a detached eddy simulation model for the study of lateral separation zones along a large canyon bound river lateral flow separation occurs in rivers where banks exhibit strong curvature in canyon bound rivers lateral recirculation zones are the principal storage of fine sediment deposits a parallelized three dimensional turbulence resolving model was developed to study the flow structures along lateral separation zones located in two pools along the colorado river in marble canyon the model employs the detached eddy simulation des technique which resolves turbulence structures larger than the grid spacing in the interior of the flow the des 3d model is validated using adcp flow measurements taken during the 2008 controlled flood release from glen canyon dam a point to point validation using a number of skill metrics often employed in hydrological research is proposed here for fluvial modeling the validation results show predictive capabilities of the des model the model reproduces the pattern and magnitude of the velocity in the lateral recirculation zone including the size and position of the primary and secondary eddy cells and return current the lateral recirculation zone is open having continuous import of fluid upstream of the point of reattachment and export by the recirculation return current downstream of the point of separation differences in magnitude and direction of near bed and near surface velocity vectors are found resulting in an inward vertical spiral interaction between the recirculation return current and the main flow is dynamic with large temporal changes in flow direction and magnitude turbulence structures with a predominately vertical axis of vorticity are observed in the shear layer becoming three dimensional without preferred orientation downstream

coupling mechanisms in double sandbar systems part 1 patterns and physical explanation crescentic sandbars and rip channels along wave dominated sandy beaches are relevant to understand localized beach and dune erosion during storms in recent years a paradigm shift from hydrodynamic template models to self organization mechanisms occurred to explain the formation of these rhythmic features in double sandbar systems both the inner and outer bar rip channels and crescentic planshapes are now believed to be free instabilities of the nearshore system arising through self organization mechanisms alone however the occasional occurrence of one or two inner bar rip channels within one outer bar crescent suggests a forced morphologically coupled origin here we use a nonlinear morphodynamic model to show that alongshore variability in outer bar depth and the relative importance of wave breaking versus wave focussing by refraction across the outer bar is crucial to the inner bar rip channel development the coupling patterns simulated by our model are similar to those observed in the field morphological coupling requires a template in the morphology outer bar geometry which through the positive feedback between flow sediment transport and the evolving morphology that is self organization enforces the development of coupling patterns we therefore introduce a novel mechanism that blurs the distinction between self organization and template mechanisms this mechanism may also be extended to explain the dynamics of other nearshore patterns such as beach cusps the impact of this novel mechanism on the alongshore variability of inner bar rip channels is investigated in the companion paper copyright 2010 john wiley and sons ltd

sediment size effects on rip channel dynamics abstract field observations indicate that both wave conditions and sediment characteristics exert the controlling effects on the beach states and determine the development of rip channel system although the role of wave conditions on the rip channel dynamics has been extensively studied little attention has been paid to the effects of sediment characteristics in this paper we use a nonlinear morphodynamic model xbeach to investigate the impact of grain size on the formation and nonlinear evolution of rip channels under the condition of uniform sediments we find that the grain size can affect a number of aspects of rip channel dynamics with increasing grain size both longshore migration speed and growth rate decrease significantly while the response and saturation times increase on the other hand the influence of grain size on the geometrical properties of the rip channel seems to be much less pronounced as the wavelength of the channels hardly changes and the three dimensionality features only vary slightly the global analysis method is applied to investigate the mechanism underlying the variations of growth rate and migration speed for varying sediment size the calculations reveal that these variations are mainly caused by the amount of sea bed sediments being stirred up which is clearly grain size dependent quantitative relationships between predicted rip channel characteristics sediment grain size and the hydrodynamic conditions are tentatively established which is amendable to improvement by extending the analysis to other or more general situations

use of numerical models to study land based sedimentation and subsequent nearshore morphological evolution a beach sedimentation problem is presented this problem involves assessing the impact and importance of land based sediment sources erosion from gullies during intense rainfall and directly from cliffs by wave action on morphodynamic changes at a beach the site motivating the study is la barrosa beach spain the location is described and a discussion of possible approaches presented a schematized representation of a gully and beach is used a hybrid approach is adopted in which sediment deposition by run off and to a lesser extent cliff erosion is modelled using wave resolving hydrodynamic models it is found that significant amounts of sediment can be supplied by gully run off during storms for small run offs the swash can be involved in determining the region of deposition within the gully area with longer period motions favouring increased sediment deposition at gully sides simulations also show that swash motions can erode gully sides and the presence of a cross shore jet associated with the swash and gullies can also impact on sediment movement longer term wave averaged morphodynamic modelling without a swash zone indicates that run off deposits subsequently diffuse laterally whether under normal or oblique incidence these simulations also reveal the possibility of underlying crescentic bar shedding dynamics that may pertain during changes of wave conditions

variability of unsaturated bromide fluxes as measured through a layered volcanic vadose zone in new zealand the measured drainage fluxes through a layered volcanic vadose zone exhibited high spatial variability as a consequence of heterogeneous flow conditions the drainage flux variability was quantified using automated equilibrium tension lysimeters installed in close proximity and resulted in high variability in the br masses recovered from a conservative tracer experiment the primary cause of the heterogeneous flow was attributed to textural changes occurring at the interface between volcanic layers resulting in development of funnel flow patterns and further enhanced by the existence of hydrophobic conditions the br recoveries in individual automated equilibrium tension lysimeters were used to determine the corresponding variable sizes of the surface areas contributing drainage to the lysimeters the tracer experiment confirmed the existence of unsaturated lateral transport occurring at the sloping interface of the coarse taupo ignimbrite material with the silty palaeosol layer at approximately 4 2 m depth this study demonstrates that measurements of both flux and solute concentrations at multiple locations are essential when heterogeneous flow is suspected to be present to be able to determine reliable estimates of contaminant leaching through the vadose zone at the plot scale copyright 2013 john wiley sons ltd

coupled barrier island resort model 1 emergent instabilities induced by strong human landscape interactions 1 as humans increasingly occupy and modify marginal landscapes previously unobserved long timescale emergent behaviors related to interactions between natural processes and human agency are possible barrier islands which are low lying strips of sand separated from a coast by lagoons cut by inlets and topped by sand dunes have been significantly modified through the development of tourist resorts resorts and barrier islands are dynamically coupled through storm damage and beach erosion and measures taken to prevent or mitigate them in response to rising sea level a natural barrier island migrates steadily up the continental shelf in contrast we show that in a novel numerical model coupling barrier island processes with resort development storm damage and hazard mitigation policy decisions driven by market dynamics destabilize barrier island response to rising sea level giving rise to emergent episodic boom and bust cycles which alternate in phase alongshore and less frequent regionally extensive resort destruction events developed barrier islands are precariously maintained at lower elevations and further offshore than their natural counterparts a situation exacerbated by insurance which can lead to island inundation our results suggest that coastal areas that have recently instituted protection measures eventually will experience a widespread upsurge in damage if these practices are sustained even in the absence of climate change induced increased storminess

large scale dynamics of sandy coastlines diffusivity and instability 1 the dynamics of small amplitude perturbations of an otherwise rectilinear coastline due to the wave driven alongshore sediment transport is examined at large time and length scales years and kilometers a linear stability analysis is performed by using an extended one line shoreline model with two main improvements 1 the curvature of the coastline features is accounted for and 2 the coastline features are assumed to extend offshore as a bathymetric perturbation up to a finite distance for high incidence angles instability is found in accordance with ashton et al 2001 however it is seen that instability is inhibited by high waves with long periods and gently sloping shorefaces so that in this case the coastline may be stable for any angle similarly there is no instability if the bathymetric perturbation is confined very close to the coast it is found that the traditional linearized one line model larson et al 1987 tends to overpredict the coastline diffusivity the overprediction is small for the conditions leading to a stable coastline and for moderate incidence angles but can be very dramatic for the conditions favoring instability an interesting finding is that high angle waves instability has a dominant wavelength at the linear regime which is in the order of 4 15 km one to two orders of magnitude larger than the length scale of surf zone rhythmic features intriguingly this is roughly the same range of the wavelength of some observed shoreline sand waves and in particular those observed along the dutch coast a model application to this coast is presented

non hydrostatic numerical modelling of nearshore wave transformation over shore oblique sandbars abstract observations from high resolution bathymetric surveys on the coast of north carolina indicate areas with shore parallel depth contours and other areas with shore oblique sandbars these shore oblique bars are large scale morphological features that extend up to 1000 m from shore and previous studies have shown that they are spatially correlated with higher shoreline change rates and induce erosional hotspots to investigate the influence the oblique sandbar morphology has on nearshore wave transformation and energy distribution a non hydrostatic wave model is used with the bathymetry corresponding to two areas with shore parallel depth contours and two areas with shore oblique sandbars the model is applied with a horizontal resolution of 5 m and a boundary condition representative of the directional spectrum of a typical southeast swell event an idealized approach with relatively short alongshore model domains and cyclic lateral boundary conditions is adopted due to limited availability of high resolution bathymetry however this approach elucidates the influence of shore oblique sandbars on the nearshore hydrodynamics the numerical results show that higher alongshore variability in depth due to the shore oblique bars drive large alongshore changes in cross shore wave energy flux and cause spatial variability in dissipation in the nearshore region the simulations indicate that alongshore variations in wave energy caused by the shore oblique bars results in a 50 75 reduction in wave setup and a 25 40 decrease in alongshore velocity averaged across the surf zone for the conditions investigated the results suggest that wave driven hydrodynamics can influence nearshore sediment dynamics to create erosional zones compared to areas with shore parallel bathymetric contours since the morphology of shore oblique sandbars are an important control on wave energy that impacts the beach

tracer and hydrometric study of preferential flow in large undisturbed soil cores from the georgia piedmont usa we studied the temporal patterns of tracer throughput in the outflow of large 30 cm diameter by 38 cm long undisturbed cores from the panola mountain research watershed georgia tracer breakthrough was affected by soil structure and rainfall intensity two rainfall intensities 20 and 40 mm hr 1 for separate cl and br amended solutions were applied to two cores one extracted from a hillslope soil and one extracted from a residual clay soil on the ridge for both low and high rainfall intensity experiments preferential flow occurred in the clay core but not in the hillslope core the preferential flow is attributed to well developed interpedal macrochannels that are commonly found in structured clay soils characteristic of the ridge site however each rainfall intensity exceeded the matrix infiltration capacity at the top of the hillslope core but did not exceed the matrix infiltration capacity at the middle and bottom of the hillslope core and at all levels in the clay core localized zones of saturation created when rainfall intensity exceeds the matrix infiltration capacity may cause water and tracer to overflow from the matrix into macrochannels where preferential flow occurs to depth in otherwise unsaturated soil

