comparison of radar and in situ measurements of atmospheric turbulence 1 we compare measurements of refractive index structure constant cn2 and energy dissipation rate e by vhf radar with in situ observations by high resolution thermosondes during a campaign near adelaide australia in august 1998 a total of 17 thermosonde soundings was performed within a distance of 120 km to the radar site the variance between estimates of cn2 from backscattered radar power and in situ thermosonde observations is found to be comparable to the observed variance of the radar estimates due to temporal and spatial variations of the turbulent parameters angle brackets denote average over the radar range resolution of 1 km the high resolution thermosonde observations allow us to test the applicability of the turbulent volume fraction model to the estimation of e from cn2 the data indicate that the turbulent volume fraction should not be modeled as the fraction of unstable layers with gradient richardson number ri 0 25

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

regional scale co seismic landslide assessment using limit equilibrium analysis abstract traditionally regional assessment of seismic slope stability has been done using the infinite slope rigid sliding block analysis a major disadvantage of this approach is the resulting overestimation of the critical acceleration of the slope due to the underlying assumption of a predefined slope failure plane and consequently the underestimation of hazard areas prone to sliding in this paper we present a modified approach for assessing seismic slope instabilities using a model based on limit equilibrium analysis and circular slip surfaces with no restriction to any predefined slope failure plane for this purpose we conduct a parametric study to identify the relationship between the critical acceleration of the slope the slope angle and the slope shear strength parameters we model typical slopes in the rocscience software slide using bishop s limit equilibrium method to identify the critical accelerations that corresponds to a failure plane with factor of safety equal to one the critical accelerations were plotted against the variables in the parametric study and the best fit equations were obtained the proposed approach was developed for global application but it was tested using the well documented co seismic landslide database of the 1994 northridge ca earthquake the predicted sliding areas were compared to the inventory of landslides that were triggered in the val verde region in los angeles by the earthquake qualitative and quantitative assessments of the proposed model clearly show its advantages in predicting potential sliding areas

present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

gravity wave propagation characteristics 60 120 km as determined by the saskatoon mf radar gravnet system 1983 85 at 52 n 107 w abstract gravity waves gw have been detected and their characteristics measured by observations with the saskatoon multiple bistatic system gravnet data are available from 50 days for two height ranges 64 97 km 100 115 km and for the four seasons of 1983 85 wave characteristics include horizontal wavelength phase velocity period and amplitude background wind data allows the corresponding intrinsic parameters to be calculated many waves are doppler shifted to near their critical levels altitude and seasonal variations in the gw characteristics are shown the strongest variation is in the horizontal direction of wave propagation with southward directions dominating but significant eastward westward fluxes in summer winter below 100 km

the influence of dunes on mixing in a migrating salt wedge fraser river estuary canada dune bedforms and salt wedge intrusions are common features in many estuaries with sand beds and yet little is known about the interactions between the two flow visualization with an echosounder and velocity measurements with an acoustic doppler current profiler over areas of flat bed and sand dunes in the highly stratified fraser river estuary canada were used to examine the effect of dunes on interfacial mixing as the salt wedge migrates upstream over the flat bed mixing is restricted to the lower portion of the water column however as the salt wedge migrates into the dune field from the flat bed there is a dramatic change in the flow and large internal in phase waves develop over each of the larger dunes with water from the salt wedge reaching the surface of the estuary the friction richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat bed and a plot of internal froude number versus obstacle dune height shows that the salt wedge flow over the dunes is mainly supercritical such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment laden density currents and may thus be influential in fluid mixing and sediment transport copyright 2010 john wiley sons ltd

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

extraordinary distance limits of landslides triggered by the 2011 mineral virginia earthquake the 23 august 2011 mineral virginia earthquake m w 5 8 was the largest to strike the eastern u s since 1897 and was felt over an extraordinarily large area although no large landslides occurred the shaking did trigger many rock and soil falls from steep river banks and natural cliffs in the epicentral area and from steep road cuts along and northwest of the blue ridge parkway we mapped the occurrence of rock falls to determine distance limits that could be compared with those from other documented earthquakes studies of previous earthquakes indicated a maximum epicentral distance limit for landsliding of 60 km for an m 5 8 earthquake the maximum distance limit for the 2011 earthquake was 245 km the largest exceedance of the historical limit ever recorded likewise the previous maximum area affected by landslides for this magnitude was 1500 km2 the area affected by landslides in the 2011 earthquake was 33 400 km2 these observations provide physical evidence that attenuation of strong shaking for eastern u s earthquakes is significantly lower than for plate boundary earthquakes also distance limits parallel to the regional structural trend are greater than those that transect the structure which suggests anisotropic attenuation related to the regional geologic structure peak ground acceleration pga at the landslide distance limits is estimated to have been about 0 02 0 04 g

