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Item Open Access Large-scale high head pico hydropower potential assessment(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2018) Schröder, Hans Christoph; Wieprecht, Silke (Prof. Dr.-Ing.)Due to a lack of site-related information, Pico hydropower (PHP) has hardly been a projectable resource so far. This is particularly true for large area PHP potential information that could open a perspective to increase the size of development projects by aggregating individual PHP installations. The present work is extending the capabilities of GIS based hydropower potential assessment into the PHP domain through a GIS based PHP potential assessment procedure that facilitates the discrimination of areas without high head PHP potential against areas with PHP potential and against areas with so called “favorable PHP potential”. The basic unit of the spatial output is determined by the underlying PHP potential definition of this work: a standardized PHP installation and the required hydraulic source, together called standard unit, are located on an area of one square kilometer. The gradation of the output is a consequence of the verification techniques. Several large area PHP potential field assessment methods, based on contemplative analysis techniques, are developed in this work. Field assessments were conducted in Yunnan Province/China, Costa Rica, Ecuador and Sri Lanka. The aim for all field assessments is to get a comprehensive view on the PHP potential distribution of the entire country/province. Application of the GIS based PHP potential assessment procedure is aimed at the global tropical and subtropical regions.Item Open Access Porosity and permeability alterations in processes of biomineralization in porous media - microfluidic investigations and their interpretation(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2022) Weinhardt, Felix; Class, Holger (apl. Prof. Dr.-Ing)Motivation: Biomineralization refers to microbially induced processes resulting in mineral formations. In addition to complex biomineral structures frequently formed by marine organisms, like corals or mussels, microbial activities may also indirectly induce mineralization. A famous example is the formation of stromatolites, which result from biofilm activities that locally alter the chemical and physical properties of the environment in favor of carbonate precipitation. Recently, biomineralization gained attention as an engineering application. Especially with the background of global warming and the objective to reduce CO2 emissions, biomineralization offers an innovative and sustainable alternative to the usage of conventional Portland cement, whose production currently contributes significantly to global CO2 emissions. The most widely used method of biomineralization in engineering applications, is ureolytic calcium carbonate precipitation, which relies on the hydrolysis of urea and the subsequent precipitation of calcium carbonate. The hydrolysis of urea at moderate temperatures is relatively slow and therefore needs to be catalyzed by the enzyme urease to be practical for applications. Urease can be extracted from plants, for example from ground jack beans, and the process is consequently referred to as enzyme-induced calcium carbonate precipitation (ECIP). Another method is microbially induced calcium carbonate precipitation (MICP), which uses ureolytic bacteria that produce the enzyme in situ. EICP and MICP applications allow for producing various construction materials, stabilizing soils, or creating hydraulic barriers in the subsurface. The latter can be used, for example, to remediate leakages at the top layer of gas storage reservoirs, or to contain contaminant plumes in aquifers. Especially when remediating leakages in the subsurface, the most crucial parameter to be controlled is its intrinsic permeability. A valuable tool for predicting and planning field applications is the use of numerical simulation at the scale of representative elementary volumes (REV). For that, the considered domain is subdivided into several REV’s, which do not resolve the pore space in detail, but represent it by averaged parameters, such as the porosity and permeability. The porosity describes the ratio of the pore space to the considered bulk volume, and the permeability quantifies the ease of fluid flow through a porous medium. A change in porosity generally also affects permeability. Therefore, for REV-scale simulations, constitutive relationships are utilized to describe permeability as a function of porosity. There are several porosity-permeability relationships in the literature, such as the Kozeny-Carman relationship, Verma-Pruess, or simple power-law relationships. These constitutive relationships can describe individual states but usually do not include the underlying processes. Different boundary conditions during biomineralization may influence the course of porosity-permeability relationships. However, these relationships have not yet been adequately addressed. Pore-scale simulations are, in principle, very well suited to investigate pore space changes and their effects on permeability systematically. However, these simulations also rely on simplifications and assumptions. Therefore, it is essential to conduct experimental studies to investigate the complex processes during calcium carbonate precipitation in detail at the pore scale. Recent studies have shown that microfluidic methods are particularly suitable for this purpose. However, previous microfluidic studies have not explicitly addressed the impact of biomineralization on