sedimentary impacts of anthropogenic alterations on the yeongsan estuary south korea abstract over the last half century coastal zones within the republic of korea s korea have experienced a wide range of engineered coastal modifications including construction of seawalls extensive land reclamation and installation of estuarine dams the yeongsan estuary has experienced all of these modifications and provides an ideal case study on how sedimentation changes within a macrotidal estuary in response to these alterations combined these alterations have considerably modulated the timing and intensity of river discharge prevented natural tidal exchange modified the shoreline profile and altered the transport of sediment and organic matter within the coastal zone these impacts have been investigated using 30 gravity cores analyzed for 210 pb radioisotope geochronology laser diffraction particle size analyses 13 c and 15 n isotope ratio mass spectrometry and x radiography average sediment accumulation rates range from 0 9 0 6 cm yr 1 to 10 0 2 9 cm yr 1 with the highest rates proximal to the downstream side of the dam and some areas determined to be either actively eroding or recently dredged these results are supported by comparison of multiple bathymetric surveys and chirp seismic data suggest an order of magnitude increase from average holocene sediment accumulation rates side scan sonograms collected adjacent to the dam reveal distinctive scouring transitioning to areas accumulating fine grained sediments shifts in the organic matter source inputs are apparent in pre post dam sediments and reflect the occluding of tidal influence above the dam resulting in increasingly terrestrial dominated signatures additionally a time series of cores collected during periods of limited and high discharge analyzed for 7 be indicates sediment deposition occurs episodically corresponding to high discharge dam releases our observations record a shift in depositional environments as a response to an extensive array of anthropogenic alterations ultimately land reclamation and dam construction have severely altered the fate and transport of sediment within the estuarine system as a consequence sedimentation rates have increased dramatically and depositional events are primarily controlled by discharges from the estuarine dam

accretion of a new england u s a salt marsh in response to inlet migration storms and sea level rise sediment accumulation rates were determined at several sites throughout nauset marsh massachusetts u s a a back barrier lagoonal system using feldspar marker horizons to evaluate short term rates 1 to 2 year scales and radiometric techniques to estimate rates over longer time scales 137cs 210pb 14c the barrier spit fronting thespartina dominated study site has a complex geomorphic history of inlet migration and overwash events this study evaluates sediment accumulation rates in relation to inlet migration storm events and sea level rise the marker horizon technique displayed strong temporal and spatial variability in response to storm events and proximity to the inlet sediment accumulation rates of up to 24 mm year 1were recorded in the immediate vicinity of the inlet during a period that included several major coastal storms while feldspar sites remote from the inlet had substantially lower rates trace accumulation to 2 2 mm year 1 during storm free periods accumulation rates did not exceed 6 7 mm year 1 but remained quite variable among sites based on137cs 3 8 to 4 5 mm year 1 and210pb 2 6 to 4 2 mm year 1 radiometric techniques integrating sediment accumulation over decadal time scales the marsh appeared to be keeping pace with the relative rate of sea level rise from 1921 to 1993 of 2 4 mm year 1 at one site the210pb based sedimentation rate and rate of relative sea level rise were nearly similar and peat rhizome analysis revealed thatdistichlis spicatarecently replaced this onces patenssite suggesting that this portion of nauset marsh may be getting wetter thus representing an initial response to wetland submergence horizon markers are useful in evaluating the role of short term events such as storms or inlet migration influencing marsh sedimentation processes however sampling methods that integrate marsh sedimentation over decadal time scales are preferable when evaluating a systems response to sea level rise

anthropogenic influence on sedimentation and intertidal mudflat change in san pablo bay california 1856 1983 analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in san pablo bay california in 1856 the morphology of the bay was complex with a broad main channel a major side channel connecting to the petaluma river and an ebb tidal delta crossing shallow parts of the bay in 1983 its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface the timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers from 1856 to 1887 high sediment delivery 14 1 10 6 m 3 yr to san francisco bay during the hydraulic gold mining period in the sierra nevada resulted in net deposition of 259 14 10 6 m 3 in san pablo bay this rapid deposition filled channels and increased intertidal mudflat area by 60 37 4 3 4 to 60 6 6 2 km 2 from 1951 to 1983 23 3 10 6 m 3 of sediment was eroded from san pablo bay as sediment delivery from the sacramento and san joaquin rivers decreased to 2 8 10 6 m 3 yr because of damming of rivers riverbank protection and altered land use intertidal mudflat area in 1983 was 31 8 3 9 km 2 similar to that in 1856 intertidal mudflat distribution in 1983 however was fairly uniform whereas most of the intertidal mudflats were in the western part of san pablo bay in 1856 sediment delivery through its affect on shallow parts of the bay was determined to be a primary control on intertidal mudflat area san pablo bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers 2007 elsevier ltd all rights reserved

controlling factors of rhythmic sedimentation processes on an intertidal estuarine mudflat role of the turbidity maximum in the macrotidal seine estuary france the aim of this study is to analyse and to quantify the fine particles transfer i e 7 1 m then deposition of spm from the turbidity maximum becomes important allowing fine particles to settle on the mudflat where the current velocities are low 0 4 m s 1 on tides of lower range 7 1 m bed elevation levels suggest that erosion of the mudflat surface dominates however dewatering processes also occur in the soft mud deposits resulting in compaction during periods of wave activity and periods of increasing river discharge the mudflat surface experiences rapid erosion these periods of erosion sudden or progressive imply a transfer of fine grained material from the mudflat surface back into the tm the long term 22 months high frequency 1 measurement every 10 min and high resolution 0 6 mm dataset obtained from the altimeter allows quantification of the volume of material exchanged between the intertidal area and the estuarine standing stock of spm the maximum of deposition on the studied mudflat during the study was of 27 cm with highest deposition occurring after the periods of highest river flow and implying that between 25 and 40 of the maximum estimated mass of spm held within the estuarine tm 300 000 500 000 t had been temporarily deposited on the mudflat likewise following periods of resuspension by wave activity bed elevations reduced by an order of 1 cm suggesting a release of between 1 1 5 of the tm load from the mudflat back into suspension the study shows that lateral exchanges of sediment between the intertidal reaches of the estuary and the water column are an important part of the sediment budget and that the supply of sediment available for deposition i e the tm has a causal relationship with sedimentation rates experienced by intertidal mudflats

patterns rates and possible causes of saltmarsh erosion in the greater thames area uk the estuary dominated coast of the greater thames in england has experienced rapid lateral erosion and internal dissection of saltmarshes this paper provides an overview of saltmarsh development in this area and re examines the role of environmental and human forcing factors it draws on documentary evidence including historical maps survey data and time series data of forcing factors lateral marsh retreat began in the 19th century in the medway and blackwater estuaries followed by other estuaries in the greater thames region at the beginning of the 20th century the outer estuaries and the wider parts of the inner estuaries especially have experienced erosion erosion has been modest in wave sheltered areas e g the colne and the inner crouch in the 1960s and more widely the 1970s a phase of rapid erosion took place with erosion rates of up to ca 16 ha year 1 per site notably along the open coast of dengie and foulness and in the blackwater and thames estuaries at all sites vertical sediment accretion was well able to keep up with sea level rise over the past century evidence indicates that there may have been several causes for the erosion of saltmarshes these are notably land claim and embankment construction increasing the tidal range and current velocities and a continuous rise of especially high and extreme water levels the latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind wave climate for example erosion at wave exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves the study shows that many factors including natural forcing factors and human activities have to be taken into account when explaining saltmarsh development

