegetation and in some instances the overhanging bank vegetation the long strap like leaves of s emersum being aligned approximately parallel to the flow and the highly variable velocity field created by the patch arrangement of macrophytes suggest that the dominant mechanism for turbulence production is vortex shedding along shear zones wake production around individual stems of s emersum close to the bed may also be important locally

flow and deposition in and around a finite patch of vegetation this laboratory study describes the flow and deposition observed in and around a finite patch of vegetation located at the wall of a channel two patch densities are considered with 2 and 10 solid volume fraction the velocity field measured in and around the patch by acoustic doppler velocimetry revealed three distinct zones first there is a diverging flow region at the leading edge of the patch where the flow in line with the patch decelerates and the bulk of the flow is diverted toward the open channel second there is a fully developed region within the vegetation where the velocity is uniform across the patch width and along the length of the patch third a shear layer forms at the interface between the patch and adjacent open channel the pattern of deposition in and around the vegetation was characterized by releasing 12 micron spherical glass particles and recording net deposition on a set of glass slides in the diverging region net deposition increases in the stream wise direction as the local velocity decreases in the fully developed region of the patch deposition decreases with longitudinal position as the concentration in the water column is depleted the deposition pattern is nearly uniform across the patch width consistent with the velocity field and suggesting that turbulent diffusive flux across the lateral edge of the patch is not a significant source of particles to the patch under the conditions studied here

shear induced instabilities of flows through submerged vegetation we consider the instabilities of flows through a submerged canopy and show how the full governing equations of the fluid structure interactions can be reduced to a compact framework that captures many key features of vegetative flow first by modelling the canopy as a collection of homogeneous elastic beams we predict the steady configuration of the plants in response to a unidirectional flow this treatment couples the beam equations in the canopy to the fluid momentum equations subsequently a linear stability analysis suggests new insights into the development of instabilities at the surface of the vegetative region in particular we show that shear at the top of the canopy is a dominant factor in determining the onset of instabilities known as monami based on numerical and asymptotic analysis of the quadratic eigenvalue problem the system is shown to be stable if the canopy is sufficiently sparse

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

mixing layers and coherent structures in vegetated aquatic flows 1 to date flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow with vegetative drag treated as an extension of bed drag however recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer this paper presents laboratory measurements obtained from a scaled seagrass model that demonstrate the applicability of the mixing layer analogy to aquatic systems specifically all vertical profiles of mean velocity contained an inflection point which makes the flow susceptible to kelvin helmholtz instability this instability leads to the generation of large coherent vortices within the mixing layer observed in the model at frequencies between 0 01 and 0 11 hz which dominate the vertical transport of momentum through the layer the downstream advection of these vortices is shown to cause the progressive coherent waving of aquatic vegetation known as the monami when the monami is present the turbulent vertical transport of momentum is enhanced with turbulent stresses penetrating an additional 30 of the plant height into the canopy

an experimental study of flow through rigid vegetation 1 better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation instead of spatial averaging this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels velocity data was collected with a one dimensional laser doppler velocimeter under emergent and submerged flow conditions the effects of dowel arrangement density and roughness were also examined the results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it however the boundaries are marked by inflection points the strongest vortices and turbulence intensities can be found there especially in the region immediately downstream of a dowel these results support the idea that the flow in the region near the bed and at the top of the dowel array is very unstable leading to the formation of coherent structures and are areas of significant mass and momentum exchange

reply to comment by luis a gimenez curto and miguel a corniero lera on characteristic dimensions of the step pool bed configuration an experimental study

velocity profiles in vegetated open channel flows combined effects of multiple mechanisms abstractvertical profile of longitudinal velocity in vegetated channels reflects complex mechanics of flow vegetation interactions and determines the bulk flow velocity and flow rate most available models of velocity profiles in vegetated channels are based on a single physical concept that underpins theoretical considerations and data interpretation however measured velocity profiles suggest that the use of a single concept is not sufficient to cover all possible scenarios of flow vegetation interactions as a result a number of models in which different concepts are applied to different flow regions have been recently developed within this framework the overall velocity profile is represented with a set of linked segments although such segment based models have improved velocity profile description there is a need for more robust approaches and better analytical formulations this paper proposes a new approach where a vertical velocity profile in vegetated channels is modelled as a linear superp

