MODELLING THE IMPACT OF COASTAL DEFENCE STRUCTURES ON THE NEARSHORE MORPHODYNAMICS A thesis submitted to Cardiff University in candidature for the degree of Doctor of Philosophy by Fernando Alvarez-Martinez Hydro-environmental Research Centre School of Engineering Cardiff University 2016 Acknowledgements ACKNOWLEDGEMENTS I would like to express my appreciation to the people and organisations that supported and accompanied me in this long journey. To the School of Engineering of Cardiff University for supporting this PhD programme. To all Cardiff University staff in the Research, Finance and Teaching offices for their support to all PhD students, making things easier for all during the process. To family and friends that always supported me and encouraged me to keep going until the end. To Dr. Shunqi Pan for his patience, advice and support during all the stages of this PhD and to Professor Roger A. Falconer for his support. i Abstract MODELLING THE IMPACT OF COASTAL DEFENCE STRUCTURES ON THE NEARSHORE MORPHODYNAMICS Fernando Alvarez-Martinez ABSTRACT Coastal areas are heavily populated in countries around the world and are a source of economic activity, both recreational and industrial. Waves and tides interact with sediments in a dynamic equilibrium which leads to coastal morphological changes at different temporal and spatial scales. Natural or human-induced changes in this equilibrium may lead to an alteration of the coastline causing environmental or economic impacts. Coastal defences are often needed in order to protect specific areas and reduce such impacts. Therefore, understanding the impact that coastal defence structures have on coastal morphological changes is important for coastal managers. There are different methods to study morphological changes in coastal areas. Process- based numerical models are powerful and precise tools but they are more effective for small to medium spatial scales (km) and short to medium-term temporal scales. Data- driven methods have been proven useful to study morphological changes in the long- term. However, data is not always available in the quantity or quality needed for such methods to provide meaningful results. This study uses jointly process-based numerical models, COAST2D, and data-driven methods, Empirical Orthogonal Functions method (EOF), taking advantage of the strengths of both methods to overcome their own weaknesses. A novel methodology for EOF components extrapolation, named Dynamic EOF method, is developed. Results show that, COAST2D is an efficient tool to simulate morphological changes in the scale of months and kilometres. These scales exceed the ones reached previously by the model, increasing the confidence on its capabilities. The Dynamic EOF method, which extrapolates both temporal and spatial EOF components, was found to yield better results than previous attempts using the EOF method to extrapolate results beyond the training period based on EOF temporal component extrapolation only. Keywords: EOF method, Dynamic EOF method, forecasting, shore-parallel breakwaters, morphological changes, COAST2D. ii Table of Contents TABLE OF CONTENTS Acknowledgements .......................................................................................................... i Abstract .......................................................................................................................... ii Table of Contents .......................................................................................................... iii List of Figures ................................................................................................................. v List of Tables................................................................................................................... x List of Publications ........................................................................................................ xi 1 Introduction ............................................................................................................. 1 2 Literature Review .................................................................................................... 5 2.1 Introduction ...................................................................................................... 5 2.2 Coastal Morphology ....................................................................................... 17 2.3 Process-based Modelling ................................................................................ 20 2.4 Reduced-physics Modelling ........................................................................... 22 2.5 Data-Driven Modelling .................................................................................. 22 2.6 Aims and Objectives ...................................................................................... 30 3 Methodology ......................................................................................................... 32 3.1 Introduction .................................................................................................... 32 3.2 EOF Method ................................................................................................... 32 3.3 Dynamic EOF Method ................................................................................... 39 3.3.1 EOF Spatial Component extrapolation ................................................... 40 3.3.2 EOF Temporal Component extrapolation ............................................... 43 3.4 Summary ........................................................................................................ 45 4 Process-based Model ............................................................................................. 47 4.1 Introduction .................................................................................................... 47 4.2 Model Description .......................................................................................... 47 4.2.1 Currents ................................................................................................... 48 4.2.2 Waves ...................................................................................................... 48 4.2.3 Sediment transport .................................................................................. 50 iii Table of Contents 4.3 Model Re-Validation ...................................................................................... 51 4.3.1 Study Area ............................................................................................... 51 4.3.2 Model Setup ............................................................................................ 52 4.3.3 Results and Discussion ............................................................................ 55 4.3.4 Summary ................................................................................................. 62 5 Data Generation .................................................................................................... 63 5.1 Introduction .................................................................................................... 63 5.2 Idealised Study Domain ................................................................................. 63 5.2.1 Boundary Conditions .............................................................................. 65 5.2.2 Model Results ......................................................................................... 66 5.3 Data preparation ............................................................................................. 74 5.3.1 Shoreline Changes ................................................................................... 75 5.3.2 Volumetric changes – alongshore sections ............................................. 76 5.3.3 Volumetric changes – computational cells ............................................. 81 5.4 Summary ........................................................................................................ 84 6 Dynamic EOF Analysis ....................................................................................... 86 6.1 Introduction .................................................................................................... 86 6.2 1D Approach .................................................................................................. 86 6.3 2D Approach .................................................................................................. 96 6.4 Dynamic EOF method advantages and limitations ...................................... 109 6.5 Summary ...................................................................................................... 112 7 Conclusions and Future Research ....................................................................... 113 7.1 Conclusions .................................................................................................. 113 7.2 Future Research ............................................................................................ 116 8 References ........................................................................................................... 118 iv List of Figures LIST OF FIGURES Figure 2.1. Coastal Regions patterns in the European Union.Error! Bookmark not defined. Figure 2.2. Managed realignment in Little Haven beach, South Shield, UK. Beach in 2012 before the works (left) and beach in 2015 after the works (right). ...................... 10 Figure 2.3. Schematic shore-parallel breakwater scheme. Initial shoreline