deformation and fault activity in space and time in high resolution numerical models of doubly vergent thrust wedges a discrete element model is used to investigate the manner in which deformation and fault activity change in space and time during the development of a doubly vergent thrust wedge in the upper crust deformation is a result of shortening at a subduction slot in the base of the model a configuration which produces a dynamic backstop within the cohesionless frictional cover material a series of experiments with differing basal decollement friction are performed the distinct manners in which thrust wedges grow and the variability of fault development and activity in space and time are then examined both predicted large scale wedge geometries and individual fault fold structures are similar to those observed in sandbox models and show the complex manner in which shortening is accommodated and localized during the development of the thrust wedge when compared to a sandbox model with similar boundary conditions model results are strikingly similar in all cases deformation initiates above the subduction slot with the formation of an axial zone the wedge is then developed by displacement on a retro wedge thrust and propagation of deformation into the pro wedge region models with low coefficients of basal friction typically develop wide shallow wedges with distributed spaced deformation and rather symmetric box like structures whereas those with high coefficients of basal friction develop narrower steeper wedges consisting of a series of stacked pro wedge thrust sheets and a high displacement retro wedge thrust in general fault initiation and linkage is extremely complex in our models with several smaller faults operating until linkage occurs to form a major through going structure of particular interest is the observation that many of the faults do not develop at the basal decollement and propagate upwards through the cover but rather initiate at high levels in the cover and propagate link downwards with other deeper structures results also indicate the utility of the discrete element approach in modelling large displacement complex deformation of geological materials

structural evolution of calderas insights from two dimensional discrete element simulations the manner in which calderas develop is a key question in volcanology and has important implications for associated volcanogenic risk and geothermal and ore exploitation to better understand the structural evolution of calderas i use a discrete element model of a frictional cover undergoing piston like subsidence at its base simulating magma chamber deflation and cover collapse these novel simulations capture not only the initiation of cal deras but also much of the complexity of faulting during their later development in all models both normal and reverse faults accommodate deeper subsidence at higher structural levels curved outward dipping reverse faults are consistently the first structures to develop subsequent caldera growth is mainly the result of movement on vertical or steeply inward dipping normal faults this may be followed by a later phase of lateral collapse on shallower normal faults the roof aspect ratio r cover thickness piston width is seen to be an important factor calderas with low aspect ratios r 1 exhibit a coherent central subsiding block while those with higher aspect ratios have a complexly faulted internal structure

the impact of waves and tides on residual sand transport on a sediment poor energetic and macrotidal continental shelf 2019 the authors the energetic macrotidal shelf off south west england was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic wave and sediment transport model residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf sea sediments morphological evolution of the coastal and inner continental shelf zones and coastal planning waves heavily influence sand transport across this macrotidal environment median 50 exceedance waves enhance transport in the tidal direction extreme 1 exceedance waves can reverse the dominant transport path shift the dominant transport phase from flood to ebb and activate sand transport below 120 m depth wave tide interactions encompassing radiation stresses stoke s drift enhanced bottom friction and bed shear stress refraction current induced doppler shift and wave blocking significantly and nonlinearly enhance sand transport determined by differencing transport between coupled wave only and tide only simulations a new continental shelf classification scheme is presented based on sand transport magnitude due to wave forcing tide forcing and nonlinear wave tide interactions classification changes between different wave tide conditions have implications for sand transport direction and distribution across the shelf nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf at neaps nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide induced transport this emphasizes the critical need to consider wave tide interactions when considering sand transport in energetic environments globally where previously tides alone or uncoupled waves have been considered