sand ripples generated by regular oscillatory flow abstract the prediction of ripple geometry is a necessary precursor to the prediction of sand transport under waves for ripple regime conditions the paper begins with a comparison of four existing methods for predicting the geometry of sand ripples generated by oscillatory flow the comparison points to substantial differences between ripple dimensions predicted by the methods especially for field scale conditions ripple geometry experiments carried out in a large oscillatory flow tunnel are then described the experiments involved a range of sand sizes and sinusoidal and asymmetric flows with periods and velocities typical of field conditions comparison of measured and predicted ripple geometries leads to the recommendation that the method of mogridge davies and willis be used to predict ripple geometry for field scale oscillatory flows the nielsen method yields good predictions of ripple length but the rapid fall off in ripple steepness predicted by the nielsen method at high mobility number is not supported by the measurements the lengths and heights of symmetric ripples produced by sinusoidal flows are found to be similar to the lengths and heights of asymmetric ripples produced by equivalent asymmetric flows three dimensional ripples occur with fine sand in long period flows typical of field conditions the dimensions of these ripples cannot be predicted using methods developed for two dimensional ripples previously suggested criteria for predicting the occurrence of three dimensional ripples fail when tested against a wide range of flow and sand conditions the occurrence of three dimensional ripples and the effects of ripple and flow history on ripple geometry require further research

double averaging concept for rough bed open channel and overland flows applications the paper briefly outlines the double averaging methodology for studying environmental rough bed flows it focuses on the applications of this methodology in environmental hydraulics by providing several examples illustrating advantages of this methodology over conventional approaches examples include 1 identification of specific flow layers and flow types 2 vertical distribution of the double averaged velocity between the roughness tops and troughs 3 vertical distribution of momentum fluxes and sinks for typical roughness types due to turbulence mean flow heterogeneity secondary currents form drag and viscous drag 4 estimates of form induced dispersive stresses and evaluation of their structure using quadrant analysis and 5 closure development for mass transfer uptake processes for stream periphyton these examples illustrate the advantages of the double averaging methodology over conventional approaches as well as highlight its potential for studying flows over very rough beds hig

regional sulfate hematite sulfide zoning in the auriferous mariana anticline quadrilatero ferrifero of minas gerais brazil the distribution of mineral deposits characterised as barite deposits hematite rich auriferous deposits and auriferous tourmaline sulfide deposits displays a regional sulfate hematite sulfide zoning along the thrust delineated limbs of the mariana anticline in the south eastern part of the quadrilatero ferrifero of minas gerais brazil cross cut relationships of barite veins and sulfide lodes indicate that sulfidation occurred in a late tectonic context which is here attributed to the collapse of the 0 6 ga brasiliano thrust front reconnaissance s isotopic data from barite and pyrite antonio pereira barite deposit and its adjacent gold deposit respectively and arsenopyrite passagem de mariana gold deposit suggest a new interpretation for the hydrothermal fluid overprint in the mariana anticline the antonio pereira barite has 33s values that are near zero constraining the sulfate source to rocks younger than 2 45 ga the barite 34s values are between 19 6 and 20 8 the passagem arsenopyrite and tourmaline have co ni ratios that define a positive linear trend with the antonio pereira pyrite the latter has homogenous 34s values between 8 8 and 8 9 which are compatible with thermochemical reduction of aqueous sulfate with the s isotopic composition of the antonio pereira barite

infrared and mossbauer study of brazilian tourmalines from different geological environments infrared ir spectra in the oh stretching region and mossbauer spectra ms have been acquired for natural tourmalines from magmatic and hydrothermal deposits in the state of minas gerais brazil in the magmatic environment samples of tourmaline were collected from granitic pegmatites and granitoids in the former the elbaite schorl series is prevalent while in the latter the schorl species is dominant tourmalines from hydrothermal gold deposits are typically intermediate members of the dravite schorl series whereas the uvite and fe bearing uvite species are present in tourmaline samples from a magnesite deposit different behaviors are discussed in terms of local lattice environment geological history fluid rock interaction or magma evolution and degree of crystallinity

characteristics of turbulent unidirectional flow over rough beds double averaging perspective with particular focus on sand dunes and gravel beds 1 we address some unsolved methodological issues in modeling of natural rough bed flows by critically examining existing approaches that parameterize rough bed flows these often utilize loosely defined variables here we suggest that double averaging in time and in a volume occupying a thin slab in a plane parallel to the mean bed provides a rigorous straightforward alternative that can aid in the parameterization process we further present two examples two dimensional bed form and gravel bed flows we argue that the double averaging approach based on momentum equations should serve as a better methodological basis for modeling phenomenological developments and parameterizations these equations explicitly include drag terms and form induced momentum fluxes due to spatial heterogeneity of the time averaged flow in the near bed region they also provide a solid basis for better definitions of basic flow variables including the shear stress partitioning into turbulent and form induced momentum fluxes skin friction and pressure form drag we show that for a range of rough bed flows the vertical distribution of the double averaged velocity consists of two distinct regions 1 a linear region below roughness tops and 2 a logarithmic region above them