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In the context of climate change and associated sea level rise, coastal dunes can provide an essential contribution to coastal protection against wave attack and flooding. Since dunes are highly dynamic systems, their potential safety levels are related to their long-term development, varying in time and space, however pertinent research that ties those aspects together are generally scarce. The objective of this study is to analyze the long-term development of a young coastal foredune at the Eiderstedt peninsula, Germany and assess its coastal protection potential. This research presents (i) a novel semi-automated Dune Toe Tracking (DTT) method to systematically extract dune toes from cross-shore elevation profiles; (ii) established tools to derive the extraction of characteristic dune parameters and (iii) a newly defined Critical Storm Surge Level (CSSL) to relate spatio-temporal dune growth with coastal storm surge protection. Based on geospatial survey data, initial dune formation was identified in the 1980s. By 2015, the foredune had developed over a 6.5 km coastal stretch with a mean annual growth of 7.4m³/m. During the course of dune evolution, the seaward dune toe shifted seaward by an average of 2.3m/yr, while simultaneously increasing in height by an average of 1.1 cm/yr. Overall, the foredune formation established a new line of defense in front of an existing dike/dune line that provides spatially varying protection against a mean CSSL of 3.4m + NHN and can serve as an additional buffer against wave attack during severe storm events.

Novel strategies in coastal protection are needed to cope with climate change-induced sea level rise. They aim at the sustainable development of coastal areas in light of intensification and land use changes. A promising approach is the design of nature-based solutions (NbS), complementing the safety levels of technical infrastructure. However, NbS lack a widespread and large-scale implementation. To address this deficit, co-design concepts are needed that combine experiences from science and practice. This work presents and discusses the approach of a coast-specific real-world laboratory (RwL) addressing the inclusive design of ecosystem-based coastal protection. Strategies of RwLs are applied for the first time in a coastal context along the North Sea coastline in Germany. We found the concept of RwLs suitable for coastal transdisciplinary research, although adaptions in the spatial reference level or flexibility in location and time of experimentation are necessary. A profound actor analysis is indispensable to specify participatory processes and interaction levels. A criteria-based cooperative selection of RwL sites helps to reveal and solve conflicting interests to achieve trust between science and practice. Addressing site-specific characteristics and practitioners’ needs, our coastal RwL provides a mutual learning space to develop and test NbS to complement technical coastal protection.

Salt marshes are a valuable ecosystem with coastal protection potential, for example by absorbing hydrodynamic energy, increasing sedimentation and stabilizing the soil. This study investigated biomechanical properties of Spartina anglica to improve future models of wave-vegetation interaction. To fully understand the correlations between hydro- and biomechanics, the biomechanical vegetation properties from December 2021 to July 2022 are investigated with specimens collected from the field monthly. 551 specimens were used to determine the vegetation properties during storm surge season with high hydrodynamic forces. Additional geometrical properties were determined for 1265 specimens. Three-point bending tests measured the stiffness S (N/mm) and maximum forces Fmax (N). Different phenological states were observed over time and separated for analysis. These states provide a novel classification of growth periods for evaluating the coastal protection potential of Spartina anglica. Especially during storm season, most specimen were identified as broken shoots with a mean stiffness of 1.92N/mm (using 304 samples) compared to the bottom part of flowering shoots in December and January with a mean stiffness of 2.98N/mm (using 61 samples). The classification of plant properties recognizing phenological differences, based on plant state and seasonality, can be used to explain and reduce variability of biomechanical properties obtained during field campaigns. Additionally, this study shows that March to April is recommended for future investigations focusing on shoot properties during storm surge season, which is the important season for coastal engineers considering vegetation state.

The analysis of soil-vegetation interactions in erosion processes along coastlines requires accurate information about various factors influencing the upper soil layer. Yet, some of these parameters were previously determined by simplified, often hand held devices, and these were often biased by the skill and experience of the operator. This study thus investigates the erosion resistance of salt marsh soils influenced by grazing conditions for providing crucial findings for policy making and land management decisions; to that end, we present and use a novel shear resistance measuring device. This measuring device, called DiCoastar, was developed with a controllable step-motor and now allows us for the first time the determination of time histories of shear resistance by repeatable in-situ measurements, gaining information about the interaction between soil and root systems. A field study was conducted in salt marshes at Cäciliengroden and at Sönke-Nissen-Koog, both foreland salt marshes at the German North Sea coast. The two sites had been chosen due to their difference in grazing intensities, featuring semi-natural/ungrazed, moderately grazed and intensively grazed salt marshes. This was to enable the investigation of influences on soil shear strength and vegetation cover. Measurements of shear resistance were conducted with the DiCoastar in the chosen sites in the vicinity of the dike toes; it is found that the new device now provides consistent and repeatable measurements, irrespective of the operator, and only based on the pre-set control parameters. Results of the field study demonstrate that a marked increase of shear strength is only found in sites with high intensity grazing, but this is accompanied by a strong reduction in the vegetation cover and plant diversity, especially with regard to the vertical density distribution of the vegetation cover. As the reduction in vegetation cover leads to reduced wave attenuation over salt marshes and increased flow vel

Underwater dunes are a morphological feature that are explored by marine scientists and coastal engineers alike. This study presents new methodologies in order to simplify bedform identification and morphodynamic analyses. Specifically, subaqueous compound dunes are decomposed with a simple yet extensive tracking algorithm, which relies on a repeated evaluation of unfiltered bed elevation profiles according to five predefined length classes. In a second step, morphological trends are assessed in the form of bed migration rates, bed slope asymmetries and net sediment changes, in which all parameters are referred to equidistant sections of the examined fairway stretch. This integrated approach not only avoids the challenges in weighting the varying size and abundance of dunes of different scales but also ensures comparability between dune-specific and areal parameters, which significantly improves the interpretation of the morphological setting as a whole. The developed methods are applied to the Outer Jade fairway, an anthropogenically influenced and regularly maintained waterway in the German Bight, and allow scrutiny of spatio-temporal trends in this region. Based on a unique data set of 100 sequential high-quality echo-sounding surveys, various types of bedforms are identified, comprising large-scale primary as well as superimposing secondary dunes that are assumed to interfere with each other. Temporal trends show a long-term rise of the troughs of major bedforms and constant maximum crest elevations near the official maintenance depth, which matches the observed long-term aggradation of sediments. The spatial distribution of integrated morphodynamic parameters reflects a previously described zone of primary dune convergence and facilitates the precise localization of this geophysical singularity. The presented findings both confirm the robustness of the proposed methodologies and, in return, enhance the understanding of morphological processes in the Outer Jade.