cross shore stratified tidal flow seaward of a mega nourishment abstract the sand engine is a 21 5 million m 3 experimental mega nourishment project that was built in 2011 along the dutch coast this intervention created a discontinuity in the previous straight sandy coastline altering the local hydrodynamics in a region that is influenced by the buoyant plume generated by the rhine river this work investigates the response of the cross shore stratified tidal flow to the coastal protrusion created by the sand engine emplacement by using a 13 h velocity and density survey observations document the development of strong baroclinic induced cross shore exchange currents dictated by the intrusion of the river plume fronts as well as the classic tidal straining which are found to extend further into the nearshore from 12 to 6 m depth otherwise believed to be a mixed zone estimates of the centrifugal acceleration directly after construction of the sand engine showed that the curvature effects were approximately 2 times stronger suggesting that the sand engine might have played a role in controlling the cross shore exchange currents during the first three years after the completion of the nourishment presently the curvature effects are minute

a new strategy for discrete element numerical models 2 sandbox applications 1 here we present a series of numerical experiments using a new formulation of the discrete element method dem that improves performance in modeling faults and shear zones in the new method named the stress based discrete element method sdem which is introduced in the companion paper by egholm stress tensors are stored at each circular particle further sdem includes rotational resistivity of particles and elastoplastic constitutive rules for governing particle deformation when combining these new features the sdem is capable of reproducing the friction properties of rocks and soils without the need for the ad hoc calibration routines normally associated with dem in contrast to the conventional dem the friction properties of a sdem particle system are in agreement with the mohr coulomb constitutive model with friction angles specified on a particle level benchmark sandbox models show that unlike most commonly used numerical methods sdem faults and shear zones develop at angles in agreement with general observations from structural geology and analogue modeling studies citation egholm d l m sandiford o r clausen and s b nielsen 2007 a new strategy for discrete element numerical models 2 sandbox applications j geophys res 112 b05204 doi 10 1029 2006jb004558

impact of a headland associated sandbank on shoreline dynamics abstract sandbanks can occur downdrift of headlands across embayments as a result of tidal currents and wave forcing and may present a potentially valuable resource of marine aggregate material large sandbanks can alter tidal flows and through refraction and dissipation increase or decrease wave exposure along the shoreline of an embayment the impact of offshore sandbanks on shoreline morphodynamics at varying timescales has not been rigorously investigated here we show for the first time that removing lowering or raising a headland associated sandbank can have a significant impact on longshore sediment transport a delft3d model of start bay and skerries bank uk validated on hydrodynamic observations was used to conduct the numerical experiments results indicate that removing or lowering the bank generally reduces dissipation and increases wave heights increasing longshore flux in the lee of the bank raising the bank generally has the opposite effect increasing dissipation and lowering flux under oblique waves the bank may protect the adjacent shoreline by refracting waves away from the coast shoreline flux for the region directly onshore of the bank acts as a continuous function of bank height r2 0 7 but correlations for distal regions are increasingly non linear or absent a raised bank would reduce transport rates to near zero across extensive sections of the bay reversing the long term net flux at points distal 5 km from bank from the bank location causing currently eroding regions to accrete our results demonstrate that moderate 5 m elevation changes to a sandbank will likely produce significant variations in wave power at the shoreline which will i modify the shoreline response for individual storms and ii substantially change shoreline morphology at decadal timescales from a broader perspective this study can be used to inform planning decisions involving naturally varying banks and or potential mining of sandbanks aiding shoreline protection strategies for locations with similar embayment sandbank configurations

behaviour of subtidal sandbars in response to nourishments the behaviour of subtidal sandbars can be strongly influenced by the introduction of sand nourishments in the coastal system this study focuses on the impact of nourishments on subtidal bar behaviour at spatio temporal scales beyond a single nourishment project it aims to determine the long term behaviour of subtidal sandbars along an entire coastal cell taking into account both the unnourished and nourished regime and covering various types of nourishments the analysis is based on over 50 years of sandbar evolution along the delfland coast a 17 km long coastal cell at the dutch north sea coastline protected by groynes and maintained with frequent sand nourishments observations reveal clearly different sandbar behaviour during the unnourished first 20 years and nourished periods of the dataset introduction of the first beach nourishments nourished sand primarily placed at the subaerial beach was found to stimulate sandbar development along previously unbarred sections of the coast shoreface nourishments nourished sand placed at the seaward face of the pre existing subtidal sandbar tended to migrate shoreward rapidly at a rate of 20 to 60 m year at this coast thereby forcing the pre existing sandbar to weld to the dry beach an abrupt transition of sandbar dynamics was observed following a major nourishment operation 37 5 mm3 of nourished sand that covered the entire coastal cell a new shallow sandbar formed with a degree of alongshore variability that was unprecedented at the delfland coast over the full study period these results imply that individual nourishments can influence the formation and migration of individual sandbars while continued nourishments can fundamentally change long term sandbar dynamics along an entire coastal cell

