a lagrangian model for boundary layer growth and bed shear stress in the swash zone abstract a new model for the boundary layer development and associated skin friction coefficients and shear stress within the swash zone is presented the model is developed within a lagrangian reference frame following fluid trajectories and can be applied to both laminar flow and smooth turbulent flow the model is based on the momentum integral approach for steady flat plate boundary layers with appropriate modifications to account for the unsteady flow regime and flow history the model results are consistent with previous measurements of bed shear stress and skin friction coefficients within the swash zone these indicate strong temporal and spatial variation throughout the swash cycle and a clear distinction between the uprush and backwash phase this variation has been previously attributed the unsteady flow regime and flow history effects both of which are accounted for in the new model fluid particle trajectories and velocity are computed using the non linear shallow water wave equations and the boundary layer growth across the entire swash zone is estimated predictions of the bed shear stress and skin friction coefficients agree reasonably well with direct bed shear stress measurements reported by barnes et al barnes m p o donaghue t alsina j m baldock t e 2009 direct bed shear stress measurements in bore driven swash coastal engineering 56 8 853 867 and for a given flow velocity give stresses which are consistent with the bias toward uprush sediment transport which has consistently been observed in measurements the data and modelling suggest that the backwash boundary layer is initially laminar which results in the late development of significant bed shear during the backwash with a transition to a turbulent boundary layer later in the backwash a new conceptual model for the boundary layer structure at the leading edge of the swash is proposed which accounts for both the no slip condition at the bed and the moving wet dry interface however further development of the lagrangian boundary layer model is required in order to include bore generated turbulence and to account for variable roughness and mobile beds

direct measurements of bed stress under swash in the field 1 utilizing flush mounted hot film anemometry the bed stress under swash was measured directly in a field experiment conducted on barret beach fire island new york the theory development and calibration of the instrument package are discussed and results from the field experiment are presented examples of bed stress time series throughout a swash cycle are presented and an ensemble averaged swash bed stress cycle is calculated strong asymmetry is observed between the uprush and backwash phases of the swash flow the maximum bed shear stress exerted by the uprush is approximately double that of the backwash while the duration of the backwash is 135 greater than that of the uprush friction coefficients in the swash zone are observed to be similar in magnitude to those from steady flow with the mean observed friction coefficient equal to 0 0037 swash friction coefficients derived from the current measurements exhibit a reynolds number dependence similar to that observed for other flows a systematic difference between coefficients for uprush and backwash is suggested

direct bed shear measurements under loose bed swash flows shear plate measurements of bed shear stress under fixed and loose bed swash uprush flows are presented and contrasted a shear plate previously developed for fixed bed flows was modified and tested for coarse and fine grain loose beds transient flows were generated by a dam break flow over initially dry horizontal and sloping beds with flows upslope analogous to swash uprush flows on beaches performance of the shear plate varied with grain size for the coarse grained loose beds only the peak shear stress at the leading edge of the swash flow was consistently obtained for fine grained loose beds the shear stress was reliably obtained over the whole uprush swash cycle data were obtained for varying thickness of loose bed material commencing with a single grain layer which correspond to partially starved bed conditions the direct measurements clearly indicate that the bed shear stress comprises of a fluid shear stress component and a grain shear stress component the grain shear stress increases linearly with sediment load and is significantly larger for the coarse loose grain bed tests due to the much larger normal stress compared to that for fine grain loose bed tests with the same number of grain layers the data show a high degree of consistency with the classical theory of bagnold 1956 and the derived coefficient of dynamic internal friction is similar to that observed by hanes and inman 1985

direct bed shear stress measurements in bore driven swash direct measurements of bed shear in the swash zone are presented the data were obtained using a shear plate in medium and large scale laboratory bore driven swash and cover a wide range of bed roughness data were obtained across the full width of the swash zone and are contrasted with data from the inner surf zone estimates of the flow velocities through the full swash cycle were obtained through numerical modelling and calibrated against measured velocity data the measured stresses and calculated flow velocities were subsequently used to back calculate instantaneous local skin friction coefficients using the quadratic drag law the data show rapid temporal variation of the bed shear stress through the leading edge of the uprush which is typically two four times greater than the backwash shear stresses at corresponding flow velocity the measurements indicate strong temporal variation in the skin friction coefficient particularly in the backwash the general behaviour of the skin friction coefficient with reynolds number is consistent with classical theory for certain stages of the swash cycle a spatial variation in skin friction coefficient is also identified which is greatest across the surf swash boundary and likely related to variations in local turbulent intensities skin friction coefficients during the uprush are approximately twice those in the backwash at corresponding reynolds number and cross shore location it is suggested that this is a result of the no slip condition at the tip leading to a continually developing leading edge and boundary layer into which high velocity fluid and momentum are constantly injected from the flow behind and above the tip region finally the measured stress data are used to determine the asymmetry and cross shore variation in potential sediment transport predicted by three forms of sediment transport formulae crown copyright c 2009 published by elsevier b v all rights reserved

