a quaternary solution model for white micas based on natural coexisting phengite paragonite pairs a thermodynamic model for the quaternary white mica solid solution with end members muscovite mg celadonite paragonite feceladonite ms mgcel pg fecel is presented the interaction energies for the mgcel pg join the fecel pg join and the ternary interactions were obtained from natural coexisting phengite paragonite pairs phengite paragonite pairs were selected based on the criteria that their chemical compositions may be represented as a linear combination of the model end member compositions and that the respective formation conditions 350 650 c 4 21kbar are accurately known previously published excess free energy expressions were used for the ms pg ms mgcel and ms fecel binaries the suggested mixing model was tested by calculating multicomponent equilibrium phase diagrams this proved to be particularly well suited to reproduce compositional variations of white micas from amphibolite facies metapelites

vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter vertical profiles of suspended sand concentration and size are obtained from multifrequency acoustic profiling data collected in 1989 during a nearshore experiment at stanhope lane beach prince edward island the data were acquired with acoustic sounders operating at 1 2 25 and 5 mhz independent estimates of concentration were made using optical backscatter sensors obss the algorithm for inversion of the three frequency backscatter data to particle size and concentration based on the ratios of the different signals was tested in laboratory experiments with an unconfined high reynolds number suspended sediment jet results from the stanhope beach experiment are presented for three different surface wave energy regimes with significant wave orbital velocities ranging from 0 3 to 0 8 m s and peak wave periods of 4 6 s the acoustic estimates of mean concentration are shown to be within 10 on average of those determined with the obs nearest the bottom at 5 to 10 cm height over time scales ranging from 6 5 min to 4 6 s one wave period the acoustic estimates of suspended sediment size near the bottom are within 5 20 of the bottom sediment mean size the statistical variability of the size estimates is high with standard deviations in the estimates ranging between 30 and 50 of the mean the time averaged concentration profiles exhibit an exponential decrease with height above an o 10 cm thick near bottom region of nonexpo nential decrease in contrast the time averaged mean size profiles decrease approximately linearly with height and rather slowly about 25 in 0 5 m

morphology and controls on the position of a gravel sand transition fraser river british columbia alluvial river channels often exhibit a relatively abrupt transition from gravel to sand bedded conditions the phenomenon is well documented but few prior studies have analyzed the spatial variability through reaches where transitions occur the downstream fining pattern observed in the fraser river is cited as a classic example of an abrupt gravel sand transition in a large alluvial channel however important questions regarding the exact location of the transition its sedimentology and morphology and what controls its location remain unanswered here we present observations of the downstream change in bed material grain size river bed topography and channel hydraulics through the reach within which the transition occurs these observations indicate that the gravel sand transition is characterized by a terminating gravel wedge but there are patches of gravel downstream of the wedge forming a diffuse extension we show that there is a dramatic decrease in shear stress at the downstream end of the wedge and a consequent cessation of general gravel mobility we argue that the patches of gravel observed beyond the wedge are the result of enhanced mobility of fine gravel over a sand bed we also find that sand in suspension declines rapidly at the downstream end of the wedge suggesting that sand is delivered to the bed completing the sedimentary conditions for a gravel sand transition we propose that the break in river slope associated with the transition is a consequential feature of the transition

sediment transport along lower fraser river 1 measurements and hydraulic computations a comprehensive program of sediment transport measurements was conducted along lower fraser river british columbia between 1966 and 1986 the data yield a detailed sediment budget annual total suspended loads at three stations are virtually identical averaging 17 106 tonnes year t yr 1 the suspended sand load is about 5 5 106 t yr 1 about one third of the total in the gravel bed reach of the river the sand behaves as wash load significant transport of gravel begins at agassiz at a discharge of about 5000 m3 s 1 the annual gravel transport was estimated to be about 0 23 106 t yr 1 only 1 of the total load all of this material is deposited in the reach upstream of mission at mission sands finer than 0 177 mm make up more than 50 of the suspended sand load but are virtually absent from the sand bed therefore a portion of the sand load at mission is wash load the total bed material load here was estimated to be 3 0 106 t yr 1 about 18 of the total sediment load virtually all of the bed material load was transported in intermittent suspension near the bed less than 5 occurring as bed load in the long term the suspended sand load upstream is approximately equal to the total sand load at mission however within individual years some of the sand is stored within the reach temporarily and then reentrained later

