gk17 ground motion prediction equation for horizontal pga and 5 damped psa from shallow crustal continental earthquakesgk17 gmpe for horizontal pga and 5 damped psa from shallow crustal continental earthquakes

dynamics of intertidal gravel dunes 1 this paper examines the dynamics of intertidal gravel dunes subjected to high energy unsteady and reversing tidal currents in the severn estuary uk the dunes were composed of shale particles with median grain size d50 around 4 mm and had mean heights and wavelengths of 60 cm and 7 m respectively acoustic instruments were deployed above a dune to measure the streamwise profile and flow turbulence radar was used to map a section of the dune field on two occasions measurements during the peak spring ebb tides showed that when the measured bed shear stress exceeded the threshold for entrainment of the coarse surface armor sediments were eroded from the upper surface of the dune the dune prograded in the direction of the ebb flow a distance o 1 m and some eroded sediments were deposited on the stoss slope downstream the dune was then reworked during the following flood tide to reestablish approximately the same pre ebb profile shape and location radar data showed also that the exposed dunes at low water occupied approximately the same location over a period of 4 days during peak spring tides the relationship between the depth mean current and the net volume of dune sediments moved was found to conform to a power law the predicted critical bed shear stress crit for d50 4 mm was approximately 1 n m2 however owing to a coarse armor layer on the surface of the dune a measured crit value o 4 n m2 was required to initiate dune erosion although the van rijn formula was found to overestimate both the height and wavelength of dunes at this site the dunes appear to be equilibrium bed forms controlled by local hydraulics and sediment supply sediment transport predicted by bed load formula were within a factor of two of the observed mass transport of dune sediments for ebb tides

equivalent roughness of alluvial bed the eguivalent roughness of a movable bed is considered relationships are given which can be used to determine the equivalent bed roughness from the bed material size and the bed form dimensions in the case of a plane bed the equivalent roughness is related to the d 9 0 of the bed material based on flume and field data the equivalent roughness may vary from 1 10 d 9 0 similar values were reported by other research workers in the case of bed forms the equivalent roughness is related to the average height and length of the bed forms both flume and field data were used to determine a functional relationship the proposed relationship yields values which are considerably smaller than other existing relationships

a model for lg propagation in the gulf coastal plain of the southern united states the southern united states experienced extensional tectonics during the early mesozoic development of the gulf of mexico and subsequent accumulation of up to 12 km of marine sediment few seismic stations have operated in the gulf coastal plain for extended periods of time and data for constraining ground motion prediction models are sparse previous studies found that the region differs from other parts of eastern north america in terms of lg attenuation the earthscope transportable array was in the south central united states in 2010 2012 during a time of increased seismicity that circumstance provided data for investigating lg propagation sixteen earthquakes with magnitudes in the 3 2 5 6 range occurred in oklahoma arkansas and texas and were recorded to distances of 1000 km stations in the coastal plain of texas arkansas louisiana and mississippi exhibit strong attenuation of the lg phase compared with stations located to the north in the ouachita orogenic belt and cratonic platform q associated with the crustal waveguide underlying the gulf coastal plain was estimated as q 365 f 0 62 however lg blockage due to crustal thinning and anelastic attenuation due to the presence of several kilometers of sedimentary deposits occurs near the gulf coast the average value south of latitude 33 n is 96 10 ms a remarkable linear correlation exists between the attenuation parameter and the thickness of post jurassic sediments in the study region such that stations near the coast of texas louisiana and mississippi which overlie 12 km of sediments exhibit values of 160 ms this strong spatial dependence of attenuation has important implications and should be incorporated in the development of ground motion prediction models using the approach suggested here online material figures showing maps of regression residuals and receiver terms for 12 frequency bands

bed load and suspended load contributions to migrating sand dunes in equilibrium dunes dominate the bed of sand rivers and are of central importance in predicting flow roughness and water levels the present study has focused on the details of flow and sediment dynamics along migrating sand dunes in equilibrium using a recently developed acoustic system acoustic concentration and velocity profiler new insights are obtained in the behavior of the bed and the suspended load transport along mobile dunes our data have illustrated that due to the presence of a dense sediment layer close to the bed and migrating secondary bedforms over the stoss side of the dune toward the dune crest the near bed flow and sediment processes are significantly different from the near bed flow and sediment dynamics measured over fixed dunes it was observed that the shape of the total sediment transport distribution along dunes is mainly dominated by the bed load transport although the bed load and the suspended load transport are of the same order of magnitude this means that it was especially the bed load transport that is responsible for the continuous erosion and deposition of sediment along the migrating dunes whereas the bed load is entirely captured in the dune with zero transport at the flow reattachment point a significant part of the suspended load is advected to the downstream dune depending on the flow conditions for the two flow conditions measured the bypass fraction was about 10 for flow with a froude number fr of 0 41 and 27 for flow with froude number of 0 51 this means that respectively 90 for the fr 0 41 flow and 73 for the fr 0 51 flow of the total sediment load that arrived at the dune crests contributed to the migration of the dunes

influence of hydraulic conditions over dunes on the distribution of the benthic macroinvertebrates in a large sand bed river 1 this study aims to relate the flow structure over mobile dunes recorded on the channel bed of the parana river argentina with the spatial distribution of the benthic macroinvertebrates the following main conclusions have been obtained 1 the dunes found in the active channel could be considered as hydraulic biotopes at a mesohabitat scale the bed forms in the thalweg region are subjected to higher shear stresses with low benthic densities 2 differences in benthic densities were also recorded at within dunes microhabitat scales the largest densities were found in the dune troughs where small bed shear stresses occur and minimum densities on the low stoss side of dunes where turbulent agitation near the bottom strongly disturb the bed particles 3 superimposed dunes on larger dunes may be considered as another microhabitat of still smaller dimensions summarizing multiscale approaches are needed if a comprehensive understanding linking hydrodynamics and morphodynamics processes with benthic ecology is intended

regionally adjustable generic ground motion prediction equation based on equivalent point source simulations application to central and eastern north america abstract we develop a generic ground motion prediction equation gmpe that can be adjusted for use in any region by modifying a few key model parameters the basis of the gmpe is an equivalent point source simulation model whose parameters have been calibrated to empirical data in california in such a way as to determine the decoupled effects of basic source and attenuation parameters on ground motion amplitudes we formulate the generic gmpe as a function of magnitude distance stress parameter geometrical spreading rate and anelastic attenuation this provides a fully adjustable predictive model allowing users to calibrate its parameters using observed motions in the target region we also include an empirical calibration factor to account for residual effects that are different from and or missing in simulations compared to observed motions in the target region as an example we show how the generic gmpe can be adjusted for use in central and eastern north america cena and calibrated with the next generation attenuation east database we provide median predictions of ground motions in cena for average horizontal component peak ground motions and 5 damped pseudospectral acceleration periods up to t 10 s for magnitudes m 3 8 and distances up to 600 km

surface deformation associated with a dipping hydrofracture crustal deformation associated with hydrofracture is modeled by a dipping rectangular dislocation beneath the surface of an elastic half space the burger s vector is taken normal to the rectangular surface analytical expressions for vertical displacements are obtained from integration of volterra s equation by using mindlin s point force solutions for the elastic halfspace in the limits of 0 and 90 dip the results agree with those obtained by maruyama 1964 for poisson s ratio 0 25 expressions for arbitrary poisson s ratio are given for elongate dislocations the displacement field agrees with curves given by pollard and holzhausen 1979 for two dimensional near surface fractures at various dips at dip 0 a deep square dislocation gives displacements indistinguishable from those of sun s 1969 model of a horizontal penny shaped crack beneath the surface of an elastic half space modifying his result for shallow depths shows that they correspond to a dislocation of semi elliptical cross section with the surface displacement field asymptotically approaching a semi elliptical shape as depth decreases to zero similarly the surface displacement field of the square dislocation approaches that of its rectangular cross section nonlinear inversion of surface tilt fields associated with hydrofracture of deep boreholes gives estimates of fracture geometry position and orientation along with their uncertainties two examples are presented one of a near horizontal and one of a near vertical fracture

mean and turbulent flow structure during the amalgamation process in fluvial bed forms 1 fluvial channels present bed forms such as dunes and ripples that alter instantaneous hydrodynamics parameters such as flow velocities water surface profiles bed shear stresses and reynolds stresses and create turbulent coherent structures that are significantly different from those presented in flat bed conditions it is known that les based models are more suitable than rans models to reproduce the complex hydrodynamics around bed forms herein a les model is applied to describe the mean and turbulent flow structure under superimposed bed forms three cases were simulated run i train of ripples run ii superimposed bed forms and run iii amalgamated bed forms the les modeling was performed using a free surface condition to allow the model to develop undulations and boils on the water surface caused by effect of the bed forms some important conclusions from this study are the division of high and low shear stresses on the stoss side of the dune the progression of the flow field topology from run i and run iii and the type of turbulent coherent structures found in each stage the region of high shear stresses was related to turbulence production in which the streamwise velocity fluctuations where strips structures are related to streaks were associated to the modification of the bed morphology the turbulence horseshoes vortices thv were more frequent in run i than in the other two cases where streamwise rolls were more frequent finally the frequency of the bursting events increased from run i to run ii and decreased from run ii to run iii implications of detailed hydrodynamics into bed forms processes are also presented and discussed