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

the influence of wave groups and wave swash interactions on sediment transport and bed evolution in the swash zone abstract large scale laboratory measurements of sediment dynamics in the swash zone are presented two bichromatic wave group conditions were generated having the same energy content but different wave group period t g 15 0 s and 27 7 s for the shortest wave group due to bore focusing the shoreline fluctuates predominantly at the t g time scale showing a large runup and the presence of wave swash interactions with strong momentum exchange in contrast for the longer wave groups the swash excursion is dominated by the individual waves the uprush generally promotes onshore sediment advection with consequent erosion at the rundown location but accretion close to the runup on the contrary the backwash promotes seaward sediment advection and accretion at the rundown location the presence of repeated wave swash interactions modifies these patterns slightly a wave overrunning a previous uprush promotes a reduction in onshore sediment advection while weak wave backwash interactions reduce seaward advection consequently the measured sediment dynamics shows stronger intra swash cross shore sediment advection for the swash events produced by the short wave groups measurements of the sheet flow layer near the shoreline show that for the shortest wave groups the vertical structure of the concentration is influenced by horizontal advection leading to large sheet flow layer thickness however for the longer wave groups the local vertical exchange of sediment in the sheet flow layer is dominant with the presence of a pick up and mirroring upper layer similar to oscillatory sheet flow measurements these results reaffirm the important effects of the wave group structure and the wave swash interactions on the swash zone sediment dynamics and beach face evolution

large scale experimental observations of sheet flow on a sandbar under skewed asymmetric waves a novel large wave flume experiment was conducted on a fixed barred beach with a sediment pit on the sandbar allowing for the isolation of small scale bed response to large scale forcing concurrent measurements of instantaneous sheet layer sediment concentration profiles and near bed velocity profiles were obtained on a sandbar for the first time two sediment distributions were used with median grain diameters d50 of 0 17 mm and 0 27 mm sheet flow occurred primarily under wave crests where sheet thickness increased with increasing wave height a proportionality constant was used to relate maximum shields parameter to maximum sheet thickness normalized by d50 with bed shear stress computed using the quadratic drag law an enhanced sheet layer thickness was apparent for the smaller sediment experiments 18 7 when directly compared to closed conduit oscillatory flow tunnel data 10 6 however varied significantly 5 31 depending on the procedure used to estimate grain roughness ds and wave friction factor fw three models for ks were compared keeping the model for fw fixed constant ks 2 5d50 and two expressions dependent on flow intensity derived from steady and oscillatory sheet flow experiments values of ks d50 varied by two orders of magnitude and exhibited an inverse relationship with where 30 for ks d50 of o 1 while 5 for ks d50 of o 100 two expressions for fw were also tested with the steady flow based model for ks yielding a difference of 69 13 versus 22

turbulence experiments in the swash zone abstract turbulence and water surface elevation measurements were carried out in the swash zone which was induced by plunging and collapsing breakers in a wave flume three different period regular waves were generated on a 1 10 smooth impermeable concrete beach and the water surface elevations were collected by a number of wave gauges and a run up meter lying on the bottom velocity measurements were carried out by a laser doppler velocimeter system at spatial steps of 1 mm from the bottom along three vertical sections in the swash zone the data have been used to describe the wave front dynamics to derive the length and velocity macro and micro scales and the eulerian frequency spectrum in some points it shows a double structure the results add to and expand on similar results obtained by other researchers in the surf zone

