93 results
Now showing1 - 10 of 93
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Evaporation dynamics from flowing water surfacesIn contrast to the wealth of information on evaporation dynamics from placid water surfaces such as lakes and reservoirs, estimating water evaporation from turbulent surfaces of streams remains a challenge. Evidence suggests considerable differences in evaporation rates from flowing water bodies relative to placid surfaces. Here, we experimentally investigate how flow characteristics (velocity and turbulence) and boundary conditions (wind and radiation) regulate evaporation from flowing water surfaces by using a controlled laboratory flume to isolate key hydrodynamic–atmospheric interactions relevant to streams and rivers. We used a closed flume (7.6 m length, 0.31 m width, and 0.5 m depth) imposing different boundary conditions over the test section of 1.5 m in length while other parts of the flume were covered to prevent evaporative losses. Our results demonstrate that the effect of turbulence on evaporation depends on the temperature profile of the water body and redistribution of radiative heat with turbulent mixing highlighting that evaporation emerges from a nonlinear coupling between hydrodynamic mixing and energy availability. Under solar radiation, increased water flow and turbulence can reduce evaporation by suppressing the formation of a warm surface layer and redistributing absorbed heat in depth of the water column. Without shortwave radiation flux, however, enhanced surface velocity and turbulent mixing may cause significant enhancement in evaporation rates up to 2–5 times that of placid water surfaces. Numerical simulations indicate that enhanced surface turbulence and wave activity increase interfacial roughness and shear, regulating the vapor boundary layer and producing spatially heterogeneous and intermittent vapor fluxes. The study offers novel insights into evaporation from wavy and turbulent flowing water surfaces for a better understanding of evaporation from riverine networks across flow regimes and climatic conditions.Publicationtype: Journal Article20 16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nature-based solutions for coastal protection based on intuitionistic fuzzy group decision making(Elsevier, 2026-06-15); ; ; Liao, Cheng HuiNature-based Solutions (NbS) use natural processes to address social, economic, and environmental challenges, including climate change, and this study explores their application for coastal protection. Before the actual implementation of NbS structures, co-creation with stakeholders to identify and assess potential NbS solutions for the selected local site is essential. However, existing frameworks for selecting NbS measures in coastal protection remain limited in handling the complex interactions among multiple indicators and the inherent uncertainty in expert evaluations. To address this gap, we develop an integrated assessment framework specifically for NbS in coastal protection. We first identified 18 distinct coastal protection measures through literature reviews. The proposed framework combines the Fuzzy Delphi Method (FDM) and entropy-based intuitionistic fuzzy TOPSIS (IF-TOPSIS) to facilitate expert-driven multi-criteria decision analysis (MCDA), both of which use fuzzy theory to address uncertainty and ambiguity in expert judgments. The 18 consensus indicators from an initial pool of 63 evaluation indicators are obtained in FDM analysis. Subsequently, IF-TOPSIS is applied to rank the 18 measures against these evaluation indicators based on membership, non-membership, and hesitancy degrees. The proposed framework is demonstrated through a case study at the Golden Coast, Tainan, Taiwan to illustrate its practical applicability.Publicationtype: Journal Article59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Concentration-dependent settling velocities of cohesive sediments from the Port of Hamburg based on ultrasound velocity profilingThe settling behavior of cohesive sediments plays a key role in estuarine sediment dynamics and harbor maintenance. This study aimed to assess the applicability of Ultrasound Velocity Profiling (UVP) to capture the spatial and temporal evolution of the settling process and to derive concentration-dependent settling velocities. Laboratory experiments were conducted in a settling column with initial sediment concentrations (C0[jls-end-space/]) of 0.3-80 g/L, using cohesive sediments from the Port of Hamburg. A 4 MHz transducer was utilized to measure the vertical particle velocities with a resolution of 0.08 mm/s and a sampling volume height of 1 mm. Effective settling velocities were derived from the UVP measurements and compared to the settling velocities obtained from the lutocline evolution. Subsequently, common mathematical models were fitted to the data. The results demonstrate that UVP is a suitable, non-intrusive method for high-resolution imaging of settling processes, revealing concentration-dependent characteristics in particle movement in unprecedented detail. The calculated effective settling velocities increased approximately linearly in the flocculation settling range until a maximum of ws,max = 2 mm/s was reached at C0 = 3.5 g/L, followed by an asymptotic decline in the hindered settling range. The associated deposition flux showed a broad maximum of approximately 0.01 kg/(m2s) for C0 in the range of 5-15 g/L. The results provide previously unavailable, site-specific data on the settling behavior of the studied cohesive sediments. Potential application areas of UVP include the execution of field experiments and the automated high-resolution tracking of the lutocline or bed level.Publicationtype: Journal Article21 20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Near-field dynamics of discrete dredged material discharge events in the Elbe estuary: Quantifying deposition fraction and plume evolutionDredging and relocation of sediments are essential to maintain navigable waterways and port access in many estuaries. The relocated volumes can significantly influence long-term morphological evolution and thus need to be represented in relevant numerical models. In morphodynamic simulations, relocation processes require parameterization, typically based