mathematical block motion model for deformation of a layer above a buried fault of arbitrary dip and sense of slip abstract an analytic series solution is obtained for the stress and deformation in an isotropic viscous or incompressible elastic layer subjected to rigid block motion at its base the block motion approximates slip on a pre existing basement fault of arbitrary dip and sense of slip deformation in the layer due to horizontally separating and horizontally converging blocks slip on a vertical basement fault and slip on 45 dipping reverse and normal basement faults is examined above horizontally diverging and converging blocks a symmetric syncline and anticline form respectively monoclines form above dipping basement faults the location of the monocline and to a lesser degree its form vary systematically with fault attitude and sense of slip for a given fault displacement the region of brittle failure in a basement normal fault model is larger than that in a reverse fault model new faults formed in the layer are arcuate in profile model results agree with observations of stress orientation and deformation from laboratory models

cover deformation above steep basement normal faults insights from 2d discrete element modeling abstract a discrete element model is used to investigate progressive cover deformation above a steep 70 basement normal fault the cover materials are homogenous with frictional material behavior in the model shown here both normal and reverse faults in the cover accommodate displacement on the underlying basement fault the earliest faults are curved reverse faults which propagate upwards from the basement fault tip into the proto hanging wall these are replaced progressively towards the footwall by subvertical to steep normal faults and finally by a normal fault which dips at an angle predicted by mohr coulomb theory thus most early secondary structures are located in the hanging wall of the final through going fault this structural evolution produces an asymmetric triangular zone of deformation above the basement fault tip which superficially resembles that associated with trishear however its progressive development is quite different results also emphasize that the occurrence of reverse faults in extensional settings is not diagnostic of inversion

assessing the impact of extreme storms on barrier beaches along the atlantic coastline application to the southern rhode island coast abstract in this work we use the 2d model xbeach to dynamically simulate coastal erosion due to a synthetic 100 year storm impacting a typical north atlantic barrier beach located in southern ri this storm was extracted from the north atlantic coast comprehensive study naccs database based on results of an extreme value analysis of more than 1000 naccs storms xbeach parameters are first calibrated validated by simulating hurricane irene august 2011 for which both nearshore wave data and pre and post storm beach profiles were available in the study area comparing results to observations allowed calibration of the wave asymmetry and skewness parameter u a 0 3 in the model resulting in a 6 mean relative error between the simulated and measured subaerial eroded volumes along 4 transects in the 100 year storm xbeach simulations that include overwash effects of land cover on beach erosion in particular vegetation are assessed by specifying a spatially varying bed friction function of high resolution land cover results show that healthy back dune vegetation is essential to prevent the dune crest from being fully eroded down to its toe level the predicted median 100 year eroded volume is 46 m3 m for the entire barrier beach in good agreement with fema s empirical value of 50 m3 m at the two official 1d transects within the study area mean post storm reductions in dune crest elevations are in similar agreement the model however predicts very large alongshore variations of these parameters with eroded volumes over 1000 m3 m where breaching and the opening of surge channels occurs overall dune segmentation simulated in the model for the 100 year storm appears to be realistic and consistent with dune topography and land cover xbeach thus provides an improved 2d methodology for assessing the impact of extreme storms on atlantic barrier beaches predicting changes in dune morphology and quantifying the protective role of vegetation and effects of land cover in general

provenance determination of volcaniclastic rocks the nature and tectonic significance of a cambrian conglomerate from the new england fold belt eastern australia abstract the murrawong creek and pipeclay creek formations of the new england fold belt of eastern australia provide one of the few records of middle cambrian early ordovician sedimentation along the eastern gondwana margin they comprise conglomerate sandstone siltstone and laminated argillite that accumulated in an inner submarine fan environment sandstones are quartz poor volcanolithic varieties conglomerate clasts are mainly andesite but range from basalt to rhyolite all these rocks are porphyritic with phenocrysts of feldspar albite after calcic plagioclase augite and uncommonly titanomagnetite the augite is a low tio2 variety and titanomagnetite has only a modest tio2 content alteration has modified the magmatic composition of the clasts but the ess mobile elements indicate they were derived from a low k orogenic suite in consonance with petrographic and mineralogical data a western source and the presence of lower paleozoic subduction complex rocks to the east of the cambrian ordovician units indicates that the latter accumulated in a forearc setting the distributive province may have been the precursor of the macquarie volcanic belt of the eastern lachlan fold belt in n s w or one of the cambrian oceanic island arcs preserved in the fragmented gondwana margin sequences in southeastern australia northern victoria land antarctica and new zealand

relative scale and the strength and deformability of rock masses abstract the strength and deformation of rocks depend strongly on the degree of fracturing which can be assessed in the field and related systematically to these properties appropriate mohr envelopes obtained from the rock mass rating rmr classification system and the hoek brown criterion for outcrops and other large scale exposures of fractured rocks show that rock mass cohesive strength tensile strength and unconfined compressive strength can be reduced by as much as a factor often relative to values for the unfractured material the rock mass deformation modulus is also reduced relative to young s modulus a cook book example illustrates the use of rmr in field applications the smaller values of rock mass strength and deformability imply that there is a particular scale of observation whose identification is critical to applying laboratory measurements and associated failure criteria to geologic structures

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

seasonal scale nearshore morphological evolution field observations and numerical modeling abstract a coupled waves currents bathymetric evolution model delft 3d is compared with field measurements to test hypotheses regarding the processes responsible for alongshore varying nearshore morphological changes at seasonal time scales a 2001 field experiment along the beaches adjacent to grays harbor washington usa captured the transition between the high energy erosive conditions of winter and the low energy beach building conditions typical of summer the experiment documented shoreline progradation on the order of 10 20 m and on average approximately 70 m of onshore sandbar migration during a four month period significant alongshore variability was observed in the morphological response of the sandbar over a 4 km reach of coast with sandbar movement ranging from 20 m of offshore migration to over 175 m of onshore bar migration the largest seasonal scale onshore migration event observed in a natural setting both observations and model results suggest that in the case investigated here alongshore variations in initial bathymetry are primarily responsible for the observed alongshore variable morphological changes alongshore varying incident hydrodynamic forcing occasionally significant in this region due to a tidal inlet and associated ebb tidal delta was relatively minor during the study period and appears to play an insignificant role in the observed alongshore variability in sandbar behavior at kilometer scale the role of fully three dimensional cell circulation patterns in explaining the observed morphological variability also appears to be minor at least in the case investigated here

extracting decadal morphological behaviour from high resolution long term bathymetric surveys along the holland coast using eigenfunction analysis abstract the understanding and prediction of coastal behaviour over a time span of decades and alongshore stretches of tens of kilometres is important in coastal management the controlling variables for coastal behaviour on these scales are yet unknown it is hypothesised that regions exhibiting different large scale coastal behaviour lscb regions are controlled by different hydrodynamic forcings or by different sedimentological or morphological constraints or by some combination of these factors the objective of this study is to elaborate a method that effectively quantifies large scale morphological changes from a large bathymetric data set large temporal and spatial extent combined with a high resolution such to define lscb regions the method of analysis consists of a combination of the empirical eigenfunction technique and a moving window approach the method has been applied on a data set of over 14 000 nearshore profiles the data set consists of yearly soundings of the nearshore profile along a coastal stretch of 115 km length the holland coast the alongshore profile spacing is generally 250 m all profiles surveyed in the period 1963 1990 are included in the analysis application of the method on the dutch data set reveals that lscb regions indeed can be identified the sizes of the lscb regions are 5 km 15 km 20 km 32 km and 42 km differences in behaviour of the secondary morphology i e morphology other than the mean profile shape e g nearshore bars are most pronounced the change in behaviour between lscb regions generally occurs over distances as short as about 2 km the boundaries between the regions are therefore surprisingly sharp in general no clear long term trends in the development of the shape of the sub aqueous profile have been observed along the holland coast along certain stretches trends in cross shore shifting of the sub aqueous profile occurred the average shape of the sub aqueous profile seems to have no relation with the trend in cross shore shifting of the shoreline the 1 m contour the sub decadal shoreline fluctuations however are possibly related to the largescale dynamics of multiple bar systems