thermodynamics of water permeated unwelded pyroclasts 1 equilibrium properties abstract we report here the results of an investigation of thermodynamic equilibrium properties of systems constituted by phlegraean unwelded pyroclasts dry or saturated with water we have experimentally measured the porosity of samples of phlegraean rocks and determined the values of the heat capacity and of thermal expansion of dry and water perfused tuffs having different texture structures also the energetics of the process of adsorption of water on the large internal surface of these porous materials has been investigated the amount of heat exchanged during the reversible formation of an adsorbed layer has been determined in dependence of its thickness and as a function of temperature the coherent picture emerging from the ensemble of all these measurements is that of a direct connection between the processes of adsorption desorption and the stress of the porous rock in very unsaturated soils these processes may constitute a much more efficient mechanism of transformation of thermal energy into soil deformation compared with that of thermal expansion of the solid matrix

sediment supply limited bedforms in sand gravel bed rivers the stability of bedforms in mixtures of gravel and sand is not well understood two bedform types are characteristic flow parallel sand ribbons and flow transverse barchans flume experi ments and field data presented here show that gradual transitions exist from sand ribbons to barchans and from barchans to fully de veloped dunes barchans and sand ribbons occur when not enough transportable sediment is available for the formation of fully devel oped ripples or dunes the reason is that a part of the bed sediment is immobile e g with an armor layer which limits the sediment sup ply and thus the volume of sediment available for the formation of bedforms bedform stability diagrams are shown to be extendable to sedi ment supply limited bedforms in sand gravel sediment if the par ticle parameters of the diagrams are derived from the transported sediment instead of the bed sediment barchans and forms transi tional to fully developed dunes plot in the dune stability fields sand ribbons on the other hand plot in the ripple lower plane bed and dune fields in the case of sediment supply limitation bedforms are partly or completely related to the characteristics of the sediment supply from upstream the sediment underlying the bedforms may be a stable armor and the exchange of sediment between this armor and the bedforms may be small or non existent consequently bedform char acteristics in sand gravel mixtures in supply limited conditions often are not predictable from the local hydraulics and sediment charac teristics

a fluid filled fracture as possible mechanism of ground deformation at phlegraean fields italy two uplift episodes have recently been recorded at phlegraean fields a volcanic region near naples south central italy the first episode occurred in 1970 and lasted up to 1972 the second has begun at the end of 1982 and is still in progress an attempt to model the ground deformations which occurred during the 1970 1972 event is made in this paper the source has been assumed to be a two dimensional fluid filled fracture similar to a sill a good fit with experimental data has been obtained for a short 1 2 km long shallow 3 km deep source and a driving pressure ranging from 60 to 210 bars rigidity values have been fixed at 3 5 4 0 1010 c g s with poisson ratio equal to 0 3 this solution which differs from previous approaches bymogi 1958 andwalsh anddecker 1971 is non unique but the present results are in good agreement with observed horizontal and vertical displacements notwithstanding the oversimplification made in assuming a homogeneous elastic semi infinite medium the predicted stress field seems to be in agreement with the fault plane solutions and the pattern of epicenters determined for the uplift seismic swarm episode that is still in progress

numerical computation of sand dune migration with free surface flow 1 this paper presents a morphodynamic model for free surface flows over bed forms the model reproduces bed form evolution and migration in a physically based manner the flow model component of the coupled morphodynamic model which is two dimensional in the streamwise and vertical directions explicitly treats unsteadiness and nonhydrostatic effects comparison with measurements shows that the flow model accurately simulates both mean flow and turbulence structure induced by bed forms under free surface flow the flow model performance is enhanced by the use of a high order godunov scheme known as the cubic interpolated pseudoparticle cip technique to compute the advection phase of the navier stokes equation in addition an enhanced k turbulence closure with nonlinear terms is incorporated in the present model in order to allow better predictions of reynolds stress anisotropy in regions with flow separation performance of the nonlinear k model is compared with standard k closure in the context of the flow as well as morphodynamic simulation nonequilibrium bed load sediment transport is treated using a eulerian stochastic formulation of the sediment exchange process in terms of pickup and deposition functions the proposed approach for sediment transport explicitly considers the local flow variability during morphodynamic computation model results show that the vertical grid distribution pattern affects the simulation result particularly for bed form morphodymics the model successfully simulates some important physical features of bed form evolution such as amalgamation and asymmetric geometry the simulation results are in agreement with laboratory experiments as well as some commonly used prediction methods for geometric characteristics of bed forms

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

tide driven dune migration and sediment transport on an intertidal shoal in a shallow estuary in devon uk abstract the migration of subaqueous dunes was investigated over a 3 month period on an intertidal shoal near the mouth of the shallow mixed wave tide dominated avon estuary on the channel coast of southwest britain the dunes characterised by heights and lengths of 0 05 0 2 m and 5 10 m respectively migrated 10 20 m over the 3 month period representing an average volumetric sediment transport rate of 0 5 m 3 per unit meter width compared to equilibrium models of dune dimensions based on the water depth the dune height was predicted well but the dune length was under predicted sediment transport on the intertidal shoal was controlled by a distinct tidal asymmetry with maximum flow velocities during flood 0 4 0 5 m s 1 significantly stronger than during ebb 0 2 0 3 m s 1 predicted bedload transport based on theory underestimates the actual transport and this is attributed to the modest flow velocities encountered and perhaps the importance of suspended load transport however when empirically calibrated and related to tide range the transport equation adequately accounts for observed rates using nearby tidal observations the predicted annual volumetric sediment transport rate is 2 6 m 3 per unit meter width this estimate compares favourably with the annual volumetric sediment transport based on dune measurements 2 0 m 3 using the notion that the transport rate decreases on the intertidal shoal in the up estuary direction to zero at its up estuary end a vertical accretion of 0 5 cm yr 1 was predicted the main implication of our study is that accurate and well designed process measurements of dune dynamics and tidal currents can provide useful information on the longer term evolution of intertidal shoals in sandy shallow flood dominant estuaries

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany i sedimentology and morphology the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine germany bed sediments dune geometry bedform migration rates and the internal structure of dunes are considered in this paper hydrodynamic and sediment transport data are considered in a companion paper the pebbles and cobbles d50 of 10 mm of the flat lag layer are rarely entrained dunes consist of well sorted medium to coarse sand d50 of 0 9 mm small pebbles move over the dunes by overpassing but there is a degree of size and shape selectivity populations of ripples in sand d50 0 6 mm and small and large dunes are separated by distinct breaks in the bedform length data in the regions of 0 7 1 m and 5 10 m ripples and small dunes may have sinuous crestlines but primarily exhibit two dimensional planforms in contrast large dunes are primarily three dimensional barchanoid forms ripples on the backs of small dunes rarely develop to maximum steepness small dunes may achieve an equilibrium geometry either on the gravel bed or as secondary dunes within the boundary layer on the stoss side of large dunes secondary dunes frequently develop a humpback profile as they migrate across the upper stoss slope of large dunes diminishing in height but increasing in length as they traverse the crestal region however secondary dunes more than 5 m in length are rare the dearth of equilibrium ripples and long secondary dunes is probably related to the limited excursion length available for bedform development on the parent bedforms large dunes with lengths between 20 m and 100 m do not approach an equilibrium geometry a depth limitation rather than a sediment supply limitation is the primary control on dune height dunes rarely exceed 1 m high in water depths of 4 m dune celerity increases as a function of the mean flow velocity squared but this general relationship obscures more subtle morphodynamics during rising river stage dunes tend to grow in height owing to crestal accumulation which slows downstream progression and steepens the dune form during steady or falling stage an extended crestal platform develops in association with a rapid downstream migration of the lee side and a reduction in dune height these diminishing dunes actually increase in unit volume by a process of increased leeside accumulation fed by secondary dunes moving past a stalled stoss toe a six stage model of dune growth and diminution is proposed to explain variations in observed morphology the model demonstrates how the development of an internal boundary layer and the interaction of the water surface with the crests of these bedload dominated dunes can result in dunes characterized by gentle lee sides with weak flow separation this finding is significant as other studies of dunes in large rivers have attributed this morphological response to a predominance of suspended load transport

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

an experimental study on the ripple dune transition flume experiments were conducted on different bed stages across the ripple dune transition as flow velocity increases an initially flat bed surface made of fairly uniform sandy material is gradually transformed into a two dimensional rippled bed with further increase in velocity two dimensional ripples are replaced by irregular linguoid ripples as the average velocity necessary for the ripple dune transition to occur is imposed on the bed surface these non equilibrium linguoid ripples are further transformed into larger two dimensional dunes for each of these stages across the transition a concrete mould of the bed was created and the flow structure above each fixed bed surface investigated an acoustic doppler velocimeter was used to study the flow characteristics above each bed surface detailed profiles were used along a transect located in the middle of the channel results are presented in the form of spatially averaged profiles of various flow characteristics and of contour maps of flow fields section view they clearly illustrate some important distinctions in the flow structure above the different bedform types associated with different stages during the transition turbulence intensity and reynolds stresses gradually increase throughout the transition two dimensional ripples present a fairly uniform spatial distribution of turbulent flow characteristics above the bed linguoid ripples induce three dimensional turbulence structure at greater heights above the bed surface and turbulence intensity tends to increase steadily with height above bed surface in the wake region a very significant increase in turbulence intensity and momentum exchange occurs during the transition from linguoid ripples to dunes the turbulent flow field properties above dunes are highly dependent on the position along and above the bed surface and these fields present a very high degree of spatial variability when compared with the rippled beds further investigations under natural conditions emphasizing sediment transport mechanisms and rates during the transition should represent the next step of analysis together with an emphasis on quadrant analysis copyright 2001 john wiley sons ltd

