role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries

interaction of lateral baroclinic forcing and turbulence in an estuary 1 observations of density and velocity in a channel in northern san francisco bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross channel baroclinic pressure gradient and vertical mixing due to turbulence profiles of velocity salinity temperature and suspended sediment concentration were measured in transects across suisun cutoff in northern san francisco bay on two days over the 12 5 hour tidal cycle during flood tides an axial density front developed between fresher water flowing from the shallows of grizzly bay into the northern side of suisun cutoff and saltier water flowing up the channel north of the front transverse currents were driven by the lateral salinity gradient with a top to bottom velocity difference greater than 30 cm s south of the front the secondary circulation was weak and along channel velocities were greater than to the north the gradient richardson number shows that stratification was stable north of the front while the water column was turbulently mixed south of the front time series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle in estuaries longitudinal dynamics predict less stratification during flood than ebb tides these data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry

infiltration on sloping terrain and its role on runoff generation and slope stability abstract a modified green and ampt model is formulated to quantify infiltration on sloping terrain underlain by homogeneous soil wetted by surficial water application this paper s theory for quantifying infiltration relies on the mathematical statement of the coupled partial differential equations pdes governing infiltration and runoff these pdes are solved by employing an explicit finite difference numerical method that yields the infiltration the infiltration rate the depth to the wetting front the rate of runoff and the depth of runoff everywhere on the slope during external wetting data inputs consist of a water application rate or the rainfall hyetograph of a storm of arbitrary duration soil hydraulic characteristics and antecedent moisture and the slope s hydraulic and geometric characteristics the presented theory predicts the effect an advancing wetting front has on slope stability with respect to translational sliding this paper s theory also develops the 1d pde governing suspended sediment transport and slope degradation caused by runoff influenced by infiltration three examples illustrate the application of the developed theory to calculate infiltration and runoff on a slope and their role on the stability of cohesive and cohesionless soils forming sloping terrain

evidence for earthquake triggering of large landslides in coastal oregon usa abstract landslides are ubiquitous along the oregon coast many are large deep slides in sedimentary rock and are dormant or active only during the rainy season morphology observed movement rates and total movement suggest that many are at least several hundreds of years old the offshore cascadia subduction zone produces great earthquakes every 300 500 years that generate tsunami that inundate the coast within minutes many slides and slide prone areas underlie tsunami evacuation and emergency response routes we evaluated the likelihood of existing and future large rockslides being triggered by pore water pressure increase or earthquake induced ground motion using field observations and modeling of three typical slides monitoring for 2 9 years indicated that the rockslides reactivate when pore pressures exceed readily identifiable levels measurements of total movement and observed movement rates suggest that two of the rockslides are 296 336 years old the third could not be dated the most recent great cascadia earthquake was m 9 0 and occurred during january 1700 while regional climatological conditions have been stable for at least the past 600 years hence the estimated ages of the slides support earthquake ground motion as their triggering mechanism limit equilibrium slope stability modeling suggests that increased pore water pressures could not trigger formation of the observed slides even when accompanied by progressive strength loss modeling suggests that ground accelerations comparable to those recorded at geologically similar sites during the m 9 0 11 march 2011 japan trench subduction zone earthquake would trigger formation of the rockslides displacement modeling following the newmark approach suggests that the rockslides would move only centimeters upon coseismic formation however coseismic reactivation of existing rockslides would involve meters of displacement our findings provide better understanding of the dynamic coastal bluff environment and hazards from future subduction zone earthquakes

density driven exchange flow in terms of the kelvin and ekman numbers 1 the pattern of density induced flow influenced by basin s width friction and earth s rotation is investigated as a function of the ekman ek and kelvin ke numbers a semianalytical solution is used to determine the conditions under which the density induced exchange flow is vertically sheared or horizontally sheared solutions are obtained over diverse laterally varying bathymetries it is found that the exchange flow is horizontally sheared under high frictional conditions ek 1 independently of the width of the basin ke the horizontally sheared pattern describes inflow in the channel and outflow over shoals with the inflow occupying the entire water column the exchange flow pattern is also horizontally sheared under weak friction ek 0 and in wide ke 2 basins in that case however the outflow is concentrated on the left looking into the basin in the northern hemisphere portion of the cross section and inflow appears on the right also under weak friction the exchange pattern becomes more vertically sheared with outflow at surface and inflow underneath as the width of the basin becomes small ke 1 bathymetry is not very influential in the weak friction exchange patterns finally under moderate friction 0 01 ek 0 1 the exchange pattern is both horizontally and vertically sheared for all widths the horizontally sheared pattern is best defined in wide basins high ke whereas the vertically sheared pattern practically dominates in narrow basins low ke these findings allow classification of various estuaries in the ek ke parameter space