hysteresis in suspended sediment to turbidity relations due to changing particle size distributions 1 turbidity t is the most ubiquitous of surrogate technologies used to estimate suspended sediment concentration ssc the effects of sediment size on turbidity are well documented however effects from changes in particle size distributions psd are rarely evaluated hysteresis in relations of ssc to turbidity ssc t for single stormflow events was observed and quantified for a dataset of 195 concurrent measurements of ssc turbidity discharge velocity and volumetric psd collected during five stormflows in 2009 2010 on yellow river at gees mill road in metropolitan atlanta georgia regressions of ssc normalized turbidity t ssc on concurrently measured psd percentiles show an inverse exponential influence of particle size on turbidity that is not constant across the size range of the psd the majority of the influence of psd on t ssc is from particles of fine silt and smaller sizes finer than 16 m this study shows that small changes in the often assumed stability of the psd are significant to ssc t relations changes of only 5 m in the fine silt and smaller size fractions of suspended sediment psd can produce hysteresis in the ssc t rating that can increase error and produce bias observed ssc t hysteresis may be an indicator of changes in sediment properties during stormflows and of potential changes in sediment sources trends in the psd time series indicate that sediment transport is capacity limited for sand sized sediment in the channel and supply limited for fine silt and smaller sediment from the hillslope

acoustic inversions for measuring boundary layer suspended sediment processes although sound has been applied to the study of sediment transport processes for a number of years it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters in particular when the attenuation due to the suspension becomes significant the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension to study this attenuation propagation problem numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters the results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters which become increasingly erroneous with range as the sound propagates through the suspension to address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion this approach is not subject to the accumulation of errors and has an explicit solution here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion

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

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

calculation of in situ acoustic sediment attenuation using off the shelf horizontal adcps in low concentration settings the use of off the shelf acoustic doppler velocity profilers adcps to estimate suspended sediment concentration and grain size in rivers requires robust methods to estimate sound attenuation by suspended sediment theoretical estimates of sediment attenuation require a priori knowledge of the concentration and grain size distribution gsd making the method impractical to apply in routine monitoring programs in situ methods use acoustic backscatter profile slope to estimate sediment attenuation and are a more attractive option however the performance of in situ sediment attenuation methods has not been extensively compared to theoretical methods we used three collocated horizontally mounted adcps in the fraser river at mission british columbia and 298 observations of concentration and gsd along the acoustic beams to calculate theoretical and in situ sediment attenuation conversion of acoustic intensity from counts to decibels is influenced by the instrument noise floor which affects the backscatter profile shape and therefore in situ attenuation we develop a method that converts counts to decibels to maximize profile length which is useful in rivers where cross channel acoustic profile penetration is a fraction of total channel width nevertheless the agreement between theoretical and in situ attenuation is poor at low concentrations because cross stream gradients in concentration sediment size or gsd can develop which affect the backscatter profiles we establish threshold concentrations below which in situ attenuation is unreliable in fraser river our results call for careful examination of cross stream changes in suspended sediment characteristics and acoustic profiles across a range of flows before in situ attenuation methods are applied in river monitoring programs

genesis and solvus relations of submicroscopically intergrown paragonite and phengite in a blueschist from northern california electron microbeam techniques have been used to examine submicroscopically intergrown paragonite phengite and chlorite from the south fork mountain schist of the franciscan terrane of northern california which was subjected to blueschist facies metamorphism the sample also contains quartz albite lawsonite and rutile the subassemblage albite lawsonite rutile requires metamorphic conditions on the low temperature side of the equilibrium albite lawsonite rutile paragonite sphene quartz h2o t 200 c and p 7 4 kbars based on thermodynamic data of holland and powell 1990 the white micas appear to be optically homogeneous but back scattered electron images can distinguish two different micas by their slight difference in contrast electron microprobe analyses empa of micas show na na k ranging from 0 2 to 0 8 the two micas are resolved by transmission electron microscopy tem as packets of phengite and paragonite that range from 20 to several hundred nm in thickness the compositions determined by analytical electron microscopy aem constrain the limbs of the phengite paragonite solvus to values of na na k 0 02 and 0 97 representing less mutual solid solution than ever reported by empa the textural relations imply that the sheet silicates were derived from reactions between fluids and detrital clays and that they are in an intermediate stage of textural development we caution that microprobe analyses of apparently homogeneous sheet silicates may yield erroneous data and lead to faulty conclusions using phengite barometry and paragonite muscovite thermometry especially in fine grained rocks that formed at relatively low temperatures

