Universität Stuttgart
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Item Open Access Quantitative evaluation of clogging phenomena in river beds(1982) Geldner, Peter; Kobus, HelmutClogging phenomena in rivers are of extremely complex nature, and a development of a clogging layer depends on a large variety of influences. In this paper a quantitative approach for the evaluation of a defined hydrodynamic clogging parameter is presented. This approach is based on the inverse use of type curves representing characteristics of the interaction between surface water bodies and the aquifer. The method is applied to field data of discharge measured in seepage ditches at levee protected sites. Since conventional approaches are limited to the assumption of quasi-steady-state flow, a stochastic method for the evaluation of time-variable hydrographs is also outlined.Item Open Access On the modelling of artificial reoxygenation(1977) Markofsky, Mark; Kobus, HelmutThe results of laboratory studies on the efficiency of oxygen transfer from two dimensional bubble curtains produced by passing compressed air through a porous filter (mean diameter 180μ) and a perforated diffusor pipe (1 mm diameter ports) are presented. Comparisons with other laboratory and field data as well as with on approximate theory for oxygen transfer are made. Surface effects are found to play an important role in the present experiments tending to increase the overall apparent oxygen transfer efficiency.Item Open Access Relating hydraulics and ecological processes(1991) Hjorth, Peder; Kobus, Helmut; Nachtnebel, Hans Peter; Nottage, Albert; Robarts, RichardAny major modification of the hydraulic system results with some retardation in a response of the ecosystem trying to adapt to the new conditions. It is difficult to imagine situations where hydraulics and ecosystems are not related. Thus, harmonizing hydraulics with ecology means to identify alternative hydraulic measures which yield simultaneously economic benefits and improvement, preservation or at least a best fit of the environmental situation. Often, these objectives are subjected to an inherent conflict and therefore harmonizing is dependent on the preference structure of the modern society, which is inclined to sustainable development. The objective of this chapter is to develop a framework (methodology) which might assist in relating hydraulics and ecology with respect to specific goals under site and problem dependent constraints.Item Open Access Grundlagen der Grundwasserströmung(1975) Zipfel, Klaus; Kobus, HelmutDas vorliegende Kapitel soll einen kurzen Überblick über die hydraulischen Grundlagen geben, auf denen Grundwassermodelle aufgebaut sind. Dabei werden nur die wichtigsten Zusammenhänge aufgezeigt, die für das Verständnis der nachfolgenden Kapitel unbedingt erforderlich sind, und es wird im Hinblick auf den hier gesteckten Rahmen auf eine eingehende Darstellung verzichtet.Item Open Access Analysis of the flow induced by air-bubble systems(1968) Kobus, HelmutThe pattern of vertical velocities induced by an orifice discharging air into water can be represented by Gaussian distribution curves with a linear spread in the vertical except for the regions near the orifice and close to the free surface. An analytical treatment considering the momentum-flux increase due to the buoyancy of the air together with experimental information about the spread of the velocity profiles and the mean rising speed of the air bubble stream, which has been obtained from velocity and density measurements over a wide range of conditions, leads to a complete description of the flow field. The ratio of the water volume flux to the air discharge rate, which has been proposed as an efficiency criterion, is now at hand as a function of depth and air supply for both single orifices and rows. The experimental evidence supports the analysis well and suggests that extrapolation to larger water depths and air supplies should be permissible, which would allow approximate predictions of the volume flux for any air-bubble system.Item Open Access The sub-systems. 