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Hydrodynamics and Morphodynamics in the Swash Zone: Hydralab Iii Large-Scale Experiments

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Hydrodynamics and Morphodynamics in the Swash Zone: Hydralab Iii Large-Scale Experiments UNIVERSITÀ DEGLI STUDI DI NAPOLI ―FEDERICO II‖ in consorzio con SECONDA UNIVERSITÀ DI NAPOLI UNIVERSITÀ ―PARTHENOPE‖ NAPOLI in convenzione con ISTITUTO PER L‘AMBIENTE MARINO COSTIERO – C.N.R. STAZIONE ZOOLOGICA ―ANTON DOHRN‖ Dottorato in Scienze ed Ingegneria del Mare XXIV ciclo Tesi di Dottorato HYDRODYNAMICS AND MORPHODYNAMICS IN THE SWASH ZONE: HYDRALAB III LARGE-SCALE EXPERIMENTS Relatore: Prof. Diego Vicinanza Co-relatore: Prof. Maurizio Brocchini Candidato: Ing. Pasquale Contestabile Il Coordinatore del Dottorato: Prof. Alberto Incoronato ANNO 2011 ABSTRACT The modelling of swash zone hydrodynamics and sediment transport and the resulting morphodynamics has been an area of very active research over the last decade. However, many details are still to be understood, whose knowledge will be greatly advanced by the collection of high quality data under controlled large-scale laboratory conditions. The advantage of using a large wave flume is that scale effects that affected previous laboratory experiments are minimized. In this work new large-scale laboratory data from two sets of experiments are presented. Physical model tests were performed in the large-scale wave flumes at the Grosser Wellen Kanal (GWK) in Hannover and at the Catalonia University of Technology (UPC) in Barcelona, within the Hydralab III program. The tests carried out at the GWK aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a beach containing a buried drainage system. Experiments were undertaken using a set of multiple drains, up to three working simultaneously, located within the beach and at variable distances from the shoreline. The experimental program was organized in series of tests with variable wave energy. While a positive effect was observed under low energy conditions, for medium and high energy conditions the benefit of having the drains operative was not always clear. In any case, it was evident that any positive effect of the drains on the beachface was confined by the position of the cone of depression in the aquifer‘s surface. The tests carried out in the large wave flume at UPC had the intent to investigate swash zone under storm conditions. The main aim was to compare beach profile response for monochromatic waves, monochromatic waves plus free long waves, bichromatic waves and random waves. Both erosive and accretive conditions were considered. The experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved nearshore morphological modelling of cross-shore beach profile evolution, and provide a very comprehensive and controlled series of tests for evaluating numerical models. It is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups, as much as the presence of the forced and free long waves induced by the groupiness. The equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux. 2 THESIS OUTLINE In Chapter 1 the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are identified and local and global hydro-morphodynamic phenomena are introduced. In Chapter 2 major emphasis is placed on illustrating the physical aspects directly considered in the two sets of experiments. Chapters 3 and 4 outline the experimental programs and fundamental results, followed by a more detailed discussion in Chapter 5. A final summary and future perspectives conclude the Thesis. KEYWORDS Swash Zone, Large Wave Flume, Beach Drainage System, Long Waves, Wave Groups, Beach Morphodynamics, Sediment Transport, Surf Beat. 3 CONTENTS 1. The Swash Zone System 15 1.1 Introduction 15 1.2 Swash zone boundary conditions 18 1.2.1 Underlying beach condition 21 1.2.2 From surf zone forcing to swash hydrodynamics: the role 24 of inner surf boundary conditions 1.3 Superficial SZ Hydrodynamics 30 1.3.1 High- and low-frequency swash motion 30 1.3.2 Internal flow kinematics 37 1.4 Beach groundwater hydrodynamics 38 1.5 Asymmetries in SZ hydro- sediment dynamics 44 1.5.1 Sediment advection as a boundary condition for SZ 45 1.5.2 Uprush hydro-sediment dynamics 48 1.5.3 Backwash hydro-sediment dynamics 53 1.6 Beachface morphodynamics 56 1.6.1 Beachface morphology 56 1.6.2 Morphing feedback processes 59 1.7 Modelling sediment processes in the SZ 61 1.7.1 Water flow through a porous medium 62 1.7.2 Forces on sediment particles 63 1.7.3 The flow-bed interaction 66 1.7.4 Sediment transport models 70 2. Literature review 76 2.1 The Beach Drainage System 76 2.2 Influence of free long waves, bichromatic wave groups and random waves 79 3. Swash zone response induced by different groundwater regimes: 84 large-scale experiments