Large-scale morphodynamic modelling of the Gironde estuary, France

2013 ◽  
Vol 166 (2) ◽  
pp. 51-62 ◽  
Author(s):  
Nicolas Huybrechts ◽  
Catherine Villaret
Keyword(s):  
Large Scale ◽  
Gironde Estuary ◽  
Morphodynamic Modelling

Modeling the influence of the gravitational circulation on estuarine sand dunes

2020 ◽  
Author(s):  
Wessel M. van der Sande ◽  
Pieter C. Roos ◽  
Suzanne J.M.H. Hulscher
Keyword(s):  
River Discharge ◽  
Large Scale ◽  
Salinity Gradient ◽  
Sand Dunes ◽  
Water Model ◽  
Geophysical Research ◽  
Gironde Estuary ◽  
Gravitational Circulation ◽  
Marine Sand ◽  
Estuarine Salinity

<p>Estuaries are hydrodynamically complex regions where a river meets saline water. In many estuaries, sand dunes can be found; these are large-scale rhythmic bedforms. Observational studies have revealed several estuarine processes that affect sand dune dimensions and dynamics. These are for instance sand-mud interactions and tidal amplification. Here, we build upon an observational study in the Gironde Estuary, France, which indicated that the gravitational circulation – present in many estuaries due to the interaction between (heavy) seawater and (light) freshwater – is significant enough to affect sand dunes (Berne et al., 1993). Our aim is to understand the effect of this circulation on bedform dimensions and dynamics, and to explain the underlying mechanisms.</p><p>To this end, we develop an idealized process-based model which contains descriptions for the motion of water and non-cohesive sediment transport within a local section of a generic estuary. On this geometry, we impose a steady river discharge, superimposed on an oscillatory tidal flow. Furthermore, we include the effect of salinity-induced density differences by following the model as presented by MacCready (2004). In here, we adopt a diagnostic approach, meaning that the along-estuarine salinity gradient is imposed on the domain instead of being an unknown which interacts with the flow. The alternative, a so-called prognostic approach, is also explored.</p><p>This model is analyzed using a so-called linear stability analysis, as applied earlier to e.g. marine sand waves (Hulscher, 1996) but not yet to estuarine dunes. Within this analysis, the reference state with a flat bed is slightly perturbed, and the model shows whether these perturbations decay (the flat bed is stable) or grow (it is unstable). The model results provide a generic insight into the role of the gravitational circulation on bedform dimensions and dynamics, particularly growth and migration; the latter possibly directed opposite to the river discharge. To test our model, it is then applied to the specific settings of the Gironde. Furthermore, a systematic sensitivity analysis shows the effect of environmental parameters on bedform development when subject to the gravitational circulation. Including this estuarine-specific process is a novel and first step in obtaining a solid understanding of the behavior of estuarine sand dunes.</p><p> </p><p><strong>References</strong></p><p>Berne, S., Castaing, P., le Drezen, E., & Lericolais, G. (1993). Morphology, Internal Structure, and Reversal of Asymmetry of Large Subtidal Dunes in the Entrance to Gironde Estuary (France). Journal of Sedimentary Petrology, 63(5), 780–793. https://doi.org/10.1306/d4267c03-2b26-11d7-8648000102c1865d</p><p>Hulscher, S. J. M. H. (1996). Tidal-induced large-scale regular bed form patterns in a three-dimensional shallow water model. Journal of Geophysical Research, 101(C9), 727–744. https://doi.org/10.1029/96JC01662</p><p>MacCready, P. (2004). Toward a unified theory of tidally-averaged estuarine salinity structure. Estuaries, 27(4), 561–570. https://doi.org/10.1007/BF02907644</p><p> </p>

scholarly journals Morphodynamic modelling for the entire German Bight: an initial study on model sensitivity and uncertainty

2014 ◽  
Vol 39 ◽  
pp. 61-68 ◽  
Author(s):  
A. Plüß ◽  
F. Kösters
Keyword(s):  
Sediment Transport ◽  
German Bight ◽  
Large Scale ◽  
Morphological Changes ◽  
Initial Study ◽  
Model Sensitivity ◽  
Morphodynamic Modelling ◽  
Transport Patterns

Abstract. Morphodynamic modelling of coastal seas and estuaries for large-scale and long-term applications is strongly affected by parameter sensitivity of process-based models. Moreover, the comparison of data-based methods with numerical model results is limited by uncertainties in measurements. These drawbacks can be partly overcome by a multi-model approach (MMA). In a case study to assess long-term sediment transport and morphodynamic processes for the German Bight, the AufMod research project applies two different methods for process-based modelling: UnTRIM-SediMorph and DELFT3D. Model sensitivity is illustrated in terms of different morphological changes for diverse porosity values. As a first step, discrepancies between individual methods are shown based on resulting sediment transport patterns.

The influence of the gravitational circulation on estuarine sand dune migration: an idealized modelling approach

2021 ◽  
Author(s):  
Wessel M. van der Sande ◽  
Pieter C. Roos ◽  
Theo Gerkema ◽  
Suzanne J. M. H. Hulscher
Keyword(s):  
Large Scale ◽  
River Flow ◽  
Salinity Gradient ◽  
Sand Dunes ◽  
Upstream Migration ◽  
Residual Flow ◽  
High Discharge ◽  
Gironde Estuary ◽  
Gravitational Circulation ◽  
Modelling Approach

<p>Estuarine sand dunes are – similar to river dunes and marine sand waves – large-scale rhythmic bed patterns. Their characteristics differ from their riverine and marine counterparts, owing to the complex and dynamic estuarine environment. Using an idealized process-based modelling approach, we investigate the effect of the gravitational circulation on estuarine sand dunes.</p><p>The gravitational circulation is a residual current typical to estuaries, as it results from a longitudinal salinity gradient. It constitutes a tide-averaged residual flow with an upstream-directed (landward) component at the bed and a downstream-directed (seaward) component at the water surface (Geyer & MacCready, 2014). Sediment transport primarily depends on the bed shear stress (and thus on the flow near the bed), and therefore this residual flow may well be responsible for upstream migration of these bedforms. Observations of sand dunes in the Gironde estuary, France, suggest that this may indeed be relevant to the migration direction of estuarine sand dunes (Berné et al., 1993).  </p><p>We incorporated the hydrodynamic features of the gravitational circulation in a morphodynamic model, which is similar to the one of Hulscher (1996). We then perform a so-called linear stability analysis, which shows that bedforms develop as free instabilities of the flat bed.</p><p>Results show that a longitudinal salinity gradient may cause upstream migration, provided that the river flow velocity is sufficiently small. During high discharge in the Gironde estuary, the salinity front is pushed outward (van Maanen & Sottolichio, 2018), thus increasing the salinity gradient at the position in the Gironde where the sand wave field is situated. Including this in the model shows that the strengthened gravitational circulation can overpower the increased river flow velocities during high discharge, and thus confirms the observation by Berné et al. (1993). We note that this mechanism is probably limited to estuaries which share similar characteristics as the Gironde estuary, i.e. symmetric tide, well-mixed, little wind and wave influence, and a small residual river flow velocity due to a significant increase in cross-sectional area. Future research will elaborate on the effects of (tidally varying) stratification through implementation of a time- and space dependent eddy viscosity.</p><p><strong>References</strong></p><p>Berné, S., Castaing, P., le Drezen, E., & Lericolais, G. (1993). Morphology, Internal Structure, and Reversal of Asymmetry of Large Subtidal Dunes in the Entrance to Gironde Estuary (France). Journal of Sedimentary Petrology, 63(5), 780–793. https://doi.org/10.1306/d4267c03-2b26-11d7-8648000102c1865d</p><p>Geyer, W. R., & MacCready, P. (2014). The Estuarine Circulation. Annual Review of Fluid Mechanics, 46, 175–197. https://doi.org/10.1146/annurev-fluid-010313-141302</p><p>Hulscher, S. J. M. H. (1996). Tidal-induced large-scale regular bed form patterns in a three-dimensional shallow water model. Journal of Geophysical Research, 101(C9), 727–744. https://doi.org/10.1029/96JC01662</p><p>van Maanen, B., & Sottolichio, A. (2018). Hydro- and sediment dynamics in the Gironde estuary (France): Sensitivity to seasonal variations in river inflow and sea level rise. Continental Shelf Research, 165(May), 37–50. https://doi.org/10.1016/j.csr.2018.06.001</p>

Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

1999 ◽  
Vol 173 ◽  
pp. 243-248
Author(s):  
D. Kubáček ◽  
A. Galád ◽  
A. Pravda
Keyword(s):  
Image Processing ◽  
Large Scale ◽  
Harvard College ◽  
Oak Ridge ◽  
Large Scale Structures ◽  
Short Period Comet ◽  
Short Period ◽  
Scale Structures ◽  
Harvard College Observatory ◽  
Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