4 : Groundwater(1991) Herrmann, Reimer; Hubert, P.; Kobus, HelmutGroundwater constitutes the most important freshwater resource of the earth, it is two orders of magnitude larger than the total water volumes of rivers and lakes. It is a renewable resource, characterized by stability of its chemical composition and stability of temperature. Percolation of water through the subsurface has a good purification effect due to the combined action of filtration, sorption, chemical reactions and microbiological processes. Groundwater is utmost important as drinking water resource, since it is less prone to pollution than surface waters due to the protection effects of the covering layers. However, industrial and agricultural activities have led to groundwater pollution problems which are sometimes irreversible and in any case very difficult and expensive to recover. This endangers the long-term use for drinking water supply, and any efforts for sustainable development have to consider the vulnerability of groundwater resources to pollution, which shows great regional diversity, by suitable groundwater protection efforts.Item Open Access Air bubble screens as a tool for water quality control(1976) Kobus, HelmutThe flow field induced by the release of compressed air in a water body has been studied analytically and experimentally. The quantitative knowledge of the flow pattern in standing water and in a cross flow serves as a basis for the design of air bubble installations, which can be used advantageously for a number of purposes in water quality control, such as pneumatic oil barriers, barriers against density currents due to differences in salinity, silt or sediment concentration or temperature, installations for combating the formation of ice, artificial destratification devices or installations for oxygenation purposes.Item Open Access Staustufen am Oberrhein: Grundwassermodelle als Planungshilfe(1977) Kobus, HelmutDurch die Errichtung von Staustufen am Oberrhein wird die natürliche Geschiebeführung des Flusses unterbrochen. Während es im Bereich der stromauf gelegenen Staustufen zu Ablagerungen des mitgeführten Geschiebes kommt, tritt unterhalb der letzten Staustufe eine erhöhte Erosion der Rheinsohle ein. Im Bereich zwischen der im Bau befindlichen Rheinstaustufe lffezheim und dem Raum Karlsruhe wäre somit nach Inbetriebnahme dieser Staustufe ohne sonstige Maßnahmen durch die zu erwartende Erosion der Rheinsohle mit einem starken Absinken des Rheinwasserspiegels und einer Behinderung der Schiffahrt zu rechnen. Außerdem würden die Grundwasserstände im Hinterland erheblich absinken. Zur Verhinderung der Erosion werden verschiedene Maßnahmen, darunter der Bau einer weiteren Staustufe bei Neuburgweier, untersucht. Den Grundwasservorkommen in der Oberrheinebene kommt große Bedeutung für die Sicherstellung der heutigen und zukünftigen Wasserversorgung zu. Bei der Planung wasserbaulicher Maßnahmen müssen deshalb die Auswirkungen auf den Grundwasserhaushalt sorgfältig untersucht und berücksichtigt werden. Zur Erfassung der Bedeutung des Rheinaufstaus im Bereich lffezheim/Neuburgweier wurden deshalb umfangreiche hydrologische und hydrogeologische Untersuchungen angestellt und in einem numerischen Grundwassermodell zusammengefaßt.Item Open Access Erosion of a uniform sand bed by continuous and pulsating jets(1973) Westrich, Bernhard; Kobus, HelmutAn experimental investigation of erosion of a uniform sand bed by a vertical submerged jet shows that the momentum flux of the jet and the distance between nozzle and sediment determines the rate of scour. Under fully turbulent conditions, the relative dimensions of the scour hole depend only upon the time parameter and the ratio between the fictitious axial jet velocity at the bed and the fall velocity of the sediment particles. There exist two distinct values of this ratio, at which the eroding action of the jet becomes particularly effective. At the same mean volume flux, the erosion rate can be more than doubled by pulsations of the jet velocity. For the relative distance between nozzle and bed investigated, the continuous jet has the least erosion capacity as compared to pulsating jets.Item Open Access Risk assessment of well contamination using a regional stochastic modelling approach(1994) Franke, Hans-Jörg; Kobus, Helmut; Teutsch, GeorgThis paper presents a stochastic risk analysis approach for contamination of water supply wells in agriculturally dominated catchment areas, using a stochastic approach, where a numerical one-dimensional pesticide transport model has been coupled with a numerical three-dimensional groundwater flow- and transport model. The risk analysis is based on Monte-Carlo simulations with multiple realizations of the entire parameter set at a scale of individual agricultural fields. For the generation of the parameter set in the saturated zone the turning band method was used according to the lognormal pdf. Based on a set of soil and aquifer data from literature, the importance of different soil parameter distributions and different agricultural area sizes, were analysed with respect to the variability of the concentration breakthrough curves as observed at an assumed groundwater supply well. Using the coupled stochastic modelling approach the risk of exceeding a given concentration limit was investigated as a result of spatially variable soil and aquifer transport properties.