authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

maintenance of continental boundary layer shear through counter gradient vorticity flux in a barotropic model the use of a classical eddy parametrization in the analysis of continental boundary currents leads to the diffusion of momentum and relative vorticity and fails to recognize that the relevant eddies are dominated by the conservation of potential vorticity which in turn may produce an increase in the mean relative vorticity to illustrate this effect we examine a non inflected barotropic shear flow destabilized by the cross steam variation in the bottom topography of a continental slope the finiteamplitude evolution of the waves is analysed in a simple model with a step like bottom topography and with a piecewise uniform potential vorticity distribution the increase in maximum mean vorticity is computed for various values of the rossby number and the topographic elevation and it is suggested that a similar effect taking into account the isopycnal topography as well as the isobaths could maintain the large inshore shear of the gulf stream cross shelf transport of different water types i e potential vorticity and passive tracers are also computed and suggested to be pertinent to the more realistic oceanic problem involving baroclinic effects the numerical calculation employs the well known method of contour dynamics and the green s function appropriate for the step like topography is derived

grain size controls on the morphology and internal geometry of river dominated deltas predictions of a delta s morphology facies and stratigraphy are typically derived from its relative wave tide and river energies with sediment type playing a lesser role here we test the hypothesis that all other factors being equal the topset of a relatively noncohesive sandy delta will have more active distributaries a less rugose shoreline morphology less topographic variation in its topset and less variability in foreset dip directions than a highly cohesive muddy delta as a consequence its stratigraphy will have greater clinoform dip magnitudes and clinoform concavity a greater percentage of channel facies and less rugose sand bodies than a highly cohesive muddy delta nine self formed deltas having different sediment grain sizes and critical shear stresses required for re entrainment of mud are simulated using deflt3d a 2d flow and sediment transport model model results indicate that sand dominated deltas are more fan shaped while mud dominated deltas are more birdsfoot in planform because the sand dominated deltas have more active distributaries and a smaller variance of topset elevations and thereby experience a more equitable distribution of sediment to their perimeters this results in a larger proportion of channel facies in sand dominated deltas and more uniformly distributed clinoform dip directions steeper dips and greater clinoform concavity these conclusions are consistent with data collected from the goose river delta a coarse grained fan delta prograding into goose bay labrador canada a reinterpretation of the kf 1 parasequence set of the cretaceous last chance delta a unit of the ferron sandstone near emery utah usa uses ferron grain size data clinoform dip data clinoform concavity and variance of dip directions to hindcast the delta s planform the kf 1 last chance delta is predicted to have been more like a fan delta in planform than a birdsfoot delta

observations and analysis of the horizontal structure of a tidal jet at deep scour holes scour in the vicinity of a hydraulic structure may compromise its geotechnical stability or that of nearby structures much fundamental research has been dedicated to the understanding and prediction of these processes in order to enable the efficient design of mitigation measures while most of these efforts consider laterally uniform flows nonuniformity is the rule rather than the exception this study presents field observations near the storm surge barrier in the eastern scheldt estuary the netherlands where significant scour holes have developed the tidal flow through this semi open barrier exhibits characteristics of a shallow jet a pronounced contraction of this jet toward the nearby scour hole during particular stages of the tidal cycle is revealed attributed to potential vorticity conservation the depth averaged vertical vorticity increases proportionally to the depth increase measurements show a vertically uniform velocity profile in the scour hole that is attributed to a reduction of the adverse pressure gradient due to the contraction that suppresses boundary layer separation from the upstream slope of the scour hole a positive feedback mechanism is thus revealed lateral velocity gradients lead to relatively high near bed velocities in the scour hole which enhances erosion causing an even stronger horizontal contraction maintaining the scouring potential if the upstream flow field is laterally uniform observed around slack tide horizontal contraction does not occur and the boundary layer separates from the upstream slope the scour depth will then tend to an equilibrium the results infer the importance of the nonuniformity of the horizontal flow field