observations of stratified turbulent mixing in an estuary neap to spring variations during high river flow abstract observations of turbulent mixing stratification and currents were made with a free falling microstructure profiler and a 600 khz adcp in the hudson river off manhattan in may 1994 the ship was anchored in a relatively straight and uniform channel about 15 m deep over 4 days of intense observations from 19 to 24 may 1994 the progression from neap tides to spring tides caused a severe reduction in stratification from an initial top to bottom salinity difference of 18 to 3 6 while low gradient richardson numbers ri occurred only in the weakly stratified bottom layer on flood during neap tides low ri spanned the water column on the second half of ebb during spring tides turbulent dissipation rates varied roughly inversely to ri during neap conditions turbulent mixing was intense only in the bottom layer on flood where eddy diffusivities k reached more than 10 2 m 2 s 1 while mixing was weak in the centre of the halocline near 5 m during spring tides strong mixing occurred throughout the water column during the latter part of ebb with typical k 5 10 3 m 2 s 1 and typical vertical salt flux of 0 0015 kg m 2 s 1 if it existed in isolation this flux would eliminate the haline stratification on a time scale of 4 h ebb time bands of low ri and intense mixing showed increasing phase lag with increasing distance from the bottom the spring tide ebb time internal turbulent stress was relatively uniform with depth with a typical magnitude of 0 4 pa 4 dyne cm 2 turbulent overturning thorpe scales ranged from below 1 cm in the neap tide halocline to a few metres in the weakly stratified bottom layer on flood the strong spring tide ebb time mixing had thorpe scales of typically 0 5 m throughout the water column ozmidov scales tracked thorpe scales except in the weakly stratified layer above the bottom

particle trapping in estuarine tidal flows particle trapping in estuarine turbidity maxima etm is caused primarily by convergent mean and or tidal fluxes of sediment the result is an approximately bell shaped along channel distribution of vertically integrated tidal cycle mean suspended sediment concentration observations from the columbia river estuary suggest that 1 strong two layer or internal along channel residual and overtide flows are generated by time varying stratification and 2 correlations between the near bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment a new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward river flow transport the divergence of velocity shear sediment stratification correlations for the mean flow and each tidal constituent and net erosion or deposition at the bed vertically integrated variables other than seaward river transport are absent from this integrated balance analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of etm found near the upstream limits of salinity intrusion the balance also shows that attempts to represent fluxes causing trapping of sediment in an etm as a product of a time mean vertically integrated along channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the etm this result occurs because the trapping process is inherently nonlinear and at least two dimensional and because a one dimensional representation is physically unrealistic

ambient noise measurements for preliminary site effects characterization in the urban area of florence italy abstract environmental noise measurements and borehole data were used for a preliminary seismic characterization of the plio quaternary sedimentary basin underlying the city of florence italy an extensive survey of ambient vibrations was conducted by using the seismic noise horizontal to vertical h v spectral ratio technique hvsr to map the fundamental resonance frequency of the sedimentary cover in order to use this information to infer main features of the basin subsurface geometry an estimate of the s wave velocity profile in the sediment layer was obtained from array noise recordings along with information on resonance frequency and direct measurements of the sediment thickness available at 23 borehole sites a first order reconstruction of the seismic bedrock topography in the area was provided which shows a good consistency with available geological log data from these pieces of information a preliminary soil classification of the whole area was attempted in order to identify situations where possible seismic amplification effects are expected during future earthquakes and where more accurate investigations are needed to parameterize the local seismic response

effects of bathymetry friction and rotation on estuary ocean exchange an analytical model that includes pressure gradient friction and the earth s rotation in both components of the flow is used to study the transverse structure of estuarine exchange flows and the nature of transverse circulation in estuaries of arbitrary bathymetry analytical results are obtained for generic bathymetry and also over real depth distributions and are compared with observations this study extends previous efforts on the topic of transverse structure of density induced exchange flows in three main aspects 1 the analytical model explores any arbitrary bathymetry 2 the results reflect transverse asymmetries relative to a midchannel centerline associated with the effects of the earth s rotation and 3 the transverse circulation produced by the analytical model is examined in detail analytical results over generic bathymetry show in addition to the already reported dependence of exchange flow structure on the ekman number two new features first the transverse structure of along estuary flows shows the earth s rotation effects even in relatively narrow systems thus producing transverse asymmetries in these flows the asymmetries disappear under strongly frictional high ekman number conditions thus illustrating the previously documented pattern of inflow in channels and outflows over shoals for typical estuaries second transverse flows resemble a sideways gravitational circulation when frictional effects are apparent ekman number greater than 0 1 responding to a transverse balance between pressure gradient and friction these transverse flows reverse direction under very weak friction and reflect coriolis deflection of along estuary flows that is geostrophic dynamics all examples of observed flows are satisfactorily explained by the dynamics included in the analytical model

fluid pressure induced seismicity at regional scales the role of high fluid pressure as a seismogenic agent has been the subject of intense study hubert and rubey 1959 hanshaw and bredehoeft 1968 healy and rubey 1968 simpson 1976 walder and nur 1984 sibson 1990 of particular interest is the so called fault valve mechanism sibson 1976 sibson 1990 a hypothesis whereby fluid pressure rises as a result of tectonic compression and pore volume reduction until crustal failure occurs triggering seismic activity and upward fluid discharge sealing and healing of the rock matrix richter and simmons 1977 sprunt and nur 1979 angevine et al 1982 following coseismic stress drop facilitates reaccumulation of fluid pressure initiating another loading cycle the fault valve mechanism is entertained as a plausible explanation for present day seismic activity in the western transverse ranges of california we provide a quantitative test of the fault valve hypothesis that uses geologic data and rates of active tectonics for a cross section through an active fold and thrust belt on the flank of a developing mountain range rates of fluid pressure buildup and average recurrence times of large earthquakes in the fold and thrust belt are estimated to be on the order of 104pa yrand hundreds of years respectively