nearshore oblique sand bars 1 the coupling between hydrodynamics and the evolving topography in the surf zone has been theoretically examined for oblique wave incidence it is shown that positive feedback can lead to the initial growth of several types of rhythmic systems of sand bars the bars can be down current oriented or up current oriented which means that the offshore end of the bar is shifted down current or up current with respect to the shore attachment in the limit of strong current compared to wave orbital motion very oblique down current oriented b ars are obtained with a spacing of several times the surf zone width when wave orbital motions are dominant systems of up current oriented bars and crescentic down current oriented bars appear with spacings of the order of the surf zone width the latter feature consists of alternating shoals and troughs at both sides of the break line with the inner shoals being bar shaped and oblique to the coast the growth e folding time of the bars ranges from a few hours to a few days and it is favored by constant wave conditions the range of model parameters leading to growth corresponds to intermediate beach states in between the fully dissipative and the fully reflective situations preliminary comparison with field observations shows qualitative agreement

role of near bed turbulence structure in bed load transport and bed form mechanics the interactions between turbulence events and sediment motions during bed load transport were studied by means of laser doppler velocimetry and high speed cinematography sweeps u 0 w 0 w 0 which contribute negatively to the bed shear stress and are relatively rare individually move as much sediment as sweeps of comparable magnitude and duration however and much more than bursts u 0 and inward interactions u 0 w 0 when the magnitude of the outward interactions increases relative to the other events therefore the sediment flux increases even though the bed shear stress decreases thus although bed shear stress can be used to estimate bed load transport by flows with well developed boundary layers in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity it is not accurate for flows with developing boundary layers such as those over sufficiently nonuniform topography or roughness in which significant spatial variations in the magnitudes and durations of the sweeps bursts outward interactions and inward interactions occur these variations produce significant peaks in bed load transport downstream of separation points thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms

impact of topography on groundwater salinization due to ocean surge inundation sea level rise and increases in the frequency and intensity of ocean surges caused by climate change are likely to exacerbate adverse effects on low lying coastal areas the landward flow of water during ocean surges introduces salt to surficial coastal aquifers and threatens groundwater resources coastal topographic features e g ponds dunes barrier islands and channels likely have a strong impact on overwash and salinization processes but are generally highly simplified in modeling studies to understand topographic impacts on groundwater salinization we modeled a theoretical overwash event and variable density groundwater flow and salt transport in 3 d using the fully coupled surface and subsurface numerical simulator hydrogeosphere the model simulates the coastal aquifer as an integrated system considering overland flow coupled surface and subsurface exchange variably saturated flow and variable density groundwater flow to represent various coastal landscape types we simulated both synthetic fields and real world coastal topography from delaware usa the groundwater salinization assessment suggested that the topographic connectivity promoting overland flow controls the volume of aquifer that is salinized in contrast the amount of water that can be stored in surface depressions determines the amount of seawater that infiltrates the subsurface and the time for seawater to flush from the aquifer our study suggests that topography has a significant impact on groundwater salinization due to ocean surge overwash with important implications for coastal land management and groundwater vulnerability assessment

the influence of sea state on formation speed of alongshore variability in surf zone sand bars abstract the formation time of alongshore morphological variability in surf zone sand bars has long been known to differ from one beach to the other and from one post storm period to another here we investigate whether the type of sea state i e distant swell waves or locally generated short period wind sea affects the formation time of the emerging alongshore topographic variability a numerical modeling approach is used to examine the emergence of alongshore variability under different shore normal wave forcing a research version of delft3d operating on the time scale of wave groups is applied to a schematised bathymetry with a single bar the model is then used to investigate several wave scenarios examining the impact of peak period frequency spread and directional spread on the formation time of alongshore variability results show that an increase in wave period has a large effect changing the formation time up to o 250 in case the wave period is changed from a representative value for the dutch coast t p 5 6 s to an australian south east coast value t p 10 12 s in contrast modifications in the directional and frequency spread of the wave field result only in a minor change in the formation time examination of hydrodynamics and potential sediment transport shows that the variations in formation time are primarily related to changes in the magnitude of the time averaged flow conditions variations in the magnitude of very low frequency f f these findings indicate that the development of alongshore topographic variability may be faster at swell dominated open coasts primarily due to the occurrence of longer period swell also at a given site the arrival of a long wave period swell after a storm can accelerate the emergence of variability

numerical computation of sand dune migration with free surface flow 1 this paper presents a morphodynamic model for free surface flows over bed forms the model reproduces bed form evolution and migration in a physically based manner the flow model component of the coupled morphodynamic model which is two dimensional in the streamwise and vertical directions explicitly treats unsteadiness and nonhydrostatic effects comparison with measurements shows that the flow model accurately simulates both mean flow and turbulence structure induced by bed forms under free surface flow the flow model performance is enhanced by the use of a high order godunov scheme known as the cubic interpolated pseudoparticle cip technique to compute the advection phase of the navier stokes equation in addition an enhanced k turbulence closure with nonlinear terms is incorporated in the present model in order to allow better predictions of reynolds stress anisotropy in regions with flow separation performance of the nonlinear k model is compared with standard k closure in the context of the flow as well as morphodynamic simulation nonequilibrium bed load sediment transport is treated using a eulerian stochastic formulation of the sediment exchange process in terms of pickup and deposition functions the proposed approach for sediment transport explicitly considers the local flow variability during morphodynamic computation model results show that the vertical grid distribution pattern affects the simulation result particularly for bed form morphodymics the model successfully simulates some important physical features of bed form evolution such as amalgamation and asymmetric geometry the simulation results are in agreement with laboratory experiments as well as some commonly used prediction methods for geometric characteristics of bed forms

a morphological stability analysis for a long straight barred coast a morphological stability analysis is carried out for a long straight coast with a longshore bar the situation with oblique wave incidence and a wave driven longshore current is considered the flow and sediment transport are described by a numerical modelling system the models comprise i a wave model with depth refraction shoaling and wave breaking ii a depth integrated model for wave driven currents and iii a sediment transport model for the bed load transport and the suspended load transport in combined waves and current the direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity neglecting the effects of a bed slope and secondary currents an instability is found to develop around the bar crest the instability is periodic in the alongshore direction and tends to form rip channels and to steepen the offshore face of the bar between the rip channels the alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile

observation and prediction of three dimensional morphology at a high energy macrotidal beach abstract three dimensional beach features such as crescentic sandbars and rip channels influence beach response to and recovery from storm waves as well as significantly affecting the safety and amenity provided by the surf zone for beach water users in this contribution temporal variations in subtidal and intertidal beach three dimensionality are observed at a high energy macrotidal beach and a simple equilibrium model is developed to predict the changes over multi year timescales a dataset of 5 5 years of quasi weekly bar measurements and quasi monthly intertidal surveys from perranporth beach cornwall uk were used to quantify seasonal to inter annual changes in three dimensionality the three dimensionality of the outer bar displayed significant annual periodicity with annual minima and maxima occurring in winter and spring respectively the lower intertidal beach displayed a similar periodicity but developed three dimensionality 1 4 months before the outer bar the model predicts increases or decreases in the scale of three dimensional features by examining the disparity between instantaneous wave conditions and a temporally varying equilibrium wave condition a tidally modulated wave power term determines the rate of morphological change negative feedback was found to be an important process governing the changes in three dimensionality while free morphological behaviour may drive three dimensional growth negative feedback exerts stability in the system making it inherently predictable using a temporally varying equilibrium value the model explained 42 and 61 of the overall variability in outer bar and lower beach three dimensionality respectively it skilfully predicted changes outside the training data range during the most energetic 8 week period of waves measured in the last 65 years off sw england in winter 2013 14 the model outperformed a simple baseline model a linear fit as well as a comparable linearized feedback model from the literature providing the first long term multi year predictions of seasonal to inter annual beach three dimensionality for a macrotidal beach

sorted bed forms as self organized patterns 1 model development 1 here we present a modified version of the exploratory numerical model originally presented by murray and thieler 2004 and use it to further investigate the development of sorted bed forms on the inner continental shelf the new version of the model is based on widely accepted parameterizations for hydrodynamics and sediment transport that are more detailed and empirically tested than the parameterizations used in the original model the shallow water wave equations are replaced by the general equations and changes in water depth related to morphological development are accounted for this model reproduces the main results of the previous one supporting the hypothesis that sorted bed forms are a self organized pattern and develop as a result of a coupling between bed composition and sediment flux the sensitivity of the model predictions evaluated in terms of the geometry of the sorted bed forms and their growth rate with respect to external forcing variables and internal model parameterizations shows increasing decreasing sorted bed form spacing height with increasing wave height and period the opposite occurs for increasing water depths more complicated behavior is observed when the ratio fine to coarse sediment diameter or the percentage of fine and coarse material is varied the shape of the suspended sediment and current profiles and the formulation used to predict the geometry of wave generated ripples can significantly affect or even inhibit growth rates of sorted bed forms results from a sensitivity analysis show that there are deficiencies in the description of small scale processes that limit the ability to quantitatively predict sorted bed form evolution highlighting gaps in our knowledge of sediment transport over mixed grain beds that need to be filled

detailed simulation of morphodynamics 3 ripples and dunes we present a 3 d physics based high resolution modeling approach to the dynamics of underwater ripples and dunes the flow is modeled by large eddy simulation on a cartesian grid with local refinements the sediment transport is modeled by computing pickup transport over the bed transport in the water column and deposition of rigid spherical particles in a lagrangian framework the morphological development of the bed is modeled by a sediment balance equation in which the pickup and deposition from the sediment motion submodels appear as source and sink terms the model realistically replicated the formation and migration of dunes model results showed a good agreement with data from five flume experiments we subsequently applied the model to investigate the effect of sediment grain size on ripples finer sediments were found to yield more superimposed ripples than coarser sediments moreover under the same hydrodynamic conditions the finer sediments yielded two dimensional bed forms whereas for coarser sediment irregularities increased we extended the tests to pronounced 3 d morphologies by simulating the development of local scour at a pier the results agreed well with experimental data the model contributes to unraveling the complex problem of small scale morphodynamics and may be used in a wide range of applications for instance to develop more reliable parameterizations of small scale processes for application in large scale morphodynamic models