surf zone cross shore boundary layer velocity asymmetry and skewness an experimental study on a mobile bed 1 an experimental study on a physical model of a beach in a two dimensional wave flume was designed to investigate velocity nonlinearities in the wave boundary layer the cross shore velocity was measured in the surf zone along a vertical profile every 3mm from free stream elevation down to the still bed level the skewness and the asymmetry of the phase averaged velocity were computed at each elevation observations indicate that the free stream asymmetry transforms into bottom velocity skewness a linear experimental relation between free stream asymmetry to skewness ratio and bottom skewness to free stream skewness ratio is established a theoretical linear relationship is discussed which predicts the phase lead of the bottom velocity this phase lead is also determined by fourier analyzing the velocity time series the first two fourier components yield the same phase lead at the bed that is found to be about 30 and nearly constant over all the experiments made

the swash of solitary waves on a plane beach flow evolution bed shear stress and run up the swash of solitary waves on a plane beach is studied using large scale experiments ten wave cases are examined which range from non breaking waves to plunging breakers the focus of this study is on the influence of breaker type on flow evolution spatiotemporal variations of bed shear stresses and run up measurements are made of the local water depths flow velocities and bed shear stresses using a shear plate sensor at various locations in the swash zone the bed shear stress is significant near the tip of the swash during uprush and in the shallow flow during the later stages of downrush in between the flow evolution is dominated by gravity and follows an explicit solution to the nonlinear shallow water equations i e the flow due to a dam break on a slope the controlling scale of the flow evolution is the initial velocity of the shoreline immediately following waveform collapse which can be predicted by measurements of wave height prior to breaking but also shows an additional dependence on breaker type the maximum onshore directed bed shear stress increases significantly onshore of the stillwater shoreline for non breaking waves and onshore of the waveform collapse point for breaking waves a new normalization for the bed shear stress which uses the initial shoreline velocity is presented under this normalization the variation of the maximum magnitudes of the bed shear stress with distance along the beach which is normalized using the run up follows the same trend for different breaker types for the uprush the maximum dimensionless bed shear stress is approximately 0 01 whereas for the downrush it is approximately 0 002

video derived near bed and sheet flow sediment particle velocities in dam break driven swash abstract this short communication considers a video based approach to quantify near bed and sheet flow swash zone sediment particle velocities over a mobile bed in a laboratory setting and relate the profile shape to sheet thickness and a velocity that can be measured outside the sheet layer by for instance a current meter near bed high speed imagery was recorded during a dam break driven swash event in a flume with optically clear walls repeated swash events for two different median sediment sizes were tested optical current meter ocm analysis was applied to bed parallel image time stacks extracted at elevations from below the at rest bed to within the lower water column ocm results were compared to in situ velocity measurements where possible obtained with an acoustic doppler profiling velocimeter adpv ocm results compared well with adpv measurements for moderate suspended sediment concentrations based on visual observation sediment concentrations were not measured too high of a sediment concentration over saturated the image and did not provide distinct sediment particle trajectories in a consistent direction for ocm analysis this saturation occurred during uprush for both sediment sizes too little of a sediment concentration provided an inadequate number of sediment particle trajectories to track such as during flow reversal for the coarser sediment for coarser sediment backwash velocities were well resolved in ocm analysis with velocities comparing well correlation coefficient 0 8 to adpv estimates the dimensionless backwash sheet flow sediment particle velocity profile normalized by the velocity at the top of the sheet scaled with the dimensionless elevation normalized by the sheet layer thickness to the 0 62 power with 95 confidence intervals for the exponent ranging from 0 47 to 0 76

flow convergence at the tip and edges of a viscous swash front experimental and analytical modeling the details of flow at the tip of a viscous swash front are important to describe the propagation of the wave the bed shear and to estimate material transport rates and impact forces this paper presents novel experimental data illustrating the convergence of fluid at swash fronts generated by dam break flows very viscous fluids detergents were used to slow the flow sufficiently to enable video tracking of particles on the free surface and within the interior of the flow the experiments were performed both up a slope and on a horizontal bed the particle tracking shows that surface particles travel faster than the mean flow converge on the swash tip and then rapidly decelerate a process that will induce a high bed shear stress at the swash tip as observed in recent experiments particles also converge on the wall boundaries because of the no slip condition a simple analytical model is developed to estimate the ratio of the velocity of surface particles and the wave front for laminar flows this ratio is found to be 3 2 independent of the bed slope and flow depth and is in good agreement with the experimental data the same model approach suggests a ratio of 8 7 for turbulent flows this flow convergence does not appear to be included in either analytical modeling of the tip region or in basal resistance laws for the swash front and would modify the momentum equation at the swash tip c f hogg and pritchard 2004 and the kinematic boundary condition at the shoreline the flow convergence is consistent with observations of the behavior and build up of buoyant debris at the leading edge of tsunami wave front and can be observed in natural swash flows on beaches

