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Many experimental and field studies of swash have been conducted but swash hydrodynamics are still poorly understood. The aim of the research presented here is to improve understanding of swash hydrodynamics through large-scale experiments and numerical modelling. The focus has been on bore-driven swash on impermeable beach slopes. A swash numerical model has been successfully established to simulate bore-driven swash events on impermeable beach slopes. The model is 1-D and solves the Depth-Integrated, Reynolds Averaged Navier Stokes' equations using a 'shock-capturing' Weighted Average Flux scheme. A critical aspect in solving the equations is the approach used to parameterize stress terms in the momentum equation. The model uses a quadratic velocity parameterization (r xu2) with friction factor (/) appropriately defined. Detailed measurements of swash water depths, velocities and turbulence characteristics have been made for two swash events using a 'large-scale' swash rig capable of generating a single, repeatable, very large swash event. The two swash events differ only in beach roughness: a 'smooth' beach made of Perspex and a rough beach made of Perspex with a pebble (d50 = 5.7mm) layer glued on. The incoming bore of height 0.23m and velocity 3.2m/s creates swash events of about 7s duration with a run-up of 5.7m and 4.7m on the smooth and rough beach respectively. Results from these novel experiments are presented and show that bed-parallel velocities are depth-uniform on the smooth beach but have significant flow structure on the rough beach. The presence of a logarithmic layer in the depth profiles of velocity allows for bed shear stresses to be obtained. Bed shear stresses in the swash zone were seen to vary significantly both in space and time. Numerical model results are compared against experimental results. Two versions of the swash numerical model were used: one with a constant friction factor and the other with a friction factor that varies with local Reynolds number and relative roughness. The results show that when the friction factor or equivalent wall roughness is tuned to give the correct run-up, the water depth and depth-averaged velocity predicted by the model are in good overall agreement with the measured results. Further insight into the detailed swash processes is achieved by analysing the individual terms contributing to the Depth-Integrated, Reynolds Averaged Navier Stokes' momentum equation. This analysis was applied to the numerical model and experimental results. The analysis shows that large amounts of momentum, associated with bore arrival, are supplied during the initial stages of uprush. During uprush, momentum extracted due to shear stress is relatively small whilst the extraction of momentum due to the weight of the fluid acting down the beach is large. Overall this results in an uprush that is dominated by gravity effects. Hydrodynamics during backwash are different. Gravity effects during backwash act to supply momentum to the flow. The effect of bed shear stress on reducing momentum becomes more significant with time. The result is that during backwash, momentum extracted via bed shear stress becomes equivalent in magnitude to that supplied by gravity.

Scroby Sands, a major nearshore sandbank on the East Anglian coast of the U.K., is constantly changing its configuration and alignment with the surrounding sandbanks and nearby coastline. This study investigates the hydro dynamical and morphological processes occurring over this complex area and provides an insight into the future morphological development of the Scroby sandbanks region. Numerical modelling, using the TELEMAC finite element system (version 5.5), is used to investigate the relative importance of waves, tidal currents, and storm surges in modifying this sandbank system and to understand the sand transport pathways and bed-evolution under a variety of hydrodynamic conditions around the sandbanks. To enhance model's performance, calibration and validation tests were conducted; field measurements of waves and tidal currents in the study area are analysed to help understand the spatial distribution of the hydrodynamic characteristics of the area. Analyses of recent and historical charts, and recentlysurveyed swathe bathymetries, are conducted to validate the morphodynamic model and to improve understanding for the morphology evolution of the study area. The model demonstrates that waves, especially northerly waves associated with a storm surge, enhance the net sand fluxes and the bed-evolution by 'stirring' the sand, while the asymmetrical tidal currents play an important role in transporting the sand. The model identifies Caister Ness as an area of sand flux convergence and a source of sand for the nearshore sandbanks (McCave, 1978), and suggests that the sand is moving to the sandbanks along features < 10 m in water depth (Caister Shoal to Cockle Shoal to Scroby Sands to Corton Sand to South Cross Sand). The relatively stable position of the -10m ODN contour on the historical charts since 1846 indicates that the regional tidal current stream dynamically maintains Scroby in its present configuration, although the exact configuration and central position of the shallowest part of Scroby varies over the time due to waves and storms. A steady increase in the area and volume of Scroby above -5 m ODN, where the major sand transport occurs, suggest a linear morphological trend rather than the recurrent cycles which were proposed by Robinson (1966) and Reeve et al. (2001a; 2001b).