viscoelastic displacement and gravity changes due to point magmatic intrusions in a gravitational layered solid earth summary we present a method for the computation of time dependent geodetic and geophysical signatures deformation potential and gravity changes due to magmatic intrusions in a layered viscoelastic gravitational medium this work is an extension of a deformation model previously developed to compute effects due to volcanic loading in an elastic gravitational layered media the model assumes a planar earth geometry useful for near field problems and consists of welded elastic and viscoelastic layers overlying a viscoelastic half space every layer can either be considered elastic or viscoelastic the intrusion treated as a point source can be located at any depth in any of the layers or in the half space several examples of theoretical computations for different media are also presented we have found that in line with previous results obtained by other authors introducing viscoelastic properties in all or part of the medium can extend the effects displacements gravity changes etc considerably and therefore lower pressure increases are required to model given observed effects the viscoelastic effects seem to depend mainly on the rheological properties of the layer zone where the intrusion is located rather than on the rheology of the whole medium we apply our model to the 1982 1984 uplift episode at campi flegrei modelling simultaneously the observed vertical displacement and gravity changes the results clearly show that for a correct interpretation of observed effects it is necessary to include the gravitational field in the anelastic theoretical models this factor can change the value and pattern of time dependent deformation as well as the gravity changes explaining cases of displacement without noticeable gravity changes or vice versa cases with uplift and incremental gravity values and other cases the combination of displacement and gravity changes is found to be especially effective in constraining the possible characteristics of the magmatic intrusion as well as the rheology of the medium surrounding it

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

flow structure and resistance over subaquaeous high and low angle dunes a prominent control on the flow over subaqueous dunes is the slope of the downstream leeside while previous work has focused on steep 30 asymmetric dunes with permanent flow separation little is known about dunes with lower lee slope angles for which flow separation is absent or intermittent here we present a laboratory investigation where we systematically varied the dune lee slope holding other geometric parameters and flow hydraulics constant to explore effects on the turbulent flow field and flow resistance three sets of fixed dunes lee slopes of 10 20 and 30 were separately installed in a 15 m long and 1 m wide flume and subjected to 0 20 m deep flow measurements consisted of high frequency vertical profiles collected with a laser doppler velocimeter we show that the temporal and spatial occurrence of flow separation decreases with dune lee slope velocity gradients in the dune leeside depict a free shear layer downstream of the 30 dunes and a weaker shear layer closer to the bed for the 20 and 10 dunes the decrease in velocity gradients leads to lower magnitude of turbulence production for gentle lee slopes aperiodic strong ejection events dominate the shear layer but decrease in strength and frequency for low angle dunes flow resistance of dunes decreases with lee slope the transition being nonlinear over the 10 20 and 30 dunes shear stress is 8 33 and 90 greater than a flat bed respectively our results demonstrate that dune lee slope plays an important but often ignored role in flow resistance

coherent flow structures in a depth limited flow over a gravel surface the influence of surface roughness 1 turbulent flows moving over a gravel bed develop large scale macroturbulent flow structures that are initiated at anchor clasts in the bed and grow and dissipate as they move upward through the flow depth this paper extends previous research in which we investigated the influence of the reynolds number on coherent flow structures generated over a gravel bed by assessing the importance of effective bed roughness here we report on flume experiments in which flows over beds of decreasing surface roughness have been quantified through the application of digital particle imaging velocimetry which allows study of the downstream and vertical components of velocity over the entire flow field these results indicate that as the effective roughness increases 1 the visual distinctiveness of the coherent flow structures becomes more defined throughout the flow depth 2 the upstream angle of slope of the coherent flow structure increases and 3 the reduction in streamwise flow velocity and turbulence intensity toward the upstream side of the structure becomes greater applying standard scaling laws these structures appear shear generated and form through a combination of both wake flapping and the reattachment of localized shear layers associated with flow separation around individual topographic protrusions as the effective protrusion decreases the scale of these coherent flow structures also decreases

surveyed and modelled one year morphodynamics in the braided lower tana river field measurements and morphodynamic simulations were carried out along a 5 km reach of the sandy braided lower tana river in order to detect temporal and spatial variations in river bed modifications and to determine the relative importance of different magnitude discharges on river bed and braid channel evolution during a time span of one year i e 2008 2009 fulfilling these aims required testing the morphodynamic model s capability to simulate changes in the braided reach we performed the simulations using a 2 d morphodynamic model and different transport equations the survey showed that more deposition than erosion occurred during 2008 2009 continuous bed load transport and bed elevation changes of 1 m and a 70 188 m downstream migration of the thalweg occurred simulation results indicated that during low water periods modifications occurred in both the main channel and in other braid channels thus unlike some gravel bed rivers the sandy lower tana river does not behave like a single thread channel at low discharge however at higher discharge i e exceeding 497 m3 s the river channel resembled a single thread channel when channel banks confined the flow although the spring discharge peaks caused more rapid modifications than slower flows the cumulative volumetric changes of the low water period were greater the importance of low water period flows for channel modifications is emphasized although the 2 d model requires further improvements the results were nevertheless promising for the future use of this approach in braided rivers

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

flow and turbulence structure across the ripple dune transition an experiment under mobile bed conditions current knowledge of flow and turbulent processes acting across the sand bed continuum is still unable to unequivocally explain the mechanism s by which ripples become dunes understanding has been improved by comparative high resolution studies undertaken over fixed bedforms at different stages in the continuum however these studies both ignore the role of mobile sediment and do not examine flow structure during the actual transition from ripples to dunes the aims of the paper are i to describe flow and turbulence characteristics acting above mobile bedforms at several stages across the transition and ii to compare these data with those arising from experiments over fixed ripples and dunes laboratory experiments are presented that examine the turbulence structure across seven distinct stages of the transition from ripples to dunes single point acoustic doppler velocimeter sampling at three flow heights above a developing mobile boundary was undertaken time averaged statistics and the instantaneous quadrant record reveal distinct changes in flow structure either side of the change from ripples to dunes initially shear related high frequency vortex shedding dominates turbulence production this increases until two dimensional 2d dunes have formed thereafter turbulence intensities and reynolds stress decline and three dimensional dunes exhibit values found over 2d ripples this is the result of shear layer dampening which occurs when the topographically accelerated downstream velocity increases at a faster rate than flow depth activity at reattachment increases due to high velocity fluid imparting high mass and momentum transfer at the bed and or wake flapping suspended sediment may also play a role in turbulence dampening and bed erosion ejections dominate over sweeps in terms of event frequency but not magnitude strong relationships between inward interactions and sweeps and ejections and outward interactions suggest that mass and momentum exchanges are dependent upon activity in all four quadrants the results contradict the notion present in most physical models that larger bedforms exhibit most shear layer activity consequently an improved model for the ripple dune transition is proposed

late flandrian coastal change and tidal palaeochannel development at hills flats severn estuary sw britain an eclectic range of stratigraphical sedimentological geochemical archaeological and historical evidence relating to a tidal palaeochannel exposed at a deep erosional level in the modern intertidal zone on the avon gloucestershire border demonstrates that tidal wetlands reclaimed during the roman period ranged much further seaward than the modern coastline vigorous late medieval early modern erosion linked to the cool disturbed conditions of the little ice age forced the coastline by the mid seventeenth century to a location inland of its present line a possible medieval landing place was destroyed and it was necessary to set back the flood defences as the result of renewed mudflat marsh growth the coast at hills flats has built outward during modern times but in three distinct stages and by no means as far seaward as its likely roman position

a flume experiment on the development of subaqueous fine gravel dunes from a lower stage plane bed 1 determining the hydraulic conditions whereby gravel dunes first develop in subaqueous environments is fundamental as their presence may influence engineering solutions designed to maintain bed stability in addition estimates of the flow conditions associated with preserved gravel bed forms in sedimentary sequences are useful for reconstructing the depositional environments and geometries of for example oil and gas bearing geological strata consequently a series of experiments considered dune initiation in these experiments defects and latterly incipient dunes developed from lower stage plane gravel beds during near threshold conditions of motion crit 1 0 1 016 and long periods of marginal bed load transport rates the three dimensional defects were almost imperceptible positive ovoid features with heights of one or two grain diameters and lengths and spans of a few decimeters after 17 hours of flow incipient low amplitude simple two dimensional dunes developed from the defects with heights ranging between 0 029 and 0 055 m nonequilibrium wavelengths of 1 4 m and spans of 0 6 0 9 m continued development over several days with crit ratios of around 1 3 resulted in near equilibrium two dimensional dunes with wavelengths averaging 2 6 3 5 m and spans equal to the flume width 4 m the inception of incipient dunes could be predicted using bulk flow models however this approach was not suitable for the prediction of defect development near bed turbulence in the form of small scale sweep events of limited breadth controls the initiation of defects but larger scale coherent turbulent structures in the outer flow are related to dune development significantly both defects and incipient dunes can exist at the same time which indicates that the effects of sweeps on the bed morphology persist at the same time as larger scale turbulent structures are beginning to effect sediment transport