hydraulic effects. Therefore, this work aims to identify relevant phenomena at the pore scale to conclude on the REV-scale parameters, porosity and permeability, and their relationship. Contributions: This work comprises three publications. First, a suitable microfluidic setup and workflow were developed in Weinhardt et al. [2021a] to study pore space changes and the associated hydraulic effects reliably. This paper illustrated the benefits and insights of combining optical microscopy and micro X-ray computed tomography (micro XRCT) with hydraulic measurements in microfluidic chips. The elaborated workflow allowed for quantitative analysis of the evolution of calcium carbonate precipitates in terms of their size, shape, and spatial distribution. At the same time, their influence on differential pressure could be observed as a measure of flow resistance. Consequently, porosity and permeability changes could be determined. Along with this paper, we published two data sets [Weinhardt et al., 2021b, Vahid Dastjerdi et al., 2021] and set the basis for two other publications. In the second publication [von Wolff et al., 2021], the simulation results of a pore-scale numerical model, developed by Lars von Wolff, were compared to the experimental data of the first paper [Weinhardt et al., 2021b]. We observed a good agreement between the experimental data and the model results. The numerical studies complemented the experimental observations in allowing for accurate analysis of crystal growth as a function of local velocity profiles. In particular, we observed that crystal aggregates tend to grow toward the upstream side, where the supply of reaction products is higher than on the downstream side. Crystal growth during biomineralization under continuous inflow is thus strongly dependent on the locally varying velocities in a porous medium. In the third publication [Weinhardt et al., 2022a], we conducted further microfluidic experiments based on the experimental setup and workflow of the first contribution and published another data set [Weinhardt et al., 2022b]. We used microfluidic cells with a different, more realistic pore structure and investigated the influence of different injection strategies. We found that the development of preferential flow paths during EICP application may depend on the given boundary conditions. Constant inflow rates can lead to the development of preferential flow paths and keep them open. Gradually reduced inflow rates can mitigate this effect. In addition, we concluded that the coexistence of multiple calcium carbonate polymorphs and their transformations could influence the temporal evolution of porosity-permeability relationships.Item Open Access Long-term lumped projections of groundwater balances in the face of limited data(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2024) Ejaz, Fahad; Nowak, Wolfgang (Prof. Dr.-Ing.)Item Open Access Stochastic and hydrological modelling for climate change prediction in the Lima region, Peru(2015) Chamorro Chávez, Alejandro; Bárdossy, András (Prof. Dr. rer. nat. Dr.-Ing.)Climate change has been an important field of research in the past years and certainly is a major concern in the present time. It involves a broad spectrum of subjects and significant different time scales, ranging from decades to thousands or millions of years. Generally speaking, in a climate change scenario a change in the pattern, average or extreme conditions of some variables is observed, and this can be due to many different causes as changing processes in the earth, human activities or extra terrestrial induced factors. This study concentrates on the influences on the climate due to human activities and focuses on the hydrological response to these influences or changes as a primarily goal, for the next few decades. The main motivation is the vulnerability and scarcity of the water availability in the capital of Peru, Lima, and how the area under study will respond to a change in the climate. An important focus of analysis in order to reduce the uncertainty in the predictions is the errors that appears when modeling a given variable or set of variables. This issue is addressed first in regionalization of precipitation and second in the calibration of hydrological models in which a robust parameter estimation is performed. In the first issue concerning to regionalization, External Drift Kriging is applied. In this part of the work the results of regionalization are analyzed with focus on the errors and systematic errors which appear during the modeling. The main goal here is the reduction of these errors through some proposed transformations. Here, three approaches are suggested, namely smoothing of the digital elevation model (DEM) considering a symmetric area, power transformation and smoothing considering a non symmetric area. The second issue concerning the uncertainty in the estimations (discharge) was addressed two-fold, namely by optimizing the objective function by means of a heuristic optimization procedure based on Monte Carlo simulation, and by means of a robust parameter estimation (ROPE) algorithm developed quite recently by Bárdossy and Singh, which in general terms can be used as a general multivariate optimization procedure. The algorithm offers a way of finding a set of “good” parameter vectors, which among other characteristics, are transferable in time. The final result comprises an ensemble of estimations for expected discharge variations accounting for the uncertainty in parameterization and processes description in the models. In this study HVB and HYMOD models are used. The assessment of the impact