groundwater fluxes and flow paths within coastal barriers observations from a large scale laboratory experiment bardex ii abstract the dynamics of groundwater at the beach face land ocean boundary have important implications to the exchange of water nutrients and pollutants between the ocean and coastal aquifers and more subtly varying groundwater levels may induce differing morphological response at the beach face as a component of the multi institution barrier dynamics experiment bardex ii groundwater fluxes and flow paths within a prototype scale sandy barrier are quantified and reported at the three fundamental spatio temporal scales individual waves the beach face and total barrier under controlled wave and water level conditions a particular feature of the experimental programme was the inclusion of a back barrier lagoon that via a pump system and an intermediate water reservoir enabled the forcing of contrasting hydraulic gradients across the barrier it was observed that the groundwater level flow paths and fluxes within the beach face region of the sand barrier were predominantly controlled by the action of waves at the beach face regardless of the overall seaward or landward directed barrier scale hydraulic gradients in the presence of waves all tests undertaken to complete this study developed a seaward gradient in this zone under the influence of waves as a further result of wave forcing at the beach face boundary localised groundwater flow divides were observed to develop further partitioning the circulation and flow paths of groundwater within the prototype scale sand barrier

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

field observations of the fluid granular boundary layer under near breaking waves numerous synchronized time series from video cameras pressure sensors current meters and hot film anemometers on natural beaches show that boundary layer development under the crest of near breaking waves can be idealized as a process composed of three distinct regimes here referred to as streaking roiling and pluming the roiling and pluming regimes fail to develop under the trough as a consequence there is a pronounced asymmetry in instantaneous sand transport and boundary layer phenomena between the wave crest and trough however laboratory waves with field scale periods and wave heights over thin sand beds do not exhibit this crest trough boundary layer asymmetry indicating that a critical element of similitude is absent in laboratory experiments we suggest that wave induced boundary ventilation is responsible

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

estimating swash zone friction coefficients on a sandy beach abstract video based swash motions from three studies on two separate beaches were analyzed with respect to theoretical swash trajectories assuming plane beach ballistic motions under quadratic friction friction coefficient values for both the uprush and backwash were estimated by comparing measured swash space time trajectories to these theoretical expectations given an initial velocity and beach slope observations were made spanning high tides and in one case during a light rain analysis of over 4500 individual swash events showed that the uprush friction coefficient was nearly constant during all three studies with a mean value of roughly 0 007 and showed no trends over a tidal cycle in contrast backwash friction coefficient values varied over the tidal cycles ranging between 0 01 and 0 07 with minimum values corresponding to the highest tides although these values are close to the theoretical estimates based on a law of the wall formulation and values commonly referenced in the literature these observations show a consistent tendency for backwash friction estimates to greatly exceed uprush friction estimates the disparity between uprush and backwash friction coefficients can be partially attributed to the exclusion of a pressure gradient term in the ballistic model however results indicate that backwash friction coefficients adjusted to account for this effect may be three times larger than the uprush friction values during lower tides this tidal dependence for backwash friction coefficients is attributed to a complex interaction between swash infiltration and entrained sediment loads these findings imply that friction estimates necessary for sediment transport calculations and hydrodynamic predictions based solely on grain roughness may not be correct for backwash flows

numerical simulation of swash zone fluid accelerations 1 a volume of fluid navier stokes solver incorporating a k closure model numerical water flume newflume lin and xu 2005 is used to investigate the temporal and spatial structure of accelerations in the swash zone of steep beaches for surging plunging and nearly spilling waves simulations for idealized swash over planar slopes show that shoreward directed local accelerations exist only for up to 22 of the swash cycle depending on wave type in general shoreward directed local accelerations were predicted to occur only near the wave run down limit baldock and holmes 1997 similarly convective accelerations had the largest magnitudes during this time and tended to be either near zero or shoreward directed for the remainder of the swash cycle this finding is in direct contrast to a modified ballistic theory for swash motion arising as a particular solution to the depth averaged nonlinear shallow water equations peregrine and williams 2001 that predicts the convective acceleration maintains the sign of the fluid velocity near bed pressure gradients are found to be poorly correlated to both the depth averaged and near bed local acceleration these numerical findings indicate that local fluid accelerations are not a proxy for pressure gradients in the swash zone for enhanced sediment transporting mechanisms or parameterizations however the numerical results require corroboration with highly resolved swash zone data

