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

on vertical advection truncation errors in terrain following numerical models comparison to a laboratory model for upwelling over submarine canyons 1 submarine canyons which indent the continental shelf are frequently regions of steep up to 45 three dimensional topography recent observations have delineated the flow over several submarine canyons during 2 4 day long upwelling episodes thus upwelling episodes over submarine canyons provide an excellent flow regime for evaluating numerical and physical models here we compare a physical and numerical model simulation of an upwelling event over a simplified submarine canyon the numerical model being evaluated is a version of the s coordinate rutgers university model scrum careful matching between the models is necessary for a stringent comparison results show a poor comparison for the homogeneous case due to nonhydrostatic effects in the laboratory model results for the stratified case are better but show a systematic difference between the numerical results and laboratory results this difference is shown not to be due to nonhydrostatic effects rather the difference is due to truncation errors in the calculation of the vertical advection of density in the numerical model the calculation is inaccurate due to the terrain following coordinates combined with a strong vertical gradient in density vertical shear in the horizontal velocity and topography with strong curvature

coastal processes and the development of shoreline erosion in 1971 the us army corps of engineers inventoried the stability of the nation s coastlines concluding in their final summary a report on the national shoreline study that of the 135 000 km of coastline some 33 000 km were seriously eroding more recently dolan et al 1983 assembled the existing data on shoreline changes for the united states reaffirming the magnitude of this problem although such inventories have not been undertaken for the entire world s shorelines coastal erosion is undoubtedly a global problem beach erosion is for the most part episodic with the major retreats in the shoreline occurring during unusually intense storms on the east coast of the united states beach erosion and property losses are produced by nor easters and hurricanes on the west coast intense storms move down from the gulf of alaska generating waves that attack the coastline this obvious association of beach erosion with the energy level of storm waves creates an oversimplified impression of the actual physical processes involved in the erosion only recently have we begun to understand and appreciatc the diversity of processes that are actually involved in coastal erosion it is now recognized that long period oscillations may dominate water motions in the nearshore sometimes containing more energy than the storm generated waves these oscillations as well as a variety of nearshore currents rearrange the beach sand to cause highly variable rates of shoreline retreat along even short stretches of beach although the long term rise in sea level has been recognized as an important factor in shoreline

field observations of swash zone infragravity motions and beach cusp evolution 1 fluid flows consistent with low mode edge waves were evident in video observations of swash motions during a field experiment in which beach cusps developed on an initially smooth beach as beach cusps grew energy lying along low mode dispersion curves increased the most energetic edge wave propagation direction changed from upcoast to downcoast as the orientation of the cusp horns rotated these observations suggest a coupling between morphodynamics and hydrodynamics and are evidence that beach cusp evolution might control low mode edge wave dynamics

observations of beach cusp evolution at melbourne beach florida usa abstract morphological observations terrestrial laser scanning and sediment analysis are used to study beach cusp morphodynamics at melbourne beach florida usa a moderately sloped beach characterized by fine sand the study couples rapid high resolution surveying with surficial sediment sampling over multiple tidal cycles surveys were run 500 m alongshore and sediment samples were collected intertidally over a period of 5 days beach cusp location within larger scale beach morphology is shown to directly influence cusp growth as either gross erosional or gross accretional sediment characteristics within the beach cusp morphology are reported coincident with cusp evolution variations in particle size distribution kurtosis are exhibited as the cusps evolve however no significant correlation is seen between grain size and position between horn and embayment during the end of the study a storm resulted in beach cusp destruction and increased sediment sorting

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

the influence of beach porosity on wave uprush and backwash abstract packwood a r 1983 the influence of beach porosity on wave uprush and backwash coastal eng 7 29 40 a numerical model is described to calculate the influence of a porous bed on the run up of a bore on a gently sloping sandy beach it is shown that fine medium grade sands have very little effect in the run up phase significant differences between impermeable and porous bed solutions are found in the backwash which might explain certain sand erosion and deposition phenomena

a primitive equation ocean circulation model using a general vertical coordinate transformation 1 description and testing of the model the ocean general circulation model of the geophysical fluid dynamics laboratory has been modified to accommodate a generalized vertical coordinate transformation the model with a slightly modified transformation z h is applied to three simple test cases a clear improvement of barotropic and baroclinic topographic rossby waves has been achieved compared with the z coordinate model a somewhat more typical time independent problem for the overflow of dense water masses over a zonal ridge exhibits the potential benefits as well as the flaws of the new model vertically integrated mass transport is very sensitive to changes in bottom slope in regions where planetary and topographic are of comparable magnitudes this translates into large errors in the z model due to the crude approximation to the actual topography the deep flow in the z model does not follow the bottom exactly horizontal overshoots of dense water lead to convective mixing on the southern side of the ridge this can be a serious problem for modeling more realistic overflow situations with the z model increased diapycnal diffusion has been identified as the most serious problem with the terrain following coordinate system for this specific application

the origin of swash cusps on beaches abstract genetically there are two types of beach cusps those formed in the surfzone by the nearshore circulation system and those formed on the beachface by the swash and backwash the latter are here called swash cusps and a simple model relating the physical dimensions of swash cusps to the properties of the incident wave field and the mean beach slope is developed as in some previous models the cusp wavelength is controlled by the longshore wavelength of edge waves but the edge waves are now required only to provide small periodic perturbations on an originally uniform beach further cusp growth occurs because of the interactions between the incident waves and the perturbed topography the maximum cusp height apex to valley is hypothesized to be proportional to the significant vertical excursion of swash motions it follows from the above assumptions that the maximum possible cusp steepness cusp height cusp longshore wavelength is proportional to the mean on offshore beach slope this result agrees with field data and the value of the ratio of maximum cusp height to beach slope differs from that obtained theoretically by guza and bowen 1981 using a complicated non linear model with rather different physics the present model implies that edge waves although necessary for initiating the initial bedform perturbation need not persist for the development of mature cusp topography