beach scarp dynamics at nourished beaches abstract beach scarps are nearly vertical seaward facing sandy cliffs within the cross shore beach profile these features are often associated with eroding nourished coastlines and can reach heights of o 2 3 m an analysis of a six year dataset of beach scarp presence at the nourished sand engine beach shows that the formation of beach scarps at the nourishment is linked to mildly erosive summer storm conditions whereas destruction is often related to extremely erosive winter storm conditions additional experiments were carried out showing the formation migration and destruction of scarps from artificially constructed mounds with linear slopes the field experiments show that steep initial slopes are more susceptible to beach scarp formation video observations at these experiments show that the scarp toe level where the vertical slope meets the gently sloping beach is related to the high wave runup events the commonly used 2 exceedance wave runup estimates can therefore be used to predict the final elevation of the scarp toe the strong connection of maximum runup elevation with the scarp toe elevation provides a direct relation between the final scarp height through nourishment platform height and hydrodynamic conditions high platform nourishments will promote the formation of beach scarps and steep initial profiles increase the speed at which scarps form this study suggests that by adjusting the design of beach nourishments beach scarp formation and persistency can be limited by regulating the natural destruction of these features

nearshore sediment pathways and potential sediment budgets in embayed settings over a multi annual timescale abstract embayed beaches constitute a large proportion of the world s rocky coastlines but there is a paucity of studies focusing on the longshore sediment exchange between embayed beaches separated by rocky stretches of coast here we investigate the nearshore sediment transport dynamics along a 15 km stretch of the embayed coastline of north cornwall sw england using delft3d numerical simulations coupled wave and tide are conducted to compute major circulation modes and sediment fluxes including order of magnitude for sediment bypassing between bays for a wide range of modal and extreme wave conditions results indicate that extreme events cause i multi embayment circulation and mega rip formation where an alongshore current is deflected offshore 0 7 m s 1 at 20 m depth in the down wave sectors ii large bypassing rates 103 104 m3 day 1 bypassing and iii exchanges extending to depths that exceed the base of the headlands accretionary phases over moderate high swell periods were associated with clockwise intra embayment circulation with simulated currents inducing redistribution towards the south in the long embayments 103 m3 day 1 longshore this circulation mode is combined with significant bypassing rates around the shallower and wider headlands 102 103 m3 day 1 predictions of sediment fluxes along the lower shoreface are based on the correlation between the modelled sediment fluxes and offshore wave conditions r 0 92 providing insights into the potential sediment budget over multi annual timescales hindcasted yearly bypassing rates around the headlands range between 103 and 105 m3 y 1 under an assumption of unlimited sediment supply with the bulk of the transport occurring mainly during high energy events hence the magnitude of the computed potential sediment fluxes presented here has implications for coastal evolution at longer timescales 10 years especially along sediment starved coastlines

role of waves and tides on depth of closure and potential for headland bypassing abstract depth of closure is a fundamental concept used to define the seaward extent of a morphodynamically active shoreface at a particular temporal scale the estimation of this limit in relation to the depth in front of the bounding headlands along embayed coastlines allows questioning whether embayments often deemed closed sediment cells experience more headland bypassing than expected wave based parameterisations developed for microtidal beaches are most widely used to estimate closure depth however a re evaluation of the concept for shorefaces influenced by geological control presence of headlands and or bedrock and strong tidal currents is appropriate here we use the macrotidal embayed and high energy coastline of sw england to identify the active nearshore limits with a multi method approach that includes observations of shoreface morphology and sedimentology offshore inshore wave formulations and bed shear stress computations we identify the basal limit of significant i e 0 14 m morphological change depth of closure doc and a maximum depth of extreme bed activity and sediment transport depth of transport dot observations of doc correspond closely to the values predicted by existing formulations based on inshore wave conditions 10 15 m for the study area relative to mean low water spring water level in this case the computed dot represented by the upper plane bed transition attained under extreme conditions exceeds 30 m depth in the study area the significant implication is that even though many headlands appear sufficiently prominent to suggest a closed boundary between adjacent embayments significant wave and tide driven sediment transport is likely to occur beyond the headland base during extreme events especially at low water levels the maximum depth for significant sediment transport dot was computed across a broad wave current parameter space further highlighting that tidal currents can increase this closure depth estimate by 10 m along macrotidal coastlines representing a 30 increase compared to tideless settings this work illustrates the importance of tidal currents in depth of closure calculations and challenges the notion that embayed beaches are generally closed cells as headland bypassing may be more wide spread than commonly assumed along exposed coastlines globally

the initial morphological response of the sand engine a process based modelling study abstract sand nourishments are presently widely applied to maintain or enhance coastal safety and beach width over the last decades global sand nourishment volumes have increased greatly and the demand for nourishments is anticipated to increase further in coming decades due to sea level rise with the increase in nourishment size and the request for more complex nourishment shapes an adequate prediction of the morphodynamic evolution is of major importance yet neither the skill of current state of the art models for such predictions nor the primary drivers that control the evolution are known this article presents the results of a detailed numerical modelling study undertaken to examine the model skill and the processes governing the initial morphological response of the sand engine and the adjacent coastline the process based model delft3d is used to hindcast the first year after completion of the mega nourishment the model reproduces measured water levels velocities and nearshore waves well the prediction of the morphological evolution is consistent with the measured evolution during the study period with brier skill scores in the excellent range the model results clearly indicate that the sand eroded from the main peninsular section of the sand engine is deposited along adjacent north and south coastlines accreting up to 6 km of coastline within just one year analysis of model results further show that the erosional behaviour of the sand engine is linearly dependent on the cumulative wave energy of individual high energy wave events with the duration of a storm event being more dominant than the maximum wave height occurring during the storm the integrated erosion volume due to the 12 events with the highest cumulative wave energy density accounts for about 60 of the total eroded volume of the peninsula indicating that the less energetic wave events with a higher probability of occurrence are also important for the initial response of the sand engine a structured model experiment using the verified delft3d model indicates that wave forcing dominates the initial morphological response of the sand engine accounting for approximately 75 of the total erosion volume in the first year the vertical tide is the second most important factor accounting for nearly 17 of the total erosion volume with surge wind and horizontal tide playing only a minor role

modelling of bed sediment composition changes at the lower shoreface of the sand motor abstract large perturbations in the coastline such as the sand motor nourishment 21 million m3 at the holland coast can initiate considerable spatial and temporal changes in the median grain size d 50 of the sea bed on the lower shoreface the relevance of hydrodynamic conditions for the development of the heterogeneity in d 50 at large scale nourishments was assessed with a numerical model delft3d which required a validation against 2 5 years of d 50 measurements a good representation of the observed spatial pattern of d 50 was obtained independent of a 2dh or 3d approach and initial condition for the d 50 of the bed five sediment size fractions and a multi layer administration of the bed composition were used the extent and magnitude of the coarsening of the bed is related to the velocity of the horizontal tide while a far less pronounced coarsening takes place during energetic conditions i e h m 0 3 m differential suspension behaviour between the size fractions which are all mobilized at the bed causes a preferential transport of fine sediment in alongshore direction away from the sand motor at the lower shoreface i e seaward of msl 6 m storm conditions may induce a partial removal of the coarse top layer due to mobilization of all of the size fractions and mixing with the relatively fine substrate material simulations also show that transport of the fine sand fraction extents to much deeper water than for the medium and coarse sand fractions models with multiple sediment fractions are therefore required for the assessment of environmental impacts of large scale coastal structures or land reclamation s and sediment transport on the lower shoreface

