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Publication Access status: Open Access , Siegener Symposium für GeomesstechnikThe expected increase in extreme weather events due to climate change poses considerable challenges to the built environment and requires the development of suitable adaptation strategies. Geomeasurement technology is of particular importance in this context, because linked with mathematical-mechanical modeling it provides the basis for the assessment of possible geomechanical risks and for the planning measures to be derived from them. In this symposium, the current developments, the possibilities and limits of geomeasurement technology will be explored in an interdisciplinary and thematically broad context.Source Type:Conference ProceedingsSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:15327 150 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Assessing changes of tidal dynamics in the North Sea(2021)Perhaps because of the close connection between the periodic and predictable nature of astronomical variations and the corresponding tidal water levels, the tidal parameters of tidal low water, tidal high water and tidal range were generally assumed to be constant on time scales over which basin geome-try undergoes only minor changes (i.e. decades to centuries, Jänicke et al., 2020). Jensen (1984) and Führböter & Jensen (1985) were the first to discuss large-scale, potentially basin-wide changes in tidal parameters for the North Sea in the second half of the 20th century. Nevertheless, the spatial extend of these changes as well as their forcing factors remain uncertain, considering the stationarity of astronomical forcing over the period of tide gauge observations. The superposition of small-scale and large-scale effects on water level has proven to be particularly problematic in causal research and been identified by many studies in the past as the most important unsolved obstacle in identifying physical causes and attributing them to observed tidal changes (Woodworth, 2010; Haigh et al., 2020; Talke & Jay, 2020). To examine the spatial extent of tidal changes in the North Sea, in this thesis the long-term trends of the three tidal parameters were considered first and significant changes were detected. A median basin-wide increase of both tidal low and high water was detected, forming a dipole-like pattern with tidal low water trends exceeding tidal high water trends in the United Kingdom (UK) and vice versa in the German Bight. As a result, negative trends of tidal range occur in the UK whereas positive trends can be detected in the German Bight. A Principal Component Analysis was then performed to separate large-scale signals appearing coherently over multiple stations from rather localized, small-scale changes. Two leading principal components (PCs) were identified for each of the three tidal parameters, representing large-scale effects, which explain a major part of the changes and resemble the dipole pattern of the trends. In a last step, physical causes were assigned to these signals and large-scale changes in both tidal low and high water could be assigned mainly to changes in Mean Sea Level. Furthermore, changes in tidal range were attributed to a baroclinic (PC1) and a barotropic large-scale signal (PC2) by applying numerical and statistical analyses. PC2 is caused by an external and basin-wide forcing mechanism from the adjacent North Atlantic, while PC1 dominates in the southern North Sea and originates, at least in part, from stratification changes in nearby shallow waters. Therefore, it was possible to not only detect and describe large-scale tidal changes, but to identify, separate, and quantify the underlying large-scale effects for the first time. These analyses not only significantly improve the fundamental understanding of the underlying processes, but could also form the basis for future forecasting of tidal changes and their consequences, e.g. in coastal protec-tion or the navigability of North Sea ports.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:14663 279 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Untersuchungen zu kinetischen Energiewandlern und Optimierungspotenziale von Zykloidalpropellern(2020)Die Nutzung der Wasserkraft als grundlastfähiger Energielieferant leistet einen wertvollen Beitrag zur Umsetzung der Energiewende. Da Standorte zur großtechnischen Wasserkraft- nutzung in Deutschland nahezu vollständig erschlossen sind, wird das kinetische Wasser- kraftpotenzial der Fließgewässer und damit einhergehend geeignete Lösungen zur Ener- gieumwandlung immer bedeutender. Eine mögliche Lösung ist die Verwendung von Zyk- loidalpropellern, die wegen ihrer besonderen Kinematik vielfältig ohne Querverbauung in kinetischen Strömungen einsetzbar sind und somit den Zielen der EU-Wasserrahmenrichtli- nie zum Erreichen des mindestens guten Zustands der Fließgewässer nicht entgegenstehen. Diese Dissertation befasst sich mit der Untersuchung, Optimierung sowie mit der Einord- nung der Technik der Zykloidalpropeller. Zu Beginn werden wichtige Begrifflichkeiten so- wie die theoretischen Grundlagen zur kinetischen Wasserkraftwandlung näher erörtert, auf denen die Erstellung der Arbeit basiert. Diese orientieren sich nach der Theorie der Wind- kraft, deren Gesetzmäßigkeiten auf einem inkompressiblen Medium zur Energieumwand- lung basieren, wodurch die Übertragbarkeit auf kinetische Wasserkraftwandler gegeben ist. Des Weiteren werden die bekanntesten Entwicklungen im Bereich der kinetischen Energie- wandlung dargestellt, womit die Einordnung