significant effect of sediment cohesion on delta morphology delta morphology is thought to be controlled by factors such as river discharge tides and waves numerical modelling shows that sediment cohesion also strongly influences the development of a delta s characteristics the morphologies of the world s deltas are thought to be determined by river discharge tidal range and wave action 1 more recently sea level rise 2 3 and human engineering4 have been shown to shape delta evolution the effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4 5 6 in particular the role of sediment cohesion which is controlled by sediment size and type of vegetation is unclear here we use a numerical flow and transport model7 8 9 10 to show that sediment cohesiveness also strongly influences the morphology of deltas we find that holding all other factors constant highly cohesive sediments form bird s foot deltas with rugose shorelines and highly complex floodplains whereas less cohesive sediments result in fan like deltas with smooth shorelines and flat floodplains in our simulations sediment cohesiveness also controls the number of channels that form within the deltas and the average angle of bifurcation of those channels as vegetation generally acts as a cohesive agent we suggest that deltas that formed before the expansion of land plants in the devonian period should show fan like characteristics a finding consistent with the limited data from the sedimentological record11

the submarine eruption of the bombarda volcano milos island cyclades greece the milos volcanic field includes a well exposed volcaniclastic succession which records a long history of submarine explosive volcanism the bombarda volcano a rhyolitic monogenetic center erupted 1 7 ma at a depth 200 m below sea level the aphyric products are represented by a volcaniclastic apron up to 50 m thick and a lava dome the apron is composed of pale gray juvenile fragments and accessory lithic clasts ranging from ash to blocks the juvenile clasts are highly vesicular to non vesicular the vesicles are dominantly tube vesicles the volcaniclastic apron is made up of three fades massive to normally graded pumice lithic breccia stratified pumice lithic breccia and laminated ash with pumice blocks we interpret the apron beds to be the result of water supported volcaniclastic mass how emplacement derived directly from the collapse of a small volume subaqueous eruption column and from syn eruptive down slope resedimentation of volcaniclastic debris during this eruptive phase the activity could have involved a complex combination of phreatomagmatic explosions and minor submarine effusion the lava dome emplaced later in the source area is made up of flow banded lava and separated from the apron by an obsidian carapace a few meters thick the near vertical orientation of the carapace suggests that the dome was intruded within the apron remobilization of pyroclastic debris could have been triggered by seismic activity and the lava dome emplacement

flow patterns and morphology of a prograding river delta the transition of flow between laterally confined channels and the unchannelized delta front controls the morphodynamic evolution of river deltas but has rarely been measured at the field scale we quantify flow patterns and bathymetry that define the evolution of the subaqueous delta front on the wax lake delta a rapidly prograding delta in coastal louisiana a significant portion of flow 59 departs the channel network over lateral channel margins as opposed to the downstream channel tips bathymetric surveys and remotely sensed estimates of flow direction allow spatial changes in flow velocity to be quantified and patterns of erosion and deposition to be estimated shallowing along channel margins produces spatial acceleration and erosion lateral spreading deceleration and deposition occur within three to eight channel widths outside of the channel margins in interdistributary bays the shape of each flow path is constrained by nourishment boundaries that separate the outflows from neighboring channels deposit elevation decreases with a basinward slope of 2 4 10 4 with distance from a channel margin along any flow path regardless of the channel or location that flow departed the network bathymetric depressions called interdistributary troughs form along nourishment boundaries where flow paths are the longest and deposit elevation is correspondingly low we conclude that the deposit morphology exerts a strong control on bathymetric evolution and that interaction between neighboring channels and even neighboring deltas can influence delta front morphology

satellite images of upwellings and cold filament dynamics as transient effects of violent air sea interactions downstream from the island of sardinia western mediterranean sea a systematic analysis of thermal satellite images of upwellings and cold filament dynamics downstream from the island of sardinia western mediterranean sea covering the years 1984 1985 1989 1990 1993 and 1994 is discussed for this sea the main transient atmospheric forcing comes from bursts of the mistral a north western wind which downstream from sardinia affects a rather calm basin the tyrrhenian sea in early summer particularly clear effects of atmospheric forcings such as gyres upwellings and cold filaments can be observed our analysis provides not only a systematic insight into these phenomena but also some experimental evidence of a novel mechanism of cold filament formation and evolution indeed in july 1989 a nice set of satellite images shows a cold filament rooted to the shallowest part of the wide shelf off olbia which meanders offshore for a few days under the effect of the mistral and of the general circulation it is of interest to underline how stably the filament is rooted to the shelf so that in only one image it appears as an elongated straight segment also the filament s potential vorticity is discussed in order to gain some insight into shelf water fluxes detachment depths and velocities relative to such phenomena