environmental controls on decadal morphologic behaviour of the holland coast a detailed comparison of alongshore variation in environmental variables along the holland coast with the observed marked regional differences in decadal nearshore morphologic behaviour reveals that neither offshore hydrodynamic parameters nor grain size are discriminating factors rather the abrupt alongshore changes in decadal behaviour coincide with sharp changes in shoreface morphology and the location of large man made structures these structures such as jetties and a protruding seawall appear to act as artificial headlands once they are built the coastal stretches on either side of the structure can develop independently of each other initially small differences in the development of the regions potentially may evolve into larger differences with time consequently on the long term large man made structures may affect the behaviour of coastal stretches over far larger distances than was previously known

sediment transport and budget of the central coastal zone of holland abstract based on the available short term morphological data 1964 1992 the net yearly averaged sand volume change in the surfzone 3 8 m nap to local datum approximately mean sea level along the coast of holland was found to be 125 000 m 3 year sedimentation including beach nourishments a sand budget model has been developed which describes the sand volume change in m 3 year in each compartment of the coastal area given known gradients of the computed longshore and cross shore transport rates and known source sink terms nourishment dumping and dredging the model area extends in cross shore direction from the 3 m nap contour to the 20 m nap contour the sand budget model has been calibrated hindcast study using the yearly averaged sand volume changes derived from bathymetry data jarkus data base collected during the period 1964 1992 input data are the gradients of the yearly averaged longshore and cross shore transport rates at the boundaries of the compartments and the available data of beach nourishment dumping and dredging in the same period a 2dv mathematical model representing the hydrodynamic waves and currents and sand transport processes in a cross shore profile was applied to compute the yearly averaged transport rates in various profiles along the coast at depths of 20 and 8 m and in the surf zone a detailed sensitivity study was performed to determine the variation ranges of the transport rates

initial spreading of a mega feeder nourishment observations of the sand engine pilot project sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety as the size of these nourishments increases new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented this paper presents the initial morphological evolution after implementation of a mega nourishment project at the dutch coast intended to feed the surrounding beaches in total 21 5 million m3 dredged material was used for two shoreface nourishments and a large sandy peninsula the sand engine peninsula a highly concentrated nourishment of 17 million m3 of sand in the shape of a sandy hook and protruding 1 km from shore was measured intensively on a monthly scale in the first 18 months after completion we examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast our observations show a large shoreline retreat of o 150 m along the outer perimeter of the peninsula with locally up to 300 m retreat the majority 72 of the volumetric losses in sediment on the peninsula 1 8 million m3 were compensated by accretion on adjacent coastal sections and dunes confirming the feeding property of the mega nourishment further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre nourishment values in the following 12 months the changes were more moderate overall the feeding property was strongly correlated to incident wave forcing such that months with high incoming waves resulted in more alongshore spreading months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross shore movement of sediment

immediate profile and planform evolution of a beach nourishment project with hurricane influences abstract in this study planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration weekly beach profiles shoreline surveys and nearshore wave measurements were conducted before during and immediately after construction of the 1100 m long upham beach nourishment project on the low energy west coast of florida this project was constructed in three segments the wide north segment the central segment and the narrow south segment with the exception of the relatively distant passage of hurricane charley calm weather prevailed for 45 days following completion of the south and central segments construction of the wide north segment was completed on august 27 2004 substantial planform diffusion occurred prior to construction completion via formation of a 300 m long spit extending from the wide north segment the shoreline orientation was changed abruptly due to this diffusion spit formation as opposed to the gradual adjustment predicted by most long term models planform adjustment was initiated prior to profile equilibration and it did not require high energy conditions a simple vector sum model for determining the orientation of a potential diffusion spit was developed this study recommends designing end transitions at the predicted diffusion spit orientation to avoid post nourishment spit formation during future projects profile equilibration occurred rapidly due to the passage of three hurricanes soon after nourishment was complete nine days after completion hurricane frances passed by the project area generating high wave conditions h sig 1 7 m for this region the steep post nourishment beach slope of 0 078 was reduced to 0 036 nearly to the equilibrium slope 0 034 due to this storm hurricanes ivan and jeanne which were nearly as energetic passed by the project area within 1 month after frances and resulted in much less profile slope change examination of the ratio of total volume to plan area remaining in the project area also suggested that a substantial portion of the total profile equilibration occurred as a result of hurricane frances this study indicates that profile equilibration can be an event driven process which contradicts the concept of longer term gradual profile equilibration both profile and planform adjustment can occur rapidly given the appropriate site conditions and energy levels