of climate change in precipitation and temperature is carried out by a statistical downscaling procedure based on a quantil-quantil transformation. Here the information given by the Global Climate Models (GCMs) outputs are transferred to the local scale. Two different GCMs and three scenarios are used in this step. This permitted the definition of a range for the expected future variations for temperature and precipitation. The last chapter of the study addresses the assessment of the discharge in the short term. The goal here is to “infer” the outcome of a random variable (discharge) in the next time step by taking information from past observations (previous steps). As we can regard the observations (time series) as a realization generated from a stochastic process, we can address this issue from a stochastic point of view. The task is addressed first by considering some of the existing autoregressive models (AR process), and second by considering a Copula-based autoregressive model. In order to perform the Copula-based autoregressive model, a given time series (modelled discharge) was transformed into three vectors representing the same original time series but shifted in time. A three dimensional Copula was then fitted to the univariate distributions. For this, a Gaussian model as well as a Beta kernel model expressed in terms of the Beta function was considered.Item Open Access Microbial stabilization of lotic fine sediments(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2018) Schmidt, Holger; Wieprecht, Silke (Prof. Dr.-Ing.)The microbial stabilization of fine sediments constitutes an essential ecosystem function with great ecological and economic implications e.g. in the context of reservoir and waterway management. Although this process is well researched in intertidal mudflats, there is still a major lack of knowledge for lotic systems. To perform fundamental research in this field and to account for the associated very high level of complexity, expertise of natural and engineering science was combined in an interdisciplinary approach. A highly sophisticated mesocosm setup was designed and constructed to guarantee fully controllable and reproducible natural-like boundary conditions during biofilm formation. The overall aim of the performed studies in this doctoral thesis was a comprehensive investigation of all relevant parameters of the cultivated biofilms, such as the microbial biomass, the produced extracellular polymeric substances (EPS), and the composition of the microbial community as well as the stability of the biofilm. This extensive approach should allow the identification of functional key parameters of the biofilm as well as essential interactions and their impact on the overall biofilm ecosystem and resulting biostabilization. In a series of long-term experiments, different influencing factors on biofilm development and corresponding biostabilization were assessed. The first potential impact factor that was analyzed was the experimental setup itself. Furthermore, the influence of the seasonal changes of the microbial community in the utilized river water and the effects of different levels of bed shear stress and illumination intensity were assessed. The results of these different experiments provided essential new insights into the process of biostabilization of lotic fine sediments. Firstly, the reliability of the used experimental setup could be proven, as no significant differences could be detected in biofilm formation and biostabilization comparing different mesocosm sections. The fact that very similar biofilms were developing when the boundary conditions were identical was a crucial prerequisite for any further investigations. In addition, the relevance of biostabilization in lotic systems, which was doubted for a long time, could be proven. However, freshwater and brackish habitat can be very different (e.g. in terms of nutrient availability). This was exemplarily indicated by significantly lower microbial biomass in the analyzed freshwater biofilms compared to biofilms from well-studied intertidal mudflats. Moreover, the very complex interplays between bacteria and diatoms in the biofilm matrix were underlined which led to a focus on this subject during further subsequent studies via an extensive genetic and microscopic profiling. Secondly, the important role of EPS during biostabilization could be demonstrated, whereby the significance of extracellular proteins, such as adhesives produced by sessile diatoms, was suggested. This observation may extend the current EPS research which focusses on extracellular carbohydrates due to their high quantitative fraction in the EPS matrix. Furthermore, the interactions between the microbes, the extracellular matrix and the overall stability of the biofilm system appeared to be much more complex than formerly assumed. Thirdly, the importance of the microbial community in the biofilm system could be elucidated. Even though a high correlation between mere microbial biomass and biostabilization could be detected, especially the seasonality experiments emphasized the impact of the life style of key players among the diatoms. These insights could be extended during the experiments analyzing the different levels of abiotic boundary conditions, where differently stable biofilms were clearly dominated by different assemblages of dominant bacteria. These observations constitute very important new insights into microbial biostabilization as a direct correlation between microbial ecology and the overall, actually measurable ecosystem function of the biofilm could be shown for the first