flow and bedform dynamics in an alluvial channel with downward seepage abstract in this paper we report the findings from an experimental study on a parabolic cross sectional sand bed channel with uniform fine sand under no seepage and downward seepage conditions through experiments we observed that an alluvial channel which remained at threshold condition of sediment movement during the no seepage experiment started transporting sediments with the application of seepage in the downward direction shields stress of the threshold channel increased significantly from its critical value after the application of downward seepage which led to the deformation of the cross sectional shape and consequent development of the bedforms the role of turbulence in the development of bedforms has also been analyzed measures of turbulent statistics show that the time mean velocities and reynolds stresses were increased significantly with the application of downward seepage under the action of seepage conditions increase in the flux of streamwise turbulent kinetic energy in the streamwise direction was observed in the region close to the channel boundary also quadrant analysis exhibited an increase in the contributions from all the bursting events and the thickness of the sweep dominated zone in near bed region after the application of downward seepage a bedform tracking tool has been used to evaluate the variability in the geometry of bedforms we have classified these developing bedforms as current ripples and linguoid ripples according to their evolution with time under the downward seepage condition it has been further observed that the variation in shields stress and corresponding bedform geometry reached an equilibrium state in the presence of downward seepage when the experiments were run over a longer period of time 24 31 h

modeling width adjustment in meandering channels widening in sinuous channels occurs when the retreat of the outer bank exceeds the advance of the opposite bank an analytical model is presented to simulate width adjustment in meandering channels of non cohesive bank material resulting from bank erosion of two interactive processes basal erosion and bank collapse bank collapse refers to the avalanche of non cohesive material in the upper part of bank above water surface resulting from over steepening of the bank surface due to basal erosion the rate of basal erosion including lateral erosion and bed degradation is calculated as a function of the longitudinal gradient of sediment transport rate and strength of secondary flow the transverse bed slope is treated as a variable that increases as channel sinuosity increases until the transverse bed slope reaches its maximum value by simplifying the bank collapse process for non cohesive materials the present study shows that the rate of bank line retreat is determined by lateral erosion rate near bank bed degradation rate sediment grain size and difference between flow depth and bank height the time dependent widening processes of two meandering channels in the laboratory are selected to test applicability of the model the result shows that the simulated bank lines at individual time intervals closely match the experimental measurements whether the sinuosity of a meandering channel will increase or decrease is primarily determined by didtribution of the lngitudinal gradient of sediment transport rate along the channel

experiments on saltation of sand in water a high speed video system was used to study saltation of sand in an open channel flow high rates of image acquisition provided the information needed to resolve details of the lagrangian properties of particle motion saltation of sand is described in terms of statistical properties of particle trajectories such as mean values and standard deviations of saltation length height and streamwise particle velocity results are compared with available empirical data saltation height seems to be independent of particle size when made dimensionless with the particle diameter however the dimensionless saltation length appears to increase as the particle size decreases particle collision with the bed is also analyzed observations of this process indicate that most of the interactions between saltating particles and the bed are of the collision rebound type which contradicts previous discussions on the subject the estimated value of the dynamic friction coefficient is about half that proposed by bagnold i

a model of stream channel adjustment assessment of rubey s hypothesis w w rubey proposed a concept of stream channel development with channel gradient and channel form as dependent variables that mutually adjust to conditions of sediment load sediment size and water discharge a similar channel development model is formulated using multiple equations and tested against a data set for 252 stream sites in the missouri river basin usa the results strongly support mutual adjustment among the gradient form width and depth aspects of the stream channel system the relation between channel form and grain size in the bed is shown to have opposite signs in the structural and reduced forms of the model this provides the basis for an explanation of a puzzling aspect of rubey s conception of the adjustment process the results suggest that channel form is more dependent on the process of mutual adjustment of morphologic elements than is channel gradient

