kinematic characteristics of a mei yu front detected by the quikscat oceanic winds abstract based on conventional surface observations and nasa quick scatterometer quikscat data a heavy rainfall event that occurred in the taiwan mei yu season was chosen to further study the kinematic characteristics of the accompanying surface front with the help of the quikscat oceanic surface winds it was found that the location and propagation of a mei yu front over the ocean to the east of taiwan during 10 12 june 2000 are better represented by the frontal wind shift line which was located approximately on the leading edge of the baroclinic zone the mesoscale system with cyclonic circulation embedded within the frontal zone was clearly shown in the wind field and kinematic parameters horizontal divergence and vorticity as well as satellite clouds and rainfall estimations the conditional instability of the second kind cisk process was suggested to be responsible for the intensification of the mei yu front and the frontal disturbance over the ocean under the influence of island topography

fault fluid interaction in porphyry copper hydrothermal systems faulted veins in radomiro tomic northern chile abstract the relationship between hydrothermal fluids and fault development is studied through a petrographic analysis of faulted veins in an open pit copper mine radomiro tomic rt northern chile brittle deformation in rt was initiated with the formation of veins disrupting low strain crystal plastic deformation following cooling shear fractures propagated along these veins with associated fluid influx leading to phyllic alteration hydrolysis converted all plagioclase to kaolinite within the damage zones and all orthoclase to illite within fault cores and the less deformed rocks surrounded by faults in turn precipitation of quartz and pyrite locally cemented gouge in the fault cores concentration of clays around faults and veins weakened the rocks and promoted shear strain along them these processes are expected to occur in any porphyry related hydrothermal system and can combine during the development of the system although cementation tends to strengthen fault cores the overall strength of the faults is expected to be reduced by hydrolysis of plagioclase reducing the friction of the faults and their capacity to accumulate stress these findings may have strong implications for understanding the evolution of ore deposit the rheology of the crust earthquake generation and natural hazard assessment

prediction of dune erosion due to storms abstract this paper presents results of experimental and mathematical modelling of beach and dune erosion under storm events re analysis of the experimental results on dune erosion in small scale and large scale flumes shows that the dune erosion for extreme conditions is somewhat smaller than that based on earlier analysis results dune erosion caused by wave impact has been modelled by a cross shore profile model crosmor model which is based on a wave by wave modelling approach solving the wave energy equation for each individual wave the model has been applied to the recent deltaflume experiments on dune erosion the three main processes affecting dune erosion have been taken into account the generation of low frequency effects the production of extra turbulence due to wave breaking and wave collision and the sliding of the dune face due to wave impact the calibrated model can very well simulate the observed dune erosion above the storm surge level during storm events in small scale facilities large scale facilities and in the protoype 1953 storm in the netherlands using the same model settings the mathematical model results have been used to develop a new simplified dune erosion rule

observations and modeling of alongshore variability in dune erosion at egmond aan zee the netherlands abstract dunes can erode within a few hours when exposed to high storm surge levels and large waves if the dunes are the primary defense such as in the netherlands this could result in flooding of the hinterland when dunes breach models are often used to analyze how dunes will respond to extreme conditions but they can also be applied to study milder events and with that gain more insight in the processes of dune erosion there is however growing demand for validating existing models under field conditions here we calibrate the xbeach dune erosion model with pre and post storm topography measurements of the dune erosion event in january 2012 at egmond aan zee the netherlands furthermore hydrodynamical data of the intertidal zone along a cross shore transect in the same area collected 3 months prior to the storm event are used to hydrodynamically calibrate and validate xbeach during the january 2012 storm the dune erosion was variable alongshore from the erosion of embryo dunes the forming of a dune scarp to considerable slumping of the entire dune face this caused the erosion volume v to range from 5 to 40 m3 m the calibrated model reproduces the alongshore variability in v with reasonable accuracy additional simulations show that the alongshore variation in v is due to variability on the initial dune topography primarily steepness and that variability in beach and nearshore bathymetry was of secondary importance

changing the face of the earth abstract man has from the very beginning influenced his environment this occurred originally on a small scale but became more outspoken with increasing technology this development has reached a stage nowadays characterised by the fact that man is changing the face of the earth these large scale anthropogenic influences may affect the geological development on a regional or even global scale engineers taking advantage of geological knowledge did not always take into account that the everlasting natural forces do not obey the will of man a change in attitude becomes apparent however with closer cooperation between engineering activities and geological modelling with the objective not to fight nature but to profit maximally from the capabilities of nature to carry out works that are far beyond human power projects under progress show that it is possible to take the local geology as a starting point for preserving a much more natural face of the earth than was realised during the past few centuries

decadal scale variation in dune erosion and accretion rates an investigation of the significance of changing storm tide frequency and magnitude on the sefton coast uk abstract monitoring of frontal dune erosion and accretion on the sefton coast in northwest england over the past 50 years has revealed significant spatial and temporal variations previous work has shown that the spatial variations primarily reflect longshore differences in beach and nearshore morphology energy regime and sediment budget but the causes of temporal variations have not previously been studied in detail this paper presents the results of work carried out to test the hypothesis that a major cause of temporal variation is changes in the frequency and magnitude of storms surges and resulting high tides dune toe erosion accretion records dating from 1958 have been compared with tide gauge records at liverpool and heysham relatively high dune erosion rates at formby point 1958 1968 were associated with a relatively large number of storm tides slower erosion at formby and relatively rapid accretion in areas to the north and south occurred during the 1970 s and 1980 s when there were relatively few major storm tides after 1990 rates of dune erosion at formby increased again and dunes to the north and south experienced slower accretion during this period high storm tides have been more frequent and the annual number of hours with water levels above the critical level for dune erosion has increased significantly an increase in the rate of mean sea level rise at both liverpool and heysham is evident since 1990 but we conclude that this factor is of less importance than the occurrence of extreme high tides and wave action associated with storms the incidence of extreme high tides shows an identifiable relationship with the lunar nodal tidal cycle but the evidence indicates that meteorological forcing has also had a significant effect storms and surges in the eastern irish sea are associated with atlantic depressions whose direction and rate of movement have a strong influence on wind speeds wave energy and the height of surge tides however preliminary analysis has indicated only a modest relationship between dune erosion accretion rates and the north atlantic oscillation index

beach and dune erosion during storm surges this paper presents the set up and results of an extensive research programme concerning the erosion of coastal dunes during storm surges a large number of two dimensional and three dimensional mobile bed model tests has been carried out to investigate the process of dune erosion the state of art after a series of small scale tests is summarized attention is focussed on large scale tests carried out in the delta flume with random waves up to 2 m significant height sediment concentration and orbital velocity measurements are discussed the large scale tests have confirmed the validity of a modelling technique based on the dimensionless fall velocity parameter h tw the model results are being applied to check the safety of existing coastal dunes as a water retaining structure that has to protect the major part of the netherlands from inundation during storm surges

an analytical model to predict dune erosion due to wave impact an analytical model is developed to calculate recession distance and eroded volume for coastal dunes during severe storms the transport relationship used in the model is based on wave impact theory where individual swash waves hitting the dune face induce the erosion combining this relationship with the sediment volume conservation equation describes the response of the dune to high waves and water levels four different data sets on dune erosion originating from the laboratory and the field were employed to validate the model and to determine the value of an empirical transport coefficient appearing in the analytical solutions the time evolution of dune recession observed in the different data sets was well described by the model but the empirical coefficient showed some variation between cases especially for the field data in practical applications of the model it is recommended to use a range of coefficient values to include an uncertainty estimate of calculated quantities such as recession distance and eroded volume

the analysis of beach profile changes using dean s method and empirical orthogonal functions abstract sea bottom changes in the cross shore direction have been analysed the cross shore profile as a major factor of beach configuration has been presented schematically as a superposition of a basic curve reflecting the mean layout and slope of the shore given by dean s function y a 2 3 and superimposed various bars troughs berms etc depicting local characteristic features of the profile the local features of the profile have been analysed by use of one 1 d and two dimensional 2 d empirical orthogonal functions on the basis of field observations and measurements the parameter a has been presented as a function of time three time scales have been distinguished short seasonal and long term with respect to which more or less regular changes of the parameter a occur the modified parameter a was applied to two different field sites namly lubiatowo baltic sea poland and gold beach black sea bulgaria it has been found that in extreme cases the parameter a can vary in time by a factor of two or more for the same grain size distribution

observations and simulations of wave runup during a laboratory dune erosion experiment abstract xbeach a process based numerical model designed to simulate morphologic change during extreme storm events was calibrated and compared to observations from a large scale laboratory dune erosion experiment wave conditions along the tan wave runup at the beach and 3 dimensional position of the dune were measured throughout the experiment seiching modes in the tank were simulated and matched the observations once the model was calibrated simulated waves were sensitive to the ratio of wave height to water depth and cf the coefficient of friction simulated runup explained 50 87 of the observed variance in observations however the magnitude of simulated wave runup was underestimated throughout the experiment errors in simulated runup were composed of a high bias and gain error in mean water level low bias in the infragravity swash and low bias and gain errors in incident swash observed probability density functions of swash were statistically consistent between times when swash was confined to the foreshore and times when swash interacted with the dune however simulated probability density functions of swash were statistically different during the collision regime despite the systematic underestimation of wave runup modeled dune erosion compared well with observations after the sediment transport parameters were calibrated modeled dune erosion was sensitive to the critical slope parameters over the wet and dry regions of the beach the depth of the interface between the wet and dry regions of the beach and the threshold depth for sediment transport and return flow

groin impacts on updrift morphology physical and numerical study abstract groins interfere with coastal dynamics and sediment transport leading to sediments accumulation at the updrift side while at downdrift the erosive process is anticipated due to the lack of sediments to improve numerical modeling capacity to simulate the groins impacts it is necessary to totally understand the shoreline evolution along time and its relationship with the cross shore profiles shape the main goal of this work was to analyze and compare the performance of physical and numerical studies on evaluating the evolution of updrift cross shore profiles geometry and shoreline position after the construction of a groin this study analyzed a coastal stretch updrift of the groin at a prototype and model scales considering the analytical formulation of pelnard considere the numerical model ltc long term configuration and the laboratory tests the laboratory tested scenario was designed with the aim to gather results which could be analyzed and compared with numerical simulations from ltc coelho 2005 allowing its improvement and with the pelnard considere 1956 analytical formulation both at model scale the developed study shows an important difference between ltc and pelnard considere 1956 approaches because the analytical solution for the shoreline in equilibrium does not include the wave refraction effects over the updated bathymetry ltc observed trend of the equilibrium shoreline is not parallel to the initial shoreline and this behavior was confirmed in the laboratory tests it was also observed that the sediment transport capacity has very small impact on the ltc shoreline configuration despite the refraction effects over the updated bathymetries along time the profile shape obtained in laboratory includes bed forms difficult to reproduce in long term numerical modeling evaluation of cross shore profiles because ltc transversal behavior is only based on geometrical considerations and does not represent cross shore sediment transport and its impact on profile geometry

modelling storm impacts on beaches dunes and barrier islands a new nearshore numerical model approach to assess the natural coastal response during time varying storm and hurricane conditions including dune erosion overwash and breaching is validated with a series of analytical laboratory and field test cases innovations include a non stationary wave driver with directional spreading to account for wave group generated surf and swash motions and an avalanching mechanism providing a smooth and robust solution for slumping of sand during dune erosion the model performs well in different situations including dune erosion overwash and breaching with specific emphasis on swash dynamics avalanching and 2dh effects these situations are all modelled using a standard set of parameter settings the results show the importance of infragravity waves in extending the reach of the resolved processes to the dune front the simple approach to account for slumping of the dune face by avalanching makes the model easily applicable in two dimensions and applying the same settings good results are obtained both for dune erosion and breaching

a case study of subtropical frontogenesis during a blocking event abstract during 8 14 june 2000 a 500 hpa blocking event occurred over mongolia and northern china near 45 n 108 e which was the only case over this region in june since 1981 as the block developed the initially weak low level mei yu front over southern china evolved into a system with strong baroclinity and subsequently moved south the frontal passage over taiwan caused temperatures to drop by 10 c the largest in june over two decades using gridded analyses manually analyzed weather maps and satellite and surface data the present study investigates the evolution of this mei yu front under the influence of the block the 925 hpa frontogenetical function is computed and effects of different processes are discussed as the blocking event developed concurrent ridge trough amplification in the lower midtroposphere produced a reversed thermal pattern the lower tropospheric high moved southward and large scale confluence and deformation were enhanced between the northerly flow and the prefrontal

modeling dune response to an east coast low coastal dunes can act as a method of soft coastal protection against inundation and direct impact of waves during storms if they are substantially large enough in volume to withstand erosion without breaching however the time evolution of sand dunes under direct wave impact is not well understood and many available models require site specific calibration and have had limited verification at field scales here we test three models of varying complexity in their ability to predict both dry beach erosion volumes and dune to a retreat for an east coast low storm event that occurred on the gold coast australia the process based model xbeach which models the entire profile was able to reproduce both dune toe retreat and dry beach volume however was sensitive to calibration parameters the two parametric models that only modeled erosion above the initial dune toe position were capable of accurately predicting dune toe retreat however under estimated dry beach erosion volumes with no calibration the parametric model proposed by palmsten and holman 2012 produced the smallest errors of dune toe retreat with mean error in final dune position of 6 6 m or 18 of the total measured dune retreat with minimal calibration estimated absolute error in average dune toe retreat was less than 13 of observed retreat for all three models

two dimensional time dependent hurricane overwash and erosion modeling at santa rosa island abstract a 2dh numerical model which is capable of computing nearshore circulation and morphodynamics including dune erosion breaching and overwash is used to simulate overwash caused by hurricane ivan 2004 on a barrier island the model is forced using parametric wave and surge time series based on field data and large scale numerical model results the model predicted beach face and dune erosion reasonably well as well as the development of washover fans furthermore the model demonstrated considerable quantitative skill upwards of 66 of variance explained maximum bias 0 21 m in hindcasting the post storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied the prediction skill ranged between 0 66 and 0 77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied the sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay the model sensitivity to the sheet flow sediment transport limiter which served as a proxy for unknown factors controlling the resistance to erosion was significantly greater than the sensitivity to the hydraulic forcing parameters if no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response

spatial and temporal evaluation of storm induced erosion modelling based on a two dimensional field case including an artificial unvegetated research dune abstract the objective of this study was to evaluate the temporal and spatial performance of the xbeach model predicting storm surge induced erosion and breaching on the basis of a two dimensional field case within the scope of a physical experiment a large scale artificial unvegetated research dune was built at the german baltic sea coastline and surveyed before during and after a surge event to generate high resolution digital elevation models of the temporal and spatial failure process the measured data was used to set up and calibrate two dimensional xbeach models the numerical results showed that the default settings of the latest xbeach x release led to a very good agreement bss 0 82 between the simulated and measured post storm bed levels in the area of the research dune while a higher agreement was observed on the overwash and inundation dominant eastern side than on the collision dominant western side evaluating the model accuracy during the storm surge using 44 digital elevation models of the seaside slope showed a spatially accurate prediction of the two observed breaches 5 m but also the occurrence of additional breaches with respect to timing and breach width evolution however the results highly deviated from the observation and were found to be very sensitive to changes in grid resolution and to changes of default parameters exchanging the nearshore bathymetry with measurements one and two months prior to the physical experiment where a 49 and 51 lower subaerial beach volume was observed resulted in a significantly overestimated dune erosion 31 and 33 and hence in a lower accuracy of the default model bss 0 69 overall the xbeach model is capable of accurately predicting the evolution of storm induced erosion during a sufficiently long and overwash inundation dominant surge event when current high resolution input data is available

laboratory investigation of the bruun rule and beach response to sea level rise abstract rising sea levels are expected to cause widespread coastal recession over the course of the next century in this work new insight into the response of sandy beaches to sea level rise is obtained through a series of comprehensive experiments using monochromatic and random waves in medium scale laboratory wave flumes beach profile development from initially planar profiles and a 2 3 power law profile exposed to wave conditions that formed barred or bermed profiles and subsequent profile evolution following rises in water level and the same wave conditions are presented experiments assess profile response to a step change in water level as well as the influence of sediment deposition above the still water level e g overwash a continuity based profile translation model ptm is applied to both idealised and measured shoreface profiles and is used to predict overwash and deposition volumes above the shoreline quantitative agreement with the bruun rule and variants of it is found for measured shoreline recession for both barred and bermed beach profiles there is some variability between the profiles at equilibrium at the two different water levels under these idealised conditions deviations between the original bruun rule the modification by rosati et al 2013 and the ptm model predictions are of the order of 15 and all these model predictions are within 30 of the observed shoreline recession measurements of the recession of individual contour responses such as the shoreline may be subject to local profile variability therefore a measure of the mean recession of the profile is also obtained by averaging the recession of discrete contours throughout the active profile the mean recession only requires conservation of volume not conservation of profile shape to be consistent with the bruun rule concept and is found to be in better agreement with all three model predictions than the recession measured at the shoreline

holocene storm surge signatures in the coastal dunes of the western netherlands abstract on five different sites along the central netherlands coast one or more sequences of shell deposits in the dunes have been observed they are believed to be the result of storm surge activity on the foreshore either through swash or overwash action and of subsequent preservation due to aeolian coverage of a basically sedimentary coastal system through their stratigraphical positions and radiocarbon dating of shell material their approximate age was determined by interpretation of the role of dynamic wave set up and run up the associated storm surge elevations relative to contemporary mean sea level are reconstructed although our data may not be statistically accurate an increasing level of storm surge elevations over the recent holocene is observed with a particular maximum during the little ice age it is our suggestion that climatic variations on the one hand and foreshore bathymetry on the other hand may be factors of relevance to explain these observations if these findings are correct this would imply that for a proper analysis of exceedance frequencies of extreme storm surge events it would be relevant to base such an analysis not only on present climate and foreshore bathymetry

shoreline evolution of the holland coast on a decadal scale the decadal evolution of the dunefoot position along 120 km of the holland coast is analysed firstly a new definition of dunefoot is introduced based on hydrodynamic and morphologic considerations which is not affected by local and instantaneous processes occurring immediately before the bathymetric survey the dunefoot evolution over decadal scales indicates the existence of spatial and temporal oscillations in the shoreline position with magnitudes of 2 3 km length and a periodicity of 4 15 years two main controlling factors of this behaviour are identified 1 influence of sub aqueous bar systems and 2 changes in the storm wave conditions reaching the coast although the precise controlling processes of the relation between the dunefoot and the subaqueous profile still remain unclarified we introduce the concept that the development of a morphological bar cycle requires a fixed amount of time integrated forcing that is proportional to the cumulative effect of storm waves beach mobility along the holland coast on decadal scales 10 20 m is similar or lower than mobility introduced by storms or by seasonal cycles however it is important to consider these changes for the possible implications on the local vulnerability of the coast to extreme events copyright 1999 john wiley sons ltd

large scale dune erosion tests to study the influence of wave periods article i nfo large scale physical model tests were performed to quantify the effects of the wave period on dune erosion attention was focussed on 2d cross shore effects in a situation with sandy dunes and extreme water levels and wave conditions besides profile measurements detailed measurements in time and space of water pressure flow velocities and sediment concentrations were performed in the near near shore area it was concluded that a longer wave period leads to a larger dune erosion volume and to a larger landward retreat of the dune face tests with double peaked wave spectra showed that the influence of the spectral shape on dune erosion was best represented by the tm 1 0 spectral mean wave period better than the peak wave period tp the effect of the wave period on dune erosion was implemented in a dune erosion prediction method that estimates erosion volumes during normative storm conditions for the dutch coast more details of the measurements and additional analyses of physical processes are described in an accompanying paper by van thiel de vries et al van thiel de vries j s m van gent m r a reniers a j h m and walstra d j r submitted for publication analysis of dune erosion processes in large scale flume experiments in this volume of coastal engineering

sedimentary balances land and sea with special reference to the icelandic south coast from torlakshofn to dyrholaey river nourishment of shores practical analogies on artificial nourishment abstract the sedimentary balances between land and sea are discussed with particular reference to the 140 km long pocket beach between two major headlands on the sandy icelandic south coast rivers supply large quantities of material to the coast comparing the known transport of material by the rivers to the area of the continental shelf and using the recorded sea level rise at the port of reykjavik a balance was found the development of equilibrium profiles in relation to profile geometry grain sizes and outer boundaries for material movement by wave action is discussed and practical suggestions on future nourishment procedures are presented profile nourishment will be more practical and economical than beach nourishment

analysis of dune erosion processes in large scale flume experiments abstract large scale physical model tests were conducted with different wave periods to examine the physical processes driving dune erosion the model tests have been carried out in a flume 2dv with a sandy dune exposed to extreme surge and wave conditions van gent m r a van thiel de vries j s m coeveld e m de vroeg j h and van de graaff j 2008 large scale dune erosion tests to study the effect of wave periods coastal engineering doi 10 1016 j coastaleng 2008 04 003 detailed measurements in time and space of water pressure flow velocities and sediment concentrations were performed in the near shore area the data revealed that both short and long waves are important to inner surf hydrodynamics depth averaged flows are directed offshore and increase towards the shore line the corresponding mean sediment concentrations rise sharply towards the dune face up to 50 g l near the bed the strong increase in the mean sediment concentration towards the dune face correlates well with the maximum wave surface slope which in turn is coupled to both the pressure gradient and the near bed wave breaking induced turbulence analysis shows that the pressure gradient is only partially coupled to the flow acceleration suggesting that the latter cannot always be used as a proxy for the first weak correlation is obtained with the near bed flows related to the bed shear stress tests with a larger wave period resulted in a larger dune erosion volume during these tests more wave energy combined incident and infragravity waves reached the dune face but more importantly this wave energy is dissipated by fewer waves resulting in more intense wave breakers and steeper wave fronts it is therefore expected that the wave breaking induced near bed turbulence increases resulting in significantly higher o 100 mean sediment concentrations in addition the mean flow velocities are comparable yielding a substantially larger offshore directed sediment transport capacity this increase in offshore directed transport is only partially compensated by a concurrent increase in the wave related onshore transport capacity associated with intrawave processes resulting in a net increase in the dune erosion rate

evolution and structure of the mesoscale convection and its environment a case study during the early onset of the southeast asian summer monsoon abstract the evolution and structure of mesoscale convection in the south china sea scs region are documented for the first time mainly using the dual doppler radar dataset collected during the south china sea monsoon experiment scsmex in 1998 in particular this study focuses on the convection associated with a subtropical frontal passage during the early onset of the southeast asian monsoon seam for the case of 15 may 1998 interaction between the tropical monsoon flow and frontal circulation played an important role in the evolution and structure of mesoscale convection in the prefrontal region the southwesterly monsoon flow converged with the southwesterly frontal flow to generate northeast to southwest oriented convection in the postfrontal region the southwesterly monsoon flow converged with the northerly frontal flow to produce a wide convective line with an east to west orientation in addition the convergence between the southerly monsoon flow and the northerly postfrontal flow gener

a comparison of the post storm recovery of two sandy beaches on hong kong island southern china abstract typhoon hagupit was one of six tropical cyclones that affected hong kong in 2008 when the typhoon made landfall the combined effect of the waves storm surge and seasonal high tides resulted in a maximum sea level of 3 53 m at the nearest tide gauge to the study site the highest since 1962 the event caused considerable damage to coastal infrastructure and large scale erosion on many sandy beaches in hong kong to study the degree of erosion and recovery of hong kong beaches we surveyed two sandy beaches tai long wan tlw a relatively high energy exposed beach system and to tei wan ttw a relatively low energy sheltered beach system we examined the two beaches for changes in their beach profiles and sediment properties tlw recovered quickly with significant post storm accretion of fine to medium grained sand within four months after the typhoon tlw regained 700 m 3 sand forming a new 1 0 m high berm with the beach face prograding approximately 5 0 m seaward in contrast within the same four months after the typhoon ttw showed little evidence of sand accretion or recovery with only minor changes in the beach profile in fact instead of post storm sand accretion the landward migration of the high tide mark shown in the pre and post storm satellite images suggested that the post storm beach elevation at ttw decreased the results which reflect the different background energy regimes of each beach indicate that different coastal management strategies should be applied in the case of relatively high energy beaches of hong kong we suggest not interfering with their natural state in contrast in the case of relatively low energy beaches of hong kong which appear unlikely to recover rapidly from erosion during storms we suggest further investigation before applying any long to medium term management strategies

case study of an unusually heavy rain event over eastern taiwan during the mei yu season abstract a heavy rain event during the mei yu season was observed over eastern taiwan on 28 may 2001 under a potentially unstable environment with high cape and copious moisture this event with an unusually high daily rainfall maximum of 307 mm was observed in the ilan area over northeastern taiwan the retrogression of a mei yu front over the nearby ocean collocated with a short wave trough provided favorable large scale conditions for the production of localized heavy rainfall latent heating was suggested to be responsible for the retrogression and the development of the mei yu front over the nearby ocean to the east of taiwan in addition to the large scale forcings the local circulations and local topography modulated the rainfall distribution over the ilan area during the daytime hours the strengthened onshore wind component due to the intensified mei yu frontal circulation and orographic lifting provided enhanced rising motion over the windward slopes of the mountain to produce the significan

critical storm thresholds for significant morphological changes and damage along the emilia romagna coastline italy abstract the definition of storm morphological thresholds along the coast of the emilia romagna region strictly depends on its configuration and variability the region is located in northern italy facing the adriatic sea the coastline is characterised by very different levels of economic development ranging from natural zones with dunes to highly developed stretches protected by breakwaters and groynes the integrated coastal zone management effort is mainly concentrated on preserving urban areas that generate significant income for the regional economy natural areas while small in comparison to the urbanised zone are important for environment preservation because of such a multiplicity of issues at stake it was decided to produce two different thresholds one for the morphological impact on natural sectors and another for inundation and damage to structures along urbanised zones the forcing component of the threshold definition for natural areas was calculated by summing the effects of surge tide waves run up elevation to find the maximum water level mwl reached by the sea during one ten and one hundred year storm return periods for urbanised zones historical storm information was collected starting from the 1960s in order to identify the forcing conditions causing real damages each storm was classified in terms of wave height period direction and surge level morphological information were obtained from lidar flights performed in 2003 and 2004 and from direct surveys undertaken in september 2008 and february 2009 as part of the monitoring programme for the micore project the computed mwl for each return period was then compared to beach elevations along natural areas in order to calculate the dune stability factor dsf an index that accounts for the eroded sediment volume above the mwl during a storm based on analysis along 41 profile lines at a 500 m spacing it was found that the 1 in 1 year return period wave height 1 in 1 year return period surge are able to erode and or overwash 2 3 of the dunes the historical storm hydrodynamic information was used to estimate which wave and surge conditions are able to inundate at least 2 3 of the beach profiles the mwl was again compared to beach elevations this time along 63 anthropogenic profiles spaced 500 m apart or 1 3 of the urbanised coastline it was found that a wave heights 2 m and surge tide levels 0 7 m are able to flood between 18 and 36 of the built up coast the defined thresholds are related to the present coastal characteristics and are not static meaning that they are likely to change according to future evolution of the coastline they are very important because they can be used as thresholds to issue warnings and alert the civil protection moreover they are the first thresholds defined for the emilia romagna coastline and will be used as starting values to generate dynamic thresholds based on numerical model predictions of morphological change for a given wave and surge level

analysis of a relatively dry front during the taiwan area mesoscale experiment abstract the evolution of a relatively dry front during the early summer rainy season of taiwan is analyzed because of the synoptic subsidence associated with a subtropical high pressure cell over the northern south china sea prefrontal soundings over the taiwan area exhibited a shallow warm moist layer in the lowest levels capped by an inversion with extremely dry air aloft over the taiwan area the southwest flow ahead of the surface front was more than 10 m s 1 at the 850 mb level it interacted with the central mountain range resulting in the windward ridge leeside trough downstream of the blocked region strong southwesterly winds 1 5 m s 1 developed in the lowest levels along the northwest coast where the flow deflected by the mountain barrier merged with the undetected southwest monsoon flow the hilly terrain along the southeastern china coast retarded the cold air behind the surface front the cold air was then ducted around the southeastern china coast at the 850 mb level a weak s

breaching in a wave dominated barrier spit the trabucador bar north eastern spanish coast the trabucador bar is a barrier coast linking the main lobe of the ebro delta with its southern spit this coastal stretch which may be considered as a microtidal transgressive barrier is the most vulnerable area of the deltaic coast to storm induced geomorphologic changes during the second week of october 1990 a severe storm affected the ebro delta causing serious erosion in which the trabucador bar was one of the most damaged zones a breach 800 m long and with a maximum depth of 0 4 m below the mean water level was created during the breaching process approximately 70 000 m3 of sand were removed from the subaerial barrier in a few hours three factors are normally responsible for the loss of sediment longshore transport gradient offshore transport and overwash processes most of the eroded sediment 60 000 m3 was transported towards the inner bay due to overwash processes the post storm recovery of the zone was slow and far from complete as the breach remained a conduit for onshore sediment transport under a regime of breaking and reforming waves an artificial dune was subsequently constructed to close the breach and thus allow beachface recovery

the effect of washover geometry on sediment transport during inundation events abstract storm induced sediment transport across a barrier island can lead to vertical accretion and onshore migration of the barrier island many barrier islands either have high dunes that prevent inundation or are so low lying that they are inundated several times a year the wadden islands in the netherlands germany and denmark typically have alongshore varying topography where high dunes alternate with low lying washover openings the effects of the geometry of the washover openings on hydrodynamics and sediment transport are still unknown and are the main focus of this research first we present data on width and for some cases also vertical elevation of bed level for all washover openings along the wadden islands the mean width is 200 m but the actual width ranges from 35 to 1100 m and the elevation is between 1 5 and 2 1 m above msl further we present results of an xbeach model study to investigate how the washover opening geometry affects sediment transport during storm induced inundation we identify two important effects of washover width firstly for narrow openings flow contraction is important causing relatively larger sediment exchange rates per unit width secondly in a wider opening sediment is transported over a larger width resulting in larger sediment mass exchange rates furthermore the elevation of the washover opening is of high importance washover openings that are 30 cm higher than the reference case significantly decrease currents and sediment transport across the island divergence of sediment transport occurs in the washover opening which leads to erosional patterns landward from the opening sediment transport converges which leads to depositional patterns the pressure gradient between north sea and wadden sea across the wadden islands is an important forcing parameter higher water levels in the back barrier reduce onshore directed currents and sediment transport

numerical simulations of the barrier jet over northwestern taiwan during the mei yu season orographic effects on the airflow over taiwan under the prevailing southwesterly monsoon flow are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in particular the orographically induced low level strong winds along the northwestern coast of taiwan are simulated in the absence of radiative forcing thermal forcing from the surface and synoptic forcing the momentum balance for the low level strong winds along the northwest coast of taiwan shows that above the mixed layer the alongshore force balance is dominated by the inertial advection term and the pressure gradient force term the significant lagrangian flow acceleration of the northern branch of the deflected airflow along the northwest coast is mainly related to the pressure gradient force as the airflow moves down the orographically induced pressure ridge along the windward coast even though the alongshore pressure gradient force along the northwest coast is largest at the surface the observed and simulated wind profiles show that the wind speed maximum in the vertical of the barrier jet occurs at a height of 800 m primarily due to frictional retardation in the lowest levels within the well mixed layer the alongshore force balance is a threeway balance between inertial advection pressure gradient force and frictional force normal to the northwest coast the force balance is approximately geostrophic in addition the location and the strength of the orographically induced low level strong winds along the northwest coast of taiwan also depend on the impinging angle and the wind speed of the prevailing winds

the role of offshore convergence on coastal rainfall during tamex iop 3 abstract the role of offshore convergence on the coastal rainfall maximum along the northwestern coast of taiwan is analyzed based on tamex taiwan area mesoscale experiment data and numerical experiments using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 from a case study during tamex iop 3 moderate rainfalls 40 mm h 1 are observed along the northwestern coast of taiwan associated with the arrival of three rainbands in succession during 1000 1600 lst these rainbands form over the taiwan strait with northeast southwest or north south orientation they intensify off the northwestern coast there is a tendency for the most intense echoes to align in a northeast southwest orientation off the northwestern coast an orographically enhanced convergence zone with a northeast southwest orientation occurs in the area where the deflected southerly flow converges with the prevailing southwesterly flow that is modified by the storm

beach morphodynamics and types of foredune erosion generated by storms along the emilia romagna coastline italy abstract the objectives of this study are to examine the response of a dune and beach system on the adriatic coastline in northern italy to the arrival of storms compare it with seasonal months and medium term 3 year morphodynamic change and evaluate results predicted by the numerical model xbeach the studied coastline stretches 4 km from the bevano river mouth to the north of the site to the township of lido di classe to the south where the beach is protected by coastal structures fieldwork consisted of topographic profile surveys using rtk dgps technology 7 times over an approx 3 year period 103 samples of surface sediment were collected along 20 of the cross shore profiles at 6 distinct cross shore positions selected on the basis of morphological beach characteristics data analyses of dune and beach slopes enabled the study area to be divided into 6 separate morphological zones using the spatial longshore and cross shore variation of morphologies located on the backshore and intertidal beach observed in a preliminary survey of the area other criteria were a spatial consistency in beach slopes and or presence absence of intertidal morphologies identified in the aerial photographs and lidar data the swash zone slope did not show any significant variability for the entire area a weak seasonal trend in the variability of the mean foredune slope was observed with steeper slopes typically during winter and flatter slopes during summer analysis of grain size revealed that the beach sediment is well sorted fine sand tending to medium with a decreasing trend in size from the bevano river mouth southwards towards lido di classe according to the masselink and short 1993 classification the natural part of the study site has an intermediate barred beach ibb and following the short 1999 classification results in a modally lbt longshore bar trough or ltt low tide terrace with a small section being tbr transverse bar and rip storms are considered the main factor controlling changes in the beach and dune slope the most significant storm was recorded in march 2010 with a peak significant wave height of 3 91 m contrary to the seasonal dune trend several foredune slopes were observed to flatten following this event which can be attributed to the action of dune slumping from the already weakened dune state modelling of foredune erosion using a process based model xbeach reproduced the erosion of the upper beach and dune toe reasonably well but is currently limited by the acceptable slope value for dune stability which does not account for biotic factors e g plant roots the comparison between the storm impact categories of sallenger 2000 and the dsf dune stability factor of armaroli et al 2012 shows a very good correspondence between the effects of the winter 2008 2009 storms and the vulnerability of the dune system predicted using both classifications

short term monitoring of foredune formation on the east coast of south africa although dunes fronted by sandy beaches constitute approximately 80 per cent of south africa s coastline few studies have addressed the formation and life cycle of coastal foredunes the small ephemeral shore parallel dune ridges typically less than 5 m high and 20 m wide which form seaward of the storm line this study used regular detailed topographic surveys of embryo and foredunes at tugela mouth an aggrading stretch of shoreline on the subtropical east coast of south africa over a 32 month period to gain insight into the formation and motion of these highly mobile landforms over the short term average wind drift potential at tugela mouth during the study period at 2 35 m s 1 was an order of magnitude lower than that typical of most parts of the eastern south african coast the dominant sand moving wind for the region was from the southwest to west southwest at 10 7 to 13 8 m s 1 with a secondary vector from north to north northeast at 10 8 to 13 8 m s 1 signi cant shoreline retreat a result of the low sediment yield of the tugela river during the study period was one of the main results this provided the context for redistribution of sand from the inland to the seaward side of the study area a consequence of the dominant wind direction and for frequent creation and destruction of short lived embryo dunes those foredunes which survived the whole study period tended to increase in height but there was no consistent directional trend in foredune crest movement throughout the 32 months the study results generally supported psuty s model of foredune development but could not con rm his contention of landward retreat of dune forms under conditions of shoreline erosion this may be due to the relatively short duration of the study or possibly to low wind drift potential at the site copyright 2003 john wiley sons ltd

modelling storm induced beach dune evolution sefton coast liverpool bay uk storm induced dune evolution on a sandy coastal system is investigated using a nested modelling approach applied to the sefton coast liverpool bay uk real time offshore water levels and waves were used as model boundary forcings a delft3d coarse grid setup is used to simulate time and space varying sea surface elevations on which offshore waves are transformed by applying the swan model to establish the wave boundary for the high resolution morphological model xbeach statistical comparisons between model predicted and measured post storm profiles at a number of locations along the coast suggest that xbeach successfully captures storm induced beach change along the sefton coast predicted bed evolution of the beach dune system shows alternate erosion and sedimentation areas in the nearshore strong bed level changes are found at the northern part of the sefton coast when north westerly nw extreme waves and winds coincide with spring high tide morphological changes in the southern part are significantly lower than that in the north as a result of nw wave dissipation on the shoals located to the north of the crosby channel which creates low wave actions in that area in addition erosion of the dune foot is observed at some locations along the beach temporal simulation of beach dune evolution as a result of variable forcing conditions during storms provides useful insight into the morphodynamic processes of beach dune systems during storms using sefton as an example which is very useful for developing coastal management strategies over the existing conceptual tools

critical storm thresholds for the generation of significant dune erosion at dziwnow spit poland abstract storm influence on the southern baltic coast was examined for a 14 km long section of the polish coast along the dziwnow spit based on 30 years of post storm dune erosion observations in this study we assumed that a significant storm causes noticeable sand dune erosion significant changes of the coast after each major storm were analysed based on reports from 1978 to 2008 provided by the maritime office szczecin thirty two storms that caused dune losses were chosen for analysis correlation and hierarchical cluster analysis allowed us to distinguish three groups of storms that caused varying amounts of dune erosion g1 small g2 medium and g3 large sea level is the main parameter that influences the amount of dune erosion caused by storms on the southern baltic coast factors such as maximum significant wave height mean wave direction storm energy and duration can also but less significantly influence dune erosion the study area was divided into two sections dziwnow where there are many protection measures in place and miedzywodzie which has no protection measures in place in both areas we observed differences in the impact of sea level and significant wave height and storm groupings approximate minimum sea level and significant wave height thresholds were defined for particular storm groups

mathematical modeling of the fate of beach fill abstract this paper describes mathematical approaches for calculating the fate of beach fill under wave action general properties of the spatial and temporal behavior of fills under average longshore sand transport conditions are first reviewed through use of simple closed form solutions of the sediment continuity equation this well known solution procedure is then extended to describe the collective movement of sediment or longshore sand waves because of the increasing use of beach fills as storm protection barriers the paper focuses on prediction of storm induced beach erosion an empirically based model is described and tested with a high quality field data set of storm induced beach erosion one synthetic tropical storm and one synthetic extratropical storm representing typical mid atlantic storms with approximate 2 5 year return period are then used to simulate the erosion of two hypothetical beach fill configurations and the subsequent post storm recovery process eroded volume and contour movement are evaluated as a function of storm type fill cross section grain size and time quantitative and qualitative features of storm erosion are reasonably well reproduced and calculated changes in beach fills impacted by the synthetic storms indicate that little erosion protection benefit is gained for moderate storms 2 5 year return period by placing fills with grain sizes greater than 0 4 mm simulation of post storm beach recovery is presently limited to qualitative reproduction of observed trends

reduction of sand demand for shore protection beach nourishment is an environmentally preferred method of shore protection but the annual sand requirement may lead to substantial maintenance costs the shoreline processes involving the surf zone beach and dune are reviewed with the aim of reducing the annual sand requirement of eroding shorelines it is shown that surf zones with equilibrium profiles on which the wave energy conversion is evenly distributed across the surf zone from experience for given conditions indicate least loss of sand on steep eroding shorelines it may be difficult to establish an equilibrium profile for such cases the use of perched surf zones is recommended which are supported at the seaward limit by an underwater sill for reduction of littoral transport the use of pervious pile groynes is recommended these are arguably more efficient than impervious groynes the sand loss from a usually dry beach by raised water levels is shown to be a function of the beach slope and is least when the storm waves at raised water levels do not cut an erosion escarpment the loss of sand from a dune by infrequent severe storm tides can be prevented with the aid of a built in membrane these sand losses are usually large and constitute an uneconomic use of this sand resource the proposed concepts and measures are linked to existing knowledge augmented by data from the large wave flume lwf in germany and field data from the north and baltic sea coasts

topographic effects on a wintertime cold front in taiwan abstract this paper describes an observational and numerical study of an intense wintertime cold front that occurred in taiwan on 8 january 1996 the front was associated with rope clouds at the leading edge and a broad area of stratiform clouds behind the front was blocked by the central mountain range of taiwan and divided into two sections on each side of the mountain range as the cold air moved southward along the east coast the increasing westward coriolis force induced a landward acceleration after the cold air piled up against the mountains a coastal pressure ridge developed the cold air damming yielded a geostrophic balance between the westward coriolis force and the eastward component of the pressure gradient force in the x direction and a southward acceleration in the y direction mainly caused by the southward pressure gradient force component over the taiwan strait southward pressure gradient forces increased when the low level stable cold air was confined over the taiwan strait lead

laboratory investigation of nourishment options to mitigate sea level rise induced erosion abstract the response of nourished beaches to sea level rise is investigated experimentally with random waves in a laboratory wave flume 20 m 1 m 1 m following on from a previous investigation of the response of non nourished beaches atkinson et al 2018 the nourishments are placed on beach profiles previously exposed to sufficient durations of waves to have approached a near equilibrium state i e with stable shoreline bars and berms nourishment was placed in three different locations on the berm within the bar trough and as a shoreline placement in the latter case and following bruun rule concepts bruun 1962 the volume of sediment placed was estimated a priori to lead to zero recession under the chosen water level rise the nourished beaches were then exposed again to sufficient durations of waves to reach a near equilibrium state at the raised water level the shoreline recession and the mean recession of the profile following a rise in water level are compared for both the nourished and non nourished beaches and to theoretical estimates based on bruun rule concepts and a previously developed profile translation model ptm quantitative agreement is found with the variants of the bruun rule that account for nourishment and with the ptm and the predicted recession is within an order of 30 of the observed recession overall the ptm provides the best estimate of the recession the mean recession of the profile is found to be in better agreement with the model predictions than the recession measured at the shoreline because the latter is affected by changes in profile shape around the still water line the efficacy of the nourishment was investigated from the reduction in the observed recession the efficacy depends on how the recession is measured for the mean recession highest efficacy was observed when all the nourishment is added into the active profile conversely for the shoreline recession highest efficacy was observed with the nourishment placed on the upper beach because it prevents additional recession through wave overtopping

forecasts of seasonal to inter annual beach change using a reduced physics beach profile model abstract the observed seasonal to inter annual variability of beach profiles has been investigated using a one dimensional beach profile model the model used here is developed on the reduced physics modelling approach the model uses a diffusion formulation as the governing equation and adopts an inverse modelling technique for solving the equation the model is calibrated and validated against historic measurements of beach profiles at hasaki coast located in the east coast of japan the beach is longshore uniform and characterised by a highly dynamic longshore bar trough system the model is then used to forecast seasonal to inter annual scale beach change the results are compared with beach change determined from measured beach profiles at hasaki between 2007 and 2011 the simple modelling approach used yields encouraging results of seasonal to inter annual scale beach change at hasaki coast

wave dune interaction and beach resilience in large scale physical model tests abstract large scale laboratory experiments focusing on the main physical processes driving dune erosion have been performed in a wave flume with a sandy dune exposed to a combination of water levels and wave conditions tomasicchio et al 2011b providing observations of different interaction regimes collapsing overwash and breaching sallenger et al 2003 the large set of data has been considered to obtain measurements of beach dune cross shore profile evolution hydrodynamic properties and suspended sediment concentration results show that erosion develops faster during the first hundred waves there is a clear influence of wave period van gent et al 2008 and water depth on the resilience of the beach dune system and that sediment concentration at a given transect depends on the bar position furthermore the observed data have been adopted to verify the predictive accuracy of two open source process based profile numerical models

unified modeling guidance based on a sedimentation parameter for beach changes abstract review of four available proposals for designing coastal movable bed models demonstrates that each suggested model scaling law contradicts all the others accurate laboratory models providing the separate empirical bases however all appear fairly consistent with the new design guidance developed here this formal development considers sediment excursions under wave action by means of a parameter including bed slope and the threshold of sediment movement the consequent relationship for sedimentation similitude between model and prototype indicates that appropriate model sediment and horizontal scale depend on the selected vertical scale along with wave period and prototype sand characteristics explicit forms derived from the general design guidance recover two expressions resembling those previously reported by e k noda 1972 and by p vellinga 1982 the route towards noda s result indicates that guidance is not appropriate for small models of large situations but the present development yields an independent basis and a needed refinement for vellinga s empirical results considerations of sedimentation similitude are also shown to be supported by successful new laboratory models using sand profiles developed in a large wave tank as prototypes spatial distortion seems to be the advisable strategy for small models but proper distortion is rather modest with prototype materials according to present results

assessment of beach and dune erosion and accretion using lidar impact of the stormy 2013 14 winter and longer term trends on the sefton coast uk abstract an important question for coastal management concerns the importance of individual storms and clusters of storms on longer term beach sediment budgets beach and dune erosion and coastal flood risk between october 2013 and march 2014 a series of deep atlantic low pressure systems crossed the northeast atlantic and strong winds high waves and high water levels affected many coastal areas in the uk and other parts of western europe net dune recession of up to 12 1 m occurred around formby point on 5 december 2013 the highest water level ever recorded at liverpool 6 22 m odn coincided with waves of hs of 4 55 m and tp of 9 3 s in liverpool bay wave trimming of the dune toe occurred along the entire length of the sefton coast but significant dune erosion occurred only where the upper beach between the mean high water spring tide level and the dune toe was

laboratory investigation of coastal beach erosion processes under storm waves of slowly varying height abstact storm induced large coastal waves are a predominant driver for coastal erosion problems but the physical processes of storm erosion have not been fully understood due to some technical difficulty in simulating storm waves with timely varying heights in the laboratory and collecting storm beach profiles in the field in this study novel series of experiments are proposed to study sandy beach processes under coastal storm conditions in a laboratory wave flume of 60 m long 3 m wide and 1 5 m high two water depths of h 0 5 m and h 0 7 m were used to investigate beach response under low and high tidal levels two initially uniform plane beach slopes of tan 1 15 for dissipation beach and tan 1 5 for reflection beach were used to study beach profile changes additionally intermediate beach tan 1 10 was also experimentally investigated under regular waves in another wave flume of 30 m long 0 6 m wide and 1 m high non intrusive instrumentation of high resolution cameras was used to record time series photo images on beach profile evolution in spatial resolution of 0 2 cm and a temporal resolution of 0 1 s image analyzing techniques were also developed to transform the recorded photo images to digital data on both beach and water surface profiles in analyzing the collected data it is found that the variation of storm wave height results in changes of wave breaking point and also sediment transport direction before and after the wave breaking point sediment transport direction was found to move onshore initially under small storm waves and then a sand bar was generated and a certain portion of sediment also moved offshore under large waves but such monotonic relationship between sediment transport and wave forcing could transform as morphology feedback and phase lags between wave orbital fluid velocity and sediment concentration the wave energy flux at the breaking point is shown to be suitable parameter in predicting beach mass change or storm erosion rate while the dimensionless sediment settling velocity parameter may not be a suitable criterion for predicting beach erosion or accretion under storm waves