morphodynamic characteristics in a tidal inlet san blas argentina abstract a tidal inlet on the argentinean coast is studied an integrated approach of combining detailed bathymetry survey seabed sampling and tidal current measurements was used to characterize the tidal inlet morphodynamics a phase measuring bathymetric system pmbs geoswath plus from geoacoustics ltd with centimetric precision and a mean swath coverage of 160 m was used to recognize bedform morphologies and to determine bedform dynamics by comparison of successive surveys tidal velocities were recorded during a complete tidal cycle using an adcp mounted on a ship operating at a frequency of 650 khz maximum tidal currents of the order of 2 m s 1 exhibit different patterns across the channel while maximum ebb currents dominate in the central and southern area of the channel flood maximum currents dominate on the northern flank the complex morphology of a dune field in an inlet and the resulting 3 d dune movement mechanism are also presented in the middle of san blas channel a field with symmetrical large dunes 10 100 m in spacing and very large dunes 100 m in spacing 4 5 to 5 m in height was found dune migration rates were measured by comparing two successive morphological maps of the field reaching a rate up to 21 m year 1 toward the ocean in contrast the smaller dunes present on the northern border of the field migrate in an inward direction at a rate of 15 7 m year 1

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

flow fields bed shear stresses and suspended bed sediment dynamics in bifurcations of a large river 1 channel bifurcations associated with bars and islands are important nodes in braided rivers and may control flow partitioning and thus affect downstream confluences as well as the formation and dynamics of bars however the morphodynamic processes associated with bar formation are poorly understood and previous studies have largely concerned laboratory experiments small natural streams or numerical analyses with large froude numbers high slopes and low shields stresses in these cases the morphologic changes at bifurcations are relatively rapid with predominant bed load transport and the suspended load playing a minor role in this paper the evolution of the flow structure and suspended bed sediment transport along four expansion diffluence units in the rio parana argentina are described the rio parana is a large multichannel river with a bed composed of medium and fine sands and possesses low froude numbers and high suspended bed material transport primary and secondary flow velocity components were measured with an acoustic doppler current profiler adcp along the expansion diffluence units and the backscatter signal of the adcp was calibrated to allow simultaneous measurements of suspended bed sediment concentrations the interactions between these variables show that the cores of primary flow velocity and suspended bed sediment concentration do not necessarily follow the thalweg at the bifurcation and that inertial effects on the suspended bed sediment may influence the morphodynamics of bar formation it is suggested that changes in flow stage as well as the presence of vegetation may further increase the deposition of suspended bed sediment at the bar head this study suggests that the ratio of suspended bed material to bed load is an important factor controlling the morphodynamics of bifurcations in large sand bed braided rivers

influence of vegetal cover on sediment particle size distribution in natural rainfall conditions in a semiarid environment abstract sediment samples were collected during four years from two plots one covered by natural vegetation and the other a replica of the same plot from which the vegetation was removed manually disturbed plot in order to evaluate the effects of vegetal cover on sediment particle size distribution particle size was measured using a coulter ls130 laser diffraction device the effective size distribution of the sediment was compared with equivalent measurements of the same samples after chemical and mechanical dispersion ultimate size distribution to investigate the detachment and transport mechanisms involved in sediment mobilisation the ratio between the ultimate particle size composition of the transported sediment and that of the parent soil provided a measure of the particle size selectivity of the transported sediment the median effective particle was coarser than the median ultimate particle for almost all the events recorded in both plots confirming that much of the sediment in the runoff includes a substantial proportion of aggregates moreover the texture of the sediment was finer than that of the matrix soil with a depletion of clay and sand in exchange for an enrichment in silt indicating the existence of transport selectivity in both plots the effect of vegetal cover on the size distribution of the sediment was particularly evident after high intensity rainfall events an i30 of 40 mm h 1 was found to be the threshold value for changes to be produced in the sediment texture of the disturbed plot with aggregates being broken down and 10 20 more sand particles being observed at this value than after events of lower intensity no differences were found in the natural plot after rainfall of varying intensities the vegetal cover in the natural plot reduced the energy available for erosion from the rainfall by 50 and the energy from the runoff by 75 hindering the break down of aggregates and the transport of dense particles moreover the presence of vegetation meant the raindrop was the predominant contributor to soil loss in contrast to the disturbed plot where both raindrop and runoff contributed to the erosion

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

measuring flow velocity and sediment transport with an acoustic doppler current profiler an acoustic doppler current profiler adcp measures three dimensional velocity profiles within the water column using the doppler shift principle whilst the bottom tracking function and acoustic backscatter can be used to measure bed load velocity and estimate suspended sediment concentration the adcp offers many advantages over traditional single point current meters and sediment samplers including deployment from a moving launch a single instrument for both velocity and sediment transport measurements profiles of three dimensional velocity and suspended sediment and the ability to map an entire flow field limitations of adcps include a large sampling diameter close to the bed coarse measurement of vertical velocity fragmented bottom track records a poor understanding of the relation between bottom tracking and the mechanisms of sediment transport and sensitivity of the acoustic backscatter to particle size

source effects on regional seismic discriminant measurements source effects on high frequency regional seismic discriminant measurements involving p s type ratios pn lg pg lg are isolated for earthquakes in southern california and southern nevada the scatter in earthquake population discriminant measurements for fixed propagation paths is statistically analyzed to assess the spatial and frequency dependent contributions from source radiation pattern and source depth variations along with variable near source scattering this is useful because procedures for reducing the variance caused by propagation effects must be constrained by knowledge of the intrinsic scatter resulting from independent source effects for which corrections are not available without a priori knowledge of the source type and depth broadband waveforms for earthquakes near the nevada test site nts and in southern california recorded at stations of the livermore nts network lnn the caltech terrascope network and the berkeley digital seismic network bdsn are used to obtain pg lg and pn lg measurements and to assess source depth and mechanism contributions to measurement variance pn lg and pg lg spectral amplitude ratios for several frequency bands between 0 5 and 10 hz from vertical velocity waveforms are computed for a total of 18 tightly located clusters of earthquakes for each cluster we examine the correlations between observed pn lg and pg lg ratios and estimated source depths or predictions based on previously determined source mechanisms focal mechanism predictions do not match the observations well likely due to strong near source scattering and directivity effects that overwhelm the point source radiation pattern however the data do show significant scatter even for sources only a few kilometers apart source depth produces some coherent trends which can be emphasized by averaging results from multiple stations these trends vary from region to region presumably due to specific local crustal layering but most of the variance is not deterministically predictable and appears to arise from strong variations in near source scattering variance estimates for logarithmic amplitude ratios normalized by mean amplitude ratios vary from 0 01 to 0 05 for different phase pairs frequency dependent variations of the mean variance minimum and maximum amplitude ratio parameters show strong distance dependence out to about 300 km and then appear to become independent of event station distance these variance parameters appear to be suitable for use in spatial interpolations of observed p s type ratios for a specific unidentified event path as needed for nuclear test monitoring

spectral discrimination of nts explosions and earthquakes in the southwestern united states using high frequency regional data a high frequency seismic station has been operating since march 1987 near nelson nv records of earthquakes at regional distances from the station show substantially more energy at frequencies above 10 hz than records of nuclear tests of comparable magnitude on the nevada test site this contradicts the predictions made by investigators who have advocated high frequency monitoring for nuclear test detection and identification measuring the slopes of the pg velocity spectra between 4 and 30 hz successfully discriminates 11 nts explosions from 36 earthquakes recorded in the first seven months of operation the spectral differences may result from the respective source depths with the earthquakes occurring deeper and in faster material than the explosions

instruments for particle size and settling velocity observations in sediment transport in this paper we describe two sensors for measurement of particle size distribution and settling velocity distribution these measurements are critical to the correct estimation of the true sediment concentration in the field as well as to evaluating models for transport rates of sediments a multi angle measurement of laser scattering is made and inverted to obtain the particle size distribution since small angle scattering is relatively insensitive to particle composition the size distribution measurements are robust and do not require particle refractive index it is shown that with a knowledge of the size distribution true particulate volume concentration can be obtained unaffected in calibration by changes in particle size distribution the data from bottom boundary layer experiments using the instrument show the presence of temporal variability in size distribution associated with the strength of forcing of the boundary layer the importance of these observations lies in the implication that historical data acquired with single parameter optical or other sensors needs to be revisited in the second instrument analyzing the observation of size distributions during settling in a settling column produces settling velocity estimates in this case the history of concentration of each size class is examined to determine the settling velocity without invoking any assumptions of settling regime settling velocity data from a field experiment off the new jersey coast fit the model wf na 0 45 10 23 a 1 2 n

an evaluation of seismic decoupling and underground nuclear test monitoring using high frequency seismic data an effective solution to the problem of the detection and identification of low yield coupled and fully decoupled underground nuclear explosions appears available via use of high frequency seismic data ranging up to 30 or 40 hz in order to evaluate detection identification capabilities when using such data it is necessary to estimate 1 spectral characteristics and relative amplitudes of both p and s waves from explosions and earthquakes over the frequency band from 5 to 40 hz 2 signal transmission characteristics over this band through pertinent types of earth structure and 3 recording system and ground noise characteristics over this frequency band in this study each of these topics is considered in turn as they relate to detection and discrimination of the signals from low yield coupled and decoupled explosions in the regional and teleseismic distance ranges estimates of the capabilities of specific hypothetical networks to detect and identify insofar as signal to noise ratio is an important factor in identification explosions within the ussr are then considered these estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability following the assessment of detection capabilities the problem of identification of small events is considered with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal to noise ratio the principal results and conclusions of this study are as follows 1 seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30 40 hz when using presently available hardware 2 average amplitudes of high frequency noise in a variety of geological environments are very low and change little with time or season 3 transmission of high frequency p and s wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 hz with effective q factors in shield areas being about 9000 and 4000 for high frequency pn and sn respectively while the effective q for pn waves in tectonic areas is about 1000 4 a properly designed and deployed network of 25 simple three component nonarray stations internal to the ussr and 15 similar stations surrounding the ussr is predicted to be capable of multistation detection at high signal to noise ratio of fully decoupled 1 kt explosions located at all potential decoupling sites within the ussr 5 by inference from the quantitative agreement of empirical observations and theoretical predictions when using lower frequency data over a great range of explosion yields we conclude that procedures based on the use of both detectable p and s waves will serve to identify explosion generated seismic signals at least as small as those expected from a fully decoupled 1 kt explosion