on the relationship between flow and suspended sediment transport over the crest of a sand dune rio parana argentina the links between large scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades with past studies illustrating the origin of such turbulence and its influence on flow resistance sediment transport and bedform morphology in this study of turbulence and sediment suspension over large sand dunes in the rio parana argentina time series of three dimensional velocity and at a point suspended sediment concentration and particle size were measured with an acoustic doppler current profiler and laser in situ scattering transmissometer respectively these time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment the analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections regions of high suspended sediment concentration are found to correlate well with such events the frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations such a finding suggests that a combination and interaction of vortex shedding and wake flapping changing length of the lee side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures including information on the topology of dune related turbulent flow structures at the flow stage investigated the turbulent flow events and their associated high suspended sediment concentrations are seen to grow with height above the bed until a threshold height ca 0 45 flow depth is reached above which they begin to decay and dissipate

subaqueous gravel dunes abstract gravel dunes are rarely reported owing to comparative rarity of occurrence and generic confusion with antidunes and classes of gravel bars a compilation of data from the literature for sediments with a median size greater than 2 mm shows that dunes have been developed in the laboratory in median grain sizes up to 28 6 mm for field conditions there are data for grain sizes up to 60 mm equilibrium and non equilibrium gravel dunes range in length from less than 0 6 m to greater than 100 m heights range from less than 0 1 m to 16 m height and length data for the steepest three dimensional 3 d gravel dunes are consistent with the h l function reported by ashley 1990 for equilibrium dunes developed in sand for a broad range of dune length 3 d gravel dunes are steeper than two dimensional 2 d dunes but for l 100 m and h 8 m there are too few data to draw any conclusion ashley s h l function does not apply to a broad range of 2 d gravel dunes a separate well defined function is proposed to describe the h l relationship for 2 d gravel dunes of maximum steepness there are few data on the hydrodynamic development of gravel dunes as a guide gravel dunes develop for a range of froude numbers up to 0 75 given that the nondimensional mean bed shear stress exceeds circa 0 1 dunes reach their maximum height at 0 25 and have reduced in height when 0 3 froude numbers of 0 84 and above lead to crestal flattening dune diminution and eventual replacement by antidunes or upper stage plane beds however owing to lag effects transitional bedforms have been recorded for froude numbers near the critical value of 1 the development of gravel dune steepness from lower stage plane bed through to upper stage plane bed is well described in only one case by dinehart 1992a fredsoe s 1975 function for equilibrium dune steepness applies reasonably well to dinehart s steepest dunes allen s 1984 bedform existence field based on and a characteristic grain size of the bed sediment has been extended from 5 mm to include bedstocks as coarse as 33 mm

the role of attached kelp seaweed in lowering threshold of coarse gravel entrainment in tidal flows lag deposits of cobble sized clasts found within the troughs of fine gravel dunes on a rock bed intertidal zone are explained by the process of enhanced fluid transport due to attached seaweed field determinations of the competence of the tidal currents demonstrated that the currents were not able to transport weed free clasts on the tidal flat controlled flume experiments were used to demonstrate that the presence of the fucoid alga fucus vesiculosus l attached to clasts reduces the critical velocities and shear stresses to levels that allow the tidal currents to entrain the clasts and move them over the backs of dunes to the lee sides subsequent burial of the weedy clasts in the dune troughs by dune progression kills the weed leaving the latterly exposed clasts as an accumulating weed free lag the weight of attached weed typically equals the submerged weight of the clast and the critical velocity and critical shear stress for initial motion are both roughly halved by the presence of the weed the drag induced by weed is four times that experienced by weed free clasts and mobile clasts exhibit near equal mobility

empirical attenuation of ground motion spectral amplitudes in southeastern canada and the northeastern united states a database of 1700 digital seismograms from 186 earthquakes of mag nitude mn 2 5 5 6 that occurred in southeastern canada and the northeastern united states from 1990 to 2003 was compiled maximum likelihood regression analysis of the database was performed to determine a model for the attenuation of fourier spectral amplitudes for the shear window for the vertical and horizontal component of motion for frequencies from 0 2 to 20 hz fourier amplitudes follow a hinged trilinear attenuation model fourier spectral amplitudes decay as r 1 3 where r is hypocentral distance within 70 km of the source there is a transition zone from 70 to 140 km as the direct waves are joined by strong postcritical reflections where the attenuation is described as r 0 2 spectral amplitudes actually increase with distance in this range for low frequencies beyond 140 km the attenuation is well described by r 0 5 corresponding to geometric spreading in two dimensions the associated model for the regional quality factor for frequencies greater than 1 hz can be ex pressed as q 893f 032 q can be better modeled over a wider frequency range 0 2 20 hz by a polynomial expression log q 3 052 0 393 log f 0 945 log f 2 0 327 log f 3 the polynomial expression accommodates the observation that q values are at a minimum about 1000 near 1 hz and rise at both lower and higher frequencies correction factors for the spectral amplitude model that describe the effects of focal depth on the amplitudes and their attenuation are developed using the subset of events with known focal depth the attenuation model is similar to that determined from an earlier study with more limited data atkinson and mereu 1992 but the enlarged database indicates more rapid near source amplitude decay and higher q the attenuation model is used to play back attenuation effects to determine the apparent source spectrum for each earthquake in the database and hence determine moment magnitude m and brune stress drop the events have moment magnitude in the range from 2 5 to 5 stress drop increases with moment magnitude for events of m 4 3 then appears to attain a relatively constant level in the range from 100 to 200 bars for the larger events as previously noted in atkinson 1993b the results of this study provide a useful framework for improving regional ground motion relations in eastern north america they further our understanding of attenuation in the region through analysis of an enlarged ground motion database in particular the inclusion of the three component broadband data gathered over the last decade allows extension of attenuation models to both horizontal and vertical components over a broad frequency range 0 2 20 hz

structure of flow over alluvial bedforms an experiment on linking field and laboratory methods this paper presents results of a field study designed to examine the structure of flow over mobile and fixed bedforms in a natural stream and to compare the results with findings of previous laboratory studies within the framework of double time space averaging approach measurements of turbulence were obtained in a small river in illinois usa over a fine spatial grid of sampling points above a mobile sandy bedform and its artificially moulded replica flow structure over the artificial bedform is similar to that observed in laboratory studies but is markedly different from the flow structure over natural bedforms these differences are most pronounced in the roughness sublayer whereas flow in the logarithmic layer over natural and artificial sand waves is fairly similar and exhibits spatial uniformity the double time space averaged distributions of turbulence statistics conform to the multilayer model of flow structure over bedforms mean velocity distributions indicate neither classical flow recirculation nor substantial reduction of velocities in the lee of bedform crests however vertical patterns of turbulence statistics over depth suggest that stacked wakes similar to those observed in laboratory studies exist above the bedforms thus despite the absence of flow separation wake development seems to be induced by the systematic influence of upstream bedforms on the vertical structure of turbulence copyright 2006 john wiley sons ltd

grain size control of large compound flow transverse bedforms in a tidal inlet of the danish wadden sea abstract flow transverse bedforms were recorded along a 2 km reach of the northernmost tidal inlet of the danish wadden sea the bed of the inlet channel is covered with large to very large compound dunes and superimposed medium sized dunes composed of medium to coarse sands the mean grain size of the bed material along the centre line of the inlet throat decreases from 0 56 mm in the inner part to 0 3 mm in the outer part both dune populations are essentially two dimensional with straight to slightly curved crest lines the ebb current is very similar in magnitude along the entire channel axis whereas the flood current is of similar magnitude in the inner half but reaches only about half of the maximum ebb current velocity in the outer section sediment transport occurs during both the ebb and flood periods the latter being less vigorous and of shorter duration as a result the inlet as a whole is ebb dominated dominant ebb current 1 01 m s 1 dominant flood current 0 79 m s 1 in agreement with the tidal dynamics a net ebb oriented bedform migration rate of 32 m yr 1 was determined from the survey data the large to very large dunes display distinct flood caps during the flooding tide whereas the medium sized dunes reverse their direction during each tide the downstream dimensional evolution of the large dunes is complex switching from initial growth to progressive decline followed by renewed growth in length but progressive decline in height this latter degradational phase begins in the middle of the survey reach and continues seawards until the large forms disappear completely at the same time the outer channel section becomes dominated by medium sized dunes which grow in size with decreasing grain size surprisingly there is no correlation between dune dimensions and water depth as would be expected at such shallow depths the complex evolution of dune dimensions as a function of grain size is discussed in terms of recent tidal bedform stability theory it is clear however that more site specific observations are required to fully explain the phenomenon

attenuation of lg waves in the new madrid seismic zone of the central united states using the coda normalization method abstract unique properties of coda waves are employed to evaluate the frequency dependent quality factor of lg waves using the coda normalization method in the new madrid seismic zone of the central united states instrument and site responses are eliminated and source functions are isolated to construct the inversion problem for this purpose we used 121 seismograms from 37 events with moment magnitudes m ranging from 2 5 to 5 2 and hypocentral distances from 120 to 440 km recorded by 11 broadband stations a singular value decomposition svd algorithm is used to extract q values from the data while the geometric spreading exponent is assumed to be a constant inversion results are then fitted with a power law equation from 3 to 12 hz to derive the frequency dependent quality factor function the final results of the analysis are q v lg f 410 38 f 0 49 0 05 for the vertical component and q h lg f 390 26 f 0 56 0 04 for the horizontal component where the term after sign represents one standard error for stations within the mississippi embayment with an average sediment depth of 1 km around the memphis metropolitan area estimation of quality factor using the coda normalization method is not well constrained at low frequencies f