colorado river sediment transport 2 systematic bed elevation and grain size effects of sand supply limitation the colorado river in marble and grand canyons displays evidence of annual supply limitation with respect to sand both prior to topping et al this issue and after the closure of glen canyon dam in 1963 systematic changes in bed elevation and systematic coupled changes in suspended sand concentration and grain size result from this supply limitation during floods sand supply limitation either causes or modifies a lag between the time of maximum discharge and the time of either maximum or minimum depending on reach geometry bed elevation if at a cross section where the bed aggrades with increasing flow the maximum bed elevation is observed to lead the peak or the receding limb of a flood then this observed response of the bed is due to sand supply limitation sand supply limitation also leads to the systematic evolution of sand grain size both on the bed and in suspension in the colorado river sand input during a tributary flood travels down the colorado river as an elongating sediment wave with the finest sizes because of their lower settling velocities traveling the fastest as the fine front of a sediment wave arrives at a given location the bed fines and suspended sand concentrations increase in response to the enhanced upstream supply of finer sand then as the front of the sediment wave passes that location the bed is winnowed and suspended sand concentrations decrease in response to the depletion of the upstream supply of finer sand the grain size effects of depletion of the upstream sand supply are most obvious during periods of higher dam releases e g the 1996 flood experiment and the 1997 test flow because of substantial changes in the grain size distribution of the bed stable relationships between the discharge of water and sand transport rates i e stable sand rating curves are precluded sand budgets in a supply limited river like the colorado river can only be constructed through inclusion of the physical processes that couple changes in bed sediment grain size to changes in sand transport rates in some rivers the upstream supply of sediment is in equi librium with the upstream supply of water whereas in others the upstream supply of sediment is decoupled either com pletely or partially from the upstream supply of water in the first type of river changes in sediment transport are controlled by changes in the discharge of water whereas in the second and perhaps more common type of river changes in sedi ment transport are also coupled to changes in sediment grain size in this paper we investigate the systematic changes in bed elevation sediment transport and sediment grain size that occur in response to changes in the upstream supply of sand in a river with an intermittent limited supply of sand specifically the colorado river in marble and grand canyons figure 1 to develop an intuitive understanding of the linkage be tween sediment grain size and the upstream supply of sediment in a river it is informative to first examine sediment transport

comparison of field observations of the vertical distribution of suspended sand and its prediction by models models for the vertical distribution of suspended sediment under waves and currents are compared with field observations the models include a diffusion based model a convection based model and a combined convection diffusion model the field observations were carried out at vilano beach florida in a water depth of approximately 3 to 4 m with a median grain diameter of 0 14 mm the rms wave height ranged from approximately 0 4 to 1 2 m under low waves the seabed was covered with very small ripples and under the higher waves sheet flow conditions were present the diffusion based model was found to best describe the observed data under high wave conditions but the convection model was more accurate under low wave conditions over all conditions the combined model was the most accurate these results are consistent with the different mechanisms for mixing suspended sediment over flat versus rippled beds

hercynian blueschist metamorphism in north portugal tectonothermal implications aegirine jadeite clinopyroxene 60 mol jadeite locally occurs within blueschists of the lower allochthon exposed in the tras os montes region of northern portugal peak conditions attained during blueschist facies metamorphism are estimated to have been c 420 c and 11 kbar porphyroblastic white mica paragonite phengite within the blueschist assemblage records a 36ar 40ar versus 39ar 40ar isotope correlation age of 329 4 1 6 ma in view of the relatively low t nature of the metamorphism the c 330 ma age is interpreted to date closely the high p recrystallization this tectonothermal activity is interpreted to have resulted from structural emplacement of a previously assembled crystalline nappe complex upper allochthon ophiolite nappe onto iberian protoliths of the lower allochthon during terminal stages of the hercynian orogeny

eclogite facies fluid infiltration constraints from δ 18 o zoning in garnet in situ analysis reveals that eclogite facies garnets are zoned in 18o with lower values in the core and rims that are 1 5 to 2 5 higher this pattern is present in 9 out of 12 garnets analyzed by sims from four orogenic eclogite terranes and correlates with an increase in the mole fraction of pyrope and mg fe ratio from core to rim indicating prograde garnet growth at the maximum temperatures and the time scales experienced by these garnets calculated intragranular diffusion distances for oxygen are small 5 from two kimberlites are homogeneous in 18o possibly due to diffusive exchange which is possible for prolonged periods at higher mantle temperatures homogeneity of 18o in garnets outside the normal mantle range 5 6 may be common in kimberlitic samples