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

formation and maintenance of single thread tie channels entering floodplain lakes observations from three diverse river systems 1 tie channels connect rivers to floodplain lakes on many lowland rivers and thereby play a central role in floodplain sedimentology and ecology yet they are generally unrecognized and little studied here we report the results of field studies focused on tie channel origin and morphodynamics in the following three contrasting systems the middle fly river papua new guinea the lower mississippi river and birch creek in alaska across these river systems tie channels vary by an order of magnitude in size but exhibit the same characteristic morphology and appear to develop and evolve by a similar set of processes in all three systems the channels are characterized by a narrow leveed single thread morphology with maximum width approximately one tenth the width of the mainstem river the channels typically have a v shaped cross section unlike most fluvial channels these channels develop as lakes become isolated from the river by sedimentation narrowing of the connection between river and lake causes a sediment laden jet to develop levees develop along the margins of the jet leading to channel emergence and eventual levee aggradation to the height of the mainstem levees bidirectional flow in these channels is common outflows from the lake scour sediment and prevent channel blockage we propose that channel geometry and size are then controlled by a dynamic balance between channel narrowing by suspended sediment deposition and incision and widening by mass failure of banks during outflows tie channels are laterally stable and may convey flow for hundreds to a few thousand of years

hydrodynamic and suspended sediment transport controls on river mouth morphology 1 river mouths building into standing bodies of water have strikingly varied growth habits this presents a compelling pattern formation problem that is also of great practical relevance for subsurface prediction and managing coastal wetlands here we present a generalized 2 5 dimensional potential vorticity pv theory that explains sedimentation patterns of a sediment laden stationary jet by coupling an understanding of vorticity with suspended sediment concentration fields we explore the physical meaning of this new sediment pv definition and its impact on outflow depositional patterns by analyzing data from a shallow wall bounded plane jet experiment and by discussing new theoretical insights a key result is that lateral advection and diffusion of suspended sediment are directly proportional to jet vorticity a feature that reveals the mechanistic process that forms elongated channels by focused levee deposition the new pv theory constitutes a more generalized mathematical framework that expands the rouse theory for the equilibrium of suspended sediment

the formation of basal type uranium deposits in south central british columbia the basal type uranium deposits in south central british columbia occur within unconsolidated late miocene fluvial paleochannel sediments that overlie major fault zones within the okanagan highlands intrusive complex prior to the formation of mineralization paleovalleys containing host sediments were flooded by pliocene valley basalts of the plateau basalt formation five uranium deposits have been outlined to date of which the blizzard 4 020 metric tons u and tyee 650 metric tons u are the largest the basement intrusive complex underlying the deposits varies in age from early cretaceous to eocene and is comprised of quartz monzonite granodiorite coryell monzonite porphyritic granite and pegmatite all these phases are fractured and altered due to repeated tectonic activity structural analysis of the complex leads to the conclusion that it is a fabric loosened body of interconnecting fault and fracture systems capable of sustaining well developed intermediate and regional ground water flow systems the mineralized host sediments comprise a complex sequence of interfingering conglomerates arkosic sandstones and mudstones organic material is abundant in many but not all mineralized beds uranium mineralization is present in the form of uranous ningyoite or uranyl saleeite autunite phosphates coating clastic grains and filling voids because of very strong reducing conditions related to large concentrations of marcasite and organic material ningyoite is the only uranium mineral in the tyee deposit whereas the blizzard deposit contains a more complex assemblage of minerals saleeite autunite ningyoite the observed paragenetic sequence of mineral precipitation in the blizzard deposit autunite saleeite ningyoite indicates that the uranyl minerals saleeite and autunite are primary small amounts of zn ni co and mo have been introduced into the blizzard deposit whereas mo is the only nonore forming element enriched in the tyee deposit mn is the only depleted element in both deposits the paleoclimate at the time of ore formation was characterized by a temperate climate accompanied by a moderate amount of uniformly distributed precipitation investigations of the source of the ore forming elements u ca mg po 4 including ground water leaching of the intrusive basement rocks volcanic rocks eocene and host sediments as well as emplacement of ore by hydrothermal activity have led to the conclusion that these elements were derived by ground water leaching of the okanagan highlands intrusive complex the deposits are believed to have formed by the infiltration into fluvial sediments of deep seated structurally controlled ground waters that migrated in a well developed regional hydrologic system within the okanagan highlands intrusive complex research indicates that the ore forming ground waters were cold slightly bicarbonated 150 400 ppm highly uraniferous 10 50 ppb and slightly oxidizing dissolved oxygen 2 4 ppm in addition the ore forming ground waters contained sufficient amounts of ca mg and po 4 to account for the observed mineralogy upon entering the host sediments the ground waters were rapidly acidified as the result of the formation of humic acids and oxidation of iron sulfides mineralization formed after a period of extensional tectonism late miocene early pliocene leading to optimum ground water leaching of the intrusive basement complex and prior to a period of epeirogenesis late pliocene pleistocene uplift which resulted in cessation of the ore forming hydrologic regime the maximum period of formation is estimated to be between 4 and 1 m y