double diffusive layering and mixing in patagonian fjords abstract double diffusive layering was quantified for the first time in the chilean patagonian fjords region 41 5 56 s approximately 600 temperature and salinity profiles collected during 1995 2012 were used to study water masses quantify diffusive layering and compute the vertical diffusivity of heat development of diffusive layering or simply layering was favored by relatively fresh cold waters overlying salty warm waters fresh waters are frequently derived from glacial melting that influences the fjord either directly or through rivers salty waters are associated with modified subantarctic msaaw and subantarctic water saaw double diffusive convection occurred as layering in 40 of the year round data and as salt fingering in 5 m 2 s 1 diffusive layering events presented a meridional gradient with less layering within the 41 47 s northern region relative to the southern region between 47 and 56 s layering occupied on average 27 and 56 of the water column in the northern and southern regions respectively thermohaline staircases were detected with microprofile measurements in martinez and baker channels 48 s showing homogeneous layers 2 4 m thick below the pycnocline 10 40 m also in this area increased vertical mixing coincided with the increased layering events high values of thorpe scale l t 7 m dissipation rate of tke e 10 5 10 3 w kg 1 and diapycnal eddy diffusivity k 10 6 10 3 m 2 s 1 were associated with diffusive layering implications of these results are that diffusive layering should be taken into account together with other mixing processes such as shear instabilities and wind driven flows in biological and geochemical studies

creation of residual flows in a partially stratified estuary the creation of residual flows in estuaries is examined using acoustic doppler current profiler data sets from northern san francisco bay the data sets are analyzed using principal component analysis to examine the temporal variability of the flows which create the residual circulation it is seen that in this periodically and partially stratified estuary the residual flows are created through a series of pulses with strong variability at the 24 hour timescale through the interaction of shear stratification and mixing this interaction is captured through the use of a dimensionless number the horizontal richardson number rix which is developed to examine the local balance between the stratifying and destratifying forces at the tidal timescale it is seen that rix is a valuable parameter in predicting the onset of the residual creating events with a threshold value of 3 on ebb tides this critical value is argued to be a threshold above which the stratification and shear flow create a feedback effect each further intensifying the other this feedback results in a highly variable exchange flow which creates the estuarine residual in intermittent pulses rather than as a steady flow although typically attributed to baroclinic forcing an argument is made that these pulses of residual creating exchange flow could be created by barotropic forcing in the presence of variable stratification which is asymmetric between flood and ebb tides this result poses a great challenge for turbulence modeling as the timing and magnitude of stratification and shear must be correctly simulated on the tidal timescale in order to reproduce the effects seen in the data sets presented

the dynamics of a partially mixed estuary measurements of velocity density and pressure gradient in the lower hudson river estuary were used to quantify the dominant terms in the momentum equation and to characterize their variations at tidal and spring neap timescales the vertical momentum flux assumed to be due mainly to turbulent shear stress was estimated indirectly based on the residual from the acceleration and pressure gradient terms the indirect estimates of stress compared favorably to bottom stress estimates using a quadratic drag law supporting the hypothesis that the tidal momentum equation involves a local balance between tidal acceleration pressure gradient and stress divergence estimates of eddy viscosity indicated that there was significant tidal asymmetry with flood tide values exceeding ebb values by a factor of 2 as a consequence of the asymmetry the vertical structure of the tidally averaged stress bore no resemblance to the tidally averaged shear in spite of the asymmetry of vertical mixing the tidally averaged estuarine circulation was found to depend simply on the intensity of bottom turbulence which could be parameterized by a rayleigh drag formulation based on the tidal velocity magnitude and the tidally averaged near bottom flow this seemingly paradoxical result indicates that the estuarine circulation can be modeled without detailed knowledge of the effective eddy viscosity only requiring an estimate of the bottom drag coefficient the tidal forcing conditions and the baroclinic pressure gradient a notable characteristic of this solution is an inverse dependence of the estuarine circulation on the amplitude of the tides

groundwater and earthquakes screening analysis for slope stability groundwater is a factor behind the occurrence of landslides and so is the action of seismic shaking in sloping terrain this paper presents closed form expressions for the factor of safety and yield coefficient of slopes subjected simultaneously to seismic forces and variable groundwater conditions two failure modes of natural slopes are considered in this work namely long slope with phreatic surface parallel to the ground surface and slope with emerging phreatic surface for these failure modes the factor of safety and yield coefficient are determined for various conditions of drainage using effective stress analysis and total stress analysis the effect of soil strength reduction by seismic loading is accounted for in the derived factors of safety and yield coefficients the specification of the lateral seismic coefficient for equivalent seismic loading relies on recent advances in geotechnical earthquake engineering and seismic engineering geology the role of liquefaction and clay softening is introduced in the analysis of seismic slope stability and slope deformation considering variable groundwater conditions several examples illustrate the application of the methods herein presented

