Medium Scale Morphodynamics of the Central Dithmarschen Bight
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Medium Scale Morphodynamics of the Central Dithmarschen Bight Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakult¨at der Christian-Albrechts-Universit¨atzu Kiel vorgelegt von Jort Wilkens Kiel 2004 Referent: Prof. Dr. Roberto Mayerle Koreferent: Prof. Dr.-Ing. Werner Zielke Tag der m¨undlichen Pr¨ufung: 5. Mai 2004 Zum Druck genehmigt Kiel, den 24. M¨arz2005 3 Contents Acknowledgements 15 Abstract 17 Zusammenfassung 19 1 Introduction 21 1.1 General . 21 1.2 Main research topic . 23 1.3 Outline of the thesis . 24 2 The Dithmarschen Bight 27 2.1 Introduction . 27 2.2 Geomorphology and classification . 28 2.2.1 Geomorphology . 28 2.2.2 Morphological classification . 29 2.3 Hydrodynamics . 31 2.3.1 Tidal conditions . 31 2.3.2 Wave conditions . 34 2.4 Salinity and water temperature . 38 2.4.1 Salinity . 38 2.4.2 Temperature . 38 2.5 Meteorology . 38 2.6 Sedimentology and bed characteristics . 40 2.7 Morphology and morphodynamics . 44 2.7.1 The central Dithmarschen Bight . 46 2.7.2 Individual morphological features and their behaviour . 50 3 The Dithmarschen Bight model – process models 63 3.1 Introduction . 63 3.2 Model domain . 63 3.2.1 General aspects . 63 3.2.2 Model domain of the Dithmarschen Bight model . 65 4 Contents 3.2.3 Grid definition and model bathymetry . 67 3.3 Tidal flow model . 70 3.3.1 Flow model set-up . 70 3.3.2 Flow model validation . 73 3.4 Wavemodel.................................. 76 3.4.1 Wave model set-up . 76 3.4.2 Wave model validation . 77 3.5 Sediment transport model . 79 3.5.1 Sediment transport model set-up . 79 3.5.2 Sediment transport model validation . 80 3.6 Discussion . 84 Appendix Chapter 3 3.A Delft3D-MOR modelling system . 86 3.A.1 Introduction . 86 3.A.2 Flow . 86 3.A.3 Waves . 88 3.A.4 Sediment transport . 90 3.A.5 Morphological evolution . 93 3.A.6 Time management of the modules . 93 4 The Dithmarschen Bight morphodynamic model 95 4.1 Introduction . 95 4.2 Model concepts for coastal area modelling . 96 4.2.1 Applied concepts for the Dithmarschen Bight model . 98 4.3 Set-up of the morphodynamic model . 99 4.3.1 General simulation set-up . 100 4.3.2 Simulation of scenarios with varying conditions . 101 4.4 Definition of the open boundary conditions . 102 4.4.1 Input filtering . 102 4.4.2 Applied input reduction methods . 103 4.4.3 Flow boundary conditions . 103 4.4.4 Swell wave boundary conditions . 108 4.4.5 Wind conditions . 113 4.4.6 Combination of swell and wind conditions . 113 4.4.7 Storm conditions . 115 4.4.8 Sediment transport and morphological boundary conditions . 115 4.5 Discussion . 116 Appendices Chapter 4 4.A Model study: Anatol storm . 118 4.A.1 Introduction . 118 5 4.A.2 Characteristics of Anatol . 118 4.A.3 Model nesting and coupling . 120 4.A.4 Hydrodynamics . 122 4.A.5 Morphodynamics . 127 4.A.6 Conclusions . 129 4.B Model study: representative tide . 130 4.B.1 Introduction . 130 4.B.2 Tidal variation . 130 4.B.3 Morphodynamic simulation set-up . 131 4.B.4 Tidal conditions only . 132 4.B.5 Including representative wind and swell climates . 132 4.B.6 Conclusions . 132 5 Calibration and validation of the MTM-model 135 5.1 Introduction . 135 5.2 Strategy for the model calibration . 135 5.3 Calibration . 136 5.3.1 Calibration for the wind and swell climate . 139 5.3.2 Calibration for the Bijker constant . 142 5.4 Validation . 147 5.5 Discussion . 152 6 Morphodynamic processes and prediction 153 6.1 Introduction . 153 6.2 Significance of the driving forces for the medium scale morphodynamics 153 6.2.1 The role of the tide on the morphodynamics . 155 6.2.2 The role of swell waves on the morphodynamics . 157 6.2.3 The role of wind and locally generated waves . 