the use of borehole video in investigating the hydrology of a temperate glacier a geovision micro colour video camera was used to investigate the internal structure of 11 boreholes at haut glacier d arolla switzerland the boreholes were distributed across a half section of the glacier with closest spacing towards the glacier margin the boreholes were used to investigate the hydrology of the glacier through automatic monitoring of borehole water level and electrical conductivity ec at the glacier bed ec profiling was undertaken in several boreholes to determine the existence of water quality stratification temporal variations in ec stratification were used to infer borehole water sources and patterns of water circulation borehole video was used to confirm the conclusions made from these indirect sources of evidence and to provide an independent source of information on the structure and hydrology of this temperate valley glacier the video showed variations in water turbidity englacial channels and voids conditions at the glacier bed and down borehole changes in ice structure based on the video observations englacial channels accounted for approximately 0 1 of the vertical ice thickness and englacial voids for approximately 0 4 overall the video images provided useful qualitative and semi quantitative data that reinforce interpretations of a range of physical and chemical parameters measured in boreholes 1997 by john wiley sons ltd

sensitivity of time lapse seismic to reservoir stress path the change in reservoir pore pressure due to the production of hydrocarbons leads to anisotropic changes in the stress field acting on the reservoir reservoir stress path is defined as the ratio of the change in effective horizontal stress to the change in effective vertical stress from the initial reservoir conditions and strongly influences the depletion induced compaction behaviour of the reservoir seismic velocities in sandstones vary with stress due to the presence of stress sensitive regions within the rock such as grain boundaries microcracks fractures etc since the response of any microcracks and grain boundaries to a change in stress depends on their orientation relative to the principal stress axes elastic wave velocities are sensitive to reservoir stress path the vertical p and s wave velocities the small offset p and sv wave normal moveout nmo velocities and the p wave amplitude versus offset avo are sensitive to different combinations of vertical and horizontal stress the relationships between these quantities and the change in stress can be calibrated using a repeat seismic sonic log checkshot or vertical seismic profile vsp at the location of a well at which the change in reservoir pressure has been measured alternatively the variation of velocity with azimuth and distance from the borehole obtained by dipole radial profiling can be used having calibrated these relationships the theory allows the reservoir stress path to be monitored using time lapse seismic by combining changes in the vertical p wave impedance changes in the p wave nmo and avo behaviour and changes in the s wave impedance

pore fluid effects on seismic velocity in anisotropic rocks a simple new technique predicts the high and low frequency saturated velocities in anisotropic rocks entirely in terms of measurable dry rock properties without the need for idealized crack geometries measurements of dry velocity versus pressure and porosity versus pressure contain all of the necessary information for predicting the frequency dependent effects of fluid saturation furthermore these measurements automatically incorporate all pore interaction so there is no limitation to low crack density the velocities are found to depend on five key interrelated variables frequency the distribution of compliant crack like porosity the intrinsic or noncrack anisotropy fluid viscosity and compressibility and effective pressure the sensitivity of velocities to saturation is generally greater at high frequencies than low frequencies the magnitude of the differences from dry to saturated and from low frequency to high frequency is determined by the compliant or crack like porosity predictions of s

estimating azimuthal stress induced p wave anisotropy from s wave anisotropy using sonic log or vertical seismic profile data most sedimentary rocks are anisotropic yet it is often difficult to accurately incorporate anisotropy into seismic workflows because analysis of anisotropy requires knowledge of a number of parameters that are difficult to estimate from standard seismic data in this study we provide a methodology to infer azimuthal p wave anisotropy from s wave anisotropy calculated from log or vertical seismic profile data this methodology involves a number of steps first we compute the azimuthal p wave anisotropy in the dry medium as a function of the azimuthal s wave anisotropy using a rock physics model which accounts for the stress dependency of seismic wave velocities in dry isotropic elastic media subjected to triaxial compression once the p wave anisotropy in the dry medium is known we use the anisotropic gassmann equations to estimate the anisotropy of the saturated medium we test this workflow on the log data acquired in the north west shelf of australia where azimuthal anisotropy is likely caused by large differences between minimum and maximum horizontal stresses the obtained results are compared to azimuthal p wave anisotropy obtained via orthorhombic tomography in the same area in the clean sandstone layers anisotropy parameters obtained by both methods are fairly consistent in the shale and shaly sandstone layers however there is a significant discrepancy between results since the stress induced anisotropy model we use is not applicable to rocks exhibiting intrinsic anisotropy this methodology could be useful for building the initial anisotropic velocity model for imaging which is to be refined through migration velocity analysis

stress dependent anisotropy in transversely isotropic rocks comparison between theory and laboratory experiment on shale understanding the effect of stress and pore pressure on seismic velocities is important for overpressure prediction and for 4d reflection seismic interpretation a porosity deformation approach originally called the piezosensitivity theory and its anisotropic extension describe elastic moduli of rocks as nonlinear functions of the effective stress this theory assumes a presence of stiff and compliant parts of the pore space the stress dependent geometry of the compliant pore space predominantly controls stress induced changes in elastic moduli we show how to apply this theory to a shale that is transversely isotropic ti under unloaded conditions the porosity deformation approach shows that components of the compliance tensor depend on exponential functions of the principal components of the effective stress tensor in the case of a hydrostatic loading of a ti rock only the diagonal elements of this tensor expressed in contracted notation are significantly stress dependent two equal shear compo

rotation of horizontal stresses in the australian north west continental shelf due to the collision of the indo australian and eurasian plates there is a 40 rotation of regional maximum horizontal stress hmax orientation between the western end of the australian north west continental shelf carnarvon basin and its eastern end bonaparte basin a total of 625 borehole breakouts covering a cumulative length of 7 7 km in 42 wells in the carnarvon basin indicates a hmax orientation of 090 100 n a total of 616 borehole breakouts over 6 8 km in 46 wells in the bonaparte basin indicates a hmax orientation of 055 n 060 n together with extant data from the world stress map these results indicate that regional hmax orientation is 050 060 n from new guinea westward through the bonaparte basin to the canning basin central north west shelf between the canning basin and the carnarvon basin hmax rotates to 090 100 n the parallelism of hmax orientation in the bonaparte basin to the australia banda arc collisional zone indicates that this collision is not generating significant net push rather the 050 060 n hmax orientation of much of the northern australian margin is probably controlled by the more mature new guinea orogen to which it is approximately orthogonal the observed rotation of hmax can be explained solely by the focusing of the forces balancing ridge push along collisional segments of the northeastern boundary of the indo australian plate such as the new guinea orogen although not required to account for the observed stress rotation a slab pull force from oceanic indo australian plate being subducted beneath the sunda arc cannot be dismissed

control of estuarine sediment dynamics by interactions between currents and waves at several scales abstract the effect of interactions between continuous tidal currents and intermittent waves processes on sediment dynamics and transport is addressed by presenting detailed field measurements of waves boundary layer currents and suspended sediment from an estuarine channel and an adjacent intertidal sandflat in manukau harbour new zealand the aim is to determine in what ways it is necessary to couple waves and currents in numerical models and thereby put limits on the fundamental structure of process based estuarine sediment transport models waves were important on the intertidal flat turbidity switched on and off with the appearance and disappearance of waves wave groups dominated entrainment of bed sediment a wave current boundary layer model explained measured bed shear stress and hydraulic roughness and the measured near bed time averaged suspended sediment concentration was mostly well predicted by a pure wave model both the waves themselves and wave related processes varied markedly over the tidal cycle the variation in the former principally changes in wave height was related to changes in fetch caused by the harbour wide emergence and submergence of intertidal regions the variation in the latter was related to changes in water depth relative to the wavelength of the waves which controlled the penetration to the bed of wave orbital currents in addition to the variation over the tidal cycle in the intensity of wave processes there was also a change in kind which occurred with the arrival at the measurement site of the turbid fringe which is the narrow highly turbid edge of the estuarine water body the relationship between suspended sediment concentration and wave orbital velocity in the turbid fringe was radically different to the relationship in the estuarine water body proper which suggests a change in dynamics perhaps related to breaking waves a hybrid modelling approach is required i e one that treats discrete events but resolves tidal cycle scale variation within the event there is a need to resolve the variation in the wave train over the tidal cycle and the penetration to the bed of wave orbital motions both of which could only be done adequately within an estuary tidal model in contrast to the situation on the intertidal flat where waves intermittently entrained sediment sediment transport in the channel was continuous driven by tidal currents to predict sediment flux in the channel we need to know the upstream sediment transporting capacity of the flow including that contributed by waves the character of the bed sediment and the sediment settling time scale these factors confounded even the simplest notion of flood and ebb dominance which frequently has been applied to understand estuarine morphodynamics