suspended sediment transport mechanisms in high energy swash abstract measurements of suspended sediment concentration at three heights above the bed and cross shore velocity at a single height were obtained using miniature optical backscatter sensors and a miniature electromagnetic current meter from the swash zone of a high energy macrotidal dissipative beach time series from relatively low h s 0 8 m and high h s 2 2 m energy conditions were chosen for analysis possible onshore and offshore sediment transport mechanisms are identified as a sudden offshore to onshore velocity transition and turbulence in the swash front leading to subsequent onshore advection by the uprush and b low frequency high velocity backwashes exceeding a certain threshold for sediment suspension these mechanisms are related to the velocity field through skewness and asymmetry an increase in negative infragravity skewness in high energy conditions suggests a potential shift towards offshore net transport time averaged vertical profiles of cross shore suspended sediment flux were calculated from the velocity and concentration time series these show a tendency towards offshore transport in high energy conditions particularly at low levels in the water column the actual sediment fluxes are believed to be more offshore than those calculated one reason for this discrepancy is the inability of the instruments to detect swash activity at very low levels in the water column

laboratory scale swash flows generated by a non breaking solitary wave on a steep slope the main goal of this paper is to provide insights into swash flow dynamics generated by a non breaking solitary wave on a steep slope both laboratory experiments and numerical simulations are conducted to investigate the details of runup and rundown processes special attention is given to the evolution of the bottom boundary layer over the slope in terms of flow separation vortex formation and the development of a hydraulic jump during the rundown phase laboratory experiments were performed to measure the flow velocity fields by means of high speed particle image velocimetry hspiv detailed pathline patterns of the swash flows and free surface profiles were also visualized highly resolved computational fluid dynamics cfd simulations were carried out numerical results are compared with laboratory measurements with a focus on the velocities inside the boundary layer the overall agreement is excellent during the initial stage of the runup process however discrepancies in the model data comparison grow as time advances because the numerical model does not simulate the shoreline dynamics accurately introducing small temporal and spatial shifts in the comparison yields adequate agreement during the entire rundown process highly resolved numerical solutions are used to study physical variables that are not measured in laboratory experiments e g pressure field and bottom shear stress it is shown that the main mechanism for vortex shedding is correlated with the large pressure gradient along the slope as the rundown flow transitions from supercritical to subcritical under the developing hydraulic jump furthermore the bottom shear stress analysis indicates that the largest values occur at the shoreline and that the relatively large bottom shear stress also takes place within the supercritical flow region being associated with the backwash vortex system rather than the plunging wave it is clearly demonstrated that the combination of laboratory observations and numerical simulations have indeed provided significant insights into the swash flow processes

full scale cfd simulation of tsunamis part 2 boundary layers and bed shear stresses abstract this paper presents results from numerical simulations of the propagation and run up of full scale tsunamis using a reynolds averaged navier stokes model with emphasis on the resulting boundary layers and bed shear stresses spatial distributions of the shields and rouse parameters during run up and draw down show that for the tsunamis considered with a sediment grain size corresponding to medium sand considerable sediment transport shields parameter o 10 o 100 can be expected during run up and that the sediment transport can be expected to be dominated by suspended load the results likewise show that the expected sediment transport during draw down will similarly be considerable and dominated by suspension the tsunami induced boundary layers are monitored in time and the observed boundary layer thickness ranges from spanning only a small fraction of the water depth to spanning the entire depth the velocity profiles beneath the tsunamis are shown to have good correspondence with a logarithmic profile within the boundary layer similarly the bed shear stresses beneath the tsunamis are investigated and a new and simple engineering model is developed for predicting the temporal variation of the bed shear stress based only on a free stream velocity signal the new engineering model is shown give better predictions for the bed shear stress than a standard manning approach and is likewise shown in the appendix to produce reasonable predictions for shorter wind scale waves it is finally also shown how the temporal evolution of the boundary layer thickness can be predicted based on the free stream velocity signal alone the results presented here are part 2 of a larger study where part 1 presents the model validation and detailed descriptions of the run up process

