basement structure and its influence on the structural configuration of the northern north sea rift the northern north sea rift basin developed on a heterogeneous crust comprising structures inherited from the caledonian orogeny and devonian post orogenic extension integrating two dimensional regional seismic reflection data and information from basement wells we investigate the pre rift structural configuration in the northern north sea rift three seismic facies have been defined below the base rift surface 1 relatively low amplitude and low frequency reflections interpreted as pre caledonian metasediments caledonian nappes and or devonian clastic sediments 2 packages of high amplitude dipping reflections 500 ms thick interpreted as basement shear zones and 3 medium amplitude and high frequency reflections interpreted as less sheared crystalline basement of proterozoic and paleozoic caledonian origin some zones of seismic facies 2 can be linked to onshore devonian shear zones whereas others are restricted to the offshore rift area interpreted offshore shear zones dip s ese and wnw in contrast to w to nw dipping shear zones onshore w norway our results indicate that devonian strain and ductile deformation was distributed throughout the caledonian orogenic belt from central south norway to the shetland platform most of the devonian basins related to this extension are however removed by erosion during subsequent exhumation basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters e g in the stord and east shetland basins pre rift structures with present day dips 15 were reactivated although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction

multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis abstract the post caledonian exhumation history of nw scotland is a controversial issue with some studies advocating largely continual emergence whereas others suggest dominantly early palaeogene plume driven exhumation apatite fission track analysis afta data for samples of precambrian basement and permian cretaceous sediments from onshore and offshore reveal multiple phases of post caledonian cooling triassic beginning 245 225 ma cretaceous 140 130 ma 110 90 ma and cenozoic 65 60 ma 40 25 ma 15 10 ma all of which are interpreted at least in part as recording exhumation basement and sedimentary cover rocks display similar thermal histories emphasizing the regional nature of these episodes and implying that sedimentary outliers represent the remnants of previously more extensive sequences significant thicknesses of jurassic rocks may once have covered nw scotland palaeocene palaeothermal effects are most pronounced in the vicinity of igneous centres probably reflecting combined effects of heating by elevated heat flow deeper burial and hydrothermal activity most of the region underwent kilometre scale neogene exhumation contrary to the common assumption of monotonic cooling and denudation histories integration of geological evidence with afta data defines an episodic thermal history involving repeated cycles of burial and exhumation we suggest that onshore passive margins and continental interiors may also best be characterized by similar histories

basement reactivation in the development of rift basins an example of reactivated caledonide structures in the west orkney basin the west orkney basin is a poorly studied palaeozoic and mesozoic rift basin that overlies a highly seismic reflective caledonian orogenic basement terrane this study presents a novel approach of using 2d seismic data to map single intra basement reflection packages and their relationship to overlying normal faults in the west orkney basin it is demonstrated that the rift architecture of the west orkney basin is more linear with a prominence of relay zones relative to previous interpretations and that rift structures form complex discordant and concordant relationships with pre rift caledonide basement structures restoration of basement fabrics to their pre extensional geometry indicates that the reactivation of basement structures as normal faults has occurred only where the pre extensional dip of basement structures is greater than 30 the relatively high density of relay zones mapped in the west orkney basin is proposed to be the result of the rift system forming a partially exploitative relationship with basement structure where extension has been accommodated between segments that have or have not reactivated basement fabrics

modelling rip current flow and bather escape strategies across a transverse bar and rip channel morphology abstract rip currents are a hazard to bathers on surf beaches worldwide yet due to logistical and ethical concerns there has been minimal examination of how bathers caught in them should attempt to escape this study presents the first numerical model of simulated bathers escaping from a rip current an understanding of the underlying coastal geomorphology and hydrodynamics form a critical basis for the model with the intention that outcomes of the model should be evaluated from a physical science perspective field observations of a transverse bar rip channel were used as model inputs escape simulations were performed with moderate energy h s 1 m oblique offshore wave forcing used to generate two non stationary asymmetric flow fields dominant surfzone exits and dominant recirculation the model treats bathers as particles that move with the underlying flow with an additional swimming velocity added iterating until a safety condition based on depth and current speed is satisfied or until a maximum time limit is reached simulations compared the strategies of stay afloat and various fixed swim directions using two bather heights and four swim speeds up to 0 4 m s the overall optimal escape strategy was to swim parallel in the direction of alongshore flow time to safety was less for i recirculating flow ii taller bathers and iii greater swim speeds across all simulations 44 of floaters reached safety within 10 min while 80 of slow swimmers 0 2 m s succeeded in the same time interval this suggests that slow sustainable swimming may be a preferable escape action to floating optimal swim direction varied with start location from onshore near the shoreline parallel to shore mid rip channel and diagonally onshore outer rip channel at lower swim speeds the optimal swim direction had greater dependence on the underlying flow field as opposed to distance to safety therefore choice of direction is more complex for slower swimmers critically no strategy succeeded in all scenarios at all locations across the surfzone and small changes to input conditions water level start time and location swim direction had major impacts on outcomes future modelling efforts should examine additional surf zone rip current morphologies and wave tide inputs with a goal of determining generalised rip escape principles that may be communicated to the general public

spatial scale and drainage basin morphometric interaction summary the effect of spatial scale changes on the interaction amongst morphometric properties of drainage basins is examined through order by order principal components analysis of eight morphometric parameters the results reveal striking similarities in the intercorrelation structures of basin morphology irrespective of the spatial scale of investigation the strength of the interaction amongst the variables in each correlation set however varies with basin order the intensity of interaction among the planimetric elements increases while that of slope attributes decreases with increase in basin size the former is attributed to the inherent capability of a stream system to regulate itself by size adjustments in stream segment number and lengths while the latter arises from the less sensitive link between valley side and stream channel slopes in higher order stream segments because of flood plain deposition these size related variations sign post the need to confine applied morphometric intercorrelation studies to samples of higher order basins the morphological properties of which are spatial averages of those of the lower order basins nested within them