methods for assessing the stability of slopes during earthquakes a retrospective abstract during the twentieth century several methods to assess the stability of slopes during earthquakes were developed pseudostatic analysis was the earliest method it involved simply adding a permanent body force representing the earthquake shaking to a static limit equilibrium analysis stress deformation analysis a later development involved much more complex modeling of slopes using a mesh in which the internal stresses and strains within elements are computed based on the applied external loads including gravity and seismic loads stress deformation analysis provided the most realistic model of slope behavior but it is very complex and requires a high density of high quality soil property data as well as an accurate model of soil behavior in 1965 newmark developed a method that effectively bridges the gap between these two types of analysis his sliding block model is easy to apply and provides a useful index of co seismic slope performance subsequent modifications to sliding block analysis have made it applicable to a wider range of landslide types sliding block analysis provides perhaps the greatest utility of all the types of analysis it is far easier to apply than stress deformation analysis and it yields much more useful information than does pseudostatic analysis

analysis of the seismic origin of landslides examples from the new madrid seismic zone by analyzing two landslides in the new madrid seismic zone we develop an approach for judging if a landslide or group of landslides of unknown origin was more likely to have formed as a result of earthquake shaking or in aseismic conditions the two landslides analyzed are representative of two groups of land slides that previous research on the geomorphology and regional distribution of landslides in this region indicates may have been triggered by the 1811 1812 new madrid earthquakes slope stability models of aseismic conditions show that neither landslide is likely to have formed aseismically even in unrealistically high ground water conditions dynamic stability analysis using newmark s method shows that both slides probably would have experienced large inertial displacements during earthquake shaking similar to that which occurred in 1811 1812 these displacements are large enough that catastrophic failure is highly probable thus the stability analyses are consistent with other lines of evidence that these landslides formed as a result of strong earthquake shaking during the 1811 1812 earthquakes our analysis yields a general relationship between newmark landslide displacement earthquake shaking intensity and the critical acceleration of a landslide using this relationship we estimate the minimum shaking intensities required to trigger the types of landslides studied an mb 5 8 or m 5 9 earthquake is the lower bound threshold at zero epicentral distance that could trigger catastrophic movement of typical block slides in the new madrid seismic zone for earth flows mb 5 4 or m 5 3 is the threshold earthquake

on the nature of the frontal zone of the choctawhatchee bay plume in the gulf of mexico river plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume which ultimately impact spreading and mixing rates with the ambient coastal ocean the degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations a field campaign was conducted in a river plume in the northeast gulf of mexico in december 2013 in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions current velocity density and turbulent kinetic energy values e were obtained using an acoustic doppler current profiler adcp a conductivity temperature depth ctd profiler a vertical microstructure profiler vmp and two acoustic doppler velocimeters advs the frontal region contained e values on the order of 10 5 m2 s 3 which were markedly larger than in the ambient water beneath o 10 9 m2 s 3 an energetic wake of moderate e values o 10 6 m2 s 3 was observed trailing the frontal edge the interfacial region of an interior section of the plume featured opposing horizontal velocities and a e value on the order of 10 6 m2 s 3 a simplified mixing budget was used under significant assumptions to compare contributions from wind tides and frontal regions of the plume the results from this order of magnitude analysis indicated that frontal processes 59 dominated in overall mixing this emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models

stratified turbulence and mixing efficiency in a salt wedge estuary abstracthigh resolution observations of velocity salinity and turbulence quantities were collected in a salt wedge estuary to quantify the efficiency of stratified mixing in a high energy environment during the ebb tide a midwater column layer of strong shear and stratification developed exhibiting near critical gradient richardson numbers and turbulent kinetic energy tke dissipation rates greater than 10 4 m2 s 3 based on inertial subrange spectra collocated estimates of scalar variance dissipation from microconductivity sensors were used to estimate buoyancy flux and the flux richardson number rif the majority of the samples were outside the boundary layer based on the ratio of ozmidov and boundary length scales and had a mean rif 0 23 0 01 dissipation flux coefficient 0 30 0 02 and a median gradient richardson number rig 0 25 the boundary influenced subset of the data had decreased efficiency with rif 0 17 0 02 0 20 0 03 and median rig 0 16 the relationship be

site effect evaluation in the basin of santiago de chile using ambient noise measurements summary we performed extensive ambient vibration measurements in the basin of santiago de chile chile and we look for testing the reliability of the horizontal to vertical amplitude spectra ratio method h v as a tool to provide qualitative and quantitative information of site effects in complex geological media the interpretation of the h v data was carried out conformably to the sesame project consensus criteria and outlines three major patterns 1 clear peaked h v curves related to sharp underground velocity contrast 2 h v peak of low amplitude and flat curve related to weak contrast and 3 broad h v peak indicating the presence of strong lateral variations of underground structure h v measurements however reveal a discrepancy between the computed soil resonance frequencies and the expected building resonance therefore not leading to a straight interpretation of the intensity distribution derived from observed damage to one storey houses in santiago after the 1985 valparaiso earthquake indeed the h v technique mostly maps the first fundamental frequency however it fails to show higher resonance modes in the case of the city of santiago this method works well for assessing the seismic hazard for high rise buildings but is questionable for smaller structures as is the case of a great percentage of constructions in the city