The macrotidally influenced harbor of Dagebüll on the North Sea coast of Germany features a piled south jetty, for which provided constructive designs are investigated regarding their potential hydro-morphological impacts on the harbor area and adjacent navigational channel. The harbor experiences a steady accumulation of sediment. This results in a reduction of navigational depth and necessitates regular maintenance dredging constituting a cost aspect. A comprehensive field study was conducted, deploying a ridged inflatable boat (RIB) equipped with differential Global Positioning System, a winch for conductivity, temperature, and depth casting as well as sediment and water sampling and an acoustic Doppler current profiler for current profiling. Measurements reveal a tidally governed alternating flow pattern inducing a vortex current inside the harbor basin. Hydrodynamic sea floor grain sorting is detected through sediment sampling. A numerical model cascade is developed and calibrated against available tide gauge and sediment inventory data as well as multibeam survey data and acquired field measurements. The calibrated model cascade is used to simulate layout variants and compare resulting impacts to identify preferable jetty designs.

Coastal engineering is tasked with designing, constructing and maintaining hydraulic works in the coastal zone. Coastal dikes form a first hard line of defense against impend- ing storm surges, developed waterways ensure safe navigation and developed terminals facilitate maritime trade and are classified as critical coastal infrastructure depending on their individual turnover and criticality. European Windstorms, intrinsic to Europe, impact the German Bight ten times a year on average, inducing storm surges, eroding coastline stretches and obstructing navigation due to agitated sea states causing large monetary losses, endangering livelihoods and ne- cessitating ensuing repairs. These extra-tropical cyclones develop on the Atlantic Ocean and follow a westward storm trajectory through the North Sea. The German Bight, with its relatively shallow water depth and intricate coastline is located at the impact end of these storm trajectories. Due to the geographic nature this coastline exerts a funneling effect on storm systems with northern or western incident angles. Ubiquitous environ- mental changes impact atmospheric and hydrospheric processes, which control the for- mation and evolution of extreme system states such as storm surges. Consequently, the assessment of individual coastal key drivers is an integral part of coastal engineering and research investigating impacts on critical coastal infrastructure and coasts against the background of environmental change. In this thesis, potential impacts stemming from changes in sea level, estuarine discharge, sea state and aeolian quantities as well as sediment transport, are investigated for the Jade-Weser estuary. Identified changes are simulated employing a numerical open source software suite and evaluated for the transshipment complex Wilhelmshaven lining the Inner Jade, comprising several critical terminals. A comprehensive model quality assess- ment is carried out and demonstrates the well-suited character of the mo, Küsteningenieurwesen ist mit der Planung, Errichtung und Erhaltung von Bauwerken in der Küstenzone betraut. Seedeiche bieten Hochwasserschutz vor anbrandenden Sturm- fluten, während ausgebaute Fahrwasser die Sicherheit der Küsten- und Seeschifffahrt gewährleisten und Hafenanlagen (Über-)Seehandel ermöglichen und je nach Umschlag- menge und Güterart als kritische Infrastrukturen klassifiziert werden. Europäische Sturmzyklone treffen die Deutsche Bucht im Durschnitt zehn Mal pro Jahr und verursachen Sturmfluten, erodieren Küstenvorländer und beeinträchtigen die Schiff- fahrt. Sturmschäden belaufen sich jährlich auf Milliarden Euro und erfordern Ertüchti- gungen von Küstenbauwerken. Diese Sturmzyklone entstehend über dem Atlantik und folgen einer Westzugbahn, die sie über Nordeuropa und die Nordsee ziehen lässt, wo sie die Deutsche Bucht mit ihrer geringen Wassertiefe und verwinkelten Küstenlinie treffen. Sich ändernde Umweltbedingungen beeinflussen atmosphärische sowie hydrosphärische Prozesse gleichermaßen, die für die Entwicklung und Zugbahn extremer Systemzustände wie Orkane und Sturmfluten entscheidend sind. Folgerichtig ist die Identifikation und Erforschung von individuellen Schlüsselprozessen, die maßgeblich zur Küstenentwick- lung beitragen und potentielle Auswirkungen auf systemkritische Küsteninfrastruktur aufweisen, ein integraler Bestandteil der Forschung im Küsteningenieurwesen. Im Rahmen dieser Arbeit werden Auswirkungen untersucht, die sich durch Meeresspiege- lanstieg, erhöhten Binnenlandabfluss, verstärkten Seegang sowie intensivierte Wind und Druckfelder für das Jade-Weser Ästuar ergeben. Identifizierte Änderungen werden mit einem quelloffenen numerischen prozessbasierten Modell berechnet und für den Hafen- komplex Wilhelmshaven in der Innenjade, der teilweise kritische Infrastrukturen um- fasst, ausgewertet. Ein umfassender Vergleich mit Beobachtungsdaten zeigt, dass das Modell in der Lage ist, komplexe hydrodynamische Prozesse aber auch Seegang, At