on the dense bubble clouds and near bottom turbulence in the surf zone 1 measurements of high frequency 100 khz acoustical backscatter in the surf zone have identified the presence of a wall formed by dense assemblages of bubbles generated by breaking gravity waves and persisting for periods up to 30 min these bubbles are advected by alongshore and cross shore rip currents and are controlled by the local wave field turbulence dissolution and buoyancy during the summer of 2000 the location of the bubble wall south of scripps pier california was tracked for a 6 week period distinct categories of bubble wall defined by the backscatter intensity data are observed distinguished by the presence or absence of rip current activity the results suggest that presence or absence of long period waves 10 20 s may play a role in controlling the bubble wall type during periods without rip currents the location of the bubble wall is controlled by the incoming wave field simultaneous turbulence dissipation measurements 0 4 m above the seafloor show clear dependence on the local water depth beneath incoming waves the acoustical backscatter data are interpreted using in situ bubble and turbulence measurements in conjunction with a simple model based on bubble sorting by buoyancy dissolution and turbulence

drifter measurements in a laboratory rip current 1 this paper investigates circulation in a laboratory rip current system using large numbers of lagrangian drifters with supplementary current meter and water level measurements these represent the most dense measurements to date of laboratory rip circulation over a large spatial area overall circulation is found to be very unsteady with strong changes in circulation apparent at many length and time scales drifter and current meter measurements are compared in the rip channel and stokes drift is found to be a significant component of drifter velocities in this region estimated generation of circulation is compared with computed bottom friction dissipation with good agreement the mean cellular circulation about a dividing streamline is found to be surprisingly small when compared with computed rates of generation of circulation finally the divergence of volume flux computed using drifters is found to be significant with depth varying wave induced mass transport depth varying eulerian velocities and velocity drifter concentration effects the likely sources of error

canonical correlation analysis in geomorphology with particular reference to drainage basin characteristics abstract problems in the analysis and interpretation of the interaction patterns of drainage basin characteristics are outlined the canonical correlation technique is suggested as capable of simplifying and producing a high level of generalization of the complex interaction patterns the technique is described and employed in structuring the relationships between the morphometric and topologic attributes of a sample of 36 monolithologic third order drainage basins in the udi awgu cuesta southeastern nigeria and the factors controlling their development the canonical solution identifies three significant patterns of association between basin planimetric properties and their causative and deterministic factors the texture of dissection is strongly associated with soil and vegetation characteristics while the stream network size and the stream bifurcation ratio are closely related to the stage of basin development and basin relief respectively some general problems of the canonical correlation analysis are outlined

observations of nearshore circulation rip currents a sector scanning doppler sonar was deployed at the end of the scripps institution of oceanography pier aimed in toward the surf zone estimates of acoustic backscatter intensity and radial velocity were obtained seaward of the break point over a wedge with an arc of about 45 and a radius of 200 to 400 m the acoustic intensity is proportional to some combination of the bubble density and the suspended sediment in the water well defined jets of water extending seaward from the surf zone or rip currents were observed these rip currents occurred episodically recurred aperiodically one to four times per hour or so and lasted several minutes each the water transported offshore within the rips was rich in suspended sediment and bubbles producing distinctive bright patterns that can be easily recognized in successive images of backscatter intensity from the sonar fluid velocities were estimated from the doppler shift of the sonar signal approaching 0 7 m s in some of the events simultaneously a transect of temperature density and turbidity within the rip current was obtained with conductivity temperature depth ctd and optical backscatter strength obs sensors these data describe the ejection of warm turbid water from the surf zone and provide a comparison between the acoustic intensity and the optical turbidity of the fluid the horizontal extent of the sonar measurements and the vertical resolution of the ctd obs measurements complement each other in the study of the dynamics of the nearshore environment exchange rates are not fully resolved here since only one seaward jet is contained within the field of view however these observations suggest that rip currents could cause significant exchange between the nearshore and offshore waters

rip currents mega cusps and eroding dunes abstract dune erosion is shown to occur at the embayment of beach mega cusps o 200 m alongshore that are associated with rip currents the beach is the narrowest at the embayment of the mega cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune to undercut the dune and to cause dune erosion field measurements of dune beach and rip current morphology are acquired along an 18 km shoreline in southern monterey bay california this section of the bay consists of a sandy shoreline backed by extensive dunes rising to heights exceeding 40 m there is a large increase in wave height going from small wave heights in the shadow of a headland to the center of the bay where convergence of waves owing to refraction over the monterey bay submarine canyon results in larger wave heights the large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale the strongly refracted waves and narrow bay aperture result in near normal wave incidence resulting in well developed persistent rip currents along the entire shoreline the alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95 confidence the alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95 confidence therefore it is concluded the mega cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega cusp

physical modeling of three dimensional intermediate beach morphodynamics experiments have been performed in a large wave tank in order to study the morphodynamics of rip current systems both accretive and erosive shore normal wave conditions were applied the beach evolving through all the states within the intermediate beach classification under the so called down state accretive and up state erosive morphological transitions results show that any prescribed change in the wave conditions drastically increases the rate at which the morphology changes the surf zone morphology tends toward a steady state when running a given wave climate for a long duration we quantitatively describe a full down state sequence characterized by the progressive evolution of an alongshore uniform bar successively into a crescentic plan shape a bar and rip channel morphology and a terrace from the analysis of a large data set of dense eulerian measurements and bathymetric surveys we depict several feedback mechanisms associated with wave driven rip current circulation wave nonlinearities and the seabed evolution at first a positive feedback mechanism drives a rapid increase in the rate of morphological change beach three dimensionality and rip intensity by the time the sandbar evolves into a bar and rip morphology a negative feedback mechanism characterized by a decaying beach change rate and an increasing beach alongshore uniformity overwhelms the former mechanism an erosive sequence characterized by both an overall offshore bar migration and an increase in beach three dimensionality is also described

open ocean surface wave measurement using doppler sonar in october november 1983 doppler sonars mounted on the research platform flip were used to scatter 75 khz sound from the underside of the sea surface at low angle as well as from the interior of the mixed layer surface gravity waves were seen in velocity estimates from the surface scattering sonar even though the wave conditions were unusually calm valid measurements of sea surface motion were obtained over the range interval 600 to 1400 m from flip a second sonar which transmitted horizontally and scattered from the interior of the mixed layer also sensed surface waves although with amplitude reduced in proportion to the decay of the motions with depth wave number frequency spectra of the observed motions are consistent with linear theory the existence emergence of this technology enables the synthesis of kilometer long surface wave arrays in the open sea without the cost and logistical support usually associated with large aperture arrays in addition the doppler acoustic approach can provide information on lower frequency surface currents and on the spatial variations in these low frequency currents such as langmuir cells which might affect wave propagation

acoustic attenuation in very shallow water due to the presence of bubbles in rip currents an experiment was performed just off the research pier at the scripps institute of oceanography to determine the acoustic effects of small bubbles in very shallow water 6 m depth the distance offshore was 300 m the propagation lengths were 2 10 m and the frequency range was from 39 to 244 khz during the experiment rip currents passed through the field of measurement instruments these rip currents were laden with bubbles created in the surf between the instruments and the shore the effects of these rip currents on the spatial distributions of the resulting acoustic attenuation are discussed from the attenuation data the bubble distributions are calculated using a new iterative approach caruthers et al in press j acoust soc am that is based on the well known resonant bubble approximation calculated bubble distributions varied from an essentially uniform lack of bubbles during quiescent periods to highly inhomogeneous and dense bubbly regions within rip events such observed distributions were consistent with measurements made by other investigators during the experiment

bubble transport in rip currents a number of remote and in situ acoustical sensors were mounted in the surf zone off scripps pier la jolla california during march 1997 and used to characterize rip currents and their ability to transport bubbles offshore from the surf zone the bubble size distributions and air fractions at the injection point were measured using an acoustical resonator and a conductivity sensor right in the surf zone the offshore moving bubble plume was tracked with a multibeam 100 khz doppler sidescan sonar giving the spatial extent and offshore variability in the rip events as well as information about the surface wave field furthermore three acoustical resonators were mounted at 2 5 m depth 55 60 m farther offshore to probe the bubble field 300 400 s after injection these results are interpreted using models that include bubble buoyancy and dissolution rip current advection and the turbulent boundary layer which is represented by the christoffersen and jonsson 1985 formulation

a critical analysis of the structure and tectonic significance of rift oblique lineaments transfer zones in the mesozoic cenozoic succession of the faroe shetland basin ne atlantic margin abstract nw se trending rift oblique lineaments transfer zones9 occur along the length of the ne atlantic margin previous workers have suggested that these lineaments played an important role in providing conduits and or barriers to sedimentation during the cretaceous and palaeocene it has also been suggested that they were active as discrete basin wide strike slip faults this study uses a well calibrated 3d seismic survey of regional extent to critically assess the structural and stratigraphic evidence for three rift oblique lineaments in the uk sector of the faroe shetland basin victory clair and judd lineaments structures previously attributed to basin wide strike slip deformation can be more simply explained as igneous intrusions hydrothermal vent complexes gas chimneys and or faults that transfer extensional strain between en echelon rift segments there is little evidence to suggest that activity along discrete basin wide lineaments controlled palaeocene sedimentation within the faroe shetland basin rather sediment transport and deposition at this time are likely to have been controlled by along and across strike variations in the magnitude of thermal subsidence which in turn reflect the 3d nature of the underlying mesozoic rift architecture

structural style of buried ediacaran basins in saudi arabia on seismic reflection data abstract several isolated ediacaran basins subcrop phanerozoic strata in saudi arabia the structural styles of these subcropping basins are reviewed here based on interpretation of 2d and 3d seismic reflection data and comparison with arabian shield outcrops the basins are distinguished by layered seismic reflectors that are interpreted as sedimentary and volcanic strata due to limited well penetrations these packages cannot be directly dated but a relative chronology is established anchored by constraints from the arabian shield and regional studies most of the basins are bound by extensional faults and the basin fills show growth architectures and angular unconformities the bounding faults trend broadly north south and are interpreted to be late to post orogenic reactivations of oceanic terrane margins based on their structural characteristics in comparison with sub basins exposed on the shield the basin fills are correlated with the ediacaran jibalah group an equivalent of the omani nafun group these sub basins experienced inversion and exhumation prior to ongoing volcanism and unconformable deposition of late ediacaran to earliest cambrian kurayshah group sediments the kurayshah group is disconformably overlain by the widespread tayma group siliciclastics this disconformity correlates to the angudan unconformity in oman the kurayshah group includes a late ediacaran stratovolcano over 40 km in diameter in the eastern basins evaporitic structural styles indicate the presence of hormuz ara evaporites with local igneous intrusions that correlate at least in part to the kurayshah group the tayma group infills significant accommodation space variations and was affected by ongoing but declining differential subsidence and reactivation of the underlying basin bounding faults

modelling infragravity motions on a rip channel beach a non linear shallow water wave model operating on the time scale of wave groups is compared with measurements of infragravity motions on a rip channel beach to verify the model concepts and assess the model performance the measurements were obtained during the rip current experiment ripex in concert with the steep beach experiment sbe performed at sand city monterey bay ca during the spring of 2001 the nearshore bathymetry was made up of shore connected shoals incised by relatively narrow rip channels spaced approximately 125 m apart the comparison considers a 20 day period during which significant changes in both the offshore wave climate and nearshore bathymetry occurred the temporal variation in infragravity conditions during the experiment is strong with computational results typically explaining 70 to 80 of the observed infragravity motions within the nearshore in contrast to the temporal variation the alongshore spatial variation in infragravity intensity during the experiment is generally weak even though the underlying bathymetry shows strong depth variations model computations suggest preferential coupling between the computed edge wave motions and the quasi periodic bathymetry is present a prerequisite for strong spatial variability however the infragravity field is dominated by cross shore infragravity motions which are only weakly coupled to the quasi periodic bathymetry resulting in a weak alongshore variability of the total infragravity motions