the shape of ground motion attenuation curves in southeastern canada the shape of the attenuation curve of the fourier spectrum of acceleration is established for southeastern canada from empirical data the dataset is comprised of 1200 digital vertical component seismograms from 100 earthquakes recorded on 30 stations of the eastern canada telemetered network the distance range of the observations is 10 to 1700 km focal depths are from 5 to 30 km results indicate that the attenuation curve has three distinct sections at distances less than 70 km corresponding to attenuation of the direct wave amplitudes decay slightly more rapidly than 1 r r 1 1 between 70 and 130 km where the direct wave is joined by sms spectral amplitudes are approximately constant beyond 130 km corresponding to the lg phase amplitudes decay at a rate that is consistent with r 0 5 and q 670 f 0 33 the findings support the hypothesis of burger et al 1987 that postcritical reflections from the moho discontinuity play an important role in determining the shape of the attenuation curve however the influence of sms is subtle allowing the shape to be approximated by simple functional forms for example the commonly assumed bilinear form r 1 r 0 5 with frequency dependent q fits well if the transition from direct wave to lg spreading is placed at approximately 60 km a linear form r 1 over all distances with constant q 2000 also provides a satisfactory fit overall we find little evidence for the dependence of attenuation on focal depth or tectonic province

modeling river dune evolution using a parameterization of flow separation this paper presents an idealized morphodynamic model to predict river dune evolution the flow field is solved in a vertical plane assuming hydrostatic pressure conditions the sediment transport is computed using a meyer peter muller type of equation including gravitational bed slope effects and a critical bed shear stress to avoid the necessity of modeling the complex flow inside the flow separation zone we follow an approach similar to one used earlier to simulate the dynamics of wind blown desert dunes in case of flow separation the separation streamline acts as an artificial bed and sediment avalanches down the leeside distributing evenly on the leeside at the angle of repose model results show that bed slope effects play a crucial role in the determination of the fastest growing wavelength from a linear analysis flow separation is shown to be crucial to take into account if the dune lee exceeds a certain threshold slope if flow separation is not included dune shapes are incorrectly predicted and the dune height saturates at an early stage of bed form evolution yielding an underprediction of dune height and time to equilibrium the local bed slope at the dune crest plays a critical role for obtaining an equilibrium dune height the simulation model is able to predict the main characteristics of dune evolution such as dune asymmetry dune growth and saturation at a certain dune height dune dimensions migration rates and times to equilibrium compare reasonably well to various data sets

interactions between bed forms topography turbulence and transport 1 results are presented examining the interaction between two sandy bed forms under low sediment transport conditions in a small laboratory flume the initial artificially made bed forms were out of equilibrium with the flow field temporal evolution of bed forms was monitored using time lapse photography in order to characterize bed form adjustment to the imposed flow velocity measurements were collected using an acoustic doppler velocimeter to characterize both mean flow and turbulence associated with different bed form geometries sandy bed forms all had identical initial geometries however the initial distance between bed form crests was varied between experiments overall deformation of the bed varied as a function of initial bed form spacing however bed forms evolved unpredictably as periods of relatively slow change were punctuated by periods of rapidly changing geometry subtle changes in bed form trough geometry were found to have a strong influence on turbulence and therefore sediment transport comparison with field studies suggests that the mechanisms described herein are active in natural systems

a simple model of bedform migration a model linking subaqueous dune migration to the effective grain related shear stress is calibrated by means of flume data for bedform dimensions and migration rates the effective shear stress is calculated on the basis of a new method assuming a near bed layer above the mean bed level in which the current velocity accelerates towards the bedform crest as a consequence the effective bed shear stress corresponds to the shear stress acting directly on top of the bedform the model operates with the critical shields stress as a function of grain size and predicts the deposition volume per unit time and width of naturally packed bed material on the bedform lee side qbcrest the model is simple built on a rational description of simplified sediment mechanics and its calibration constant can be explained in accordance with estimated values of the physical constants on which it is based predicted values of qbcrest correlate with measured values of bedform height multiplied by bedform migration rate with r2 0 83 copyright 2010 john wiley sons ltd

observations of coherent flow structures over subaqueous high and low angle dunes large scale coherent flow structures cfs above dunes are the dominant source of flow resistance and constitute the principal mechanism for sediment transport and mixing in sand bed river and estuarine systems based on laboratory observations cfs formation has been previously linked to flow separation downstream of high angle dunes with lee slopes of 30 how cfs form in natural deep rivers and estuaries where dunes exhibit lower lee slopes and intermittent flow separation is not well understood here we present particle image velocimetry piv measurements from an experiment where dune lee slope was systematically varied 30 20 10 while other geometric and hydraulic parameters were held constant we show that cfs form downstream of all three dune geometries from shear layer vortices in the dune lee the mode of cfs formation undergoes a low frequency oscillation with periods of intense vortex shedding interspersed with periods of rare vortex shedding streamwise alignment of several vortices during periods of intense shedding results in wedge shaped cfs that are advected above the dune stoss side streamwise length scales of wedge shaped cfs correspond to large scale motions lsm we hypothesize that the advection of lsm over the dune crest triggers the periods of intense shedding in the dune lee lsm are weaker and smaller above low angle dunes however the low frequency oscillation in cfs formation periods persists the formation of smaller and weaker cfs results in a reduction of flow resistance over low angle dunes

shape and dimensions of stationary dunes in rivers the shape and dimensions length height of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward facing step the transport of sediment is split up into bed load and suspended load which makes it possible to explain the transition to plane bed the model can predict flow resistance curves in alluvial streams

recent ground movement and seismic activity in campi flegrei southern italy episodic growth of a resurgent dome leveling surveys in campi flegrei an active volcanic caldera in southern italy show that this caldera has undergone both subsidence and uplift of a few meters during the past 85 years a single source located at a depth of about 3 km beneath the center of the caldera can account for almost all elevation changes recorded in campi flegrei since the first leveling survey conducted in 1905 1907 this includes leveling surveys that span periods of subsidence such as between 1905 1907 and 1919 and between january 1985 and october 1986 and periods of rapid uplift between march 1970 and october 1971 and between january 1981 and december 1984 a possible geometry for the source of uplift and subsidence beneath campi flegrei is a rectangular horizontal sheet located at a depth of about 3 km and centered a few hundred meters east of the city of pozzuoli the horizontal dimensions of this sheet are about 1 5 km by 3 0 km the long axis is oriented n70 w this sheet lies adjacent to the most intense area of seismicity that occurred from mid 1983 to december 1984 during an uplift episode this sheet may represent the top of a magma body undergoing internal pressure changes possibly by intrusion of additional magma subsidence is caused by groundwater removal from the water saturated deposits that fill this caldera to a depth of a few kilometers a temporary increase in subsidence rate after an uplift episode is caused by increased rate of groundwater removal from newly fractured regions that lie immediately above the magma body the close proximity of this water saturated region and the magma body makes it impossible to separate the depth to these two sources from the results of leveling surveys two observations indicate that uplift has occurred in the center of campi flegrei for at least the past several thousand years first marine deposits in the center of campi flegrei were uplifted at least 40 m between 4000 and 8000 years ago second continuous seismic profiles of the undersea portion of campi flegrei have identified only one region where rocks are fractured and faulted adjacent to the uplifted marine deposits that surround the point of maximum uplift indicated by recent leveling surveys on the basis of these observations and the historical record of activity we suggest that campi flegrei caldera is in a stage of growing a resurgent dome the present diameter of the resurgent dome is about 4 km and the maximum amount of vertical uplift during the past 10 000 years has probably not exceeded 100 m the episodes of rapid uplift and shallow earthquake swarms during the past 20 years are probably related to the growth of this resurgent dome

on the role of fluid infiltration into gravel dunes using a 3d numerical model abstract both the hydrodynamic conditions as well as the related sediment transport processes of sandy bedforms are understood fairly well however little is known about the genetic processes of bedforms involved in environments dominated by gravel in the coastal environment storm waves spring tides bore waves and to a lower frequency tsunamis are common phenomena that can provide the required energy to form gravel bedforms given the high energy of such wave events and the formidable practical difficulties of fixed instrumentation and in situ measurements knowledge on the hydrodynamic processes in the direct vicinity and in the interior of gravel bedforms is still limited a 3d numerical flume tank model using smoothed particle hydrodynamics sph was generated to study the nature of flows for an extreme wave above and in the interior of gravel bedforms as a complementary method to in situ measurements with typical flume tank dimensions x 2 68 m y 0 25 m z 0 8 m three experiments were undertaken to test a range of simplified bedform geometries stoss side slopes 42 23 13 using a unimodal grain fraction the water column was represented by 11 million fluid particles and the bedforms by 480 immobile solid particles a single numerical wave was introduced using a vertical paddle that moved to x 0 3 m perpendicular to the bottom of the tank fluid velocities extracted at each timestep at each point of the tank were used to determine free stream pore water flow velocities and residence times from all experiments results showed that when the wave crest was positioned before the bedform crests pore water flows appeared predominantly in the downstream direction however when the position of wave crest was located after the bedform crests a vortex developed at the leeside of all bedforms causing a change of the pore water flow towards the upstream direction regions of inflow outflow and pore water flow through the pore spaces were evident in all experiments but changed as the stoss side slope angles were decreased it is concluded that variations in the stoss side steepness appear to control the locations and the position of the wave crest the directions of pore water flow which was illustrated in a conceptual model