time. Concluding, the insights into the fundamental principles of biostabilization gathered during this thesis can be seen as important steps for further fundamental research. The construction of a reliable unique setup is complete, the reproducible biofilm cultivation in this setup is verified and first investigations of different driving factors during biostabilization were performed. These analyses paved the way for further studies to analyze currently hardly assessed boundary conditions and deeper assessments in order to generate a sound database for future modelling approaches of the dynamics of microbially stabilized lotic fine sediments.Item Open Access Entwicklung eines ökologisch-ökonomischen Vernetzungsmodells für Wasserkraftanlagen und Mehrzweckspeicher(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2018) Fenrich, Eva Katrin; Wieprecht, Silke (Prof. Dr.-Ing.)Die Bereitstellung von Frischwasser für die Bewässerung, Trink- und Brauchwasser sowie umweltfreundlich produzierter elektrischer Energie ist eine der wichtigsten Grundlagen für die Entwicklung einer Region oder eines Landes. Viele unterschiedliche Nutzungsansprüche auf begrenzte Ressourcen sind zu beachten und abzuwägen. Die vernetzten Versorgungsrisiken im Nexus „Wasser, Energie, Nahrung“ sind gleichermaßen eine große Herausforderung für Politik und Ingenieure. Wasserkraft stellt eine saubere, CO2-neutrale, regenerative Energiequelle dar. Jedoch sind aufgrund der Veränderung des Abflussregimes und der Querverbauung der Gewässer große Auswirkungen auf die lokale Ökologie zu erwarten. Diese Auswirkungen auf die lokale oder auch globale Flussökologie bedingen, dass bei der Planung von Wasserkraftanlagen und Mehrzweckspeichern auf ein komplexes System an Einflüssen eingegangen werden muss. Die Wechselwirkungen zwischen den unterschiedlichen Nutzungsarten einerseits und der Fluss- und Auenökologie andererseits müssen in ihrer Gesamtheit erfasst werden. Aufgrund der langen Lebensdauer der Anlagen ist es notwendig sehr eingehend die Auswirkungen eines Projekts in allen Bau- und Betriebsphasen zu untersuchen, da es sich hierbei nicht um kurzfristige Eingriffe, von denen sich das natürliche Gewässer wieder erholen kann, handelt. Ebenso ist es bei Wasserkraftanlagen und Mehrzweckspeichern, wie bei allen großen Infrastrukturmaßnahmen wichtig, dass Entscheidungsträger die Möglichkeit bekommen, übersichtlich Einblicke in die Wirkungszusammenhänge zu gewinnen und Projektvarianten zu vergleichen. Dies ist insbesondere auch dann relevant, wenn verschiedene Interessengruppen oder Projektpartner eine Einigung über die Weiterverfolgung bestimmter Projektvarianten erzielen sollen. Ausgehend von der vorgestellten Problematik wird eine ganzheitliche qualitative und quantitative Bewertung von Wasserkraftanlagen und Mehrzweckspeichern sowohl für die Planung als auch für den Betrieb vorgestellt. Hierzu wurde ein Bilanzierungsmodell entwickelt, das auf Grundlage Leontief'scher Input-Output-Analyse als Entscheidungsunterstützung für Projektentscheidungen beim Neubau und der Erneuerung von Anlagen dienen kann. Die Input-Output-Analyse, ein Verfahren der empirischen Wirtschaftsforschung, das für volkswirtschaftliche Analysen eingesetzt wird, ist ein geeignetes Werkzeug, um Verflechtungen zwischen verschiedenen Aspekten eines Systems zu beschreiben. Durch die Möglichkeit, Stoff- und Wirtschaftsströme in unterschiedlichen Einheiten miteinander zu verknüpfen, eignet sich die Input-Output-Analyse sehr gut zur Modellierung komplexer vernetzter Strukturen. Zunächst wurden qualitative Modelle für die jeweiligen Anlagentypen aufgestellt und anschließend an die Bedingungen des betrachteten Projekts angepasst. Hierzu wurden die Systemgrenzen festgelegt und bestimmt, welche Nutzungsarten zum aktuellen Betrachtungszeitraum relevant sind. Mit Hilfe von Input-Output-Graphen werden die Gesamtsysteme anschaulich dargestellt. Traditionell stehen die Knoten des Graphen für die Sektoren einer Volkswirtschaft und die Kanten stellen die jeweiligen Verflechtungen dar. Produkte eines Sektors einer Volkswirtschaft werden zur Produktion von Gütern und Dienstleitungen anderer Sektoren benötigt. Die Richtung der jeweiligen Kante des Graphen stellt eine Lieferbeziehung dar. Bei der Bewertung von Wasserkraftanlagen und Mehrzweckspeichern werden an Stelle von Sektoren einzelne Aspekte innerhalb des Projektes, wie beispielsweise die Trinkwassergewinnung oder die Erzeugung elektrischer Energie, sowie als Primärinputs natürliche Ressourcen betrachtet. Die Input-Output-Graphen können anschließend teilweise mit Hilfe graphentheoretischer Überlegungen vereinfacht werden. Beispielsweise können Teilgraphen zusammengefasst oder zirkuläre Abhängigkeiten aufgedeckt werden. Von besonderem Interesse sind häufig die indirekten Lieferbeziehungen zwischen Sektoren, die zunächst nicht direkt ersichtlich sind, im Input-Output-Modell aufgrund der Darstellung als Systemgraph jedoch deutlich erkennbar werden. Ein wichtiger Grund, qualitative Modelle zu erstellen, kann unter anderem auch sein, verschiedene Projekte oder Projektvarianten zunächst aufgrund ihrer Struktur zu vergleichen, oder um schon vorhandene Projekte unterschiedlicher Größe als Grundlage für die Datenbeschaffung neu geplanter Projekte zu nutzen. Dieses qualitative Modell wird jeweils für eine bestimmte Anlagengröße und Nutzungsart quantifiziert und anschließend werden iterativ Nutzungs-Szenarien evaluiert. Bei Bedarf kann als abschließende Untersuchung das so entwickelte Input-Output-Modell als Grundlage einer linearen Optimierung verwendet werden. Quantitative Gesamtmodelle und lineare Optimierungsmodelle