large flume experiments on the stable straight gravel bed channel a set of experiments is described that obtain the shape of stable straight uniform mobile bed channels with cohesionless banks these experiments were carried out in an outdoor flume at length scales at least twice those used by previous experimenters but otherwise using similar techniques including the use of a half channel against the flume wall in order to suppress meandering eight flume runs are reported including channels farther from threshold conditions than those previously tested the resulting data might prove useful both in validating theories for the stable shape of the straight channel and for advancing models of the adjustment to that shape

streamwise streaks induced by bedload diffusion a fluid flowing over a granular bed can move its superficial grains and eventually deform it by erosion and deposition this coupling generates a beautiful variety of patterns such as ripples bars and streamwise streaks here we investigate the latter sometimes called sand ridges or sand ribbons we perturb a sediment bed with sinusoidal streaks the crests of which are aligned with the flow we find that when their wavelength is much larger than the flow depth bedload diffusion brings mobile grains from troughs where they are more numerous to crests surprisingly gravity can only counter this destabilising mechanism when sediment transport is intense enough relaxing the long wavelength approximation we find that the cross stream diffusion of momentum mitigates the influence of the bed perturbation on the flow and even reverses it for short wavelengths viscosity thus opposes the diffusion of entrained grains to select the most unstable wavelength this instability might turn single thread alluvial rivers into braided channels

scale dependence of lithological control on topography bedrock channel geometry and catchment morphometry in western scotland abstract we propose that a scale dependent topographic signature of erodibility arises due to fluvial and glacial erosion acting on different parts of the landscape at different times for 14 catchments in western scotland we define three levels of substrate erodibility in order of decreasing resistance quartzite rocks nonquartzite rocks and zones of fault related fracture then using digital topographic and planimetric data coupled with field measurements we identify regression based scaling relationships between substrate erodibility and morphometric parameters at two spatial scales catchment scale morphometry shows a weak to variable relationship with substrate metrics overall erodibility can be inferred from catchment steepness indices i e channel steepness index and relief ratio but the existence of multiple exceptions could confound a more general application of this approach nonetheless major valley troughs trace fault zones and nonquartzite rocks leaving much of the higher and stee

large grains matter contrasting bed stability and morphodynamics during two nearly identical experiments while the stabilizing function of large grains in step pool streams has long been recognized the role they play in gravel bed streams is less clear most researchers have ignored the role of large grains in gravel bed streams and have assumed that the median bed surface size controls the erodibility of alluvial boundaries the experiments presented herein challenge this convention two experiments were conducted that demonstrate the significant morphodynamic implications of a slight change to the coarse tail of the bed material the two distributions had the same range of particle sizes and nearly identical bulk d50 values 1 6 mm however the d90 of experiment gsd1 was slightly finer 3 7 mm than that for experiment gsd2 3 9 mm transport rates during gsd1 were nearly four times greater than during gsd2 even though the dimensionless shear stress was slightly lower and the channel developed a sinuous pattern with well developed riffles pools and bars during gsd2 the initial rectangular channel remained virtually unchanged for the duration of the experiment the relative stability of gsd2 seems to be associated with a slightly larger proportion of stable large grains on the bed surface at the beginning of gsd1 3 5 of the bed was immobile while almost twice as much of it 6 1 was immobile at the beginning of gsd2 the results demonstrate that the largest grains not the median size exert first order control on channel stability copyright 2017 john wiley sons ltd

ranging bowhead whale calls in a shallow water dispersive waveguide this paper presents the performance of three methods for estimating the range of broadband 50 500 hz bowhead whale calls in a nominally 55 m deep waveguide conventional mode filtering cmf synthetic time reversal str and triangulation the first two methods use a linear vertical array to exploit dispersive propagation effects in the underwater sound channel the triangulation technique used here while requiring no knowledge about the propagation environment relies on a distributed array of directional autonomous seafloor acoustics recorders dasars arranged in triangular grid with 7 km spacing this study uses simulations and acoustic data collected in 2010 from coastal waters near kaktovik alaska at that time a 12 element vertical array spanning the bottom 63 of the water column was deployed alongside a distributed array of seven dasars the estimated call location to array ranges determined from cmf and str are compared with dasar triangulation results for 19 whale calls the vertical array ranging results are generally within 10 of the dasar results with the str results providing slightly better agreement the results also indicate that the vertical array can range calls over larger ranges and with greater precision than the particular distributed array discussed here whenever the call locations are beyond the distributed array boundaries

