For thousands of years, tides have had a great influence on coastal areas globally and their residents. Today they play a critical role in influencing economic considerations, nautical safety, renewable energy schemes, assessments of land erosion, and the definition of geodetic datums (Haigh et al., 2020; Pugh & Woodworth, 2014). Tides not only control the navigability of some ports and sea routes, but also have a major influence on the intensity and timing of extreme sea levels during storm surges (e.g., Arns et al., 2020; Horsburgh & Wilson, 2007; Prandle & Wolf, 1978). Given their close connection to the periodic and predictable nature of astronomical variations, the amplitudes and phases of tidal constituents, and corresponding tidal water levels, are generally assumed to be constant on time scales over which basin geometry undergoes only minor changes (i.e., decades to centuries). However, Keller (1901) showed increased tidal amplitudes due to reflection and local resonance changes as a result of building measures such as weirs (e.g., in the Ems River). Similarly Doodson (1924) pointed to appreciable secular perturbations in the local tidal regimes of
<p>Tide gauges throughout the North Sea basin show significant changes in the local tidal regime since the mid-20th century, especially in the German Bight area. These changes were analyzed within the DFG-funded project TIDEDYN (Analyzing long term changes in the tidal dynamics of the North Sea, project number 290112166) and the final results were recently published in J&#228;nicke et al. (2020, https://doi.org/10.1029/2020JC016456).</p><p>In this paper, we document an exceptional large-spatial scale case of changes in tidal range in the North Sea, featuring pronounced trends between -2.3 mm/yr at tide gauges in the UK and up to 7 mm/yr in the German Bight between 1958 and 2014. These changes are spatially heterogeneous and driven by a superposition of local and large-scale processes within the basin. We use principal component analysis to separate large-scale signals appearing coherently over multiple stations from rather localized changes. We identify two leading principal components (PCs) that explain about 69% of tidal range changes in the entire North Sea including the divergent trend pattern along UK and German coastlines that reflects movement of the region&#8217;s semidiurnal amphidromic areas. By applying numerical and statistical analyses, we can assign a baroclinic (PC1) and a barotropic large-scale signal (PC2), explaining a large part of the overall variance. A comparison between PC2 and tide gauge records along the European Atlantic coast, Iceland and Canada shows significant correlations on time scales of less than 2 years, which points to an external and basin-wide forcing mechanism. By contrast, PC1 dominates in the southern North Sea and originates, at least in part, from stratification changes in nearby shallow waters. In particular, from an analysis of observed density profiles, we suggest that an increased strength and duration of the summer pycnocline has stabilized the water column against turbulent dissipation and allowed for higher tidal elevations at the coast.</p><p>We would like to present these research results and the content of the paper (cf. J&#228;nicke et al., 2020) at vEGU21, hoping to encourage subsequent questions and further discussions.</p>
In course of the evolution of the next Eurocode 7 CEN TC 250/SC7 Task Group C3 is developing a guideline on reliability-based methods for geotechnical design and assessment. As part of this work, a survey was prepared to identify best practices and examples that could be used for illustration in the guidelines. Beside this, information on possible benefits and limitations of using reliability-based methods in the engineering practice were requested from the participants. The survey was distributed in summer 2021 among the international geotechnical community. The results reveal that the main benefits are seen in the identification and visualization of uncertainties and risks as well as in the possibilities for design and cost optimization. However, as major limitations an often insufficient data basis but generally a lack of acceptance on the side of the clients and an insufficient knowledge on the side of possible practitioners were identified. Consequently, clear guidance on how to use reliability-based methods and how to implement them in decision processes are needed. The TG C3 guideline therefore is a step in the right direction. On the other hand, integrating methods of reliability analysis in the engineering education already at an early stage is also considered to be important.
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