gravity fields and the interpretation of volcanic structures geological discrimination and temporal evolution abstract a review of gravity data reflecting shallow concealed structures on volcanoes demonstrates that valuable information may be derived on the geological development of such structures and on the dynamic evolution of active volcanoes to a first approximation all recorded examples of anomalous gravity fields associated with volcanoes are concentric with and have sources that lie within the volcanic edifice positive anomalies with wavelengths less than 20 km and amplitudes up to ca 30 mgal characterise mainly basaltic volcanoes from various tectonic settings and are caused by a relatively dense intrusive complex magma body which contrasts with its surroundings either because the body is more mafic than average or more likely because near surface previously erupted materials are uncompacted negative anomalies with wavelengths up to 100 km and amplitudes up to ca 60 mgal occur over much larger volcanic calderas many of which have erupted highly silicic pyroclastic ash and pumice uncompacted silicic caldera infill with a possible contribution from low density magma bodies is responsible for the observed anomalies there is some evidence for a continuum of gravity anomaly types that corresponds to the geological evolution of volcanic systems generally from primitive rift or subduction related basaltic andesite to mature high level silicic calderas repeated microgravity observations over active volcanoes enable magma movements variations in magma input and changes in magma density to be monitored closely dynamic modelling of volcanic systems is providing new evidence on the behaviour of concealed magma bodies and could have considerable potential for predicting eruptive events

evolution of a potential vorticity front over a topographic slope abstract using the methodology of contour dynamics the evolution of an interface separating two regions of constant potential vorticity is considered the model equations are those for barotropic nondivergent flow over a topographic slope adjoined by a coastal barrier the main focus is on the processes which lead to wave breaking for small amplitude waves and in general agreement with previous related work it is found that wave steepening leads to the formation of thin filaments the key parameter is found to be the ratio of the background potential vorticity to the discontinuity of potential vorticity across the front with other parameters such as the topographic slope and the distance to the coast playing a relatively less significant role

geochemistry of uranium in the late pleistocene holocene sediments from the southern part of the black sea basin abstract a total of 53 cores from the southern part of the black sea was used to investigate the geochemical distribution of uranium in three units of late pleistocene holocene sediments vertical and areal distribution of u together with selective extraction studies suggest that in the reduced sediments of units 1 and 2 deposited on the abyssal plain u is mainly associated with organic matter high concentrations of u 5 ppm occur characteristically in sediments having 2 organic carbon and in those deposited on abyssal plains with low sedimentation rates high carbonate contents appear to have a dilution effect on the u concentrations in the sediments of the total uranium the ionexchangeable uranium constitutes an average of 50 organic uranium tightly bound as organo uranium complexes 25 and the residual uranium bound in the silicates the remaining 25 the relative proportions of the residual u in the clastic rich unit 1 sediments collected on the continental slope and in unit 3 sediments are generally higher than 25 of the total u vertical distribution of u together with the presence of mobile u with an average of 15 of the total u suggest that some u has been mobilized from u rich unit 2 into the overlying unit 1 and the underlying unit 3