source level and calling depth distributions of migrating bowhead whale calls in the shallow beaufort sea automated and manual acoustic localizations of migrating bowhead whales were used to estimate source level and calling depth distributions of their frequency modulated modulated calls over seven years between 2008 and 2014 whale positions were initially triangulated using directional autonomous seafloor acoustic recorders deployed between 25 and 55 m water depth near kaktovik alaska during the fall westward migration calling depths were estimated by minimizing the discrepancy between source level estimates from at least three recorders detecting the same call applying a detailed waveguide propagation model to the data yielded broadband source levels of 161 9 db re 1 pa2 s at 1 m sel for calls received between 20 and 170 hz applying a simpler 15 log10 r power law propagation model yielded sel source levels of 158 10 db the most probable calling depths lay between 22 and 30 m optimal depths for long range acoustic signal transmission in this particular environment

downstream changes in the channel geometry of a large gravel bed river 1 field data obtained on a nearly contiguous segment of the colorado river in western colorado and eastern utah are used to examine the mechanisms driving downstream changes in channel geometry measurements characterizing the bank full hydraulic geometry bed material grain size and average channel gradient were made at closely spaced intervals in 10 alluvial and quasi alluvial reaches covering 260 km of the river these data indicate that changes in surface and subsurface grain sizes are small in relation to the change in channel slope over the full length of the study area the median grain size of the surface sediment decreases by a factor of a little more than 2 whereas the average channel slope decreases by a factor of about 5 the decreases in slope and median grain size are offset by a large increase in bank full depth relative to width such that the bank full shields stress b is constant downstream for the reach as a whole b averages 0 049 which is roughly 50 higher than the threshold for bed load transport

design for hydraulic geometry of alluvial channels a new solution to the stable channel paradox has been derived based on the contribution of secondary flow to the redistribution of boundary shear stress this new solution was then combined with the entropy based bank profile equations the flow continuity condition an appropriate frictional resistance relation and a sediment transport relation to develop a new geometric model for straight stable alluvial channels furthermore the effect of nonuniform boundary particle sizes was introduced to make the new geometric model applicable to a wide range of both laboratory experiments and natural alluvial rivers a fortran program was developed to compute the design procedure the comparisons between the cross sectional shapes depths and widths calculated by the new geometric model and field and laboratory data show that the proposed geometric model is in reasonable agreement with the data both for well graded and for nonuniform bed materials

the morphology of graded gravel rivers a network perspective analytical hydraulic geometry equations are combined with a watershed model to quantify downstrem trends in equilibrium fluvial morphology in gravel streams the hydraulic geometry equations relaet fluvial morphology to discharge bedload transport rate and grain size these independent variables are in turn determined by routing gravel supplied at zero order basins through a channel network as gravel is routed downstream it decreases in size according to an empirical power law the resulting model specifies the discharge bedload transport rate grain size width depth slope and river bed elevation at every point in the drainage basin when the downstream fining law is calibrated using data from central pennsylvania dowstream hydraulic geometry exponents for the width and depth are accurately reproduced longitudinal profiles calculated from the model fit observed profiles in largerwatersheds but are inaccurate in smaller watersheds the model also reproduces hack s 1957 empirical result relating slope to the 0 6 power of a ds where a is the drainage basin area and ds is the mean grain size unfortunately the model requires an equilibrium time scale which is unreasonably long suggesting that the channels of the study area are best described as systems with multiple time scales and multiple rates of response the model probably is successful because the width and depth have relatively short relaxation times and also because downstream trends in discharge and sediment transport rate are controlled by network topology thus downstream hydraulic geometry equations do not necessarily provide strong evidence for the equilibrium of fluvial landscapes rather they reflect the constancy of network topology and the rapid response times of width and depth