using both free surface effect and sediment transport mode parameters in defining the morphology of river dunes and their evolution to upper stage plane beds doi 10 1061 asce hy 1943 7900 0000873 dunes are common bed forms in sand bed rivers and are of central interest in water management purposes due to flow separation and associated energy dissipation dunes form the main source of hydraulic roughness a large number of dune dimension data sets was compiled and analyzed in this study 414 experiments from flumes and the field showing a significantly different evolution of dune height and length in flows with low froude numbers negligible free surface effects and flows with high froude numbers large free surface effects for high froude numbers 0 32 0 84 relative dune heights are observed to grow only in the bed load dominant transport regime and start to decay for u w s suspension number exceeding 1 dunes in this case are not observed for suspension numbers greater than 2 5 for low froude numbers 0 05 0 32 relative dune heights continue to grow from the bed load to suspended load dominant transport regime dunes in this case are not observed for suspension numbers greater than 5 it was concluded that for reliable predictions of dune morphology and their evolution to upper stage plane beds it is essential to address both free surface effects and sediment transport mode

the adaptation of dunes to changes in river flow abstract the dunes that cover the beds of most alluvial channels change in size and shape over time and in space which in turn affects the flow and sediment transport dynamics of the river however both the precise mechanisms of such adaptation of dunes and the hydraulic variables that control these processes remain inadequately understood this paper provides an overview of the processes involved in the maintenance and adaptation of dunes provides new tools for the analysis of dune dynamics and applies these to a series of bespoke experiments dunes that grow compete for space and dunes that decay need to shed excess sediment therefore dune adaptation necessarily involves the redistribution of sediment over and among dunes the details of sediment redistribution are not captured by mean geometric parameters such as dune height and wavelength therefore new analyses of dune kinematics bed elevation distributions and dune deformation are presented herein that aid the identification and analysis of dune dynamics dune adaptation is often described as a morphological response to changes in water depth at a rate that depends on sediment mobility which itself is a product of flow depth and velocity however depth and velocity are out of phase during the passage of flood waves and they vary spatially across rivers from the thalweg to bar tops and downstream along the river profile in order to improve our understanding of the hydraulic controls on dune morphology and kinematics a series of experiments was performed to investigate the response of dunes in fully mobile sand d50 240 m to changes in flow depth and velocity the experimental results illustrate that water depth and flow velocity have separate effects on the processes that control dune adaptation and that the crests and troughs of dunes do not respond simultaneously to changes in flow trough scour increases with flow velocity but superelevation of the dune crests appear to show only a weak relation with flow depth flattening out of dune crests is related to decreasing depth and increasing flow velocity bedform superimposition a key feature of bedform kinematics was associated with increased flow depth but was also systematically associated with local increases in the crest to crest distance following the dissipation of an upstream dune thus local flow form interactions have a significant effect on the manner in which sediment is redistributed over and among dunes the splitting of dunes decreased in the downstream direction along the length of the flume illustrating that the dunes continue to interact even after dune height has stabilised other processes such as differential migration and dune merging are ubiquitous during all flow conditions these varied responses support the notion that the processes of dune adaptation vary over time and in space analysis of dune deformation through examination of the residuals of cross correlations between successive dune profiles illustrates that local sources and sinks of sediment exist within mobile dune fields these findings highlight that dune adaptation to changes in flow is a dynamic response involving multiple interconnected dunes the redistribution of sediment that is required for dunes to change shape and adapt to new conditions is expected to be an important cause of variability in sediment transport these detailed analyses and findings provide a foundation for further study of dune dynamics in different environments on earth as well as other planetary bodies

morphologic properties derived from a simple cross shore sediment transport model this paper builds on the now classical discussions by bowen 1980 and bailard 1981 on the applicability and implications of bagnold s 1963 sediment transport model to nearshore profile modeling we focus on the morphologic implications of both the strengths and weaknesses of bagnold s model isolating the transport terms that are well predicted i e mean flow terms from those that are not well predicted i e transport due to correlations between flow and sediment load we factor bagnold s model into a dimensional transport magnitude and a nondimensional term the nondimensional term describes the relative importance of transport due to undertow gravity and correlations between flow and sediment load the transport magnitude largely determines the response time of nearshore profiles for typical nearshore environments this response time was estimated to vary as a function of incident rms wave height hrms from 500 years hrms 0 5 m to 2 years hrms 3 m the relative importance of competing transport mechanisms is shown to depend strongly on the relative wave height defined as the ratio of the rms wave height to the local depth simplified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles several differences from previously computed equilibrium profiles were noted first because the relative wave height saturates in natural surf zones equilibrium profiles converge to a relatively flat profile near the shoreline second under some situations a seaward sloping equilibrium profile may not exist third the long response times combined with unknown stability of an equilibrium profile make it difficult to assess the physical connection between theoretical equilibrium profiles and profiles observed in nature

formation and migration of transverse bars along a tidal sandy coast deduced from multi temporal lidar datasets a field of long crested transverse bars was monitored from a 2 5 year series of topographic lidar surveys in the vicinity of a tidal inlet on the macrotidal mean spring tidal range 7 to 12 m west coast of cotentin normandy france the bar field the alongshore extent of which is about 1 8 km is composed of a total of 8 bars with lengths varying from 320 m to 1300 m and mean heights comprised between 0 5 m and 2 5 m bar cross sections are variable between bars and for a single bar and also over time the surveys show a consistent northward migration of the bars at a mean rate of about 2 m month but the rate is larger in winter than in summer the lidar observations show that the tidal inlet located at the southern limit of the bar field where the bars start forming comprises a large sediment platform that acts as a source of sand for the bars the ebb jet debouching from the inlet is deflected northward by the ambient strong shore parallel tidal currents in this large tide range setting and this may be the primary mechanism leading to the emplacement of the bars smaller wave formed swash bars that further feed the development of these large transverse bars have also been observed monitoring of bar migration in the course of six consecutive spring tides with fair weather conditions showed that strong spring tidal currents are sufficient to drive bar mobility in the absence of waves storm wave resuspension of sand is thus expected to enhance bar mobility rates as shown by the higher rates of winter bar migration compared to the summer rates the ebb jet explains the slower bar migration rates at the vicinity of the inlet these rates increasing with distance northward of the inlet as the tidal currents become unimpeded the main difference between these macrotidal transverse bars and their counterparts in microtidal settings resides in these strong tidal currents that are the essential driver of bar migration unlike the wave driven migration of microtidal bars the large tidal range in conjunction with storm wave activity also induces longshore and seasonal variability in bar morphology the transverse bars of normandy appear to be inscribed in a sand circulation system involving the west cotentin coast the large ebb tidal delta from which they are formed and the central cotentin embayment where they are ultimately incorporated into the nearshore sand pool longer term field hydrodynamic monitoring and modelling will be required in order to further elucidate the mode of formation of these transverse bars

quantification of variability in bedform geometry we analyze the variability in bedform geometry in laboratory and field studies even under controlled steady flow conditions in laboratory flumes bedforms are irregular in size shape and spacing also in case of well sorted sediment our purpose is to quantify the variability in bedform geometry we use a bedform tracking tool to determine the geometric variables of the bedforms from measured bed elevation profiles for each flume and field data set we analyze variability in 1 bedform height 2 bedform length 3 crest elevation 4 trough elevation and 5 slope of the bedform lee face each of these stochastic variables is best described by a positively skewed probability density function such as the weibull distribution we find that except for the lee face slope the standard deviation of the geometric variable scales with its mean value as long as the ratio of width to hydraulic radius is sufficiently large if the ratio of width to hydraulic radius is smaller than about ten variability in bedform geometry is reduced an exponential function is then proposed for the coefficients of variation of the five variables to get an estimate of variability in bedform geometry we show that mean lee face slopes in flumes are significantly steeper than those in the field the 95 and 98 values of the geometric variables appear to scale with their standard deviation the above described simple relationships enable us to integrate variability in bedform geometry into engineering studies and models in a convenient way

bedform response to flow variability laboratory observations and computational results for the response of bedform fields to rapid variations in discharge are compared and discussed the simple case considered here begins with a relatively low discharge over a flat bed on which bedforms are initiated followed by a short high flow period with double the original discharge during which the morphology of the bedforms adjusts followed in turn by a relatively long period of the original low discharge for the grain size and hydraulic conditions selected the froude number remains subcritical during the experiment and sediment moves predominantly as bedload observations show rapid development of quasi two dimensional bedforms during the initial period of low flow with increasing wavelength and height over the initial low flow period when the flow increases the bedforms rapidly increase in wavelength and height as expected from other empirical results when the flow decreases back to the original discharge the height of the bedforms quickly decreases in response but the wavelength decreases much more slowly computational results using an unsteady two dimensional flow model coupled to a disequilibrium bedload transport model for the same conditions simulate the formation and initial growth of the bedforms fairly accurately and also predict an increase in dimensions during the high flow period however the computational model predicts a much slower rate of wavelength increase and also performs less accurately during the final low flow period where the wavelength remains essentially constant rather than decreasing in addition the numerical results show less variability in bedform wavelength and height than the measured values the bedform shape is also somewhat different based on observations these discrepancies may result from the simplified model for sediment particle step lengths used in the computational approach experiments show that the particle step length varies spatially and temporally over the bedforms during the evolution process assuming a constant value for the step length neglects the role of flow alterations in the bedload sediment transport process which appears to result in predicted bedform wavelength changes smaller than those observed however observations also suggest that three dimensional effects play at least some role in the decrease of bedform wavelength so incorporating better models for particle hop lengths alone may not be sufficient to improve model predictions published in 2011 this article is a us government work and is in the public domain in the usa