der Technik der Zykloidalpropeller erfolgt. Im Zentrum der vorliegenden Arbeit stehen die Entwicklungs- und Optimierungsarbeiten am Strömungswandler StECon als Vertreter der Zykloidalpropeller, auf dessen Grundlage die Konstruktion eines verbesserten Prototyps sowie die Ermittlung aller wichtigen Betriebspa- rameter erfolgt. Am Prototyp wird darauffolgend das Leistungs- und Effizienzverhalten un- ter unterschiedlichen Strömungsbedingungen in der freien Strömung durch physikalische Untersuchungen an zwei Standorten ermittelt, wodurch anschließend die Einordnung der Zykloidalpropeller durch einen Vergleich mit anderen kinetischen Wasserkraftwandlern so- wie gängigen Windkraftwandlern ermöglicht wird. Abschließend erfolgt eine Betrachtung der Wirtschaftlichkeit für kinetische Wasserkraftwandler im Insel- und Netzbetrieb. Letzte- res dient zur Bewertung der Rentabilität von kinetischen Wasserkraftwandlern in Abhängig- keit von der Strömungsgeschwindigkeit. Dieser Arbeit liefert somit einen wesentlichen Bei- trag zur Optimierung und Einordnung der Zykloidalpropeller sowie zur Wirtschaftlichkeit kinetischer Wasserkraftwandler.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:13541 682 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Untersuchungen zur hochauflösenden Wasserstandsvorhersage an der gesamten deutschen Nordseeküste(2020)Sea and estuarine dikes protect more than 2.4 million people in Germany, making them one of the most important coastal protection structures. A failure of these structures would have serious consequences as e.g. during the Hamburg flood in 1962, where one sixth of the city were flooded and more than 300 people lost their lives as a result of several dike failures. Therefore, early recognition of dangers and disaster prevention are elementary to ensure reliable coastal protection. Existing early warning systems for coastal protection in Germany are based on water level measurements and forecasts provided e.g. by the Federal Maritime and Hydrographic Agency in cooperation with the German Weather Service. The predictions of the water level are currently provided selectively for individual tide gauge locations. However, it is known from water level records and their investigations that such tide gauge based water level information is not representative for a larger area, e.g. for the German Bight, or for smaller geographical units, e.g. a Hallig. Thus, local effects and nonlinear interactions can result in spatial water level differences in a range of decimetres along a single coastal section. Especially along complex coastlines, such as the German North Sea with islands, bays, estuaries and tidal flats, a simple interpolation between tide gauge locations is inaccurate. This thesis deals with the development of a new methodology for the prediction of water levels at higher resolution based on existing approaches and models for the entire German North Sea coastline. A hydrodynamic numerical model is used to simulate water levels for the entire coastline of the German North Sea. The modelling is carried out on the basis of currently available bathymetric information, meteorological and astronomical boundary conditions as well as the observed changes in the mean sea level. Next, the water level information is separated into tidal and non-tidal components. The non-tidal residual is applied to derive empirical-statistical models using multiple linear regression relationships. Regression coefficients are derived using meteorological boundary conditions as input. The statistical approaches presented here also aim at incorporating the nonlinear interaction between tide and non-tidal residual into the model chain (tidal synthesis and non-tidal residual prediction). As a result, a first of its kind water level prediction at high spatial and temporal resolution along the entire coastline of the German North Sea (including islands and Halligen, point distance ~1 km, hourly values) is presented. Based on the 2013 storm surge “Xaver“, the procedure was applied practically and then successfully integrated into an operational test operation. This work thus makes a significant contribution to the extension and optimisation of existing early warning systems for coastal protection.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:12851 1190 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Untersuchungen zu Änderungen und Einflussgrößen des mittleren Meeresspiegels in der südwestlichen Ostsee(2019)Climate change induced global mean sea level rise is neither spatially nor temporally uniform, since regional or local processes lead to deviations from the global mean. The development of adapting coastal protection strategies thus poses special challenges for society worldwide. Based on local and regional sea level studies, sea level development can be determined and the individual contributing factors can be separated. For this purpose, mean sea level (MSL) time series are of major importance. This thesis focuses on the compilation and analysis of high quality and long-term MSL time series for the southwestern Baltic Sea coast, considering all available tide gauge records. For the southwestern Baltic Sea a linear trend of 1.2 ± 0.1 mm/a (corrected for glacial isostatic adjustment) is calculated over the 20th century. Due to the predominant westerly wind conditions as well as the temperature and salinity gradients this trend is smaller than in the entire Baltic Sea with 1.7 ± 0.1 mm/a. The interannual sea level variability in the southwestern Baltic Sea is dominated by the compensation of the main influencing factors wind, dynamics (internal steric and external mass input), and sea level pressure. On decadal time scales, on the other hand, sea level variability of the entire Baltic Sea is connected to the North Sea, since the driving force is mainly generated externally by dynamic processes in the North Atlantic (especially variations in steric in the deep ocean). Global sea-level rise is thus also reflected in Baltic Sea MSL change, but superimposed by local effects. This work contributes to the understanding of past and present sea level changes in the southwestern Baltic Sea and thus provides important knowledge for the assessment of the hydrodynamic load on coastal defences.