northern scotland as an atlantic north sea divide president9s anniversary address 1984 from the end of the caledonian orogeny until the present northern scotland has acted as a structural high separating the north sea and atlantic basins or their forerunners the geological history of this positive massif is discussed in relation to that of the adjacent cratonic basins with the objective of determining the extent to which it adapted to regional tectonic developments and the manner in which its responses were modified by the pre existing basement structure from devonian to early palaeocene times the massif was generally low lying and its behaviour with respect to vertical movements was essentially neutral the land surface carved in the crystalline basement during the devonian period was preserved with relatively small modifications and little metamorphic detritus was supplied to the adjacent basins tectonic events of major importance in the basins such as the formation of the north sea and hebridean rift systems produced little change of conditions in the intervening massif it is inferred that the underlying keel of lithospheric mantle was protected from the effects of lithospheric stretching the uneventful history of the massif was interrupted by two phases of mafic igneous activity in late carboniferous and palaeocene times which record responses to regional plate motions the formation of the palaeocene igneous province was followed by a unique phase of uplift as a result of which the ancient sub devonian land surface was elevated and dissected and abundant crystalline detritus was supplied to the north sea the style of these events and the anomalous character of the continental margin off nw britain may have been determined by the refractory nature of the precambrian basement which inhibited stretching prior to sea floor spreading

bubble clouds and their transport within the surf zone as measured with a distributed array of upward looking sonars a collaborative multi institute experiment called the scripps pier experiment was conducted in the vicinity of the scripps pier in la jolla california in march 1997 to study the fate of bubbles in the surf zone and the effects of these bubbles on acoustic propagation this paper discusses data gathered by the applied physics laboratory university of washington using a set of four upward looking sonars frequency 240 khz which simultaneously measured vertical profiles of acoustic volume scattering from bubbles at four locations the transport of bubbles via rip currents emerged as an important though episodic and localized feature of the acoustic environment in the surf zone images of volumetric backscattering strength vs time and depth reveal the episodic events of increased scattering level lasting between 5 and 10 min caused by the passage of bubble clouds over the sonar time lags for the onset of increased scattering at the four locations are consistent with a seaward velocity of the bubble clouds of order 10 cm s and the length scales of these bubble clouds in the seaward direction are inferred to be in the range 50 100 m the influence of the incoming surface wave field is also discussed

a model for the horizontal directionality of breaking wave noise in the surf zone a model is presented for the horizontal directionality of the noise generated by individual breaking waves in the surf zone the model is based on the interaction between sound radiated by ringing bubbles created in a breaking wave crest and the population of acoustically quiescent bubbles left on the seaward side of the wave in the shallow water waveguide the effect of the quiescent bubbles is to absorb sound from all but the very ends of the breaking crest resulting in the formation of acoustic hot spots the model calculations are in good agreement with observations of the horizontal directionality of noise from individual breaking waves in the surf zone

the moine thrust in the birps data set a second generation of birps profiles combine with older data to form a loose 10 by 40 km spacing grid over the offshore projection of the moine thrust these profiles show clear reflections that arguably represent fault plane reflections from the moine and related caledonian thrust structures in the location suggested by some earlier workers reflectors predominate at two structural levels 8 10 km 2 5 3 5 stwt and 13 16 km 4 0 5 5 stwt depths the deeper set appears to define an antiformal stack of thrusts or duplex with possible continuation to deeper levels by analogy with onshore sections and after subsequent extension is restored this deeper set correlates with the moine thrust onshore the shallower set aligns with normal faults that bound half grabens filled with devonian and permo triassic rocks this set correlates with the naver thrust after similar restoration normal faulting appears to have reactivated some of the thrusts increasing their reflectivity detailed stacking and interval velocity studies indicate that an increase of about 1 2km s 1 occurs across the reflections here associated with the two fault zones the overall reflection pattern is consistent with a complex stack of thrust sheets but lack of resolution prevents a complete structural analysis

rip current types circulation and hazard abstract rip currents are narrow and concentrated seaward directed flows that extend from close to the shoreline through the surf zone and varying distances beyond rip currents are ubiquitous on wave exposed coasts each year they cause hundreds of drowning deaths and tens of thousands of rescues on beaches worldwide and are therefore the leading deadly hazard to recreational beach users the broad definition above masks considerable natural variability in terms of rip current occurrence in time and space flow characteristics and behaviour in particular surf zone rip currents have long been perceived as narrow flows extending well beyond the breakers flushing out the surf zone at a high rate exit flow circulation regime while more recent studies have shown that rip flow patterns can consist of quasi steady semi enclosed vortices retaining most of the floating material within the surf zone circulatory flow circulation regime building upon a growing body of rip current literature involving numerical modelling and theory together with emergence of dense lagrangian field measurements we develop a robust rip current type classification that provides a relevant framework to understand the primary morphological and hydrodynamic parameters controlling surf zone rip current occurrence and dynamics three broad categories of rip current types are described based on the dominant controlling forcing mechanism each category is further divided into two types owing to different physical driving mechanisms for a total of six fundamentally different rip current types hydrodynamically controlled 1 shear instability rips and 2 flash rips which are transient in both time and space and occur on alongshore uniform beaches bathymetrically controlled 3 channel rips and 4 focused rips which occur at relatively fixed locations and are driven by hydrodynamic processes forced by natural alongshore variability of the morphology in both the surf zone and inner shelf zone and boundary controlled 5 deflection rips and 6 shadow rips which flow against rigid lateral boundaries such as natural headlands or anthropogenic structures for each rip current type flow response to changes in hydrodynamic and morphologic forcing magnitude is examined in regard to velocity modulation and changes in circulation regime providing key force response relationships of rip currents we also demonstrate that in the real world rip currents form through a mixture of driving mechanisms and the discrete rip types defined in fact form key elements in a wide and complex spectrum of rip currents on natural beaches it is anticipated that this rip current type classification will serve as a resource for coastal scientists and non specialists with an interest in the rip current hazard and as a platform for future rip current studies finally we suggest some important future research directions highlighting the need for coastal and beach safety communities to collaborate in order to improve rip current education and awareness