sand dunes in steady flow at low froude numbers dune height evolution and flow resistance the development of sand dunes in an erodible bed exposed to flowing water is considered using a numerical flow model the bed is initially given a small perturbation which is followed in the time domain examples are given where a sinusoidal perturbation reaches the fully developed steady equilibrium shape the flow modeling is based on a k turbulence closure the sediment transport is assumed to be bed load only with an avalanche like movement on the steep dune front the model is also found capable of predicting the growth in wavelength if the initially prescribed wavelength is sufficiently short results of the dune development are presented for different initial wavelengths it is demonstrated that an equilibrium shape is developed for a range of wavelength depth ratios as long as this ratio is sufficiently small

significance of preferential flow at the rock soil interface in a semi arid karst environment abstract in many semi arid environments the surface materials are frequently characterized by thin soils and large proportions of bare rock both of which are expected to considerably influence infiltration and groundwater recharge processes in this study small plot scale irrigation experiments in combination with dye tracer application as well as real time and subsequent soil moisture measurements and soil particle size analysis were conducted to investigate the significance of preferential flow at the rock soil interface large scale assessments of soil depth and surface type distribution were used to upscale the findings of the irrigation experiments to the scale of a complete hillslope and further to estimate percolation properties of a hypothetical rainfall event the two experimental plots were each located in the west bank mountains close to ramallah each irrigation experiment was designed with 50 mm of precipitation applied on an area of 1 m 2 during the course of ca 2 5 h each irrigation plot had a surface share of approximately 50 rock outcrop and 50 soil surface percolation properties were investigated by subsequent soil moisture measurements at high spatial resolution on vertical soil profiles on the irrigated plot dye tracer application on the rock outcrop during the sprinkling allowed for tracking of resulting outcrop runoff in the subsurface the soil depth survey included 2100 measurement points on 7 transects which allowed the estimation of local soil depth distribution results of the irrigation experiments showed that precipitation induced runoff from rock outcrops continued below ground as preferential flow along the rock soil interface while water from the soil surface percolated mainly vertically and much more homogeneously this was evident from the high density soil moisture measurements as well as from the dye tracer patterns outcrop runoff percolated faster and to greater depths than water infiltrating directly from the soil surface thus possessing a greater potential for groundwater recharge

longitudinal and lateral dispersion in an unsaturated field soil lateral and longitudinal dispersion was quantified in a field soil under water unsaturated conditions the relatively mobile dye tracer brilliant blue fcf was applied as a line source and leached into the soil at two different rates of infiltration 4 and 24 mm d 1 respectively the resulting tracer plume was photographically recorded at vertical soil profiles excavated perpendicularly to the line source after 50 100 and 200 mm of cumulative infiltration an image analysis technique was used to determine two dimensional concentration distributions from the photographs average horizontal and vertical concentration distributions were analyzed using the two dimensional advection dispersipn equation model parameters were fitted to optimize the agreement between measured and modeled averaged concentration profiles in both horizontal as well as vertical directions dispersivities showed a dependency on flow rates and amount of cumulative infiltration but this dependency appeared to be related to the degree of irregularities of observed flow patterns large dispersivities were associated with higher degree of irregularities in the flow patterns and vice versa layer boundaries played a significant role for redirecting flow when flow rates were high and cumulative infiltration was large this study demonstrates 1 that more than just the vertical concentration profiles are needed to define the transport regime under unsaturated conditions and 2 that even subtle layer boundaries affect the lateral mixing regime and exert a marked influence on the transport in the main flow direction

mechanisms and pathways of lateral flow on aspen forested luvisolic soils western boreal plains alberta canada rainfall simulation experiments by redding and devito 2008 hydrological processes 23 4287 4300 on two adjacent plots of contrasting antecedent soil moisture storage on an aspen forested hillslope on the boreal plain showed that lateral flow generation occurred only once large soil storage capacity was saturated combined with a minimum event precipitation of 15 20 mm this paper extends the results of redding and devito 2008 hydrological processes 23 4287 4300 with detailed analysis of pore pressure soil moisture and tracer data from the rainfall simulation experiments which is used to identify lateral flow generation mechanisms and flow pathways lateral flow was not generated until soils were wet into the fine textured c horizon lateral flow occurred dominantly through the clay rich bt horizon by way of root channels lateral flow during the largest event was dominated by event water and precipitation intensity was critical in lateral flow generation lateral flow was initiated as preferential flow near the soil surface into root channels followed by development of a perched water table at depth which also interacted with preferential flow pathways to move water laterally by the transmissivity feedback mechanism the results indicate that lateral flow generated by rainfall on these hillslopes is uncommon because of the generally high available soil moisture storage capacity and the low probability of rainfall events of sufficient magnitude and intensity copyright 2010 john wiley sons ltd

a surfzone morphological diffusivity estimated from the evolution of excavated holes downslope gravity driven sediment transport smooths steep nearshore bathymetric features such as channels bars troughs cusps mounds pits scarps and bedforms downslope transport appears approximately as a diffusive term in the sediment continuity equation predicting changes in bed level with a morphological diffusivity controlling the rate of seafloor smoothing despite the importance of surfzone sediment transport and morphological evolution the size of the downslope transport term in nearshore models varies widely and theories have not been tested with field measurements here observations of the infill of large excavated holes in an energetic inner surf zone provide the first opportunity to infer the morphological diffusivity in the field the estimated diffusion coefficient is consistent with a theoretical bedload morphological diffusivity that scales with the three halves power of the representative bed shear stress

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

generation and nonlinear evolution of shore oblique transverse sand bars the coupling between topography waves and currents in the surf zone may self organize to produce the formation of shore transverse or shore oblique sand bars on an otherwise alongshore uniform beach in the absence of shore parallel bars this has been shown by previous studies of linear stability analysis but is now extended to the finite amplitude regime to this end a nonlinear model coupling wave transformation and breaking a shallow water equations solver sediment transport and bed updating is developed the sediment flux consists of a stirring factor multiplied by the depth averaged current plus a downslope correction it is found that the cross shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars either transverse or oblique to the shore in the latter case they can open an acute angle against the current up current oriented or with the current down current oriented at the initial stages of development both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude the former being somewhat stronger as bars keep on growing their finite amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs leading to a final saturated amplitude the overall shape of the saturated bars in plan view is similar to that of the small amplitude ones however the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger in the case of alongshore migrating bars the asymmetry of the longshore sections the lee being steeper than the stoss is well reproduced complex dynamics with merging and splitting of individual bars sometimes occur finally in the case of shore normal incidence the rip currents in the troughs between the bars are jet like while the onshore return flow is wider and weaker as is observed in nature

spatial variability of saturated hydraulic conductivity in shallow macroporous soils in a forested basin field single ring infiltrometer and laboratory constant head parameter measurements of saturated hydraulic conductivity kh were used in combination to examine macropore effects on kh in shallow forest soils in a small basin in southern ontario canada soil matrix kh generally decreased with depth for hillslope podzols and stream valley gleysols differences in average maximum and minimum matrix kh were observed between soil types with lowest values occurring in the valley gleysols bulk profile kh assumed to include the effects of macropores had no apparent spatial pattern within a given soil type and mean bulk kh did not differ between soil types kh of macroporous soil was similar to matrix hydraulic conductivities for the porous hillslope podzols however it could be several orders of magnitude greater than the minimum matrix kh observed at a given site for the gleysols this difference increased with total profile thickness geostatistical analyses revealed anisotropic distributions of both bulk and matrix kh in the basin with the maximum and minimum directions of spatial correlation being parallel and normal to the stream valley respectively degree of anisotropy and scale of spatial dependence were lower for bulk kh relative to the minimum matrix kh values

annual regime of bedforms roughness and flow resistance lillooet river british columbia bc a field study to examine the statistical character of dune morphology and the correlation among dune morphology discharge and flow resistance was conducted in a meandering reach of lillooet river near pemberton british columbia canada the field season spanned the 1995 1996 hydrologic year with sample day discharge events ranging between 33 and 425 m3 s 1 surveys of the bed morphology along the thalweg in two dune fields a and b were completed using an echo sounder with chart recorder that enabled the measurement of more than 4000 dunes dune height ranged between 0 08 and 0 96 m length between 2 01 and 20 99 m and steepness between 0 02 and 0 10 histograms of each dune shape height length steepness sample most often displayed positive skewness and non gaussian distributions gamma beta and weibull median sample height and length histograms displayed positive skewness and steepness was nearly gaussian histograms of all dimensionless dunes i e measurement divided by average measurement of sample were gaussian and slightly leptokurtic neither the height nor length of dunes measured in this investigation were successfully predicted by the empirical models of allen allen j r l 1984 developments in sedimentology sedimentary structures their character and physical basis 2nd edn elsevier new york vol 30 a and b 1256 pp fredsoe j hydraul div am soc civ eng 108 hy8 1982 932 or yalin j hydraul div am soc civ eng 90 hy5 1964 105 least squares regression models for dune height relations produced here are similar to models published by other field researchers regression models for dune length only conform to those developed elsewhere if the discharge of the study rivers was similar the energy gradient in dune field a varied within a smaller range than in field b enabling dune size to become more fully equilibrated with respect to flow environment although the average froude numbers were much less than critical dunes appeared to wash out towards a plane bed as discharge increased due to a change from a bedload to suspended load dominated sediment transport regime flow resistance increased most rapidly during changes in base flow and at the beginning and end of the seasonal flood resistance tended to be smaller in field a than b reflecting local differences in energy gradient flow resistance increased until a dune steepness of 0 070 was attained and then decreased the steepness value was considered to be coincident with kolk generation dyer k r 1986 coastal and estuarine sediment dynamics wiley ny 342 pp suggesting that macroturbulent flow structures play an important role in defining the roughness of dunes on a channel bed

quantifying the morphology of flow patterns in landslide affected and unaffected soils summary in mountainous regions landslides are a common natural phenomenon they are often triggered by a combination of steep relief and long lasting rainfalls therefore hydrological conditions in the soil are crucial for their initiation because direct measurements of water flow are difficult and model predictions uncertain we used a dye to visualise flow patterns directly we combined dye tracer experiments with field observations root density and rock fragment content and measurements of soil properties bulk density soil water retention curve and saturated hydraulic conductivity we quantified the morphology of flow patterns by image indices and mutual information that measures the overall dependency between variables and compared two shallow landslides of different ages with a landslide unaffected hillslope our results showed that flow patterns on the landslides were more fragmented and contained larger stained objects than on the landslide unaffected site we relate these findings to a larger stone content and a stronger macropore soil matrix interaction moreover we detected a fissure network on the younger landslide that probably affects its hydrological behaviour field observations soil hydraulic properties and dye tracer studies describe different hydrological aspects of the studied sites and complement the information provided by the morphological image indices