near bed cross shore velocity profiles bed shear stress and friction on the foreshore of a microtidal beach abstract new high resolution acoustic doppler current profilers are used to quantify the vertical structure of cross shore fluid velocities in the very inner surf and swash zones on two west central florida beaches field data are collected at an unprecedented 0 001 m vertical resolution over the lower 0 02 m of the water column and at up to 100 hz swash events defined based on the timing of sensor submergence and emergence and inner surf zone flow cycles defined based on the timing of zero upcrossings are normalized around flow reversal and ensemble averaged to investigate the vertical profiles of cross shore flow the ensemble averaged cross shore velocity profile is generally well represented by the logarithmic model r2 0 9 within 0 02 m of the bed the maximum elevation over which the model was applied the logarithmic model fails near flow reversal when velocities are weak friction velocities are used to estimate the corresponding bed shear stress with maximum values of 6 45 and 4 25 n m 2 for swash events and inner surf zone wave cycles respectively friction coefficient estimates adopting the quadratic drag law and the velocity at 0 02 m above the bed are 0 024 0 008 and 0 022 0 007 mean standard deviation for onshore directed motion and 0 034 0 005 and 0 027 0 006 for offshore directed motion for swash zone events and inner surf zone flow cycles respectively

sediment suspension events in the inner surf and swash zone measurements in large scale and high energy wave conditions abstract the present study presents a database of hydrodynamic properties and suspended sediment concentration collected within the inner surf and swash zones aiming to improve the current understanding of the sediment dynamics occurring within the beach area closest to the shoreline experimental measurements were conducted in a large scale wave flume under high energy wave conditions at three cross shore locations representing inner surf and swash zone conditions 47 tests each one comprising 500 wave trains with identical wave conditions were measured obtained hydrodynamic properties and suspended sediment concentrations were observed to be highly repeatable between successive tests despite the sediment suspension event like pattern the beach evolution between tests and the apparent randomness of the sediment suspension phenomenon the hydrodynamics close to the shoreline inner surf and swash zone is dominated by short incident broken waves and long wave water level oscillations induced by wave grouping the analyzed time series of measured water surface elevation horizontal velocity computed turbulent kinetic energy tke and sediment concentration revealed that the suspended sediment concentration in this coastal zone does not correlate strongly with either the incident bore height or the short wave horizontal velocity or the tke in other words high low values of these variables do not always promote high low values of sediment suspension in contrast the highest suspended sediment concentrations were observed to occur by the combined action of incident bores and the trough of long period water level oscillations this pattern was more apparent in the inner surf than in the swash zone high suspended sediment concentrations were also observed to coincide with negative peaks in long wave horizontal velocity modulation resulting in enhanced negative sediment transport rates and beach erosion close to the shoreline

eulerian flow velocities in the swash zone field data and model predictions measurements of eulerian flow velocity obtained within the swash zone on a relatively steep beach face gradient 1 23 are compared with an extended ballistic swash model the model only requires a friction factor beach slope and terminal bore velocity as input the following model predictions matched well with observations 1 the maximum eulerian flow velocity is the shoreline velocity when it arrives at the fixed point of interest on the beach face 2 at any location the time of flow reversal occurs prior to the shoreline reaching its maximum landward excursion 3 the maximum flow velocity in the backwash is the velocity recorded as the shoreline recedes past the fixed point of interest and this is less than the maximum uprush velocity and 4 the duration of the uprush flow is shorter than the duration of the backwash flow previous studies have already confirmed that the ballistic swash model including friction can accurately predict shoreline motion and maximum run up on steep beaches this study shows that it is similarly successful in predicting eulerian flow velocities during individual swash events the model does not presently account for interacting swash however and so may be less appropriate on gently sloping beaches

large scale laboratory investigation into the effect of varying back barrier lagoon water levels on gravel beach morphology and swash zone sediment transport abstract it is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea specifically a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion while the reverse is thought to hold for a high beach groundwater table here we use the results of a carefully designed series of tests conducted in the delta flume the netherlands as part of the barrier dynamics experiment bardex to unequivocally demonstrate the validity of this assertion during the experiment a 4 m high and 50 m long gravel barrier d 50 11 mm was constructed within the central region of the 250 m long and 7 m deep wave flume enabling a back barrier lagoon to be located at its landward side the groundwater table in the beach was manipulated by lowering and raising the lagoon level and the gravel beach was subjected to variable wave conditions and sea lagoon levels using as the initial beach profile the morphology resulting from 90 min of wave forcing with the sea and lagoon at the same level the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion the divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the bulk swash hydrodynamics i e based on single point velocity measurements arising from a difference in the amount of swash infiltration into the unsaturated beach instead application of a sediment transport model that accounts for the effects of in exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface due to the large hydraulic conductivity of gravel k o 0 1 m s 1 the effect of altered shear stresses due to in exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches

modeling swash zone hydrodynamics and shear stresses on planar slopes using reynolds averaged navier stokes equations 1 a numerical model solving the reynolds averaged navier stokes equations with a volume of fluid tracking scheme and turbulence closure is employed for estimating hydrodynamics in the swash zone model results for run up distance water depth and near bed velocity are highly correlated r2 0 97 with ensemble averaged dam break driven swash data moreover modeled bed shear stresses are within 20 of estimates derived from measured velocity profiles dam break driven swash simulations are conducted to determine the effect of foreshore characteristics bed roughness and foreshore slope on bore induced swash zone hydrodynamics and bed shear stresses numerical results revealed that the boundary layer vanishes during flow reversal grows during the backwash and becomes depth limited at the end of the swash cycle in general the uprush experiences larger shear stresses but for a shorter duration than the backwash some variability in this pattern is observed depending on the bed roughness foreshore slope and cross slope location in the swash zone implying that large spatial gradients in shear stresses can occur on the foreshore the mean tangential force per unit area supplied to the bed is offshore directed for the simulated cases with the exception of the mild slope 1 25 cases owing to the skewed nature of swash flows the temporal evolution of the momentum balance inside the swash zone shows an important contribution to the total force from turbulence and advection at the early final stage of the swash cycle whereas the local acceleration does not appear to be a significant contribution

the influence of seaward boundary conditions on swash zone hydrodynamics abstract the influence of the seaward boundary condition on the internal swash hydrodynamics is investigated new numerical solutions of the characteristics form of the nonlinear shallow water equations are presented and applied to describe the swash hydrodynamics forced by breaking wave run up on a plane beach the solutions depend on the specification of characteristic variables on the seaward boundary of the swash zone equivalent to prescribing the flow depth or the flow velocity it is shown that the analytical solution of shen and meyer shen m c meyer r e 1963 climb of a bore on a beach part 3 runup j fluid mech 16 113 125 is a special case of the many possible solutions that can describe the swash flow but one that does not appear appropriate for practical application for real waves the physical significance of the boundary conditions is shown by writing the volume and momentum fluxes in terms of the characteristic variables results are presented that illustrate the dependence of internal flow depth and velocity on the boundary condition this implies that the internal swash hydrodynamics depend on the shape and wavelength of the incident bore which differs from the hydrodynamic similarity inherent in the analytical solution a solution appropriate for long bores is compared to laboratory data to illustrate the difference from the analytical solution the results are important in terms of determining overwash flows flow forces and sediment dynamics in the run up zone

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

the impact of zircon garnet ree distribution data on the interpretation of zircon u pb ages in complex high grade terrains an example from the rauer islands east antarctica abstract the responsiveness of zircon to granulite metamorphism and post peak fluid infiltration in polymetamorphic terranes has been investigated utilising a case study from the rauer islands of east antarctica imaging bse cl textural analysis in situ ion microprobe trace element analysis of zircon garnet orthopyroxene plagioclase and apatite and ion microprobe oxygen isotope analysis of zircon have been integrated to establish the event significance of c 510 ma zircon age domains that occur within and on c 2840 ma protolith magmatic zircons initial magmatic zircon is characterised by moderate th u 0 4 0 6 and elevated steep hree yb n gd n 20 c 510 ma zircon domains feature lobate cuspate and planar bse and cl zones that have lower th u to 0 05 and either decreased mree or decreased mree and hree metamorphic garnet initially characterised by flat hree shows extensive replacement by orthopyroxene and plagioclase accompanied by near rim increases in hree to values that are consistent with equilibrium between garnet rims and product orthopyroxene zircon garnet mree hree distribution coefficients d ree calculated using compositions of modified zircon domains coupled with both initial metamorphic garnet cores and rims are far removed from presently accepted equilibrium values with the zircon mree being strongly depleted relative to garnet these d ree indicate that the observed modification of zircon did not occur in response to the major high grade metamorphic events recorded in the studied rock mineralogy but instead occurred after the high grade metamorphism the zircon was blind to these metamorphic events but instead was responsive to a later post peak fluid infiltration episode that shifted zircon 18 o values downwards by some 3 the likelihood of blind or unresponsive behaviour of zircon to high grade metamorphism must be considered when reconstructing crustal histories and terrane scenarios based on u pb age data and tested for using an integrated approach that includes in situ ree and other trace element analysis of zircon and its potentially coexisting minerals