case study of precision of gps differential correction strategies influence on adcp velocity and discharge estimates the precision of four differential global positioning systems dgps was evaluated in the context of fluvial water velocity and discharge measurement dgps is used to resolve water velocities measured with an acoustic doppler current profiler adcp into earth coordinates if bottom tracking is unavailable the dgps systems assessed were 1 the dual frequency real time kinematic rtkl1l2 2 the single frequency real time kinematic rtkl1 3 the code phase canadian coast guard cg and 4 the code phase wide area augmentation system waas repeat discharge surveys n 22 were conducted at a transect of the gatineau river canada simultaneously collecting bottom track boat velocity vbt and boat velocity from all four dgps vdgps the mean absolute single ping differences between vbt and vdgps were 3 1 rtkl1l2 3 2 rtkl1 8 9 cg and 9 8 cm s waas errors were observed more often near channel margins presumably due to obstruction and multipath associated with riverbank vegetation

earthquake induced ground failures in italy abstract the national catalog of ground failures induced by strong earthquakes in italy cedit is described the catalog holds data on ground failures triggered by the earthquakes that occurred in italy in the last millennium and which had a nominal epicentral intensity equal to or greater than viii in the mercalli cancani sieberg mcs intensity scale the ground effects reported in the catalog are the following landslides fractures liquefaction surface faulting and topographic changes of the ground level subsidence settlements tilting and so on each effect is described in terms of seismological parameters of the triggering earthquake site coordinates and administrative code lithology and kinematic type of the ground failure the catalog represents a tool to assess the susceptibility of geologic materials to ground shaking and to validate predictive models of seismically induced ground displacements scenarios of earthquake induced geologic risks in the context of this study a simple statistical analysis of the database yielded useful relations between the parameters of the triggering earthquakes and the related effects

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

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

seasonal variation of momentum flux in the mesosphere observed with the mu radar we have regularly monitored mesospheric winds at 60 85km for three years with the mu radar 35 n 136 e and have found that the variance of wind velocity fluctuations for periods from 5 min to 2 hr shows a semi annual variation with a significant peak in summer centered in july and irregular enhancements in winter the zonal momentum flux induced by gravity waves shows eastward and westward maxima in july august and december february respectively typical eastward accelerations at the 70km altitude range from 7 to 13 m s day and from 8 to 11 m s day in summer and winter respectively which agree fairly well with theoretical predictions

first observations of turbulence parameters in the troposphere over the bay of bengal and the arabian sea using radiosonde 1 this paper discusses the turbulence characteristics of the free atmosphere over the bay of bengal and the arabian sea during the premonsoon season of 2006 the turbulence scaling concepts developed over the past decades for application to oceanic mixing are used for retrieving turbulence properties in the free atmosphere from high resolution soundings as described by clayson and kantha 2008 the variability in the vertical turbulence structure over a large spatial region is studied using this novel method for the first time investigations revealed the presence of a highly turbulent band at upper troposphere below the cold point tropopause cpt with significant enhancements in thorpe length and eddy diffusion coefficient this increased turbulence is studied in conjunction with the observations of the tropical tropopause layer ttl it is seen that the lower and upper boundaries of this turbulence band nearly coincide with the height where the potential temperature lapse rate begins to show a decrease lrhmin and cold point tropopause respectively the ttl is the transition regime from convectively dominated troposphere to radiatively dominated stratosphere and is characterized by a decrease in the static stability the enhanced zonal and meridional wind shear observed in this region shows that the stability in this region is further weakened because of the breaking of kelvin helmholtz waves which results in the enhancement of turbulence the study reveals the potential of high resolution soundings to be used in the investigations of turbulence in the free atmosphere