an experimental study of the interaction of two successive solitary waves in the swash a strongly interacting case and a weakly interacting case abstract the interaction of successive solitary waves in the swash zone have been studied using large scale experiments with a simple bathymetry of a constant depth region where the water depth was 1 72 m and a plane beach whose slope was 1 12 two wave cases were considered where two successive solitary waves of the same height were generated one after the other so that the wave crests were separated by the effective wavelength associated with a single solitary wave in the weakly interacting case the swash period associated with a single solitary wave is smaller than the time period separating the successive wave crests which leads to similar run ups for the first and second wave whereas in the strongly interacting case the swash period associated with a single solitary wave is larger than the time period separating the successive wave crests which leads to a significant reduction in the run up of the second wave the degree to which there is an interaction between the swash uprush of the second wave and the downrush of the first wave is found to be related to the solitary wave slope parameter which predicts breaker type of the first wave previous data from literature are found to support this claim measurements of bed shear stress bed pressure and the free surface displacement at a location near the stillwater shoreline are used to describe how the dynamics of the boundary layer differ when the downrush of the first wave meets the incoming second wave in both cases

morphodynamical modelling of field scale swash events in the present work data for three single swash events are selected from those available for an accretive tide that occurred at le truc vert beach france during a measurement field campaign at that location these events are primarily chosen because of the different final bed change they produced namely variable accretion seaward erosion landward deposition and variable erosion along the swash zone these data are compared to results obtained from a state of the art numerical fully coupled 1d morphodynamical shallow water solver driven by measurements made of those events in the lower swash inner surf zone it is found that the hydrodynamics is reasonably well represented although the computed results exhibit reduced maximum inundations in comparison with the observed ones the model reproduces the correct order of magnitude of the morphodynamic change after each event and sometimes the pattern of erosion and deposition but this change is generally underestimated sensitivity analyses are conducted with respect to more uncertain physical parameters and assumed initial conditions they suggest that initial spatial distributions for velocity and pre suspended sediment concentration play a key role in the quantitative and qualitative prediction of the bed change

measurement and modelling of the influence of grain size and pressure gradient on swash uprush sediment transport the paper examines the dependency between sediment transport rate q and grain size d i e q dp in the swash zone experiments were performed using a dam break flow as a proxy for swash overtopping on a mobile sediment beach the magnitude and nature of the dependency i e p value is inferred for different flow parameters the initial dam depth or initial bore height do the integrated depth averaged velocity u3 dt and against the predicted transport qp using the meyer peter muller mpm transport model experiments were performed over both upward sloping beds and a horizontal bed the data show that negative dependencies p 0 are obtained for u3 dt this indicates that a given do and qp transport less sediment as grain size increases whereas transport increases with grain size for a given u3 dt the p value is expected to be narrow ranged 0 5 p 0 5 a discernible difference observed between the measured and predicted transport on horizontal and sloping beds suggests different modes of transport the incorporation of a pressure gradient correction dp dx using the surface water slope i e piezometric head in the transport calculation greatly improved the transport predictions on the horizontal bed where dp dx is positive on average the incorporation of a pressure gradient term into the mpm formulation reduces qp in the uprush by 4 fine sand to 18 coarse sand and increases qp over a horizontal bed by 1 fine sand to two orders of magnitude coarse sand the measured transport for fine and coarse sand are better predicted using mpm and mpm dp dx respectively poor predictions are obtained using nielsen 2002 because the pressure gradient in the uprush is of opposite sign to that inferred from velocity data in that paper it is suggested that future swash sediment transport models should incorporate the grain size effect partly through the pressure gradient although the dp dx influence is small for fine sands because of the grain size scaling contained in the stress term

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

experimental study of bore driven swash hydrodynamics on impermeable rough slopes abstract a detailed experimental investigation of the hydrodynamics of large scale bore driven swash on impermeable rough beach slopes is described the experiments were carried out on 1 10 impermeable rough slopes with three different surface roughnesses based on 1 3 mm sand 5 4 mm gravel and 8 4 mm gravel the large scale discrete swash event was produced by the collapse of a dambreak generated bore on the beach simultaneous depths and velocities were measured using lif laser induced fluorescence and piv particle image velocimetry respectively yielding better resolution of the hydrodynamics than previous studies depth time series instantaneous velocity profiles depth averaged velocities instantaneous turbulent kinetic energy profiles depth averaged turbulent kinetic energy reynolds stress profiles and bed shear stresses are presented for five cross shore measurement locations in the swash the measurements resolve the backwash shoreline position and the late backwash period when depths are shallow and velocities are high the detailed data can be used to test and develop advanced numerical models for bore driven waves on rough slopes