acoustic tracking of sperm whales in the gulf of alaska using a two element vertical array and tags between 15 and 17 august 2010 a simple two element vertical array was deployed off the continental slope of southeast alaska in 1200 m water depth the array was attached to a vertical buoy line used to mark each end of a longline fishing set at 300 m depth close to the sound speed minimum of the deep water profile the buoy line also served as a depredation decoy attracting seven sperm whales to the area one animal was tagged with both a limpet dive depth transmitting satellite and bioacoustic b probe tag both tag datasets were used as an independent check of various passive acoustic schemes for tracking the whale in depth and range which exploited the elevation angles and relative arrival times of multiple ray paths recorded on the array analytical tracking formulas were viable up to 2 km range but only numerical propagation models yielded accurate locations up to at least 35 km range at beaufort sea state 3 neither localization approach required knowledge of the local bottom bathymetry the

turbulent characteristics and evolution of sheet flow in an alluvial channel with downward seepage abstract experimental investigation of the flow hydrodynamics and temporal changes in the cross sectional profile of an alluvial channel has been studied in the present work experiments were carried out in a curvilinear cross sectional shaped channel with no seepage and with a downward seepage condition to ascertain seepage effects on channel geometry and turbulent characteristics of flow measures of turbulent characteristics such as time averaged near bed velocities and reynolds stresses were found to increase with the application of downward seepage stream power and the value of shields parameter are increased under the action of downward seepage causing bed particles to move in the form of a sheet layer integral scales of flow suggest that the size of eddies increases with the application of downward seepage which is linked to the evolution of the sheet layer sheet development causes reduction in flow depth and rapid channel widening cross sectional parabolic shape of the threshold channel is transformed into a trapezoidal shape with the presence of the sheet layer with the passage of time 11 h the channel attains another equilibrium geometrical state with the value of shields stress around 0 074 from the no seepage value of 0 0399 an empirical equation for sheet flow rate is derived with the consideration of seepage in the downward direction

effects of pile dikes on flow retardation and sediment transport a mathematical model for defining lateral distributions of fluid velocity and suspended sediment concentration in straight channels with pile dikes near the banks is presented singular perturbation and matched asymptotic expansion techniques are employed to derive the distributions it is found that suspended sediment is transported toward the pile dike region due to lateral turbulent diffusion the amount of which is predicted by the theory laboratory work has revealed that the lateral diffusivities of fluid momentum and suspended sediment are identical with those observed for flows without pile dikes the vertical diffusivity of suspended sediment is found not to be affected by pile dikes the laboratory tests support the present model

advances in carbonate exploration and reservoir analysis carbonate reservoirs contain an increasingly important percentage of the world s hydrocarbon reserves this volume presents key recent advances in carbonate exploration and reservoir analysis as well as a comprehensive overview of the trends in carbonate over the years the volume focuses on four key areas 1 emerging plays and techniques with special reference to lacustrine plays in syn rift basins and development of super giant heavy oil plays 2 improved reservoir characterization with examples from the middle east and europe and case studies of how outcrop analogues can provide key data for input to geological models 3 impact of fractures and faults in carbonates contributors highlight the need for integrated structural and diagenetic approaches in order to understand how fractures evolve as fluid flow conduits 4 advances in geomodelling of carbonate reservoirs several papers discuss the application of new and innovative geomodelling and geostatistical techniques to carbonate reservoirs

