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Die Küste, 69 PROMORPH (2005), 25-62 25 Patterns of Hydrodynamics in a Tide-Dominated Coastal Area in the South-Eastern German Bight By FERNANDO TORO,ROBERTO MAYERLE,POERBANDONO and JORT WILKENS Summary The results of an analysis of field measurements leading to an identification of the basic pat- terns of hydrodynamics in a tidally-dominated area on the German North Sea coast are presented in this paper. The analysis was carried out within the framework of the research project “Pre- dictions of medium-scale morphodynamics-PROMORPH” funded by the German Ministry of Education and Research from 2000 to 2002. The investigation area is the central Dithmarschen Bight between the Elbe and Eider estuaries. Recommendations for the set-up of the process-based models for flow and waves taking into account the available data and the dynamics of the study area were proposed. Continuous monitoring of water levels and waves by the relevant authorities was supplemented by field measurements at key locations. The planning and execution of field surveys specially intended to obtain a dense spatial and temporal coverage of current velocities is described. The tidal analysis, based on records from a number of tide gauge stations, yielded the 39 harmonic constituents that best represent the measured water level time series at several locations. An analysis of the seasonal variation of tidal asymmetries on the basis of water level measurements at several locations enabled flood or ebb dominance to be identified in the cross-sections of the tidal system. The current velocity measurements provided a good description of the spatial and temporal variation of current velocities. The measured wave data provided a better understanding of wave characteristics and wave transformation throughout the study area. The field measure- ments not only form a basis for identifying the most dominant physical processes governing the hydrodynamics of the study area but also provide a valuable data set for clarifying several as- pects for developing and evaluating process-based models for the simulation of flow and waves. Zusammenfassung In diesem Artikel werden die Analysenergebnisse von Naturuntersuchungen vorgestellt, welche die grundlegende Verteilung der Hydrodynamik in einem tidedominierten Seegebiet der Deutschen Nordseeküste identifizieren. Diese Analyse wurde durchgeführt im Rahmen des For- schungsprojekts „Vorhersage mittelskaliger Morphodynamik – PROMORPH“, das vom Bundes- ministerium für Bildung und Forschung von 2000 bis 2002 finanziert wurde. Auf der Grundlage von mehreren Tidepegelstationen lieferte die Tideanalyse etwa 39 harmonische Komponenten, welche die gemessenen Wasserstand-Zeitreihen am besten repräsentieren. Um die räumlichen und zeitlichen Variationen der Strömung in den Hauptgezeitenrinnen besser zu verstehen, wurden über mehrere Querschnitte und Lokalitäten selektive Messungen der Strömungsgeschwindig- keit durchgeführt. Die maximalen Punktgeschwindigkeiten und tiefengemittelten Geschwindig- keiten lagen in den Gezeitenrinnen bei 2,8 m/s bzw. 1,7 m/s. Aufgrund der geringen Rauigkeit der Bodenformen ist die Geschwindigkeitsverteilung über die Vertikale nahezu gleichförmig. Es war möglich, in den Querschnitten nahe der seewärtigen Grenzen des Untersuchungsgebiets unter normalen Bedingungen eine Flutdominanz zu erkennen und einen signifikanten Anstieg der Strömungsgeschwindigkeit mit steigendem Tidehub. Etwa 10 km weiter seewärts der äußeren Wattflächen wurden Wellenhöhen bis 3,5 m aufgezeichnet. Landwärts wurde ein grader Abfall der Wellenhöhe gemessen, der mit dem immer stärker werdenden Effekt abnehmender Wasser- tiefe (führt zur Wellenenergie-Dissipation durch Wellenbrechen und Bodenreibung) wie auch mit der Hubwirkung der Wattflächen in Zusammenhang steht. Die maximalen Wellenhöhen entlang der äußeren Wattenkanten und in der zentralen Gezeitenrinne lagen bei jeweils 2,0 m und 1,5 m. Näher zur Küste weiter östlich lagen die Wellenhöhen generell unter 0,7 m. Aus der Analyse der Wellenperioden war zu schließen, dass die Dünung bis zum zentralen Bereich der äußeren Watt- flächen reichte, während weiter östlich lokal erzeugte Wellen die Hauptenergiequelle bilden. Die Küste, 69 PROMORPH (2005), 25-62 26 Keywords Gauge Stations, Waverider Buoy, Tides, Tidal Analysis, Swell, Wind Waves, Tidal Channels, Tidal Flats, Measurements, Dithmarschen Bight, North Sea, PROMORPH Contents 1. Introduction ............................................................................................................................... 26 2. Investigation Area ...................................................................................................................... 27 3. Data Requirements .................................................................................................................... 28 3.1 General Knowledge from Ad-hoc Modelling .................................................................. 28 3.2 Data Needs for Model Development ................................................................................ 29 3.3 Available Data and Information Gaps .............................................................................. 29 3.4 Clarification of Various Aspects of Model Settings ........................................................ 31 4. Measurements of Current Velocity .......................................................................................... 32 4.1 Measuring Devices and Experimental Set-up .................................................................. 32 4.2 Environmental Conditions ................................................................................................ 35 5. Data Analysis ............................................................................................................................. 37 5.1 Tides ..................................................................................................................................... 37 5.2 Storm Surges ........................................................................................................................ 47 5.3 Currents ............................................................................................................................... 47 5.4 Waves .................................................................................................................................... 53 5.4.1 Data from the CRS.................................................................................................... 53 5.4.2 Data from the ALR and BSH................................................................................... 56 5.5 Salinity and Temperature .................................................................................................... 57 6. Conclusions ................................................................................................................................ 59 7. Acknowledgements ................................................................................................................... 60 8. References ................................................................................................................................... 61 1. Introduction Hydrodynamic phenomena constitute the underlying mechanisms governing sediment transport and reaction processes such as morphodynamics in coastal areas. Process-based numerical models for simulating morphological changes over time scales of several years have been developed, evaluated and applied within the framework of the research project “Predic- tions of Medium-Scale Coastal Morphodynamics – PROMORPH” funded by the German Ministry of Education and Research (PALACIO et al., in this volume; WILKENS et al., in this volume; WINTER et al., in this volume; JUNGE et al., in this volume; WILKENS and MAYERLE, in this volume). The investigation area considered in this project is the central Dithmarschen Bight located between the Elbe and the Eider estuaries. This paper gives an overview of the data used to assist in identifying the basic features of hydrodynamics and to provide sets of data for the development of process-based models for simulating flow and waves in the investigation area. Gaps in information were identified, focusing on the requirements for the proper development of the coastal model. The planning and execution of field surveys specially designed to obtain a dense spatial and temporal cover- age of current velocities is also described. Results of an analysis of field measurements of tidal flows, storm surge levels, current velocities and waves are presented. The main tidal constitu- ents and asymmetries based on water level records at several locations as well as the results of an analysis of the spatial and temporal distribution of current velocities in the tidal channels are presented. Wave data provided by several authorities from waverider buoy recordings Die Küste, 69 PROMORPH (2005), 25-62 27 were analysed to investigate the distribution of wave characteristics and wave transformation throughout the study area. Vertical profiles of salinity and temperature were additionally measured at various locations along the current velocity measurement transects. Although extensive measurements covering a wide area and a wide range of conditions were made during the investigations, only typical results are presented here for the sake of compactness. 2. Investigation Area The investigation area consists of a tidal region on the German North Sea coast (Fig. 1). It is part of the Wadden

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