This work focuses on the multi-scale variability of beach profiles. This includes the spatial variability over a range of scales of surveyed beach profiles and the complex temporal variability of beach elevation at given positions along the profile. The aims of this work are to characterize the variability of beach profiles in both time and space, to identify the predominant spatial and temporal patterns of beach profile changes, to identify the extreme profile changes due to infrequent storms/storm groups, to understand the nature of beach profile change in depth, to quantify the non-stationarity of beach profile and to provide insight into the prediction of beach profiles. This thesis includes a critical literature review of the existing profile models, such as numerical and data-driven models, to predict beach profiles. Particular focus is on the data-driven models since they characterize the beach in a site-dependent manner. The main weakness of the existing data-driven approaches is that many of the techniques assume stationarity and yet the processes in question are non-stationary, which necessitates more advanced techniques for investigating the variability of beach profiles. Hence in this thesis the wavelet technique is introduced, which is a relatively new technique. It is also shown how the use of a wavelet basis for decomposing the profile signals spatially allows a more satisfactory value for the depth of closure associated with a data set to be defined. Particular interests are in the beach profile data from the Field Research Facility (FRF) at Duck, North Carolina, USA. The field data and previous works by other researchers are introduced and preliminary studies are conducted including the interpolation of data and the empirical orthogonal function (EOF) analysis. A connection is established between EOF and wavelet analysis. In addition to the identification of basic patterns of beach profile changes, emphasis is given to the non-stationary investigation of beach profile changes in both time and space locally. In this way, the infrequent events are identified at different temporal scales. The responses of beach profile changes to different wave/storm conditions are discussed. The intermittent character of beach profile change is displayed in both time and space, providing much insight to the argument by Southgate and Moller (2000). Also, the depth of closure is presented by analysing the local components of wavelet variance in space, which is scale-dependent. The results agree with Larson and Kraus(1994). The wavelet analysis is validated on the beach profile data at the Coastal Research Station (CRS), Lubiatowo, Poland. Focus is on the spatial variability across the beach profile. Due to the multi-bar system, the spatial scale contents of beach profile changes at Lubiatowo are more complicated than Duck. The predominant spatial scales indicate that wave breaking may be the major factor of bar formation at this site. This is consistent with Pruszak et al. (1997).

A composite approach is used to study hydrodynamic and sediment dynamic processes, in the vicinity of offshore breakwaters situated in a macro-tidal environment; this combines field measurements, numerical modelling and grain size trend analysis. Field measurements were undertaken at an offshore breakwater scheme (Elmer, West Sussex), in order to investigate the key processes in the vicinity of the breakwaters. The investigation into the hydrodynamics included measurements offshore and inshore of the breakwaters, under various wave and tidal conditions. The dependence of sediment transport on wave asymmetries and water depth, especially during higher energy conditions, was identified. Numerical modelling was utilised for simulating the tidal and wave processes, at different stages of the tidal cycle. The interaction of the tidal currents with the structures, over the entire area of the scheme, was studied for a spring-neap tidal cycle. Significant alterations of the tidal currents in the landward area of the breakwater were observed; these included flow channelisation between the structures and the coastline, together with flow acceleration over the salients. The design characteristics of the scheme, (i.e. gap width, offshore distance, relative angle in respect to the tidal currents) are found to influence the magnitude of the acceleration. The accelerated currents increase the sediment transport locally over the top of the salients, regulating their growth. Wave energy immediately to seaward of the structures was regulated by the tidal elevation. However, in the shadow areas of the structure and over the salients wave height and associated sediment transport were controlled, by the water level (i.e. tidal stage) and the period of the incoming wave. The identification of the sediment transport pathways in the vicinity of the offshore islands was undertaken using the ‘Gao and Collins Method’; this is based upon correlating spatial resolution of sediment parameters. A sensitivity analysis of the transport pathways, under different sampling strategies (regular vs. irregular grids and variable grid spacing) and the analytical techniques (settling velocity vs. sieving), was undertaken. The importance of settling velocity in determining the statistical parameters of the grain-size distribution was identified, especially for the coarser-grained sediments (fine-medium sand). The combination of the results obtained using the different methodologies verify the processes controlling sediment dynamics in the vicinity of the structures; these are applicable to schemes located in similar environments.

"March 2002" / Includes bibliographical references (leaves 145-161) / xvii, 198 leaves : ill. (some col.), maps (some col.), plates ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / An analogue for shallow marine carbonate sedimentation and deposition on a broad passive margin is described from the eastern Great Australian Bight. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 2002

Στην παρούσα εργασία μελετάται η συμπεριφορά ιζήματος σε αιώρηση που προκαλείται λόγω θραύσης κύματος σε πυθμένα σταθερής κλίσης. Η αριθμητική προσομοίωση επιτυγχάνεται με παράλληλη επίλυση των εξισώσεων κίνησης (Navier-Stokes και Συνέχειας) και της εξίσωσης Μεταγωγής-Διάχυσης για τη μεταφορά ιζήματος σε αιώρηση. Επιλέγονται οι κατάλληλες οριακές συνθήκες ελεύθερης επιφάνειας, εισόδου και εξόδου, ενώ για την οριακή συνθήκη πυθμένα χρησιμοποιούνται εμπειρικοί τύποι που συνδέουν τη διατμητική τάση πυθμένα με τη συγκέντρωση πυθμένα. Οι εξισώσεις μετασχηματίζονται κατάλληλα ώστε το υπολογιστικό πεδίο να γίνει ανεξάρτητο του χρόνου. Για τη χρονική διακριτοποίηση χρησιμοποιείται ένα σχήμα κλασματικής μεθόδου ολοκλήρωσης με σταθερό χρονικό βήμα. Για τη χωρική διακριτοποίηση χρησιμοποιείται ένα υβριδικό σχήμα, το οποίο περιλαμβάνει διακριτοποίηση των εξισώσεων με χρήση πεπερασμένων διαφορών κατά τη διεύθυνση της ροής και εφαρμογή της φασματικής μεθόδου παρεμβολής με πολυώνυμα Chebyshev για την κατακόρυφη διεύθυνση. Μελετώνται περιπτώσεις κόκκων ιζήματος με διάμετρο κανονικοποιημένη ως προς το χαρακτηριστικό βάθος ροής, =10-4, =2∙10-4 και =5∙10-4. Κατά την θραύση παρατηρείται σημαντική ανύψωση του ιζήματος πυθμένα στη στήλη του ύδατος και για τις τρεις περιπτώσεις. Η καθαρή παροχή ιζήματος σε αιώρηση παρουσιάζει τη τάση να κινείται προς τα ανάντη της ροής με τη μέγιστη τιμή να εμφανίζεται μετά τη θραύση. Τέλος, διαπιστώνεται ότι η καθαρή παροχή αιωρούμενου ιζήματος είναι σημαντικά μεγαλύτερη από αυτή του ιζήματος κλίνης. / The simulations are based on the coupled numerical solution of the flow equations (continuity and Navier-Stokes) with the transport equation for suspended sediment load subject to the fully nonlinear free-surface boundary conditions and appropriate bottom, inflow and outflow boundary conditions. The equations are properly transformed so that the computational domain becomes time-independent. A hybrid scheme is used for the spatial discretization with finite differences in the streamwise direction and a pseudospectral approximation with Chebyshev polynomials in the vertical direction. A fractional time-step scheme is used for the temporal discretization. We seek results for the behavior of the suspended sediment load induced by broken waves for different particle sizes of bed material. The aim is to identify critical particle sizes for strong uplift and transport of sediment.

Στην παρούσα διατριβή διερευνάται η επίδραση παράκτιων μη-θραυόμενων κυματισμών στη μορφολογική ισορροπία αμμώδους πυθμένα με πτυχώσεις, η θραύση εκχείλισης κυμάτων πάνω από πυθμένα σταθερής κλίσης, καθώς και τα συνεπαγόμενα κυματογενή ρεύματα στη ζώνη απόσβεσης. Για το σκοπό αυτό αναπτύσσονται μοντέλα αριθμητικής προσομοίωσης, τα οποία πραγματοποιούν επίλυση των δισδιάστατων και τρισδιάστατων εξισώσεων ασυμπίεστης, συνεκτικής ροής με ελεύθερη επιφάνεια. Η αριθμητική επίλυση των εξισώσεων ροής, Navier-Stokes, επιτυγχάνεται με τη χρήση κλασματικής μεθόδου για τη χρονική ολοκλήρωση, ενώ η χωρική διακριτοποίηση πραγματοποιείται μέσω ενός υβριδικού σχήματος πεπερασμένων διαφορών και ψευδο-φασματικών μεθόδων προσέγγισης. Στις προσομοιώσεις της θραύσης εκχείλισης κύματος γίνεται χρήση της μεθόδου προσομοίωσης μεγάλων κυμάτων LWS, σύμφωνα με την οποία επιλύονται μόνο οι μεγάλες χωρικές διακυμάνσεις της ταχύτητας και της ελεύθερης επιφάνειας, ενώ η επίδραση των μικρότερων διακυμάνσεων περιγράφεται μέσω ενός μοντέλου διατμητικών τάσεων υποκλίμακας (SGS), ανάλογα με ότι ισχύει στη μέθοδο προσομοίωσης μεγάλων δινών, LES. Ένα ανεξάρτητο μοντέλο για την προσομοίωση της μεταβολής μορφολογίας πυθμένα, μέσω μεταφοράς φορτίου πυθμένα, αναπτύσσεται και χρησιμοποιείται σε σύζευξη με τα μοντέλα προσομοίωσης δισδιάστατης ροής. H παροχή του φορτίου πυθμένα υπολογίζεται μέσω τροποποίησης γνωστών εμπειρικών σχέσεων, σε συνδυασμό με τη στιγμιαία διατμητική τάση πυθμένα από τη μονάδα προσομοίωσης της ροής. Από τις προσομοιώσεις ροής πάνω από πυθμένα με πτυχώσεις, προκύπτει ότι η παρουσία των πτυχώσεων επηρεάζει σημαντικά το κυματογενές οριακό στρώμα, ενώ οι μορφολογικές προσομοιώσεις οδηγούν στο συμπέρασμα ότι, η μακροπρόθεσμη ισορροπία των πτυχώσεων επέρχεται για συγκεκριμένη τιμή της γωνίας/συντελεστή δυναμικής τριβής, η οποία συσχετίζεται με τις διαστάσεις των πτυχώσεων και τα χαρακτηριστικά του κύματος. Για τη θραύση εκχείλισης εξετάζονται οι περιπτώσεις κάθετης αλλά και υπό γωνία, ως προς την ακτογραμμή, διάδοσης κυμάτων πάνω από πυθμένα σταθερής κλίσης 1/35. Τα αποτελέσματα για τα χαρακτηριστικά της κάθετης θραύσης (ύψος και βάθος θραύσης, Ηb και db, αντίστοιχα) και του συνεπαγόμενου υποβρύχιου ρεύματος, συγκρίνονται με δημοσιευμένες πειραματικές μετρήσεις και η συμφωνία είναι ικανοποιητική. Το μοντέλο είναι σε θέση να προσομοιώσει την ανάπτυξη του επιφανειακού στροβίλου στο μέτωπο του θραυόμενου κύματος, η οποία συνοδεύεται από αύξηση της ισχύος των SGS τάσεων (μέχρι βάθους d/db ≈ 0.75) και διαδοχική μείωσή τους, μέχρι μηδενισμού, στα ρηχά της ζώνης απόσβεσης. Από τα αποτελέσματα για το πεδίο στροβιλότητας και τις SGS τάσεις, κατά την προσομοίωση της υπό γωνία θραύσης, παρατηρείται η σταδιακή θραύση του κύματος κατά μήκος της κορυφογραμμής, ενώ προκύπτει ότι οι τελευταίες παραμένουν ενεργές για περίπου δύο μήκη κύματος. Επίσης, η μέση ταχύτητα του παράλληλου ρεύματος προκύπτει πιο ενισχυμένη σε ρηχά βάθη στη ζώνη απόσβεσης (d/db < 0.5), ενώ η κατακόρυφη κατανομή του παρουσιάζεται σαφώς επηρεασμένη από την παρουσία του υποβρύχιου ρεύματος κοντά στον πυθμένα. / In the present thesis, the impact of nearshore, non-breaking waves on the morphological