temporal and spatial variability of vertical salt flux in a highly stratified estuary 1 the temporal and spatial variability of vertical salt flux in the fraser river estuary british columbia was investigated observationally using several different direct and indirect indicators of buoyancy flux data were collected from the estuary using shipboard instrumentation primarily an acoustic doppler current profiler and a towed conductivity temperature depth unit direct estimates of buoyancy flux were made from along channel control volume analyses and from measurements of overturn scales the spatial and temporal evolution of the salt wedge structure through a tidal cycle was evaluated using the results of these buoyancy flux calculations as well as gradient richardson number froude number and stratification profiles observations indicate that buoyancy flux is driven primarily by interfacial stress and not bottom stress as is common in many estuaries vertical salt flux as opposed to seaward advection of high salinity fluid was found to be the dominant mechanism responsible for removal of salt from the estuarine channel during each daily tidal cycle buoyancy flux was highly variable in time and space however with vertical salt flux during ebb tides on the order of 2 to 3 times greater than that estimated during floods this is due to an increase in the vertical shear of horizontal velocity and a sharp increase in stratification which was observed during early ebb enhanced mixing was observed spatially within a region dominated by a channel constriction in which the channel narrows by approximately 25

flow and sediment suspension events over low angle dunes fraser estuary canada 1 the morphodynamics of large sand bedded rivers and estuaries are ultimately controlled by the way bed material is moved and the development of large subaqueous sand dunes that control hydraulic flow resistance it is widely thought that the primary mechanism for moving sandy bed material in these channels is large scale coherent flow structures that cause suspension events whose properties vary with flow especially in tidally influenced environments here we examine mean flow and sediment suspension events over low angle dunes lee face angle 30 in the unsteady flow of the fraser estuary canada at high tide flow nearly ceased and a salt wedge entered the channel forcing salt water under the downstream moving fresh water the salt wedge persisted in the channel until late in the falling tide causing stratification in the water column and instabilities along the saline fresh water interface at low tide mean velocities peaked and forced the saline water out of the channel flow over the low angle dunes displayed topographically induced patterns previously observed over high angle dunes but permanent flow separation was not observed large scale sediment suspension events dominated sediment flux during low tide and became larger scale yet less frequent as the tide began to rise the suspension events appeared to form over the lower stoss of the dunes and grew up over the bed forms and less commonly emerged downstream of the crest suspension events move 69 of the total sediment in the flow above low angle dunes when they are present

global distribution of ct2 at altitudes 30 50 km from space borne observations of stellar scintillation 1 locally isotropic turbulence in the stratosphere consists of isolated sporadic patches with random values of temperature structure characteristic ct2 stellar scintillations measured aboard gomos envisat through the earth atmosphere provided the first global distribution of the effective characteristic ct eff2 averaged along sounding ray for zonal mean the largest values are achieved in winter polar regions this observed intense turbulence is probably related to the polar night jet relatively weak turbulence is observed at low latitudes turbulence intensity map is shown for altitude 42 km in the latitude band 35 where the maxima follow the sub solar latitude with enhancements located mainly over continents turbulence enhancements are not related with orography despite a noticeable correlation with typical regions of deep convection the overall distribution of ct eff2 displays a more complicated structure analyzed data suggest that the main turbulence sources at altitudes 40 km are instabilities of stratospheric circulation and gravity wave breaking

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

variability in bedform morphology and kinematics with transport stage bedform geometry is widely recognized to be a function of transport stage bedform aspect ratio height length increases with transport stage reaches a maximum then decreases as bedforms washout to a plane bed bedform migration rates are also linked to bedform geometry in so far as smaller bedforms in coarser sediment tend to migrate faster than larger bedforms in finer sediment however how bedform morphology height length and shape and kinematics translation and deformation change with transport stage and suspension have not been examined a series of experiments is presented where initial flow depth and grain size were held constant and the transport stage was varied to produce bedload dominated mixed load dominated and suspended load dominated conditions the results show that the commonly observed pattern in bedform aspect ratio occurs because bedform height increases then decreases with transport stage against a continuously increasing bedform length bedform size variability increased with transport stage leading to less uniform bedform fields at higher transport stage total translation related and deformation related sediment fluxes all increased with transport stage however the relative contribution to the total flux changed at the bedload dominated stage translation related and deformation related flux contributed equally to the total flux as the transport stage increased the fraction of the total load contributed by translation increased and the fraction contributed by deformation declined because the bedforms got bigger and moved faster at the suspended load dominated transport stage the deformation flux increased and the translation flux decreased as a fraction of the total load approaching one and zero respectively as bedforms washed out to a plane bed