a case study of the seismic source function salmon and sterling reevaluated as part of a larger joint effort by the defense advanced research project agency and the department of energy to study the seismic source problem a comprehensive reevaluation of the 1964 salmon and 1966 sterling nuclear explosions in dome salt was carried out the sterling source function originally estimated by springer et al 1968 conveys the impression that the cavity was badly overdriven on reexamination this does not appear to be the case the work of glenn et al 1987 on the sterling free field data is expanded upon confirming that the cavity response was close to the theoretical expectation sterling s source function is estimated and is found to be comparable to patterson s 1966 slightly weakened salt model a source model for salmon is derived from the sterling source model and the five seismic stations that recorded both events the new source model has a reduced displacement potential of about half that previously estimated a temporary nonlinear two wave system developed during the salmon explosion as the compressional wave evolved from a shock wave the separation of these two waves resulted in a high frequency roll off of the reduced velocity potential of 3 in addition it is shown that the comer frequency is much higher and is created much closer to the cavity than the eigenfrequency for both salmon and sterling the radial stresses are approximately a low passed damped sinusoid superimposed on a small step function the decoupling value of 72 obtained by springer et al 1968 is confirmed a revision of patterson s 1966 partial decoupling curve shows that the value for full decoupling in a shot generated cavity would be only slightly higher contrary to previous studies decoupling as a function of frequency for the surface waves is found to be the same as for the p waves a new definition of decoupling appropriate to threshold test ban treaty monitoring is also proposed

the influence of flow discharge variations on the morphodynamics of a diffluence confluence unit on a large river 2017 the authors earth surface processes and landforms published by john wiley sons ltd bifurcations are key geomorphological nodes in anabranching and braided fluvial channels controlling local bed morphology the routing of sediment and water and ultimately defining the stability of their associated diffluence confluence unit recently numerical modelling of bifurcations has focused on the relationship between flow conditions and the partitioning of sediment between the bifurcate channels herein we report on field observations spanning september 2013 to july 2014 of the three dimensional flow structure bed morphological change and partitioning of both flow discharge and suspended sediment through a large diffluence confluence unit on the mekong river cambodia across a range of flow stages from 13 500 to 27 000 m 3 s 1 analysis of discharge and sediment load throughout the diffluence confluence unit reveals that during the highest flows q 27 000 m 3 s 1 the downstream island complex is a net sink of sediment losing 2600 2000 kg s 1 between the diffluence and confluence whereas during the rising limb q 19 500 m 3 s 1 and falling limb flows q 13 500 m 3 s 1 the sediment balance is in quasi equilibrium we show that the discharge asymmetry of the bifurcation varies with discharge and highlight that the influence of upstream curvature induced water surface slope and bed morphological change may be first order controls on bifurcation configuration comparison of our field data to existing bifurcation stability diagrams reveals that during lower rising and falling limb flow the bifurcation may be classified as unstable yet transitions to a stable condition at high flows however over the long term 1959 2013 aerial imagery reveals the diffluence confluence unit to be fairly stable we propose therefore that the long term stability of the bifurcation as well as the larger channel planform and morphology of the diffluence confluence unit may be controlled by the dominant sediment transport regime of the system 2017 the authors earth surface processes and landforms published by john wiley sons ltd

spectral discrimination between soviet explosions and earthquakes using short period array data summary spectral ratio discriminants are applied to 61 presumed nuclear explosions five large chemical explosions and 44 earthquakes in the soviet union recorded at the four uk teleseismic arrays the nuclear explosions were mainly from the shagan test site sts and from peaceful nuclear explosions pne ranging in magnitude from 4 2 to 6 2 the earthquakes were mostly located in the south central soviet union and range in magnitude from 4 4 to 5 9 for each event station pair the p wave spectrum is calculated out to 10 hz using a 5 s window from the time domain array beam and from a spectral stack the spectral ratios from the array beam in the 0 5 1 0 hz and 2 0 3 0 hz frequency bands appear to give the best discrimination performance at higher frequencies reduced signal to noise ratios particularly for the earthquakes result in fewer measurements and increased scatter in general the explosions are characterized by the existence of more high frequency energy than the shallow crustal earthquakes a least squares matrix factorization approach is used to separate out source and path effects the separation of earthquakes and explosions is generally quite good down to magnitude 4 5 where the two populations merge because of signal to noise problems the spectral values from the pnes shows increased scatter relative to those from sts presumably due to their wider range of emplacement conditions and geologic environment previous studies using regional phases indicate that nts explosions are deficient in high frequencies relative to western us earthquakes these contrasts in frequency content between nts and sts explosions may be caused by differences in the near source dynamic material response to the passage of the explosion shock wave or to depth dependent effects of q

sedimentology and geochemistry of lacustrine terraces of three middle atlas lakes paleohydrological changes for the last 2300 cal bp in morocco western mediterranean region abstract in the moroccan middle atlas mountains three lakes were used to characterize climate variability in the late holocene the methodology is based on sedimentological geochemical and mineralogical analysis of lacustrine terraces lake ifrah is a natural lake waters are calc magnesian relatively very alkaline and oxygenated lake afourgagh is of karst origin with maximum depth 1 5 m lake iffer is a smaller lake sub circular and relatively deep its area is 3 5 ha its maximum depth is 6 5 m at the center of the lake seven terraces located in the borders of the lakes were sampled and studied seven radiocarbon dates were obtained on organic matter and shells the time period concerned is between 2300 cal bp and 400 cal bp the results show high lake levels at about 2300 cal bp related probably to the wetter iberian roman period in northern mediterranean lake iffer was deeper by about 30 m from its current level 1000 cal bp probably marks the beginning of the decline with a drop in lake level of 20 m which is ongoing in connection with drier climate and the beginning of the medieval climate anomaly

suspended sediment concentration and calibre in relation to surface flow structure in squamish river estuary southwestern british columbia surface grabs of suspended sediments from boils and the background flow in squamish estuary revealed strong differences between the two environments boils exhibit higher sediment concentrations and larger particle sizes than the background flow the higher sediment concentrations and larger grain sizes in boils are related to tidal phase with maximum concentrations and sediment sizes occurring in the early decelerating phase of the tidal flow sediment concentrations and grain sizes in the background flow are comparatively invariant with tidal phase boils appear to play an important if not dominant role in suspending and transporting sand sized sediments in squamish estuary

field measurements of three dimensional hydraulics in a step pool channel we investigated the effects of morphologic position and discharge on flow structure in a steep 0 10m m mountain channel by collecting three dimensional measurements of time averaged and turbulent velocity components with a sontek flowtracker handheld adv acoustic doppler velocimeter on a 30 m reach of a step pool channel in the colorado rockies velocity profiles were measured at morphologic positions characteristic of steep channels above steps step lips base of steps pools cascades runs and at five different discharges a marked three dimensionality of flow structure was documented in east st louis creek velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes cross stream and vertical components contributed averages of 20 and 15 respectively to overall vector magnitudes turbulence intensities were especially multi dimensional however with large contributions to turbulent kinetic energy from the vertical component of velocity analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities with substantially higher velocities upstream from steps than in pools discharge and morphology effects on cross stream and vertical velocity components however were not significant discharge and morphologic position also significantly affected turbulence intensities for all flow components with the greatest turbulence intensities occurring in pools and at high discharges these results illustrate the strong discharge dependence of hydraulics in step pool channels where relative submergence of bedforms changes rapidly with discharge and the substantial spatial variation in hydraulics created by step pool sequences

measuring suspended sediment concentrations using acoustic backscatter devices abstract in recent years the requirement to develop a technique for measuring suspended sediment concentration profiles with similar temporal and spatial resolution to that of electromagnetic current meter measurements of the flow has led to the development of an acoustic approach acoustic backscatter devices have been constructed and deployed in marine environments and measurements of backscattered signal profiles obtained however the translation from acoustic returns to suspended load has been an empirical procedure resulting in some uncertainty regarding the accuracy and reliability of the conversion process to address this problem a series of laboratory measurements of acoustic backscattering from marine suspensions were conducted using two acoustic backscatter instruments operating at 3 0 and 5 65 mhz a simple semi empirical backscattering theory has been developed to predict the form of the scattered signal and comparisons have been made of the concentrations predicted from the theory against concentration measurements made in laboratory tanks the results show that the main features of the backscattering signal can be explained and accurate concentration estimates can be made from the acoustic returns it is concluded that acoustic backscatter techniques are potentially powerful tools for examining at high resolution the structure of suspended sediment concentration profiles near the seabed

size characteristics of sediment in interrill overland flow on a semiarid hillslope southern arizona this study examines the size characteristics of sediment removed from a semiarid hillslope by interrill overland flow rainfall simulation experiments were conducted on a runoff plot 18 m wide and 35 m long established on a piedmont hillslope in southern arizona the top of the plot coincided with the hillslope divide and its outlet was located within a shallow rill samples of runoff were obtained from two cross sections located in the interrill portion of the plot upslope of the rill and from a calibrated flume through which was directed interrill overland flow reaching the bottom of the plot analyses of sediment contained in these samples showed that sediment in interrill flow is finer than the matrix soil the fineness of the interrill sediment compared to the matrix soil appears to be due to the inability of interrill overland flow to transport the coarser fraction of the sediment supplied to it by raindrop detachment this finding implies that the rate of soil erosion in interrill areas is not as is commonly supposed limited by the rate at which raindrops can detach sediment but by the rate at which they detach sediment of a size that the overland flow is competent to transport the relative fineness of sediment eroded from this hillslope is consistent with other evidence for the recent evolution of shrub covered hillslopes in southern arizona