seismic performance of loess mudstone slope in tianshui centrifuge model tests and numerical analysis abstract dynamic behavior and failure mechanism of slope during earthquake are hot topics in geotechnical engineering community in tianshui area northwest of china the deformation features of loess mudstone slopes induced by earthquakes are still not well understood the current study aims to discuss the dynamic behavior of the slope under earthquake by performing a series of centrifuge shaking table tests and numerical simulations the results are processed for pga amplificatory effect study and to evaluate the earthquake induced deformation mechanism better agreement is obtained between the results of numerical simulations and centrifuge tests the results indicated that the acceleration response of the loess mudstone slope showed several amplifying characteristic the height effect lithologic effect and surface effect it also proves that the displacements in the loess layer are much larger than mudstone as the input amplitude increased the shear plastic zone developed along a further slide surface tension plastic zone mainly occurred at the crest roughly the regions of earthquake induced deformation state increased with the increase in amplitude of earthquake wave deformations occurred at the upper part of the slope tensile cracks evolved on the crest and the upper part of slope in loess layer moreover failures occurred at slope surface and only slight deformation at slope toe deformations with continuous shear cracks and slope surface upheavals developed at the middle part of slope

a new method of seismic site classification using hvsr curves a case study of the 12 november 2017 mw 7 3 ezgeleh earthquake in iran abstract on the 12th of november 2017 a strong earthquake with a moment magnitude of 7 3 struck the west of iran causing massive damage in sarpolezahab and surrounding areas in this study the horizontal to vertical spectral ratio hvsr or h v technique of strong ground motion recorded at 60 stations is used for identifying of site response and subsequent site classification very clear amplification is observed at stiff and soft soil sites empirical equations from the literature relating frequency of hvsr peak to average shear wave velocity in the upper 30m vs30 commonly used as a proxy for site classification were found to be unreliable making site classification difficult to overcome this problem a soft computing method based on the generalized regression neural networks grnn algorithm is used this algorithm relies on hvsr curves at the recording stations and uses pattern recognition against a set of pre defined curves for different site types in this approach site characterization is based on the overall features of the hvsr curves rather than just the peak frequency the stations are classified into four different site classes and the results are consistent with local geotechnical information where available rather than relying on vs30 which has been found deficient in many studies and is known to have difficulty in reliably estimating when geotechnical data is lacking site classification proposed in this study uses the overall characteristics of hvsr curves of response spectra of recorded strong motion data this method is proposed as a more reliable and direct method for site characterization in seismically hazardous regions

circulation of tampa bay driven by buoyancy tides and winds as simulated using a finite volume coastal ocean model 1 the circulation of tampa bay is investigated using a high resolution three dimensional density dependent finite volume coastal ocean model fvcom that includes tampa bay the intracoastal waterway and the inner portion of the west florida continental shelf model performance over the three month interval september to november 2001 is assessed against available tide gauge and velocity profiler data before using the model to describe the circulation as driven by rivers tides and winds because of a mean wind velocity vector directed down the estuary axis we ran a parallel model experiment without winds to distinguish the estuarine circulation by gravitational convection from the mean wind effects with or without winds tampa bay exhibits a robust two layered estuarine circulation that concentrates on the deep channels the mean outflow at the surface tends to converge on the channels where the free surface elevation is locally minimum the mean inflow near the bottom also concentrates in the channels where the baroclinic pressure gradient force is largest geometry thus guides the mean circulation and salinity distributions at the tampa bay mouth mean outflows exist both in the deeper egmont channel and the shallower south pass whereas a mean inflow is limited to the egmont channel a residence time based on the egmont channel influx is estimated to be about 100 days consistent with previous studies we conclude that gravitational convection is a major contributor to the water property distributions of tampa bay and that the fvcom is suitable for estuary shelf interaction studies

quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries abstract this numerical modeling study quantifies for the first time the contribution of various processes to estuarine circulation in periodically stratified tidal flow under the impact of a constant horizontal buoyancy gradient the one dimensional water column equations with periodic forcing are first cast into nondimensional form resulting in a multidimensional parameter space spanned by the modified inverse strouhal number and the modified horizontal richardson number as well as relative wind speed and wind direction and the residual runoff the along tide momentum equation is then solved for the tidal mean velocity profile in such a way that it is equated to the sum of the contributions of tidal straining resulting from the temporal correlation between eddy viscosity and vertical shear gravitational circulation resulting from the depth varying forcing by a constant horizontal buoyancy gradient wind straining and depth mean residual flow resulting from net freshwater runoff this definitio