simulation and prediction of swash oscillations on a steep beach this paper presents numerical simulations and analytical predictions of key aspects of swash oscillations on a steep beach simulations of the shoreline displacement based on bore run up theory are found to give excellent agreement with recent experimental data for regular waves wave groups and random waves the theory is used to derive parameters that predict the onset of swash saturation and the spectral characteristics of the saturated shoreline motion these parameters are again in good agreement with the measured laboratory data and are also consistent with previous experimental data simulation of irregular wave run up using a series of overlapping monochromatic swash events is found to reproduce typical features of swash oscillations and can accurately describe both the low and high frequency spectral characteristics of the swash zone in particular the low frequency components of the run up can be modelled directly using a sequence of incident short wave bores with no direct long wave input to the numerical simulations this suggests that wave groupiness must be accounted for when modelling shoreline oscillations

morphological evolution of beach cusps and associated swash circulation patterns abstract a numerical model capable of simulating the motion of water particles on beach cusp morphology under the influence of an initial velocity and gravity is presented the model indicates that the typical swash pattern on beach cusps is three dimensional with wave uprush diverging at the cusp horns resulting in concentrated backwash streams in the embayment the degree of horn divergence is an increasing function of the parameter e s 2 where e quantifies the prominence of the beach cusps s is the horizontal swash excursion length and is the cusp spacing the numerical experiments are supplemented with detailed field measurements of beach cusp morphological change the field data include three types of morphological response each characterised by a particular pattern of swash circulation that can be delineated using e s 2 when e s 2 beach cusp morphology is large and or subdued in relation to the swash length swash circulation is essentially two dimensional oscillatory flow and results in steepening of the beachface and infilling of the cusp embayments for e s 2 0 015 to 0 15 wave uprush is deflected from the cusp horns and flows into the embayments where it exits in a concentrated backwash stream horn divergent flow the ensuing swash backwash inequality reinforces cusp development and maintains existing cusp morphology when e s 2 0 15 beach cusps are small and or pronounced in relation to the length of the swash overtopping and ponding of the cusp horn takes place and swash circulation is from the embayment to the horn horn convergent flow as a result cusp horns are eroded and accretion occurs in the embayments

on the pressure gradient force over steep topography in sigma coordinate ocean models abstract the error in computing the pressure gradient force near steep topography using terms following coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by arakawa and suarez the truncation error is estimated by substituting known buoyancy profiles into the finite difference hydrostatic and pressure gradient terms the error due to hydrostatic inconsistency which is not simply a space truncation error is also documented the results show that the pressure gradient error is spread throughout the water column and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled removing a reference state as suggested for the atmosphere by gary reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3 as an example the error in computing the pressure gradient using a standard 10 level primitive equation model appl

a numerical experiment on nearshore circulation in standing edge waves abstract the unsteady shallow water vorticity equation dominating nearshore flow on a gently sloping plane beach has been solved by using the implicit finite difference technique under the assumption of constant viscosity over the flow field the result of computation showed that pairs of nearshore circulation cells are generated through the nonlinear effect of flow in the boundary layer formed by the run up movement of a standing edge wave along a shoreline and the paired cell has the spacing of half a wavelength of the edge wave when the leaky mode standing wave of lamb with the same wave period as the edge wave and the wave crest parallel to a shoreline was superposed on the edge wave field the alongshore spacing of circulation cell doubled and seaward flow in the cell concentrated in the narrow zone like a rip current although no effect of breaking waves is considered in the computation such a mechanism may also generate some kinds of nearshore circulation systems observed in a sea

well balanced and flexible morphological modeling of swash hydrodynamics and sediment transport abstract existing numerical models of the swash zone are relatively inflexible in dealing with sediment transport due to a high dependence of the deployed numerical schemes on empirical sediment transport relations moreover these models are usually not well balanced meaning they are unable to correctly simulate quiescent flow here a well balanced and flexible morphological model for the swash zone is presented the nonlinear shallow water equations and the exner equation are discretized by the shock capturing finite volume method in which the numerical flux and the bed slope source term are estimated by a well balanced version of the slic slope limited centered scheme that does not depend on empirical sediment transport relations the satisfaction of the well balanced property is demonstrated through simulating quiescent coastal flow the quantitative accuracy of the model in reproducing key parameters i e the notional shoreline position the swash depth the flow velocity the overtopping flow volume the beach change depth and the sediment transport rate is shown to be satisfactory through comparisons against analytical solutions experimental data as well as previous numerical solutions this work facilitates an improved modeling framework for the swash hydrodynamics and sediment transport

lateral heat exchange after the labrador sea deep convection in 2008 abstractthe mechanisms through which convected water restratifies in the labrador sea are still under debate the labrador sea restratification after deep convection in the 2007 08 winter is studied with an eddy resolving numerical model the modeled mixed layer depth during wintertime resembles the argo observed mixed layer very well and the lateral heat flux during the subsequent restratification is in line with observations the irminger rings irs are reproduced with fresher caps above the 300 m depths and they are identified and tracked automatically the model underestimates both the number of irs in the convection area and the heat they carry the underestimation is most likely caused by the errors in the direction of the west greenland currents in the model which causes more irs propagating westward and only the irs originating south of 61 5 n are able to propagate southward yet with speed much slower than observed speed the model still observed three eddies propagating into the convection