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

the gravel sand transition sediment dynamics in a diffuse extension as gravel bedded rivers fine in the downstream direction they characteristically exhibit an abrupt transition from gravel to sand bedded conditions the prevailing theory for why abrupt gravel sand transitions emerge is based on bed load sorting of a bimodal sediment the abruptness is thought to be a consequence of sand overwhelming the gravel sand mixture once it reaches a critical coverage on the bed the role suspension plays in the development of gravel sand transitions has not been fully appreciated the fraser river british columbia is an archetypical abrupt gravel sand transition with a diffuse extension composed of a sand bed with some patches of gravel we examine flow shear stress and suspended sediment flux in the diffuse extension to better understand sediment dynamics where the sand bed emerges sand is carried in suspension upstream of the primary abrupt gravel sand transition but in the diffuse extension sand is moved as both bed load and suspended load we do not observe downstream gradients in shear stress or suspended sand flux through the diffuse extension that would suggest a gradual rain out of sand moving downstream which raises the question how is the sand bed formed sediment advection length scales indicate that with the exception of very fine sand that moves as wash load in the diffuse extension fractions coarser than the median sand size cannot be carried in suspension for more than one channel width this suggests that sand is deposited en masse at the beginning of the diffuse extension forming a sediment slug at low flood flows that is smeared downstream at high flood flows to form the sand reach

rocket vapor trail releases revisited turbulence and the scale of gravity waves implications for the imaging doppler interferometry incoherent scatter radar controversy the rate of diffusion of a trimethyl aluminum trail released by a skylark rocket over woomera australia 31 s 137 e in 1969 is interpreted in terms of molecular and turbulent diffusion and is related to the scale of internal atmospheric gravity wave winds implications for disagreement between imaging doppler interferometry and incoherent scatter radar winds are explored

macroturbulence generated by dunes fraser river canada abstract a selectable frequency acoustic profiler and electromagnetic current meter were deployed in the lower fraser river canada to examine large turbulent structures features were generated on the lower stoss sides of dunes and appeared at the surface tens of metres downstream as strong upwellings boils they were identified with acoustic clouds in the acoustic profile event recurrence periods measured from acoustic time series and from ejection events identified in the current meter record had similar two component frequency distributions but the acoustic values lacked the highest frequencies a comparison of measured periods with predictions from the strouhal law indicate that both dune amplitude and the internal boundary layer developed over the dunes are significant length scales associated with the generation of the macroturbulence our data give no support to the notion that boils develop from microturbulent bursts

seismically induced landslides by a low magnitude earthquake the mw 4 7 ossa de montiel event central spain this work has been funded by spanish ministry of economy and competitiveness research project cgl2011 30153 c02 02 and by the research groups rnm 374 junta de andalucia tectac ucm 910368 and vigrob 184 universidad de alicante mr loffredo acknowledges funding of the universita di roma la sapienza post graduate grant concorso a n 480 area cun 04

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

attenuation of intensity with epicentral distance in the iberian peninsula we have classified the attenuation of the medveded sponheuer and karnik msk intensity into five types each as a function of the epicentral intensity i o based on the mean radii of 254 isoseismal maps mainly historical earthquakes in the iberian peninsula geographically representing each earthquake with its corresponding attenuation tendency it can be seen that those with low attenuation lie west of the peninsula and those with high attenuation in the south and east this regionalization seems to be due as much to the seismotectonic characteristics different crustal types and size of the earthquakes as to the different construction types in each region these attenuation values are similar to those of southern europe but much higher than those found in the united states from the point of view of seismic hazard evaluation these laws represent an improvement with regard to those used so far we have extended previous attenuation studies to the whole of the iberian peninsula and in some points differences of attenuation assignment of almost two degrees of intensity have been corrected