new typologies for estuarine morphology new theories to explain how tides and river flow determine estuarine bathymetries have been developed the range of validity of these theories has been subsequently assessed against a recently available observational data set success in reproducing the evolution of estuarine bathymetries that has occurred over the last 10 000 years provides the basis for the translation here of these theories into new typologies these then provide reference frameworks to enhance our perspective on existing morphologies and identify anomalous estuaries further refinement of these new theories requires analyses of causal factors responsible for such anomalies drawing on classical morphological experience these frameworks can also be used for calculating likely future bathymetric adjustments for prescribed changes in mean sea level tidal amplitudes river flow and sediment supply

linking the infilling of the north branch in the changjiang yangtze estuary to anthropogenic activities from 1958 to 2013 abstract many tidally dominated estuaries of the world are experiencing variations in bottom topography due to changes in natural forcings and intensive human activities here we focus on the morphological evolution of the north branch nb a tidally dominated distributary of the changjiang estuary our analysis is based on long term bathymetric and hydrological data collected between 1950 and 2010 the results show that mean water depth channel volume below 0 m and channel volume below 5 m have respectively decreased by 43 53 and 92 in the last 50 years a reduction of the whole estuarine surface with aggradation in elongated tidal sand bars and erosion at the mouth are the main morphological variations of the nb while a decrease in channel volume below 5 m due to infilling is the second mode of morphological change while the drastic decrease in sediment load from upstream is likely unrelated to the silting of the nb local land reclamation along the banks is directly responsible for the reduction of estuarine surface area and related tidal prism between 1958 and 2013 enhanced flood tide currents resulted in a large import of sediments from offshore into the nb triggering a sustained decrease in channel volume below 0 m it is argued that the recovery of the funnel shaped configuration of the estuary by restoring mud flats over 0 m dredging the southern part of the estuary bend and forbidding land reclamation could prevent the silting of the nb otherwise the nb will likely vanish in few decades

parameterization of elastic stress sensitivity in shales stress dependency and anisotropy of dynamic elastic properties of shales is important for a number of geophysical applications including seismic interpretation fluid identification and 4d seismic monitoring using sayerskachanov formalism we developed a new model for transversely isotropic ti media that describes stress sensitivity behavior of all five elastic coefficients using four physically meaningful parameters the model is used to parameterize elastic properties of about 20 shales obtained from laboratory measurements and the literature the four fitting parameters namely specific tangential compliance of a single crack ratio of normal to tangential compliances characteristic pressure and crack orientation anisotropy parameter show moderate to good correlations with the depth from which the shale was extracted with increasing depth the tangential compliance exponentially decreases the crack orientation anisotropy parameter broadly increases with depth for most of the shales indicating that cracks are getting more aligned in the bedding plane the ratio of normal to shear compliance and characteristic pressure decreases with depth to 2500 m and then increases below this to 3600 m the suggested model allows us to evaluate the stress dependency of all five elastic compliances of a ti medium even if only some of them are known this may allow the reconstruction of the stress dependency of all five elastic compliances of a shale from log data for example

predicting stress induced velocity anisotropy in rocks a simple transformation using measured isotropic vp and vs versus hydrostatic pressure is presented for predicting stress induced seismic velocity anisotropy in rocks the compliant crack like portions of the pore space are characterized by generalized compressional and shear compliances that are estimated from the isotropic vp and vs the physical assumption that the compliant porosity is crack like means that the pressure dependence of the generalized compliances is governed primarily by normal tractions resolved across cracks and defects this allows the measured pressure dependence to be mapped from the hydrostatic stress state to any applied nonhydrostatic stress predicted p and s wave velocities agree reasonably well with uniaxial stress data for barre granite and massillon sandstone while it is mechanically similar to methods based on idealized ellipsoidal cracks the approach is relatively independent of any assumed crack geometry and is not limited to small crack densities

an analytic model for the stress induced anisotropy of dry rocks one of the main causes of azimuthal anisotropy in sedimentary rocks is anisotropy of tectonic stresses in the earth s crust we have developed an analytic model for seismic anisotropy caused by the application of a small anisotropic stress we first considered an isotropic linearly elastic medium porous or nonporous permeated by a distribution of discontinuities with random isotropic orientation such as randomly oriented compliant grain contacts or cracks the geometry of individual discontinuities is not specified instead their behavior is defined by a ratio b of the normal to tangential excess compliances when this isotropic rock is subjected to a small compressive stress isotropic or anisotropic the number of cracks along a particular plane is reduced in proportion to the normal stress traction acting on that plane this effect is modeled using the sayers kachanov noninteractive approximation the model predicts that such anisotropic crack closure yields elliptical anisotropy regardless of

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

modeling elastic anisotropy resulting from the application of triaxial stress abstractelastic wave velocities in rocks vary with stress due to the presence of discontinuities and microcracks within the rock we analytically derived a model to account for stress dependency of seismic velocities when a rock is subjected to triaxial stresses we first considered a linearly isotropic elastic medium permeated by a distribution of cracks with random orientations the geometry of cracks is not specified instead their behavior is defined by a ratio b of their normal to tangential excess compliances when this isotropic rock is subjected to triaxial stresses cracks tend to close depending on their orientation with respect to the applied stresses for small stresses the model predicts ellipsoidal anisotropy and expresses the ratios of thomsen s parameters in the three orthogonal planes of symmetry as a function of the compliance and poisson s ratios it also establishes relationships between anisotropy parameters and stress ratios deriving the model for larger stresses shows that su

facies and architecture of an estuarine tidal bar the trompeloup bar gironde estuary sw france abstract this study describes the sedimentary facies and internal architecture of a modern estuarine tidal bar present in the bay head delta of a wave and tide dominated estuary the gironde estuary in southwest france based on 51 cores 2 to 5 m long this work demonstrates that such bars are composite sedimentary bodies made up of individual sigmoidal sand units isolated from one another by thick muddy layers the bar appeared in the study area around 1874 since then its evolution has been characterized by phases of rapid downstream bar migration alternating with periods of bar abandonment during the periods of active bar progradation which commonly last between 10 and 20 years the bar progrades up to 7 km seaward and forms a narrow 200 800 m wide sand ridge up to 6 m thick during abandonment phases which also last around 10 20 years the bar is starved of sand and a mud layer 1 to 3 m thick is deposited the vertical succession formed by the seaward progradation of the tidal bar records these alternating phases of growth and abandonment a typical vertical succession in the bar system is 8 m thick and comprises several superimposed upward coarsening units of cross stratified sand deposited during phases of seaward progradation separated by a thick layer of thinner bedded mud and sand laminae deposited during phases of bar abandonment when a tidal bar builds up to the supratidal zone marshes accumulate and the bar becomes a permanent island in the estuary the large scale architecture of the bar is thus made of an alternation of potential sandy reservoir units and muddy internal seals the reservoir units are characterized by a sigmoidal shape the muddy layer which is deposited between the two sigmoidal units is a thick continuous potential internal seal this complex internal architecture is due to the fact that there is a considerable amount of mud present in the bay head delta of the gironde estuary it is thought to be representative of the architecture of tidal bars in the inner part of wave and tide dominated estuaries

