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Chemical transformations and hydraulic processes in soil and groundwater often lead to an apparent retention of nitrate in lowland catchments. Models are needed to evaluate the interaction of these processes in space and time. The objectives of this study are i) to develop a specific modelling approach by combining selected modelling tools simulating N-transport and turnover in soils and groundwater of lowland catchments, ii) to study interactions between catchment properties and nitrogen transport. Special attention was paid to potential N-loads to surface waters. The modelling approach combines various submodels for water flow and solute transport in soil and groundwater: The soil-water- and nitrogen-model mRISK-N, the groundwater flow model MODFLOW and the solute transport model RT3D. In order to investigate interactions of N-transport and catchment characteristics, the distribution and availability of reaction partners have to be taken into account. Therefore, a special reaction-module is developed, which simulates various chemical processes in groundwater, such as the degradation of organic matter by oxygen, nitrate, sulphate or pyrite oxidation by oxygen and nitrate. The model approach is applied to different simulation, focussing on specific submodels. All simulation studies are based on field data from the Schaugraben catchment, a pleistocene catchment of approximately 25 km², close to Osterburg(Altmark) in the North of Saxony-Anhalt. The following modelling studies have been carried out: i) evaluation of the soil-water- and nitrogen-model based on lysimeter data, ii) modelling of a field scale tracer experiment on nitrate transport and turnover in the groundwater as a first application of the reaction module, iii) evaluation of interactions between hydraulic and chemical aquifer properties in a two-dimensional groundwater transect, iv) modelling of distributed groundwater recharge and soil nitrogen leaching in the study area, to be used as input data for subsequent groundwater simulations, v) study of groundwater nitrate distribution and nitrate breakthrough to the surface water system in the Schaugraben catchment area and a subcatchment, using three-dimensional modelling of reactive groundwater transport. The various model applications prove the model to be capable of simulating interactions between transport, turnover and hydraulic and chemical catchment properties. The distribution of nitrate in the sediment and the resulting loads to surface waters are strongly affected by the amount of reactive substances and by the residence time within the aquifer. In the Schaugraben catchment simulations, it is found that a period of 70 years is needed to raise the average seepage concentrations of nitrate to a level corresponding to the given input situation, if no reactions are considered. Under reactive transport conditions, nitrate concentrations are reduced effectively. Simulation results show that groundwater exfiltration does not contribute considerably to the nitrate pollution of surface waters, as most nitrate entering soils and groundwater is lost by denitrification. Additional sources, such as direct inputs or tile drains have to be taken into account to explain surface water loads. The prognostic value of the models for the study site is limited by uncertainties of input data and estimation of model parameters. Nevertheless, the modelling approach is a useful aid for the identification of source and sink areas of nitrate pollution as well as the investigation of system response to management measures or landuse changes with scenario simulations. The modelling approach assists in the interpretation of observed data, as it allows to integrate local observations into a spatial and temporal framework.
Subsurface stormflow is thought to occur mainly in humid environments with steep terrains. However, in semi-arid areas, preferential flow through macropores can also result in a significant contribution of subsurface stormflow to catchment runoff for varying catchment conditions. Most hydrological models neglect this important subsurface preferential flow. Here, we use the process-oriented hydrological model Hillflow-3D, which includes a macropore flow approach, to simulate rainfall-runoff in the semi-arid Parapunos catchment in Spain, where macropore flow was observed in previous research. The model was extended for this study to account for sorptivity under very dry soil conditions. The results of the model simulations with and without macropore flow are compared. Both model versions give reasonable results for average rainfall situations, although the approach with the macropore concept provides slightly better results. The model results for scenarios of extreme rainfall events (>13.3mm30min(-1)) however show large differences between the versions with and without macropores. These model results compared with measured rainfall-runoff data show that the model with the macropore concept is better. Our conclusion is that preferential flow is important in controlling surface runoff in case of specific, high intensity rainfall events. Therefore, preferential flow processes must be included in hydrological models where we know that preferential flow occurs. Hydrological process models with a less detailed process description may fit observed average events reasonably well but can result in erroneous predictions for more extreme events. Copyright (c) 2013 John Wiley & Sons, Ltd.