do fluid inclusions preserve δ18o values of hydrothermal fluids in epithermal systems over geological time evidence from paleo and modern geothermal systems milos island aegean sea stable isotope compositions of quartz d 18 oquartz and fluid inclusion waters d 18 ofi and ddfi were analysed from profitis ilias a low sulphidation epithermal gold mineralisation deposit on milos island greece to establish if d 18 ofi preserve a record of paleogeothermal processes previous studies show that mineralisation at profitis ilias resulted from extreme boiling and vaporisation with a zone located at approximately 430 m above sea level asl representing the transition between liquid and vapor dominated systems miner depos 36 2001 32 the deposit is also closely associated with an active geothermal system whose waters have a well characterised stable isotope geochemistry pflumio c boulegue j liakopoulos a briqueu l 1991 source transport and deposition of metals balkema rotterdam the samples were collected over an elevation interval of 440 m 210 650 m asl to give information on the liquid and vapor dominated sections of the paleosystem the data show systematic variations with sample elevation samples from the highest elevations ca 650 m asl have the lightest d 18 ofi 7 3x and ddfi 68 0x whilst the deepest ca 210 m asl are isotopically heavier d 18 ofi 0 3x ddfi 19 0x relative changes in d 18 ofi closely parallel those in ddfi d 18 oquartz shows an opposite trend from the lightest values 13 9x at the lowest elevations to the heaviest 15 1x at the highest elevations d 18 ofi shows correlations with other parameters for example variable fluid inclusion homogenisation temperatures in the vapor dominated part of the system correlate with a rapid shift in ddfi 33 3xto 50 5x and d 18 ofi 4 1xto 6 2x gold contents also increase in the same zone up to 50 ppm au comparable correlations in d 18 oquartz or d 18 ocalculated estimated geothermal fluid from fluid inclusion homogenisation data are absent d 18 ocalculated are always 5 10xheavier than d 18 ofi comparison with the present day geothermal field shows that ddfi and d 18 ofi are similar isotope data for the modern system and fluid inclusion waters fall on linear trends subparalleling the meteoric water line and project towards seawater values numerical modelling favours kinetically controlled fractionation to explain differences in d 18 ocalculated and d 18 ofluid rather than diffusive posttrapping reequilibration the evidence suggests that in low temperature epithermal systems d 18 ofi may represent

scaling relationships and evolution of distributary networks on wave influenced deltas 1 no genetic model can explain the variability in distributary network pattern on modern deltas here we derive scaling relationships for two processes known to create distributary channels and with these laws construct a simple model for distributary network evolution the first process is mouth bar deposition at the shoreline and subsequent channel bifurcation the second is avulsion the wholesale abandonment of a channel in favor of a new path the former creates relatively small networks with power law distributions of channel length the latter generates relatively few backwater scale distributaries frequency magnitude plots of channel length on natural deltas agree with theoretical predictions and show a clear separation in scale that reflects these processes mouth bar distributary lengths scale with the width of the parent channel and avulsive distributary lengths scale with the backwater length intermediate channel lengths are relatively rare wave energy controls network topology by suppressing mouth bar development thereby preferentially eliminating smaller scale distributaries

turbulent characteristics of a shallow wall bounded plane jet experimental implications for river mouth hydrodynamics jets arising from rivers streams and tidal flows entering still waters differ from most experimental studies of jets both in aspect ratio and in the presence of a solid bottom boundary and an upper free surface despite these differences the applicability of experimental jet studies to these systems remains largely untested by either field or realistically scaled experimental studies here we present experimental results for a wall bounded plane jet scaled to jets created by flow discharging into floodplain lakes a characteristic feature of both our prototype and experimental jets is the presence of large scale meandering turbulent structures that span the width of the jets in our experimental jets we observe self similarity in the distribution of mean streamwise velocities by a distance of six channel widths downstream of the jet outlet after a distance of nine channel widths the velocity decay and the spreading rates largely agree with prior experimental results for plane jets the magnitudes and distributions of the cross stream velocity and lateral shear stresses approach self preserving conditions in the upper half of the flow but decrease in magnitude and deviate from self preserving distributions with proximity to the bed the presence of the meandering structure has little influence on the mean structure of the jet but dominates the jet turbulence a comparison of turbulence analysed at time scales both greater than and less than the period of the meandering structure indicates that these structures increase turbulence intensities by 3 5 times and produce lateral shear stresses and momentum diffusivities that are one and two orders of magnitude greater respectively than turbulence generated by bed friction alone