analysis of high frequency pg lg ratios from nts explosions and western u s earthquakes the high frequency pg lg discriminant is studied between frequencies of 0 5 and 10 hz using 294 nts explosions and 114 western u s earthquakes recorded at four broadband seismic stations operated by lawrence livermore national laboratory the stations are located at distances of about 200 to 400 km from the nevada test site nts event magnitudes ranged from about 2 5 to 6 5 and propagation paths for the earthquakes range from approximately 175 to 1300 km the discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased because of propagation effects it is important to apply distance corrections directly to the amplitude ratios or to the magnitude corrected amplitudes prior to computing the ratios multivariate discrimination analysis using both maximum likelihood gaussian classifiers and a backpropagation neural network show that approximately 95 of the events can be correctly identified both classification procedures were designed to handle missing data filled in using a nearest neighbor algorithm except for a few notable exceptions most of the earthquake misclassifications occur for mb 4 which is expected for events having reduced signal to noise ratios all of the explosion misclassifications occur for mb 4 suggesting a source or near source effect rather than an effect of poor signal to noise ratio the explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb ms or love wave energy the main drawback of the pg lg discriminant is that because of signal to noise considerations and propagation effects the number of measurements are reduced considerably at higher frequencies it is expected that the problem will be amplified as magnitudes are reduced and event receiver distances are increased

transpressional tectonics in the marrakech high atlas insight by the geomorphic evolution of drainage basins the ouzzelarh massif extends across the marrakech high atlas mha and forms the highest elevated mountain belt to better understand the evolution of collision related topography we present the results of a geomorphological study in which elevation changes generated by reactivated pre alpine variscan and triassic jurassic faults drive a landscape evolution model we aim to evaluate the relationship between the geometry of the drainage network and the main fault systems in this region new insight into geomorphological changes in drainage patterns and related landforms is based on geological fieldwork combined with dem analysis to quantitatively measure landscape features we used several classical geomorphic indices spacing ratio hypsometric curves and integral stream frequency drainage stream length gradient the ouzzelarh massif is bounded to the north by the tizi n test fault zone ttfz and to the south by the sour fault zone sfz these faults delimit a pop up structure by using the above geomorphic parameters we ascertained that the ouzzelarh massif is affected by a high spatial variability of uplift the actual landscape of the ouzzelarh massif reveals remnants of an uplifted ancient erosional surface and the heterogeneity of exposed rocks in the range explaining the possibility that the topographic asymmetry between north and south flanks is due to differences in lithology controlled resistance to erosion drainage topography and fault pattern all concur to show uplifted rhomboidal shaped blocks it exhibits high stream frequency drainage and uplift in separate tectonically uplifted blocks such as jebel toubkal which is characterized by asymmetric drainage basins

application of a roughness length representation to parameterize energy loss in 3 d numerical simulations of large rivers 1 recent technological advances in remote sensing have enabled investigation of the morphodynamics and hydrodynamics of large rivers however measuring topography and flow in these very large rivers is time consuming and thus often constrains the spatial resolution and reach length scales that can be monitored similar constraints exist for computational fluid dynamics cfd studies of large rivers requiring maximization of mesh or grid cell dimensions and implying a reduction in the representation of bedform roughness elements that are of the order of a model grid cell or less even if they are represented in available topographic data these subgrid elements must be parameterized and this paper applies and considers the impact of roughness length treatments that include the effect of bed roughness due to unmeasured topography cfd predictions were found to be sensitive to the roughness length specification model optimization was based on acoustic doppler current profiler measurements and estimates of the water surface slope for a variety of roughness lengths this proved difficult as the metrics used to assess optimal model performance diverged due to the effects of large bedforms that are not well parameterized in roughness length treatments however the general spatial flow patterns are effectively predicted by the model changes in roughness length were shown to have a major impact upon flow routing at the channel scale the results also indicate an absence of secondary flow circulation cells in the reached studied and suggest simpler two dimensional models may have great utility in the investigation of flow within large rivers

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

pleistocene plateau ice fields in the high atlas morocco large ice fields 25 km2 formed over the tazaghart and iouzagner plateaux of the high atlas morocco during the late pleistocene the plateau ice fields were drained by large valley glaciers forming a series of moraine assemblages four moraine units have been mapped and subdivided on the basis of morphostratigraphy and the degree of soil weathering soil profile development index pdi values indicate that the moraine units are widely separated in time with the oldest moraines deeply weathered and degraded whereas soils are absent on the youngest moraines the highest moraine unit was formed by a small niche glacier which was present as recently as the mid 20th century pleistocene glaciers are likely to have been associated with wetter conditions than today in addition to colder air temperatures combined with ice in neighbouring areas such as the toubkal massif the sw high atlas supported some of the largest glaciers in africa during the pleistocene the extent of glaciation with ice exploiting and breaching drainage divides has major implications for landscape development the evolution of the high atlas is therefore strongly shaped by glaciation and this is closely intertwined with tectonic fluvial and slope processes

near source effects on regional seismograms an analysis of the nts explosions pera and queso a comparative analysis of two closely spaced nevada test site explosions pera and queso is made to study the effects of near source phenomena on regional wave excitation although the two explosions were of similar size burial depth and only separated by 4 km the 1 to 2 and 6 to 8 hz regional wave spectral ratio for queso is anomalously low a factor of 10 smaller than that of pera examination of the regional and close in spectra for each event shows a remarkable similarity and suggests that queso has less low frequency and more high frequency energy than pera these observations may be caused by a 564 m3 funnel shaped region filled with unconsolidated sand and a possible void directly above the queso detonation point close in observations suggest that this region may have partially decoupled the up going energy from queso resulting in a reduction of the low frequency energy the high frequency enhancement for queso may be due to the rapid loss of energy to nonlinear effects such as greater pore collapse and fracturing in the anomalous region this resulted in the radiation of more impulsive shorter duration waveforms producing a higher corner frequency and less rapid high frequency spectral decay for queso for pera the loss of energy to a two wave system occurred more slowly and over a larger volume resulting in a broader source pulse typical of explosions in porous materials comparison of shock radius versus time data suggests that the shock wave was strongly affected in the anomalous zone a few meters above the queso device one dimensional finite difference calculations with and without a partial decoupling region within 8 m of the device are consistent with the observations although spallation was reduced for queso simulations using a finite spall model indicate that the spall spectral peak should be centered at about 3 to 7 hz and probably did not significantly contribute to the reduced spectral ratio the remarkable similarity of the pera queso spectral ratios taken at distances of 90 m and 400 km suggests that the spectral characteristics of explosions are established in close proximity to the source although depth dependent effects of attenuation acting at small strains may enhance the differences in spectral ratios between nts explosions and western u s earthquakes these effects are probably secondary to the high pressure high strain rate dynamic material response to the radiated explosion shock wave these observations point out the importance of up going energy on the generation of regional phases from explosions because of reduced overburden pressures above the detonation point large nonlinear deformations predominate in this region and appear to affect all of the signals except perhaps the very initial part of the pn waveform

acoustic doppler current profiler measurements in coastal and estuarine environments examples from the tay estuary scotland acoustic doppler current profilers adcps provide a means to measure the components of water current velocities in three dimensions such instruments have been used widely by the oil industry in deep offshore waters but their application to nearshore coastal and estuarine environments has been principally confined to the usa using examples of adcp datasets acquired from the macrotidal tay estuary eastern scotland the principles of field deployment data acquisition and forms of output are critically summarised it is shown for the first time in the tay estuary that vertical current velocities are significant and are particularly so in downwelling zones associated with the development and passage of axially convergent tidal fronts the improved understanding of three dimensional water and suspended sediment dynamics in coastal and estuarine waters is crucial to inter alia the sustainable management of effluent discharges and in more general terms it is predicted on the basis of the tay case study that adcp measurements afford significant opportunities to refine understanding of geomorphological processes in a variety of aquatic environments worldwide

on the remote acoustic detection of suspended sediment at long wavelengths experimental results are presented which indicate a linear relation between the time averaged amplitude of the envelope of the backscattered acoustic pulse at 192 khz and the square root of suspended sediment concentration in the 10 to 103 mg 1 1 range particle sizes ranged from 2 to 140 m the measurements were made in a negatively buoyant mine tailing discharge plume in a submarine channel at depths of 60 to 90 m in rupert inlet british columbia from the theory of acoustic backscatter from a solid elastic sphere in the rayleigh region it is shown that if the pressure amplitude of the backscattered wave is rayleigh distributed then such a linear relation is to be expected expressions for the optimum acoustic frequency for the detection of dilute suspensions at a given range and for the minimum detectable concentration are obtained assuming a thermal noise background the possibility that bubbles contribute to the backscatter is considered and found to be unlikely on the basis of probable bubble lifetimes

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

a field comparison of three pressure difference bedload samplers abstract the movement of bedload over a cross section is often sampled using a pressure difference bedload sampler such as the helley smith whereas several types are in use no one device has gained universal acceptance as the standard for use in all types of streams moreover evidence suggests that similar devices may collect substantially different amounts of bedload because of only slight modifications in design in this study sample weights collected by three types of pressure difference samplers are compared to determine whether differences are statistically significant or whether sampler performance is so irregular and overlapping that one might regard them as being the same the results confirm that the weights of samples collected by the devices are significantly different generally the us blh 84 collected less material the sheetmetal helley smith collected more material and the original helley smith was intermediate these tendencies were consistent at two sites where bedload was measured the implication of these results is that measured transport rates will vary depending on the sampler used and therefore they are not directly comparable without some mode of calibration to place this finding in a larger context sediment rating curves determined from weights of samples and measurements of flow were integrated over available flow records and used to estimate annual yield three estimates of annual yield one for each device were then compared with measures of annual accumulation from a weir pond below one of the collection sites the results indicate that despite differences between the devices data obtained with pressure difference samplers estimated annual accumulations of sediment reasonably well predicted accumulations were within 40 50 of the measured yield for two samplers whereas the third sampler predicted within 80