preferential flow mechanisms identified from staining experiments in forested hillslopes field staining experiments in five different plots at two sites in japan okaya in nagano prefecture and konohara in mie prefecture were undertaken to improve understanding of subsurface stormflow runoff within organic layers of natural forested hillslopes this type of shallow lateral subsurface flow specifically referred to as biomat flow was observed only at the okaya site based on staining experiments conducted under controlled water application rates when the same irrigation rate 50 100 mm h 1 was applied to the konohara site overland flow without a significant shallow subsurface component was the dominant flow mechanism even in gently sloping 15 20 forest soils at the okaya site biomat flow was responsible for lateral dye transport over much longer distances than sub surface flow in the matrix of mineral soil layers based on analysis of staining pattern images observed in the okaya site we conclude that i the organic biomat layer could be divided into two sub layers of different structure ii biomat flow transported the dye tracer longer distances than subsurface flow in the matrix and iii the biomat layer topography affected biomat flow by generating preferential flowpaths and subsequent percolation into the deeper soil based on field experimental results and pore scale consideration of water infiltration into pores of soils with varying wettability properties we hypothesized and developed a conceptual model for two key biomat flow mechanisms the first mechanism considers lateral subsurface flow due to a permeability contrast between the much more porous and hence permeable biomat layer and the underlying mineral soil the second mechanism involves a hydrophobic soil layer between the biomat and the underlying mineral soil flow across the hydrophobic layer is believed to occur when a threshold pore pressure is exceeded i e as a result of a perched water table within the biomat layer lower pore pressures are needed to initiate flow when preferential flow paths exist that are less hydrophobic than the surrounding organic layers numerical models of catchment hydrology should include lateral biomat flow when such layers are present in hillslope soils in addition to typical subsurface flow within the soil matrix this article is protected by copyright all rights reserved

dye tracer visualization of flow patterns and pathways in glacial sandy till at a boreal forest hillslope abstract dyes are valuable tracers in visualizing flow patterns and pathways in soil we applied the dye acid blue 9 to unsaturated and saturated soil profiles at a boreal forest hillslope consisting of glacial sandy till and determined the soil physical properties from soil samples the objective was to characterize preferential flowpaths investigate their porosity extent and connectivity and complement earlier findings on subsurface flow formation at the site according to the results preferential flowpaths were formed by roots erosion related to soil water flow freezing thawing cycles and soil fauna the role of roots and stones in the formation of preferential flowpaths was emphasized porosity of preferential flowpaths was 5 1 1 8 and they extended to a depth of about 55 cm from the soil surface the deepest roots reached the same depth when the soil saturated individual preferential flowpaths self organized into continuous and well connected lateral flow systems along the slope at the slope shoulder preferential flow network covering the entire soil profile as well as preferential flowpaths on the underlying bedrock surface were considered crucial for runoff generation in the midslope area runoff generation was characterized by lateral preferential flow and the transmissivity feedback phenomenon at the slope foot preferential flowpaths in soil below the eluvial horizon were the major runoff contributors a full saturation of the soil profile at the slope is unlikely under natural conditions however lateral flow was found to occur also in unsaturated soil

sediment detachment and transport processes associated with internal erosion of soil pipes subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping the development of perched water tables in duplex soils fosters lateral flow that can result in seepage at the surface of hillslopes and or formation of soil pipes by internal erosion of lateral preferential flow paths continued internal erosion of soil pipes can lead to gullies dam and levee failures however the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented this paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes

direct numerical simulation of bedload transport using a local dynamic boundary condition temporally and spatially averaged models of bedload transport are inadequate to describe the highly variable nature of particle motion at low transport stages the primary sources of this variability are the resisting forces to downstream motion resulting from the geometrical relation pocket friction angle of a bed grain to the grains that it rests upon variability of the near bed turbulent velocity field and the local modification of this velocity field by upstream protruding grains a model of bedload transport is presented that captures these sources of variability by directly integrating the equations of motion of each particle of a simulated mixed grain size sediment bed experimental data from the velocity field downstream and below the tops of upstream protruding grains are presented from these data an empirical relation for the velocity modification resulting from upstream grains is provided to the bedload model the temporal variability of near bed turbulence is provided by a measured near bed time series of velocity over a gravel bed the distribution of pocket friction angles results as a consequence of directly calculating the initiation and cessation of motion of each particle as a result of the combination of fluid forcing and interaction with other particles calculations of bedload flux in a uniform boundary and simulated pocket friction angles agree favourably with previous studies

self organization mechanisms for the formation of nearshore crescentic and transverse sand bars the formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow water equations and on a simplified sediment transport parameterization by assuming normally approaching waves and a saturated surf zone rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed two types of bedforms appear one is a crescentic bar pattern centred around the breakpoint and the other herein modelled for the first time is a transverse bar pattern the feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations basically the waves stir up the sediment and keep it in suspension with a certain cross shore distribution of depth averaged concentration then a current flowing with against the gradient of sediment concentration produces erosion deposition it is shown that inside the surf zone these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro morphodynamic input conditions to which of the patterns develops it is suggested that crescentic bar growth would be favoured by high energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment in intermediate conditions mixed patterns may occur

a sharp view on river dune transition to upper stage plane bed sandy river beds are dominated by rhythmic features known as dunes experimental investigations of turbulent flow and sediment transport over dunes have predominantly focused on equilibrium flows that are rare in natural rivers using a novel acoustic instrument over migrating dunes in a laboratory setting we quantify a number of dynamical properties that are crucial in our understanding and modeling of dune morphology and kinematics particularly under nonequilibrium flows during dune transition to upper stage plane bed measured sediment transport distributions reveal a positive spatial lag between dune crest and maximum sediment transport rate that eventually caused washing out of dunes bed load was entirely captured in dune troughs contributing to dune translation where most of suspended load was advected further downstream contributing to dune deformation measured bypass fraction was about 76 which means that only 24 of the total sediment load at the dune crest contributed to dune migration

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

how do disconnected macropores in sloping soils facilitate preferential flow runoff from hillslopes is generated by processes such as infiltration excess and saturation overland flow subsurface stormflow and subsurface return flow preferential flow through macropores can affect any one of these runoff generation processes field studies at the hitachi ohta experimental watershed in japan have noted that self organization processes may manifest the connectivity of such subsurface flow paths particularly via macropores from hillslopes to stream channels it is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at hitachi ohta where subsurface flow and streamflow respond to thresholds of wetness numerical solutions to the three dimensional richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes shapes and orientations solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions the preferential flow network expands as the degree of saturation increases the expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain although the individual macropores are disconnected it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion in addition to the importance of these findings related to stormflow generation in catchments they add support to the concept of self organization of subsurface flow systems in soils copyright 2010 john wiley sons ltd

algorithm for resistance to flow and transport in sand bed channels an algorithm is developed that relates depth to discharge and determines bed and suspended load transport for the entire range of bed forms found in sand bed channels equilibrium state geometry of lower flow regime bedforms is also predicted grain shear stress and form resistance are differentiated using a drag coefficient closure and a two segment logarithmic velocity profile a meyer peter type formulation is used to compute sand transport in the bed load layer and for computing suspended sand transport mclean s procedure of 1991 and 1992 is adopted a bed form classification scheme is developed that uses a particle size parameter and the transport strength to predict bed form type it correctly identifies 73 of the 1 192 mostly flume scale calibration data sets for 194 sets of dune transition bed form calibration data a modified version of van rijn s 1984 bed form geometry predictor yields a geometric average predicted to observed height ratio of 1 00 after calibration the algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1 00 for a verification data set of 855 observations mostly from rivers and canals the overall geometric averages of predicted to observed depth and transport are 0 87 and 1 14

vegetation influences near surface hydrological characteristics on a surface coal mine in eastern usa abstract mining processes alter natural landscapes worldwide and methods for restoration of mined areas are widely studied establishment of vegetation is essential to mined land restoration prior research has addressed vegetative influence on erosion and runoff but effects of vegetation type on surface hydrologic processes are less studied we measured infiltration rates and observed subsurface flow paths in mine soils on a reforested area and a grassed area on a former surface coal mine in the eastern united states the two areas were constructed and reclaimed fourteen years prior to our study using processes similar in all aspects except vegetation minidisk tension infiltrometers and brilliant blue fcf dye staining analyses were utilized to evaluate near surface flow processes in the vegetated mine soils mean infiltration rates were 16 5 10 7 cm h 1 and 10 4 7 7 cm h 1 for the reforested and grassed areas respectively infiltration rates hydraulic conductivities dye coverage and dye stained areas were significantly higher in the reforested area the grassed area had constant dye coverage with depth but more flow paths than the reforested area a transition from vegetation controlled subsurface flow to abiotic control at greater depths was evident in the stained soil profiles results highlight the heterogeneous nature of mine soils and the influence of vegetation type in development of mine soil hydrologic processes

inferring flow types from dye patterns in macroporous soils in this study we exploit dye patterns to identify flow types in macroporous soils as a step forward from using dye patterns simply as qualitative pictures that illustrate preferential flow dye tracer experiments at different irrigation rates and initial soil moisture conditions were carried out on three hillslope sites several vertical and horizontal soil sections were prepared after each experiment to analyze the patterns of the dye tracer brilliant blue fcf photographs of the soil sections were processed by image analysis to discriminate between stained and unstained areas and to classify stained areas into three classes of dye concentration the images of the vertical sections were first analyzed according to conventional approaches e g dye coverage then a new approach was developed using the extent and distribution of the stained objects to classify flow into five types two of these flow types occur only in the soil matrix and three of them are related to the degrees of water flow between macropores and soil matrix interaction from horizontal sections the macropore distribution was classified and in combination with the dye pattern the interaction quantified based on statistical description of the spatial relationship between macropores and stained areas categorized flow type profiles showed a logical sequence in each of our experiments and we think the concepts will have broad application in soil science and infiltration research to compare the infiltration regimes of soils