on limited empirical data, as dedicated field measurements of near-field processes during discharge at relocation sites are scarce. Therefore, this study aims to quantify (i) the spatiotemporal evolution of the suspended sediment plume, (ii) the deposition fraction and resulting changes in bed morphology, and (iii) the sediment mass balance for individual discharge events.Publicationtype: Conference Poster38 18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Erosion threshold of cohesive sediments in the German Wadden Sea: temporal variability and comparison of in-situ and laboratory experimentsA newly developed in-situ setup of the Closed Gust Erosion Microcosm System (C-GEMS) was utilized for erosion experiments in a tidal mudflat in the mouth of the Elbe in the German Wadden Sea to investigate the temporal variability of the erosion threshold τc of cohesive sediments. In addition, erosion experiments with extracted sediment cores from the same site were conducted in the field and in the laboratory with the identical device to analyze the influence of sample extraction and transport on the derived erosion threshold. A total of 21 erosion experiments were carried out in four measuring campaigns between April and September 2024. The erosion thresholds derived from the in-situ experiments exhibit considerable temporal variability across campaigns, with values of τc = 0.1–0.27 N/m²>, while repeated experiments within the individual campaigns demonstrate a high degree of reproducibility. Accompanying analyses of surface sediment particle size distribution and bulk density revealed that mud concentration (clay and silt) varied with wind conditions and the associated hydrodynamic load prior to the measurement campaigns. The observed temporal variability in τc is reasonably well captured by a mathematical model based on mud concentration and particle size, suggesting that τc can be plausibly estimated from these parameters. For campaigns with a cohesive surface sediment layer, erosion thresholds derived in the ex-situ experiments are consistently lower than those obtained in the in-situ experiments. This is attributed to the disturbance of the surface sediments due to mechanical extraction and liquefaction during transport. The findings offer insights into the transport dynamics of cohesive sediments and help guide decisions on whether future erosion experiments should be conducted in situ, despite the significant effort involved, or whether extracted sediment cores are a suitable alternative.Publicationtype: Journal Article65 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effects of climate change on coastal hydrodynamics along the German Baltic Sea coast(2025-05-29); ; ; The German federal state of Schleswig-Holstein is developing a Baltic Sea Coast 2100 strategy under the leadership of the Ministry for Energy Transition, Climate Protection, Environment and Nature. The aim of the strategy is a sustainable adaptation of the coastal region to climate change, taking into account the demands of nature conservation, tourism and coastal protection. Basis for this strategy is detailed information on the current status and possible future changes in coastal hydrodynamics and sediment dynamics, including morphological changes. In a joint research project from 2019 to 2023, the Institute of River and Coastal Engineering of Hamburg University of Technology (TUHH) carried out model-based investigations to describe and analyze currents and transport processes along the entire Baltic Sea coast of Schleswig-Holstein (greater than 400 km) for the current state as well as for possible future conditions, taking into account various scenarios for sea level rise and climate change-induced changes of wind conditions.Publicationtype: Conference Paper16 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Evaporation dynamics from flowing water surfaces(2025-04); ; ; ; In contrast to the wealth of information on evaporation dynamics from placid water surfaces such as lakes and reservoirs, estimating water evaporation from turbulent surfaces of streams remains a challenge. Evidence suggests a considerable change in evaporation from flowing surfaces relative to placid surfaces with local modifiers such as chemical, physical and biological processes that alter the energy budget and water temperature. While the studies on evaporation from wavy surfaces of oceans offer valuable insights, significant differences in hydrodynamics and heat exchange processes distinguish evaporation in oceans from that in rivers. Here we experimentally investigate how water flow characteristics (velocity and turbulence) and atmospheric boundary conditions (wind and radiation) affect evaporation rates and temperature dynamics in a flume. A closed flume (7.6 m length, 0.31 m width, and 0.5 m depth) is used to impose different boundary conditions over a test section of the flume (length of 1.5 m) while other parts of the flume are covered to reduce evaporative losses. Our preliminary findings show significant enhancement in evaporation rates, reaching 2-5 times that of placid water surfaces, driven by increases in surface velocity and turbulence characteristics. Furthermore, we observe that radiative and aerodynamic factors contribute nonlinearly to evaporation enhancement and affect temperature distribution in the water body. The study offers novel insights into evaporation from wavy and turbulent flowing water surfaces for better prediction of evaporation from riverine networks across flow regimes and climatic conditions.Publicationtype: Conference Poster44 18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Deriving erosion thresholds of freshly deposited cohesive sediments from the port of Hamburg using a closed microcosm systemThe quantification of the erodibility of cohesive sediments is fundamental for an advanced understanding of estuarine sediment transport processes. In this study, the surface erosion threshold τc for cohesive sediments collected from two sites in the area of the Port of Hamburg in the River Elbe is investigated in laboratory experiments. An improved closed microcosm system (C-GEMS) is used for the erosion experiments, which allows the accumulation of suspended sediment concentration (SSC) over an experimental run. A