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  • 1
    Unknown
    Coastal and Shelf Sediment Transport (2007)
    London : The Geological Society
    Details
    Description / Table of Contents: For the geoscientist, interest in sediment dynamics relates to the understanding of modern processes, together with their extrapolation to the interpretation of ancient deposits within the stratigraphic record. Over the years, various measurement techniques and scientific approaches have been applied to the determination of sediment transport pathways and the derivation of erosion, transport and deposition rates. Recently, a number of new techniques and approaches have been developed, associated with different temporal and spatial scales, and it is appropriate and timely to review a representative selection, by reference to recently undertaken coastal and shelf investigations. The various contributions in the volume cover, for example: optical and acoustic backscatter measurements; particle tracking; the use of mutibeam imagery; grain-size trend analysis; and analytic, numerical and conceptual modelling. Although no single method provides a complete solution to the problem posed, this overview will assist sedimentologists and sediment dynamicists in their selection of the most appropriate approaches, towards the establishment of ‘high confidence’ in the interpretation of sediment transport rates and directions.
    Pages: Online-Ressource (162 Seiten)
    ISBN: 9781862392175
    URL: http://sp.lyellcollection.org/content/vol274/issue1/
    Language: English
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    E-BOOK
  • 2
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    Unknown
    Surface sediment grain size, carbonate content and clay mineralogy of Thermaikos shelf (Table 1)
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Description: The area under investigation is located within 22°45' to 23°45'E, and from 39°15' to 40°15'N. Sedimentological, bathymetric and shallow geophysical data were collected from here during the 7/78 cruise of R.R.S. "Shackleton". Twenty-seven sea-bed (surface) samples were collected, using a Day grab, from different environments; these were analysed for grain-size distribution, carbonate content, and clay mineralogy. On the basis of the bathymetric and shallow geophysical data, the area has been classified into five major physiographic environments, according to their bathymetry and topography: (1) shelf (Thermaicon Plateau); (2) slope; (3) marginal plateau; (4) the "canyon system" and valleys; and (5) (Sporades) basin. Based on the sedimentological analyses, the surface sediments have been classified into four major Provinces, as follows: (1) Province 1 - shelf muds; (2) Province 2 - muddy sands; (3) Province 3 - outer margin muds; and (4) Province 4 - outer shelf/shelf break. It is concluded that modern sedimentation in the N.W. Aegean Sea is dominated by the (terrigenous) river inputs and by the circulation of both high and low salinity masses.
    Keywords: Aegean Sea; Calcium carbonate; Calculated after FOLK; DEPTH, sediment/rock; Event label; Grab; GRAB; Grain size, mean; Grain size, pipette analysis; Grain size, sieving; Gravimetric analysis; Illite; Kaolinite+Chlorite; Latitude of event; Longitude of event; NA/78/1; NA/78/10; NA/78/19; NA/78/2; NA/78/28; NA/78/3; NA/78/32; NA/78/33; NA/78/34; NA/78/35; NA/78/36; NA/78/37; NA/78/38; NA/78/39; NA/78/4; NA/78/40; NA/78/41; NA/78/42; NA/78/44; NA/78/45; NA/78/46; NA/78/47; NA/78/5; NA/78/6; NA/78/7; NA/78/8; NA/78/9; Sand; Shackleton; Shackleton78/7; Silt; Size fraction 〈 0.002 mm, clay; Smectite; Thermaikos Gulf; X-ray diffraction, clay fraction
    Type: Dataset
    Format: text/tab-separated-values, 249 data points
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    DATA PANGAEA
  • 3
    Electronic Resource
    Electronic Resource
    Short-term changes in sedimentological and hydrographic characteristics over a sandy intertidal zone, the Wash, U. K. (1982)
    Springer
    Geo-marine letters 2 (1982), S. 55-60 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Observations of tidal current velocities, their structure throughout the water column and associated sediment distribution patterns were made in 1972 and 1980. The results demonstrated: 1. an increase in the tidal current speeds and an enhancement in the longshore component; 2. a trend toward a more logarithmic velocity distribution in the water column; and 3. a general increase in grain size, but the development of alower mud flat. Such significant changes could relate to the construction of an embankment, as part of a land reclamation scheme, or to the reversion to a longer-term period of erosion over this region of intertidal flat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462800
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  • 4
    Electronic Resource
    Electronic Resource
    Sand grain threshold, in relation to bed ‘stress history’: an experimental study (2005)
    Oxford, UK : Blackwell Science Ltd
    Sedimentology 52 (2005), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Besides particle size, density and shape, the erodibility of a sediment bed depends also upon the exposure to prethreshold velocities in the overlying flow. Such flow effectively rearranges the grains (at and below the bed surface), causing them to become more resistant to subsequent erosion. The effects of the ‘stress history’, leading up to the critical condition for sediment movement, are investigated for unidirectional flows generated in a recirculating laboratory flume. The sediment beds investigated consisted of cohesionless quartz sand grains, with mean grain diameters of 0·194 mm (fine sand), 0·387 mm (medium sand) and 0·774 mm (coarse sand), with narrow particle-size distributions. The critical (threshold) shear velocity (target value) for the three beds was established, within 2·5 min of increasing the flow from zero velocity. The subsequent experiments were performed under prethreshold velocities at 70% (for 5, 10, 20, 40 and 80 min exposure duration), 80% (for 5, 10, 20, 40 and 80 min exposure duration), 90 and 95% (for 5, 10, 20, 40, 80 and 120 min exposure duration) of the target value. