Numerical and laboratory investigation of the hydrodynamic complexity of a river confluence

The paper deals with the hydrodynamic investigation of the junction of two rivers in north-west Hungary in an urban area. The goal of the investigation was to study the flow conditions by means of a 3D k-ε turbulence CFD model and hydraulic scale model. The project gave the opportunity to compare the outcome of the distorted scale model with the ones of the CFD model in field scale, in the distorted hydraulic model scale as well as in undistorted scale, converting all the results to real field scale by assuming Froude similarity. Overall flow patterns, the effect of distortion and the robustness of the k-ε turbulence model in such complex confluence conditions were analysed. Satisfactory agreement was found except for the region straight downstream of the confluence where significant differences between laboratory and numerical results were seen due most probably to the complex swirling and shearing character of the flow. Large scale vortex formation interacting with anisotropic local turbulence would certainly need differential Reynolds stress turbulence closure

Flow Analysis in River Danube by Field Measurement and 3D CFD turbulence modelling

Spatial complexity of turbulent flow conditions has been investigated by means of ADCP measurements and CFD modelling in river Danube. The study area was a meandering river reach, characterized by shallows and strongly influenced by various river training works. High resolution bed survey and freezing plate sampling provided input river bed data for model implementation. The applied k-ε turbulence model could well reproduce velocity distributions measured in nature. Strong spatial variability of the velocity and turbulent kinetic energy fields demonstrated the necessity of 3D model approach under such fluvial conditions

NUMERICAL MODELLING OF FLOW PATTERNS TO ASSIST THE REVITALISATION OF SECONDARY RIVER BRANCHES IN GEIVIENC AREA

Depth-averaged numerical modelling of steady-state horizontal flow patterns carried out in the framework of the revitalisation project of the secondary branches in Gemenc Protected Landscape Area is presented. The feasibility of different variants is investigated in order to increase the water exchange in the secondary branches without creating unfavorable hydraulic and related sediment transport as well as navigation conditions. The applied mathematical model is based on the usual shallow water assumptions. The numerical solution is performed using finite differences and multigrid iteration technique. The model is able to reproduce recirculation zones and the horizontal velocity distribution in an acceptable manner

Determining clast and magnetic fabric of a subaqueous lahar deposit as a tool for reconstructing paleoflow directions and emplacement processes.

Flow-related fabric of a subaqueously emplaced laharic deposit (Rám Hill Pumiceous Sandstone) were investigated around the middle Miocene Keserűs Hill lava dome group (northern Hungary). A twofold methodology, consisting of image analyis on rock surfaces and low-field anisotropy of magnetic susceptibility (AMS), was used to determine large-scale flow paths and emplacement processes. In addition, comparative measurements of magnetic anisotropy were performed by using an MFK1-FA multifunction kappabridge with 3D rotator (Studynka et al. 2014) at Agico, Inc. (Brno, Czech Republic). The results indicate a very good agreement between the azimuths of a-axis of the most elongated clasts from image analysis and the orientation of K1 susceptibilities from the measurements of the two laboratories. This agreement of fabric direction obtained by the two different methods allows to draw the following implications: 1) Fabric direction-derived large-scale flow paths show a near-radial pattern around the proposed eruption centre (Karátson et al. 2007) of the Keserűs Hill lava dome group (Fig. 1). Thus, our new data on paleoflow directions quantitatively confirm the former, one central vent-dominated volcano-structural reconstruction which was proposed on the basis of facies analysis. 2) Aggradation from multiple lahar pulses is presumable due to the vertical variation of shear direction within the exposures

A kora-miocén Pétervásárai Homokkő diagenezis-története

Az eggenburgi korú, sekélytengeri környezetben képződött Pétervásárai Homokkő Formációt, mint ismert rezervoár kőzet felszíni analógját vizsgáltuk. A szemcseösszetétel, a diagenezistörténet és a porozitásfejlődés rekonstrukciójához terepi vizsgálatokat és petrográfiai megfigyeléseket végeztünk, melyeket geokémiai mérések egészítettek ki. A vizsgált, apró-durvaszemcsés, kőzettörmelékes homokkőben a komponensek mennyiségi aránya alapján négy litofácies külön - böztethető meg; ezek a porózus (LF1), mátrixgazdag (LF2), cementgazdag (LF3), és mátrix- és cementgazdag (LF4) homokkőtípusok. A diagenezis során, az eogenezis tartományában képződött autigén ásványok a glaukonit, a fram - boidális pirit, sziderit, káliföldpát továbbnövekedési cement, kaolinit és a feltételezhetően nagyon kis mennyiségű kalcit - cement. A legalább 80 °C-os hőmérsékletet elérve, a mezogenezis tartományában megjelent a kvarc tovább növekedési cement, kevert szerkezetű illit/szmektit és albit keletkezett. Így a fokozatosan betemetődött homokkőben a porozitás folyamatosan csökkent a kompakció és a megjelenő új ásványfázisok miatt. A legnagyobb mennyiségben megjelenő,egyik legkésőbbi autigén ásványfázis a kalcit. Ez főleg ásványhelyettesítésként, kisebb részben pedig cementként,elszigetelt lencsékben van jelen. A rendelkezésre álló geokémiai adatok alapján, figyelembe véve a terület földtani felépítését, a kalcit eredete több genetikai modellel is magyarázható. Ezek szerint képződhetett egyrészt a mezogenezis tartományában, az üledékkel betemetődött módosult tengeri eredetű pórusfluidumból, másrészt keletkezhetett törések mentén a kőzettestbe áramlott egzotikus fluidumból. Ez utóbbi esetben is két változat lehetséges, vagy egy magas hőmérsékletű formációs fluidumból vált ki, vagy egy mélyre cirkulált és felmelegedett meteorikus eredetű fluidumból. A homokkő jelentős porozitással rendelkezik, főleg a kalcitot nem tartalmazó részeken. Ez a porozitás a kiemelkedés során, a felszín közelében alakulhatott ki a beszivárgó meteorikus vizek oldó hatása révén. A feltárásban megjelenő különleges mállási formák kialakulásában a homokkő diagenezistörténetének jelentős szerepe volt. For this paper, the Eggenburgian Pétervására Sandstone — a shallow marine siliciclastic formation — was studied as a surface analogue for known reservoir rocks. Field observation in the area of Kishartyán, detailed petrography (including SEM, CL) and geochemical analysis (XRD, SEM-EDS, stable isotope analysis) were applied to find out more about the diagenetic processes, the burial history, the porosity evolution, and their relationship with the weathering forms. The composition of the fine to very coarse-grained sandstones varies between subarenite and litharenite. The most common detrital grains are mono- and polycrystalline quartz and sedimentary rock fragments (cherts, dolomites and metamorphic rock fragments). Ductile grains are represented by micas and altered volcanoclastic rock fragments. Based on the proportion of components, four lithofacies were distinguished: porous sandstone (LF1), matrix-rich sandstone (LF2),cement-rich sandstone (LF3), and matrix and cement rich sandstone (LF4). The eogenetic minerals are: glauconite,framboidal pyrite, flattened rhombohedral siderite crystals, K-feldspar overgrowth cement, kaolinite, and (supposedly)small amounts of calcite. The maximum burial temperature was likely reached at around 80 °C; this is indicated by the presence of quartz overgrowth cement, mixed layer illite/smectite, and replacive and cementing albite. These minerals were formed in the mesogenetic realm. During eogenesis and mesogenesis, the porosity of the sandstone progressively decreased due to compaction and the precipitation of authigenic minerals. Calcite is one of the latest diagenetic minerals and occurs both as a replacive phase and as cement. The distribution of calcite within the studied sandstone is heterogeneous. Calcite is present in elongated lenses where the sandstone has a very low porosity. Considering the geochemical data and the geological setting, the origin of the calcite can be explained by several genetic models. According to these models, the formation of the calcite may have taken place either in the mesogenetic realm from modified marine pore waters (buried together with the sediment), or from an exotic fluid channelled along fault zones. In the second scenario, there are two possibilities regarding the origin of the parent fluid: namely, (a) a formational fluid or (b) a deeply circulated, warmed-up meteoric fluid. The high porosity of the sandstone is the result of dissolution by meteoric water during uplift. Diagenetic evolution of the sandstone had a crucial role in the formation of the weathering morphology

A Dunántúli-középhegység felső kréta telérkalcitjainak genetikai vizsgálata = Genesis of late Cretaceous calcite dykes from the Transdanubium Central Range

A Dunántúli-középhegységben számos helyen felfedezett vörös kalcit előfordulások genetikájának további tisztázásához járult hozzá a Vértesben található édesvizi mészkőkúp és hat további kalcit kibukkanás kőzettani és geokémiai vizsgálata. A karbonát tipusos travertinó szövettel rendelkezik, jellemző akcesszóriái: cirkon, monacit és xenotim, amelyek mélységi fluidumokhoz köthetők. A minták szén- és oxigénizotóp értékei, valamint az izotóp-tartománya arra utal, hogy magmás eredetű CO2-nak fontos szerepe volt a karbonát keletkezésében. A további vörös kalcit telérek és karbonát előfordulások (Pilisjászfalu, Keselő-hegy, Mindszentpuszta, Csáki-vár és Nagykovácsi) szöveti jellege hasonló. Járulékos ásványaik: Fe-oxid, Fe-szulfid, szfalerit, rutil, ilmenit, cirkon, apatit, monacit, xenotim és csillám. A stabilizotóp-geokémiai adatok összhangban vannak a korábban vizsgált minták adataival. A folyadékzárványok kis szalinitásúak (max. 3.4 wt% NaCl ekv.) és a homogenizációs hőmérsékletük kicsi (100-180 ºC). Előzetes irodalmi adatok, valamint kőzettani és geokémiai vizsgálataink (SEM+EDX, stabilizotóp-geokémia, mikrotermometria) alapján a vizsgált karbonát előfordulások hidrotermás rendszerekhez köthetők, amelyek az esetek többségében kapcsolatba hozhatók a terület lamprofíros magmatizmusával. | Petrographic and geochemical studies of a travertine cone and six calcite vein occurrences (in Vértes Mts.) were carried out to understand formation of the widely spread red calcite occurrences. The carbonate investigated has a typical travertine texture, the characteristic accessory minerals: zircon, monacite, and xenotime can be related to deep-derived fluids. Their stable carbon and oxygen isotope compositions and the isotopic ranges indicate that magmatic CO2 played an important role during the carbonate formation. The other red calcite veins and carbonate occurrences studied (Pilisjászfalu, Keselő-hegy, Mindszentpuszta, Vitányvár, Csáki-vár, Nagykovácsi) show similar textural features. Accessory minerals are: Fe-oxide, Fe- sulfide, sphalerite, rutile, ilmenite, zircon, apatite, monazite, xenotime and mica. Their stable isotopic compositions are in agreement with the previously studied calcite dykes. The fluid inclusions have low salinity (max. 3.4 wt% NaCl eq.) and low homogenization temperature (between 100-180 ºC). Based on previous and our petrography and geochemical measurements (SEM+EDX, stable isotope studies and microthermometry), the studied carbonate occurrences were originated from a hydrothermal system and in most of cases magmatic fluids, may be associated with lamprophyre dykes, were also recognized in the area