steady state phreatic surfaces in sloping aquifers 1 steady state groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented using the dupuit approximation by an ordinary differential equation of the abel type y x y x a y x x 0 whose analytical solution is derived in this work this article first investigates the case of zero saturated thickness at the upstream boundary a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary a variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary this variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer the latter being on sloping terrain in this instance analytical solutions for the phreatic surface s steady state geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface these solutions are of practical interest in drainage studies slope stability and runoff formation investigations it is shown that the flow factor a tan where k n and tan are the hydraulic conductivity vertical recharge and aquifer slope respectively has a commanding role on the phreatic surface s solutions two computational examples illustrate the implementation of this article s results

the importance of tidal and lateral asymmetries in stratification to residual circulation in partially mixed estuaries measurements collected in the york river estuary virginia demonstrate the important impact that tidal and lateral asymmetries in turbulent mixing have on the tidally averaged residual circulation a reduction in turbulent mixing during the ebb phase of the tide caused by tidal straining of the axial density gradient results in increased vertical velocity shear throughout the water column during the ebb tide in the absence of significant lateral differences in turbulent mixing the enhanced ebb directed transport caused by tidal straining is balanced by a reduction in the net seaward directed barotropic pressure gradient resulting in laterally uniform two layer residual flow however the channel shoal morphology of many drowned river valley estuaries often leads to lateral gradients in turbulent mixing tidal straining may then lead to tidal asymmetries in turbulent mixing near the deeper channel while the neighboring shoals remain relatively well mixed as a result the largest lateral asymmetries in turbulent mixing occur at the end of the ebb tide when the channel is significantly more stratified than the shoals the reduced friction at the end of ebb delays the onset of the flood tide increasing the duration of ebb in the channel conversely over the shoal regions where stratification is more inhibited by tidal mixing there is greater friction and the transition from ebb to flood occurs more rapidly the resulting residual circulation is seaward over the channel and landward over the shoal the shoal channel segregation of this barotropically induced estuarine residual flow is opposite to that typically associated with baroclinic estuarine circulation over channel shoal bathymetry

residual currents induced by asymmetric tidal mixing in weakly stratified narrow estuaries abstract residual currents induced by asymmetric tidal mixing were examined for weakly stratified narrow estuaries using analytical and numerical models the analytical model is an extension of the work of r k mccarthy with the addition of tidal variations of the vertical eddy viscosity in the longitudinal momentum equation the longitudinal distribution of residual flows driven by asymmetric tidal mixing is determined by the tidal current amplitude and by asymmetries in tidal mixing between flood and ebb in a long channel the magnitude of the residual flow induced by asymmetric tidal mixing is maximum at the estuary mouth and decreases upstream following the longitudinal distribution of tidal current amplitude larger asymmetry in tidal mixing between flood and ebb produces stronger residual currents for typical tidal asymmetry mixing is stronger during flood than during ebb and results in two layer residual currents with seaward flow near the surface and landward flow near the bottom for revers

turbulence dynamics at the shoal channel interface in a partially stratified estuary abstractturbulence observations at the shoal channel interface in south san francisco bay are described and analyzed in this work profiles of turbulent kinetic energy tke shear production and dissipation rate are estimated from adcp beam velocities over a nine day period during winter 2009 when the estuary was partially stratified the tke shear production profiles are consistent with a tidally driven bottom boundary layer except late in the ebb when shear production intensifies and the region of maximum production is located in the upper half of the water column a simple scaling for the depth averaged tke shear production based on bed friction performs well except during this late ebb period when it fails to predict the peak in shear production which suggests that a mechanism other than bottom drag drives turbulence dynamics during this period the profiles of tke dissipation rates also display a late ebb peak a lateral circulation develops at the shoal channel interface during this late ebb perio

landslide inventories the essential part of seismic landslide hazard analyses abstract a detailed and accurate landslide inventory is an essential part of seismic landslide hazard analysis an ideal inventory would cover the entire area affected by an earthquake and include all of the landslides that are possible to detect down to sizes of 1 5 m in length the landslides must also be located accurately and mapped as polygons depicting their true shapes such mapped landslide distributions can then be used to perform seismic landslide hazard analysis and other quantitative analyses detailed inventory maps of landslide triggered by earthquakes began in the early 1960s with the use of aerial photography in recent years advances in technology have resulted in the accessibility of satellite imagery with sufficiently high resolution to identify and map all but the smallest of landslides triggered by a seismic event with this ability to view any area of the globe we can acquire imagery for any earthquake that triggers significant numbers of landslides however a common problem of incomplete coverage of the full distributions of landslides has emerged along with the advent of high resolution satellite imagery

inversion of surface wave data for subsurface shear wave velocity profiles characterized by a thick buried low velocity layer the study formed part of the simit project integrated italy malta cross border system of civil protection b1 2 19 11 part financed by the european union under the italiamalta cross border cooperation programme 2007 2013