entry flux and exit of potential vorticity in ocean circulation the flux form of the potential vorticity pv equation is employed to derive simple expressions for the boundary and interior flux of pv in ocean circulation using bernoulli functions the formulas are discussed and physically interpreted and used to map the flux of pv through a model of ocean circulation

morphodynamics of subaqueous levee formation insights into river mouth morphologies arising from experiments 1 levee formation by deposition from sediment laden flows debouching into open waters has been conceptually and analytically linked to jet hydrodynamics since the middle of the 20th century despite this long standing association between jets and levees the morphodynamics controlling subaqueous levee development remain largely unquantified and poorly understood here we report the results of physical experiments on subaqueous levee development modeled on floodplain tie channel processes in the laboratory we created subaqueous levees from a sediment laden jet entering a basin of still water levee formation occurred where the local shear velocity of the jet declined below the critical shear velocity for entrainment of sediment into suspension the rate of levee deposition depended on the rate of lateral sediment transfer to the jet margins and the settling velocity of suspended sediment in our friction dominated flows lateral sediment flux to the levees was primarily due to dispersive lateral transport driven by turbulence high rates of sediment transfer from the jet core to the margins led to levee growth that outpaced deposition along the flow centerline under hypopycnal conditions we failed to produce levees we observed distinct differences in levee morphology due to changes in the size and density of suspended sediment under identical hydrodynamic conditions our experimental results and review of published data on hypopycnal river mouths suggest that suspended sediment characteristics relative magnitude of bed friction and channel outlet aspect ratios may have a more significant influence on river mouth morphology than the buoyancy of discharging waters as envisioned in existing conceptual models

interpretation of the bouguer anomaly of milos island greece abstract the interpretation of the bouguer gravity anomaly on the island of milos greece reveals the major tectonic features that affected the metamorphic basement the island has one of the most promising geothermal fields in europe and therefore the study of the basement tectonic setting contributes to the understanding of the hot fluid circulation the basement underlies the volcanic cover which was formed during various episodes from the middle to late pliocene this is the impermeable seal of the geothermal field the relief of the basement is evaluated mainly by means of the recently introduced multiple source werner deconvolution which is an inversion method for automatic interpretation 2 5 d semi automatic marquardt inversion is employed to verify the results of the multiple source werner deconvolution terracing of the field is also employed and a 3 d model for the eastern part of the island is constructed the basement appears uplifted in the eastern and the southwestern parts of the island another deeper basement of undefined lithology underlies the metamorphics as indicated by the regional gravity field and other geophysical studies a gravity low which appears in the residual anomaly map shows a concentric character it resembles the anomaly produced by the known caldera of santorini thera island which belongs to the same volcanic arc this fact along with geological indications make the data permissive of a caldera

delta progradation driven by an advancing sediment source coupled theory and experiment describing the evolution of elongated deltas 1 most of the models of alluvial fan and delta morphodynamics to date have used one of two assumptions concerning the upstream boundary condition 1 a fixed sediment feed point at the vertex or 2 a feed point corresponding to a bedrock alluvial transition that e g migrates upstream under conditions of constant base level here however we present both experimental and numerical results pertaining to a new configuration i e one in which the sediment feed point migrates downstream the research is motivated by the operation of the tailings pond of a mine in which a delta forms the mine operators must frequently move the outfalls of their slurry pipelines downstream to avoid their burial under sediment as the delta aggrades this downstream migration results in a characteristic delta configuration under the right conditions as the tailings delta progrades downstream it does not have time to fill all the available space in the lateral direction thus leaving unfilled open water on either side the result is the formation of an elongated delta here we use both experiments and numerical modeling to characterize the control of the feed point migration rate on the lateral extent of the prograding deltas we use these results to obtain a partial explanation of natural elongated deltas in the case of such deltas the downstream progradation of natural levees provides an analog to the downstream migration of the outfall of a slurry pipeline