factors controlling the field settling velocity of cohesive sediment in estuaries abstract it has long been recognized that the suspended sediment concentration ssc is one of the major determinants for the flocculation of cohesive particles into sediment flocs in estuaries it is furthermore well known that the turbulent shear of the water significantly influences the flocculation process and the equilibrium settling velocity of flocculated sediment in a turbulent flow a vast number of authors have reported algorithms relating the median settling velocity w 50 to suspended sediment concentration however only a few studies have dealt with the impact of the turbulent shear in this paper expressed as the root mean square rms velocity gradient g in the water on the w 50 in situ there is a strong need to establish algorithms based on in situ measurements describing the dual impact of both ssc and g on the flocculation process and hence w 50 the present paper addresses this topic field settling velocities of suspended cohesive sediment have been measured in micro meso and macro tidal estuaries regression analyses between the w 50 ssc and g are presented it is shown that by including both g and ssc in the regression analyses a significant increase in the correlation of the description of w 50 and the controlling parameters from each area can be obtained a generic algorithm describing the data from all the investigated areas is suggested it works well within specific tidal areas but fails to give a generic description of the field settling velocity

sedimentation on intertidal mudflats in the lower part of macrotidal estuaries sedimentation rhythms and their preservation the objective of this study is to propose an original approach to the analysis of the formation of intertidal rhythmites their preservation and the evaluation of sedimentation rates on estuarine mudflats three mudflats one from each of three estuaries were analysed using a combination of long term a year high frequency 1 burst 10 or 20 min and high resolution 0 2 cm altimeter datasets and x ray images of sediment cores collected during topographic surveys the results highlight the roles played by sediment supply hydrodynamics and morphology of the lower estuaries on the sedimentation rhythms while the sediment starved medway estuary kent uk remains stable at different time scales the annual sedimentation rates on the sheltered authie mudflat pas decalais france and the open seine mudflat normandy france are relatively high at 18 and 15 cm yr 1 respectively on the authie mudflat sedimentation rhythms correspond to the semi lunar cycle with a good correlation between tidal range and deposit thickness sedimentation occurs at the beginning of the recovery mean value of 0 25 cm per semi diurnal cycle and is not disturbed by wind induced waves in the lower seine estuary semi diurnal mechanisms of deposition occur mainly when the mudflat is covered by a minimal water height tidal range threshold value 7 1 m sedimentation rhythms are discontinuous and deposition occurs only during the highest spring tides mean deposit thickness is 0 6 cm per semi diurnal cycle controlled by the turbidity maximum and the long high tide slack 2 3 h the fluid mud is sensitive to wind waves in this open funnel shaped estuary which undergoes wind induced erosion 0 2 to 2 cm about 10 times per year comparison of altimeter datasets and lithology of the sediments cored at the same points provided improved understanding of the sediment record rhythms and the sedimentation events on the sediment starved medway mudflat the result of sediment processes is a single superficial lamina the elementary deposit in the authie bay corresponds to a semi lunar linked layer typical of sheltered environments on the lower seine mudflat sedimentation rhythms are linked to the highest spring tides i e the lunar cycle resulting from increased sediment availability related to the high suspended matter concentration in the turbidity maximum these results underline the complex response of intertidal mudflats to hydrodynamics and sediment supply conditions from the semi diurnal to the annual scales

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

hydrodynamics and sedimentation induced by large scale coastal developments in the keum river estuary korea abstract the macro tidal keum river estuary located in the eastern yellow sea has been suffering siltation and morphological change since 1994 to understand the effects of the large scale coastal developments on the sedimentation processes in the estuary hydrodynamic and sedimentary data collected from 1985 to 2002 were analyzed and numerical experiments of hydrodynamics were performed the sedimentation rate in the estuary increased by a factor of 1 9 from 3 5 10 6 to 6 7 10 6 m 3 y 1 after the construction of a dam in the upper reaches of the estuary in 1994 large part of the estuary is veneered by the muddy sediments noticeably which were rarely found before dam construction since then siltation has concentrated in the upper estuary rather than the lower the upstream transport and accumulation of fine grained sediments is due to 1 the change to flood dominance in the main channel i e the relative intensification of flood current and the flood directed residual current and 2 the decrease in transport capacity in the upper estuary i e the marked decrease in current velocity which was induced by dam construction the former has resulted in the ebb dominance of the gaeya channel a distributary in the north of the main channel the tidal pumping of fine sediments was reinforced not by the freshwater saltwater interaction but by the residual tidal circulation the sediment fluxes observed in 2001 2002 demonstrate year round net inflow both at the entrance of the jetties and at the gaeya channel which implies that the sediments delivered by the keum river are entirely confined to the estuary incapable of escaping to the sea the net inward transport of fine sediments may accumulate pollutants adsorbed to or absorbed in the sediment grains in the estuary thus deteriorating the benthic environment gradually and the water quality eventually

recent drumlins flutes and lineations at vestari hagafellsjokull iceland in the foreland of the vestari hagafellsjokull glacier langajokull central iceland three scales of subglacial bed forms are found drumlins flutes and lineations the smaller bed forms are superimposed upon the larger these three bed forms probably formed as a result of the presence of a rigid subglacial core producing a lee side low pressure area into which sediment flowed and collected the cores of the drumlins are tumuli lava blisters whilst the cores of the flutes and lineations were large clasts differences between the three scales of bed forms are that a the flutes and lineations are far more mobile features as their cores could move within the deforming layer whilst the drumlin bedrock cores were fixed b the lineations formed in association with a clast pavement the change in scale of the bed forms may be related to changes in thickness of the deforming layer and size of the core at this site smaller bed forms were superimposed upon larger bed forms and these may have formed as the deforming layer progressively thinned in association with glacial retreat

seasonal reorganization of subglacial drainage inferred from measurements in boreholes the effect of the formation of a major subglacial drainage channel on the behaviour of the subglacial drainage system of haut glacier d arolla switzerland was investigated using measurements of borehole water level and the electrical conductivity and turbidity of basal meltwaters electrical conductivity profiles were also measured within borehole water columns to identify the water sources driving water level changes and to determine patterns of water circulation in boreholes prior to channel formation boreholes showed idiosyncratic and poorly coordinated behaviour diurnal water level fluctuations were small and driven by supraglacial englacial water inputs even when boreholes were connected to a subglacial drainage system this system appeared to consist of hydraulically impermeable patches interspersed with storage spaces and transmitted a very low water flux drainage reorganization which occurred around 31 july 1993 in response to rapidly rising meltwater and rainfall inputs seems to have involved the creation of a connection between an incipient channel and a well established channelized system located further down glacier once a major channel existed within the area of the borehole array borehole water level fluctuations were forced by discharge related changes in channel water pressure although a diversity of responses was observed these included i synchronous ii damped and lagged iii inverse and iv alternating inverse lagged responses synchronous responses occurred in boreholes connected directly to the channel while damped and lagged responses occurred in boreholes connected to it by a more resistive drainage system pressure variations within the channel resulted in diurnal transfer of mechanical support for the ice overburden between connected and unconnected areas of the bed producing inverse and alternating patterns of water level response 1998 john wiley sons ltd

stress induced seismic azimuthal anisotropy sand shale content and depth trends offshore north west australia abstractseismic azimuthal anisotropy is apparent when p wave velocities vary with source receiver azimuth and downward propagating s waves split into two quasi s waves polarized in orthogonal directions not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations there are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand shale lithology and depth we develop a model that does so in unconsolidated sand shale sequences offshore north west australia our method naturally introduces two new concepts critical anisotropy and anisotropic depth limit critical anisotropy is the maximum amount of azimuthal anisotropy expected to be observed at the shallowest sediment burial depth where the confining pressure and sediment compaction are minimal the anisotropic depth limit is the maximum depth where the stress induced azimuthal anisotropy is ex