improved estimation of adcp apparent bed load velocity using a real time kalman filter an estimate of apparent bed load velocity v can be derived from the difference between differential global positioning system dgpss and acoustic doppler current profiler adcp bottom track bt measurements when bt is biased by a moving bottom a kalman filter has been developed to integrate gps and bottom track data to improve estimation of boat velocity during adcp measurements under moving bed conditions rennie and rainville 2008 j hydraulic eng in review the boat velocity estimated using the kalman filter is superior to boat velocity from raw gps data in this paper we assess the improvement in estimation of v using the kalman filter as opposed to raw gps data specifically a synthetic moving bed bias was generated for 22 repeat transects of the gatineau river quebec the synthetic moving bed bias had mean variance and distribution across the section as typically observed during bed load transport conditions and had the advantage that it was known explicitly the errors in estimated

the separated polar winter stratopause a gravity wave driven climatological feature abstract an examination of satellite derived temperatures reveals that the winter polar stratopause is usually elevated and warmer than the adjacent midlatitude stratopause this separated stratopause occurs in both hemispheres but is more pronounced and persistent in the southern winter it descends with time towards spring and exhibits week to week variability observational diagnostics and results from a two dimensional 2 d model suggest that gravity wave driving can account for this separated polar stratopause by driving a meridional circulation with downwelling over the winter pole in the model the solar heating pattern induces stronger winter westerlies than summer easterlies which leads to a stronger gravity wave driven circulation in the winter hemisphere spherical geometry and the high latitude location of the winter westerly jet combine to yield a concentrated region of downwelling model results suggest that descent of the temperature maximum with time is probably caused by wave mean f

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

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

observation and analysis of shear instability in the fraser river estuary 1 we investigate the occurrence of shear instability in the fraser river estuary instabilities observed with an echo sounder are compared with a linear stability analysis based on observed velocity and density profiles we find that each set of observed instabilities coincides with an unstable mode predicted by the taylor goldstein equation each of these instabilities occurs in a region where the gradient richardson number is less than the critical value of 1 4 both the taylor goldstein predictions and the echo soundings indicate the instabilities are concentrated either above or below the density interface this one sidedness is in contrast to the archetypal kelvin helmholtz instability although the dominant source of mixing in the estuary appears to be caused by shear instability when the tide produces strong near bed velocities small scale overturning due to boundary layer turbulence is apparent throughout the depth

dunes and associated sand transport in a tidally influenced sand bed channel fraser river british columbia dunes form annually on the sand bed of the tidally influenced south arm of fraser river british columbia bathymetric surveys along the center of the main channel throughout a snow melt freshet provided measurements of dune geometry and migration dune length height and steepness all increase with river discharge however lag between the highest flow conditions and development of the largest steepest dunes reflects the influence of antecedent flow conditions on dune geometry population averages of dune height and steepness ratio change more rapidly than dune length whilst coefficients of variation of dune height length and steepness ratio indicate high variability in dune geometry within the estuarine reach during periods of dune growth and decay unlike dune geometry dune migration rates display little lag with flow conditions the largest coefficients of variation for dune migration occur during periods of rapid change in discharge and tidal fall corresponding to the onset of rapid change in

low angle dunes in the changjiang yangtze estuary flow and sediment dynamics under tidal influence it has long been highlighted that important feedbacks exist between river bed morphology sediment transport and the turbulent flow field and that these feedbacks change in response to forcing mechanisms however our current understanding of bedform dynamics is largely based on studies of steady flow environments and cohesionless bed conditions few investigations have been made under rapidly changing flows here we examine flow and sediment dynamics over low angle dunes in unsteady flows in the changjiang yangtze estuary china topography flow and sediment data were collected over a reach ca 1 8 km long through a semi diurnal tidal cycle in a moderate tide of flood season the results show that 1 roughness length derived from the upper flow changes little with the flow reversing and displays the same value on both the ebb and flood tide moreover the variability of individual bedform features plays an important role in roughness length variation 2 shear stress over the crest of low angle dunes roughly represents the total spatially averaged stress over dunes in this study area which has significant implications for advancing numerical models 3 changes in morphology flow and sediment dynamics over dunes through time reveal how low angle dunes evolve within a tidal cycle 4 the clockwise hysteresis loops between flow dynamics and bedform features height and aspect ratio are also observed the combination of suspended sediment transport and bedload transport on dune transformation and migration attributes to the clockwise hysteresis the specific sediment composition of the riverbed in some extent affects the mechanism of sediment transport related to the exchange between suspended sediment and riverbed but further investigation is needed to figure out the mechanism behind this for extended series of tides such as spring neap tide and tides in flooding and dry season

can low magnitude earthquakes act as a triggering factor for landslide activity examples from the western carpathian mts poland abstract there are numerous examples of the impact of strong earthquakes on landslide activity there is however very little information about the ability of low magnitude earthquakes m