pebble abrasion during fluvial transport experimental results and implications for the evolution of the sediment load along rivers 1 in actively eroding landscapes fluvial abrasion modifies the characteristics of the sediment carried by rivers and consequently has a direct impact on the ability of mountain rivers to erode their bedrock and on the characteristics and volume of the sediment exported from upland catchments in this experimental study we use a novel flume replicating hydrodynamic conditions prevailing in mountain rivers to investigate the role played by different controlling variables on pebble abrasion during fluvial transport lithology controls abrasion rates and processes with differences in abrasion rates exceeding two orders of magnitude attrition as well as breaking and splitting are efficient processes in reducing particle size mass loss by attrition increases with particle velocity but is weakly dependent on particle size fragment production is enhanced by the use of large particles high impact velocities and the presence of joints based on our experimental results we extrapolate a preliminary generic relationship between pebble attrition rate and transport stage c where fluvial shields stress and c critical shields stress for incipient pebble motion this relationship predicts that attrition rates are independent of transport stage for c 3 and increase linearly with transport stage beyond this value we evaluate the extent to which abrasion rates control downstream fining in several different natural settings a simplified model predicts that the most resistant lithologies control bed load flux and fining ratio and that the concavity of transport limited river profiles should rarely exceed 0 25 in the absence of deposition and sorting

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

incipient motion of sand particles on side slopes several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes however no laboratory work has ever been done on this problem a theoretical study of the incipient motion of sediment particles on side slopes is presented including the effects of viscous sublayer turbulence and lift force as a special case of level beds the theory describes the experimental values reported by several workers a specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes and the experiment supports the theory these works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion

stable width and depth of straight gravel rivers with heterogeneous bed materials mathematical model for defining stable width and depth of straight gravel rivers is presented in which it is revealed that the major agency for maintaining stable channel is lateral diffusion of longitudinal fluid momentum due to turbulence the primary quantities which determine the stable channel geometry are found to be flow discharge longitudinal free surface slope the median size of bed material and gradation of the bed material increasing gradation is found to increase the depth and decrease the width introduction of one loose and the other rigid bank in laboratory experiments provides good examples to test the model in which four kinds of sand were used to test the gradation effect these laboratory data support the mathematical model presented herein the theory also performs well when it is applied to natural gravel rivers

width adjustment in experimental gravel bed channels in response to overbank flows 1 we conducted a series of flume experiments to investigate the response of self formed gravel bed channels to floods of varying magnitude and duration floods were generated by increasing the discharge into a channel created in sand and gravel sized sediment with a median grain size of 2 mm flooding increased the shields stress along the channel perimeter causing bank erosion and rapid channel widening the sediment introduced to the channel by bank erosion was not necessarily deposited on the channel bed but was rather transported downstream a process likely facilitated by transient fining of the bed surface at the end of each experiment bank sediments were no longer in motion partial bed load transport characterized the flat bed portion of the channel and the shields stress approached a constant value of 0 056 about 1 2 times the critical shields stress for incipient motion furthermore the discharge was entirely accommodated by flow within the channel the creation of a stable channel entirely eliminated overbank flows we speculate that similar processes may occur in nature but only where bank sediments are non cohesive and where channel narrowing processes cannot counteract bank erosion during overbank flows we also demonstrate that a simple model of lateral bed load transport can reproduce observed channel widening rates suggesting that simple methods may be appropriate for predicting width increases in channels with non cohesive unvegetated banks even during overbank flows last we present a model for predicting the equilibrium width and depth of a stable gravel bed channel with a known channel forming shields stress

effect of bank stability on geometry of gravel rivers a bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel bed channel the new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability the bank stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment cementing by fines and binding of the sediment by root masses the two key parameters in the bank stability analysis are the median grain diameter of the bank sediment d50bank and the modified friction angle of the bank sediment a sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry this is supported by testing the theory on published field data the bank sediment size was assumed to equal the bed sediment size and the variation of the friction angle was investigated the estimated values are seen to increase systematically