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:111061 1194 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , 19. Treffen junger WissenschaftlerInnen deutschsprachiger Wasserbauinstitute(2017)Das JuWi-Treffen wurde erstmalig 1999 in Weimar veranstaltet und findet seitdem jährlich im Wechsel an Wasserbauinstituten verschiedener Universitäten statt. Vorherige Treffen wurden unter anderem in Zürich, Dresden, Braunschweig und Graz ausgetragen. Ziel der Treffen ist es, wissenschaftliche MitarbeiterInnen und insbesondere DoktorandInnen aus dem Bereich des Wasserbaus zusammenzuführen und einen fachlichen Austausch in einem informellen Rahmen zu ermöglichen. Die in diesem Tagungsband zusammengestellten Beiträge fassen die Vorträge des diesjährigen Treffens in Form von jeweils vierseitigen "Extended Abstracts" zusammen.Source Type:Conference ProceedingsSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:101460 814 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Zur Ermittlung von hydrologischen Bemessungsgrößen an Flussmündungen mit Verfahren der multivariaten Statistik(2015)The design of flood protection structures in the direct reach of river confluences is exceptionally challenging for engineers. This is mainly because commonly applied univariate statistical methods are not valid to derive the hydrological design parameters. In this thesis various aspects are investigated to determine hydrologic and hydraulic parameters for the design of flood protection structures in the direct reach of river confluences to meet safety and economic requirements. First, general aspects influencing statistical analyses of hydrological time series are investigated. Therefore, the influence of different discretisation time spans of discharge time series as well as non-stationarities of the univariate parameters on statistically derived design values are explored. The main focus of the thesis is on estimating design events for flood protection structures in the direct reach of river confluences. A new methodology is introduced for cases where long discharge time series are available at both rivers the main stream and the tributary. The approach uses Copula functions and is based on overlapping quantile-isolines for the derivation of bivariate design events if the variables to be modeled not necessarily occur simultaneously. For river confluences where no discharge time series are available, a general approach is developed to estimate the discharge combinations of both streams in the context of joint occurrence. This thesis provides a significant contribution to the reliable identification of design relevant flood discharges at river confluences.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:9904 400 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Sea level variability and its role for coastal flood risk in the southeastern North Sea : insights into past, present and future sea level changes(2014)This thesis provides a contribution to the consideration of intra-annual to multi-decadal sea level variability in coastal enginnering concepts. Coastal structures are usually designed for a lifetime of several decades. Nowadays a sustainable design requires the consideration of long-term changes in the loading factors due to enhanced greenhouse gas emissions throughout the 21st century. Hence, policy makers and managers need to know as early as possible which climate change pathway the Earth’s climate is following and by how far regional sea levels are changing to support adequate and timely adaption. This, however, is challenging since superimposed on any deterministic long-term trend in sea level there is a considerable fraction of intra-annual to decadal variability linked to climate internal processes. Such variability patterns may be as large as the secular change observed through the 20th century and persist over at least one decade, (i) hampering an early detection of long-term changes or accelerations and (ii) increasing/decreasing the risk of coastal flooding during these periods. This thesis therefore investigates variability patterns in two of the most important loading factors for coastal infrastructure: mean sea level and storm surges. Different filtering techniques in combination with statistical regression models and physical theory are used to characterize the sea level variability in the North Sea (German Bight) over various time scales and to discover the contribution of different oceanographic and atmospheric forcing factors. After identifying the main contributors to the sea level variability, the long-term changes are reassessed over the past 140 years and the atmospherically induced variability patterns are projected over the ongoing century up to the target year of 2100. It is demonstrated that an improved understanding and the subsequent removal of interannual to decadal variability reduces the uncertainties when estimating long-term trends and allows for earlier detection of accelerations (up to 60 years depending on the considered location scenario). This in turn increases the statistical certainty about possible future states, which can be considered in the process of decision making for possible adaption strategies.