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

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

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

relationship between earthquake induced excess pore water pressure and strong ground motion observed in a monitored fill slope abstract the generation of excess pore water pressures during ground shaking can be an important earthquake induced landslide trigger we measured pore water pressures and seismic ground motion in filled slopes and examined their relationships obtained from 29 observed earthquakes we characterized pore water pressure and seismic waveforms by calculating several parameters that described their magnitudes and durations we demonstrate that whilst the instantaneous magnitude of strong ground motion is responsible for the generation of excess pore water pressure the magnitude of excess pore water pressure generated is related to the peak ground acceleration pga and arias intensity ai in the observed pga range of 0 12 1 9 m s2 the magnitude of peak ground velocity pgv also produced a strong correlation although a few exceptional events where long period component 1 s of seismic waves is dominant were observed lastly the time span over which excess pore water pressure continues to rise is affected by the duration of seismic ground motion our study shows how excess pore water pressures can be generated in fill slopes during seismic events this new knowledge could be used to improve future earthquake induced landslide hazard assessment

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

widespread landslides induced by the mw 5 1 earthquake of 11 may 2011 in lorca se spain abstract on 11 may 2011 a moderate magnitude mw 5 1 earthquake struck the city of lorca se spain and nearby areas causing notable damage injuries and fatalities field inspection of the area affected allowed the location and characterization of more than 250 induced landslides mainly of disrupted type rock soil falls disrupted soil slides and rock avalanches this number was very high when compared with the inventories of previous events of similar magnitude mw 4 7 to 5 0 in the zone and with the results of previous models for predicting slope behavior during earthquakes several factors are proposed here to explain the observed differences i the comparatively high magnitude mw 4 5 of a foreshock of the seismic series that may have weakened the slopes ii the high peak ground motion values recorded for these events and iii the occurrence of topographic site effects the results of this study point out the importance of including such effects as improvements in the models for studying the regional behavior of slopes

seasonal variability of vertical eddy diffusivity in the middle atmosphere 1 three year observations by the middle and upper atmosphere radar the vertical eddy diffusivity k due to atmospheric turbulence with spatial scales of 100 102 m has been computed from the echo power spectral width observed by the middle and upper atmosphere radar for almost every month from january 1986 to december 1988 the method of analysis follows lilly et al 1974 sato and woodman 1982 and hocking 1983a 1985 1988 and the contamination due to beam broadening vertical shear and transience has been removed although observations for horizontal wind speeds larger than approximately 40 m s such as occur near the tropopause jet stream in winter have been omitted because of excessive beam broadening sufficient numbers of observations have been accumulated to produce a reasonable climatology for the upper troposphere and lower stratosphere 6 20 km altitude and for the mesosphere 60 82 km altitude the monthly median of k shows a local maximum near the tropopause jet stream altitude it becomes larger in the mesosphere increasing gradually with height maxima of k are observed in winter near the tropopause and in summer in the mesosphere and the seasonal variability of k reaches approximately an order of magnitude a semiannual variability is apparent in the mesosphere with minima in the equinoctial seasons

impact of tensile strength and incident angles on a soil slope under earthquake sv waves abstract the tensile strength and incident angles play important roles in seismically induced slope failures in this paper a new criterion for tension shear coupling is proposed based on several sets of relevant lab data and is verified using the experimental data provided by previous researchers this criterion can perfectly depict the tension region as well as the compression region in the entire stress space moreover the tension shear criterion was converted into an expression that could be directly used in a numerical method and it was verified by a numerical example in addition the sv waves were input using the equivalent nodal force method based on a viscous spring artificial boundary this process was implemented by the abaqus software and two numerical examples were used to verify this method subsequently based on the proposed new criterion and input method the impacts of the strength criterion and incident angles on an analysis of seismically induced slope failures were studied the results indicated that the evaluation of the tension shear region is extremely important in the analysis of the seismically induced slope failures the tensile strength of the seismically induced landslides was overestimated by the calculation of mohr coulomb criterion owing to the ambiguous description of the tensile failure or the tension shear failure the assessment of the slope stability was thus not conservative the incident angles of seismic waves affected the travel path and the directivity of slope seismic responses the sliding displacement of the slope side near the epicenter rose with increasing angles of wave incidence the critical slip surface deepened and the hazard aggravated therefore it is important to introduce both the tensile strength and incident angles when evaluating the stability of slopes subjected to seismic loads