rip current circulation and surf zone retention on a double barred beach abstract rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants between the surf zone and inner shelf concurrent in situ eulerian and lagrangian gps drifter data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy double barred beach the data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current and the exchange process on both days there was a prominent clockwise eddy in the surf zone for which the seaward heading portion formed a rip current in a well defined channel rip incised into the inner bar exit rate measured with drifters from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar from 71 exits to 6 over the two days exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone under higher wave conditions there were stronger pulsations in surf zone currents and more surf zone exits however higher wave conditions caused wave breaking over the outer bar this breaking increases vorticity around the outside of the surf zone eddy which increases surf zone retention this is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies under such conditions drifter exits were rare and occurred due to vortex shedding during lower incident wave conditions eddy vorticity was lower and drifters could relatively freely exit the surf zone this is one of the few studies that investigate surf zone circulation on a high energy double barred beach

infragravity rip current pulsations 1 the origins of rip current pulsations within the infragravity frequency band 0 004 0 04 hz are determined from measurements made with arrays of colocated pressure and velocity sensors deployed on a beach with persistent rip current channels the observations indicate significant energy in cross shore infragravity velocities that varies spatially in the alongshore due to the presence of rip channels infragravity velocities are smaller within the rip channel than on the shore connected shoal owing to differences in water depth rip current pulsations at infragravity frequencies are linked to standing infragravity motions but not to the ponding and subsequent release of water by wave group pumping

terrane boundary reactivation barriers to lateral fault propagation and reactivated fabrics rifting across the median batholith zone great south basin new zealand prominent pre existing structural heterogeneities within the lithosphere may localise or partition deformation during tectonic events the ne trending great south basin offshore new zealand formed perpendicular to a series of underlying crustal terranes including the dominantly granitic median batholith zone which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics we find that the crustal to lithospheric scale southern terrane boundary of the median batholith zone is associated with a crustal scale shear zone that was reactivated during late cretaceous extension between zealandia and australia this reactivated terrane boundary is oriented at a high angle to the faults defining the great south basin we identify a large granitic laccolith along the southern margin of the median batholith expressed as sub horizontal packages of reflectivity and acoustically transparent areas on seismic reflection data the presence of this strong granitic body inhibits the lateral south westward propagation of ne trending faults which segment into a series of splays that rotate to align along the margin as they approach further we also identify two e w and ne sw oriented basement fabrics likely corresponding to prominent foliations which are exploited by small scale faults across the basin we show that different mechanisms of structural inheritance are able to operate simultaneously and somewhat independently within rift systems at different scales of observation the presence of structural heterogeneities across all scales need to be incorporated into our understanding of the structural evolution of complex rift systems

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

the role of structural inheritance in the development of high displacement crustal faults in the necking domain of rifted margins the klakk fault complex froya high offshore mid norway abstract the role of inherited structures during the development of normal faults in continental rifts and proximal domains of passive margins have been extensively studied few studies however have a focus on deciphering the role of inheritance in the development of high displacement 10 km low angle 25 km is present during rifting

geological constraints structural evolution and deep geology of the northwest scottish caledonides the front of the caledonian orogenic belt in nw scotland is marked by a zone of foreland thrusting which contains imbricates of lewisian basement proterozoic cover and cambrian shelf sediments faults within this moine thrust belt in most localities propagated in a foreland directed sequence therefore the earliest of these thrusts was the moine thrust which carried a basement assemblage of moine and lewisian rocks over the cambrian shelf the development of large duplex and imbricate structures in the footwall postadted movement on this thrust hence a restoration of these imbricates provides a minimum estimate of the eastern extent of the cambrian shelf no synsedimentary or prethrust extensional features are recognised within the cambrian succession which displays a remarkable stratigraphic and thickness consistency this implies a corresponding consistency in crustal structure beneath these cover rocks immediately prior to caledonian thrusting a balanced cross section constructed across the northern part of the moine thrust belt has given a restored width for the cambrian shelf of 54 km geophysical data suggest that the present foreland crustal thickness is 28 km if this is taken to be the crustal thickness beneath the cambrian shelf during caledonian thrusting a minimum cross sectional area of 1512 km of lewisian rocks must remain beneath the present outcrop of the moine thrust sheet this foreland basement wedge may have been imbricated subsequent to the development of the cambrian imbricates caledonian structures within the moine thrust sheet are interpreted as forming an imbricate stack with the moine thrust acting as a floor thrust the ductile imbricate thrusts possibly roofed into the naver slide late open folds which warp foliation slides and metamorphic isograds within the moine sheet may represent culminations in the foreland lewisian imbricates beneath the moine thrust these postulated culminations may have been sufficient to initiate gravity driven structures this may explain late movements on high level faults within the moine thrust belt

semi determinate hydraulic geometry of river channels south island new zealand data to describe the morphologic hydrologic and sedimentologic characteristics of 72 south island new zealand rivers were collected and analysed nearly 70 per cent of variation in channel morphology is accounted for by differences in cross sectional area slope and cross section shape only 53 per cent of the morphologic variability could be statistically explained by the hydrologic and sediment variables used the level of explanation varied for different morphologic variables nearly 90 per cent of the variability in cross sectional area could be explained but aspect ratio maximum depth divided by hydraulic radius was completely independent apart from the inadequacy of the measured variables as indices of the true underlying controlling factors and the imperfect measurement and sampling procedures the low level of explanation is probably due to the influence of factors such as floodplain vegetation high quasi random variability in bark sediment character boundary effects imposed by bedrock bluffs and the precise sequence of flood events none of which are easily quantified in addition observations indicate that there is a large random variation in channel form which cannot be related to any factor an attempt to relate channel morphology to flow variability using simple indices of the latter was unsuccessful

analysis of surf zone turbulence measurements of turbulent kinetic energy k under surf zone waves are analyzed to show how k varies over depth between breaker point and shoreline and how k depends on the beach slope it is found that the variation of k over depth is remarkably weak large values being measured a few percent of the depth above the bottom a simple model for the dissipation mechanism makes it possible to derive an empirical formula for the time averaged k that accurately describes all the data considered reliable

lagrangian observations of circulation on an embayed beach with headland rip currents abstract this study describes the first comprehensive measurements of nearshore current patterns across the entire extent of an embayed beach bounded by headland rip currents a field experiment at whale beach nsw australia provides valuable insights into i embayment wide spatial and temporal flow behaviour ii rates of cross and alongshore water exchange and iii the influence of geological control by headlands on morphology and circulation lagrangian flow data was obtained using 34 gps drifters with 293 individual deployments over a single ebbing tidal cycle during moderate low energy h s 1 m oblique wave forcing in situ wave and current data and bathymetric data were also collected beach morphology was dominated by a large mid beach rip channel with lesser headland rip channels mean flow rates were 0 6 ms 1 in the mid beach channel and 0 4 ms 1 in the headland channels with the majority of cross shore water volume flux 60 through the central channel a weak alongshore current o 0 1 ms 1 was forced by the oblique offshore wave angle rip current velocities flow variability and rate of surfzone exits by lagrangian drifters increased as water level decreased transient currents on a planar bar along the northern half of the beach with velocity standard deviation up to 0 2 ms 1 were not tidally modulated lagrangian time series were used to differentiate four current regimes rip cell rip head planar bar and offshore low energy zone based on mean velocity velocity variability and degree of tidal modulation an increase in surfzone exit rates by drifters was observed from south upwave to north downwave with exit rates per drifter deployment of 22 at the south headland rip 65 at the mid beach open rip and 80 at the north headland rip the high rate of drifter exits contrasts previous observations on open coast beaches observed flow behaviours are attributed to wave shadowing at the upwave protected end of the beach and longshore currents forced by oblique waves deflected offshore at the downwave headland these field observations are in good agreement with recent numerical modelling a relationship between bathymetric variability and current intensity was determined with cross shore average mean velocity correlating with a parameterisation of bathymetric alongshore non uniformity this study demonstrates that flow behaviour and exchange rates can vary along the length of an embayed beach due to geological control this research has implications for transport of organisms nutrients and pollutants is relevant to beach safety practitioners and can be used in calibration of numerical models

air entrainment processes and bubble size distributions in the surf zone abstract a new optical instrument was deployed in the surf zone in a trial experiment to measure bubble size distributions and visualize air entrainment and bubble formation mechanisms within breaking surf images of bubbles and the evolving air water mixture inside and beneath breaking wave crests are presented the images resolve features of the air water mixture to length scales of hundreds of microns across a 3 7 cm field of view two qualitatively different large scale air entrainment processes are observed first intrusions of air and water thought to be created by jets penetrating the water s surface fragment into plumes of bubbles second an air cavity trapped by the overturning wave crest is observed to disintegrate into bubbles the timescale for the evolution from a compacted air water mass to individual bubbles was on the order of 90 ms or less for both of these processes in addition small scale air filaments hundreds of microns wide and millimeters long have been discovered beneath wave

the influence of structural inheritance and multiphase extension on rift development the northern north sea the northern north sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement the geometry and evolution of syn rift depocentres during this multiphase evolution and the mechanisms and extent to which they were influenced by pre existing structural heterogeneities remain elusive particularly at the regional scale using an extensive database of borehole constrained 2d seismic reflection data we examine how the physiography of the northern north sea rift evolved throughout late permian early triassic rp1 and late jurassic early cretaceous rp2 rift phases and assess the influence of basement structures related to the caledonian orogeny and subsequent devonian extension during rp1 the location of major depocentres the stord and east shetland basins was controlled by favorably oriented devonian shear zones rp2 shows a diminished influence from structural heterogeneities activity localises along the viking sogn graben system and the east shetland basin with negligible activity in the stord basin and horda platform the utsira high and the devonian lomre shear zone form the eastern barrier to rift activity during rp2 towards the end of rp2 rift activity migrated northwards as extension related to opening of the proto north atlantic becomes the dominant regional stress as rift activity in the northern north sea decreases through documenting the evolving syn rift depocentres of the northern north sea rift we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics controlling the segmentation of depocentres as well as the locations styles and magnitude of fault activity and reactivation during subsequent events

longshore current and wave height modulation at tidal frequency inside the surf zone data were acquired continuously during the 19 day delilah nearshore experiment with a specific objective of examining variability of the longshore current at tidal frequencies it is hypothesized that breaking wave heights inside the surf zone are strong functions of the depth which are modulated by the tidal variations and since radiation stress is a function of the wave height longshore currents are forced at the tidal frequency inside the surf zone the measured longshore current variations at tidal frequency are the same order of magnitude as the mean longshore current variations for moderate wave height conditions indicating that the tide is a dominant mechanism associated with longshore current variability simulations of the magnitude and phase of the longshore current variability with tide elevation using the model by thornton and guza 1986 are used to explain observations the measured tidal elevation and longshore current are in phase in the inner surf zone and out of phase in the outer surf zone as predicted by the model verifying the hypothesis

the vertical structure of low frequency motions in the nearshore part i observations abstractfield observations of oscillating currents in the surfzone of a natural beach show significant vertical structure in energy phase and rotation at low frequencies around 0 005 hz where most of the energy is associated with vorticity motions energy levels in the cross shore component of the flow seaward of the sandbar decay near the bottom shoreward of the bar crest the flow decays nearly linearly over the water column conversely a weaker alongshore component of the flow increases near the bottom seaward of the sandbar and is roughly depth uniform inside the bar crest near this 0 005 hz frequency band the coherence between the uppermost and successive vertically separated sensors drops off quickly with as much as a 70 80 coherence drop over the water column ranging from 2 5 to 4 m the phase relative to the uppermost sensor shifts approximately linearly over depth with as much as 50 phase lag at the bottom that can lag or lead the surface rotary coefficients also vary across the su

nearshore circulation over transverse bar and rip morphology with oblique wave forcing there is a paucity of field data to describe the transition in nearshore circulation between alongshore meandering and rip current systems a combination of in situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at pensacola beach florida in the presence of relatively low energy oblique waves current speeds vary in response to the relative wave height ratio hs h which defines the degree and extent of breaking over the shoal in the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves as waves begin to break across the shoal 0 2 0 5 the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone the increase in wave dissipation is associated with an increase in very low frequency vlf variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow the unsteady nature of the nearshore circulation is responsible for 55 of all surf zone exits under these more dissipative conditions in contrast only 29 of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore meandering current while the currents had a low velocity maximum of 0 4 m s 1 and would not pose a significant hazard to the average swimmer the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low energy rip circulation systems under oblique wave forcing copyright 2013 john wiley sons ltd

ripex observations of a rip current system rip current kinematics and beach morphodynamics were measured for 44 days at sand city monterey bay ca using 15 instruments composed of co located velocity and pressure sensors acoustic doppler current profilers and kinematic gps surveys the morphology consisted of a low tide terrace with incised quasi periodic rip channels representative of transverse bars offshore 17 m depth significant wave height and peak period ranged 0 20 3 0 m and 5 20 s the mean wave direction was consistently near 08 resulting in rip channel morphology which evolved in response to the changing wave characteristics an inverse relationship between sediment accreting on the transverse bar and eroding in the rip channel was found the spatial distribution of sediment is reflected in the background rip current flow field the mean velocity magnitudes within the rip channel transverse bars increased offshore onshore with decreasing tidal elevations and increased with increasing sea swell energy eulerian averaged flows were predominantly shoreward on the transverse bars and seaward within the rip channel throughout the experiment resulting in a persistent cellular circulation except during low wave energy the rip current spacing to the rip channel width was less than or equal to two which suggests that the rip currents are influenced by each other and that no two dimensional bar return flow should be present the vertical velocity profile on the bar indicated that the flow was predominantly shoreward the flow field within the surf zone was depth uniform except for significant shear occurring near the surface owing to stokes drift the wave induced transport hypothesis is evaluated d 2005 elsevier b v all rights reserved

field observations of surf beat 1 progressive edge waves nineteen biaxial electromagnetic current meters have been used to determine the longshore and on offshore structure of currents at surf beat periods 1 4 min the sensors formed two linear arrays a long shore array within the surf zone and an on offshore array stretching from the shoreline to well beyond the breaker line analysis of the longshore current components yields a clear picture of progressive low mode edge waves with frequency wave number dispersion relations which are in remarkably good agreement with predictions some separation of edge wave modes is found with mode zero energy dominating in the frequency band 0 006 and 0 011 hz and mode one between 0 015 and 0 025 hz on offshore currents present a rather different picture which while not inconsistent with the longshore currents suggests that other sources of energy are also important to the on offshore currents these include standing edge waves probably formed by reflections at nearby scripps canyon and motions which are nonresonantly forced by incoming wave groups

morphodynamic instabilities of planar beaches sensitivity to parameter values and process formulations the initial growth of bed perturbations on planar sloping beaches under the forcing of obliquely incident breaking waves is investigated using a state of the art numerical model this allows for a systematic investigation of the sensitivity of the spatial structures of the bed perturbations and their growth and migration rates to different model formulations and parameterizations if the sediment is only transported in the direction of the net current velocity and sediment stirring is taken proportional to the wave height squared growing up current oriented crescentic bars are found with a preferred spacing of 800 m and a down current migration rate of 10 m d 1 varying the angle of wave incidence drag coefficient and bed slope results in qualitatively similar growing bed forms using an engelund and hansen transport formula very oblique down current oriented bars are obtained that grow in time no preferred wavelength however is found using the bailard transport formula results in growing up current oriented bars with a preferred spacing smaller than 300 m for wave angles smaller than 7 when using either the engelund and hansen or bailard sediment transport formulation it is essential to take the transport in the direction of the wave orbital velocity into account in order to have growing bed perturbations

high energy surf zone currents and headland rips at a geologically constrained mesotidal beach we analyze eulerian and lagrangian measurements of wave induced circulation collected during a 3 week field experiment at a high energy mesotidal barred beach with the presence of a 500 m headland and a submerged reef small changes in wave and tide conditions were found to largely impact circulation patterns three main regimes were identified depending on offshore wave obliquity 1 under shore normal configuration the flow was dominated by cross shore motions except for moderate waves at low tide with the presence of a quasi steady circulation cell on the reef 2 under shadowed configuration an onshore directed current flowing away from the headland and a weak oscillating eddy were present outside and inside the shadow region respectively 3 under deflection configuration a deflection rip flowing against the headland and extending well beyond the surf zone was present with activity maximized around low tide for moderate waves under 4 m oblique waves the deflection rip was active regardless of the tide with mean depth averaged velocities up to 0 7 m s 800 m offshore in 12 m depth with energetic low frequency fluctuations our results emphasize the ability of deflection rips to transport materials far offshore suggesting that such rips can transport sediment beyond the depth of closure this study indicates that a wide variety of wave driven circulation patterns can occur and sometimes coexist on beaches with prominent geological settings changes in the dominant driving mechanism can occur as a result of small changes in wave and tide conditions resulting in more spatially and temporally variable circulation than along open sandy beaches plain language summary most field experiments about wave induced circulation patterns have been conducted along open sandy beaches while experiments in geologically constrained environments are scarce we performed intensive field measurements at a high energy beach with the presence of a 500 m headland and a submerged natural reef three main circulation patterns were identified depending on the offshore wave obliquity for shore normal waves cross shore motions dominated the nearshore region while oblique wave configurations resulted in more complex horizontal circulation in particular under intense headland directed longshore current the flow was deflected seaward against the headland this deflection resulted in an intense seaward flowing jet deflection rip extending well beyond the surf zone edge particularly during storm conditions such findings highlight the ability of these deflection rips to dominate water and sediment exchanges between the nearshore and the inner shelf region our study further outlines the more spatially and temporally variable circulation patterns occurring along geologically constrained beaches compared to open sandy beaches ranging from small recirculating cells across the reef to a large deflection rip extending hundreds of meters beyond the surf zone

rip current review rip currents are shore normal narrow seaward flowing currents that originate within surf zone extend seaward of the breaking region rip head and can obtain relatively high velocities within the last decade there have been a significant number of laboratory and field observations within rip current systems an overview of rip current kinematics based on these observations and the scientific advances obtained from these efforts are synthesized rip current flows are partitioned into mean infragravity very low frequency vorticity and tidal contributions and it is found that each contributes significantly to the total data from the laboratory and the field suggest that the rip current strength increases with increasing wave energy and decreasing water depths the maximum mean current occurs inside the surf zone where the maximum forcing is present owing to the dissipation of waves

field observations of surf zone inner shelf exchange on a rip channeled beach cross shore exchange between the surf zone and the inner shelf is investigated using lagrangian and eulerian field measurements of rip current flows on a rip channeled beach in sand city california surface drifters released on the inner shelf during weak wind conditions moved seaward due to rip current pulses and then returned shoreward in an arcing pattern reentering the surf zone over shoals the cross shore velocities of the seaward and shoreward moving drifters were approximately equal in magnitude and decreased as a function of distance offshore the drifters carried seaward by the rip current had maximum cross shore velocities as they exited the surf zone and then decelerated as they moved offshore the drifters moving shoreward accelerated as they approached the surfzone boundary with maximum cross shore velocities as they reentered the surf zone over shoals it was found that stokes drift was not solely responsible for the onshore transport across the surfzone boundary the cross shore diffusivity on the inner shelf was greatest during observations of locally contained cross shore exchange these field observations provide evidence that the cross shore exchange between the surf zone and inner shelf on a rip channeled beach is due to wave driven rip current circulations and results in surface material being contained within the nearshore region

surf zone eddies coupled with rip current morphology 1 energetic very low frequency vlf frequencies 0 004 hz surf zone eddies szes were observed on a beach composed of shore connected shoals with quasi periodic 125 m incised rip channels at sand city monterey bay california incident waves consisted of predominantly shore normal narrow banded swell waves szes were located outside the gravity region in alongshore wave number ky spaced within the vlf band and did not appear to exist in higher frequency bands the szes were significant urms vlf 0 25 m s and constant in intensity within the surf zone shore connected shoals and rip channels and rapidly decreased offshore the alongshore and cross shore sze velocity variances were similar in magnitude vlf sze velocities were not forced by vlf surface elevations and were not well correlated with rip current flows r2 0 18 there is an indication that the szes were related to wave forcing with the szes statistically correlated with incoming sea swell wave height r2 0 49 f ky spectral estimates illustrate a strong relationship between rip channel spacing and sze cross shore velocities ky 0 008 m 1 and minimal sze alongshore velocity variation ky 0 m 1 data analysis suggests that the szes are not simply instabilities of an unstable rip current jet a simple conceptual model suggests that sze f ky spectra can be explained by the entire rip current circulation cells oscillating predominantly in the cross shore and slightly in the alongshore

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

mean currents and sediment transport in a rip channel measurements of hydrodynamics and suspended sediment transport were carried out along a cross shore transect in a rip channel a tidally induced threshold for rip flow initiation was found this threshold depended upon the degree of wave energy dissipation and could be identified through a critical value of the ratio of significant wave height to water depth s in the rip neck with normally incident waves rip current velocities were well correlated with velocities predicted from a simple model involving the onshore mass transport in asymmetric breaking waves crossing the bar hydrodynamics and sediment transport were tidally modulated with strong offshore directed rip currents and associated offshore sediment transport due to the mean flow at low tide at high tide when the rip was inactive the tendency was for weak onshore directed mean flows and or oscillatory incident waves transporting smaller amounts of sediment landward the net result was a gradual lowering of the topographic relief along the rip channel with net deposition seaward of the rip outside the surf zone transport was mainly landward due to oscillatory incident waves

canonical correlation analysis as a tool in the provenance study of overbank sediments from the small mountainous watersheds canonical correlation analysis cca is used in this study in order to trace the lineage of overbank sediment from the initial erosion of the parent rocks down to deposition of detrital material in alluvium of the small mountainous watersheds of the umberak area croatia it helps to elucidate relations between the hierarchically structured systems rocks minerals elements represented by the ensembles of lithological mineralogical and geochemical variables taking their place in the vertical order of hierarchical complexity geochemistry and mineralogy of the recent material are considered dependent variable regarding the related watershed lithology with geochemical variables major and trace elements last in the chain three canonical models are built and cross compared in order to unravel the between level relationships and infer the basic patterns of mineral and geochemical flux from the source rocks to basin from these the two hierarchical provenance chains epitomized in recombination of the first two canonical functions have been derived highlighting complementary provenances weathering styles and dispersion avenues in alluvial sedimentation of the study area the first clearly separates carbonate from siliciclastic sedimentary source while the second illuminates the origin of phyllosilicate and ferric oxyhydroxide phases with associated suite of elements in absence of clear carbonate signal