observations of turbulence within the surf and swash zone of a field scale sandy laboratory beach abstract current coastal evolution models generally lack the ability to accurately predict bed level change in shallow

subsurface processes generated by bore driven swash on coarse grained beaches 1 large scale laboratory experiments presented in this paper involved bore driven swash on permeable immobile coarse grained beaches two different sediments were used d50 1 5 and 8 5 mm resulting in different beach permeability and surface roughness the experiments yielded detailed measurements of swash depth and velocities wetting front pressure and groundwater levels across the swash zone this paper is focused on the processes occurring within the beach the measurements provide the shape of the wetting front and the groundwater table and reveal the behavior of air in the unsaturated region of the beach air is initially at atmospheric pressure but the pressure builds up when air becomes encapsulated between the saturated region formed below the swash and the groundwater table for the 1 5 mm beach entrapped air significantly affected the water exchange between the swash and the subsurface the considerable buildup of interstitial air pressure reduced vertical hydraulic gradients and thus infiltration rates at the lower end of the beach the hydraulic gradients even became negative indicating flow reversal and exfiltration in contrast for the 8 5 mm beach the rate of infiltration was only slightly affected by the buildup of pore air pressure the vertical hydraulic gradients were more than twice the magnitude of those within the 1 5 mm beach the results presented in the paper clarify the mechanisms that drive and impede the water exchange between the surface and subsurface flow in particular infiltration into the initially unsaturated part of the beach and the resulting air entrapment play a significant role in swash and similar flows

rans v2 f simulation of a swash event detailed flow structure the flow structure of a swash event over a uniform slope is studied using a rans vof numerical model coupled with a v2 f turbulence closure the model is compared with experimental data of recent laboratory experiments the ability of the turbulence modelling for simulating swash flow and the evolution of the computed bed shear stress during run up and run down are investigated the agreement between numerical results and measured data such as water depth depth averaged velocity and bed shear stress is very good during run up main discrepancies are found during run down the paper also examines the aeration of the water layer in the swash flow taking advantage of the plic method for computing the air water interfaces air is continuously entrapped in the swash front and released at its rear during run up a detailed analysis indicates that the flow reversal is initiated near the bottom at the outer boundary of the swash zone and progresses landward the study highlights the asymmetry between run up and run down during run up the swash front propagation determines the turbulence properties and the bed shear stress profile on the beach whereas the flow properties are more homogeneously distributed in the swash area during run down

laboratory and numerical study of dambreak generated swash on impermeable slopes new laboratory experiments have produced detailed measurements of hydrodynamics within swash generated by bore collapse on a steep beach the experiments are based on a dambreak rig producing a highly repeatable large scale swash event enabling detailed measurements of depths and velocities at a number of locations across the swash zone experiments were conducted on two beaches differentiated by roughness results are presented for uprush shoreline motion flow depths depth averaged velocity velocity profiles and turbulence intensity estimates of the time and spatially varying bed shear stress are obtained via log law fitting to the velocity profiles and are compared with the shear plate measurements of barnes et al 2009 for similar experimental conditions experimental results are compared with model predictions based on a nlswe model with momentum loss parameterised using the simple quadratic stress law in terms of the depth averaged velocity predicted and measured flow depths and depth averaged velocities agree reasonably well for much of the swash period but agreement is not good at the time of bore arrival and towards the end of the backwash the parameterisation of total momentum loss via the quadratic stress law cannot adequately model the swash bed shear stress at these critical times