spectral analysis of turbulent flow and suspended sediment transport over fixed dunes laboratory measurements of turbulent fluctuations in velocity and suspended sediment concentration were obtained synchronously over fixed two dimensional dunes in a sediment starved flow contour maps of turbulent flow parameters demonstrate that the flow separation cell and a perturbed shear layer are the main sources of turbulence production and that the distribution of suspended sediment is controlled by spatially dependent macro turbulent flow structures spectral analysis reveals that peak spectral energies generally occur at 1 2 hz for the stream wise velocity component and 2 4 hz for the cross stream and vertical velocity components spectra show larger and better defined energy peaks near the shear layer peak spectral energies for suspended sediment concentration occur near 1 hz throughout the flow squared coherency values for cospectral analysis of velocity and sediment concentration are insignificant integral timescales for velocity range from 0 20 s for the streamwise component to 0 06 s for the cross stream and vertical components integral length scales for velocity range from 0 065 to 0 135 m for the streamwise component which is comparable to flow depth and from 0 020 to 0 030 m for the crossstream and vertical components which is comparable to dune height for suspended sediment concentration integral timescales and length scales are similar to the streamwise velocity component

a numerical investigation into the importance of bed permeability on determining flow structures over river dunes although permeable sediments dominate the majority of natural environments past work concerning bedform dynamics has considered the bed to be impermeable and has generally neglected flow between the hyporheic zone and boundary layer herein we present results detailing numerically modelled flow which allow the effects of bed permeability on bedform dynamics to be assessed simulation of an isolated impermeable bedform over a permeable bed shows that flow is forced into the bed upstream of the dune and returns to the boundary layer at the leeside in the form of returning jets that generate horseshoe shaped vortices the returning flow significantly influences the leeside flow modifying the separation zone lifting the shear layer adjoining the separation zone away from the bed simulation of a permeable dune on a permeable bed reveals even greater modifications as the flow through the dune negates the formation of any flow separation in the leeside with two dunes placed in series the flow over the downstream dune is influenced by the developing boundary layer on the leeside of the upstream dune for the permeable bed case the upwelling flow lifts the separated flow from the bed modifies the shear layer through the coalescence with vortices generated and causes the shear layer to undulate rather than be parallel to the bed these results demonstrate the significant effect that bed permeability has on the flow over bedforms that may be critical in affecting the flux of water and nutrients

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

on the applicability of available regression models for estimating newmark displacements for low to moderate magnitude earthquakes the case of the betic cordillera s spain abstract newmark displacement estimation is generally computed using empirical models these models are estimated from large datasets that mainly comprise moderate to high magnitude events mw 6 0 in this work we study the performance of several of these models to study moderate to low magnitude scenarios for this purpose data from the betic cordillera s spain with magnitudes ranging from mw 3 5 to 6 3 were used to compare with model predictions the results show that errors in the estimates depend on the magnitude of events or on the yielding acceleration considered to estimate the displacement the availability of an appropriate range of data magnitude and yielding acceleration when defining the regression model may overcome the differences due to specific characteristics of the seismotectonic context of the area where data derives from the results also show that performance of models including several ground motion predictors is better than those based on a single parameter regardless of the combination these predictors furthermore regression models with polynomial forms present a better performance than other functions based on the logarithm of these predictors finally new specific models for the betic cordillera are proposed especially suitable for low magnitude events