the role of swash infiltration in determining the beachface gradient a numerical study on sand and gravel beaches the increase of the gradient of the beachface with increasing sediment size has been attributed to swash infiltration the present study uses a process based numerical model to examine in detail the role of swash infiltration in determining the beachface gradient it is found that swash infiltration increases the onshore asymmetry in the swash flow thereby enhancing onshore sediment transport and resulting in relatively steep beachface gradients however the accretionary effects of swash infiltration are only evident when the rate of infiltration is sufficiently large i e when the total infiltration volume over a wave cycle exceeds c 2 of the uprush volume this threshold is attained when the hydraulic conductivity exceeds 1 cm s which is approximately equivalent to a grain size coarser than 1 5 mm this finding suggests that the correlation between beachface gradient and sediment size observed on sandy beaches is not due to enhanced swash asymmetry caused by swash infiltration for gravel beaches however swash infiltration is likely to be the dominant factor in controlling the beachface gradient with increased hydraulic conductivity i e sediment size resulting in steeper beachface gradients c 2001 elsevier science b v all rights reserved

numerical modelling of the flow and bed evolution of a single bore driven swash event on a coarse sand beach abstract this paper examines the numerical prediction of the sediment transport and bed evolution for a single swash event on a coarse sediment beach in these conditions bed load is the dominant mode of sediment transport laboratory experiments of a single bore driven swash event are simulated numerically using a fully coupled model that solves the system of non linear shallow water equations and the exner sediment conservation formula the analysis focuses on two aspects the optimal choice of parameters for the meyer peter and muller sediment transport formula and the model used for computing the shear stress the methods tested for the bed shear stress are the momentum integral method and the chezy formulation in which the friction factor is computed using two different formulae infiltration into the beach and its effects on the shear stress and sediment transport are also modelled results show that the basic meyer peter and muller sediment transport formula provides good results in the run up on the other hand the sediment transport in the early stage of the backwash is overestimated a reduction of the sediment mobility constant in the formula in the backwash marginally improves the results however the causes of the overestimation of the sediment transport at the early stage of the backwash is the overestimation of the shear stress while at later stages there are several contributions that are identified i e modelling of the sediment transport and infiltration it is also suggested that the meyer peter and muller sediment transport formula might not capture the complexity of the processes involved during the backwash the comparison of the methods for the estimate of the bed shear stress show that comparable results can be obtained using the momentum integral method and the chezy formulation with time and space varying friction factor the resulting bed evolution is also described in the predicted final profile deposition is found in the upper part of the beach and erosion in the lower part a bed step is formed just below the position of the initial shoreline this feature is determined by the onset of a hydraulic jump during the backwash

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

sedimentary features observed in the tsunami deposits at rikuzentakata city abstract the march 11 2011 tohoku oki tsunami triggered by an earthquake off the east coast of northeastern honshu island tohoku region japan deposited large amounts of sediment on land including the sendai plain and sanriku coast this study reports on the characteristics of the tsunami deposits in rikuzentakata city southeastern iwate prefecture northeastern japan a field survey identified the inundation pattern of the tsunami in this region and the facies model of the tsunami deposits at the bay head deltas of estuarine systems the tsunami deposits in rikuzentakata city generally consist of one to four units that represent a discrete runup or backwash flow each unit is characterized by initial inverse grading and successive normal grading that correspond to the accelerating and decelerating stages of the flow respectively an internal erosional surface often developed between the inverse graded and normal graded units it corresponds to the maximum shear velocity of the flow and truncates the underlying inverse graded unit in the case of the runup unit silty fine grained drapes overlay the graded sandy interval a correlation of the sedimentary structures and grain fabric analysis revealed that the tohoku oki tsunami inundated rikuzentakata city at least twice and that the flow velocity exceeded 2 4 m s paleontological analysis of the sediment and kriging estimation of the total volume of the tsunami deposit implied that the sediments were sourced not only from eroded beach sands but also from the seafloor of hirota bay or more offshore regions

test of self organization in beach cusp formation 1 field observations of swash flow patterns and morphology change are consistent with the hypothesis that beach cusps form by self organization wherein positive feedback between swash flow and developing morphology causes initial development of the pattern and negative feedback owing to circulation of flow within beach cusp bays causes pattern stabilization the self organization hypothesis is tested using measurements from three experiments on a barrier island beach in north carolina beach cusps developed after the beach was smoothed by a storm and after existing beach cusps were smoothed by a bulldozer swash front motions were recorded on video during daylight hours and morphology was measured by surveying at 3 4 hour intervals three signatures of self organization were observed in all experiments first time lags between swash front motions in beach cusp bays and horns increase with increasing relief representing the effect of morphology on flow second differential erosion between bays and horns initially increases with increasing time lag representing the effect of flow on morphology change because positive feedback causes growth of beach cusps third after initial growth differential erosion decreases with increasing time lag representing the onset of negative feedback that stabilizes beach cusps a numerical model based on self organization initialized with measured morphology and alongshore uniform distributions of initial velocities and positions of the swash front at the beginning of a swash cycle reproduces the measurements except for parts of one experiment where limited surveys and a significant low frequency component to swash motions might have caused errors in model initialization