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

the lowermost mississippi river a mixed bedrock alluvial channel in this study the distribution of channel bed sediment facies in the lowermost mississippi river is analysed using multibeam data complemented by sidescan sonar and compressed high intensity radar pulse seismic data as well as grab and core samples of bed material the channel bed is composed of a discontinuous layer of alluvial sediment and a relict substratum that is exposed on the channel bed and sidewalls the consolidated substratum is made up of latest pleistocene and early holocene fluvio deltaic deposits and is preferentially exposed in the deepest thalweg segments and on channel sidewalls in river bends the exposed substratum commonly displays a suite of erosional features including flutes that are quantitatively similar in form to those produced under known laboratory conditions a total of five bed facies are mapped three of which include modern alluvial deposits and two facies that are associated with the relict substratum a radius of curvature analysis applied to the mississippi river centreline demonstrates that the reach scale distribution of channel bed facies is related to river planform from a broader perspective the distribution of channel bed facies is related to channel sinuosity higher sinuosity promotes greater substratum exposure at the expense of alluvial sediment for example the ratio of alluvial cover to substratum is ca 1 5 1 for a 45 km segment of the river that has a sinuosity of 1 76 and this ratio increases to ca 3 1 for a 120 km segment of the river that has a sinuosity of 1 21 the exposed substratum is interpreted as bedrock and given the relative coverage of alluvial sediment in the channel the lowermost mississippi river can be classified as a mixed bedrock alluvial channel the analyses demonstrate that a mixed bedrock alluvial channel boundary can be associated with low gradient and sand bed rivers near their marine outlet

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

a rouse based method to integrate the chemical composition of river sediments application to the ganga basin 1 the ganga river is one of the main conveyors of sediments produced by himalayan erosion determining the flux of elements transported through the system is essential to understand the dynamics of the basin this is hampered by the chemical heterogeneity of sediments observed both in the water column and under variable hydrodynamic conditions using acoustic doppler current profiler adcp acquisitions with sediment depth profile sampling of the ganga in bangladesh we build a simple model to derive the annual flux and grain size distributions of the sediments the model shows that ca 390 30 mt of sediments are transported on average each year through the ganga at haring bridge bangladesh modeled average sediment grain size parameters d 50 and d 84 are 27 4 and 123 9 mm respectively grain size parameters are used to infer average chemical compositions of the sediments owing to a strong grain size chemical composition relation the integrated sediment flux is characterized by low al si and fe si ratios that are close to those inferred for the himalayan crust this implies that only limited sequestration occurs in the gangetic floodplain the stored sediment flux is estimated to c a 10 of the initial himalayan sediment flux by geochemical mass balance the associated globally averaged sedimentation rates in the floodplain are found to be ca 0 08 mm yr and yield average himalayan erosion rate of ca 0 9 mm yr this study stresses the need to carefully address the average composition of river sediments before solving large scale geochemical budgets citation lupker m c france lanord j lave j bouchez v galy f metivier j gaillardet b lartiges and j l mugnier 2011 a rouse based method to integrate the chemical composition of river sediments application to the ganga basin

influences of climate cattle density and lake morphology on sporormiella abundances in modern lake sediments in the us great plains sporormiella a genus of coprophilous fungus is increasingly used as a qualitative proxy for megafaunal density decreased spore abundances in late pleistocene and holocene sediments are thought t

secondary ferrimagnetic minerals in welsh soils a comparison of mineral magnetic detection methods and implications for mineral formation summary a range of low temperature and isothermal magnetic measurements are used to identify the secondary ferrimagnetic mineral sfm grain sizes in 10 representative soil samples from wales a comparison of percentage frequency dependent susceptibility fd percentage and low temperature remanence measurements shows that they are sensitive to different ranges of superparamagnetic sp grains the relative distributions of sp grains and stable single domain ssd grains are similar in nine of the samples typical distributions for soils dominated by sfms are 20 30 per cent ssd and 70 80 per cent sp multidomain md grains were not detected in the samples studied there is evidence that some soils contain significant numbers of ultrafine sp grains 0 010 m that are not detected by low temperature remanence measurements at 20 k and which will have the effect of depressing values of low field susceptibility lf and fd percentage a mixing model suggests that fd percentage may be used semi quantitatively to estimate the proportion of sp grains in a sample the positively skewed grain size distributions strongly suggest a mechanism of sfm formation that is driven by processes at the 10 8 m scale thus supporting weathering and fermentation as controlling processes rather than the degradation of ssd bacterial magnetosomes and primary minerals

microscopic charcoal in sediments quaternary fire history of the grassland and savanna regions in south africa the microscopic charcoal content of several quaternary pollen sequences is used to investigate fire history in south africa both during the holocene and the late pleistocene although fluctuations in charcoal composition are recorded it is difficult to link them directly to either human made or natural fires strong long term variations in microscopic charcoal of middle and upper pleistocene layers are independent of pollen indications of past temperature and moisture conditions holocene charcoal sequences from different areas show no correlation so no phases of regional burning are found some fluctuations in charcoal probably are the result of local burning in the various regions the arrival of iron age people some 2000 yr ago apparently did not coincide with widespread wild fires as these events do not consistently appear in regional microscopic charcoal records the only exception appears to be the wonderkrater spring deposit relatively open savanna environments which are implied by pollen analysis at some sites during this period and the generally low microscopic charcoal contents were either caused by climate change or controlled burning by iron age people copyright 2002 john wiley sons ltd

using interstation amplitude correction factors to predict regional phase amplitudes abstract developing regional discriminants at any given seismic station requires a ground truth database of waveforms from both earthquakes and explosions recently installed stations used for seismic monitoring have no single charge explosions on which to base discriminants we have developed a procedure to map regional seismic amplitudes from surrogate stations which have a long recording history to newly installed operational stations this procedure uses an interstation amplitude correction factor iacf computed using a set of commonly recorded calibration earthquakes between the surrogate and operational station pair to predict seismic amplitudes at the new station using the iacf and historical explosion amplitudes from the surrogate station we tested the method using an earthquake aftershock sequence in pakistan recorded at the kyrgyzstan broadband seismic network the aftershocks had a range of depths and were clustered in a linear trend defining the fault rupture plane of the mainshock we computed iacfs for all possible station combinations at knet 45 combinations for all events and then computed a mean iacf value for each station pair using the mean iacf values we calculated predicted phase amplitudes at each station and compared the predictions to the actual values the observed predicted relationship performed well r 2 values 0 8 for all phases and frequency bands at frequencies above 6 hz the observed predicted relationship showed more scatter a trend not due to interstation distance source depth or spatial location of the calibration earthquakes we were able to reduce scatter in the observed predicted relationship by applying path corrections to the data suggesting that sensitivities in differing paths between certain surrogate operational station combinations do play a role in the effectiveness of the method we used this methodology to predict explosion values at the lop nor nuclear test site in china using a suite of nearby calibration earthquakes to calculate iacf values the results indicate good correlation between the observed and predicted amplitudes suggesting that the method can be used to simulate explosion characteristics at stations that have never recorded explosions comparing the iacf values from the calibration dataset near lop nor to those calculated for the earthquakes in pakistan we see some similarity for certain station combinations however on the whole there are differences that suggest that iacfs have a spatial variance and must be tuned to the region and path of interest for the method to be successful

catastrophic rock avalanches in a glaciated valley of the high atlas morocco 10be exposure ages reveal a 4 5 ka seismic event surface modification processes leading to large debris accumulations in high relief mountain areas are important for understanding landscape evolution especially in some of earth s most active orogens the arroumd rock avalanche at the foot of the nw face of mount aksoual 3912 m above sea level masl in the jebel toubkal area of the high atlas morocco represents one of the largest mass movement landforms in north africa the age and origin of this extensive feature have been contested for over a century late pleistocene moraines are also present in the same valley adjacent to the avalanche debris the mean of six 10 be cosmogenic exposure ages shows that a series of catastrophic rock slope failures occurred at 4 5 0 5 ka while a set of eight exposure ages from two of the three mapped moraines has a far larger spread from 1 5 to 7 5 ka this suggests that the avalanche events were effective agents in modifying the true surface exposure age of the pleistocene moraines in the arroumd valley this has resulted in similar mean 10 be apparent exposure ages for the preexisting late pleistocene moraine surfaces and holocene catastrophic rock slope failures similar rock avalanche deposits are present in other glaciated valleys in the high atlas we conclude that the trigger for collapse was seismic activity related to proximity of the major tizi n test fault these findings have important implications for interpreting and dating glacial landforms in tectonically active settings

mean flow and turbulence structure over fixed two dimensional dunes implications for sediment transport and bedform stability detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed two dimensional dunes in a laboratory channel laser doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength the density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters which are assessed using higher moment measures and quadrant analysis these flow field maps illustrate that 1 the time averaged downstream and vertical velocities agree well with previous studies of quasi equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest 2 the maximum root mean square rms of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell 3 the maximum vertical rms values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream extending almost to the next crest 4 positive downstream skewness values occur within the separation cell whereas positive vertical skewness values are restricted to the shear layer 5 the highest reynolds stresses are located within the zone of flow separation and along the shear layer 6 high magnitude high frequency quadrant 2 events ejections are concentrated along the shear layer kelvin helmholtz instabilities and dominate the contribution to the local reynolds stress and 7 high magnitude high frequency quadrant 4 events occur bounding the separation zone near reattachment and close to the dune crest and are significant contributors to the local reynolds stress at each location these data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation magnitude and downstream extent of the flow separation zone and resultant shear layer furthermore the origin of dune related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting the fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the kelvin helmholtz instabilities which are both greater for dunes than ripples these instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates

an analysis of spectral differences between nevada test site and shagan river nuclear explosions spectral ratio discrimination studies carried out on events located in the western united states and soviet union s u illustrate that pronounced differences in radiated explosion source spectra relative to nearby earthquakes exist between the two regions nevada test site nts explosions are characterized by the existence of more low frequency and or less high frequency energy greater low to high frequency spectral ratios than western u s earthquakes the opposite pattern is observed in the s u with nuclear explosions appearing to have more high frequency and or less low frequency energy than earthquakes these observations may be caused by at least two principal effects that are probably acting in parallel 1 variations in depth dependent effects of attenuation acting between the shallow explosions and deeper earthquakes and 2 differences in the dynamic response of the near source geology to the passing explosion shock wave anelastic synthetic seismogram calculations illustrate that depth dependent attenuation effects may explain the spectral observations however a number of observations using near and far field data from nts explosions suggest that near source effects are the dominant factor a quasi empirical explosion source model is proposed that simultaneously fits the spectral ratio data from both the u s and s u relative to earthquakes in each of the respective regions additionally the model fits the trends of the spectral ratios observed as a function of magnitude the key to the model is the shape of the pressure time history acting at the elastic radius for explosions detonated in weak porous rock the radiated shock wave divides into a two wave system consisting of an elastic precursor followed by a plastic wave the generation of this two wave system introduces a rise time into the pressure time history in the frequency domain a second corner frequency is established in a third order model with an 3 high frequency decay whose value is inversely proportional to the time separation of the two waves in higher strength saturated rocks or for overburied explosions the effective rise time is short and a second order model is appropriate with an 2 high frequency decay the second order model provides a good fit to the s u data in contrast a hybrid model is required to fit the nts data with an 3 high frequency decay for shallow explosions detonated in unsaturated tuff that evolves to an 2 decay as depth of burials reach higher strength saturated rocks below the water table

on the causes of pulsing in continuous turbidity currents velocity pulsing has previously been observed in continuous turbidity currents in lakes and reservoirs even though the input flow is steady several different mechanisms have been ascribed to the generation of these fluctuations including rayleigh taylor rt instabilities that are related to surface lobes along the plunge line where the river enters the receiving water body and interfacial waves such as kelvin helmholtz instabilities however the understanding of velocity pulsing in turbidity currents remains limited herein we undertake a stability analysis for inclined flows and compare it against laboratory experiments direct numerical simulations and field data from lillooet lake canada and xiaolangdi reservoir china thus enabling an improved understanding of the formative mechanisms for velocity pulsing both rt and kelvin helmholtz instabilities are shown to be prevalent in turbidity currents depending on initial conditions and topography with plunge line lobes and higher bulk richardson numbers favoring rt instabilities other interfacial wave instabilities holmboe and taylor caulfield may also be present while this is the most detailed analysis of velocity pulsing conducted to date the differences in spatial scales between field direct numerical simulations and experiments and the potential complexity of multiple processes acting in field examples indicate that further work is required in particular there is a need for simultaneous field measurements at multiple locations within a given system to quantify the spatiotemporal evolution of such pulsing

the micromorphology of glaciolacustrine varve sediments and their use for reconstructing palaeoglaciological and palaeoenvironmental change abstract former glaciolacustrine systems are an important archive of palaeoglaciological palaeoenvironmental and palaeoclimatic change the annually laminated varved sediments that under certain conditions accumulate in former glacial lakes offer a rare opportunity to reconstruct such changes e g glacier advance and retreat cycles glacier ablation trends permafrost melt nival events at annual or even sub annual temporal resolution data of this kind are desirable for their ability to guide and test numerical model simulations of glacier dynamics and palaeoclimatic change that occur over rapid time intervals with implications for predicting future glacier response to climatic change or the effects of weather and climate events on lake sedimentation the most valuable records preserved in glaciolacustrine systems are continuous varved sequences formed in the distal parts of glacial lakes where microscale lamination structures can accumulate relatively undisturbed technological advances in the last few decades have enabled improved characterisation of glaciolacustrine varve microfacies and the precise measurement of varve thickness at the micrometre scale however unlike in cognate fields e g soil science protocols for the robust and consistent description and interpretation of glaciolacustrine varve sediments are lacking to fill this gap and to provide a resource for future studies of glaciolacustrine varved sediments this paper reviews the processes of sedimentation in glacial lake basins and presents the defining microfacies characteristics of glacial varves using a descriptive protocol that uses consistent examination of grain size sorting structure nature of contacts development of plasmic fabrics and features such as dropgrains and intraclasts within individual laminations these lamination types are then combined into lamination sets whose structures can be interpreted as glaciolacustrine varves within this framework we define five principal assemblages of glaciolacustrine varve microfacies which if clearly identified in palaeoglaciolacustrine settings enable more detailed palaeoenvironmental interpretations to be made finally we discuss the utility and complexities of reconstructing the evolution of former glacial lake systems using varve microfacies and thickness datasets

estimating shear stress from moving boat acoustic doppler velocity measurements in a large gravel bed river 1 moving boat acoustic doppler current profiling adcp is increasingly used to measure discharge in large rivers we investigate whether useful information about bed shear stress can be recovered from such data alternative ways to estimate local bed shear stress using the logarithmic law of the wall and spatial averaging are tested using adcp transects across lower fraser river canada repeatability is assessed by comparing estimates from outward and return boat tracks the most precise method uses the vertically averaged mean velocity and a zero velocity height based on bed grain size information the accuracy of the assumed zero velocity height can be judged by consistency between estimates using mean velocity and near bed velocity shear stress estimates from unconstrained log law fits are less repeatable and tend to overpredict and mean shear stress estimates using the depth slope product are unreliable in this river because of nonuniform flow

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

bedform transport rates for the lowermost mississippi river 1 new methods of data collection and processing are developed to provide quantitative reach scale measurements of bedform transport mass within the tidally influenced mississippi river a multibeam swath profiler was used to collect daily bathymetry over a range of water discharges and bed elevation changes induced by dune migration are measured these values are coupled with bulk physical properties of the bed sediment to constrain mass flux and annual bedform transport is estimated at 2 2 x 10 6 metric tons mt the total annual sand flux from the mississippi river calculated by combining measured bedform transport rates and suspended sediment flux is estimated to be 20 x 10 6 mt survey data also provide information about the spatial distribution of dunes across the channel bottom straight reach segments are commonly mantled by dunes for the entire cross section while bends are typically areas of focused scour devoid of bedforms presumably any sediments associated with migrating dunes are propelled into suspension within bends before redepositing in the subsequent straight reach movement via suspension is therefore an important component for the downriver transport of bed materials in the lower mississippi river

timing of pleistocene glaciations in the high atlas morocco new 10be and 36cl exposure ages abstract this paper presents data from 42 new samples yielding late pleistocene cosmogenic 10be and 36cl exposure ages of moraine boulders across a series of glaciated valleys in the toubkal massif 4167 m a s l high atlas morocco this represents the first comprehensive pleistocene glacial chronology in north africa and one of the largest datasets from the mediterranean region the timing of these glacier advances has major implications for understanding the influence of atlantic depressions on moisture supply to north africa and the mediterranean basin during the pleistocene the oldest and lowest moraines which span elevations from 1900 to 2400 m a s l indicate that the maximum glacier advance occurred from mis 5 to 3 with a combined mean 10be and 36cl age of 50 2 19 5 ka 1 sd n 12 7 outliers the next moraine units up valley at higher elevations 2200 2600 m a s l yielded exposure ages close to the global last glacial maximum lgm with a combined mean 10be and 36cl age of 22 0 4 9 ka 1 sd n 9 7 outliers the youngest exposure ages are from moraines that were emplaced during the younger dryas with a combined mean 10be and 36cl age of 12 3 0 9 ka 1 sd n 7 no outliers and are found in cirques at the highest elevations ranging from 2900 to 3300 m a s l from moraines predating the younger dryas a large number of young outliers are spread evenly between 6 and 13 ka suggesting a continuing process of exhumation or repositioning of boulders during the early to mid holocene this attests to active seismic processes and possibly intense erosion during this period

frequency spectra and intermittency of the turbulent suspension process in a sand bed river previous research suggests that the turbulence driven suspension process in sand bed channels is dominated by intermittent energetic eddies with length scales of the order of channel depth because of the scarcity of data on the turbulent suspension process in alluvial channels the possible variability in suspension intermittency and turbulent frequency content due to contrasts in flow depth velocity or bedforms remains unclear however the present study analyses eddy correlation suspension signals from seven deployments in varied flow conditions around a sandy meander bend deployment depths at near bankfull flow stages varied from 2 to 5 5 m velocities at 0 75 1 m height from 0 6 to 0 9 m s 1 and local mean suspended sand concentrations ranged from 30 to 150 mg l 1 in the intermittence and spectral content of sand suspension between the various deployments are analysed and results are compared with previously published findings study data suggest that the dominant eddy sizes involved in sediment mixing across the sensor level are consistently of the order of 1 5 times flow depth and lie within the energy bearing turbulent range when sand suspension is analysed in the time domain in the various deployments energetic burst like suspension events occupying only 1 5 of the record duration account for 20 90 of the suspension work the degree of intermittence in the suspension process was observed to increase in deeper flows where mixing events contributing extreme vertical sediment fluxes appear to be relatively more frequent