calculated phase relations in high pressure metapelites in the system nkfmash na2o k2o feo mgo al2o3 sio2 h2o using an internally consistent thermodynamic dataset and updated models of activity composition relation for solid solutions petrogenetic grids in the system nkfmash na2o k2o feo mgo al2o3 sio2 h2o and the subsystems nkmash and nkfash have been calculated with the software thermocalc 3 1 in the p t range 5 36 kbar and 400 810 c involving garnet chloritoid biotite carpholite talc chlorite kyanite sillimanite staurolite phengite paragonite albite glaucophane jadeite with quartz coesite and h2o in excess these grids together with calculated afm compatibility diagrams and p t pseudosections are shown to be powerful tools for delineating the phase equilibria and p t conditions of na bearing pelitic assemblages for a variety of bulk compositions from high p terranes around the world these calculated equilibria are in good agreement with petrological studies moreover contours of the calculated phengite si isopleths in p t pseudosections for different bulk compositions confirm that phengite barometry is highly dependent on mineral assemblage

high pressure relics in meta sediments intercalated with the weissenstein eclogite munchberg gneiss complex bavaria the mineral assemblages in the eclogites and meta sediments of the munchberg gneiss complex suggest minimum pressures of about 15 kbar and temperatures of 600 30 c for the eclogite facies metamorphism both rock types underwent a subsequent amphibolite facies metamorphism at almost the same temperature range in the weissenstein borehole the eclogites and meta sediments show an intimate interlayering on a centimetre scale contacts between the two rock types are often sharp and untectonized suggesting in situ metamorphism of the eclogites the following features indicate that the gneisses were subjected to eclogite facies metamorphism 1 phengite relics and phengite inclusions in garnet contain up to 3 45 si per formula unit while amphibolite facies phengites have considerably lower si contents 3 0 3 25 p f u 2 omphacite relics occur in the form of na augite 6 9 mol jadeite oligoclase symplectites 3 garnets with up to 40 mol of the pyrope component occur

petrology of very high pressure eclogitic rocks from the brossasco isasca complex dora maira massif italian western alps petrographical and mineral chemical data are given for the eclogites which occur in the garnet kyanite micaschists of the penninic dora maira massif between brossasco isasca and martiniana italian western alps and for a sodic whiteschist associated with the pyrope coesite whiteschists of martiniana the brossasco isasca bi eclogites are fine grained foliated and often mica rich rocks with a strong preferred orientation of omphacite crystals and white micas porphyroblasts of hornblende are common in some varieties whilst zoisite and kyanite occur occasionally in pale green varieties associated with leucocratic layers with quartz jadeite and garnet these features differentiate the bi eclogites from the eclogites that occur in other continental units of the western alps which all belong to type c garnet sodic pyroxene and glaucophane are the major minerals in the sodic whiteschist sodic pyroxene in the eclogites is an omphacite often close to jd50di50 with very little acmite and virtually no aliv and impure jadeite in the leucocratic layers and in the sodic whiteschist garnet is almandine with 20 30 mol for each of the pyrope and grossular components in the eclogites and a pyrope rich variety in the sodic whiteschist white mica is a variably substituted phengite and paragonite apparently only occurs as a replacement product of kyanite amphibole is hornblende in the eclogites but the most magnesian glaucophane yet described in the sodic whiteschist quartz pseudomorphs of coesite were found occasionally in a few pyroxenes and garnets the p t conditions during the vhp event are constrained in the eclogites by reactions which define a field ranging from 27 28 kbar to 35 kbar and from 680 to 750 c these temperatures are consistent with the results of garnet pyroxene and garnet phengite geothermometry which suggest that the eclogites may have equilibrated at around 700 c in the sodic whiteschist pressures ranging from 29 to 35 kbar can be deduced from the stability of the jadeite pyrope garnet glaucophane compatibility as in the eclogites water activity must have been low such conditions are close to the p t values estimated for the early alpine recrystallization of the pyrope coesite rock and like petrographical and mineralogical features set aside the bi eclogites from the other eclogites of the western alps instead indicating a close similarity to some of the eclogite bodies occurring in the adula nappe of the central alps an important corollary is that glaucophane stability at least in na and mg rich compositions and under very high pressures may extend up to 700 c in agreement with the ht stability limit suggested by experimental studies