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

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

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

case study bed resistance of rhine river during 1998 flood detailed field measurements during the 1998 flood of the rhine river in the netherlands show that both manning in and darcy weisbach friction factor if increase with discharge the changes in bedform roughness height and friction factors are attributed to the increased dune height during floods there is a near peak hysteresis in the dune height measurements at a given discharge dunes are significantly larger after than before the peak discharge the trend is most apparent for the bovenrijn with weaker variations for the waal the methods of engelund and vanoni hwang provide similar estimates of form drag when combined with van rijn s method to estimate grain resistance both methods tend to overpredict the measured bed friction factor after the peak discharge these methods perform best when field bedform measurements are available to estimate form drag the composite effect of primary and secondary dunes should be considered in the analysis of resistance to flow

sand ripples under sea waves part 1 ripple formation in the present paper we formulate a predictive theory of the formation of sand ripples under sea waves the theory is based on a linear stability analysis of a flat sandy bottom subject to a viscous oscillatory flow the conditions for decay or amplification of a bottom perturbation are determined along with the wavelength of the most unstable component as a function of the reynolds number of the flow and of the froude and reynolds numbers of the sediments a comparison between theoretical findings and experimental data supports the validity of the present theory an analytical solution for viscous oscillatory flow over a small amplitude wavy bottom is determined for arbitrary values of the ratio r between the amplitude of fluid displacement and the wavelength of bottom waviness previous works by lyne 1971 and sleath 1976 who considered small or large values of r are thus extended

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

morphological diversity and complex sediment recirculation on the ebb delta of a macrotidal inlet normandy france a multiple lidar dataset approach the shoreline in the vicinity of inlets can exhibit considerable variability in morphology in both space and time most studies on inlets and their adjacent shores have focused on the morphodynamics of sediment by passing mechanisms generated by longshore transport for the first time the morphology sedimentary features sediment budgets and patterns of evolution of the shoreline and ebb delta in a macrotidal inlet system have been investigated using seven lidar topographic surveys in normandy france over a period of 3 7 years fromfebruary 2009 to october 2012 the ebb delta shows strong development on the northern flank of the inlet expressed by a large sand spit and two types of superimposed dynamic sandy features eight long crested and highly mobile transverse bars and a large swash bar sand transport fromn s on the updrift beach feeds the growth of the distal part of the spit this sand supply is further augmented by the onshore movement of a large swash barwelding to the upper foreshore however the main topographic changes were induced by the northward migration of the transverse bars on the ebb platform this is driven by strong northward directed tidal currents parallel to the shore the bars exhibit a more complex morphology and dynamics along the seaward margin of the ebb delta where their mobility is controlled by wave action topographic measurements suggest a clear sand recirculation pattern in this morphodynamic model sand coming from the updrift upper beach is transported southward and deposited at the distal end of the spit where it serves to construct transverse bars close to the tidal inlet transverse bar migration ends in the wave exposed northern margin of the ebb delta where they are integrated into the shallow dissipative shoreface sand sink this sink nourishes the southward longshore transport to feed growth of the large swash bar and southward spit elongation this semi circular recirculation cell model involves an inversion of sand movement close to the inlet and emphasizes the combined role of tidal currents and waves in the large scale 3d ebb delta sediment dynamics in this macrotidal setting in contrast to the much more commonly reported alongshore sediment by passing mode of microtidal inlets

numerical simulation of dune flat bed transition and stage discharge relationship with hysteresis effect 1 this work presents recent advances on morphodynamic modeling of bed forms under unsteady discharge this paper includes further development of a morphodynamic model proposed earlier by giri and shimizu 2006a this model reproduces the temporal development of river dunes and accurately replicates the physical properties associated with bed form evolution model results appear to provide accurate predictions of bed form geometry and form drag over bed forms for arbitrary steady flows however accurate predictions of temporal changes of form drag are key to the prediction of stage discharge relation during flood events herein the model capability is extended to replicate the dune flat bed transition and in turn the variation of form drag produced by the temporal growth or decay of bed forms under unsteady flow conditions some numerical experiments are performed to analyze hysteresis of the stage discharge relationship caused by the transition between dune and flat bed regimes during rising and falling stages of varying flows the numerical model successfully simulates dune flat bed transition and the associated hysteresis of the stage discharge relationship this is in good agreement with physical observations but has been treated in the past only using empirical methods a hypothetical relationship for a sediment parameter the mean step length is proposed to a first level of approximation that enables reproduction of the dune flat bed transition the proposed numerical model demonstrates its ability to address an important practical problem associated with bed form evolution and flow resistance in varying flows

detailed simulation of morphodynamics 2 sediment pickup transport and deposition the paper describes a numerical model for simulating sediment transport with eddy resolving 3 d models this sediment model consists of four submodels pickup transport over the bed transport in the water column and deposition all based on a turbulent flow model using large eddy simulation the sediment is considered as uniform rigid spherical particles this is usually a valid assumption for sand bed rivers where underwater dune formation is most prominent under certain shear stress conditions these particles are picked up from the bed due to an imbalance of gravity and flow forces they either roll and slide on the bed in a sheet of sediment or separate from the bed and get suspended in the flow sooner or later the suspended particles settle on the bed again each of these steps is modeled separately yielding a physics based process model for sediment transport suitable for the simulation of bed morphodynamics the sediment model is validated with theoretical findings such as the rouse profile as well as with empirical relations of sediment bed load and suspended load transport the current model shows good agreement with these theoretical and empirical relations moreover the saltation mechanism is simulated and the average saltation length height and velocity are found to be in good agreement with experimental results

detailed simulation of morphodynamics 1 hydrodynamic model we present a three dimensional high resolution hydrodynamic model for unsteady incompressible flow over an evolving bed topography this is achieved by using a multilevel cartesian grid technique that allows the grid to be refined in high gradient regions and in the vicinity of the river bed the grid can be locally refined and adapted to the bed geometry managing the cartesian grid cells and faces using a hierarchical tree data approach a ghost cell immersed boundary technique is applied to cells intersecting the bed topography the governing equations have been discretized using a finite volume method on a staggered grid conserving second order accuracy in time and space the solution advances in time using the fractional step approach large eddy simulation is used as turbulence closure we validate the model against several experiments and other results from literature model results for stokes flow around a cylinder in the vicinity of a moving wall agree well with wannier s analytical solution at higher reynolds numbers computed trailing bubble length separation angle and drag coefficient compare favorably with experimental and previous computational results results for the flow over two and three dimensional dunes agree well with published data including a fair reproduction of recirculation zones horse shoe structures and boiling effects this shows that the model is suitable for being used as a hydrodynamic submodel in the high resolution modeling of sediment transport and formation and evolution of subaqueous ripples and dunes

burst like sediment suspension events in a sand bed river in a much quoted paper jackson 1976 hypothesized that turbulent bursting motions such as those documented in laboratory boundary layers play a major role in alluvial sediment suspension to date the hypothesis remained largely untested due to difficulties in monitoring turbulent suspension in rivers this study provides field data documenting burst like turbulent motions over a sandy bed channel and quantifying the role of these motions in sand suspension the data were collected in a 10 m deep channel of the fraser river near mission british columbia canada turbulent fluctuations of both flow components downstream and normal to the bed along with the output of an optical suspended sediment sensor were monitored 1 m above the river bed typical flow velocities averaged 0 9 ms 1 at the sensors where mean suspended sediment concentrations were 500 mgl 1 decimetre height small dunes on the backs of larger half metre amplitude dunes covered the channel bed in the area brief but intense burst like ejection and inrush events were identified in the flow records where they are responsible for a high degree of intermittency in shear stress over the dunes 80 per cent of the turbulent momentum exchange across the 1 m level can be ascribed to such brief 3 8 s duration events active under 12 per cent of the time in addition the record of fluctuating sediment concentrations reveals these burst like motions to be highly effective in vertically mixing suspended sediment and thus ultimately in maintaining suspended sediment transport above the dune bed the bulk 60 and 90 per cent in two deployments of the vertical sediment mixing was accomplished by intense events active some 10 per cent of the time no discrete recurrence timescale for these burst like mixing events is evident however rather a continuous variation of return periods was observed as a function of the magnitude of vertical mixing event considered to that extent conceptual models of sediment transport in terms of burst events with a predictable recurrence such as proposed by jackson 1976 may be misleading

computational modeling of dissipation and regeneration of fluvial sand dunes under variable discharges it is observed during flood events that bed forms initially grow in height and make the riverbed rougher but later under high discharge the bed forms grow longer with the opposite effect of making the riverbed smoother after the discharge drops to a lower value new bed forms regenerate on top of the elongated bed forms this mechanism leads to a significant variation in the bed roughness and the water stage and hence determines the behavior of floods and the risk of flood disasters this work presents detailed modeling of bed forms under discharge hydrographs and simulates the conditions under which the bed is flattened out in the upper plane bed regime the flow was simulated by large eddy simulation and the sediments were considered as rigid spheres and modeled in a lagrangian framework the bed morphodynamics were the result of entrainment and deposition of sediment particles we examined several discharge hydrographs in the first case we increased the discharge linearly and then kept it constant after reaching the upper plane bed condition the dunes were generated and grew during the rising stage of discharge when the flow conditions reached the upper plane bed regime high frequency ripples were generated and helped to flatten the bed the results also showed that in contrast with mechanisms in the dune regime the flattening of the bed was associated with a distinct pattern of sediment transport which deposited sediment mainly in the lee side of the dunes and led to flattening of the bed after flattening the sediments were mainly transported in suspension mode as long as flow conditions stayed in the upper plane bed regime the bed remained flat with small high frequency ripples we also examined two other scenarios one with an immediate falling stage of discharge after the rising stage and the other with a period of constant discharge between the rising and falling stages dunes were regenerated during the falling stage of discharge for both cases in the first case the dunes were regenerated before the bed was flattened because of a time lag between the flow and the bed deformation bed flattening was followed by dune regeneration in the second case moreover a significant reduction in the form drag coefficient was observed after the flattening in the second case the reduction in form drag led to a reduction in the flood intensity the model showed its ability to reproduce the key phenomena of the development of subaqueous dunes under conditions of a passing flood wave

impacts of logging disturbance on hillslope saturated hydraulic conductivity in a tropical forest in peninsular malaysia using a constant head permeameter we found an abrupt natural decrease in saturated hydraulic conductivity ks within the upper 1 0 m soil profile of an orthoxic tropudult at the bukit tarek experimental catchments research area in tropical peninsular malaysia the depth at which low ks could cause a perched water table in response to high intensity rainfall however was too great to generate saturation overland flow on planar hillslopes in the study area the effects of logging activity on ks at five subsurface depths 0 1 0 25 0 5 0 75 and 1 0 m on the non roaded portion of the harvest area were examined at the three following sites which differed in the degree of disturbance and recovery since timber harvesting 1 selective logging conducted in the 1960s 2 mechanized selective tree removal conducted 4 years ago and 3 high impact clear cutting just prior to measurement this recent logging greatly disturbed the soil surface via compaction topsoil subsoil mixing burning and produced comparatively high variability in near surface ks changes in ks at or below 0 25 m however were not detected with certainty at any sites in terms of hillslope hydrologic response the connectivity of zones of low ks in the harvest area with dense networks of skid trails and terraces was identified as one of the most important consequences of timber harvesting although this phenomenon was not quantified we estimate the recovery time for near surface ks on the non roaded hillslope to be less than 40 years d 2006 elsevier b v all rights reserved

scale dependent evanescence of river dunes during discharge extremes during high river discharge extremes the growth of dunes can reach a maximum beyond which a transition to upper stage plane bed may occur enhancing the river s conveyance capacity and reducing flood risk our predictive ability of this bedform regime shift in rivers is exclusively built upon high froude number flows dominated by asymmetric dunes with steep downstream facing slipfaces that are rare in natural rivers by using light weight polystyrene particles as a substrate in an experimental flume setting we present striking dune morphodynamic similarity between shallow laboratory flow conditions and deep rivers preconditioned that both flow and sediment transport parameters are accurately scaled our experimental results reveal the first observation of upper stage plane bed in a shallow laboratory flume that is reached for a froude number well below unity this work highlights the need to rethink widely used dune scaling relationships bedform stability diagrams predictions of flow resistance and flood risk

storm driven changes in rip channel patterns on an embayed beach this paper introduces a semi automatic computer algorithm designed to detect rip current channels in video imagery as a case study this method is applied to 3 3 years of video data from an embayed beach to demonstrate the link between antecedent surf zone morphology wave energy and up down transitions in beach state an objective measure of rip channel change was developed to define six significant rip reconfiguration events and relate these events to wave energy over the period of study no complete resets of the nearshore morphology occurred the analysis indicates that direct correlation of rip patterns with the instantaneous wave conditions is not a useful way to demonstrate how rips and waves interact the average wave energy over a period of ten days combined with storm duration were good indicators of rip channel change demonstrating that in general beach morphology responds with a time lag to changes in forcing rip channels with a short cross shore length and narrow alongshore spacing responded faster to changes in wave conditions than rips with a long cross shore length and wider alongshore spacing to force changes in the rip morphology longer rip channels required wave events of higher energy and or a longer duration offshore islands protect the beach under certain wave approach angles sometimes resulting in a dual width surf zone which was narrow at the sheltered end and wide at the exposed end of the beach the wider surf zone end was characterised by three dominant and persistent rip channels whereas the narrow surf zone section contained a number of smaller rips which evolved rapidly under wave forcing our observations demonstrate the importance of rip channel size in controlling the response time of nearshore morphology

study of suspended sediment distribution in the coastal zone abstract in the present paper observations of the suspended sediment dynamics in the coastal zone of the baltic black and mediterranean seas are briefly described a special method for performing field experiments was developed with this method a large amount of data have been collected during storms of various force these data characterize concentration fields on a vast aquatory from the water edge to the significant depth of sediment movement in the zone seaward of the breaker line the changes in concentration at fixed levels follow directly the storm changes a significant amount of sand and aleurite particles are suspended near the bottom at a depth of 30 m or even deeper in the breaking zone the concentration change with time is mostly governed by storm migration of the breaker location and not by a direct change of storm force here the distribution of mean grain size of sediment dispersion asymmetry and excess of composition coefficients is nearly uniform in the vertical direction whereas on the adjacent sites variation in these quantities is significant in the surf zone the amount of suspended material in the water is slightly but monotonously decreasing shoreward different types of vertical profiles of suspended sediment concentration are established for various locations in the coastal zone characterized by different deformation of surface waves a method of predicting the suspended sediment distribution over a large part of the coastal zone was developed examples of concentration field calculations for different probabilities are presented for a site on the north african coast

rip channel development on nonbarred beaches the importance of a lag in suspended sediment transport 1 on approximately planar beaches rip channel development is often preceded by a period in which jet like rip currents develop in apparently random locations and dissipate after minutes to tens of minutes the subsequent development of sharp edged trough like channels extending across the surf zone suggests that rip currents on planar beaches cause local erosion conversely channels are known to cause localized offshore directed flow and once channels have formed on approximately planar beaches rip currents no longer occur in apparently random locations but are restricted to the locations of the channels apparently the excavation of channels by rip currents on planar beaches triggers a positive feedback between the morphological development and the flow however theoretical analysis indicates that when depth increases with distance from shore and sediment transport is treated as a function only of local flow conditions channel development in the vicinity of a rip current may not occur in numerical simulations using a cellular model of nonbathymetrically driven rip currents in which sediment flux on a planar beach is driven by approximately realistic rip current velocity patterns deposition occurs under parts of the rip currents especially in the seaward half of the surf zone and these rip ridges cause a negative feedback in these simulations as in most models treating surf zone sediment transport sediment flux is assumed to be strictly a function of local hydrodynamic conditions however observations of sediment laden rip current plumes extending well beyond the surf zone suggest that suspended sediment transport is not always in equilibrium with local conditions other simulations employ a treatment of suspended sediment transport that allows for a lag in the adjustment of fluxes to the changes in local hydrodynamic conditions that the sediment is advected through with this nonlocal sediment transport the flux of sediment out of the surf zone in a rip current is increased ridges do not develop under any part of the rip currents and the morphodynamic feedback becomes positive

morphodynamic instabilities of planar beaches sensitivity to parameter values and process formulations the initial growth of bed perturbations on planar sloping beaches under the forcing of obliquely incident breaking waves is investigated using a state of the art numerical model this allows for a systematic investigation of the sensitivity of the spatial structures of the bed perturbations and their growth and migration rates to different model formulations and parameterizations if the sediment is only transported in the direction of the net current velocity and sediment stirring is taken proportional to the wave height squared growing up current oriented crescentic bars are found with a preferred spacing of 800 m and a down current migration rate of 10 m d 1 varying the angle of wave incidence drag coefficient and bed slope results in qualitatively similar growing bed forms using an engelund and hansen transport formula very oblique down current oriented bars are obtained that grow in time no preferred wavelength however is found using the bailard transport formula results in growing up current oriented bars with a preferred spacing smaller than 300 m for wave angles smaller than 7 when using either the engelund and hansen or bailard sediment transport formulation it is essential to take the transport in the direction of the wave orbital velocity into account in order to have growing bed perturbations

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

characteristics and dynamics of surfzone transverse finger bars 1 patches of transverse finger bars have been identified in the surf zone of noordwijk beach netherlands they consisted of three to nine elongated accumulations of sand attached to the low tide shoreline the bars extended up to 50 m into the inner surf zone had an oblique orientation with respect to the shore normal and were quasiregularly spaced in the alongshore direction we analyzed nearly 6 years of video data and observed a significant presence of finger bars 14 of the time with good data bars were visible on 193 days gathered in 44 events that persisted from 2 days to 2 months obliquely incident waves of intermediate and approximately constant height were dominant during finger bar presence shore normal incident or more energetic wave fields destroyed the bar patches the underlying bathymetry affected finger bar formation inner surfzone troughs with cross shore areas of 100 m2 and inner surfzone slopes of 0 02 were more conducive to their growth the mean alongshore wavelength of the finger bar patches was 39 m ranging from 21 to 75 m bar crests deviated up to 40 degrees from the shore normal against the alongshore current direction up current orientation and bar patches migrated at rates up to 22 m day in the direction of the alongshore current we used these observations to test existing theoretical self organization mechanisms for transverse bar formation the bed flow mechanism was the most viable explanation for the generation and persistence of noordwijk finger bars our observations were consistent with most of the predictions of two models that included this interaction but migration rates differed by 1 order of magnitude

analysing decadal scale crescentic bar dynamics using satellite imagery a case study at anmok beach south korea abstract understanding long term sandbar dynamics can be crucial for informed coastal zone management but is often hampered by data availability to increase the number of sandbar observations available from bathymetric surveys this study proposes and evaluates a method to manually extract the sandbar location using freely available satellite imagery for the case study of anmok beach in south korea validation of the satellite extracted sandbar locations against 9 in situ measurements shows good agreement with errors well within the pixel resolution of the satellite imagery i e 30 m for landsat missions the applicability of the method is constrained to locations where 1 the cross shore crescentic length scales are larger than the image resolution 2 frequent wave breaking and clouds are absent and 3 the water clarity is sufficient to enable the manual extraction of the sandbar crest line using the additional sandbar observations from the satellite imagery significantly increases the temporal extent and resolution of the dataset for anmok beach this allows the study of sandbar characteristics dynamics and impacts of human interventions to an extent that would not have been possible without the satellite imagery within the study period 1990 2017 it is found that the sandbar maintains a persistent crescentic pattern that is only altered during prolonged and very intense storm conditions the cumulative alongshore migration of the sandbars is investigated and found to be in the order of hundreds of meters over the 27 years study period comparing the sandbar characteristics prior and after the construction of gangneung port shows that both the amplitudes and wavelengths of the sandbar crescents near the port have decreased after its construction