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

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

an experimental study of turbulent flow over a low angle dune 1 many large sand bed alluvial channels are dominated by dunes that possess low angle lee sides often 10 which play a critical role in the transportation of sediment and generation of significant bed form roughness despite the fact that these low angle dunes are very common in such channels many current models of dune flow dynamics are based on bed forms with an angle of repose slip face that generates a zone of permanent separated flow in the dune lee study of flow associated with low angle dunes in the field is inherently difficult since it is usually both hard to measure very near the bed and hard to quantify the nature of turbulence over these bed forms results from a detailed scale model experimental study of flow over a low angle dune which is based on a prototype dune from the fraser river canada present a necessary link between flume and field studies and document the origins of macroturbulence associated with these bed forms two dimensional laser doppler anemometer measurements over a low angle dune maximum lower lee side slope 14 show that dune morphology exerts a dominant control on the turbulent flow causing flow deceleration in the lower lee and development of an intermittent layer of shear at the interface with the higher velocity flow above the scale model confirms that permanent flow separation does not occur over low angle dunes but instead is replaced by a small region here 7 of the dune wavelength in length of intermittent flow reversal which may be present for up to 4 of the time shear layers generated along this small zone of decelerated and or separated flow in the lower lee have a much smaller velocity differential than is characteristic of shear layers generated by flow separation in the lee of angle of repose dunes turbulence production associated with low angle dunes is dominated by eddies generated along this shear layer which produce highly variable horizontal and vertical velocities and large reynolds stresses in this region these results show that macroturbulence associated with low angle dunes is generated by intermittent separation or shear layer generation due to velocity gradients established in the zone of lee side flow expansion velocity profiles and maps of turbulence structure from the scale model are in reasonable agreement with field measurements from low angle dunes in natural sand bed rivers these results highlight the need to consider the temporal evolution and intermittency of shear layer behavior often very near the bed when interpreting the generation of macroturbulence and dispersal of sediment associated with low angle dunes

field measurements of flow fields and sediment transport above mobile bed forms 1 field measurements of hydrodynamic conditions bed forms and suspended sediments obtained using a suite of approximately colocated sensors above a mobile bed composed of coarse sand d50 1 28 mm in a strong tidal current with superimposed waves are used to investigate the mean and turbulent flow fields bed forms and the resuspension and transport of sediments in suspension and as bed load while there is no evidence for flow separation properties of the local turbulent flow field are found to vary spatially in response to the bed morphology time averaged suspended sediment concentration profiles c profiles are found to be spatially variable with higher concentrations observed in the trough regions between bed form crests well known expressions used to predict c profiles are found to agree well with measured time averaged c profiles the instantaneous suspended sediment concentration field sscf is found to comprise a series of semiperiodic resuspension events interspersed by relatively quiescent periods using a modified quadrant analysis scheme these events are shown to be correlated closely with times when current and wave induced flows combine and exceed the threshold for suspension the effectiveness of a given combined wave current flow event in resuspending bed sediments is found to depend upon its location relative to bed morphology it is considered that local bed response may be influenced by spatial differences in grain size and compaction brought about by the processes of bed load transport over the bed forms the total mass of sediment in suspension is found to be less than the potential transport capacity of the flow suggesting strongly that the supply of fine sediments is source limited while measured bed form geometry agrees well with predicted dimensions for ripples grain size alone suggests only dunes should be present these were not detected bed load transport qb calculated from measured bed form migration speeds and the measured suspended sediment flux qs was found to agree favorably with empirical predictions

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

bar and dune development during a freshet fraser river estuary british columbia canada bi weekly multi track sonar surveys collected along a 2 km reach of the estuarine south arm of the fraser river british columbia canada during seasonal high flows document the initiation development and interaction of dune and bar morphologies bedforms of several scales developed in well delineated fields bedforms that appear to fit accepted equilibrium depth scaling developed in the main channel during rising discharge when there was little local aggradation during the rising stage a bar also formed along the tidal shelf of the channel migrated downstream and expanded into the main channel dunes that formed along the bar crest a region of rapid deposition lagged flow conditions and were larger than expected based on depth scaling relations the larger dunes developed simultaneously although bar growth lagged dune development and was initially partially obscured by the more rapidly developing dune field it appears that rapid deposition enhances dune development along the channel tidal shelf to dimensions larger than would be expected by simple depth scaling rules smaller dunes that fit equilibrium depth scaling relations re established themselves throughout the study area during falling discharge when there was again little or no aggradation bed material transport rates estimated from the migration rates of the large dunes suggest that at high flows the dunes transport the majority of the material found within the bar

subaqueous yardangs analogs for aeolian yardang evolution landforms morphologically similar to aeolian yardangs but formed by erosion of bedrock by currents on an estuarine rock platform are described for the first time the geometries of the yardangs are described and related to semi lemniscate shapes that minimize hydraulic drag the processes of bedrock erosion by the reversing sediment laden tidal currents are described and a semi quantitative model for landform evolution is proposed the model casts doubt on the simple role of the maximum in the two dimensional vertical suspended sediment flux distribution and the consequent distribution of potential kinetic energy flux in the process of shaping the rock wall facing the ebb flow rather although the kinetic energy flux increases away from the bed the sediment becomes finer and abrasion likely is insignificant compared with coarse sand abrasion lower in the profile in addition the vertical distribution of sediment flux is mediated by topographic forcing which raises the elevation at which bed load intersects the yardang prow consequent erosion leads to ebb facing caprock collapse and yardang shortening in contrast the role of ebb flow separation is paramount in mediating the abrasion process that molds the rock surface facing the flood flow the length of yardangs is the least conservative dimension reducing through time more rapidly than the height and width width is the more conservative dimension which implies that once the caprock is destroyed scour over the obstacle is significant in reducing body height more so than scour of the flanks which reduces width the importance of vertical fissures in instigating the final breakdown of smaller yardangs and their extinction is noted similarities to aeolian yardang geometries and formation principles and processes are noted as are the differences the model has implications for aeolian yardang models generally

transport of fine sediment over a coarse immobile riverbed sediment transport in cobble boulder rivers consists mostly of fine sediment moving over a coarse immobile bed transport rate depends on several interrelated factors boundary shear stress the grain size and volume of fine sediment and the configuration of fine sediment into interstitial deposits and bed forms existing models do not incorporate all of these factors approaches that partition stress face a daunting challenge because most of the boundary shear is exerted on immobile grains we present an alternative approach that divides the bed into sand patches and interstitial deposits and is well constrained by two clear end member cases full sand cover and absence of sand entrainment from sand patches is a function of their aerial coverage entrainment from interstices among immobile grains is a function of sand elevation relative to the size of the immobile grains the bed sand coverage function is used to predict the ratio of the rate of entrainment from a partially covered bed to the rate of entrainment from a completely sand covered bed which is determined using a standard sand transport model we implement the bed sand coverage function in a morphodynamic routing model and test it against observations of sand bed elevation and suspended sand concentration for conditions of nonuniform fine sediment transport in a large flume with steady uniform flow over immobile hemispheres the results suggest that this approach may provide a simple and robust method for predicting the transport and migration of fine sediment through rivers with coarse immobile beds

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

the morphodynamics and internal structure of intertidal fine gravel dunes hills flats severn estuary uk in the macrotidal severn estuary uk the dynamics of intertidal fine gravel dunes were investigated these dunes are migrating across a bedrock platform systematic observations were made of hydraulic climate geometry migration rates and internal sedimentary structures of the dunes during spring tides the ebb flow is dominant dunes grow in height and have ebb orientated geometry with bedrock floors in the troughs during neap tides a weak flood flow may dominate dunes then are flood orientated or symmetrical neap dune heights decrease and the eroded sediment is stored in the dune troughs where the bedrock becomes blanketed by muddy gravel during spring tides instantaneous bed shear stresses reach 8 n m 2 sufficient to disrupt a 9 mm gravel armour layer however a sustained bed shear stress of 4 n m 2 is required to initiate dune migration at which time the critical depth mean velocity is 1 m s 1 ebb and flood inequalities in the bed shear stress explain the changes in dune asymmetry and internal structures during flood tides the crests of the dunes reverse such that very mobile sedimentary caps overlie a more stable dune core because ebb tides dominate internal structures of the caps often are characterised by ebb orientated steep open work foresets developed by strong tidal currents and some lower angle crossbeds deposited as weaker currents degrade foresets the foresets forming the caps may be grouped into cosets tidal bundles and are separated from mud infused cores of crossbeds that lie below by reactivation and erosion surfaces blanketed by discontinuous mud drapes the cores often exhibit distinctive muddy toe sets that define the spacing of tidal cosets

modelling gravity variations consistent with ground deformation in the campi flegrei caldera italy abstract in recent years 1970 72 and 1982 84 two inflation episodes took place in the campi flegrei caldera italy characterized by significant ground uplift and gravity variations an elastic half space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers following the inflation of a spherically symmetric deformation source contributions to gravity variations are produced by dilation contraction of the medium by the displacements of density interfaces the free surface and subsurface layers and of source boundaries and possibly by new mass input from remote distances into the source volume three cases were examined in detail in case i the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances in case ii deformation is due to magma differentiation within the magma chamber deformation source with constant mass in case iii the geothermal system is identified as the deformation source and a pressure increase possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber is assumed to play a dominant role from the comparison between measured and computed gravity residuals free air corrected gravity variations we can assess that in case i an inflation source with constant density would predict gravity residuals compatible with observations whereas an expansion at constant mass case ii would predict gravity residuals much lower than observed the resolving power of gravity data however prevents accurate assessment of the density of the emplaced material in case iii the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations the average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be 10 a value which is compatible with measured porosity values at campi flegrei in deep wells the subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case iii as more plausible even if a suitable combination of cases i and iii cannot be discarded

