1,721,006 research outputs found
Data set from Gorla R, De Marco F, Morganti S, Finotello A, Brambilla N, Testa L, Agnifili ML, Tusa M, Auricchio F, Bedogni F. Transcatheter aortic valve implantation with the Portico and Evolut R bioprostheses in patients with elliptic aortic annulus. EuroIntervention. 2020 Apr 3;15(18):e1588-e1591. doi: 10.4244/EIJ-D-19-00115. PMID: 31186219.
No full textData set from Gorla R, De Marco F, Morganti S, Finotello A, Brambilla N, Testa L, Agnifili ML, Tusa M, Auricchio F, Bedogni F. Transcatheter aortic valve implantation with the Portico and Evolut R bioprostheses in patients with elliptic aortic annulus. EuroIntervention. 2020 Apr 3;15(18):e1588-e1591. doi: 10.4244/EIJ-D-19-00115. PMID: 31186219
Reading tidal processes where their signature is cryptic: The Maastrichtian meandering channel deposits of the Tremp Formation (Southern Pyrenees, Spain)
No full textTidal currents can propagate tens of kilometres landward from the shoreline, forming dense networks of meandering channels, which drain vegetated areas and range in width from tens to hundreds of metres. Sedimentary products of these inland tidal channels are poorly documented in the stratigraphic record, as most studies on tidal processes occurring in inland areas are focused on fluvio-tidal interaction. The present study contributes to filling this gap, investigating Late Maastrichtian meandering-channel deposits of the Tremp-Graus Basin (Southern Pyrenees, Spain). These deposits accumulated in a growth syncline, which allowed the development of a 20 to 30 km wide, 80 to 100 km long, tidal embayment. Sporadic occurrence of poorly-developed rhythmites and bidirectional currents confirms the occurrence of tidal processes, whereas their local dominance is inferred from several pieces of evidence, including: (i) disproportion between depth of the larger channels and related catchment area; (ii) landward-accretion of point-bar bodies; (iii) landward fining of point-bar bodies, and (iv) reconstruction of palaeo-flow patterns at the meander bend scale. This work shows that three-dimensional architectural modelling and reconstruction of bar planform transformation styles can provide a critical contribution to the understanding of tidal control on sedimentation in inland areas
Planform-asymmetry and backwater effects on river-cutoff kinematics and clustering
No full textRiver bends occasionally meander to the point of cutoff, whereby a river shortcuts itself and isolates a portion of its course. This fundamental process fingerprints a river's long-term planform geometry, its stratigraphic record, and biogeochemical fluxes in the floodplain. Although meander cutoffs are common in fast-migrating channels, timelapse imagery of the Earth surface typically does not offer a long enough baseline for statistically robust analyses of these processes. We seek to bridge this gap by quantifying cutoff kinematics along the Humboldt River (Nevada) – a stream that, from 1994 to 2019, hosted an exceptionally high number of cutoffs (specifically, 174 of the chute type and 53 of the neck type). A coincidence between major floods and cutoff incidence is first suggestive of hydrographic modulation. Moreover, not just higher sinuosity but also upstream planform skewness is associated with higher cutoff incidence and channel widening for a sub-population of chute cutoffs. We propose a conceptual model to explain our results in terms of channel-flow structure and then examine the distances between adjacent cutoffs to understand the mechanisms governing their clustering. We find that both local and nonlocal perturbations together trigger the clustering of new cutoffs, over distances capped by the backwater length and over yearly to decadal timescales. Our research suggests that planform geometry and backwater controls might sway the occurrence of cutoff clusters – both local and nonlocal – thereby offering new testable hypotheses to explore the evolution of meandering-river landscapes that have significant implications for river engineering and stratigraphic modelling. © 2020 John Wiley & Sons, Ltd
Remotely-sensed planform morphologies reveal fluvial and tidal nature of meandering channels
