In situ measurements of fine sediment infiltration (FSI) in gravel-bed rivers with a hydropeaking flow regime

The overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel-bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so-called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze-core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de-clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

The role of sediments in the phosphorus cycle in Lake Lugano. II. Seasonal and spatial variability of microbiological processes at the sediment-water interface

P, Fe, Mn, and S species were analyzed in water samples from the sediment-water interface collected at four seasonally different times during the course of a year at two sampling sites in the southern basin of Lake Lugano (Lago di Lugano). The results reveal the strong influence of the biogeochemical processes in the sediment on the chemical composition of the lake water above. Consumption of oxygen and nitrate under oxic to microoxic conditions in the water column as well as sequential release of reduced manganese and iron under anoxic conditions was observed as a direct or indirect consequence of microbially mediated degradation of organic matter. The seasonal pattern observed for the release and the retainment of dissolved reduced iron and manganese correlates well with the one for dissolved phosphate. Iron, manganese and phosphorus cycling are coupled tightly in these sediments. Both sediment types act as sinks for hydrogen sulfide and sulfate. An inner-sedimentary sulfur cycle is proposed to couple iron, manganese and phosphorus cycling with the degradation of organic matter. Nutrient cycling at the sediment-water interface might thus be driven by a microbially regulated electron pumping mechanism. The results contribute to a better understanding of the role of sediment processes in the lake's internal phosphorus cycle and its seasonal dynamics.     

Strengthening of moment‐resisting frame structures against near‐fault ground motion effects

Near‐fault ground motions with forward directivity are characterized by a large pulse. This pulse‐like motion may cause a highly non‐uniform distribution of story ductility demands for code‐compliant frame structures, with maximum demands that may considerably exceed the level of code expectations. Strengthening techniques for multi‐story frame structures are explored with the objective of reducing maximum drift demands. One option is to modify the code‐based SRSS distribution of story shear strength over the height by strengthening of the lower stories of the frame. The modified distribution reduces the maximum story ductility demand, particularly for weak and flexible structures. However, this strengthening technique is less effective for stiff structures, and is almost ineffective in cases in which the maximum demand occurs in the upper stories, i.e. strong and flexible structures. As an alternative, the benefits of strengthening frames with elastic and inelastic walls are evaluated. The effects of adding walls that are either fixed or hinged at the base are investigated. It is demonstrated that strengthening with hinged walls is very effective in reducing drift demands for structures with a wide range of periods and at various performance levels. Wall inelastic behavior only slightly reduces the benefits of strengthening with hinged walls.Copyright © 2004 John Wiley & Sons, Ltd.     

GRAVEL SLUICING IN ALPINE RUN-OF-RIVER HYDROPOWER PLANTS

1 INTRODUCTIONNdsral rivers entering reservoirs carry also sediment, partly as bedload and patly in suspension. At theentrance of the reservoir flow velocity is considerably reduced and the capability of sediment transport isdrashcally fading. Bedload maerial is deposited totally at the reservoir entrance fondng a delta, material...in suspension is cAned further intO the reservoir ulh.. it is partly deposited and partly dischargedthrough the dam towards downstreaxn (depending on the trapp…     

Heterotype Mischbarkeit zwischen Wolframit- und Rutilgruppe

Zusammenfassung Untersucht wurden die heterotypen Mischsysteme zwischen Wolframit- und Rutilgruppe FeNbO₄-TiO₂, FeNbO₄-FeTaO₄, FeWO₄- FeTaO₄ und FeWO₄-TiO₂. Aus der Stereometrie der Gitter läßt sich abschätzen, daß ein statistischer Übergang beider Gittertypen nicht wahrscheinlich ist.Im System FeWO₄-FeTaO₄ verkleinert sich die Mischungslücke mit sinkender Temperatur und verschwindet nach unten am FeTaO₄-Rand. Infolge des gleichsinnig geneigten Verlaufes beider Phasengrenzen ist die Temperatur der Umwandlung Rutil-Wolframitgitter für FeTaO₄ nicht extrapolierbar, die wahrscheinlich noch unter 570° C liegt.In den Systemen FeNbO₄- TiO₂ und FeNbO₄-FeTaO₄ hat die Mischungslücke ebenfalls gleichsinnig geneigte Begrenzungen. Die Mischungslücke verschwindet in diesen Systemen mit steigender Temperatur schon vor dem Systemrand. Es koexistieren dann in 1. Ordnung zwei heterotype Mischkristalle gleicher Zusammensetzung, aber verschiedenen Molvolumens. Der experimentell gefundene Diagrammtyp wird diskutiert.Aus Extrapolationen von Gitterkonstanten und Volumen von Mischkristallreihen gegen die Systemränder lassen sich diese Daten für die Rutilmodifikation von FeNbO₄ und die Wolframitmodifikation von FeTaO₄ finden, die beide in den experimentell untersuchten Zustandsbereichen instabil gegen die Wolframitmodifikation von FeNbO₄ bzw. die Rutilmodifikation von FeTaO₄ sind.Die Gehalte von Fe₂O₃ + Nb₂O₅ in Rutil (Ilmenorutil) sind Rutil-FeNbO₄-Mischkristalle.     

Die rezente hydrothermal-sedimentäre Lagerstätte Atlantis-II-Tief im Roten Meer

Zusammenfassung Die in Entstehung befindliche hydrothermal-sedimentäre Lagerstätte Atlantis-II-Tief im Roten Meer wurde in den Jahren 1969, 1971 und 1972 von den Forschungsschiffen Wando River und Valdivia aus genauer untersucht. Die Detailkartierung zeigt eine Fallenstruktur, die hauptsächlich durch NW-streichende Grabenrandverwerfungen hervorgerufen wurde. Die in die se Depression in ihren tiefsten Teil einströmenden metallhaltigen Solen hielten das für die Lagerstättenbildung, besonders das für die Sulfidausfällung nötige Milieu über längere Zeit aufrecht. Diese seit dem ausgehenden Pleistozän anhaltende stabile Situation wurde einige Male von Lava-Ausflüssen, tektonischen Ereignissen und Verlagerung der Quellen unterbrochen. Diese Vorgänge und die komplizierte Morphologie der solegefüllten Becken führten zu einer sehr komplexen Faziesentwicklung und stratigraphischen Abfolge. Insgesamt läßt sich, von den Quellen ausgehend, eine Zonierung von sulfidisch-silikatischer zu manganitischlimonitischer Ausfällung beobachten.

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The Atlantis II Deep, a hydrothermal-sedimentary metal depositin statu nascendi has been investigated in detail 1969, 1971 and 1972 with the research vessels Wando River and Valdivia. The new bathymetric map reveals a trap structure mainly caused by NW-striking faults, limiting local grabens. The metalliferous brines discharging into the deepest part of this depression maintained the conditions necessary for the formation of the deposit, esp. of the sulfides, for a long time.This stabil situation active since the end of the Pleistocene was several times disturbed by lava flows, tectonic events and displacement of the discharge vents.These events and the complicate morphologic structure of the brine-filled deep are responsible for a very complex development of lithologic facies and the stratigraphic sequence. There is a general deposit differentiation from sulfidic-silicatic precipitation near the discharge points and formation of limonite and manganite outside the brines.

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Résumé Pendant les années 1969, 1971 et 1972 les gisements hydrothermaux sédimentaires Atlantis II, en voie de formation dans la Mer Rouge, ont fait l'objet de campagnes scientifiques détaillées entreprises par les navires océanographiques Wando River et Valdivia.La carte morphologique montre une structure de descente qui a été formée principalement par des failles de direction NW délimitant des graben. Les saumures métallifères affluant dans la partie la plus profonde de cette dépression ont maintenu pendant une certaine durée le milieu nécessaire à la formation du gisement, et surtout à la précipitation des sulfures. Cette situation restée stable depuis la fin du Pléistocène a été interrompue plusieurs fois des émissions basaltiques, par des dislocations tectoniques et par le déplacement des sources. Ces événements, ainsi que la morphologie compliquée du bassin rempli de saumures, ont conduit à un développement très complexe des faciès lithologiques et de la séquence stratigraphique. Dans l'ensemble on peut constater une zonation des faciès avec précipitations sulfurosilicatées près des points d'entrée des saumures et manganolimonitiques plus à l'écart.

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