linkage between lateral circulation and near surface vertical mixing in a coastal plain estuary microstructure and current velocity measurements were collected at a cross channel transect in the james river under spring and neap tidal conditions in may 2010 to study cross estuary variations in vertical mixing results showed that near surface mixing was related to lateral circulation during the ebb phase of a tidal cycle and that the linkage was somewhat similar from neap to spring tides during neap tides near surface mixing was generated by the straining of lateral density gradients influenced by the advection of fresh riverine water on the right side looking seaward of the transect spring tide results revealed similar findings on the right side of the cross section however on the left side the straining by velocity shears acted in concert with density straining weak along estuary velocities over the left shoal were connected to faster velocities in the channel via a clockwise lateral circulation looking seaward these results provided evidence that in the absence of direct wind forcing near surface vertical mixing can occur from mechanisms uncoupled from bottom friction

observations of turbulence in a partially stratified estuary the authors present a field study of estuarine turbulence in which profiles of reynolds stresses were directly measured using an adcp throughout a 25 h tidal day the dataset that is discussed quantifies turbulent mixing for a water column in northern san francisco bay that experiences a sequence of states that includes a weak ebb and flood that are stratified followed by a strong and eventually unstratified ebb and flood these measurements show that energetic turbulence is confined to a bottom mixed layer by the overlying stratification examination of individual reynolds stress profiles along with profiles of richardson number and turbulent froude number shows that the water column can be divided into regions based on the relative importance of buoyancy effects using the measured turbulence production rate p the dissipation rate e is estimated the observed turbulence had values of e nn 2 20 all of the time and e nn 2 200 most of the time suggesting that the observed motions were buoyancy affected turbulence rather than internal waves however at times turbulent froude numbers in much of the upper water column were less than one indicating important stratification effects taken as a whole the data show that stratification affects the turbulent velocity variance q2 most severely that is observed reductions in u9w9 are largely associated with small values of q2 rather than with a dramatic reduction in the efficiency with which turbulent motions produce momentum fluxes finally the dataset is compared to predictions made using the popular mellor yamada level 2 5 closure these comparisons show that the model tends to underestimate the turbulent kinetic energy in regions of strong stratification where the turbulence is strongly inhomogeneous and to overestimate the turbulent kinetic energy in weakly stratified regions the length scale does not appear to compensate for these errors and as a result similar errors are seen in the eddy viscosity predictions it is hypothesized that the underestimation of q2 is due to an inaccurate parameterization of turbulence self transport from the near bed region to the overlying stratification

tidal bore dynamics in funnel shaped estuaries the formation and dynamics of tidal bores in funnel shaped estuaries is investigated from both a global tidal wave scaling analysis and new quantitative field observations we show that tidal bore occurrence in convergent estuaries can be estimated from a dimensionless scaling parameter characterizing the relative intensity of nonlinear friction versus local inertia in the momentum equation a detailed analysis of tidal bore formation and secondary wave structure is presented from a unique long term database observations of more than 200 tides acquired during four campaigns in the two main french tidal bore estuaries the seine and gironde garonne estuaries we describe the effect of freshwater discharge on the global tidal wave transformation at the estuarine scale and on local tidal bore occurrence in the upper estuary our field data suggest that the tidal bore intensity is mainly governed by the dimensionless tidal range which characterizes the local tidal wave nonlinearity we also show that the secondary wavefield associated with tidal bore propagating in natural estuaries differs significantly from those associated to undular bores in rectangular channels in particular we observe an abrupt decrease of the whelp steepness when the froude number goes below 1 1 this secondary field transition can explain why tidal bore occurrence in worldwide estuaries is certainly underestimated

the role of advection straining and mixing on the tidal variability of estuarine stratification abstractdata from the hudson river estuary demonstrate that the tidal variations in vertical salinity stratification are not consistent with the patterns associated with along channel tidal straining these observations result from three additional processes not accounted for in the traditional tidal straining model 1 along channel and 2 lateral advection of horizontal gradients in the vertical salinity gradient and 3 tidal asymmetries in the strength of vertical mixing as a result cross sectionally averaged values of the vertical salinity gradient are shown to increase during the flood tide and decrease during the ebb only over a limited portion of the cross section does the observed stratification increase during the ebb and decrease during the flood these observations highlight the three dimensional nature of estuarine flows and demonstrate that lateral circulation provides an alternate mechanism that allows for the exchange of materials between surface and bottom waters even when direct turbu

lateral entrapment of sediment in tidal estuaries an idealized model study two physical mechanisms leading to lateral accumulation of sediment in tidally dominated estuaries are investigated involving coriolis forcing and lateral density gradients an idealized model is used that consists of the three dimensional shallow water equations and sediment mass balance conditions are assumed to be uniform in the along estuary direction a semidiurnal tidal discharge and tidally averaged density gradients are prescribed the erosional sediment flux at the bed depends both on the bed shear stress and on the amount of sediment available in mud reaches for resuspension the distribution of mud reaches over the bed is selected such that sediment transport is in morphodynamic equilibrium that is tidally averaged erosion and deposition of sediment at the bed balance analytical solutions are obtained by using perturbation analysis results suggest that in most estuaries lateral density gradients induce more sediment transport than coriolis forcing when frictional forces are small ekman number e 0 02 the lateral density gradient mechanism dominates and entraps sediment in areas with fresher water results also show that the lateral sediment transport induced by the semidiurnal tidal flow is significant when frictional forces are small e 0 02 model predictions are in good agreement with observations from the james river estuary