total of 34 erosion experiments has been conducted with homogenized samples and bulk densities between 1050 kg/m³ and 1250 kg/m³. The covered range of bulk densities is seen to represent the values commonly exhibited by freshly deposited cohesive sediments. Two approaches to derive τc based on the erosion rate (ε-method) and the SSC (SSC-method) were elaborated and compared. For both approaches, only one parameter has to be set in order to facilitate transferability to other devices. The results show a better performance of the SSC-method in terms of lower uncertainties, especially at the upper application limits of the utilized C-GEMS. The application of the SSC method yields values for τc between 0.037 N/m² and 0.305 N/m², continuously increasing with bulk density. Repetition tests proved the repeatability of the experimental procedure and utilized methods to derive τc. The derived data for τc is used to fit two mathematical models: i) a highly empirical model relating τc to dry bulk density and ii) a recently proposed model relating τc to the physical properties of the sediment-mixture. While the derived parameters for the first model vary widely for the two sampling sites, the fit-parameter for the latter model is virtually independent of the investigated site, suggesting the superiority of this approach.Publicationtype: Journal Article49 145 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Soil salinization due to saltwater intrusion in coastal regions : the role of soil characteristics and heterogeneity(The International Society for Porous Media (InterPore), 2024-04-26); ; ; ; Soil plays a vital role in maintaining ecosystem functionality, supporting biodiversity, facilitating successful crop production, and ensuring socio-economic stability. Soil quality is, however, constantly threatened by various factors, such as adverse climate conditions, hydrogeological processes, and human activities. One particularly significant stressor is soil salinity, which has a detrimental effect on soil quality. This study focuses specifically on understanding how soil properties contribute to the accumulation of surface soil salinity in the presence of shallow saline groundwater. To achieve this objective, advanced groundwater modeling techniques are employed to simulate saltwater intrusion in a riparian area known as Altes Land in northern Germany. A realistic representation of the salinization process is created and evaluated using a comprehensive dataset of hydrogeological information specific to the region. Additionally, the study examines the influence of soil heterogeneity on regional soil salinity by varying soil properties through devising six distinct scenarios for generating the numerical models that represent variations in soil texture and structure. The study reveals that regional soil texture and layering arrangement significantly influence the availability of water and the propagation of saline water in the vadose zone, and are major contributors to surface soil salinity. Subtle alterations and simplifications, often inconspicuous or deemed inconsequential in the context of small-scale experiments, may carry substantial ramifications for the formulation of enhanced management strategies in regions characterized by low elevation and influenced by groundwater salinity. Furthermore, the insights gained from this research provide valuable information for applications in agricultural practices and environmental conservation. Saltwater intrusion occurs when seawater enters coastal groundwater. In low-lying coastal regions, saline groundwater can rise close to the soil surface, leading to soil salinization that negatively impacts soil health and plant growth. The extent of soil salinization can be impacted by soil texture and heterogeneity, which is not fully understood at regional scales. In this study, we developed a new decision-support framework capable of describing and predicting salt transport through unsaturated zones lying over groundwater affected by seawater intrusion, and evaluated it against field measurements. This enabled us to investigate soil salinity under a variety of conditions and quantify the effects of important parameters, including soil texture, heterogeneity, and layering arrangement, on salt deposition close to the surface. Our study offers new quantitative insights into and tools for revealing the mechanisms governing the spatial distribution of soil salinity, as well as its health, hence contributing to global efforts for sustainable resource management and United Nations Sustainable Development Goals, particularly UN SDG15.Publicationtype: Journal Article35 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effects of sea level rise and tidal flat growth on tidal dynamics and geometry of the Elbe estuary(Copernicus Publications, 2024-03-18); ; ; Future global mean sea level rise (SLR) will affect coastlines and estuaries in the North Sea and therefore also coastal protection structures, unique local ecosystems and important waterways. SLR will not only raise water levels but also influence tidal dynamics and morphodynamics, which is why the tidal flats of the Wadden Sea can grow to a certain extent with SLR. Investigations on the effects of climate-change-induced SLR and the related potential bathymetric changes inside of estuaries form an important basis for identifying vulnerabilities and developing appropriate adaptation strategies. To analyse the influence of potential SLR and tidal flat elevation scenarios on the tidal dynamics in the Elbe estuary, we used a highly resolved hydrodynamic numerical model of the German Bight. The analysis results show increasing tidal range in the Elbe estuary solely due to SLR. They also reveal strongly varying changes with different tidal flat growth scenarios: while tidal flat elevation up to the mouth of the estuary can cause tidal range to decrease relative to SLR alone, tidal flat elevation in the entire estuary can lead to an increase in tidal range relative to SLR alone. Further analyses show how the geometric parameters of the Elbe estuary are changing due to SLR and tidal flat elevation. We discuss how these changes in estuarine geometry can provide an explanation for the changes in tidal range.Publicationtype: Journal Article16 72