magma reservoir subsidence mechanics theoretical summary and application to kilauea volcano hawaii an analytic model has been developed for the prediction of the three dimensional deformation field generated by the withdrawal of magma from a sill like storage compartment during an intrusion or eruption cycle the model is based on the work of berry and sales 1961 1962 and predicts the vertical displacement components over the areal plane model parameters are the depth of burial h the intrusion half width a the intrusion half length b the thickness of the magmatic interior at the moment of melt withdrawal tm and the planform aspect ratio a b the products of the model include areal deformation maps systematic variation in model parameters within the context of kilauea volcano hawaii have revealed that circular and elliptical deformation patterns result from the collapse of draining rectilinear intrusions at depth moreover the geometric parameters of a storage compartment may interact in complex ways to produce similar deformation patterns the model has been applied to kilauea volcano for three periods of pronounced summit subsidence 1 1921 1927 bracketing the steamblast eruptive phases of 1924 2 june 1972 to december 1972 and 3 december 1972 to may 1973 application of the model requires the simultaneous optimization of five predicted deformation features with respect to field measurements and the derivative deformation maps 1 the vertical displacement maxima 2 the vertical displacement gradients over the areal plane 3 the lateral extent of the deformation field 4 the aspect ratio of the subsidence pattern and 5 the strike of the major axis of the deformation field the constrained geometries and volumes of the inferred collapsed storage cavities for each period are 1 1921 1927 depth 3 km a 1500 m b 4500 m tm 20 m v 540 106 m3 2 june 1972 to december 1972 depth 3 3 km a 600 m b 2000 m tm 1 m v 4 8 106 m3 and 3 december 1972 to may 1973 depth 2 2 km a 500 m b 1612 m tm 1 m v 3 2 106 m3 for 2 and 3 calculated magmatic thicknesses tm happen to be in the range 3 48 0 15 m of measurements for sill like bodies in deeply dissected hawaiian shield volcanoes the fits obtained between calculated and observed deformation patterns allow quantification of the location overall dimensions orientation and volume of the discrete still molten interior of sill like compartments from which magma is tapped during eruption or intrusion

back flow ripples in troughs downstream of unit bars formation preservation and value for interpreting flow conditions back flow ripples are bedforms created within the lee side eddy of a larger bedform with migration directions opposed or oblique to that of the host bedform in the flume experiments described in this article back flow ripples formed in the trough downstream of a unit bar and changed with mean flow velocity varying from small incipient back flow ripples at low velocities to well formed back flow ripples with greater velocity to rapidly migrating transient back flow ripples formed at the greatest velocities tested in these experiments back flow ripples formed at much lower mean back flow velocities than predicted from previously published descriptions this lower threshold mean back flow velocity is attributed to the pattern of velocity variation within the lee side eddy of the host bedform the back flow velocity variations are attributed to vortex shedding from the separation zone wake flapping and increases in the size of and turbulent intensity within the flow separation eddy controlled by the passage of superimposed bedforms approaching the crest of the bar short duration high velocity packets whatever their cause may form back flow ripples if they exceed the minimum bed shear stress for ripple generation for long enough or if much faster may wash them out variation in back flow ripple cross lamination has been observed in the rock record and by comparison with flume observations the preserved back flow ripple morphology may be useful for interpreting formative flow and sediment transport dynamics

field investigation of ridge runnel dynamics on an intertidal mudflat flow parallel linear ridge runnel r r bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at hills flats in the severn estuary uk it is argued that the sequences of sand mud laminae in the ridge sediments indicate strongly that r r are depositional bedforms faint r r topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion mechanical erosion by turbulent flows that may also carry sand and or gravel during spring tidal flow ca 60 cm s differences in flow characteristics between ridges and runnel are minor corrasion to erode or be eroded by abrasion by sparse coarse sediment largely prevents net deposition in the runnels over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and or sediment supply

sedimentary structures sorby and the last decade henry clifton sorby pioneered in the last century the description and especially the hydrodynamic interpretation of sedimentary structures together with their use as palaeocurrent indicators research completed since the last syntheses were published a decade ago shows that work along these lines continues to be necessary and relevant particularly as regards the physical explanation of structures and to present significant challenges and opportunities perhaps the most pressing needs are for a better understanding of 1 bedforms in gravels silts and carbonate sediments 2 tidal and especially sand wave bedding 3 hummocky and swaley cross stratification and 4 soft sediment and dewatering structures in turbidites many sedimentary structures present a little exploited opportunity to quantify process rates and define short time periods from the rock record

flow and grain size control of depth independent simple subaqueous dunes 1 in the gradyb tidal inlet danish wadden sea simple medium to large dunes which are superimposed on large to very large dunes increase in size with decreasing grain size under quasi constant ebb dominated mean flow conditions the mean height of the superimposed dunes increases from 0 1 m to 0 5 m and the mean dune length from 7 m to 12 m this happens over a distance of 1 5 km from the inner to the outer part where mean depth 12 m and the dominant ebb current 1 0 m s 1 remain constant over this reach the grain size changes from 0 6 mm in the inner part to 0 3 mm in the outer part as the water depth is constant and more than 1 order of magnitude larger than the height of the dunes these are regarded as being depth independent relationships between dune dimensions and grain size established in previous studies are transformed into more general statements bed form dimensions being directly related to the form corrected shields parameter in this way dune dimensions and flow strength grain size have for the first time been directly related to both bed load and free stream velocity in deeper flow systems the former relationship is based on a recalibrated form migration version of the meyer peter and muller bed load formula four diagrams describing flow conditions and dune migration rates as a function of grain size and dune length are presented

sill intrusion as a source mechanism of unrest at volcanic calderas the interpretation of dynamic processes that occur in volcanic calderas is not simple the ground deformations and the local seismicity which in other volcanic contexts are usually regarded as precursors to eruption in caldera environment in many cases are not followed by any eruption we formulate a general hypothesis that can explain these behaviors our hypothesis is that the intrusion of a sill can be responsible for the dynamics observed during unrest at calderas in order to investigate the reliability of this hypothesis we developed a dynamic model of sill intrusion in a shallow volcanic environment in our model the sill fed by a deeper magma reservoir intrudes below a horizontal elastic plate representing the overlying rocks and expands with axisymmetric geometry the model is based on the numerical solution of the equation for the elastic plate coupled with a navier stokes equation for simulating the dynamics of the sill intrusion we performed a number of simulations with the objective of showing the main features of the model in the experiments when the feeding process stops the vertical movement reverses its trend and the area of maximum uplift undergoes subsidence under certain conditions the subsidence can occur even during the intrusion of the sill the stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front the features predicted by the model are consistent with many observations carried out on different calderas as reported in the scientific literature

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany ii hydrodynamics and sediment transport the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine during daylong surveys suspended sediment concentration bedload transport rate water depth flow velocity turbulence intensity near bed shear stress and water temperature were recorded over individual isolated dunes this paper considers the hydrodynamic environment and sediment transport over the dunes a companion paper details the sedimentology and morphology of the dunes flow over the flat gravel lag upstream of large dunes is more uniform than that over dunes and gravels are rarely entrained by in bank discharges unsteady and non logarithmic velocity profiles are common within the boundary layer above the stoss side of large dunes and the near bed flow demonstrates evidence of large scale coherent low frequency flow structures these may reflect stacked sequences of separated boundary layers generated by secondary dunes however the low amplitude morphology of large dunes does not affect the statistical properties of turbulence production over the stoss sides bed roughness and near bed shear stress commonly increase steadily over the stoss of dunes but may decrease near the crest especially where a crestal platform exists that is devoid of secondary bedforms bed roughness scales with the physical size of bed roughness elements however variability in roughness lengths is large owing to the composite nature of bed roughness bedload transport over stoss slopes is spatially variable but often shows an increase with increasing bed shear stress over the stoss well formed wakes only develop downstream of lee slopes which are close to the angle of repose otherwise separation is weak and suspension and settling of fine sediments is of little consequence to dune evolution wake flow is characterized by turbulence production one order of magnitude greater than over the stoss side which may be related to vortex shedding from the dune however wake current speeds are extremely low and variable in direction reverse flow is not sustained and no retrogressive bedforms occur in the lee of large dunes near bed shear stress and bed roughness are usually low within the wake reflecting low current speeds weak wake flow reattachment occurs at a variable distance downstream up to several times the duneform height a two dimensional numerical model for flow over dune topography calibrated using average parameter values provided a reasonable description of the flow upstream and over the backs of large dunes as far as the crestal region wake flow could not be modelled however the temporal and spatial complexity of natural three dimensional flow over the dunes resulted in variance in parameter estimates this variance precluded modelling of flow and bedload transport consequently it was not possible to model dune evolution in a deterministic sense