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

librations of the galilean satellites the influence of global internal liquid layers the four galilean satellites are thought to harbor one or even two global internal liquid layers beneath their surface layer the iron core of lo and ganymede is most likely partially liquid and also the core of europa may be liquid furthermore there are strong indications for the existence of a subsurface ocean in europa ganymede and callisto here we investigate whether libration observations can be used to prove the existence of these liquid layers and to constrain the thickness of the overlying solid layers for lo the presence of a small liquid core increases the libration of the mantle by a few percent with respect to an entirely solid lo and mantle libration observations could be used to determine the mantle thickness with a precision of several tens of kilometers given that the libration amplitude can be measured with a precision of 1 m for europa ganymede and callisto the presence of a water ocean close to the surface increases by at least an order of magnitude the ice shell libration amplitude with respect to an entirely solid satellite the shell libration depends essentially on the shell thickness and to a minor extent on the density difference between the ocean and the ice shell the possible presence of a liquid core inside europa and ganymede has no noticeable influence on their shell libration for a precision of several meters on the libration measurements in agreement with the expected accuracy with the nasa esa ejsm orbiter mission to europa and ganymede an error on the shell thickness of a few tens kilometers is expected therefore libration measurements can be used to detect liquid layers such as lo s core or water subsurface oceans in europa ganymede and callisto and to constrain the thickness of the overlying solid surface layers c 2010 elsevier inc all rights reserved

bed level fluctuations in the inner surf and swash zone of a dissipative beach abstract a field study was conducted on a dissipative beach to quantify inner surf and swash zone bed level change during periods of inundation and throughout a tidal cycle elevation changes were acquired at millimeter resolution with a new conductivity concentration profiler that allowed quantification of the bed level throughout the duration of the wave swash cycle and also during periods of bed exposure bed level change spectra showed the highest energy at low frequencies even though event scale net bed level changes were observed to exceed the tidal scale net bed level change net bed level change for individual events was nearly normally distributed with most individual events displaying little or no net bed level change large erosion and accretion events with bed level elevation magnitudes that exceeded net tidal elevation change occurred with similar frequency the similarity between the frequency of large erosion and large accretion events suggests that a few events may be ultimately responsible for the observed net elevation change over the tidal cycle the large events displayed different hydrodynamic characteristics erosion events had longer duration onshore directed flow and higher maximum onshore directed velocity magnitude than offshore directed velocity magnitude the opposite was found for accretion events that had longer duration offshore directed flow and a higher maximum offshore directed velocity magnitude than onshore directed velocity magnitude

suspended sediment transport in the swash zone of a dissipative beach abstract simultaneous high frequency field measurements of water depth flow velocity and suspended sediment concentration were made at three fixed locations across the high tide swash and inner surf zones of a dissipative beach the dominant period of the swash motion was 30 50 s and the results are representative of infragravity swash motion suspended sediment concentrations loads and transport rates in the swash zone were almost one order of magnitude greater than in the inner surf zone the vertical velocity gradient near the bed and the resulting bed shear stress at the start of the uprush was significantly larger than that at the end of the backwash despite similar flow velocities this suggests that the bed friction during the uprush was approximately twice that during the backwash the suspended sediment profile in the swash zone can be described reasonably well by an exponential shape with a mixing length scale of 0 02 0 03 m the suspended sediment transport flux measured in the swash zone was related to the bed shear stress through the shields parameter if the bed shear stress is derived from the vertical velocity gradient the proportionality coefficient between shear stress and sediment transport rate is similar for the uprush and the backwash if the bed shear stress is estimated using the free stream flow velocity and a constant friction factor the proportionality factor for the uprush is approximately twice that of the backwash it is suggested that the uprush is a more efficient transporter of sediment than the backwash because the larger friction factor during the uprush causes larger bed shear stresses for a given free stream velocity this increased transport competency of the uprush is necessary for maintaining the beach otherwise the comparable strength and greater duration of the backwash would progressively remove sediment from the beach

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

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 suspension and turbulence in the swash zone of dissipative beaches abstract this paper investigates mechanisms for stirring and transport of suspended sediment by infragravity scale swash using high frequency field measurements of horizontal and vertical flow velocities water depths and sediment concentration profiles the field data suggest that vertical velocity fluctuations generated by coherent eddies can be important to the process of sediment suspension and can contribute to asymmetrically distributed sediment transport rates between the uprush and backwash phases of the swash cycle this result indicates that the traditional and often used proxy for bed shear stress based solely on measurements of the horizontal component of flow u i e b fu 2 where is the water density and f is a friction factor may be inadequate when used in energetics type sediment transport models applied to the swash which is indeed the case we demonstrate that a bed shear stress formulation which is more consistent with the physics leads to improved predictive capability for energetics type transport models this formulation is based on the correlation between the horizontal and turbulent vertical components of the flow i e b uw despite the improvement it is evident that considerable amounts of calibration data are still required before each application of this model type moreover our data shows that the issue of calibration coefficients is more problematic than generally appreciated the calibration coefficients for energetics type models on a given beach not only differ between uprush and backwash but also vary with position within the swash zone particularly on the uprush phase

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

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

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