a field study of turbulence and sediment dynamics over subaqueous dunes with flow separation this study examines flow turbulence and sand suspension over large dunes in canoe pass a distributary channel of the fraser river delta canada dune morphology is characterized by a symmetrical shape and steep leeside slopes over 30 velocity was measured with an electromagnetic current meter and suspended sand concentration with four optical backscatter obs probes the general patterns of time averaged velocity and sand suspension are consistent with previous studies including an increase in mean velocity and decrease in turbulence intensity and sand concentration with height above the bed reversed flow with high turbulence intensity and high sand concentrations in the leeside flow separation zone and an increase in near bed velocity and sand concentration along the stoss side of the dune frequency spectra of near bed velocity and obs records from leeside separation zones are composed of two distinct frequencies providing field confirmation of scale relations based on flume experiments the low frequency spectral signal probably results from wake flapping and the high frequency signal from vortex shedding the wake flapping frequency predominates outside the separation zone and is linked to turbulent structures that suspend sand predictions from a depth scale strouhal law show good agreement with measured wake flapping frequencies cross correlations of obs records reveal that turbulent sand suspension structures advect downstream at 23 25 above the horizontal these advection angles are similar to coherent flow structures measured in flumes and to sand suspension structures visualized over large dunes in the field

contrasted sediment processes and morphological adjustments in three successive cutoff meanders of the danube delta abstract since the 1980s intensive anthropogenic disturbances have affected the channel of the st george branch the southern distributary of the danube river the meander cutoff programme since 1984 1988 induced different hydrosedimentary impacts on the local distribution of river flow velocities discharge and sediment fluxes between the former meanders and the man made canals ichim and radoane 1986 popa 1997 panin 2003 this paper selects three large cutoff meander reaches of the st george branch the mahmudia dunav de sus and dunav de jos meanders noted here as m1 m2 and m3 respectively as an example to analyse the human impact in the danube river delta the diversion of the flow induces strong modifications by acceleration of the fluxes through the artificial canals combined with dramatically enhanced deposition in the former meander where it was observed in two cases m1 and m3 with slight modifications in m2 an exceptional flood that occurred in april 2006 offered a good opportunity for scanning different cross sections of the meander systems bathymetry flow velocity suspended load concentration and liquid and solid discharge data were acquired throughout several cross sections of both natural channels and artificial canals of the three cutoffs using acoustic doppler current profiler adcp technology in order to investigate the distribution of the flow and sediment and its impact on the hydrosedimentary processes in each channelized reach and adjacent former meander therefore the results obtained during the 2006 flood were referred to a long term evolution 1970 2006 analysed by gis techniques

a discrimination analysis of short period regional seismic data recorded at tonto forest observatory abstract a new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well the test data consisted of a well constrained set of 30 nevada test site nts explosions and 21 earthquakes located within about 100 km of nts which were recorded on short period seismographs at the tonto forest observatory in central arizona at an epicentral distance averaging 530 km the events in the data set cover a magnitude range from 3 3 to 4 8 m b for which p n p g and l g phases have been analyzed we found that although l g phases from earthquakes are typically more prominent than for explosions with comparable p wave amplitude levels simple time domain l g p amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination however spectral analyses of the data over the frequency band from 0 5 to 5 0 hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant in particular both the p g and l g spectra from earthquakes have been found to be richer in high frequency content than corresponding explosion spectra a discriminant measure defined as the ratio of average l g spectral amplitude level in the 0 5 to 1 0 hz passband to that in the 2 0 to 4 0 hz passband provides good separation of earthquake and explosion populations

flow and sediment processes in a cutoff meander of the danube delta during episodic flooding abstract this article analyzes the water and suspended solid fluxes through a straightened meander of the southern branch of the danube delta the st george branch during episodic flooding the mahmudia study site corresponds to a vast natural meander which was cut off in 1984 1988 by an artificial canal opened to shipping the meander correction accelerated fluxes through the artificial canal and dramatically enhanced deposition in the former meander after his formation the cutoff meander acted as sediment storage locations essentially removing channel and point bar sediments from the active sediment budget of the main channel increases in slope and stream power in reaches upstream and downstream have also occurred but to a lesser degree during the one hundred year recurrent flood in april 2006 bathymetry flow velocity and discharge data were acquired across several sections of both natural and artificial channels with an acoustic doppler current profiler adcp workhorse sentinel 600 khz teledyne rdi in order to investigate the distribution of the flow and sediment and his impact on sedimentation in a channelized reach and its adjacent cutoff the contrasting hydro sedimentary processes at work in both channels and bifurcation confluence nodal points are analyzed from the measured flux distribution morphological profiles and velocity and concentration patterns in the cutoff a diminishing of the intensity of the flow velocity c 50 and of the ssc was observed correlated with the aggradation of the river bed in the bifurcation confluence nodal points and in the artificial canal were observed the most intensive hydrodynamic activity high flow velocity ssc concentration degradation of the river bad both the event scale and long term morphological trends of the alluvial system are discussed analyzing the boundary shear stress and ssc variability excess boundary shear stress in the sub reaches directly affected by cutoffs resulted in scour that increased downstream bed material load these high sediment loads play a key role in driving morphological adjustments towards equilibrium in the cutoff channel the approach followed in this paper combines detailed episodic in situ adcp measurements and robust numerical 1d modeling in order to provide a practical comprehension of the relevant morphodynamical processes the 1d model reproduces robustly the continuity of hydrodynamical variables along the streamwise axes of the two channel network the simulated are used in the paper for highlighting reach scale morphological processes at both event and long term scales

spectral discrimination analysis of eurasian nuclear tests and earthquakes recorded by the israel seismic network and the noress array abstract the energy spectral ratio and the innovative spectral semblance discriminants successfully performed previously on a local israeli events were verified on teleseismic short period recordings the events tested include 29 nuclear explosions and 41 earthquakes mb 5 2 6 5 mainly from china and kazakhstan recorded by the israel seismic network isn and the noress array a 15 s window comprising p and p coda waves was selected for the analysis the semblance statistic commonly used in seismic prospecting for phase correlation in the time domain was modified and utilized as a measure of coherency of the smoothed spectra across the network array the semblance and the average spectral ratio of low to high frequency energy were evaluated using a subset of 7 10 stations for a given event semblance and spectral ratio values calculated from isn seismograms were found to be higher for earthquakes where the analyzed waves are richer in low frequency energy and have more coherent spectral shapes than explosions these observations are contrary to those observed for local events the best performance is provided in the frequency bands 0 6 1 hz 1 3 hz for the ratio and 0 6 2 hz for the semblance joint application of the two discriminants showed almost full separation 95 between the two populations some explosions exhibited pronounced minima nulls near 1 hz which could be interpreted in terms of interference of p and pp waves from a source at the depth of several hundreds of meters nevertheless this feature could not be utilized as a discriminant many explosions revealed strong variability of this minimum across the isn network and some earthquakes also distinctly exhibited this feature the isn and noress discrimination performances were compared the latter records showed the same as the isn relation between spectral ratio values for earthquakes and explosions whereas the character of semblance was reversed the ratios in the frequency bands 0 6 0 8 hz 0 6 10 hz yield full separation of the two populations in general the spectral ratio performance appears to be better for noress recordings whereas the spectral semblance is better for the isn data

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

modelling gravel transport and morphology for the fraser river gravel reach british columbia a two dimensional 2d numerical hydrodynamic morphological model is developed to investigate gravel transport and channel morphology in a large wandering gravel bed river the fraser river gravel reach in british columbia canada the model takes into count multi fraction bedload transport including the effects of surface coarsening hiding and protrusion model outputs together with river discharge statistics were analyzed producing distributed sediment budget and well defined localised zones of aggradation and degradation along the gravel reach long term channel response to gravel extraction from aggrading zones as a flood hazard mitigation measure was also investigated numerically to assess the effectiveness of such an extraction the total computed sediment budget agrees well with results based on field measurements of gravel transport available to us this study points to the importance of a number of factors to bedload predictions the gravel to sand ratio the adequacy of resolving the wandering planform and the distinction between bed shear stress driving bedload transport and bed resistance on the flow these are in addition to the physical processes governing the flow field and gravel mobilization the methodology presented in this paper can provide a scientific basis for gravel management including monitoring and extraction in order to maintain adequate flood protection and navigation while preserving the ecosystem

moroccan speleothem and tree ring records suggest a variable positive state of the north atlantic oscillation during the medieval warm period we present a magnesium mg and strontium sr record from an aragonitic speleothem grotte de piste morocco 34 n 04 w providing a reconstruction of effective rainfall from 619 to 1962 ad the corresponding drip site was monitored over 2 yr for drip water mg ca and sr ca ratios results show evidence for prior aragonite precipitation which can explain negative correlations between speleothem mg and sr concentrations the data shown here have important climate implications concerning the evolution of the north atlantic oscillation nao a comparison of the stalagmite data from grotte de piste with an updated tree ring based drought reconstruction from morocco and other nao related proxy records confirms that the medieval warm period mwp was dominated by nao conditions the stalagmite record and multiple proxy records from the iberian peninsula however suggest that considerable rainfall variability occurred during the mwp this implies that the nao has been more variable during the mwp than formerly suggested

quaternary evolution of the marrakech high atlas and morphotectonic evidence of activity along the tizi n test fault morocco here we consider the ourika and rheraia drainage basins on the tizi ntest fault zone in the mountains of the marrakech high atlas western morocco with regard to late pleistocene tectonic activity new insights into geomorphological changes in drainage patterns and related landforms are based on geological fieldwork in conjunction with dem analysis lithological and structural data combined with certain geomorphometric indices provide clues to the ongoing uplift of quarternary surfaces in this region five geomorphological indices are utilized 1 drainage network 2 shape of stream long profiles 3 hypsometric integral and curves 4 valley floor width valley height ratio vf index and 5 stream gradient index sl index we also considered the temporal evolution of alluvial deposit complexes with diverse lithofacies such as debris flows channel gravels rockslide debris avalanche stratified slope deposits terrace gravels and fan deposits in the ourika and rheraia valleys pleistocene talus deposits and fluvial sediments are offset by the tizi n test fault in the upper ourika and upper rheraia valleys such deformation of thick continental deposits strongly points to thrust reactivation along the tizi n test fault we define the chronology and overall aggradation phases or lateral incision phases showing how they are the consequences of variations in tectonic uplift and climate as a result we are better able to access recent morphotectonic evolution in part of the marrakech high atlas