observations of shoreline sandbar coupling on an embayed beach we analyse a seven year dataset 1999 2005 of shoreline and sandbar variations derived from video observations at the embayed tairua beach new zealand to explore sandbar shoreline coupling and to determine how this coupling is related to alongshore averaged sandbar shoreline separation and beach rotation our results quantify the coupling between the sandbar and the shoreline which is directly related to the reduced separation between the sandbar and the shoreline using a simple predictive shoreline model we show that this behaviour is related to the energy of the incoming waves our observations are obtained from a headland enclosed beach and show aspects of the morphological state that relate to the existence of headlands that are not considered in the wright and short beach state classification both the sandbar and shoreline at tairua beach rotate relatively quickly 1 month during the winter storm events when the storms are accompanied by strong alongshore components gradually returning during the summer months the sandbar shoreline coupling length scale is controlled by this rotation with large wavelengths occurring when the sandbar is strongly rotated

modelling gravel beach dynamics with xbeach abstract numerical cross shore profile evolution models have been good at predicting beach erosion during storm conditions but have difficulty in predicting the accretion of the beach during calm periods this paper describes the progress made in modifying and applying the public domain xbeach code to the prediction and explanation of the observed behaviour of coarse grained beaches in the laboratory and the field under accretive conditions the paper outlines in details the changes made to the original code version 12 including the introduction of a new morphological module based upon soulsby s sediment transport equation for waves and currents and the incorporation of packwood s infiltration approach in the unsaturated area of the swash region the competence of this modified model during calm conditions for describing the steepening of the profile and the growth of the beach berm is demonstrated preliminary results on the behaviour of the beach subject to both waves and tides are presented good agreement is found between the model simulations and large scale laboratory measurements as well as field observations from a composite beach in the uk the reasons for the model s capabilities are discussed

timescales of beach cusp evolution on a steep megatidal mixed sand gravel beach abstract field observations are presented of the morphological evolution of beach cusps on a 1 10 slope megatidal 8 12 m range mixed sand gravel beach at the head of the bay of fundy nova scotia cusps had mean wavelengths of 3 6 m and displayed pronounced horn bay sediment size segregation with sand sized material in the bays and gravel sized material in the horns cusp occurrence was limited to the upper third of the beach face shoreline position during the tidal cycle was estimated at three minute intervals from time averaged video imagery three cusp events are examined in detail two exhibiting pronounced topographic relief and the third demonstrating sensitivity of the rate of cusp evolution to the beach surface grain size distribution forcing conditions were weak with significant offshore wave heights of 10 20 cm and peak periods of 4 7 s relict cusp morphology was inundated with the rising tide and destroyed or reworked during high tide new cusps formed during the falling tide through a combination of accretion at the horns and erosion in the embayments timescales of growth and decay were short ranging from 10 to 30 min the location and dynamics of cusp horns appeared to depend on the high water line and its location relative to any pre existing cusp morphology the apparent sensitivity of cusp formation timescales to the local grain size distribution suggests that size segregation is intrinsic to the process of mixed sand gravel cusp evolution

hydraulic criticality of the exchange flow through the strait of gibraltar abstract the hydraulic state of the exchange circulation through the strait of gibraltar is defined using a recently developed critical condition that accounts for cross channel variations in layer thickness and velocity applied to the output of a high resolution three dimensional numerical model simulating the tidal exchange the numerical model uses a coastal following curvilinear orthogonal grid which includes in addition to the strait of gibraltar the gulf of cadiz and the alboran sea the model is forced at the open boundaries through the specification of the surface tidal elevation that is characterized by the two principal semidiurnal and two diurnal harmonics m2 s2 o1 and k1 the simulation covers an entire tropical month the hydraulic analysis is carried out approximating the continuous vertical stratification first as a two layer system and then as a three layer system in the latter the transition zone generated by entrainment and mixing between the atlantic and mediterranean flows

erosion accretion patterns and multiple beach cusp systems on a meso tidal steeply sloping beach abstract this study examines daily variations in intertidal topography and beach cusps on a meso tidal steeply sloping beach during a five month period the observations are based on coastal imagery and frequent topographic surveys and are extracted from patterns of contours positioned 1 and 3 m above msl lower higher beach face respectively the intertidal topography was very sensitive to variations in the wave regime triggering rapid transitions from erosive to accretive states and vice versa as well as transformations of the cusp systems often involving severe horn erosion and beach face scarping distinct beach cusp systems were observed at different levels of the beach with their evolution being controlled by i wave forcing ii tidal modulation of the wave power at different levels of the beach and iii interactions between the existing beach cusp systems the lower beach face rhythmical patterns changed constantly and merged with the upper beach face cuspate features typically when the significant wave height exceeded h o 1 5 m the upper beach face pattern was persistent during the monitoring period re emerging with similar spacing and alignment despite being eroded during energetic events this persistence is also maintained by the interactions between swash and irregularities e g embayments in the dune backshore morphology the spacing of the observed beach cusps ranged from c min 8 m to c max 67 m these values were underestimated by the edge wave and self organization theories and were better predicted by the sunamura 2004 formula beach cusp growth was linked to breaker angles of near normal incidence and narrow banded frequency wave conditions bay infilling was found to be the most dominant cusp reduction mechanism for larger features c 30 m while smaller features vanished during erosive conditions the most intense cusp growth episodes were linked to accretive conditions while larger features were shown to emerge during more energetic erosion events these findings highlight the need for more longer term observations of diverse beach morphologies to formulate a global theory regarding beach cusp formation and evolution