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:8877 292 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Regional to local assessment of extreme water levels : methods and application to the northern part of the German North Sea coastline(2014)This thesis investigates the use of extreme value statistics to estimate both the heights (i.e. return levels) and occurrence probabilities (i.e. return periods) of extreme water levels, which can cause considerable loss of life and millions of dollars of damage (Cunnane, 1987). Over the past five decades, several approaches for estimating extreme water levels have been developed. Currently, different methods are applied not only on transnational, but also on national scales, resulting in a heterogeneous level of protection. Applying different statistical methods can yield significantly different estimates of return water levels, but even the use of the same technique can produce large discrepancies, because there is subjective parameter choice at several steps in the model setup. In this thesis, the main direct methods (i.e. the block maxima method and the peaks over threshold method) to estimate return levels and periods are compared, considering a wide range of strategies to create the extreme value datasets and a range of different model setups. The focus is on testing the influence of the main factors, which can significantly affect the estimates of extreme value statistics. Finally, to provide guidance for coastal engineers and operators, an objective approach for setting up the model is recommended. If this is applied routinely around a country, it will help overcome the problem of heterogeneous levels of protection resulting from different methods and varying model setups. However, these recommendations can often not be considered for practical applications as the availability of water level data is a limitation in many regions. For example, for the North Frisian part of the German North Sea there are only a few water level records available and these are currently too short to apply traditional extreme value analysis methods. As tidal characteristics in the German Bight are highly influenced by shallow water effects and the shape of the coastline, they can differ significantly between stations (see e.g. Jensen and Müller-Navarra, 2008). It is thus difficult to directly convey information about the likelihood of extreme hydrologic events from gauged to surrounding un-gauged sites. To transfer water level information measured at gauged sites to un-gauged sites in the study region, the regional frequency analysis (RFA) concept (which has been previously applied to a riverine setting) is adopted and adjusted for application to a coastal setting. The proposed method is based on a numerical multi-decadal model hindcast of water levels for the whole of the North Sea. Predicted water levels from the hindcast are bias-corrected using the information from the available tide gauge records. Hence, the simulated water levels agree well with the measured water levels at gauged sites. Combining the bias-corrected water levels and the recommendations that were made in the first part of this thesis provides a procedure to estimate return water levels suitable for coastal defence design conditions. The return levels are estimated continuously along the entire coastline of the study area, including the offshore islands. A similar methodology to that applied here could be used in other regions of the world. One of the most discussed aspects in coastal engineering at the moment is concerned with the possible impact of sea level rise (SLR) and the associated changes in extreme water levels on coastal defense structures. The methodologies presented above can be used to calculate present day design levels for coastal defenses but do not account for SLR and potential nonlinear changes in the tidal characteristics, which in turn may affect the results from extreme value statistics. This is why the impact of SLR on extreme water levels is investigated using a numerical model that covers the entire North Sea and has its highest spatial resolution in the northern part of the German Bight. At most locations, the model run highlights that storm surge and return water levels are significantly different from the changes in MSL alone, a finding somewhat different from former studies in that area having major implications for the design of coastal defenses. Furthermore, the analyses indicate that these increases in storm surge water levels are mainly caused by nonlinear changes in the tidal components which are spatially not coherent. The response of the tidal propagation to SLR is investigated based on the results from a tidal analysis of each individual event. These analyses point to changes in individual constituents, such as increases in the M2 amplitude and decreases in the amplitudes of frictional and overtides accompanied by less tidal wave energy dissipation. Attributed effects are changes in phase lags of individual constituents leading to a different tidal modulation, thus additionally increasing tidal water levels.Source Type:Doctoral ThesisSeries:Mitteilungen des Forschungsinstituts Wasser und Umwelt der Universität SiegenVolume number:7717 220