at GWK 3.1 Experimental procedure and setup 84 3.1.1 Wave flume and instrumentation 84 3.1.2 Measurement instruments 90 3.1.3 Test program 100 3.1.3.1 Static tests 100 3.1.3.2 Dynamic tests 102 3.2 Pre-processing and data analysis 108 3.2.1 Signal processing 108 4 3.2.2 Groundwater Hydrodynamics Measurement methods 122 3.2.3 Morphodynamic Measurement methods 125 3.3 Results 126 3.3.1 Hydrodynamic response 126 3.3.1.1 Water table and wave set up 126 3.3.1.2 Hydraulic regime of drains Undertow current profiles 129 3.3.1.3 Wave set up 132 3.3.1.4 Undertow current profiles 133 3.3.1.5 Analysis of surf beat 136 3.3.2 Morphodynamic response 138 3.3.2.1 Morphodynamic analysis under High Energy conditions 138 3.3.2.2 Morphodynamic analysis under Medium Energy 146 conditions 3.3.2.3 Morphodynamic analysis under Low Energy conditions 150 4. Swash Zone Response induced by long waves, wave groups and random waves: 154 large-scale experiments at LIM 4.1 Experimental procedure and setup 154 4.1.1 Wave flume and instrumentation 154 4.1.2 Test program 161 4.2 Data analysis 167 4.3 Results 170 4.3.1 Hydrodynamic results 170 4.3.1.1 Waves data 170 4.3.2 Morphodynamic results 172 4.3.2.1 Erosive conditions 172 4.3.2.2 Accretive conditions 178 4.3.2.3 Morphological pattern 181 4.3.3 Sediment dynamic results 184 4.3.3.1 Cross-shore Sediment transport patterns 184 4.3.3.2 Total net sediment transport direction and magnitude 191 5. Discussion and Conclusions 197 5.1 Discussion 197 5.1.1 Large experiment at GWK 197 5.1.2 Large experiment at CIEM 198 5.1.3 Implication on SZ modeling 202 5.2 Summary of key results and Conclusion 208 References 212 5 Acknowledgements This large scale experiment at GWK and at CIEM has been supported by European Community's Sixth Framework Programme through the grant to the budget of the Integrated Infrastructure Initiative HYDRALAB III within the Transnational Access Activities, Contract no. 022441. The Author is grateful to participants from all other partners in the projects carried out at GWK, and particularly to: Paolo Ciavola (Università di Ferrara), Leonardo Damiani (Politecnico di Bari), Paolo Veltri and Francesco Aristodemo (Università della Calabria), Rui Taborda and Ana Silva (University of Lisbon), Gonzalo Malvarez (University Pablo de Olavide), Lincoln Heitman and Charles Lemckert (Griffith University), Mouncef Sedrati and Elisa Fontana (Università di Ferrara), Alessandra Saponieri and Marino L‘Abbruzzi (Politecnico di Bari), Vincenzo Ferrante (Seconda Università di Napoli), and Biancamaria Verbeni (Università della Calabria). The Author also thank the other members of the SUSCO project: Tom Baldock and Hannah Power (University of Queensland, Australia), Maurizio Brocchini and Matteo Postacchini (Università Politecnica delle Marche, Italy), Josè Alsina and Ivan Caceres (UPC, Spain), Peter Frigaard and Thomas Lykke Andersen (Aalborg University, Denmark), Daniel Conley and Peter Ganderton (University of Plymouth, United Kingdom), and Paolo Ciavola (Università di Ferrara, Italy), Quim Sospedra (UPC). The Author show appreciation for the Technical Staff at the GWK and CIEM for their assistance with planning and running the experiments. Finally, I am heartily thankful to my supervisor, Prof. Diego Vicinanza (Seconda Università degli Studi di Napoli) whose encouragement, guidance and support from the initial to the final level enabled me to develop this doctoral thesis. I wish to say a special thank you to my co-supervisors Prof. Maurizio Brocchini (Università Politecnica delle Marche) and Prof. Ciavola (Università di Ferrara) for the many useful comments and suggestions provided, and to my colleagues Dr. Vincenzo Ferrante (Seconda Università degli Studi di Napoli) and Dr. Francesco Aristodemo (Università della Calabria) for their continued support. This thesis would not have been possible without the help and support of my family. Above all, I would like to thank my wife Tiziana for her personal support and great patience at all times. This thesis is dedicated to my son Gianfranco, who has been a great source of motivation and inspiration (especially at night…). 6 Declarations Part of the work presented in this thesis is being published as: Baldock, T. E., Alsina, J., Caceres, I., Vicinanza, D., Contestabile, P., Power, H., Sanchez- Arcilla, A. (2011). ―Large-scale experiments on beach profile evolution and sediment transport induced by long waves, wave groups and random waves‖, Coastal Engineering, ISSN 0378-3839, vol. 58, pp. 214-227. Ciavola P., Vicinanza D., Aristodemo F., Contestabile P., (2011). ―Large-scale morphodynamic experiments on a Beach Drainage System‖, Journal of hydraulic research, Vol. 49, n. 4, pp. 523-528. Contestabile, P., Aristodemo, F., Vicinanza, D., Ciavola, P.
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