modeling geometrical spreading and the relative amplitudes of vertical and horizontal high frequency ground motions in eastern north america abstract horizontally layered velocity models were used with point source and finite fault sources to investigate geometrical spreading and the relative amplitudes of vertical and horizontal ground acceleration within 120 km of the source full wave field simulations were done for a range of focal depths and for strike slip and reverse focal mechanisms the attenuation of the geometric mean of randomly oriented horizontal component maximum acceleration amplitudes averaged over all azimuths significantly exceeds the theoretical geometrical spreading for far field body waves in a homogeneous whole space for hypocentral distances less than approximately 60 km the behavior of the vertical component is different from the horizontal vertical attenuation near the epicenter is greater and is more dependent on source mechanism and depth because of the rapid near source decay of the direct s wave reflections from the mid lower crust and moho control the maximum amplitude of the vertical component acceleration in the 60 120 km hypocenter distance range resulting in a flattening of the vertical amplitude distance relation near source vertical maximum amplitudes averaged over all source receiver azimuths tend to be less than the geometric mean horizontal amplitude for strike slip focal mechanisms but near the source for reverse faults the azimuthally averaged vertical component amplitude exceeds that of the geometric mean horizontal the modeling indicates that similar vertical and horizontal component geometrical spreading and approximately constant horizontal vertical amplitude ratios observed in connection with the lg phase at distances greater than approximately 100 km in eastern north america may not hold at smaller distances ground motion prediction models for the vertical component near the source may need to incorporate strong geometrical spreading and dependence on radiation pattern

ground motion prediction equations for central and eastern north america a new ground motion prediction equation gmpe model for central and eastern north america cena is presented the graizer 2016 g 16 model is based on the next generation attenuation east nga east database for this horizontal peak ground acceleration and 5 damped pseudospectral acceleration rotd50 component goulet et al 2014 the cena database is not sufficient for creating purely empirical gmpe with recordings covering mostly a range of moment magnitudes m 6 0 and a limited number of near fault recordings the functional forms of the g 16 model are derived from filters representing a particular physical phenomenon affecting the seismic wave radiation from the source following the approach developed by graizer and kalkan 2007 2009 and 2011 for active tectonic environment main changes in the functional forms for cena relative to the western united states model graizer and kalkan 2015 are a shift of maximum frequency of the acceleration response spectrum rs toward higher frequencies and an increase in rs amplitudes at high frequencies the developed site correction is based on multiple runs of representative v s 30 profiles through shake type equivalent linear codes site amplifications are calculated relative to the hard rock definition used in nuclear industry v s 2800 m s the number of model predictors is limited to a few measurable parameters such as moment magnitude m closest distance to fault rupture plane r rup v s 30 and anelastic attenuation factor q incorporating q as an input parameter allows adjustments based on the regional crustal properties the model is applicable for the stable continental regions and covers the following range 4 0 m 8 5 0 r rup 1000 km 450 v s 30 2800 m s and frequencies 0 1 f 100 hz

structural and rheological constraints on source depth and overpressure estimates at the campi flegrei caldera italy ingv gruppo nazionale per la vulcanologia ministero dell istruzione universita e ricerca firb project

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

determination of shear and compressional wave velocity variations and hypocenter locations in a rapidly inflating caldera the campi flegrei during 1982 1985 the campi flegrei caldera underwent a large h 1 7 m rapid hmax 2 mm day 1 and localized radius 6 km uplift p and s arrival times from three component digital seismograms recorded during this period have been used to invert for hypocenter locations and for three dimensional shear and compressional velocity to 3 km first order residual based tomography shows a significant and well resolved high p s ratio anomaly for the volume encompassing the central caldera and the active solfatara crater three dimensional tomographic inversion resolves this central anomaly as a zone of depressed p and s with a high 2 1 p s ratio the three dimensional velocity model and hypocenter distribution are consistent with modeling the central caldera as a zone of nearly water saturated cracks presumably a result of recurrent inflation and deflation in a zone with a shallow water table although the presence of small shallow magma bodies is not precluded

hydrodynamics of a forced riffle pool in a gravel bed river 2 scale and structure of coherent turbulent events 1 in the companion article we present mean velocity and turbulence intensity statistics at a range of discharges in a forced riffle pool unit and show that the distributions of mean velocity and turbulence are characteristic of nonuniform flows the objectives of this paper are to describe the spatial and temporal variability of the structure of turbulence in the forced riffle pool unit and to examine turbulence generation mechanisms and the links between the scales of macrobed forms and coherent turbulent flow structures our results show that while larger scale structures develop outside of the thalweg the scales of coherent turbulent flow structures decrease with velocity and discharge in the forced riffle pool flow separation is shown to be an important factor with full separation occurring in lateral shear zones and intermittent separation near the bed in the pool head these zones generate new turbulence that disrupts a number of coherent turbulent flow structures that are typical of uniform flows coherent turbulent flow structures do not appear to be the source of morphological scaling in the forced riffle pool

an experimental study into the geometry of supply limited dunes the relationship between dune geometry and the volume of mobile sediment was studied in flume experiments in these flume experiments the volume of mobile sediment on top of an immobile coarse sediment layer was increased stepwise and the bedform characteristics were observed a strong relationship was found between the volume that is mobile and therefore available for bedform formation and the dune dimensions and regularity if the sediment supply is limited dunes are smaller and more regular series of experiments with a decreasing supply limitation were conducted for different flow velocities and water depths the relationship between the dune dimensions and the available volume is different for each series the observed relationships between dune dimensions and layer thickness collapse to one relationship for height and one for length if scaling parameters are introduced current models for bedform dimensions under alluvial conditions can be extended to partial transport conditions using this relationship

a statistical model for ground motion produced by earthquakes at local and regional distances to adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models we constrain the parameters of duration geometrical spreading and spectral shape by modeling the main ground motion as being the result of major contributions by the direct s wave and supercritically reflected s waves the results of our modeling are constrained to be consistent with values from full wave synthetics for the test models the combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements velocities and accelerations of the 1982 miramichi earthquakes in new brunswick canada in addition upon considering the effects of source depth and crustal structure for the november 25 1988 saguenay earthquake m 5 8 in quebec canada the predicted mean peak horizontal ground accelerations match the observed data very well the effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges

sand wave migration predictor based on shape information 1 migration of offshore seabed waves which endangers the stability of pipelines and communication cables is hard to measure the migration rates are small compared to the measurement errors here sandwave migration rates are determined from the change in the crest position deduced from long time series of bathymetric echo sounding data the crests are identified as local extremes in a bathymetric profile after low pass filtering this approach is applied to both two dimensional data and to profiles along pipelines a consistent migration rate of several meters per year is found a strong correlation between the sandwave shape and the migration rate is translated in a migration predictor the predictor assumes that the sandwaves migrate in the direction of the steepest slope following a quadratic relation with the asymmetry furthermore it is included that longer waves travel faster but higher waves travel slower the predictor is calibrated against data from nine areas and validated using three additional areas an error analysis using markers shows that the error of the predictor is small compared to the noise in the individual crest position observations

response of low angle dunes to variable flow current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments there are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides as a consequence the ability to predict bedform response to variable flow is rudimentary using high resolution multibeam bathymetric data this study explores the dynamics of a dune field developed by tidally modulated fluvially dominated flow in the fraser river estuary british columbia canada the dunes were dominantly low lee angle features characteristic of large deep river channels data were collected over a field ca 1 0 km long and 0 5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet yielding the most comprehensive characterization of low angle dunes ever reported the data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs then increasing as the tide rises and the flow velocities decrease bedform lengths do not appear to respond to the changes in velocity caused by the tides changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity indicating that changes in the bedform geometry lag changes in the flow the data reveal that lee angle slope responds directly to suspended sediment concentration supporting previous speculation that low angle dune morphology is maintained by erosion of the dune stoss and crest at high flow and deposition of that material in the dune trough

discriminating between pore filling load and bed structure load a new porosity based method exemplified for the river rhine sediments contained in the river bed do not necessarily contribute to morphological change the finest part of the sediment mixture often fills the pores between the larger grains and can be removed without causing a drop in bed level the discrimination between pore filling load and bed structure load therefore is of practical importance for morphological predictions in this study a new method is proposed to estimate the cut off grain size that forms the boundary between pore filling load and bed structure load the method evaluates the pore structure of the river bed geometrically only detailed grain size distributions of the river bed are required as input to the method a preliminary validation shows that the calculated porosity and cut off size values agree well with experimental data application of the new cut off size method to the river rhine demonstrates that the estimated cut off size decreases in a downstream direction from about 2 to 0 05 mm covariant with the downstream fining of bed sediments grain size fractions that are pore filling load in the upstream part of the river thus gradually become bed structure load in the downstream part the estimated mass percentage of pore filling load in the river bed ranges from 0 in areas with a unimodal river bed to about 22 in reaches with a bimodal sand gravel bed the estimated bed porosity varies between 0 15 and 0 35 which is considerably less than the often used standard value of 0 40 the predicted cut off size between pore filling load and bed structure load dc p is fundamentally different from the cut off size between wash load and bed material load dc w irrespective of the method used to determine dc p or dc w dc w values are in the order of 10 1 mm and mainly dependent on the flow characteristics whereas dc p values are generally much larger about 100 mm in gravel bed rivers and dependent on the bed composition knowledge of dc w is important for the prediction of the total sediment transport in a river including suspended fines that do not interact with the bed whereas knowledge of dc p helps to improve morphological predictions especially if spatial variations in dc p are taken into account an alternative to using a spatially variable value of dc p in morphological models is to use a spatially variable bed porosity which can also be predicted with the new method in addition to the morphological benefits the new method also has sedimentological applications the possibility to determine quickly whether a sediment mixture is clast supported or matrix supported may help to better understand downstream fining trends sediment entrainment thresholds and variations in hydraulic conductivity