barotropic and baroclinic m2 tides in the monterey bay region abstract a high resolution 250 m primitive equation model is used to simulate the depth averaged and baroclinic m2 tides in the monterey bay region the model shows a high level of skill in comparisons with sea level observations adcp current observations within the submarine canyon are reasonably well reproduced the modeled depth averaged currents have a complex spatial pattern with magnitudes in excess of 0 1 m s 1 near moss landing during the second half of flood ebb tide the flow is into out of the bay through the canyon but out of into the bay over the shelf regions this depth averaged flow pattern is not evident in a diagnostic run implying a feedback between the internal tides and the pressure gradient in the bay the depth integrated baroclinic total minus depth averaged energy fluxes show a complex beamlike pattern due to the interaction of energy from multiple sources the beams have magnitudes up to 1 kw m 1 interspersed with regions of near zero depth integrated flux energy en

test of edge wave forcing during formation of rhythmic beach morphology 1 this paper reports on concurrent measurements of evolving rhythmic beach morphology and the associated water motion on a macrotidal coarse sandy beach beach cusps with a spacing of 19 m developed over a 3 day period of low energy swell after which they were destroyed by energetic wind waves the beach cusps were clearly accretionary features and developed mainly during the rising tide detailed hydrodynamic measurements were conducted at three locations in the swash and inner surf zone in the vicinity of a developing cusp horn and revealed that energetic standing mode zero subharmonic edge waves were not present during the initiation of the beach cusps specifically analysis of the hydrodynamic data indicated that 1 the amount of subharmonic energy was limited 10 of the total energy 2 none of the computed energy spectra exhibited a significant peak at the subharmonic frequency 3 the cross shore velocity amplitude at the subharmonic frequency was 2 3 times larger than the longshore velocity amplitude 4 the longshore current motion at the subharmonic frequency was barely coherent between adjacent locations in the surf zone and 5 the time series of pressure and cross shore current were in phase at either side of the developing cusp horn it is concluded that at least during this event of beach cusp formation energetic standing edge waves are not a prerequisite to initiate the development of rhythmic beach morphology

shoreline motion in nonlinear shallow water coastal models abstract different shoreline boundary conditions for numerical models of the non linear shallow water equations based on godunov type schemes are compared the study focuses on the peregrine and williams peregrine d h williams s m 2001 swash overtopping a truncated plane beach journal of fluid mechanics 440 391 399 problem of a single bore collapsing on a slope this is considered the best test to assess performances of the shoreline boundary treatments in terms of all the parameters of interest in swash zone modelling emphasis is given to the shoreline trajectory and flow velocity modelling a mismatch of the velocity at the early stage of the motion is highlighted most of the tested techniques perform similarly in terms of maximum run up the backwash phase is critical in all cases starting from the brocchini et al brocchini m bernetti r mancinelli a albertini g 2001 an efficient solver for nearshore flows based on the waf method coastal engineering 43 2 105 129 shoreline boundary treatment a simple technique that improves the accuracy of velocity predictions is also developed a sensitivity analysis of the domain resolution and the threshold value of the water depth that defines a wet cell is also presented

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

tides of the northwestern ross sea and their impact on dense outflows of antarctic bottom water abstract moored and depth profile measurements of hydrography and currents during the 2003 2005 antarctic slope anslope program on the shelf slope region near drygalski trough sill in the northwest ross sea have revealed an energetic benthic outflow of cold dense antarctic bottom water aabw produced near the shelf break this outflow couples dense water production processes on the continental shelf to ventilation of the global deep ocean we use time series of bottom pressure and currents on the anslope moorings and a high resolution three dimensional primitive equation numerical model to explore the hypothesis that the tidal currents near the shelf break have a significant impact on outflow volume transport and hydrographic properties tidal currents exceed 1 m s 1 at spring tide over the outer shelf and upper slope tidal advection at spring tide carries water parcels 20 km across slope during a half tidal cycle sufficient to advect water from northern drygalski trough across the sill to the shelf break or similarly from the shelf break 500 m water depth down to the 1600 m isobath a tidally rectified lagrangian mean flow of order 0 05 0 1 m s 1 over the outer shelf and upper slope accompanies the spring tide thickness and water mass properties of the benthic layer over the sill and upper slope exhibit pronounced tidal cycles due to advection of hydrographic gradients and to energetic mixing that can extend more than halfway up from the seabed to the ocean surface maximum parameterized diapycnal diffusivity in the benthic layer at spring tides approaches 1 m 2 s 1 the addition of tides has a profound effect on time averaged outflows of aabw primarily through an increase in benthic layer thickness during spring tide downslope volume fluxes of aabw over the slope averaged over a tidal cycle are 2 5 times larger at spring tide than at neap indicating a need to include the effect of tides in large scale ocean models attempting to represent shelf water contributions to the global ocean circulation

on the pressure gradient error in sigma coordinate ocean models a comparison with a laboratory experiment boundary fitted vertical coordinates are frequently used in three dimensional primitive equation models the sigma coordinate transformation in which the water column is divided into a number of layers independently of the water depth is commonly used unfortunately it is well known that this transformation can produce an error in the calculation of the pressure gradient terms the error can be significant in regions with steep topography and large density gradients the importance of this error in simulations of coastal currents is difficult to test in reality the competing effects of the models dynamics its sensitivity for example to the chosen grid resolution or numerical techniques are hard to separate in the following we first identify the pressure gradient error and assess its magnitude in relation to two analytical reference solutions a number of commonly used techniques to reduce the error are compared of these techniques z level based pressure gradient calculations are shown to improve the simulation results we then take a step in the direction of a more realistic simulation and use a laboratory experiment as our reference solution the results demonstrate that a sigma coordinate model can be used in a region such as the skagerrak where steep topography and large density gradients are present errors do exist which need to be taken into account when interpreting the model results this is important as the skagerrak dominates the north sea and baltic sea system and models that run with a coarse grid resolution may lead to artificial flows