rapid coastal geomorphic change in the river murray estuary of australia abstract the river murray estuary a ramsar wetland site has experienced considerable rapid coastal change during the quaternary the interplay of aeolian processes river flows tidal oscillations wave action and variations in relative sea level due to global sea level changes and land subsidence provides the energy for the ongoing dynamism often accelerated by human impacts the estuary is the terminus of the murray darling catchment which covers 1 073 million km 2 of the australian continent terminal lakes alexandrina albert and the coorong lagoon are holocene features occupying tectonically subsiding quaternary interdune areas they formed in response to eustatic sea level rise following the last glacial maximum ca 20 ka the last interglacial shoreline 125 000 yr bp parallels the modern shoreline several kilometres inland dislocation of the last interglacial shoreline demonstrates ongoing tectonic subsidence as does historical seismic activity the northern half of hindmarsh island formed during last interglacial times when it was the sink for dominant longshore transport from the southeast which pushed the river murray westward partly explaining the large bend in the river murray at goolwa the modern coastal barriers of sir richard peninsula and younghusband peninsula formed from 7000 yr ago following glacier melt and sea level rise subsequently the barriers have migrated landward sporadically exposing lagoonal sediments on the ocean beaches differential loading of the soft lagoonal sediments by advancing dunes possibly in conjunction with seismic events has deformed and elevated them to up to 10 m above present sea level apsl during the mid holocene an extensive sand flat with associated dunes formed immediately inland of the coastal barrier at least six generations of late pleistocene dune systems occur in the region for example during last glacial times the climate was drier colder and windier than at present and a system of parallel west east trending yellow red desert dunes developed around the lakes aeolian processes remain important with occasionally up to 5000 tonnes of sand being in motion along 10 km of the modern shoreline during mouth migration dunes up to 2 m high have been formed and vegetated in 12 months directly inland from the mouth and replicating the formation of older dunes on hindmarsh island elsewhere sand blown directly from the barrier system infills channels barrage construction on the beach facies of the last interglacial shoreline transformed the estuary into freshwater lakes with permanently raised water levels and reduced the tidal prism by 90 increased deposition upstream and downstream accompanied barrage construction as have accelerated lakeshore erosion and the growth and consolidation of the flood tidal delta bird island these human accelerated changes provide rapidly formed analogues of older quaternary features and aid their interpretation the shape and location of the murray mouth is constantly changing migrating over 1 6 km since the 1830s migrations of up to 6 km over the past 3000 yr have influenced sedimentation on the landward shore of the back barrier lagoonal system

changes in shear wave polarization azimuth with depth in cymric and railroad gap oil fields shear wave s wave polarization azimuths although consistent over large depth intervals changed abruptly and by large amount of various depths in nine component vertical seismic profiling vsp data from the cymric and railroad gap oil fields of the southwest san joaquin basin a simple layer stripping technique made it possible to follow the polarization changes and determine the s wave birefringence over successive depth intervals because the birefringence and polarization azimuth are related to in situ stresses and fracture information from such analysis could be important for reservoir development near offset vsp data from cymrix indicated that the subsurface could be appproximated roughly as two anisotropic layers the upper layer from the surface to 800 ft 240 m had vertical s wave birefringence as large was about 6 percent down to 1300 ft 400 m in the upper layer the polarization azimuth of the fast s wave was n 60 e while in the lower layer it was about n 10 e refinement of the laye

the multi decadal morphodynamic changes of the mouth bar in a mixed fluvial tidal estuarine channel abstract inner channel mouth bars imb are common and vital geomorphological structures in estuaries that can efficiently promote the progradation of a fluvial delta however these significant structures face serious interferences by natural and human forces this study mainly focuses on imb deposited in the mixed fluvial tidal dominated south passage sp of the changjiang estuary between 1959 and 2018 to reveal how multidecadal morphodynamic variability in a mouth bar responds to natural forcing and human interferences the results show that the volume of the imb in the sp increased from 1128 106 m3 in 1959 to 1636 106 m3 in 1989 and then decreased to 462 106 m3 in 2018 meanwhile the evolution of the imb could be divided into five stages the growing phase 1959 to 1979 which showed a v shape the partial adjustment phase 1999 2003 which showed a crest dent shape the stable phase which showed a flat shape 2004 2010 the partial adjustment phase 2011 2017 when jiangyanan shola inserted into the sp and finally evolved into a flat shape in 2018 fluvial water discharge and suspended sediment discharge ssd did not control the variation in the mouth bar enso events were normally responsible for not only the periodic variations in the landward slope and the water depth of the crest of the imb but also occasional extreme changes in the imb moreover local sandbar insertion sediment from the seaside induced by strong tidal power and intensified engineering projects resulted in the continual shrinkage of the mouth bar by depositing more sediment at the mouth bar our work implies that understanding and governing this imb will bring additional economic benefits to this fast developing society but the protection of this delicate estuarine geomorphology system should still receive great attention

exploring trends in microcrack properties of sedimentary rocks an audit of dry core velocity stress measurements rock physics models are used increasingly to link fluid and mechanical deformation parameters for dynamic elastic modeling we explore the input parameters of an analytical stress dependent rock physics model to do this we invert for the stressdependent microcrack parameters of more than 150 sedimentary rock velocity stress core measurements taken from a literature survey theinversionschemeisbasedonamicrostructuraleffective medium formulation defined by a second rank crack density tensor scalar crack model or by a second and fourth rank crack density tensor joint inversion model then the inversion results are used to explore and predict the stress dependent elastic behavior of various sedimentary rock lithologies using an analytical microstructural rock physics model via the initial model inputparameters initialcrackaspectratioandinitialcrackdensity estimates of initial crack aspect ratio are consistent among most lithologies with a mean of 0 0004 but for shales they differ uptoseveraltimesinmagnitudewithameanof0 001 estimates of initial aspect ratio are relatively insensitive to the inversion method although the scalar crack inversion becomes less reliableatlowvaluesofnormal to tangentialcrackcomplianceratio bn bt initialcrackdensityissensitivetothedegreeofdamage as well as the inversion procedure an important implication is thatthefourth rankcrack densitytermisnotnecessarilynegligible for most sedimentary rocks and evaluation of this term or bn bt is necessary for accurate prediction of initial crack density this is especially important because recent studies suggest thatbn btcanindicatefluidcontentincracks

the use of salt injection and conductivity monitoring to infer near margin hydrological conditions on vestari hagafellsjokull iceland vestari hagafellsjokull is a surge type outlet glacier from the langjokull ice cap iceland intensive hydrological investigations were carried out during non surge conditions in the summers of 1999 and 2000 and 14 boreholes were drilled using pressurized hot water over an area 800 m from the margin and approximately 5000 m 2 in size where ice thickness ranged from 60 to 70 m initial investigations showed that a large fraction of the boreholes drilled to the bed did not drain and were assumed not to connect to the subglacial drainage system subsequently we investigated the hypothesis that boreholes which remain full may do so as a consequence of a balance between englacial inflow and basal drainage rather than the standard assumption that such boreholes are simply unconnected in testing this hypothesis we developed a new technique for measuring water motion within the borehole by monitoring the passage of a saline solution down the borehole s water column the technique allows rates of motion to be established as well as allowing the quantification of net addition and loss of water from the borehole observations based on the motion of saline plumes within the boreholes lead us to the conclusion that some boreholes do indeed remain full as a consequence of a balance between englacial inflow and subglacial drainage the abrupt dilution that occurs at the top of these boreholes suggests inflow from a near surface englacial water source while the descent of the saline plumes implies that water is being lost at the base to the subglacial system the system appears to be driven by excess water head in the boreholes over flotation and implies that the borehole bedrock interface can be leaky

estimation of azimuthal anisotropy from vsp data using multicomponent s wave velocity analysis observation of azimuthal shear wave anisotropy can be useful for characterization of fractures or stress fields shear wave anisotropy is often estimated by measuring splitting of individual shear wave events in vertical seismic profile vsp data however this method may become unreliable for zero offset marine vsp where the seismogram often contains no strong individual shear events such as direct downgoing shear wave but often contains many low amplitude ps mode converted waves we have developed a new approach for estimation of the fast and slow shear wave velocities and orientation of polarization planes based on the multicomponent linear traveltime moveout velocity analysis this technique is applicable to zerooffset vsp data and should take advantage of the presence of a large number of shear wave events with the same apparent velocity which for a horizontally layered medium should be close to the interval velocity the approach assumes that the vsp data are acquired in a vertical well drilled in an orthorhombic medium with a horizontal symmetry plane including horizontal transverse isotropy the main idea is to estimate the dominant apparent velocity for a given polarization direction by measuring the coherency of the seismic signal of a large number of events as a function of the apparent velocity the algorithm was tested on marine three component 3c vsp acquired in the north west shelf of australia and on land 3c vsp acquired with different sources in the same borehole located in otway basin victoria these tests show good agreement between anisotropy parameters magnitude and orientation derived from the vsp and cross dipole sonic log data