equilibrium of small scale patterns that appear in sandy beds, well-known as ripples, the spilling wave breaking over a bed of constant slope and the wave-induced currents developing in the surf zone, are investigated. Numerical models are developed for the simulation of the aforementioned phenomena, based on the numerical solution of the two/three-dimensional, incompressible, viscous, free-surface flow. The numerical solution of the flow equations, i.e. the Navier-Stokes equations, is accomplished by means of a time-splitting scheme of three stages for the temporal discretization and a hybrid scheme for the spatial discretization, with central finite differences along the streamwise direction and pseudo-spectral approximations, with Fourier modes and Chebyshev polynomials along the spanwise and vertical directions, respectively. The simulations of spilling wave breaking are performed employing the so-called large-wave simulation (LWS) method, according to which, large velocity and free-surface scales are fully resolved, while the effect of subgrid scales is modeled by eddy-viscosity stresses, similar to large-eddy simulation (LES) methodology. The bed morphology evolution, driven by the bed load sediment transport, is simulated by a morphology model, which performs the numerical solution of the sediment mass conservation equation, utilized coupled with the two-dimensional flow model. The bed load transport rate, is computed inserting bed shear stress timeseries (by the flow model) into published empirical formulas that have been modified to fit the characteristics of the investigated cases. For the case of rippled bed, it was found that the structure of the wave boundary layer is substantially influenced by the presence of the ripples, and that for a certain value of the dynamic friction angle/coefficient, which is correlated to the ripple dimensions and the wave characteristics, the ripples remain in quasi-steady equilibrium after each wave period. Wave breaking is investigated by the simulation of normal and oblique to the shoreline propagation, transformation and spilling breaking of incoming Stokes waves, over a bed of constant slope, tanβ = 1/35. Our numerical results are compared to published experimental measurements, and it is found that the LWS model predicts adequately the wave breaking parameters - breaking height, Ηb, and depth, db- and the distribution of the undertow current in the surf zone. The development of the surface roller in the breaking wavefront is also captured, while is connected to the increase of the strength of the sub-grid (SGS) stresses in the outer surf zone (up to d/db ≈ 0.75) and their successive decrease at shallower depths close to the shoreline. For the case of oblique wave breaking, the vorticity and the SGS stresses distribution in the surf zone clearly indicate the gradual breaking along the wave crestline, while the latter (SGS stresses) remain active for about two wavelenghts. Finally, the magnitude of the longshore current is found to be enhanced at shallower depths in the surf zone (d/db < 0.5), while its vertical distribution is affected by the interaction with the undertow current.