flow velocity and sediment transport in the swash zone of a steep beach detailed measurements of flow velocity and total sediment load were obtained in the swash zone on a steep beach swash motion was measured using ducted impeller flow meters and capacitance water level probes during wave uprush the onshore flow increased almost instantaneously from zero to its maximum velocity after the arrival of the leading edge of the swash lens and subsequently decreased gradually to zero for the remainder of the uprush during backwash the offshore flow increased steadily from zero to its maximum towards the end of the backwash and dropped rapidly to zero as the beach fell dry the duration of backwash was typically longer than that of uprush and maximum water depth on the beach was attained just prior to the end of the uprush the total sediment load was measured for 35 individual wave uprush events using a sediment trap the amount of sediment transported by a single uprush was typically two to three orders of magnitude greater than the net transport per swash cycle difference between uprush and backwash inferred from surveys of beach profile change the measured immersed weight total load transport rate displayed a strong relationship with the time averaged velocity cubed which is consistent with equations for both bedload transport and total load transport under sheet flow conditions the bagnold 1963 1966 bedload transport model was tested against our field data and yielded ib ku3tu tan tan where ib is the immersed weight of bedload transported during the entire uprush kg m 1 k is a coefficient kg m 4 s2 u is the time averaged flow velocity for the uprush m s 1 tu is the uprush duration s is the friction angle of the sediment and is the beach slope the empirically determined value for the coefficient k was 1 37 0 17

large eddy simulation of dam break driven swash on a rough planar beach turbulence characteristics in the swash zone are investigated using a 3d large eddy simulation model the numerical model is implemented based on openfoam which solves the filtered navier stokes equations for two immiscible fluids with a standard smagorinsky sub grid scale closure the numerical model is validated with laboratory data for swash flow driven by a dam break apparatus the model results demonstrate that the main characteristics of turbulence in the swash zone are different from those in the surf zone which are mainly induced by surface wave breaking during uprush phase bore generated turbulence has 2d turbulence characteristics because of limited water depth near bed generated turbulence is mainly observed during backwash turbulence production and turbulent dissipation rate estimated from the model results indicate an imbalance possibly due to advection at swash front and large roughness used touching down of turbulent coherent structure tcs is observed during uprush which drives intense bed shear stress during the backwash interaction between tcs and bed is less clear however finger like patterns in the spatial extent of bed shear stress and vertical components of vorticity are predicted during the backwash the location of the strongest finger patterns in the vertical direction is collocated with that of maximum turbulence production these finger patterns are likely caused by boundary layer instabilities injected vertically from the bed this article is protected by copyright all rights reserved

flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well sorted and graded sands oscillatory flow tunnel measurements of velocities and fluxes for sands in oscillatory sheet flow conditions are presented the experiments involved a range of well sorted and graded sands in two asymmetric flows velocities were measured using an ultrasonic velocity profiler uvp capable of measuring deep within the sheet flow layer velocity profiles are found to be similar for the same flow but different sand beds and display expected features of oscillatory boundary layer flow the near bed velocity leads the main flow velocity by approximately 21 and a small offshore directed current is generated near the bed measures of the boundary layer thickness are in good agreement with those predicted using an equation formulated for the boundary layer thickness over fixed beds velocity data have been combined with concentration data to produce time dependent sand flux profiles covering the sheet flow and suspension regions there are fundamental differences in the transport processes of sands of different size and grading caused by unsteady effects which dominate in the case of fine sand and are largely absent in the case of coarse sand 1 time averaged flux is onshore directed positive in the case of coarse sand and is confined to a region immediately above the bed in contrast time averaged flux in the case of fine sand extends high above the bed is offshore directed negative in the sheet flow layer and becomes onshore directed in the suspension layer 2 net transport in the case of coarse sand is directed onshore as the percentage of fine sand in the bed increases offshore transport becomes increasingly dominant as the percentage of fine sand increases 3 net transport in the suspension layer is onshore while net transport in the sheet flow layer may be onshore or offshore depending on sand size and grading

non linear shallow water modelling of bore driven swash description of the bottom boundary layer abstract the paper presents a simple approach to estimate the bottom shear stress in the swash zone by coupling the non linear shallow water equations with the momentum integral equation for the bottom boundary layer the approach allows not only the computation of the frictional dissipation term in the equations but also to have an insight into the flow structure in the water column during a swash event the numerical results have been compared with a new set of experiments involving a single dam break generated swash event three different grain sizes ranging from coarse sand to gravel have been tested in the laboratory a sensitivity analysis on the only calibration parameter of the model the bed roughness is presented and its optimal value is chosen the numerically predicted free surface depth averaged velocity and velocity profiles have been compared with the measured ones results are very good in the run up stage where also the bottom shear stress is well modelled in the backwash the frictional energy dissipation is better modelled for the gravel beach than for the coarse sand one results show that the simple model accurately predicts the flow parameters during the swash event also the velocity profiles are reasonably well predicted especially during the run up