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

on beach cusp formation a system of shallow water equations and a bed evolution equation are used to examine the evolution of perturbations on an erodible initially plane beach subject to normal wave incidence both a permeable under darcy s law and an impermeable beach are considered it is found that alongshore periodic morphological features reminiscent of swash beach cusps form after a number of incident wave periods on both beaches on the permeable impermeable beach these patterns are accretional erosional in both cases flow is horn divergent spacings of the cusps are consistent with observations and are close to those provided by a standing synchronous linear edge wave an analysis of the processes leading to bed change is presented two physical mechanisms are identified concentration gradient and flow divergence which are dominant in the lower and upper swash respectively and their difference over a wave cycle leads to erosion or deposition on an impermeable beach infiltration enters this balance in the upper swash a bed wave of elevation is shown to advance up the beach at the tip of the uprush with a smaller wave of depression on the backwash it is found that cusp horns can grow by a positive feedback mechanism stemming from decreased increased backwash on positive negative bed perturbations

interactions among adriatic continental margin morphology deep circulation and bedform patterns abstract within the mediterranean region the adriatic basin is one of the key sites for the formation and spreading of dense shelf water once formed in the northern shallow region as a response to strong wintry cold air outbreaks dense water masses move southeastwards as bottom hugging gravity currents eventually reaching the south adriatic continental margin a fraction of the dense water mass is thus intercepted by the shelf break whence it flows down the continental slope driven by its negative buoyancy and interacting with ambient water and seafloor topography this process generates a wide variety of dynamics and morphological features such as erosional moats furrows giant comet marks sediment drifts and sediment waves in this study we merge the outcomes of a state of the art wave ocean coupled numerical model with the geological evidence from the analysis of southern adriatic bedform patterns the model was run to reproduce an exceptional cold event that occurred in winter 2012 and benefits from a high resolution bottom topography produced from data collected during recent bathymetric surveys model results allow the identification of flow pathways along and across the continental shelf and slope with particular emphasis on the role of large scale margin geometry in controlling morphodynamic processes and its implications in terms of resolution requirements for modelling purposes although modelled overall water fluxes and basin renewal ratios are mostly controlled by regional circulation and large scale morphology local topographic features and singularities appear crucial in triggering concentrating and modulating bottom currents dynamics and sediment transport towards the south adriatic pit as well as enhancing mixing and entrainment of ambient water as long as this degree of information is provided within the bathymetric constraint modelled hydrodynamic pathways in the study case are consistent with observed bedform morphology and their spatial pattern for different zones in the continental slope temporal variability of the flows has been investigated permitting to disentangle the relative contribution of dense water cascading and background circulation at the basin and sub basin scale in controlling bedform dynamics this study gives a first quantitative insight on the hydrodynamic mechanisms responsible for south adriatic margin reshaping suggesting a modelling approach to the interpretation of the high resolution bathymetric and stratigraphic data made available by recent survey technologies

circulation in the south china sea during summer 2000 as obtained from observations and a generalized topography following ocean model 1 on the basis of the recently obtained hydrographic data in the south china sea the improved princeton ocean model with a generalized topography following coordinate system is used to study the circulation in the region during summer 2000 several sensitivity experiments are carried out to achieve reasonable model parameters for the south china sea scs it is shown from the resting stratification experiments that the generalized topography following coordinate scheme is better than the standard sigma grid scheme for reducing the pressure gradient errors the combination of sea surface height anomaly derived from topex poseidon and numerical results with both diagnostic and semidiagnostic simulations provides a consistent circulation pattern for the scs in august and the main circulation features can be summarized as follows 1 there is a notable anticyclonic warm eddy southeast of vietnam with a horizontal scale of 300 km and there is a cyclonic cold eddy the simultaneous existence of these cold and warm eddies is one of the important circulation characteristics in the scs during summer 2000 2 a secondary cold eddy is found east of vietnam 3 the northwestern part of the scs is dominated by an anticyclonic circulation system 4 there is also a secondary warm eddy southwest off the luzon island 5 a cyclonic eddy is found west off the borneo island 6 a western intensification phenomenon obviously occurs in the scs the dynamical mechanisms of the above mentioned circulation pattern in the scs are the interaction between the wind stress and bottom topography and the joint effect of baroclinicity and relief

beach cusps as self organized patterns computer simulations of flow and sediment transport in the swash zone on a beach demonstrate that a model that couples local flow acceleration and alongshore surface gradient is sufficient to produce uniformly spaced beach cusps the characteristics of the simulated cusps and the conditions under which they form are in reasonable agreement with observations of natural cusps the self organization mechanism in the model is incompatible with an accepted model in which standing alongshore waves drive the regular pattern of erosion and deposition that gives rise to beach cusps because the models make similar predictions it is concluded that currently available observational data are insufficient for discrimination between them

numerical model of swash motion and air entrapment within coarse grained beaches abstract the paper presents a numerical model for bore driven swash on permeable coarse grained beaches the surface flow module is modelled using the non linear shallow water equations nlswes solved using the godunov based finite volume ader scheme which is suitable for handling steep bores as well as large source terms in the nlswes the subsurface flow comprises i infiltration and exfiltration modelled as vertical piston like flow ii horizontal pore air movement within the unsaturated region of the beach iii the horizontal groundwater flow model predictions of the surface and subsurface flow are in good agreement with measurements from large scale laboratory experiments for swash on permeable immobile beaches in these simulations air velocity was sufficiently small to justify using darcy s resistance law for the air flow whereas the quadratic forchheimer law had to be used for the infiltration and groundwater flow the validated numerical model provides insight into the surface subsurface water exchange for bore driven swash on coarse grained beaches the impact of air entrapped between the wetting front and the groundwater level on the water exchange is examined in particular