sind jeweils stark abhängig von den betrachteten Projektvarianten. Durch eine vernetzte Formulierung ökonomischer und ökologischer Fragestellungen wird eine quantitative Bewertung der gegenseitigen Beeinflussung ermittelt. Anhand von Fallstudien wurde die Anwendbarkeit der zuvor erarbeiteten Methodik auf verschiedene Anlagentypen und -größen verifiziert und das Modell weiterentwickelt. Um die grundsätzliche Anwendbarkeit der Input-Output-Analyse auf Wasserkraftanlagen und Mehrzweckspeicher zu untersuchen, wurde zunächst ein sehr einfaches schwach vernetztes System eines Ausleitungskraftwerks an der Drau in Österreich untersucht. Hierbei wurde vor allem auf die Vernetzung von Wasserdargebot, energetischer Nutzung und Flussökologie eingegangen. Die Integration von Bewässerung und Landnutzungsparametern in einem Input-Output-Modell wurde anhand eines Bewässerungssystems in Venezuela untersucht. Hierbei werden vor allem auch sozioökonomische Aspekte mit integriert. In einer weiteren Fallstudie wurde ein Ausleitungskraftwerk an der unteren Argen mit gleichzeitiger Wasserentnahme zur Bewässerung untersucht. Als sehr stark vernetztes System wird das Kandadji-Projekt am Niger, ein typisches Mehrzweckspeicher-Projekt mit Bewässerung, Wasserkraft und Trinkwassergewinnung, betrachtet. Schließlich wird, um die Bandbreite der Anwendbarkeit des entwickelten Modells darzustellen, eine Fallstudie für ein Gezeitenkraftwerk zusammen mit einer Landnutzungs-Wassergütemodellierung im Küstenbereich erstellt. Die verschiedenen Fallstudien geben einen Überblick über die Bandbreite der Anwendungsbereiche des hier entwickelten Modells. Deutlich zu erkennen ist, dass qualitative Modelle und auch quantifizierte Teilmodelle jeweils übertragbar auf andere Projekte und Projektvarianten sein können. Damit wurde Ingenieuren und Entscheidungsträgern ein wertvolles Werkzeug in die Hand gegeben, um die Auswirkungen von Wasserkraftanlagen und Mehrzweckspeichern in allen Planungs- und Betriebsphasen zu bewerten.Item Open Access Impacts of the existing water allocation scheme on the Limarí watershed : Chile, an integrative approach(2015) Kretschmer, Nicole; Bárdossy, András (Prof. Dr. rer. nat. Dr.-Ing. )The research is motivated by an interest in evaluating the special Chilean water management framework, relating to the 1981 Water Code legislation, introduced by the military government. This law mainly strengthened private property rights and increased private autonomy in water use. In particular, it is of interest to assess the impacts of this legislation in the context of the current highly stressed water availability situation in central and northern Chile, combined with intensive and increasing agricultural demands. The reason to look at this region first is to test a catchment with a more or less vivid water market. The purpose of this research is to investigate the influence of water rights on water management practices under the present situation as well as changing situations. Here changing situation refer on one hand to improvement and extension of infrastructure, on the other hand to different use of the water in magnitude and further time and space. The latter one mainly based on the water market. The main objective of this study is to investigate if the proposed WRAP Modelling System (Water Rights Analysis Package) which is used in the whole state of Texas, is able to model the consequences of the allocation scheme in the present, as well changing situations, incorporating the Chilean legal framework, here especially the allocation according to water rights. The main changes are subject to i. new legislation to incorporate in the allocation of water resources ii. further development, like new reservoirs in the upstream sub-catchments, iii. water right transfers as well as iv. different operation policies WRAP was chosen to investigate the impacts of the water management practices. It combines detailed information describing water resource development, management, allocation and use with natural river system hydrology represented by naturalized streamflows, assuming that the hydrological pattern of a catchment stays the same in the future (Wurbs, 2011). Beside the development of the spatial configuration of the system, which has been defined as a set of control points (CP) that represent pertinent sites in the river basin, geospatial data, time series data, census data, operational data sheets of the organisations as well as information and data about the water rights of each stakeholder have been statistically and spatially pre-processed in order to be able to estimate agricultural water demand, understand the legal system in general and of the basin under study in particulary. Further information of the Food and Agricultural Organisation (FAO), monitored data of the National Water Authority (DGA), elaborated data of the National Centre of Natural Resources (CIREN) and historical and actual regional as well as local studies were consulted to elaborate all the needed information to model the system. With this information and preprocessed data the WRAP modelling system was implemented, to quantify the impacts of decision making and its consequences on the whole system. Model results include water supply reliabilities (including reliability indices) as well as flow and storage frequency statistics developed from the simulation results representing long-term probabilities or percent-of-time estimates. Furthermore shortage metrics have been developed by the model and evaluated for each scenario. The model includes the following frequency statistics for concisely summarizing modelling