morphological responses of an estuarine intertidal mudflat to constructions since 1978 to 2005 the seine estuary france abstract since 1834 the seine estuary france has been the site of numerous construction projects with the aim to accommodate and secure boat traffic since 1978 the increasing of the activities of le havre port located at the mouth of the estuary has accelerated the construction work rate several dykes a bridge and new port facilities have been constructed in rapid succession modifying considerably the hydrodynamic conditions which sustain a partially vegetated sandy muddy tidal flat located in the north bank of the estuary between the new port of le havre and the normandy bridge achieved in 1995 the present study deals with the morphological evolution of this zone from 1978 to 2005 the use of a low altitude remote sensing technique combined with traditional methods of ground survey and probes allow to demonstrate the impact of human activities on sedimentary and vegetation dynamics the northern mudflat of the estuary is the most affected by these human activities which surface have reduced of 62 during the last 27 years with an intensified local erosion during the last 27 months corresponding to a loss 1 250 000 m 3 of fine grained sediment at the same time the general sanding up in the channel of the zone has caused a loss of more than 31 of the tidal prism more than three quarters of which occurred during the last three years results also establish that the response times of the sedimentary or topographic readjustment to an installation depend on the extent and the nature of the construction in fact the sedimentary readjustments to an installation can be delayed by up to 10 years in the case of the seine estuary this delay is explained by a rapid succession of construction works which may occult the effect of a single installation except in the case of a dyke built perpendicular to ebb and flood currents the impacts of these installations reach a hydro sedimentary equilibrium on the level between 1 and 7 years after their completion

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

evolution of the jiuduansha wetland and the impact of navigation works in the yangtze estuary china abstract the estuarine wetlands in the yangtze estuary face increasing threats due to large scale engineering projects and huge land requirements as a wetland national nature reserve and important stopover site for migratory shorebirds of the east asian australasian flyway the jiuduansha wetland one of four main islands in the estuary is of both national and international importance since 1998 the previously undisturbed wetland has been considerably modified by the adjacent deep water navigation channel project dnc in order to understand the role of the dnc for the evolution of the jiuduansha wetland we performed a diagnostic study from multiple perspectives including deposition rate area change evolution track geometric characteristics and geomorphological change by coupling gis geostatistics and remote sensing techniques this study demonstrates the impact of the dnc on the jiuduansha wetland in a spatially explicit way multi temporal bathymetric maps and landsat images from before and after the dnc was constructed were adopted to conduct our study we find that deposition has occurred in most parts of the wetland over the past almost 30 years accounting for 67 3 of the total area however over 40 of the study area shows a decreasing trend in deposition rate the spatial distribution of deposition erosion patterns is closely linked to the dnc we also find that the dnc has substantial effects on the evolution of the jiuduansha wetland the 0 2 and 5 m isobaths in the jiuduansha shoal jds as well as in the jiangya shoal jys the upper shoal us and the middle lower shoal mls show different response patterns to the dnc specifically the south training jetty of the dnc has an adsorption effect on the jds above the 2 m isobaths intersecting with it as a result the evolution track geometric and geomorphological characteristics of the jds were markedly altered in the short term our comprehensive analysis suggests that in the future the jds will become more elongated in both the upstream and downstream direction along the south training jetty and that the south side of the jds will be eroded

human impacts on the changjiang yangtze river basin china with special reference to the impacts on the dry season water discharges into the sea abstract the annual mean discharge from the upper changjiang yangtze basin has shown a significant decreasing trend since the end of the 19th century since the 1970s the monthly mean discharge to the sea has also shown a dramatic decrease during dry seasons this paper examines the human impacts on the major hydrological processes in the changjiang river basin with a special focus on their influence on the discharge from the drainage basin to the sea during the dry season climatic warming has been obvious since the 1960s in the headwater area resulting a continuous retreat of glaciers while the increased evaporation is responsible for the dropping of lake water levels and decrease in water area such a trend continuing into the coming decades will significantly change the seasonal hydrological processes especially the dry season discharges from the upper basin the decreasing vegetation cover and the increasing reservoir volume capacity also impacted on the water discharge over the past decades although in different ways the possible impacts of the three gorges dam on the monthly variation of water discharge to the sea are discussed with special emphasis in the middle basin discussions are focused on the effect of decreasing lake area of increasing reservoir capacity and of irrigated agriculture on the temporal changes of water discharge since the 1950s the human impacts on water discharge from the lower basin to the sea are mostly attributed to water transfer to both tributary and neighboring drainage basins by a large number of electric pumping stations and sluices the total water transferring capacity is more than 5000 m3 s along the lower river studies indicate that in a dry season the water discharge to the sea is greatly reduced and results in strong saltwater intrusion in the estuary

borehole drainage and its implications for the investigation of glacier hydrology experiences from haut glacier d arolla switzerland studies of glacier hydrology rely increasingly on measurements made in boreholes as a basis for reconstructing the character and behaviour of subglacial drainage systems in temperate glaciers in which boreholes remain open to the atmosphere following drilling the interpretation of such data may be complicated by supraglacial or englacial water flows to and from boreholes we report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at haut glacier d arolla switzerland results are used to define a number of borehole drainage types examples of each drainage type are presented along with the manner in which they influence interpretations of borehole water levels borehole water quality data and borehole dye traces the analysis indicates that a full understanding of possible borehole drainage modes is required for the correct interpretation of many borehole observations and that those observations provide an accurate indication of subglacial conditions only under relatively restricted circumstances copyright 2001 john wiley sons ltd

rapid human induced siltation of the macro tidal ord river estuary western australia field studies on the sediment dynamics of the two arms of cambridge gulf tropical western australia were undertaken the system is macro tidal with 8 m tides the west arm is the estuary of the durack and pentecost rivers which are largely untouched by human activities the east arm is the estuary of the ord river affected by land clearing which started 100 years ago and by two river dams constructed 30 years ago prior to damming of the ord river the natural flow in all rivers was highly seasonal characterized by small at times negligible flow during the dry season which lasts eight months and occasional river floods during the wet season which lasts four months the river flow has been regulated in the east arm as a result of damming this resulted in suppressing large river floods the salinity intrusion length has decreased by about 50 in the east arm following river damming the east arm has silted measurably over the last 30 years with the stream cross sectional area decreasing by about 50 field and numerical studies suggest that this is due to the dam induced suppression of large river floods which has in turn allowed a greater amount of tidal pumping of sediment into the east arm from cambridge gulf since tidal pumping is increasing as the system is silting the east arm appears to now be geomorphologically unstable as a result of human activities numerical studies suggest it may take as little as 100 years for the ord river to reach a new equilibrium modelling suggests that this equilibrium may be characterized by a salinity intrusion length half that before damming a channel width and depth reduced by 70 and a much stronger tidal asymmetry characterized by an increasing size of the tidal bore the west arm appears to be at equilibrium since there has been no net loss or gain of sediment for the last 111 years tidal dynamics and river floods appear responsible for self scouring this channel