159 6.2.4 Synthesis of the results . 161 6.3 Prediction of the medium scale morphodynamics over ten years . 163 6.3.1 Summary . 167 7 Conclusions and recommendations 169 7.1 Conclusions . 169 7.2 Recommendations for future research . 171 References 178 Nomenclature 180 About the author 181 6 Contents 7 List of Figures 1.1 Scale range in coastal morphology (morphological time scale Tm in sec- onds). After [De Vriend, 1997]. 22 2.1 Location of the Dithmarschen Bight in the southeastern part of the North Sea. ...................................... 27 2.2 Dike constructions in the Meldorf Bight in 1972 and 1978. 29 2.3 Morphological variations depending on the tidal range according to Hayes [1975]. 29 2.4 Adapted model for dependency of the morphological variations on the tidal range. From [Ehlers, 1988]. 30 2.5 Amphidromic systems in the North Sea, with co-tidal and co-range lines in metres [Brown et al., 1989]. 31 2.6 Direction and magnitude of the tidal currents in the German Bight. The rectangle indicates the Dithmarschen Bight. Adapted from Ehlers [1988], after Reineck [1978]. 32 2.7 Locations of the transects along which vessel-based ADCP-measurements have been made. 34 2.8 Wave rose - probability of occurrence per combination of direction (nau- tical convention) and significant wave height interval. Based on mea- surement data at Sylt from 1986 to 1993 from Froehle & Kohlhase [1995]. 35 2.9 Location of the wave buoys from the measurements by [Niemeyer et al., 1995]. 36 2.10 Time series of the significant wave heights at the five wave buoys. 37 2.11 Comparison of wind speed (m/s) and direction (◦N) from the measure- ment station at Buesum (Research and Technology Centre Westcoast) and the PRISMA wind model. Based on measurements between March, 1991 and December, 1998. 39 2.12 Wind rose for the Dithmarschen Bight - probability of occurrence per combination of wind direction (nautical convention) and wind speed in- terval. Based on data from 1989 to 2000, from the PRISMA data assim- ilation model by [Luthardt, 1987] . 40 8 Contents 2.13 Thickness of the non-cohesive sediment layer above the Dithmarscher Klei clay layer [Asp, 2003]. 41 2.14 Location and results of the bed sediment measurements during 1999 and 2000. Adapted after Reimers [2003]. 42 2.15 Distribution of sediment types, after Vela Diez [2001]. 43 2.16 Classification of tidal areas, differentiated on the mean tidal range and mean wave height. The western (dark grey) and eastern part (light grey) of the Dithmarschen Bight are indicated by the two rectangles. Adapted after Hayes [1979]. 44 2.17 Location of the morphological features in the central Dithmarschen Bight (bathymetry from 1977). 46 2.18 Measured bathymetry in the central Dithmarschen Bight. 48 2.19 Morphodynamics in the central Dithmarschen Bight. 49 2.20 Location of the channel cross-sections for the channel profile analysis. The cross-sections have been defined approximately equidistantly along the main channels (bathymetry from 1977). 50 2.21 Location of the considered sub-domains in the volume analysis. 51 2.22 Measured channel profile at cross-section 15 in the Piep. 52 2.23 Measured channel profile at cross-section 18 in the Piep. 53 2.24 Changes in the wet volume below mean sea level of sub-domain Piep. 53 2.25 Measured channel profile at cross-section 2 in the Norderpiep. 54 2.26 Measured channel profile at cross-section 4 in the Norderpiep. 55 2.27 Changes in the wet volume below mean sea level of sub-domain Norderpiep. 55 2.28 Measured channel profile at cross-section 10 in the Suederpiep. 56 2.29 Measured channel profile at cross-section 12 in the Suederpiep. 57 2.30 Changes in the wet volume below mean sea level of sub-domain Suederpiep. 58 2.31 Changes.