least action principle equilibrium states iterative adjustment and the stability of alluvial channels the energy based least action principle lap has proven to be very successful for explaining natural phenomena in both classical and modern physics this paper briefly reviews its historical development and details how in three ways it governs the behaviour and stability of alluvial rivers first the lap embodies the special stationary equilibrium state of motion and so its incorporation with the principle of energy conservation explains why so many optimizing hypotheses have been proposed in fluvial geomorphology second the variational approach underlying the lap provides a more straightforward and simpler fuzzy object orientated method for solving river regime problems than do the various complex newtonian formulations third it is shown that in fluvial systems with surplus energy the surplus can be expended with slope and or channel geometry adjustments with the degree of channel geometry adjustment quantified by the dimensionless numbers f for depth dominated adjustment and h for width depth dominated adjustment different planforms are preferred at different energy levels with h providing a quantitative measure of the flow s efficiency for moving sediment in rivers with insufficient energy the interactions of endogenous and exogenous factors are shown to be capable in certain circumstances of achieving a stationary equilibrium condition which acts as the attractor state importantly this study describes how iterative changes enable systems to achieve such a stable equilibrium copyright 2007 john wiley sons ltd

stable channel cross sections of straight sand rivers a mathematical model is presented for defining the size and cross section of self formed straight sand rivers in which sediments are actively transported everywhere as bedload and suspended load a balance of lateral bedload and lateral diffusive transport of suspended sediment is imposed to maintain a stable channel cross section singular perturbation technique is employed to solve the sediment balance equation from which a relation for stable depth is derived a resistance formula for dune covered beds is used to obtain stable width it is revealed theoretically that the channel center depth relative to sediment size is approximately proportional to s 0 8 for natural sand rivers in which s is longitudinal slope the analysis is found to agree reasonably well with available laboratory and field data

continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins abstract depth uniform stretching is not the dominant deformation process for thinning continental lithosphere leading to breakup it cannot explain the observed depth dependent lithosphere stretching and mantle exhumation at rifted continental margins depth dependent lithosphere thinning in which stretching of the lower crust and lithosphere mantle greatly exceeds that of the upper crust has been observed at many non volcanic and volcanic rifted continental margins including conjugate margin pairs passive continental margins show a paucity of brittle deformation in the upper crust during continental lithosphere thinning leading to breakup and sea floor spreading initiation a new model of rifted continental margin formation has been developed that assumes that deformation and thinning of continental lithosphere leading to breakup occurs in response to an upwelling divergent flow field within continental lithosphere and asthenosphere and that this deformation evolves into sea floor spreading the new model successfully predicts depth dependent stretching of continental margin lithosphere for both non volcanic and volcanic margins and mantle exhumation at non volcanic margins both of which are observed but are not explained by existing depth uniform continental lithosphere stretching models the new model provides a balance of extensional strain supplies an explanation for the paucity of synrift brittle deformation and offers a simple transition from prebreakup lithosphere thinning to sea floor spreading the observed diversity of rifted continental margin structure and width of the ocean continent transition can be explained by variability in the form of the upwelling divergent flow field the new upwelling divergent flow model of continental lithosphere thinning leading to continental breakup successfully predicts the observed bathymetry and margin geometry for the most recent segment of sea floor spreading initiation in the woodlark basin in the western pacific and the observed bathymetry and free air gravity anomaly for the newfoundland and iberian margins

methods for identification of isolated carbonate buildups from seismic reflection data isolated carbonate buildups icbs are commonly attractive exploration targets however identifying icbs based only on seismic data can be difficult for a variety of reasons these include poor quality two dimensional data and a basic similarity between icbs and other features such as volcanoes erosional remnants and tilted fault blocks to address these difficulties and develop reliable methods to identify icbs 234 seismic images were analyzed the images included proven icbs and other features such as folds volcanoes and basement highs which may appear similar to icbs when imaged in seismic data from this analysis 18 identification criteria were derived to distinguish icbs from non icb features these criteria can be grouped into four categories regional constraints analysis of basic seismic geometries analysis of geophysical details and finer scale seismic geometries systematically assessing the criteria is useful because it requires critical evaluation of the evidence present in the available data working from the large scale regional geology to the fine details of seismic response it is also useful to summarize the criteria as a numerical score to facilitate comparison between different examples and different classes of icbs and non icbs our analysis of scores of different classes of features suggests that the criteria do have some discriminatory power but significant challenges remain