sediment transport partitioning in the swash zone of a large scale laboratory beach abstract swash zone sheet flow and suspended sediment transport rates are estimated on a coarse sand beach constructed in a large scale laboratory wave flume three test cases under monochromatic waves with wave heights of 0 74 m and wave periods of 8 and 12 2 s were analyzed sediment flux in the sheet flow layer exceeds several hundred kg m 2 s 1 during both uprush and backwash suspended sediment flux is large during uprush and can exceed 200 kg m 2 s 1 instantaneous sediment flux magnitudes in the sheet layer are nearly always larger than those for suspended sediment flux however sediment transport rates those integrated over depth indicate that suspended load transport is dominant during uprush for all cases and during the early stages of backwash except in the case for the 12 2 s wave case when the foreshore was steeper results could not be obtained for an entire swash event and were particularly truncated during backwash when water depths fell below the elevation of the lowest current meter

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

an integral swash zone model with friction an experimental and numerical investigation abstract experimental and numerical analyses have been used to assess the validity and potentialities of the integral swash zone model by brocchini and peregrine proc coastal dynamics 95 asce 1 1996 221 which is extended to include seabed friction effects previously neglected applications of the model to experimental data show it represents a simple and useful tool for modelling swash zone flows the model allows for computation of integral swash zone properties and shoreline motion from local variables defined at the seaward limit of the swash for most properties correlation between local and integral properties is very good correlation coefficient about 0 80 a suitable parametric form of frictional forces in the swash zone is defined on the basis of both experimental data and analytical investigation numerical tests showed that the proposed parameterization models well integral frictional forces within the swash zone the parametric friction force improves capabilities of the integral swash zone model of representing real swash motions this is particularly evident when considering the momentum equation the correlation coefficient between the rate of change of the onshore momentum in the swash zone and its forcings increases from about 0 85 to about 0 95 due to the inclusion of the seabed friction

enhanced deformation of limestone and sandstone in the presence of high fluids 1 geological repositories subject to the injection of large amounts of anthropogenic carbon dioxide will undergo chemical and mechanical instabilities for which there are currently little experimental data this study reports on experiments where low and high 8 mpa aqueous fluids were injected into natural rock samples the experiments were performed in flow through triaxial cells where the vertical and confining stresses temperature and pressure and composition of the fluid were separately controlled and monitored the axial vertical strains of two limestones and one sandstone were continuously measured during separate experiments for several months with a strain rate resolution of 10 11 s 1 fluids exiting the triaxial cells were continuously collected and their compositions analyzed the high fluids induced an increase in strain rates of the limestones by up to a factor of 5 compared to the low fluids injection of high fluids into the sandstone resulted in deformation rates one order of magnitude smaller than the limestones the creep accelerating effect of high fluids with respect to the limestones was mainly due to the acidification of the injected fluids resulting in a significant increase in solubility and reaction kinetics of calcite compared to the limestones the much weaker response of the sandstone was due to the much lower solubility and reactivity of quartz in high fluids in general all samples showed a positive correlation between fluid flow rate and strain rate x ray tomography results revealed significant increases in porosity at the inlet portion of each core the porosity increases were dependent on the original lithological structure and composition the overall deformation of the samples is interpreted in terms of simultaneous dissolution reactions in pore spaces and intergranular pressure solution creep

boundary layer dynamics in the swash zone under large scale laboratory conditions this paper presents the results of a laboratory experiment of swash hydrodynamics on a coarse sand barrier beach backed by a lagoon boundary layer dynamics have been analyzed using the high resolution near bed velocities measured by acoustic doppler velocity profilers deployed in the swash zone swash events have been ensemble averaged in order to study mean hydrodynamic patterns a proposed velocity gradient criterion allowed identification of the boundary layer growth during the backwash phase but it was unable to characterize boundary layer variability during uprush cross shore velocity profiles were well represented by the logarithmic model for a large portion of the ensemble averaged swash duration uprush and backwash logarithmic estimated friction factors were of the same order of magnitude with a strong variability related to the boundary layer growth during the backwash the momentum integral method provided smaller bed shear stresses than the logarithmic model a result possibly related to either the assumptions involved in the momentum integral method or to an underestimation of the boundary layer thickness during uprush a decrease of friction coefficients for increasing reynolds numbers at the early backwash was observed this behavior is consistent with traditional results for steady and uniform flows in a transitional regime