results: (a) volume and period reliability tables for water supply diversion, (b) frequency tables for naturalized, regulated and unappropriated flows, reservoir storage volumes, as well as instream flow shortages and (c) reservoir storage-reliability tables. After all the different scenario simulations and analysis of the results it can be stated that the WRAP modelling system is applicable for the questions under study based on the legal Chilean water management framework. Flexibility is provided for adaption of a broad range of modelling approaches. A huge variety of management records can be combined in many different ways to be able to model any application. Ingenuity is required from the modeller to achieve the incorporation of sometimes quite complex allocation rules, apply different target options, demands, administrate a variety of users and include new developments within a multiple and multipurpose reservoir-river management system. Although some simplification of the independent sub-catchments was necessary, the achieved results show that the consequences of allocation decisions, including water transfer and future development are simulated in a satisfactory manner and can therefore be much better understood. The model system is adequate to serve as a basis for decision making within the chilean legal framework.Item Open Access Stochastic model comparison and refinement strategies for gas migration in the subsurface(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2023) Banerjee, Ishani; Nowak, Wolfgang (Prof. Dr.-Ing.)Gas migration in the subsurface, a multiphase flow in a porous-medium system, is a problem of environmental concern and is also relevant for subsurface gas storage in the context of the energy transition. It is essential to know and understand the flow paths of these gases in the subsurface for efficient monitoring, remediation or storage operations. On the one hand, laboratory gas-injection experiments help gain insights into the involved processes of these systems. On the other hand, numerical models help test the mechanisms observed and inferred from the experiments and then make useful predictions for real-world engineering applications. Both continuum and stochastic modelling techniques are used to simulate multiphase flow in porous media. In this thesis, I use a stochastic discrete growth model: the macroscopic Invasion Percolation (IP) model. IP models have the advantages of simplicity and computational inexpensiveness over complex continuum models. Local pore-scale changes dominantly affect the flow processes of gas flow in water-saturated porous media. IP models are especially favourable for these multi-scale systems because using continuum models to simulate them can be extremely computationally difficult. Despite offering a computationally inexpensive way to simulate multiphase flow in porous media, only very few studies have compared their IP model results to actual laboratory experimental image data. One reason might be the fact that IP models lack a notion of experimental time but only have an integer counter for simulation steps that imply a time order. The few existing experiments-to-model comparison studies have used perceptual similarity or spatial moments as comparison measures. On the one hand, perceptual comparison between the model and experimental images is tedious and non-objective. On the other hand, comparing spatial moments of the model and experimental images can lead to misleading results because of the loss of information from the data. In this thesis, an objective and quantitative comparison method is developed and tested that overcomes the limitations of these traditional approaches. The first step involves volume-based time-matching between real-time experimental data and IP-model outputs. This is followed by using the (Diffused) Jaccard coefficient to evaluate the quality of the fit. The fit between the images from the models and experiments can be checked across various scales by varying the extent of blurring in the images. Numerical model predictions for sparsely known systems (like the gas flow systems) suffer from high conceptual uncertainties. In literature, numerous versions of IP models, differing in their underlying hypotheses, have been used for simulating gas flow in porous media. Besides, the gas-injection experiments belong to continuous, transitional, or discontinuous gas flow regimes, depending on the gas flow rate and the porous medium's nature. Literature suggests that IP models are well suited for the discontinuous gas flow regime; other flow regimes have not been explored. Using the abovementioned method, in this thesis, four macroscopic IP model versions are compared against data from nine gas-injection experiments in transitional and continuous gas flow regimes. This model inter-comparison helps assess the potential of these models in these unexplored regimes and identify the sources of model conceptual uncertainties. Alternatively, with a focus on parameter uncertainty, Bayesian Model Selection is a standard statistical procedure for systematically and objectively comparing different model hypotheses by computing the Bayesian Model Evidence (BME) against test data. BME is the likelihood of a model producing the observed data, given the prior distribution of its parameters. Computing BME can be challenging: exact analytical solutions require strong assumptions; mathematical approximations (information criteria) are often strongly biased; assumption-free numerical methods (like Monte Carlo) are computationally impossible for large data sets. In this thesis, a BME-computation