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

regime theories in gravel bed rivers models controlling variables and applications in disturbed italian rivers downstream hydraulic geometry relationships describe the shape of alluvial channels in terms of bankfull width flow depth flow velocity and channel slope recent investigations have stressed the difference in spatial scales associated with these variables and thus the time span required for their adjustment after a disturbance the aim of this study is to explore the consequences in regime models considering the hypothesis that while channel width and depth adjust quickly to changes in water and sediment supply reach slope requires a longer time span three theoretical models were applied one model incorporates an extremal hypothesis millar rg 2005 theoretical regime equations for mobile gravel bed rivers with stable banks geomorphology 64 207 220 and the other two are fully physically based ikeda s parker g kimura y 1988 stable width and depth of straight gravel rivers with heterogeneous bed materials water resources research 24 713 722 parker g wilcock pr paola c dietrich w pitlick j 2007 physical basis for quasi universal relations describing bankfull hydraulic geometry of single thread gravel bed rivers journal of geophysical research 112 doi 10 1029 2006jf000549 in order to evaluate the performance of models introducing the slope as an independent variable we propose two modifications to previous models the performance of regime models was tested against published data from 142 river reaches and new hydraulic geometry data from gravel bed rivers in patagonia argentina and north eastern italy models that assume slope as a control ikeda et al 1988 or millar 2005 predict channel depth and width reasonably well parker et al s 2007 model improved predictions because it filters the scatter in slope data with a relation slope discharge the extremal hypothesis model of millar 2005 predicts comparably to the other physically based models millar s model was chosen to describe the recent changes in the piave and brenta rivers due to human intervention mainly in channel gravel mining the change in sediment supply and recovery was estimated for these rivers this study supports the interpretation that sediment supply is the key factor guiding morphological changes in these rivers

matched field processing geoacoustic inversion and source signature recovery of blue whale vocalizations matched field processing mfp and global inversion techniques have been applied to vocalizations from four whales recorded on a 48 element tilted vertical array off the channel islands in 1996 global inversions from selected whale calls using as few as eight elements extracted information about the surrounding ocean bottom composition array shape and the animal s position these inversion results were then used to conduct straightforward mfp on other calls the sediment sound speed inversion estimates are consistent with those derived from sediment samples collected in the area in general most animals swam from the east to west but one animal remained within 500 m of its original position over 45 min all whales vocalized between 10 and 40 m depth three acoustic sequences are discussed in detail the first illustrating a match between an acoustic track and visual sighting the second tracking two whales to ranges out to 8 km and the final sequence demonstrating high resolution dive profiles from

width and depth of self formed straight gravel rivers with bank vegetation the influence of bank vegetation on the stable channel cross sectional geometry of stable straight gravel rivers is studied theoretically singular perturbation and matched asymptotic expansion techniques are employed to derive the lateral distribution of depth averaged fluid velocity and the bed shear stress a condition of sediment incipient motion is imposed at the junctions of the bed and the banks to derive the stable depth and a formula for resistance to flow is used to obtain the stable width the theory reveals that a thicker vegetation yields a larger depth and a smaller width increasing discharge increases the effect of vegetation the analysis agrees reasonably well with available field data

using nonlinear time warping to estimate north pacific right whale calling depths in the bering sea calling depth distributions are estimated for two types of calls produced by critically endangered eastern north pacific right whales nprws in the bering sea using passive acoustic data collected with bottom mounted hydrophone recorders nonlinear time resampling of 12 nprw upcalls and 20 gunshots recorded in a critical nprw habitat isolated individual normal mode arrivals from each call the relative modal arrival times permitted range estimates between 1 and 40 km while the relative modal amplitudes permitted call depth estimates provided that environmental inversions were obtained from high signal to noise ratio calls gunshot sounds were generally only produced at a few meters depth while upcall depths clustered between 10 and 25 m consistent with previously published bioacoustic tagging results from north atlantic right whales a wilcoxon rank sum test rejected the null hypothesis that the mean calling depths of the two call types were the same p 2 9 10 5 the null hypothesis was sti

the importance of the catchment area length relationship in governing non steady state hydrology optimal junction angles and drainage network pattern abstract analytical and numerical models of landscape evolution in general either assume steady state hydrology or use empirically based functions in the form of a drainage area power law to model runoff a method to compute non steady state runoff on the basis of the area length relationship of river basins is proposed for application in landscape evolution models this shape sensitive runoff function is derived analytically for environments with short storm duration storm duration