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

turbulent flow over a dune green river colorado detailed echo sounder and acoustic doppler velocimeter measurements are used to assess the temporal and spatial structure of turbulent flow over a mobile dune in a wide low gradient alluvial reach of the green river based on the geometric position of the sensor over the bedforms measurements were taken in the wake in transitional flow at the bedform crest and in the internal boundary layer spatial distributions of reynolds shear stress turbulent kinetic energy turbulence intensity and correlation coefficient are qualitatively consistent with those over fixed two dimensional bedforms in laboratory flows spectral and cospectral analysis demonstrates that energy levels in the lee of the crest i e wake are two to four times greater than over the crest itself with minima over the stoss slope within the developing internal boundary layer the frequency structure in the wake is sharply defined with single dominant peaks peak and total spectral and cross spectral energies vary over the bedform in a manner consistent with wave like perturbations that break or roll up into vortices that amalgamate grow in size and eventually diffuse as they are advected downstream fluid oscillations in the lee of the dune demonstrate strouhal similarity between laboratory and field environments and correspondence between the peak frequencies of these oscillations and the periodicity of surface boils was observed in the field copyright 2005 john wiley sons ltd

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

observations of a reversal in long term average vertical velocities near the jet stream wind maximum abstract analysis of vertical velocity measurements made for four days each month over the period from 1986 to 1988 by the mu radar in japan shows a reversal in direction near the peak in the zonal wind profile during the winter months more specifically the reversal is noted during periods when the peak horizontal wind speeds 60 m s 1 the vertical velocities associated with the circulation have magnitudes of 10 20 cm s 1 and the depth of the circulation is of the order of several kilometers in 6 out of 14 cases when the feature was observed the direction of the vertical circulation although not the magnitude could be explained by adiabatic ascent or subsidence along the average potential temperature surface slopes for the observation intervals the direction of the circulation was such that it would tend to produce cooling and heating for the ascent and subsidence respectively that would tend to strengthen or at least maintain the jet in the remaining eight cases the direction of the vertical

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

on far field occurrence of seismically induced landslides abstract earthquakes may induce landslides at large distances from the epicentral area in the last two decades there have been many studies of this phenomenon to determine the causes that contribute to the occurrence of landslides at very long distances from earthquake epicenter in this study which is based on previously published works a worldwide database comprising 270 earthquakes including 150 during the instrumental period was compiled to analyse the features of those landslides that occur at much further distances than maximum expected distances from the analysis of the compiled data it was observed that susceptible slopes can be grouped into five broad geological categories jointed rock marly clayey cohesive soils granular alluvial and or colluvial sediments volcanic soils and residual soil slopes these categories were equally likely to be associated with far field disrupted landslides whereas far field coherent landslides were more frequent on cohesive soil slopes other factors along with slope susceptibility may also contribute to far field landslides and increase the size of the area affected among these factors site effects antecedent rain and occurrence of seismic series have been cited the analysis of available data also showed that for events of the same magnitude far field disrupted landslides may occur at greater distances than coherent ones the same database has also been employed to determine for the first time the upper bound curves for the maximum observed epicentral distances of several types of landslides and the maximum area observed to be affected by landslides both based on the epicentral intensity of the events

tide induced variation of the dynamics of a salt wedge estuary abstract the time variations of the salt wedge intrusion in the fraser estuary british columbia were monitored during a variety of tidal and run off conditions using instruments and sampling methods that provided high resolution of the velocity and water properties in space and time the salt wedge was found to vary considerably in position and vertical structure through the tidal cycle due to the interaction of the tidal flow with the density driven motion of the salt wedge during the flood the salt wedge progressed up the estuary as a gravity current while during the ebb the salinity structure was eroded by shear instability the difference in character of the flow between flood and ebb is attributed to the transition between a subcritical and supercritical internal froude number during flood tide the internal state is subcritical and the estuarine shear flow is maintained with a small amount of vertical mixing while in the supercritical ebb flow vertical shears become so large that the pycnoc

earthquake induced landslides in central america central america is a region of high seismic activity and the impact of destructive earthquakes is often aggravated by the triggering of landslides data are presented for earthquake triggered landslides in the region and their characteristics are compared with global relationships between the area of landsliding and earthquake magnitude we find that the areas affected by landslides are similar to other parts of the world but in certain parts of central america the numbers of slides are disproportionate for the size of the earthquakes we also find that there are important differences between the characteristics of landslides in different parts of the central american isthmus soil falls and slides in steep slopes in volcanic soils predominate in guatemala and el salvador whereas extensive translational slides in lateritic soils on large slopes are the principal hazard in costa rica and panama methods for assessing landslide hazards considering both rainfall and earthquakes as triggering mechanisms developed in costa rica appear not to be suitable for direct application in the northern countries of the isthmus for which modified approaches are required

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