method is developed to use BME as a ranking criterion for such infeasible scenarios: The \emph{Method of Forced Probabilities} for extensive data sets and Markov-Chain models. In this method, the direction of evaluation is swapped: instead of comparing thousands of model runs on random model realizations with the observed data, the model is forced to reproduce the data in each time step, and the individual probabilities of the model following these exact transitions are recorded. This is a fast, accurate and exact method for calculating BME for IP models which exhibit the Markov chain property and for complete "atomic" data. The analysis results obtained using the methods and tools developed in this thesis help identify the strengths and weaknesses of the investigated IP model concepts. This further aids model development and refinement efforts for predicting gas migration in the subsurface. Also, the gained insights foster improved experimental methods. These tools and methods are not limited to gas flow systems in porous media but can be extended to any system involving raster outputs.Item Open Access Coupled free-flow-porous media flow processes including drop formation(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2023) Veyskarami, Maziar; Helmig, Rainer (Prof. Dr.-Ing.)Behavior of a coupled free-flow-porous medium system is determined by the interface between the two domains. Formation of droplets at the interface governs transport processes in the whole system by enormously affecting the exchange of mass, momentum, and energy between the free flow and the porous medium. A droplet that forms at the interface might grow or shrink due to the flow from the porous medium and evaporation from its surface into the free flow. It also might be detached from the interface by the free flow. An example of such phenomena in nature is formation of sweat droplets on the skin by perspiration and the resulted cooling effect through their evaporation into the surrounding air. Water management in fuel cells, cooling systems, and inkjet printing are just a few technical applications in which droplet formation at the interface between a free flow and a porous medium appears. In this work, we developed a novel model to describe the formation, growth and detachment as well as evaporation of droplets at the interface between a coupled free-flow-porous medium system. Pore-network modeling is used as a tool to capture pore-scale phenomena occurring in porous media. New coupling concepts between the free flow and the porous medium are developed, which include storing mass, momentum and energy in the droplet. The formation and growth of a droplet is described and a new approach is developed to include the impact of the growing droplet on the free-flow field. Description of the forces acting in the system is given and accordingly the droplet detachment is predicted. A clear description of the droplet evaporation is provided and the impact of free-flow and porous medium properties on the droplet evaporation have been analyzed.Item Open Access Optimal planning of hydropower and energy storage technologies for fully renewable power systems(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2019) Haas, JannikGreenhouse gas emissions need to stop shortly after mid-century to meet the Paris Agreement of keeping global warming well below 2°C. Fully renewable energy systems arise as a clear solution. To cope with their highly fluctuating power output (wind and solar photovoltaic), power systems need to become more flexible than they are today. Energy storage is one source of flexibility and is widely esteemed as a key-enabler for the energy transition. Hydropower often has storage, and can also help in this task. To assess how much energy storage is needed, expansion planning tools are commonly used. In general terms, they aim to minimize system-wide investment and operational costs, while meeting a set of techno-economic constraints. In the task of quantifying the need for energy storage, the present thesis makes four contributions, related to the overarching research question: how to plan the optimal energy storage mix for fully renewable power systems with important shares of hydropower? These contributions aim to assist the energy transition and to be relevant for energy system modelers, energy policy makers, and decision makers from ecohydrology, storage companies, and the renewable industry. - First contribution: The last couple of years have seen a particularly strong enrichment of such expansion tools. In response, the first contribution of this thesis is to provide a comprehensive review of the existing models, including a clear classification of the approaches and derivation of the current modeling trends. This review culminates by identifying the following open challenges for storage planning. First, the many available storage devices are quite diverse in their technical and economic parameters (including efficiency and lifetime), and this must be considered in the models. The tools also need to count with a high resolution of space and time to adequately capture the challenges of integrating renewable generation. Second, the many services that storage technologies can provide (beyond energy balancing, such as power reserves) need to be acknowledged. And third, the different energy sectors (electricity, heat, transport) all have sources of flexibility; thus, planning has to become multi-sectoral. - Second contribution: Many storage expansion studies have been produced within the last 5 years, but these resulted in a very broad range of storage requirements. To shed light