In our fast-changing world, human-machine interfaces (HMIs) are of ever-increasing importance. Among the most ubiquitous examples are touchscreens that most people are familiar with from their smartphones. The quality of such an HMI can be improved by adding haptic feedback-an imitation of using mechanical buttons-to the touchscreen. Thin-film actuators on the basis of electro-mechanically active polymers (EAPs), with the electroactive material sandwiched between two compliant electrodes, offer a promising technology for haptic surfaces. In thin-film technology, the thickness and the number of stacked layers of the electroactive dielectric are key parameters for tuning a system. Therefore, we have experimentally investigated the influence of the thickness of a single EAP layer on the electrical and the electro-mechanical performance of the transducer. In order to achieve high electro-mechanical actuator outputs, we have employed relaxor-ferroelectric ter-fluoropolymers that can be screen-printed. By means of a model-based approach, we have also directly compared single- and multi-layer actuators, thus providing guidelines for optimized transducer configurations with respect to the system requirements of haptic applications for which the operation frequency is of particular importance.
To investigate the reliability and stability of spherical harmonic models based on archeo/-paleomagnetic data, 2000 Geomagnetic models were calculated. All models are based on the same data set but with randomized uncertainties. Comparison of these models to the geomagnetic field model gufm1 showed that large scale magnetic field structures up to spherical harmonic degree 4 are stable throughout all models. Through a ranking of all models by comparing the dipole coefficients to gufm1 more realistic uncertainty estimates were derived than the authors of the data provide.
The derived uncertainty estimates were used in further modelling, which combines archeo/-paleomagnetic and historical data. The huge difference in data count, accuracy and coverage of these two very different data sources made it necessary to introduce a time dependent spatial damping, which was constructed to constrain the spatial complexity of the model. Finally 501 models were calculated by considering that each data point is a Gaussian random variable, whose mean is the original value and whose standard deviation is its uncertainty. The final model arhimag1k is calculated by taking the mean of the 501 sets of Gauss coefficients. arhimag1k fits different dependent and independent data sets well. It shows an early reverse flux patch at the core-mantle boundary between 1000 AD and 1200 AD at the location of the South Atlantic Anomaly today. Another interesting feature is a high latitude flux patch over Greenland between 1200 and 1400 AD. The dipole moment shows a constant behaviour between 1600 and 1840 AD.
In the second part of the thesis 4 new paleointensities from 4 different flows of the island Fogo, which is part of Cape Verde, are presented. The data is fitted well by arhimag1k with the exception of the value at 1663 of 28.3 microtesla, which is approximately 10 microtesla lower than the model suggest.
This study presents the development of 1D and 2D Surface Evolution Codes (SECs) and their coupling to any lithospheric-scale (thermo-)mechanical code with a quadrilateral structured surface mesh.
Both SECs involve diffusion as approach for hillslope processes and the stream power law to reflect riverbed incision. The 1D SEC settles sediment that was produced by fluvial incision in the appropriate minimum, while the supply-limited 2D SEC DANSER uses a fast filling algorithm to model sedimantation. It is based on a cellular automaton. A slope-dependent factor in the sediment flux extends the diffusion equation to nonlinear diffusion. The discharge accumulation is achieved with the D8-algorithm and an improved drainage accumulation routine. Lateral incision enhances the incision's modelling. Following empirical laws, it incises channels of several cells width.
The coupling method enables different temporal and spatial resolutions of the SEC and the thermo-mechanical code. It transfers vertical as well as horizontal displacements to the surface model. A weighted smoothing of the 3D surface displacements is implemented. The smoothed displacement vectors transmit the deformation by bilinear interpolation to the surface model. These interpolation methods ensure mass conservation in both directions and prevent the two surfaces from drifting apart.
The presented applications refer to the evolution of the Pamir orogen. A calibration of DANSER's parameters with geomorphological data and a DEM as initial topography highlights the advantage of lateral incision. Preserving the channel width and reflecting incision peaks in narrow channels, this closes the huge gap between current orogen-scale incision models and observed topographies.
River capturing models in a system of fault-bounded block rotations reaffirm the importance of the lateral incision routine for capturing events with channel initiation. The models show a low probability of river capturings with large deflection angles. While the probability of river capturing is directly depending on the uplift rate, the erodibility inside of a dip-slip fault speeds up headward erosion along the fault: The model's capturing speed increases within a fault.
Coupling DANSER with the thermo-mechanical code SLIM 3D emphasizes the versatility of the SEC. While DANSER has minor influence on the lithospheric evolution of an indenter model, the brittle surface deformation is strongly affected by its sedimentation, widening a basin in between two forming orogens and also the southern part of the southern orogen to south, east and west.
ArcticBeach v1.0
(2022)
In the Arctic, air temperatures are increasing and sea ice is declining, resulting in larger waves and a longer open water season, all of which intensify the thaw and erosion of ice-rich coasts. Climate change has been shown to increase the rate of Arctic coastal erosion, causing problems for Arctic cultural heritage, existing industrial, military, and civil infrastructure, as well as changes in nearshore biogeochemistry. Numerical models that reproduce historical and project future Arctic erosion rates are necessary to understand how further climate change will affect these problems, and no such model yet exists to simulate the physics of erosion on a pan-Arctic scale. We have coupled a bathystrophic storm surge model to a simplified physical erosion model of a permafrost coastline. This Arctic erosion model, called ArcticBeach v1.0, is a first step toward a physical parameterization of Arctic shoreline erosion for larger-scale models. It is forced by wind speed and direction, wave period and height, sea surface temperature, all of which are masked during times of sea ice cover near the coastline. Model tuning requires observed historical retreat rates (at least one value), as well as rough nearshore bathymetry. These parameters are already available on a pan-Arctic scale. The model is validated at three study sites at 1) Drew Point (DP), Alaska, 2) Mamontovy Khayata (MK), Siberia, and 3) Veslebogen Cliffs, Svalbard. Simulated cumulative retreat rates for DP and MK respectively (169 and 170 m) over the time periods studied at each site (2007-2016, and 1995-2018) are found to the same order of magnitude as observed cumulative retreat (172 and 120 m). The rocky Veslebogen cliffs have small observed cumulative retreat rates (0.05 m over 2014-2016), and our model was also able to reproduce this same order of magnitude of retreat (0.08 m). Given the large differences in geomorphology between the study sites, this study provides a proof-of-concept that ArcticBeach v1.0 can be applied on very different permafrost coastlines. ArcticBeach v1.0 provides a promising starting point to project retreat of Arctic shorelines, or to evaluate historical retreat in places that have had few observations.
The southern Central Andes (SCA) (between 27 degrees S and 40 degrees S) is bordered to the west by the convergent margin between the continental South American Plate and the oceanic Nazca Plate. The subduction angle along this margin is variable, as is the deformation of the upper plate. Between 33 degrees S and 35 degrees S, the subduction angle of the Nazca plate increases from sub-horizontal (< 5 degrees) in the north to relatively steep (similar to 30 degrees) in the south. The SCA contain inherited lithological and structural heterogeneities within the crust that have been reactivated and overprinted since the onset of subduction and associated Cenozoic deformation within the Andean orogen. The distribution of the deformation within the SCA has often been attributed to the variations in the subduction angle and the reactivation of these inherited heterogeneities. However, the possible influence that the thickness and composition of the continental crust have had on both short-term and long-term deformation of the SCA is yet to be thoroughly investigated. For our investigations, we have derived density distributions and thicknesses for various layers that make up the lithosphere and evaluated their relationships with tectonic events that occurred over the history of the Andean orogeny and, in particular, investigated the short- and long-term nature of the present-day deformation processes. We established a 3D model of lithosphere beneath the orogen and its foreland (29 degrees S-39 degrees S) that is consistent with currently available geological and geophysical data, including the gravity data. The modelled crustal configuration and density distribution reveal spatial relationships with different tectonic domains: the crystalline crust in the orogen (the magmatic arc and the main orogenic wedge) is thicker (similar to 55 km) and less dense (similar to 2900 kg/m(3)) than in the forearc (similar to 35 km, similar to 2975 kg/m(3)) and foreland (similar to 30 km, similar to 3000 kg/m(3)). Crustal thickening in the orogen probably occurred as a result of stacking of low-density domains, while density and thickness variations beneath the forearc and foreland most likely reflect differences in the tectonic evolution of each area following crustal accretion. No clear spatial relationship exists between the density distribution within the lithosphere and previously proposed boundaries of crustal terranes accreted during the early Paleozoic. Areas with ongoing deformation show a spatial correlation with those areas that have the highest topographic gradients and where there are abrupt changes in the average crustal-density contrast. This suggests that the short-term deformation within the interior of the Andean orogen and its foreland is fundamentally influenced by the crustal composition and the relative thickness of different crustal layers. A thicker, denser, and potentially stronger lithosphere beneath the northern part of the SCA foreland is interpreted to have favoured a strong coupling between the Nazca and South American plates, facilitating the development of a sub-horizontal slab.
The southern Central Andes (SCA) (between 27 degrees S and 40 degrees S) is bordered to the west by the convergent margin between the continental South American Plate and the oceanic Nazca Plate. The subduction angle along this margin is variable, as is the deformation of the upper plate. Between 33 degrees S and 35 degrees S, the subduction angle of the Nazca plate increases from sub-horizontal (< 5 degrees) in the north to relatively steep (similar to 30 degrees) in the south. The SCA contain inherited lithological and structural heterogeneities within the crust that have been reactivated and overprinted since the onset of subduction and associated Cenozoic deformation within the Andean orogen. The distribution of the deformation within the SCA has often been attributed to the variations in the subduction angle and the reactivation of these inherited heterogeneities. However, the possible influence that the thickness and composition of the continental crust have had on both short-term and long-term deformation of the SCA is yet to be thoroughly investigated. For our investigations, we have derived density distributions and thicknesses for various layers that make up the lithosphere and evaluated their relationships with tectonic events that occurred over the history of the Andean orogeny and, in particular, investigated the short- and long-term nature of the present-day deformation processes. We established a 3D model of lithosphere beneath the orogen and its foreland (29 degrees S-39 degrees S) that is consistent with currently available geological and geophysical data, including the gravity data. The modelled crustal configuration and density distribution reveal spatial relationships with different tectonic domains: the crystalline crust in the orogen (the magmatic arc and the main orogenic wedge) is thicker (similar to 55 km) and less dense (similar to 2900 kg/m(3)) than in the forearc (similar to 35 km, similar to 2975 kg/m(3)) and foreland (similar to 30 km, similar to 3000 kg/m(3)). Crustal thickening in the orogen probably occurred as a result of stacking of low-density domains, while density and thickness variations beneath the forearc and foreland most likely reflect differences in the tectonic evolution of each area following crustal accretion. No clear spatial relationship exists between the density distribution within the lithosphere and previously proposed boundaries of crustal terranes accreted during the early Paleozoic. Areas with ongoing deformation show a spatial correlation with those areas that have the highest topographic gradients and where there are abrupt changes in the average crustal-density contrast. This suggests that the short-term deformation within the interior of the Andean orogen and its foreland is fundamentally influenced by the crustal composition and the relative thickness of different crustal layers. A thicker, denser, and potentially stronger lithosphere beneath the northern part of the SCA foreland is interpreted to have favoured a strong coupling between the Nazca and South American plates, facilitating the development of a sub-horizontal slab.