effect of antecedent soil moisture on preferential flow in a texture contrast soil summary the effect of soil moisture status on preferential flow in a texture contrast soil was investigated by applying 25 mm brilliant blue dye tracer to soil profiles at high and low antecedent soil moisture differences in soil morphology and chemistry between soil profiles had little effect on the depth of dye infiltration and dye distribution down the profile antecedent soil moisture strongly influenced the type depth and rate of dye tracer movement in the wet treatment the dye tracer infiltrated to depths between 0 24 and 0 40 m at an average rate of 120 mm h 1 whilst in the dry treatment the same volume of dye tracer infiltrated to between 0 85 and 1 19 m depth at an average rate of 1160 mm h 1 in dry antecedent conditions finger flow developed in the a1 horizon as a result of water repellency in the wet treatment the wetting front developed permutations but did not break into fingers despite similar particle size distributions flow in the a2 e was slower than the a1 horizon due to the absence of macropores in the dry treatment the dye tracer ponded on the upper surface of the b21 horizon which then spilled down the sides of the large clay columns as rivulets at rates of between 2000 and 3000 mm h 1 the dye tracer accumulated at the base of the columns resulting in backfilling of the inter column shrinkage cracks at an estimated rate of 750 mm h 1 in the subsoil water movement occurred via shrinkage cracks which resulted in flow by passing 99 of the soil matrix in the b21 horizon and 94 of the soil matrix in the b22 horizon evidence of rapid and deep infiltration in dry texture contrast soils has implications for water and solute management this knowledge could be used to i improve irrigation and fertilizer efficiency ii explain variations in crop yield iii reduce salinity through improved leaching practices iv reduce the risk of agrochemicals contaminating shallow groundwater

effect of sea level rise and tidal current variation on the long term evolution of offshore tidal sand ridges abstract tidal sand ridges are large scale bedforms that occur in the offshore area of shelf seas they evolve on a time scale of centuries due to tide topography interactions while being further shaped by wind waves during their evolution ridges are also affected by changes in sea level strength and direction of the tidal current according to their present day behavior ridges are classified as active sand transport everywhere quasi active sand transport only on parts of the ridges and inactive no sand transport anywhere using a nonlinear morphodynamic model the present study extends earlier work by investigating the effect of sea level rise and changes in the amplitude and principal direction of the tidal current on the growth time and height of active tidal sand ridges besides the role of sea level rise and tidal current variation in the presence of quasi active inactive ridges is explored two specific settings are considered which are characteristic for the dutch banks in the north sea and for sand ridges in the celtic sea the time range considered here is less than 20 000 years roughly the period from the last glacial maximum to the present generally active tidal sand ridges occur if the tidal current amplitude is larger than 0 5 m s for these ridges with increasing rates of sea level rise their growth time becomes longer and the root mean square height keeps on increasing a smaller initial tidal current amplitude gives rise to a larger growth time while changes in the principal current direction have a minor effect on the characteristics of the ridges on the considered time scale assuming a constant wave climate quasi active tidal sand ridges occur mainly as a result of a decreasing tidal current amplitude such that the effective velocity in the sense of stirring sand becomes smaller than the critical velocity for sand erosion the ridges further become inactive on a time scale that depends inversely on the rate of sea level rise modeled ridges are compared with observed ridges similarities are found and quantitative differences are explained

sequential stage development of crescentic bars hahoterim beach southeastern mediterranean abstract sequential bar development involving in order multiple bars ridge and runnels transverse oblique bars and meandering or crescentic shore attached or detached bars of both outer and nested inner systems were delineated at hahoterim beach northern israel the concomitant wave data including wave directions energy spectrum significant wave height and length of the calm period showed strong correlation with the bar stages there is a notable lack of correlation between bar stages and incident wave periods which were quite variable even on a daily basis two bar developmental sequences were delineated one shore normal and the other initially oblique but gradually rotating to shore normal in the mature stage threshold conditions for the initial stage development of shore normal crescentic systems were defined as h1 3 1 0 m peak spectral density of 1 m2 hz and swell directions within 7 from the normal the outer crescentic systems formed within 1 to 2 weeks the nested inner crescentic bar system formed under different wave conditions development of inner micro cresentic bars required 3 to 7 weeks of calm waves h1 3 0 3 m except for a short initiating pulse of wave energy from waves of about i m in height the double crescentic pattern indicates the optimal evolutiona y stage of crescentic systems the residence time of bar types was determined by the frequency of crossing of these threshold conditions the outer bars and the mega rip channels composed the most stable inshore elements out of phase relationships between inner and outer bar systems resulted from the lag in response of the outer bars behind changes in wave direction among the inner crescentic bars and shore rhythms phase correlation was the was the rule regional aerial photography and wave data indicate that the bar wave relationships at hahoterim axe representative of the eastern flank of the nile including most of the israeli coast although the bar types described from other coasts are similar to those mapped at hahoterim and the threshold wave conditions for initiation of bar stage development appear to be similar the frequency of occurrence of specific bar types appears to be different at hahoterim

on the variation of infiltration into a homogeneous soil matrix containing a population of macropores a population of channels penetrates a soil matrix that is otherwise homogeneous the channels are assumed to be vertical and of circular cross section with constant diameter but channel depths and radii are allowed to vary over the population this paper uses a model based on the green ampt assumptions to predict infiltration rates through the walls and bases of channels resulting in a mathematical description of the way in which infiltration develops in the soil and in which channels fill with water until eventually overland flow is initiated this model takes account of the fact that there may be a random distribution of channels in space expressions for the expected mean and variance of infiltration volumes are derived some example results are given and show that below the matrix wetting front the variance of the change in water content with 30 and 50 channels per square meter may be of the same order as the mean change in water content the presence of channels can lead to significant increases in predicted channel volumes

development of crescentic bars for a periodically perturbed initial bathymetry 1 the development of crescentic bed patterns starting from an undisturbed beach i e one only perturbed so as to simulate background noise and thereby initiate morphological development is compared with that starting from a beach where monochromatic and in some cases bichromatic bed patterns pre exist using a fully non linear model morfo55 a wide range of different lengthscales and amplitudes is investigated the findings suggest that the pre existence of crescentic bed forms can influence the subsequent morphological development of this beach significantly but that this development is related to the undisturbed beach development whether a pre existing bed form remains under certain forcing conditions depends on the position of the pre existing lengthscale along the undisturbed linear growth rate curve if the pre existing mode shows significant linear growth in the undisturbed scenario this pre existing lengthscale remains otherwise the pre existing mode will be replaced by a bed form with a lengthscale closer to the undisturbed fastest growing mode a pre existing lengthscale that is significantly longer than the undisturbed fastest growing mode will be replaced by a higher harmonic of the original lengthscale for shorter pre existing lengthscales this will be the linear fastest growing mode an increased amplitude of the pre existing bed form accelerates the development toward a new stable situation for small initial amplitudes the initial response of the system to pre existing bed forms could theoretically be described using linearized equations alone the migration rates of both the pre existing and newly arising modes correspond to the migration rate of these modes in the undisturbed scenario

quasi three dimensional modelling of the morphology of longshore bars a morphological quasi three dimensional q3d area model for barred coasts has been developed the model combines a two dimensional depth integrated model for wave driven currents with a model for undertow circulation currents the combined model makes a simultaneous simulation of the bar forming processes associated with the undertow and the horizontal wave driven circulation currents which may cause instabilities of the bar and the formation of rip channels situations with normal and oblique wave incidence are considered compared to the depth integrated approach the q3d model produces less pronounced alongshore irregularities for obliquely incident waves for normal incident waves the q3d model produces a crescentic bar while the depth integrated model predicts almost straight sections of the bar interrupted by rip channels the sensitivity to variation of wave angle and beach slope is further investigated

macropores as preferential flow paths in meander bends macropores are subsurface connected void spaces caused by processes such as fracture of soils micro erosion and fauna burrows they are common near streams e g hyporheic and riparian zones and may act as preferential flow paths between surface and groundwaters affecting hydrologic and biogeochemical processes we tested the hydrologic function of macropores by constructing an artificial macropore within the saturated zone of a meander bend open macropore om and later filling its upstream end partially filled macropore pfm for each treatment we injected saline tracer at an upgradient monitoring well within the meander and monitored downgradient hydraulics and tracer transport pressure transducers in monitoring wells indicated hydraulic gradients within the meander were 32 higher perpendicular to and 6 higher parallel to the macropore for the om than for the pfm additionally hydraulic conductivities measured via falling head tests were 29 to 550 times higher along the macropore than in nearby sediment we used electrical conductivity probes in wells and electrical resistivity imaging to track solute transport transport velocities through the meander were on average 9 and 21 higher per temporal moment analysis and observed tracer peak respectively for the om than for the pfm furthermore temporal moments of tracer breakthrough analysis indicated downgradient longitudinal dispersion and breakthrough tracer curve tailing were on average 234 and 182 higher for the om respectively this suggests the om enabled solute transport at overall shorter timescales than the matrix but also increased tailing our results demonstrate the importance of macropores to meander bend hydrology and solute transport copyright 2012 john wiley sons ltd

observations of nearshore crescentic sandbars 1 the temporal and spatial variability of crescentic sandbars is analyzed with hourly long term months video observations collected at four barred sites and are qualitatively compared to the temporal and spatial variability predicted by hypotheses underpinning existing approaches and models for crescentic bar formation edge wave template model linear stability analysis and nonlinear models the observations coming from the single barred beaches at duck north carolina usa and miyazaki kyushu japan and from the double barred beaches at the northern gold coast queensland australia and noordwijk netherlands show that crescentic sandbar wavelength and amplitude variations over space and time are very common for instance at any moment in time the wavelength of the smallest and longest crescentic bar can differ by a factor of 2 temporal changes in wavelength and amplitude result from merging and splitting of individual crescents causing the final configuration of a crescentic sandbar system to be very different from the initial configuration the gold coast data indicate that these intrinsically nonlinear interactions are an attempt of the crescentic bar system to self organize into a more uniform pattern as splitting is usually confined to the longest crescentic bar observed whereas merging usually combines the smallest crescentic bars into a longer bar the observed spatial and temporal crescentic bar behavior contrasts qualitatively with behavior predicted from the edge wave template model and implies that the predictive skill of linear stability models is limited nonlinear models are potentially better suited for a comparison against these field observations several suggestions to improve these models and hence to facilitate a data model comparison are made