on their recommendations, the second contribution systemizes over 400 scenarios of these studies for the U.S., Europe, and Germany. This exercise revealed that, as the share of renewable generation grows, the power capacity (e.g. GW, in pumped hydro, related to the number of turbines) and energy capacity (e.g. GWh, in pumped hydro, related to the water held by its reservoir) of storage systems increase linearly and exponentially, respectively. As grids become highly renewable, especially when based on solar photovoltaic, the need for storage peaks. The power capacity is around 40-75% of the peak demand, and the energy capacity 10% of the annual demand. A final finding of this analysis is that assumptions on electrical grid modeling, grid expansion, and energy curtailment have strong impacts on the found storage sizes. - Third contribution: Developing a new optimization tool for storage expansion planning in the power sector is the third contribution: LEELO (Long-term Energy Expansion Linear Optimization). LEELO extends the available models by including further services in the planning approach: power reserves and energy autonomy. A further novelty of LEELO is a detailed representation of hydropower cascades, which is a convenient source of flexibility in many regions of the world. A case study about Chile for the year 2050 assesses the impact of including these multiple services in the planning stage on the final storage recommendations. Indeed, the found deviations in total power capacities and energy capacities of storage are large; up to 60% and 220%, respectively. Moreover, the resulting storage mix (i.e. the sizes of the individual storage technologies) is also strongly affected. Lastly, planning with such services revealed a 20% cost increase that would otherwise remain hidden to the planners. Overall, modeling multiple services in expansion planning is relevant when designing fully renewable systems, as controllable (dispatchable) generators disappear. - Fourth contribution: In the final contribution, two optimization-objectives are added to LEELO. The first one relates to reducing hydropeaking, a highly fluctuating operational scheme of hydropower reservoirs that threatens the downstream river ecology. The second objective minimizes new transmission lines, as they have numerous externalities that result in delays and social opposition. Multi-objective LEELO is able to find the Pareto Front of these three dimensions (costs, hydropeaking, new transmission). In a case study, again about Chile, the found trade-offs are assessed from the perspective of the involved stakeholders. It found that the minimum cost solution requires doubling the existing transmission infrastructure while operating at severe hydropeaking. Avoiding all transmission projects will cost between 3 and 11% (depending on the allowed level of hydropeaking). In other words, the upside of new transmission is rather limited. As transmission is avoided, the generation turns significantly more solar while investments in wind decrease. At the same time, and to support a solar grid, the requirements for storage technologies grow. Demand for storage also grows when hydropeaking is constrained, as a direct response to the missing flexibility from hydropower. Severe hydropeaking can be mitigated for as little as 1% of additional costs (if new transmission is installed), which is good news to environmental organizations. Completely avoiding both hydropeaking and new transmission lines is the most extreme scenario, costing an additional 11% and requiring about 20% more storage power capacity. In short, cheap storage and solar technologies emerge as key-enablers for reaching such attractive solutions that can avoid both externalities (transmission and hydropeaking). A clear investment strategy for these technologies is needed and, if done right, can make the generation more sustainable and socially acceptable. When comparing the storage requirements for Chile to those for Europe and the U.S., it becomes clear that the storage power capacities needed for Chile are on the higher end (>70% of peak demand). This is related to the fact that Chile’s power system is about 20 times smaller and has highly correlated energy resources. The needed energy capacities are also on the higher end (9-13% of annual demand). Here, however, the existing hydropower park already provides a buffer of 6%, making the remaining demand much lower (3-7%). If new transmission projects are to be avoided, the need for storage increases very strongly in terms of power capacity (adding 5 to 30 percentage points) and only slightly in terms of energy capacity (adding 1 percentage point). Mitigating hydropeaking also increases the need for power capacity but without exceeding the range above. The strongest storage requirements arise from the multi-service simulations; in particular for meeting high levels of energy autonomy, the (storage) energy capacity needs to be doubled. Relating back to the main question on how to plan the mix of energy storage systems, it became evident that multi-service, multi-sector, and multi-objective approaches are needed. This thesis took a first step in that direction. Two detailed extensions (multi-service, multi-objective) for storage planning determined a higher need for these technologies in a case study on Chile, where the future for storage looks promising. In general, the performed case study provides the first 100% renewable scenarios for Chile. Altogether, the gained insights showed to be relevant for stakeholders from the energy and environmental sectors on the path to a zero-carbon energy supply.