shoal morphodynamics of the changjiang yangtze estuary influences from river damming estuarine hydraulic engineering and reclamation projects abstract concerns regarding estuarine shoal morphodynamics have increased worldwide because of intensive anthropogenic activities to explore response of estuarine shoals to possible couplings of multiple artificial interferences in river basins and within estuaries the link between the morphodynamic processes of the nanhui shoal nhs which is located along the southern margin of the changjiang estuary the largest estuary in asia and river damming estuarine hydraulic engineering and reclamation projects is discerned in this study the results reveal that the nhs exhibited secular polarization during 1998 2013 with a significant accretion of 1 8 10 8 m 3 landward from the tidal ridge and an erosion of 0 3 10 8 m 3 on the seaward edge respectively forming a steep slope with an elevation between 2 and 3 m meanwhile the nhs morphodynamics could be divided into 3 stages mild accretion with an undisturbed tidal channel during 1998 2002 strong sedimentation with a disrupted tidal channel during 2003 2008 and large scale landward accretion with an infilled tidal channel after 2009 moreover the nhs s volume variations exhibited an 18 month cycle even though an increased area of 35 km 2 above 2 m and a decreased area of 45 km 2 between 2 and 5 m were observed the primary causes of theses periodic changes in the nhs s volume are determined as the fluctuating changjiang water discharge and cyclically altered hydrodynamics of the south passage the deep waterway project dwp and reclamation projects were responsible for the polarization of seaward erosion and landward accretion respectively moreover these reclamation projects dominated the staggered changes in nhs morphodynamics by inducing continuous accretion within the tidal channel compared to estuarine engineering river damming induced dramatic declines in distal sediment may have played a minor role in flat changes of nhs

approximate fluid substitution for vertical velocities in weakly anisotropic vti rocks despite the prevalence of elastic anisotropy in rocks most models used routinely for wave propagation imaging and rock physics assume an isotropic earth the main reason for using isotropic approximations is that we seldom measure enough parameters to characterize the stiffness tensor of a rock completely fluid substitution is an important example because of an incomplete knowledge of the stiffness tensor often we choose isotropic equations over their anisotropic form assuming weak anisotropy we derive an approximate form of the anisotropic fluid substitution equation for seismic waves propagating along the symmetry axis of a transversely isotropic medium the approximation takes the form of the usual isotropic calculation with a simple first order correction proportional to the thomsen anisotropic parameter thus requiring only three elastic constants because can be either greater than or less than zero in a vti medium we can explain why isotropic fluid substitution sometimes overpredicts

basal hydraulic system of a west antarctic ice stream constraints from borehole observations pressure and tracer measurements in boreholes drilled to the bottom of ice stream b west antarctica are used to obtain information about the basal water conduit system in which high water pressures are developed these high pressures presumably make possible the rapid movement of the ice stream pressure in the system is indicated by the borehole water level once connection to the conduit system is made on initial connection here also called breakthrough to the basal water system the water level drops in a few minutes to an initial depth in the range 96 117 m below the surface these water levels are near but mostly somewhat deeper than the flotation level of about 100m depth water level at which basal water pressure and ice overburden pressure are equal which is calculated from depth density profiles and is measured in one borehole the conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed the thickness of the gap has to be about 2 mm to account for the water level drop on breakthrough and about 4 mm to fit the results of a salt tracer experiment indicating downstream transport at a speed of 7 5 mm s 1 the above gap conduit model is however ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole and also by the large hole to hole variation in measured basal pressure which if present in a gap conduit system with 2 or 4 mm would result in unacceptably large local water fluxes an alternative model that avoids the e objections called the gap opening model involves opening a gap as injection proceeds starting with a thin film the injection of water under pressure lifts the ice mass a round the borehole creating a gap 3 or 4 mm wide at the ice bed interface evaluated quantitatively the gap opening model accounts for the volume of water that the basal watery system accepts on breakthrough which obviates the gap conduit model in order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits of which the most promising type is the canal conduit proposed theoretically by walder and fowler 1994 flat low conduits incised into the till 0 1 m deep and perhaps 1 m wide with a flat ice roof the basal water pressure data suggest that the canals are spaced 50 300 m apart much closer than r tunnel would be the deepest observed water level 117 m i the most likely to reflect the actual water pressure in the canals corresponding to a basal effective pressure of 1 6 bar in this interpretation the shallower water levels are affected by loss of hydraulic head in the narrow passageway s that connect along the bed from borehole to canal s once a borehole has frozen up and any passageways connecting with canals have become closed a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till given enough time for pressure equilibration this pressure varies considerably with time over the equivalent water level range from 100 to 113 m basal pressure sensors 500 m apart report uncorrelated variations whereas sensors in boreholes 25 m apart report mostly but not entirely well correlated variations of unknown origin in part of the record remarkable anticorrelated variations are interspersed with positively correlated one and there are rare abrupt excursions to extreme water levels as deep as 125m and as shallow as 74 m a diurnal pressure fluctuation intermittently observed may possibly be caused by the ocean tide in the ross sea the lack of any observed variation in ice stream motion when large percentagewise variations in basal effective pressure were occurring according to our data suggests that the observed pressure variations are sufficiently local and so randomly variable from place to place that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed

elastic wave propagation in media with parallel fractures and aligned cracks a model of parallel slip interfaces simulates the behaviour of a fracture system composed of large closely spaced aligned joints the model admits any fracture system anisotropy triclinic the most general monoclinic orthorhombic or transversely isotropic and this is specified by the form of the 3 3 fracture system compliance matrix the fracture system may be embedded in an anisotropic elastic background with no restrictions on the type of anisotropy to compute the long wavelength equivalent moduli of the fractured medium requires at most the inversion of two 3 3 matrices when the fractures are assumed on average to have rotational symmetry transversely isotropic fracture system behaviour and the background is assumed isotropic the resulting equivalent medium is transversely isotropic and the effect of the additional compliance of the fracture system may be specified by two parameters in addition to the two isotropic parameters of the isotropic background dilute systems of flat aligned microcracks in an isotropic background yield an equivalent medium of the same form as that of the isotropic medium with large joints i e there are two additional parameters due to the presence of the microcracks which play roles in the stress strain relations of the equivalent medium identical to those played by the parameters due to the presence of large joints thus knowledge of the total of four parameters describing the anisotropy of such a fractured medium tells nothing of the size or concentration of the aligned fractures but does contain information as to the overall excess compliance due to the fracture system and its orientation as the aligned microcracks which were assumed to be ellipsoidal with very small aspect ratio are allowed to become non fiat i e have a growing aspect ratio the moduli of the equivalent medium begin to diverge from the standard form of the moduli for flat cracks the divergence is faster for higher crack densities but only becomes significant for microcracks of aspect ratios approaching 0 3

long term morphological change and its causes in the mersey estuary nw england changes in the morphology of the mersey estuary and their possible causes have been investigated using historical trend analysis and expert geomorphological assessment historical bathymetric charts were digitised and analysed within a gis to provide quantitative estimates of changes in areas and sediment volumes above and below selected elevation planes the results show that the estuary experienced major changes over the last 150 years notably between the late 19th century and ca 1950 an analysis of data relating to possible natural and human factors which could have influenced these changes suggests that training wall construction and dredging in the outer estuary and liverpool bay was the most significant factor contributing to change during this period these activities modified the hydrodynamic and sediment transport regime in a way which enhanced an existing natural tendency for movement of sediment from liverpool bay and the outer estuary into the inner estuary changes in other factors including sea level tidal range wind wave climate freshwater flow and embanking land reclamation were of relatively minor importance between 1950 and 1977 the rate of sediment accumulation in the inner estuary declined as the estuary approached a new condition of dynamic equilibrium and since 1977 there has been a slight net loss of sediment under these conditions the changes in natural forcing factors such as sea level and storminess are likely to have a relatively greater effect on the estuary than in the past