spells of low frequency oscillations and weather regimes in the northern hemisphere abstract the low frequency variability in the midlatitudes is described through an analysis of the oscillatory phenomena in order to isolate nearly periodic components of the atmospheric flow the multichannel version of the singular spectrum analysis m ssa is developed and applied to an nmc 32 year long set of 700 hpa geopotential heights in the same way that principal component analysis identifies the spatial patterns dominating the variability m ssa identifies dynamically relevant space time patterns and provides an adaptive filtering technique three major low frequency oscillations lfos are found with periods of 70 days 40 45 days and 30 35 days the 70 day oscillation consists of fluctuations in both position and amplitude of the atlantic jet with a poleward propagating anomaly pattern the 40 45 day oscillation is specific to the pacific sector and has a pronounced pacific north american pna structure in its high amplitude phase the 30 35 day mode is confined over the atlantic region

a multi frequency acoustic concentration and velocity profiler acvp for boundary layer measurements of fine scale flow and sediment transport processes the use of acoustics to measure sediment transport boundary layer processes has gained increasing acceptance over the past two decades this has occurred through the development of increasingly sophisticated measuring systems and theoretical developments which have enabled flow and suspended sediment parameters to be obtained from acoustic data with a high degree of accuracy until relatively recently separate acoustic systems were used to measure flow and suspended sediment concentration over the past few years however the technology has become sufficiently advanced so that flow and sediment measurements can be integrated into a single system this integration provides quasi instantaneous non intrusive co located high temporal spatial resolution measurements of benthic flow and sediment processes here the development of such an instrument the acoustic concentration and velocity profiler acvp is described the theory underpinning its application is outlined new approaches to velocity de aliasing and suspended sediment inversion instabilities using multi frequency capabilities are presented and the application of the system to sediment transport processes over a sandy ripple bed is illustrated the observations clearly show the value of such instrumentation for studying the dynamical interaction between the bed the flow and the sediments at and within the bottom boundary layer

geochronologic and thermobarometric constraints on the metamorphic history of the fairbanks mining district western yukon tanana terrane alaska this study presents new petrologic and thermochronologic information from the fairbanks district of east central alaska that indicate a complex metamorphic and structural history for the western yukon tanana terrane garnet biotite and garnet pyroxene thermometry and jadeite barometry yield prograde temperatures and pressures for the chatanika eclogite 523 c 14 15 kbar 1 kbar 100 mpa cooling from peak eclogitization is estimated from 40 ar 39 ar single grain geochronology at 210 180 ma secondary white mica ages of 140 115 ma along the fault contact between eclogite and underlying lower amphibolite facies rocks constrain the age of the event that placed the chatanika eclogite over the fairbanks schist based on observations from field mapping and diamond drill samples we interpret this structural contact as a thrust fault garnet biotite mineral pairs are reset by as much as 200 c within this fault zone biotite and white mica ages of 100 110 ma combined with jurassic amphibole ages in fairbanks schist samples indicate the fairbanks schist and chatanika eclogite cooled through biotite and white mica argon closure temperatures in the early cretaceous intrusion of mid cretaceous calc alkalic gold related granitic plutons in the fairbanks district are evidenced by loss of radiogenic argon in many of the 40 ar 39 ar age fractions eocene basalt is visible in six widely separated localities within the eastern part of the fairbanks district however the pervasiveness of a 50 ma resetting event in samples as far as 30 km from present day basalt localities indicates the eocene flows were either deposited throughout the fairbanks area or are associated with large plutons at depth

oxygen and carbon isotopic constraints on the development of eclogites holsnoy norway abstract eclogite formation on the island of holsnoy required the addition of water to anhydrous granulite facies protoliths in order to assess this process oxygen and carbon isotope ratios of whole rock powders and mineral separates from eclogites and granulites have been measured whole rock oxygen isotope ratios range from 7 3 to 6 0 smow in granulites average 6 38 and 7 2 to 6 1 in eclogites average 6 55 field relations permit identification of the granulite protolith of eclogites oxygen isotope measurements show shifts of up to 0 5 between some eclogites compared to their corresponding granulite protoliths indicating open system and locally heterogeneous fluid behavior mineral pair fractionations in the eclogites show disequilibrium are incompatible with slow cooling and diffusive exchange between phases and suggest that open system fluid movement continued after eclogite facies metamorphism carbonate is also present in some of the eclogites as a primary mineral dolomite and as part of a retrograde assemblage calcite textural evidence suggests that carbonate formation occurred during and after eclogite formation however all measured carbonate is out of isotopic equilibrium with eclogite facies minerals due to the influx of retrograde fluids massive calcite marble pods containing amphibolite facies cale silicate minerals have average 18 o of 9 5 0 6 while calcite in retrograded eclogites has 18 o 17 7 2 7 the 13 c 4 0 8 is indistinguishable between these two groups both whole rock and carbonate stable isotope data are interpreted as indicating a continued history of fluid infiltration during and after peak eclogite facies metamorphism the most probable source of fluids are from dewatered sediments tectonically juxtaposed during the caledonian orogeny