The Andes are a ~7000 km long N-S trending mountain range developed along the South American western continental margin. Driven by the subduction of the oceanic Nazca plate beneath the continental South American plate, the formation of the northern and central parts of the orogen is a type case for a non-collisional orogeny. In the southern Central Andes (SCA, 29°S-39°S), the oceanic plate changes the subduction angle between 33°S and 35°S from almost horizontal (< 5° dip) in the north to a steeper angle (~30° dip) in the south. This sector of the Andes also displays remarkable along- and across- strike variations of the tectonic deformation patterns. These include a systematic decrease of topographic elevation, of crustal shortening and foreland and orogenic width, as well as an alternation of the foreland deformation style between thick-skinned and thin-skinned recorded along- and across the strike of the subduction zone. Moreover, the SCA are a very seismically active region. The continental plate is characterized by a relatively shallow seismicity (< 30 km depth) which is mainly focussed at the transition from the orogen to the lowland areas of the foreland and the forearc; in contrast, deeper seismicity occurs below the interiors of the northern foreland. Additionally, frequent seismicity is also recorded in the shallow parts of the oceanic plate and in a sector of the flat slab segment between 31°S and 33°S. The observed spatial heterogeneity in tectonic and seismic deformation in the SCA has been attributed to multiple causes, including variations in sediment thickness, the presence of inherited structures and changes in the subduction angle of the oceanic slab. However, there is no study that inquired the relationship between the long-term rheological configuration of the SCA and the spatial deformation patterns. Moreover, the effects of the density and thickness configuration of the continental plate and of variations in the slab dip angle in the rheological state of the lithosphere have been not thoroughly investigated yet. Since rheology depends on composition, pressure and temperature, a detailed characterization of the compositional, structural and thermal fields of the lithosphere is needed. Therefore, by using multiple geophysical approaches and data sources, I constructed the following 3D models of the SCA lithosphere: (i) a seismically-constrained structural and density model that was tested against the gravity field; (ii) a thermal model integrating the conversion of mantle shear-wave velocities to temperature with steady-state conductive calculations in the uppermost lithosphere (< 50 km depth), validated by temperature and heat-flow measurements; and (iii) a rheological model of the long-term lithospheric strength using as input the previously-generated models.
The results of this dissertation indicate that the present-day thermal and rheological fields of the SCA are controlled by different mechanisms at different depths. At shallow depths (< 50 km), the thermomechanical field is modulated by the heterogeneous composition of the continental lithosphere. The overprint of the oceanic slab is detectable where the oceanic plate is shallow (< 85 km depth) and the radiogenic crust is thin, resulting in overall lower temperatures and higher strength compared to regions where the slab is steep and the radiogenic crust is thick. At depths > 50 km, largest temperatures variations occur where the descending slab is detected, which implies that the deep thermal field is mainly affected by the slab dip geometry.
The outcomes of this thesis suggests that long-term thermomechanical state of the lithosphere influences the spatial distribution of seismic deformation. Most of the seismicity within the continental plate occurs above the modelled transition from brittle to ductile conditions. Additionally, there is a spatial correlation between the location of these events and the transition from the mechanically strong domains of the forearc and foreland to the weak domain of the orogen. In contrast, seismicity within the oceanic plate is also detected where long-term ductile conditions are expected. I therefore analysed the possible influence of additional mechanisms triggering these earthquakes, including the compaction of sediments in the subduction interface and dehydration reactions in the slab. To that aim, I carried out a qualitative analysis of the state of hydration in the mantle using the ratio between compressional- and shear-wave velocity (vp/vs ratio) from a previous seismic tomography. The results from this analysis indicate that the majority of the seismicity spatially correlates with hydrated areas of the slab and overlying continental mantle, with the exception of the cluster within the flat slab segment. In this region, earthquakes are likely triggered by flexural processes where the slab changes from a flat to a steep subduction angle.
First-order variations in the observed tectonic patterns also seem to be influenced by the thermomechanical configuration of the lithosphere. The mechanically strong domains of the forearc and foreland, due to their resistance to deformation, display smaller amounts of shortening than the relatively weak orogenic domain. In addition, the structural and thermomechanical characteristics modelled in this dissertation confirm previous analyses from geodynamic models pointing to the control of the observed heterogeneities in the orogen and foreland deformation style. These characteristics include the lithospheric and crustal thickness, the presence of weak sediments and the variations in gravitational potential energy.