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

range estimation of bowhead whale balaena mysticetus calls in the arctic using a single hydrophone bowhead whales generate low frequency calls in shallow water arctic environments whose dispersive propagation characteristics are well modeled by normal mode theory as each mode propagates with a different group speed a call s range can be inferred by the relative time frequency dispersion of the modal arrivals traditionally at close ranges modal arrivals are separated using synchronized hydrophone arrays here a nonlinear signal processing method called warping is used to filter the modes on just a single hydrophone the filtering works even at relatively short source ranges where distinct modal arrivals are not separable in a conventional spectrogram however this warping technique is limited to signals with monotonically increasing or decreasing frequency modulations a relatively common situation for bowhead calls once modal arrivals have been separated the source range can be estimated using conventional modal dispersion techniques with the original source signal structure being recovered as a by product twelve bowhead whale vocalizations recorded near kaktovik alaska in 2010 with signal to noise ratios between 6 and 23 db are analyzed and the resulting single receiver range estimates are consistent with those obtained independently via triangulation from widely distributed vector sensor arrays geoacoustic inversions for each call are necessary in order to obtain the correct ranges

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

tectonic setting and stratigraphic architecture of an early cretaceous lacustrine carbonate platform sugar loaf high santos basin brazil abstract the sugar loaf high is an extensive basement structure within the santos basin offshore brazil in which all of the elements of the pre salt hydrocarbon play are present following a clastic dominated early synrift phase the later synrift and sag phases are characterized by an extensive non marine carbonate platform over the basement high the study area within this new 3d seismic dataset contains carbonates stratigraphically equivalent to the reservoirs within the lula and sapinhoa fields analysis of the 3d seismic data shows that the pre salt carbonates onlap the basement of the sugar loaf high and form aggradational geometries on a platform that has a proximal to distal width of about 100 km and an interpreted relief of some 900 m the carbonate platform has an aggradational and mounded basinward facing gullied margin with slope deposits progradational units are imaged on the platform top that may be either carbonate or clastic in composition the platform is preserved beneath evaporites that form the regional seal within the santos basin platforms of this size are previously unknown from lacustrine settings outside the pre salt stratigraphy of the santos and campos basins brazil

a stability criterion inherent in laws governing alluvial channel flow the stability criterion of maximum flow efficiency mfe has previously been found inherent in typical alluvial channel flow relationships and this study investigates the general nature of this criterion using a wider range of flow resistance and bedload transport formulae for straight alluvial channels in which the effect of sediment sorting is insignificant our detailed mathematical analysis demonstrates that a flow efficiency factor e occurs generally as the ratio of sediment bedload discharge qs to stream power qs in the form of when e is maximized i e qs is maximized or is minimized maximally efficient straight channel geometries derived from most flow resistance and bedload transport formulae are found compatible with observed bankfull hydraulic geometry relations this study provides support for the use of the criteria of mfe maximum sediment transporting capacity and minimum stream power for understanding the operation of alluvial rivers and also addresses limitations to the direct application of its findings copyright 2002 john wiley sons ltd

geoacoustic inversion in a dispersive waveguide using warping operators this paper presents a single receiver geoacoustic inversion method adapted for low frequency impulsive sources it is applied to light bulb data collected during the shallow water 2006 experiment the inversion is carried out by extracting dispersion curves from the received signal and comparing them to simulated replicas to achieve dispersion curve estimation in the time frequency domain modal separability is improved using a signal processing method called warping the inversion scheme allows for a reliable estimation of the new jersey shelf sediment properties compressional sound speed and density it also provides an accurate estimation of the source receiver range