colorado river sediment transport 1 natural sediment supply limitation and the influence of glen canyon dam analyses of flow sediment transport bed topographic and sedimentologic data suggest that before the closure of glen canyon dam in 1963 the colorado river in marble and grand canyons was annually supply limited with respect to fine sediment i e sand and finer material furthermore these analyses suggest that the predam river in glen canyon was not supply limited to the same degree and that the degree of annual supply limitation increased near the head of marble canyon the predam colorado river in grand canyon displays evidence of four effects of supply limitation 1 seasonal hysteresis in sediment concentration 2 seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration 3 production of inversely graded flood deposits and 4 development or modification of a lag between the time of a flood peak and the time of either maximum or minimum depending on reach geometry bed elevation analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply limited with respect to fine sediment but it was not supply limited with respect to fine sediment during all seasons in the average predam year sand would accumulate and be stored in marble canyon and upper grand canyon for 9 months of the year from july through march when flows were dominantly below 200 300 m3 s this stored sand was then eroded during april through june when flows were typically higher after closure of glen canyon dam because of the large magnitudes of the uncertainties in the sediment budget no season of substantial sand accumulation is evident because most flows in the postdam river exceed 200 300 m3 s substantial sand accumulation in the postdam river is unlikely

eddy formation in unsteady flows unsteadiness of flow at m2 s2 tidal frequencies is demonstrated to be a dominant factor forming eddies in natural shallow water and continental shelf environments numerical hydrodynamic modelling and field measurements show that during the later stages of the half tidal cycle in a low friction environment currents in the lee of an obstruction accelerate with supporting sea gradients opposite to the adjacent inertial free stream which is still decelerating these opposed currents appear as a phase eddy and ideally can endure for 3 hours in m2 s2 reversing currents case studies are cited and numerical hydrodynamic modeling is applied to examine the formation of these circulation patterns

estimating suspended solids concentrations from backscatter intensity measured by acoustic doppler current profiler in san francisco bay california abstract the estimation of mass concentration of suspended solids is one of the properties needed to understand the characteristics of sediment transport in bays and estuaries however useful measurements or estimates of this property are often problematic when employing the usual methods of determination from collected water samples or optical sensors analysis of water samples tends to undersample the highly variable character of suspended solids and optical sensors often become useless from biological fouling in highly productive regions acoustic sensors such as acoustic doppler current profilers that are now routinely used to measure water velocity have been shown to hold promise as a means of quantitatively estimating suspended solids from acoustic backscatter intensity a parameter used in velocity measurement to further evaluate application of this technique using commercially available instruments profiles of suspended solids concentrations are estimated from acoustic backscatter intensity recorded by 1200 and 2400 khz broadband acoustic doppler current profilers located at two sites in san francisco bay california adcp backscatter intensity is calibrated using optical backscatterance data from an instrument located at a depth close to the adcp transducers in addition to losses from spherical spreading and water absorption calculations of acoustic transmission losses account for attenuation from suspended sediment and correction for nonspherical spreading in the near field of the acoustic transducer acoustic estimates of suspended solids consisting of cohesive and noncohesive sediments are found to agree within about 8 10 of the total range of concentration to those values estimated by a second optical backscatterance sensor located at a depth further from the adcp transducers the success of this approach using commercially available doppler profilers provides promise that this technique might be appropriate and useful under certain conditions in spite of some theoretical limitations of the method

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

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

trace element geochemistry of metabasaltic rocks from the yukon tanana upland and implications for the origin of tectonic assemblages in east central alaska we present major and trace element geochemical data for 27 amphibolites and six greenstones from three structural packages in the yukon tanana upland of east central alaska the lake george assem