Full text linkMeandering channels extensively dissect fluvial and tidal landscapes, critically controlling their morphodynamic evolution and sedimentary architecture. In spite of an apparently striking dissimilarity of the governing processes, planform dimensions of tidal and fluvial meanders consistently scale to local channel width, and previous studies were unable to identify quantitative planimetric differences between these landforms. Here we use satellite imagery, measurements of meandering patterns, and different statistical analyses applied to about 10,000 tidal and fluvial meanders worldwide to objectively disclose fingerprints of the different physical processes they are shaped by. We find that fluvial and tidal meanders can be distinguished on the exclusive basis of their remotely-sensed planforms. Moreover, we show that tidal meanders are less morphologically complex and display more spatially homogeneous characteristics compared to fluvial meanders. Based on existing theoretical, numerical, and field studies, we suggest that our empirical observations can be explained by the more regular processes carving tidal meanders, as well as by the higher lithological homogeneity of the substrates they typically cut through. Allowing one to effectively infer processes from landforms, a fundamental inverse problem in geomorphology, our results have relevant implications for the conservation and restoration of tidal environments, as well as from planetary exploration perspectives
Tidal Flow Asymmetry and Discharge of Lateral Tributaries Drive the Evolution of a Microtidal Meander in the Venice Lagoon (Italy)
No full textTidal landscapes are extensively characterized by the presence of meandering channels, the latter being important for the ecomorphodynamic evolution of these environments. It remains unclear whether changes in the relative strength of maximum flood and ebb currents (i.e., tidal flow asymmetries), together with the widespread presence of lateral tributaries, cause tidal meanders to evolve differently from their fluvial relatives. Here, we investigate the evolution of a meandering channel in the Venice Lagoon (Italy) that receives water from two major tributaries along its outer bank. Using a 2-D numerical model, we first analyze the changes in local tidal flow asymmetries, both natural and anthropogenically induced, which occurred during the last 120 years. The effects of these modifications on the meander morphodynamics are then investigated by means of a 3-D numerical model, and results are compared to modern and historical field data spanning more than one century. We show that under asymmetric tidal flows, tidal meanders develop depositional patterns according to the dominant flow direction, similar to that of fluvial meanders. In addition, the morphological effects of the nondominant tidal flow become increasingly negligible as tidal flow asymmetry increases. We also show that enhanced sediment and water fluxes from major lateral tributaries, sourced from wind-wave exposed tidal flats, can critically influence the development of erosional and depositional patterns within tidal meanders otherwise sheltered from wind action by the presence of salt marshes
Suspended transport of gravel in rivers: Empirical evidence from the 2022 flood in the Misa River (Eastern Apennines, Italy)
Full text linkIn September 2022, an exceptional flood in the Misa River basin (Eastern Apennines, Italy) resulted in the unusual deposition of gravelly lobes on terraces up to 6 m higher than the riverbed. These deposits suggest that coarse bed sediments were transported in suspension rather than as bedload, as typically occurs under competent flow conditions. To verify this hypothesis, we combined field evidence-obtained from geomorphological and sedimentological surveys-with theoretical insights based on sediment transport theory. Our findings indicate that medium-sized gravels, which are part of the riverbed material, were transported in suspension within the water column. This phenomenon required specific conditions to generate the necessary shear stress and energy, including (i) a high-magnitude flood enriched with fine sediments, which increased the fluid density and viscosity, and (ii) an entrenched channel with stable banks that limited channel widening during the flood event. When these processes coincided with alluvial plain inundation by overbank flows, gravel transported in suspension was able to reach and settle on elevated surfaces, such as terraces far above the active channel. These observations highlight the potential for gravel-bed rivers to support the transport of coarse sediment in suspension under extreme flood conditions and specific geomorphological constraints on the active river channels. By demonstrating the role of sediment concentration, channel morphology and flood dynamics, our research provides new insights into sediment transport mechanisms and contributes to a broader understanding of the morphodynamic processes governing gravel-bed rivers under such exceptional conditions, with broad implications for refining flood hazard models and improving sediment transport predictions in fluvial systems
About this title - Meandering Streamflows: Patterns and Processes across Landscapes and Scales
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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