with or against the tide the influence of bed form asymmetry on the formation of macroturbulence and suspended sediment patterns this study examines tide dependent variations in the formation and dynamics of suspended sediment patterns coupled to mean flow and turbulence above asymmetric bed forms in the danish knudedyb inlet very large primary bed forms remain ebb oriented during a tidal cycle while smaller superimposed bed forms reverse direction with each tidal phase hydroacoustic in situ observations reveal pronounced differences in suspended sediment transport patterns between tidal phases caused by the relative orientation of primary bed forms and the mean tidal flow and flow unsteadiness during a single tidal phase when flow and primary bed form orientation are aligned water depth scale macroturbulence develops in the bed form lee sides in the presence of flow separation macroturbulent flow structures occur at high flow stages and are coupled to increased amounts of sediment in suspension when flow and bed form orientation are opposed no evidence of flow separation associated with primary bed forms is found sediment laden macroturbulence at high flow velocities is of a smaller scale and attributed to the superimposed secondary bed forms the flow structures are advected along the primary bed form stoss side temporary hydraulic lee side the steep primary bed form lee side temporary hydraulic stoss side however limits transport capabilities beyond the scale of primary bed forms

terrigenous sedimentation processes along the continental margin off nw africa implications from grain size analysis of seabed sediments the terrigenous fraction of seabed sediments recovered along the north west african continental margin illustrates spatial variability in grain size attributed to different transport mechanisms three subpopulations are determined from the grain size analyses n 78 of the carbonate free silt fraction applying an end member modelling algorithm g j weltje 1997 the two coarsest endmembers are interpreted as representing aeolian dust and the fine grained end member is related to fluvial supply the end member model thus allows aeolian fallout to be distinguished from fluvial sourced mud in this area the relative contributions of the end members show distinct regional variations that can be related to different transport processes and pathways understanding present day sediment dispersal and mixing is important for a better understanding of older sedimentary records and palaeoclimate reconstructions in the region

acoustic doppler current profiler surveys along the yangtze river an acoustic doppler current profiler is used to characterize the river velocity against the morphology of the yangtze river from chonqing to the sea high flow velocities occur in the three gorges section and lower velocities in the middle and lower reaches of the river this is largely due to the change in river pattern from a high gradient deeply cut valley to a flat fluvial plain flow velocities fluctuate in the middle yangtze due to the presence of meander bends of different length there are numerous smaller velocity fluctuations in the lower yangtze channel that reflect multichannel pattern with numerous sand bars and a river morphology affected by bedrock outcrops water depths of 40 100 m occur in the three gorges valley but decrease to 15 40 m in the middle and lower yangtze at the gezhou reservoir 30 km downstream of the three gorges damsite velocity drops to low 1 0 m s 1 20 km reach a second low velocity 0 5 m s 1 zone about 20 km in length is located in the lower yangtze near the coast probably due to the tidal influence the results from this research will serve as a datum for evaluating changes to the river once the three gorges dam is completed in 2009

quantification and characterization of regional seismic signals from cast blasting in mines a linear elastic model summary cast blasts in coal mines designed to move large volumes of overburden are a source of large 1 5 kt frequent explosions in parts of the world with near surface coal resources mining events of this source type are triggering the prototype international monitoring system for the comprehensive test ban treaty being tested under the group of scientific experts technical test 3 gsett 3 we wish to develop techniques to distinguish between the seismic signals produced by these explosions and equivalent size single or point sources to that end we have developed a linear elastic model to simulate regional distance seismograms from mining cast blasts cast blasting involves a shot array with delayed detonations casting rock horizontally into a pit we model the effects of the millisecond delay firing pattern the depth of the pit and the cast of material into the pit we attempt to separate the effects due to the explosion the vertical movement of mass and the horizontal movement of mass in order to produce a physical understanding of the resulting waveforms which can be used to assess potential discriminants for these types of explosions these physical models of source processes are constrained by near surface measurements of cast blasts in ne wyoming that are triggering gsett 3 two observational results at regional distances that are replicated by these models are the excitation of 8 12s surface waves by the cast blasts and the insensitivity of peak amplitude to total explosive size for normal blasting practices the insensitivity of peak amplitudes from the cast blast to total source size is a consequence of the delay firing practice under normal procedures this practice was initiated to reduce ground motions in the near source region around the mine and it appears that it is also successful in controlling peak amplitudes at regional distances the mass transfer into the pit has both a vertical and a horizontal force component each of which contribute to the final seismogram the latter being azimuthally dependent assuming maximum coupling the contribution to the seismogram due to the vertical force component is approximately equal to the explosion contribution for pit depths of about 10 m but dominates for pit depths of 20 m or greater the contribution due to the horizontal force component is mainly in the enhanced rayleigh waves comparison of high frequency seismic radiation from the single shot and cast blast shows little qualitative difference in the regional waveforms

a model dependent method for inverting vertical profiles of scattering to obtain particle size spectra in boundary layers abstract a method for obtaining particle size spectra from vertical profiles of scattering strength in planetary boundary layers is presented it is assumed that the boundary layer is horizontally homogeneous and that the vertical turbulent diffusion of particles can be modeled from a knowledge of the surface friction velocity equilibrium boundary layer profiles for each class of suspended particles are assumed to be established resulting from the balance between vertical turbulent diffusion and gravitational settling the forward problem thus models the depth dependent scattering as the sum across size classes weighted by number density and scattering cross section in accordance with established scattering theory constrained inverses produce the size spectra results of inversions from synthetic ocean data are presented for optical transmissometry and acoustic backscattering inversions of acoustic field data from the hebble experiment are also presented finally the applications of the work presented for the design of ocean boundary layer experiments its application in other fields and the directions for future research are discussed

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

measurement of frequency dependent lg attenuation in the great basin measurement of the spatial decay of spectral amplitudes of the higher mode seismic surface wave train lg indicates that in the great basin the apparent seismic quality factor q is a function of frequency observations along a 300 km profile recording of a nuclear explosion yield the function q 206 0 68 over the band 0 3 10 0 hz similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the great basin crust gives q 214 15 0 54 0 09 for 0 3 5 0 hz if the crustal sampling by lg energy from nuclear explosions surface sources is primarily in the shallow crust as has been suggested then these results indicate a greater frequency dependence of apparent q there than at depth

corner frequency scaling of regional seismic phases for underground nuclear explosions at the nevada test site model fits are used to estimate source spectral corner frequencies of regional seismic phases pn pg and lg from underground nuclear explosions unes at the nevada test site nts based on recordings by lawrence livermore national laboratory llnl nts network stations the spectra are corrected for instrument response distance and station effects and then network averaged explicit information regarding geophysical working point properties depth of burial and some announced yields for nts explosions springer et al 2002 is utilized for the spectral modeling scaling of pn pg and lg corner frequencies with source yield is examined for sets of explosions at yucca flat pahute mesa and rainier mesa with similar material properties medium type density velocities and gas porosity the unes are limited to those in media with gas porosity of 10 or less so that a source spectral model with a rolloff of f 2 is applicable model comparisons are also examined for regional p lg discriminants a key result is that lg corner frequencies for ntsunes exhibit similar scaling with source size as for p waves but shifted lower analogous to observations by fisk 2006 for the lop nor semipalatinsk and novaya zemlya test sites this appears to corroborate an important effect that is that major contributions to s wave generation by explosions occur near the source with a similar length scale comparable to the elastic radius as for p waves from explosions although the explicit physical mechanism is not yet understood the implications are important regarding where and perhaps how s waves are predominantly generated by explosions a related key result is that the increasing separation of p lg at higher frequencies between nts explosions and earthquakes has a consistent model based explanation as at other nuclear test sites in terms of the difference between explosion p and s corner frequencies

turbulence structure in a river reach with sand bed measurements and analysis of the three dimensional turbulence structure in a straight lowland river reach are presented accurate measurements of velocity profiles were taken with an acoustic doppier velocimeter adv and a multichannel micropropeller based system it is shown that analytical expressions derived from investigations of laboratory open channel flows agree well with the measured data only in the central part of the river where flow can be considered weakly three dimensional at the same time clear differences of empirical parameters between river and laboratory flows are detected it was established that river turbulence is isotropic for spatial scales smaller than the river depth the data also allowed the detection and analysis of the turbulence anisotropy impact on the formation of secondary currents special attention is paid to the investigation of coherent structures their spatial scales were evaluated applying the conditional average procedure based on uw quadrant analysis on average the scales of ejection and sweep events are as large as 1 5 times the flow depth