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

sandbar and beach face evolution on a prototype coarse sandy barrier abstract on steep beaches the cross shore movement of sand in response to erosive storm waves and accretive swell waves can lead to temporal changes between a barred winter profile and a non barred summer profile with a pronounced berm in the upper swash zone despite recent improvements in predicting berm formation and evolution within process based morphodynamic models substantial demand for improvement in understanding swash processes and associated surf swash sand exchange remains here we analyze bed level data collected on a near prototype 4 5 m high and 75 m wide sandy beach median grain diameter d50 430 m with a lagoon situated at its landward side in particular we distinguish between surf swash sand exchange time scale of tens of minutes to hours the net effect of single and multiple swash events on the entire beach face time scale of a few seconds to hours and instantaneous bed variability at 3 cross shore locations within individual swashes during erosive waves hs 0 8 m tp 8 s sand on the initially 1 15 planar profile was predominantly eroded from the inner surf zone to be deposited in the outer surf zone as a sandbar indicating minimal surf swash sand exchange subsequent accretive waves hs 0 6 m tp 12 s caused substantially larger surf swash sand exchange the pre existing sandbar migrated onshore and decayed with the sand ending up on the beach face in a prominent up to 0 7 m high steep 1 6 berm we found the dynamics of the berm to be governed primarily by wave conditions and the antecedent morphology with ground water gradients of additional importance when morphodynamic feedback between swash flow and the berm is small the observed bed level change within a swash and averaged over a swash event could be substantial several centimeters during all wave conditions but the net i e averaged over multiple swash events bed level change was strongly suppressed because erosive and accretionary swashes nearly balanced in addition the local beach face slope could be instantaneously 25 steeper or shallower than the median slope or the initial or final slope we anticipate that our data will stimulate new model development as to increase the range of conditions and settings in which morphodynamic models can be applied realistically and reliably

a 2d numerical model of wave run up and overtopping a two dimensional 2d numerical model of wave run up and overtopping is presented the model called ott 2d is based on the 2d nonlinear shallow water nlsw equations on a sloping bed including bed shear stress these equations are solved using an upwind finite volume technique and a hierarchical cartesian adaptive mesh refinement amr algorithm the 2d nature of the model means that it can be used to simulate wave transformation run up overtopping and regeneration by obliquely incident and multi directional waves over alongshore inhomogeneous sea walls and complex submerged or surface piercing features the numerical technique used includes accurate shock modeling and uses no special shoreline tracking algorithm or shoreline coordinate transformation which means that noncontiguous flows and multiple shorelines can easily be simulated the adaptivity of the model ensures that only those parts of the flow that require higher resolution such as the region of the moving shoreline receive it resulting in a model with a high level of efficiency the model is shown to accurately reproduce analytical and benchmark numerical solutions existing wave flume and wave basin datasets are used to test the ability of the model to approximate 1d and 2d wave transformation run up and overtopping finally we study a 2d dataset of overtopping of random waves at off normal incidence to investigate overtopping of a sea wall by long crested waves the data set is interesting as it has not been studied in detail before and suggests that in some instances overtopping at an angle can lead to more flooding than at normal incidence

sediment distribution and transport across the continental shelf and slope under idealized wind forcing abstract resuspension transport and deposition of sediments over the continental shelf and slope are complex processes and there is still a need to understand the underlying spatial and temporal dynamical scales as a step towards this goal a two dimensional slice model zero gradients in the alongshore direction based on the primitive flow equations and a range of sediment classes has been developed the circulation is forced from rest by upwelling or downwelling winds which are spatially uniform results are presented for a range of wind speeds and sediment settling speeds upwelling flows carry fine sediments low settling speeds far offshore within the surface ekman layer and significant deposition eventually occurs beyond the shelf break however coarser sediments quickly settle out of the deeper onshore component of the circulation which can lead to accumulation of bottom sediments within the coastal zone downwelling flows are more effective at transporting coarse sediments off the shelf however strong vertical mixing at the shelf break ensures that some material is also carried into the surface ekman layer and returned onshore the concentrations and settling fluxes of coarse sediments decrease offshore and increase with depth under both upwelling and downwelling conditions consistent with trends observed in sediment trap data however finer sediments decrease with depth upwelling or reach a maximum around the depth of the shelf break downwelling it is shown that under uniform wind conditions suspended sediment concentrations and settling fluxes decay offshore over a length scale of order s f ws where s is the wind stress the water density f the coriolis parameter and ws is the sediment settling velocity this scaling applies to both upwelling and downwelling conditions provided offshore transport is dominated by wind driven advection rather than horizontal diffusion

coastal trapped waves alongshore pressure gradients and the california undercurrent abstractthe california undercurrent cuc a poleward flowing feature over the continental slope is a key transport pathway along the west coast of north america and an important component of regional upwelling dynamics this study examines the poleward undercurrent and alongshore pressure gradients in the northern california current system ccs where local wind stress forcing is relatively weak the dynamics of the undercurrent are compared in the primitive equation navy coastal ocean model and a linear coastal trapped wave model both models are validated using hydrographic data and current meter observations in the core of the undercurrent in the northern ccs in the linear model variability in the predominantly equatorward wind stress along the u s west coast produces episodic reversals to poleward flow over the northern ccs slope during summer however reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south