automatic zonation of urban areas based on the similarity of h v spectral ratios abstract in this article we propose an automatic procedure that performs thezonation of urban areas based on a set of horizontal to vertical h v spectral ratiosfrom ambient noise recordings collected at many measurement points the techniquesearches for the connected areas where the similarity among the spectral ratios ismaximized the problem is posed as one of the optimal partitioning of the delaunaytriangulation of the available measurement points the technique explores and triesto partition some random variations of a euclidean minimum spanning tree of thetriangulation the optimization is performed using a genetic algorithm thetechniqueis applied to the zonation of the town of vittorio veneto in northeastern italy and toa synthetic data set that tries to simulate the effects of some typical geological con ditions introduction seismic microzonation concerns the identi cation andmapping at local or site scales of areas having different po tentials of hazardous earthquake effects such as ground shaking intensity liquefaction or landslide potential akiand lee 2003 it is commonly performed by experts takinginto account geophysical and geological information of dif ferent natures for ground shaking intensity a useful sup port comes from the computation of horizontal to vertical

joint inversion of h v ratios and dispersion curves from seismic noise estimating the s wave velocity of bedrock 1 a joint inversion of phase velocity and h v ratio curves both obtained from seismic noise recordings permits the retrieval of the shear wave velocity structure of local sedimentary cover our inversion scheme uses a genetic algorithm and considers the influence of higher modes on the data sets encouraged by the results published previously on joint inversion parolai et al 2005 we went one step further we found using a synthetic data set that the impedance contrast at the sediment bedrock interface has a strong influence on the shape of the h v ratio curve which therefore allows the bedrock s wave velocity to be well constrained in the joint inversion procedure our observations were further confirmed using a real data set

modeling the lateral circulation in straight stratified estuaries the dynamics of lateral circulation in an idealized straight estuary under varying stratification conditions is investigated using a three dimensional hydrostatic primitive equation model in order to determine the importance of lateral circulation to the momentum budget within the estuary for all model runs lateral circulation is about 4 times as strong during flood tides as during ebbs this flood ebb asymmetry is due to a feedback between the lateral circulation and the along channel tidal currents as well as to time varying stratification over a tidal cycle as the stratification is increased the lateral circulation is significantly reduced because of the adverse pressure gradient set up by isopycnals being tilted by the lateral flow itself when rotation is included a timedependent cross channel ekman circulation is driven and the tidally averaged bottom lateral circulation is enhanced toward the right bank when looking toward the ocean in the northern hemisphere this asymmetry in the tidally averaged bottom lateral circulation may lead to asymmetric sediment transport leading to asymmetric channel profiles in straight estuaries for the weakly stratified model run advection due to lateral currents is a dominant term in both the along channel and cross channel momentum equations over a tidal cycle and for the tidally averaged momentum equations in the tidally averaged along channel momentum equation lateral advection acts as a driving term for the estuarine exchange flow and can be larger than the along channel pressure gradient therefore it should not be ignored when estimating momentum budgets in estuaries

geomaterial segmentation method using multi dimensional frequency analysis based on electrical resistivity tomography abstract the determination of specific geotechnical materials in complex geotechnical environment is of great significance for engineering construction and geological disaster risk management such as karst cave fracture zone etc as a fast and convenient field test method electrical resistivity tomography is extensively applied in geotechnical engineering investigation the resistivity distribution of underground rock mass and soil can be obtained after inversion of apparent resistivity to quantitatively determine the resistivity threshold of specific geotechnical materials we referred to the multi dimensional frequency analysis and threshold determination algorithm of image segmentation based on the structural similarity between resistivity grid data and image pixels the frequency distribution of resistivity data is analyzed from two dimensions of resistivity magnitude and neighbouring difference the neighbouring difference is introduced to describe the variation degree of resistivity in space and otsu algorithm is adopted to determine resistivity threshold to identify certain kind of geotechnical material in order to verify the validity of material segmentation method two cases under rock mass condition and soil condition are studied respectively for goaf in rock mass multi dimensional frequency analysis can effectively show the frequency components of void resistivity for ancient soil landslide with narrow distribution range of resistivity multi dimensional frequency analysis can not only determine the resistivity threshold of soil sliding body quantitatively but also determine the materials with small proportion in whole area such as sliding zone according to the correlation between neighbouring difference and material properties

estimating liquefaction induced lateral displacements using the standard penetration test or cone penetration test a semiempirical approach to estimate liquefaction induced lateral displacements using standard penetration test spt or cone penetration test cpt data is presented the approach combines available spt and cpt based methods to evaluate liquefaction potential with laboratory test results for clean sands to estimate the potential maximum cyclic shear strains for saturated sandy soils under seismic loading a lateral displacement index is then introduced which is obtained by integrating the maximum cyclic shear strains with depth empirical correlations from case history data are proposed between actual lateral displacement the lateral displacement index and geometric parameters characterizing ground geometry for gently sloping ground without a free face level ground with a free face and gently sloping ground with a free face the proposed approach can be applied to obtain preliminary estimates of the magnitude of lateral displacements associated with a liquefaction induced lateral spread