vorticity and instability during flow reversals on the continental shelf abstract flow reversals during relaxation of the equatorward wind on the northern california shelf are studied with observations and a simple numerical model data from the code experiment are used to document the changes in the cross shelf profiles of alongshelf currents and potential vorticity when the wind forcing changes from upwelling favorable to near zero upwelling vorticity dynamics are considered using a simple equation where also the importance of stress curls is discussed during the wind relaxation events the usually equatorward flow reveres to poleward on the inner shelf resulting in a region of high shear and occasionally a localized maximum in potential vorticity on the shelf in the course of such an episode a single eddylike structure on the shelf was observed with satellite imagery in order to simulate the basic dynamics of the flow reversals and instability a contour dynamics model is developed for barotropic flow on an exponentially sloping bottom in which potential vorticity i

the dynamics of a river bay delta system an analysis has been made to aid our understanding of various phenomena associated with turbulent plane jets that issue from river outlets and discharge into quiescent bays an integrated form of the hydrodynamic equations of flow continuity and momentum balance coupled with advective diffusion mass transport equations has been formulated into a two dimensional spatial domain closed form analytical solutions are obtained with the aid of similarity functions for the velocity and sediment concentration profiles a numerical procedure for estimating the areal and volume deposition of the delta sediments is presented the atchafalaya river delta a newly developing delta in the south central louisiana coast is used to illustrate analytical techniques the results of analytical predictions are compared with the results predicted by other statistical and generic approaches an agreement is found a sensitivity analysis is performed to assess the relative importance of various parameters in the river bay delta system

a potential vorticity theory for the formation of elongate channels in river deltas and lakes 1 rivers empty into oceans and lakes as turbulent sediment laden jets which can be characterized by a gaussian horizontal velocity profile that spreads and decays downstream because of shearing and lateral mixing at the jet margins recent experiments demonstrate that this velocity field controls river mouth sedimentation patterns in nature diffuse jets are associated with mouth bar deposition forming bifurcating distributary networks while focused jets are associated with levee deposition and the growth of elongate channels that do not bifurcate river outflows from elongate channels are similar in structure to cold filaments observed in ocean currents where high potential vorticity helps to preserve coherent structure over large distances motivated by these observations we propose a hydrodynamic theory that seeks to predict the conditions under which elongate channels form our approach models jet velocity patterns using the flow vorticity both shearing and lateral spreading are directly related to the vertical component of vorticity we introduce a new kind of potential vorticity that incorporates sediment concentration and thus allows study of jet sedimentation patterns the potential vorticity equation reduces the number of fluid momentum equations to one without losing generality this results in a compact analytical solution capable of describing the streamwise evolution of the potential vorticity of a sediment laden jet from initial conditions at the river mouth our theory predicts that high potential vorticity is a necessary condition for focused levee deposition and the creation of elongate channels comparison to numerical laboratory and field studies indicates that potential vorticity is a primary control on channel morphology our results may be useful for designing river delta restoration schemes such as the proposed mississippi delta diversion

a terracing operator for physical property mapping with potential field data the terracing operator works iteratively on gravity or magnetic data using the sense of the measured field s local curvature to produce a field comprised of uniform domains separated by abrupt domain boundaries the result is crudely proportional to a physical property function defined in one profile case or two map case horizontal dimensions this result can be extended to a physical property model if its behavior in the third vertical dimension is defined either arbitrarily or on the basis of the local geologic situation the terracing algorithm is computationally fast and appropriate to use with very large digital data sets where gravity and magnetic data are both available terracing provides an effective means by which the two data sets can be compared directly results of the terracing operation somewhat resemble those of conventional susceptibility or density mapping in contrast with conventional susceptibility mapping however the terraced function is a true step function which cannot be depicted by means of contour lines magnetic or gravity fields calculated from the physical property model do not in general produce an exact fit to the observed data by intent the terraced map is more closely analogous to a geologic map in that domains are separated by hard edged domain boundaries and minor within domain variation is neglected the terracing operator was applied separately to aeromagnetic and gravity data from a 136 km x 123 km area in eastern kansas results provide a reasonably good physical representation of both the gravity and the aeromagnetic data superposition of the results from the two data sets shows many areas of agreement that can be referenced to geologic features within the buried precambrian crystalline basement the emerging picture of basement geology is much better resolved than that obtained either from the scanty available drill data or from interpretation of the geophysical data by inspection