energetics of the global ocean the role of layer thickness form drag abstract understanding the role of mesoscale eddies in the global ocean is fundamental to gaining insight into the factors that control the strength of the circulation this paper presents results of an analysis of a high resolution numerical simulation in particular the authors perform an analysis of energetics in density space such an approach clearly demonstrates the role of layer thickness form drag residual effects of hydrostatic pressure perturbations which is hidden in the classical analysis of the energetics of flows for the first time in oceanic studies the global distribution of layer thickness form drag is determined this study provides direct evidence to verify some basic characteristics of layer thickness form drag that have often been assumed or speculated about in previous theoretical studies the results justify most of the previous assumptions and speculations including those associated with i the presence of an oceanic energy cycle explaining the relationship between layer th

a case study of sea surface temperature cooling dynamics near the indian tip during may 1997 1 the sea surface temperature sst off the southwest coast of india is important to the indian summer monsoon onset which generally occurs in late may off this coast it is known that both locally and remotely forced coastal processes contribute to the sst cooling in this paper we focus on the latter by studying the sst cooling dynamics near the indian tip it during 1 15 may using advanced very high resolution radiometer avhrr sst nasa scatterometer nscat winds national centers for environmental prediction national center for atmospheric research surface meteorological variables and the princeton ocean model high spatial resolution 9 km daily mean avhrr sst maps indicate that the sst cooling near the it is a recurrent phenomenon wherein the cold sst water occupies the southwest india shelf and extends southward of the it during the 15 day period the nscat observed winds increased from near zero the net surface heat flux into the ocean changed by 62 w m2 and the sst decreased by 1 8 c near the it under these conditions the model integration is carried out as an initial value problem with realistic bottom topography climatological density stratification and observed nscat winds the results show that the ekman dynamics along the west india shelf promote upwelling and initiate sst cooling shallow and spatially variable shelf topography near the it enhance wind mixing while sharp gradients in the isobaths at the shelf break and stratification enhance upwelling downwelling intensity through cross isobath flow it is inferred that the sst cooling near the it is a locally forced process that is dictated by shelf topography

flow near submarine canyons driven by constant winds circulation over coastal submarine canyons driven by constant upwelling or downwelling wind stress is simulated and analyzed with a primitive equation ocean model astoria canyon on the west coast of north america is the focus of this study and model results are consistent with most major features of mean canyon circulation observed in astoria canyon near surface flow crosses over the canyon while a closed cyclone occurs within the canyon upwelling prevails within the canyon and is larger than wind driven upwelling along the adjacent shelf break water rises from depths reaching 300 m to the canyon rim and subsequently onto the adjacent shelf onshore flow within the canyon is driven by the onshore pressure gradient force due to the free surface slope created by the upwelling wind and is enhanced by the limitation to alongshore flow by the canyon topography density gradients largely compensate the surface slope with realistic stratification but continual upwelling persists near the edges of the canyon within the upper canyon 50 150 m below the canyon rim a cyclone is created by flow turning into the canyon mouth separating from the upstream edge and advecting toward the downstream rim below this layer the cyclone is created by vortex stretching due to the upwelling downwelling winds create nearly the opposite flow in which compression and momentum advection create a strong anticyclone within the canyon momentum advection is found to be important both in creating strong circulation within the canyon and in allowing the surface flow to cross the canyon undisturbed model results indicate that astoria like submarine canyons produce across shore transport of sufficient volume to flush a continental shelf in a few 2 5 years

swash overtopping a truncated plane beach swash on a plane beach is modelled by using a solution of the shallow water equations due to shen meyer 1963 the equations are used in a form appropriate for a plane at a finite angle to the horizontal the beach is cut off at a level below that of the maximum run up and the water is taken to fall freely over the end of the beach an explicit solution is found which permits evaluation of the overtopping flow and total volume for one swash event

rhythmic morphology in a microtidal low energy beach abstract observations of rythmic features along the inner side of the trabucador barrier beach are coupled to two numerical models to unravel the mechanisms of its formation the trabucador is a long 6 km narrow 125 m barrier and microtidal beach at the sw side of the ebro delta catalonia its inner side is a low energy beach with a sandy shallow terrace featuring an intricate alongshore rhythmic morphology sixteen aerial orthophotos from 1946 to 2014 have been analyzed and complemented with field observations from 1986 to present this morphology is dynamic but it is usually characterized by a long finger transverse bars lftb and b large scale shoreline undulations lssu the lftb are thin and elongated with a length of the order of their spacing they are intertidal and typically attach to the shoreline by a megacusp commonly opening an anti clockwise angle of 10 40 with the shore normal there can be many up to 90 with both the mean and the most frequent alongshore spacing in the range 15 25 m spectral analysis always shows peaks in this range and sometimes additional peaks in the range 30 65 m that correspond to the spacing between the largest bars with smaller bars in between the lssu typically have wavelengths in the range 150 250 m their apexes sometimes coincide with the shore attachment of the largest bars but not always numerical modelling shows that both features could emerge out of feedbacks between hydrodynamics and morphology during the sw wind events involving a deflection of the longshore current by the bars combined with the refractive wave focusing and b gradients in total alongshore sediment transport rate triggering the high angle wave instability

3d numerical model for pearl river estuary a 3d numerical model with an orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction has been developed this model is based on pom princeton ocean model in this model a second moment turbulence closure submodel is embedded and the stratification caused by salinity and temperature is considered furthermore to adapt to estuary locations where the flow pattern is complex the horizontal time differencing is implicit with the use of a time splitting method instead of the explicit method in pom this model is applied to the pearl river estuary which is the largest river system in south china with hong kong at the eastern side of its entrance the computation is verified and calibrated with field measurement data the computed results mimic the field data well