Specific conditions occur in the cold and strong northern foreland, which is characterized by active seismicity and thick-skinned structures, although the modelled crustal strength exceeds the typical values of externally-applied tectonic stresses. The additional mechanisms that could explain the strain localization in a region that should resist deformation are: (i) increased tectonic forces coming from the steepening of the slab and (ii) enhanced weakening along inherited structures from pre-Andean deformation events. Finally, the thermomechanical conditions of this sector of the foreland could be a key factor influencing the preservation of the flat subduction angle at these latitudes of the SCA.
Complete protection against flood risks by structural measures is impossible. Therefore flood prediction is important for flood risk management. Good explanatory power of flood models requires a meaningful representation of bio-physical processes. Therefore great interest exists to improve the process representation. Progress in hydrological process understanding is achieved through a learning cycle including critical assessment of an existing model for a given catchment as a first step. The assessment will highlight deficiencies of the model, from which useful additional data requirements are derived, giving a guideline for new measurements. These new measurements may in turn lead to improved process concepts. The improved process concepts are finally summarized in an updated hydrological model. In this thesis I demonstrate such a learning cycle, focusing on the advancement of model evaluation methods and more cost effective measurements. For a successful model evaluation, I propose that three questions should be answered: 1) when is a model reproducing observations in a satisfactory way? 2) If model results deviate, of what nature is the difference? And 3) what are most likely the relevant model components affecting these differences? To answer the first two questions, I developed a new method to assess the temporal dynamics of model performance (or TIGER - TIme series of Grouped Errors). This method is powerful in highlighting recurrent patterns of insufficient model behaviour for long simulation periods. I answered the third question with the analysis of the temporal dynamics of parameter sensitivity (TEDPAS). For calculating TEDPAS, an efficient method for sensitivity analysis is necessary. I used such an efficient method called Fourier Amplitude Sensitivity Test, which has a smart sampling scheme. Combining the two methods TIGER and TEDPAS provided a powerful tool for model assessment. With WaSiM-ETH applied to the Weisseritz catchment as a case study, I found insufficient process descriptions for the snow dynamics and for the recession during dry periods in late summer and fall. Focusing on snow dynamics, reasons for poor model performance can either be a poor representation of snow processes in the model, or poor data on snow cover, or both. To obtain an improved data set on snow cover, time series of snow height and temperatures were collected with a cost efficient method based on temperature measurements on multiple levels at each location. An algorithm was developed to simultaneously estimate snow height and cold content from these measurements. Both, snow height and cold content are relevant quantities for spring flood forecasting. Spatial variability was observed at the local and the catchment scale with an adjusted sampling design. At the local scale, samples were collected on two perpendicular transects of 60 m length and analysed with geostatistical methods. The range determined from fitted theoretical variograms was within the range of the sampling design for 80% of the plots. No patterns were found, that would explain the random variability and spatial correlation at the local scale. At the watershed scale, locations of the extensive field campaign were selected according to a stratified sample design to capture the combined effects of elevation, aspect and land use. The snow height is mainly affected by the plot elevation. The expected influence of aspect and land use was not observed. To better understand the deficiencies of the snow module in WaSiM-ETH, the same approach, a simple degree day model was checked for its capability to reproduce the data. The degree day model was capable to explain the temporal variability for plots with a continuous snow pack over the entire snow season, if parameters were estimated for single plots. However, processes described in the simple model are not sufficient to represent multiple accumulation-melt-cycles, as observed for the lower catchment. Thus, the combined spatio-temporal variability at the watershed scale is not captured by the model. Further tests on improved concepts for the representation of snow dynamics at the Weißeritz are required. From the data I suggest to include at least rain on snow and redistribution by wind as additional processes to better describe spatio-temporal variability. Alternatively an energy balance snow model could be tested. Overall, the proposed learning cycle is a useful framework for targeted model improvement. The advanced model diagnostics is valuable to identify model deficiencies and to guide field measurements. The additional data collected throughout this work helps to get a deepened understanding of the processes in the Weisseritz catchment.