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.

<p>Natural coastal dunes covered by vegetation are an essential component on many sandy coastlines worldwide and often provide the only physical protection against flooding by dissipating wave energy and enhancing erosion resilience. However, sea level rise, changing and widely intensifying coastal wave climates and storm surges constitute severe exacerbated stresses, calling into question the perseverance of such unique coastal ecosystems as dunes and their protective functions taken for granted.</p><p>Here we investigate the extensive coastal dune system of St. Peter-Ording, a major tourist draw of the German North Sea within a marine high energy zone. Lining the coast along 15 km, extending up to 1.5 km in cross-shore direction it covers an area of 18 sqkm characterized by overgrown dunes separating the tidal foreshore from the topographically flat hinterland. Featuring a dedicated, Germany wide unique, coastal protection function sets it apart from other national coastal dune systems - potentially creating a role model for mitigating coastal squeeze related driving factors, further adding to its awe-inspiring landscape character.</p><p>Consequently, the joint-research project ''Sandküste St. Peter Ording'' examines whether the local flood protection dune “Maleens Knoll”, a 16.6 m high natural coastal dune stretching a roughly 1.2 km long gap in the sea-dike defense, will continue to offer adequate protection in the future. Current hypothesis is, that due to the overgrowth with non-endemic and invasive vegetation species, the natural dynamic and self-adaptation of the system is impaired and will not withstand projected changes in coastal drivers. Therefore, the long-term goal is to develop a variety of nature-friendly flood protection measures to reinforce the dune and reduce its probability of failure during an extreme storm surge.</p><p>Possible options comprise the installation of hybrid systems, combining the existing dune core with one of the following structures: 1) a vertical wall to gain more stability during erosion of the sand cover, 2) rock filling to increase wave dissipation and reduce wave reflection and erosion and 3) geotextiles to provide a temporary and more environmentally protection against runup. The built-in materials will be covered with sand, to mimic the original landform and yield its previous degree of freedom regarding topographic adaptation. Another approach is to strengthen the resistance of the sand surface against aeolian and fluvial erosion. Through a microbiological process based on calcium carbonate precipitation (MICP), the strength can be increased in a particularly environmentally friendly way that saves raw materials. Furthermore, adapted or additional planting with a site-typical vegetation can promote sand accumulation at the surface and thereby stabilize the dune.</p><p>Large-scale physical model experiments will be performed in a wave flume to investigate the protection potential of the dune. First, the natural dune condition will be recreated and tested under a combination of water levels and wave conditions to investigate current and future load cases. Based on the findings, a second series of experiments will be conducted to determine which engineering methods are most appropriate to reinforce the dune and ensure its coastal protection character and retain its naturalness at the same time.</p>

<p>The joint-research project "Gute Küste Niedersachsen" is a multidisciplinary approach across spatial and temporal scales investigating ecosystem services for coastal protection. Current national coastal protection concepts predominantly target flood protection and rarely consider additional benefits to coastal ecosystems or vice versa. How maritime landscapes, such as salt marshes, coastal white dunes or a diversification of dike vegetation, can be integrated into approaches of coastal protection without compromising protection levels is the driving question in "Gute Küste Niedersachsen" and heeds recent European Framework directives calls for the restoration of a good ecological status. An in-depth understanding of dynamics within coastal ecosystems, covering eco-hydrodynamics and eco-geomorphodynamics is developed in real world laboratories at the German North Sea coast, as part of the project.<br>Systematic field observations in collaboration between biologists, geo-ecologists and coastal engineers are conducted to identify seasonal changes of vegetation regarding zonation, height, root length density and bio-mechanical parameters like bending stiffness or tensile strength. The differences of bio-mechanical vegetation traits from specific plant species, e.g. the European beach grass <em>Ammophila arenaria</em>, will indicate differences in bio-stabilization states.<br>Complementary field data of topography and soil parameters, e.g. shear and pull-out resistance, among other parameters, are acquired, employing specifically developed instrumentation like the DiCoastar for automatic and digital measurements of shear resistance over rotation angle. Additionally, values such as water and biomass content obtained from soil samples help to elucidate erosion stability of coastal ecosystems.<br>Field campaigns are focused on two real world laboratories, the tidal barrier island of Spiekeroog, Germany, and a coastal mainland section. Spiekeroog offers a variety of dune systems exposed to divergent environmental conditions such as established and recently developing natural dunes at the north-eastern coast, dunes that are used for coastal protection at the north-western coast, dunes in combination with a sea wall that are already supported by sand nourishment at the western coast or established dunes along the south-western tip of the island. Furthermore, the island holds a unique setting with an engineered dune, which was created to integrate a dike system into the landscape. This offers a one-of-a-kind opportunity to investigate differences between six different dune system types within close proximity regarding their vegetation bound bio-mechanical properties and linked soil-bound erosion resistance.<br>In addition, Spiekeroog offers an abandoned dike line, for which a sectional re-planting is rolled out with alternative seed combinations for ecologically upgrading grass dikes and boost plant diversity while coastal protection is maintained. A direct comparison against a sea dike is made at the second real world laboratory situated at the adjacent mainland coast. This setting facilitates the comparison between different biological revetment types and their respective performance in coastal protection regarding wave-soil-vegetation interactions.<br>In a subsequent step, the extensive data set will be used to develop surrogate plant models and mimic nature in hydraulic laboratories and numerical simulations to project system performance under climate change scenarios. Finally, technical guidance as well as policy recommendations will be derived for enhancing ecosystem services of artificial structures for coastal protection.</p>