long term morphological change in the ribble estuary northwest england morphological change in the ribble estuary northwest england has been studied using bathymetric charts topographical surveys and remote sensing data a sediment budget has been prepared from the analysis of these data the results reveal a net accretional trend over the last 150 years the main channels experienced major infilling sediment also accumulated in higher parts of the intertidal zone salt marshes and sand banks while the sediment volume in the lower intertidal zone remained essentially the same there were both zones of net erosion and deposition in the outer estuary with a small net gain in subtidal sediment volume infilling associated with major morphological change was accelerated in the nineteenth century and early twentieth century principally as a result of human activities the triggering factors for increased sedimentation were embankment construction and reclamation after 1810 which progressively reduced the intertidal area tidal prism and current velocities within the estuary additionally construction of a trained channel between 1847 and 1910 to secure navigation and maintenance of this channel by dredging concentrated the ebb flow in this overdeepened channel and reduced periodic scour over the sand banks on both sides enhancing sedimentation thus the effects of human activities have outstripped those of changes in natural forcing factors on the morphological development in the area

river flow control on intertidal mudflat sedimentation in the mouth of a macrotidal estuary abstract the objective of this study is to analyze the impact of hydrological variability influenced by climatic phenomena upon the sedimentary exchange between the turbidity maximum tm and a river mouth intertidal mudflat this study carried out over a period of 10 years 1997 2006 in the seine estuary france is specifically focused on two extreme periods a wet one from 2001 to 2002 and a drier one from 2005 to 2006 this study is based on an original approach combining data gathered via low altitude remote sensing with altimeter readings and ground level measurements during this 10 year period we observed a link between climate change and the sedimentary processes on the mudflat surface the modifications of sedimentary processes are mainly connected to the multiannual variability of hydrological flow rates that control the positioning of the turbidity maximum the source of the sedimentary material deposited in this intertidal zone the tm at the mouth of the seine estuary is well developed its maximum mass is estimated to be between 300 000 tons and 500 000 tons avoine et al 1981 with maximum concentrations in the surface waters ranging from 1 to 2 g l 1 le hir et al 2001 most of the fine particles stored within the tm have been found to originate from within the catchment area dupont et al 1994 in the seine estuary the dynamics of the estuarine tm in response to hydrodynamic forcings have been previously described avoine et al 1981 and modeled e g brenon and le hir 1999 le hir et al 2001 the tm is upstream of the northern mudflat when the river flow is low

waterways ice permeability at depth and water pressures at glacier d argentiere french alps pour eclaircir les changements survenus a la prise d eau sous glaciaire du glacier d argentiere une etude approfondie a ete realisee en 1979 80 avec 31 forages et un carottage jusqu au fond 240m juste en amont de la prise dans une zone surcreusee on observe que la glace en dessous d environ 100 m de profondeur est legerement permeable on a mesure la pression interstitielle de l eau dans la glace profonde le gradient piezometrique entre les trous de forage et le dephasage entre les fluctuations du niveau d eau qui augmente lorsqu on s eloigne de la rive droite il n y a pas de torrent sous glaciaire au fond du surcreusement sauf a son extremite amont la plupart de l eau de fonte doit s ecouler entre glace et rocher le long de la rive droite sa surface libre s elevant d environ 150 m au moment de l engorgement de juin on n a pas trouve de correlation nette entre la pression de l eau interstitielle profonde et la temperature de l air ou le debit a la prise sous glaciaire en aval

sediment transport and trapping in marsh systems implications of tidal flux studies although the concept that marshes act as major sediment sinks may be accurate when viewing them over the last few millennia tidal transport studies suggest considerable variability with most marshes presently exporting material on an annual basis high salinity marshes along the mid atlantic coast of the united states appear to be losing 1 2 kg m 2 yr 1 while submerged upland marshes on the delmarva peninsula are eroding at rates of up to 14 kg m 2 yr 1 by comparison at least one deltaic marsh on the dutch coast along with several estuarine marshes appear to be accumulating sediment in order to assess the trapping ability of marshes in large estuaries we constructed a sediment budget for chesapeake bay which included a variety of wetland types calculations indicate that estuarine marshes trap 5 11 of the annual chesapeake bay sediment input or about one half that previously estimated it appears that most sedimentation in estuaries and perhaps other coastal systems occurs in subtidal flats below the limit of emergent marsh vegetation as mud flats become vegetated and estuarine infilling proceeds there may be a tendency for tidal currents to become ebb dominated which promotes a net export of particulates the extent to which major storm events are capable of returning enough material to balance the long term accretionary budget of tidal marshes and keep them abreast of rising sea level is open to question differences in tidal dynamics seasonal changes in sea levels and higher temperatures may help explain why in the u s southern marshes are more susceptible to export and eventual erosion than northern marshes we hypothesize that another factor the recent reductions of terrigenous sediment inputs from the southern river systems of the u s may also be critical sediment starvation may have led to undernourishment of wetland systems of the coastal zone over the last half century which may be reflected in the net export measured in the tidal marshes in this region furthermore we postulate that changes in sediment inputs are more important than eustatic sea level rise in causing the past losses of marshes which are now undergoing mass erosion thus future wetland survival will depend as much as particulate inputs to the coastal zone as on the prospects of a global rise in sea level and more efforts should be made to quantify the sediment budgets of tidal marshes

nonlinear rock physics model for estimation of 3d subsurface stress in anisotropic formations theory and laboratory verification we develop a rock physics model based on nonlinear elasticity that describes the dependence of the effective stiffness tensor as a function of a 3d stress field in intrinsically anisotropic formations this model predicts the seismic velocity of both p and s waves in any direction for an arbitrary 3d stress state therefore the model overcomes the limitations of existing empirical velocity stress models that link p wave velocity in isotropic rocks to uniaxial or hydrostatic stress to validate this model we analyze ultrasonic velocity measurements on stressed anisotropic samples of shale and sandstone with only three nonlinear constants we are able to predict the stress dependence of all five elastic medium parameters comprising the transversely isotropic stiffness tensor we also show that the horizontal stress affects vertical s wave velocity with the same order of magnitude as vertical stress does we develop a weakanisotropy approximation that directly links commonly measured anisotropic thomsen parameters to the principal stresses each thomsen parameter is simply a sum of corresponding background intrinsic anisotropy and stressinduced contribution the stress induced part is controlled by the difference between horizontal and vertical stresses and coefficients depending on nonlinear constants thus isotropic rock stays isotropic under varying but hydrostatic load whereas transversely isotropic rock retains the same values of dimensionless thomsen parameters only unequal horizontal and vertical stresses alter anisotropy since thomsen parameters conveniently describe seismic signatures such as normal moveout velocities and amplitudevariation with offset gradients this approximation is suitable for designing new methods for the estimation of 3d subsurface stress from multicomponent seismic data

investigation of core data reliability to support time lapse interpretation in campos basin brazil quantitative interpretation of time lapse seismic data requires knowledge of saturation and pressure effects on seismic velocities although the former can usually be modeled adequately using the gassmann equation the latter is obtained mainly by laboratory measurements which can be affected by core damage we investigate the magnitude of this effect on compressional wave velocities by comparing laboratory experiments and log measurements we use gassmann fluid substitution to obtain low frequency saturated velocities from dry core measurements thus mitigating the dispersion effects taken at reservoir pressure the analysis is performed for an unusual densely cored well from which 43 cores were extracted over a 45 m thick turbidite reservoir these computed velocities show very good agreement with the sonic log measurements this confirms that for this particular region the effect of core damage on ultrasonic measurements is less than the measurement error consequently stress sensitivity of elast

elevation change mass balance dynamics and surging of langjokull iceland from 1997 to 2007 in situ mass balance survey is a joint effort of the glaciology group institute of earth sciences university of iceland and the national power company landsvirkjun we thank philippe crochet and tomas johannesson from the icelandic meteorological office for providing the gridded climate data and for useful discussions about the climatology of langjokull the 2007 lidar data were collected by the uk natural environment research council airborne research and survey facility grant ipy 07 08 additional funding was provided by the united states national science foundation grant no dge 1038596 st catharine s st john s and trinity colleges and the university of cambridge b b roberts and scandinavian studies funds we thank cameron rye for initial help coding the mass balance model