Some applications of electron beam microanalysis techniques in VLSI process evaluation

1983 ◽  
Vol 41 ◽  
pp. 160-161
Author(s):  
Simon Thomas
Keyword(s):  
Integrated Circuits ◽  
Process Evaluation ◽  
Large Scale ◽  
Technology Development ◽  
Analytical Techniques ◽  
Successful Implementation ◽  
Analysis Of Failures ◽  
Characterization Of Materials ◽  
Circuits Vlsi

Trends in the technology development of very large scale integrated circuits (VLSI) have been in the direction of higher density of components with smaller dimensions. The scaling down of device dimensions has been not only laterally but also in depth. Such efforts in miniaturization bring with them new developments in materials and processing. Successful implementation of these efforts is, to a large extent, dependent on the proper understanding of the material properties, process technologies and reliability issues, through adequate analytical studies. The analytical instrumentation technology has, fortunately, kept pace with the basic requirements of devices with lateral dimensions in the micron/ submicron range and depths of the order of nonometers. Often, newer analytical techniques have emerged or the more conventional techniques have been adapted to meet the more stringent requirements. As such, a variety of analytical techniques are available today to aid an analyst in the efforts of VLSI process evaluation. Generally such analytical efforts are divided into the characterization of materials, evaluation of processing steps and the analysis of failures.

Electron microscopy study of reactively sputter-deposited Ti/N films on silicon

1992 ◽  
Vol 50 (2) ◽  
pp. 1362-1363
Author(s):  
V. C. Kannan ◽  
A. K. Singh ◽  
R. B. Irwin ◽  
S. Chittipeddi ◽  
F. D. Nkansah ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Large Scale ◽  
Hexagonal Phase ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Process Conditions ◽  
Tin Films ◽  
Wide Range ◽  
Fcc Phase ◽  
Circuits Vlsi

Titanium nitride (TiN) films have historically been used as diffusion barrier between silicon and aluminum, as an adhesion layer for tungsten deposition and as an interconnect material etc. Recently, the role of TiN films as contact barriers in very large scale silicon integrated circuits (VLSI) has been extensively studied. TiN films have resistivities on the order of 20μ Ω-cm which is much lower than that of titanium (nearly 66μ Ω-cm). Deposited TiN films show resistivities which vary from 20 to 100μ Ω-cm depending upon the type of deposition and process conditions. TiNx is known to have a NaCl type crystal structure for a wide range of compositions. Change in color from metallic luster to gold reflects the stabilization of the TiNx (FCC) phase over the close packed Ti(N) hexagonal phase. It was found that TiN (1:1) ideal composition with the FCC (NaCl-type) structure gives the best electrical property.

Evolution of the microstructure of Cu(Ti)/SiO2 layers annealed in NH3

1995 ◽  
Vol 53 ◽  
pp. 452-453
Author(s):  
J. Liu ◽  
N. D. Theodore ◽  
D. Adams ◽  
S. Russell ◽  
T. L. Alford ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Titanium Nitride ◽  
Large Scale ◽  
Standard Procedure ◽  
Alloy Film ◽  
Electron Beam Evaporation ◽  
Copper Metallization ◽  
Nominal Composition ◽  
Ti Alloy ◽  
Thermally Grown

Copper-based metallization has recently attracted extensive research because of its potential application in ultra-large-scale integration (ULSI) of semiconductor devices. The feasibility of copper metallization is, however, limited due to its thermal stability issues. In order to utilize copper in metallization systems diffusion barriers such as titanium nitride and other refractory materials, have been employed to enhance the thermal stability of copper. Titanium nitride layers can be formed by annealing Cu(Ti) alloy film evaporated on thermally grown SiO2 substrates in an ammonia ambient. We report here the microstructural evolution of Cu(Ti)/SiO2 layers during annealing in NH3 flowing ambient.The Cu(Ti) films used in this experiment were prepared by electron beam evaporation onto thermally grown SiO2 substrates. The nominal composition of the Cu(Ti) alloy was Cu73Ti27. Thermal treatments were conducted in NH3 flowing ambient for 30 minutes at temperatures ranging from 450°C to 650°C. Cross-section TEM specimens were prepared by the standard procedure.

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