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

numerical modelling of erosion rates life span and maintenance volumes of mega nourishments mega nourishments aiming at providing long term coastal safety nature qualities and recreational space have been applied recently at the holland coast and are considered at various other places in the world methods to quickly evaluate the potential and lifetime of these coastal mega nourishments are therefore very much desired which is the main objective of this research two types of mega nourishments can be distinguished feeder type mega nourishments may erode freely to feed adjacent coasts for a more natural dynamic dune growth while permanent mega nourishments are designed to preserve safety levels and need to maintain their size and shape and thus needs to be nourished themselves the design and impact assessment studies for both types of mega nourishments require detailed morphological studies to determine the morphological evolution in this paper 2dh delft3d and 1d unibest cl and longmor numerical models were calibrated using data of the sand motor mega nourishment and were then applied to model a series of mega nourishments with various width over length ratios and volumes in order to derive relations and design graphs for erosion rates life span and maintenance volumes these relations and design graphs can be used in project initiation phases and feasibility studies the magnitude of the modelled wave driven longshore sediment transport rates in 1d coastline models depend on the representation of wave refraction on the lower shoreface since a distinction should be made between the non rotating lower shoreface and active surfzone it was shown that the life time of nourishments is mainly determined by the dimensions of the nourishment and incoming wave energy

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

process based modelling of a shoreface nourishment abstract a state of the art process based model is applied to hindcast the morphological development of a shoreface nourishment along the barrier island of terschelling the netherlands the applied morphodynamic model is delft3d for fully three dimensional flow and sediment transport in coastal environments owing to a complex geomorphological setting of the study area the curvi linear model includes adjacent tidal inlets and covers 40 70 km with an increasing grid size resolution towards the nourishment site in the center of the island in 1993 a total of 2 mm3 of sand was supplied to the nearshore bar zone off terschelling filling up the trough between the middle and outer bar by spring 1994 most of the nourished sediment had been redistributed onshore and welded onto the middle bar where it remained in the following years the morphodynamic model is applied to the prediction of this rapid nearshore profile behaviour the calibration of the model against an extensive set of full scale hydrodynamic data at several locations throughout the nearshore bar zone shows a good representation of the measured hydrodynamics morphodynamic results show a dependency on spatial scale on the scale of precise bed level evolution with respect to bar migration and growth model predictions are poor as the nearshore bars are predicted to flatten out resorting to bulk volumes integrated over larger spatial scales the model clearly has skill in predicting the overall effects of the nourishment the lack of phase shift between sediment transport and bathymetry is identified as the key controlling factor for the poor sandbar predictions

kinematic modelling of extensional fault propagation folding abstract many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation in particular folding at higher levels such extensional fault propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement strain the folds are cut by faults as they propagate upwards into the cover to date however there has been little investigation into the kinematics of linked basement faulting and extensional fault propagation folding here we present a two dimensional kinematic model of linked basement faulting and fault propagation folding which is based upon trishear the model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them the evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model the kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies

sediment connectivity a framework for analyzing coastal sediment transport pathways connectivity provides a framework for analyzing coastal sediment transport pathways building on conceptual advances in graph theory from other scientific disciplines connectivity schematizes sedi