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

yield estimation using regional mb pn seismic yield estimation at regional distances will become increasingly important in monitoring a low yield threshold test ban lyttb in order to investigate seismic yield estimation using regional data we have examined regional mb pn values for a large population of nevada test site nts underground nuclear explosions that occurred in widely varying geologic media with a range of yields from less than 1 kt to 300 kt magnitude yield relationships were developed using data from a set of pre 1985 events calibration set to obtain an independent estimate of the uncertainty in estimating yields of events at nts using mb pn alone the calibrated relationships were applied to a set of post 1984 events prediction set we found that the average uncertainty in the yield estimate based on a weighted combination of the yield estimates from the four livermore nts network lnn seismic stations is about 1 8 at the 2 level if data are available from all four lnn stations the uncertainty is about 1 7 at the 2 level by including a term for the gas filled porosity of the rock near the working point in the magnitude yield relationship we were able to develop a single relationship valid for events both above and below the water table as well as those in alluvium and tuff we have found however systematic differences in the relationships for events in yucca flat pahute mesa and rainier mesa

measuring velocity and shear stress over dunes with acoustic doppler profiler this study evaluates the use of an acoustic doppler profiler adp for measurement of velocity profiles over dunes in an estuary the adp can be deployed from a moving launch and provides three dimensional velocity profiles that can be used to describe flow structure and to provide rough estimates of shear stress quadratic stress models are recommended for shear stress because they estimate skin friction and form stress whereas the law of the wall only reliably estimates total stress over dunes the most serious limitation of the adp is a beam geometry that results in a large sampling diameter close to the bed that does not adequately measure velocity in dune troughs

flow structure and channel morphodynamics of meander bend chute cutoffs a case study of the wabash river usa received 25 october 2012 revised 23 september 2013 accepted 25 september 2013 published 12 december 2013 1 this paper documents the three dimensional structure of flow and bed morphology of two developing chute cutoffs on a single meander bend on the lower wabash river usa and relates the flow structure to patterns of morphologic change in the evolving cutoff channels the upstream end of the cutoff channels is characterized by 1 a zone of flow velocity reduction stagnation and bar development in the main channel across from the cutoff entrance 2 flow separation and bar development along the inner left bank of the cutoff channel immediately downstream from the cutoff entrance and 3 helical motion and outward advection of flow momentum entering the cutoff channel leading to erosion of the outer right bank of the cutoff channel at the downstream end of the cutoff channels the majorhydrodynamic and morphologic features are 1 flow stagnation along the bank of the main channel immediately upstream of the cutoff channel mouth 2 convergence of flows from the cutoff and main channels 3 helical motion of flow from the cutoff 4 a zone of reduced velocity along the bank of the main channel immediately downstream from the cutoff channel mouth and 5 development of a prominent bar complex that penetrates into the main channel and extends from the stagnation zone upstream to downstream of the cutoff mouth these results provide the basis for a conceptual model of chute cutoff dynamics in which the upstream and downstream ends of a cutoff channel are treated as a bifurcation and confluence respectively

discrimination of nuclear explosions and earthquakes from teleseismic distances with a local network of short period seismic stations using artificial neural networks abstract seismic discrimination capability of artificial neural networks anns was studied using earthquakes and nuclear explosions from teleseismic distances the events were selected from two areas which were analyzed separately first 23 nuclear explosions from semipalatinsk and lop nor test sites were compared with 46 earthquakes from adjacent areas second 39 explosions from nevada test site were compared with 27 earthquakes from close by areas the basic discriminants were complexity spectral ratio and third moment of frequency the spectral discriminants were computed in five different ways to obtain all the information embedded in the signals some of which were relatively weak the discriminants were computed using data from six short period stations in central and southern finland the spectral contents of the signals of both classes varied considerably between the stations the 66 discriminants were formed into 65 optimum subsets of different sizes by using stepwise linear regression a type of ann called multilayer perceptron mlp was applied to each of the subsets as a comparison the classification was repeated using linear discrimination analysis lda since the number of events was small the testing was made with the leave one out method the ann gave significantly better results than lda as a final tool for discrimination a combination of the ten neural nets with the best performance were used all events from central asia were clearly discriminated and over 90 of the events from nevada region were confidently discriminated the better performance of anns was attributed to its ability to form complex decision regions between the groups and to its highly non linear nature

anthropogenic trigger for late holocene soil erosion in the jebel toubkal high atlas morocco abstract the assif n imserdane valley located in the jebel toubkal area of the high atlas morocco is a highly dynamic geomorphological setting the valley was glaciated during the late pleistocene and subsequently experienced a catastrophic rock avalanche leading to the formation of one of the largest mass movement landforms in north africa recent research hughes et al gsa bulletin 126 1093 1104 has dated the formation of the rock avalanche to the mid holocene at 4 5 0 5 ka in this paper we examine the sedimentological organic matter content magnetic susceptibility particle size and xrf and palaeoecological pollen and spores non pollen palynomorphs npps microcharcoal and conifer tracheid fragments record of a small infilled basin located adjacent to a late pleistocene moraine and close to the rock avalanche in the arroumd sector the deposits primarily fine grained and minerogenic with a low concentration of organic microfossils including pollen coprophilous ascospores wood and charcoal microfragments are enriched in fine silts and ferrimagnetic minerals consistent with erosional sources from surrounding slope soils three radiocarbon dates from the deposit indicate that the infill event occurred during the first millennium ad after 430 640 ad as such the deposits point to a phase of slope instability and erosion that is not linked to either deglaciation processes or to the mid holocene rock avalanche instead the nature and timing suggest that an anthropogenic trigger of degradation to the natural vegetation cover may be implicated consistent with an increasing scale and intensity of pastoral activity in the southern high atlas during the early islamic period in morocco the record casts light on a previously undocumented phase of landscape instability in the dynamic setting of the assif n imserdane valley and highlights the potential for further exploration of small infilled basins in the high atlas to illuminate the geoecological history of the region

use of adcps for suspended sediment transport monitoring an empirical approach a horizontally mounted 300 khz acoustic doppler current profiler was deployed in fraser river at mission british columbia to test its capability to detect size classified concentration of suspended sediment bottle samples in beam provide a direct calibration of the hadcp signals we also deployed a 600 khz vertically mounted adcp from a boat in combination with bottle samples fraser river at mission is 525 m wide with moderate suspended sediment concentration up to 350 mg l 1 in our measurements mostly silt and a modest sand load only at high flows we use an entirely empirical approach to calculate the sediment load using adcps to test the reliability of acoustic methods when assumptions embedded in the sonar equation about the relation between suspended sediment size and concentration and acoustic signals are violated vadcp calibration using matched individual bottle samples and acoustic backscatter departed from the expected theoretical relation calibration using depth averaged sediment concentration and acoustic backscatter more closely matched theoretical expectations but varied through the season hadcp calibrations conformed with theoretical expectations and did not exhibit seasonal variation silt and sand were successfully discriminated however silt dominates the correlations we found no coherent relation between acoustic attenuation and silt concentration in beam results are extended by correlation to estimate mean sediment concentration and total suspended flux in the entire channel this auxiliary correlation cancels any calibration bias and permits monitoring of size classified suspended sediment in absence of detailed information of sediment grain size distribution

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

the iberian roman humid period 2600 1600 cal yr bp in the zonar lake varve record andalucia southern spain abstract the iberian roman humid period irhp 2600 1600 cal yr bp is the most humid phase of the last 4000 yr in southern spain as recorded in the sedimentary sequence of zonar lake 37 29 00 n 4 41 22 w 300 m a s l a varve chronology supported by several ams 14 c dates allows study of the lake evolution at annual scale in response to human impact and climate changes there are four climate phases within this period i gradual transition 2600 2500 yr ago 650 550 bc from a previous arid period ii the most humid interval during the iberian early roman epoch 2500 2140 yr ago 550 190 bc iii an arid interval during the roman empire epoch 2140 1800 yr ago 190 bc ad 150 and iv a humid period synchronous with the decline of the roman empire 1800 1600 yr ago ad 150 350 varve thickness and geochemical proxies show a multi decadal cyclicity similar to modern north atlantic oscillation nao 60 20 years and solar variability cycles 11 yr the timing and the structure of this humid period is similar to that described in eastern mediterranean and northern european sites and supports the same large scale climate control for northern latitudes and the mediterranean region

amplitude corrections for regional seismic discriminants a fundamental problem associated with event identification lies in deriving corrections that remove path and earthquake source effects on regional phase amplitudes used to construct discriminants our goal is to derive a set of physically based corrections that are independent of magnitude and distance and amenable to multivariate discrimination by extending the technique described in taylor and hartse 1998 for a given station and source region a number of well recorded earthquakes is used to estimate source and path corrections the source model assumes a simple brune 1970 earthquake source that has been extended to handle non constant stress drop the discrimination power in using corrected amplitudes lies in the assumption that the earthquake model will provide a poor fit to the signals from an explosion the propagation model consists of a frequency independent geometrical spreading and frequency dependent power law q a grid search is performed simultaneously at each station for all recorded regional phases over stress drop geometrical spreading and frequency dependent q to find a suite of good fitting models that remove the dependence on m b and distance seismic moments can either be set to pre determined values or estimated through inversion and are tied to m b through two additional coefficients we also solve for frequency dependent site phase excitation terms once a set of corrections is derived effects of source scaling and distance as a function of frequency are applied to amplitudes from new events prior to forming discrimination ratios thus all the corrections are tied to just m b or m 0 and distance and can be applied very rapidly in an operational setting moreover phase amplitude residuals as a function of frequency can be spatially interpolated e g using kriging and used to construct a correction surface for each phase and frequency the spatial corrections from the correction surfaces can then be applied to the corrected amplitudes based only on the event location the correction parameters and correction surfaces can be developed offline and entered into an online database for pipeline processing providing multivariate normal corrected amplitudes for event identification examples are shown using events from western china recorded at the station makz

acoustic mapping velocimetry knowledge of sediment dynamics in rivers is of great importance for various practical purposes despite its high relevance in riverine environment processes the monitoring of sediment rates remains a major and challenging task for both suspended and bed load estimation while the measurement of suspended load is currently an active area of testing with nonintrusive technologies optical and acoustic bed load measurement does not mark a similar progress this paper describes an innovative combination of measurement techniques and analysis protocols that establishes the proof of concept for a promising technique labeled herein acoustic mapping velocimetry amv the technique estimates bed load rates in rivers developing bed forms using a nonintrusive measurements approach the raw information for amv is collected with acoustic multibeam technology that in turn provides maps of the bathymetry over longitudinal swaths as long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bed forms successive acoustic maps capture the progression of the bed form movement two dimensional velocity maps associated with the bed form migration are obtained by implementing algorithms typically used in particle image velocimetry to acoustic maps converted in gray level images furthermore use of the obtained acoustic and velocity maps in conjunction with analytical formulations e g exner equation enables estimation of multidirectional bed load rates over the whole imaged area this paper presents a validation study of the amv technique using a set of laboratory experiments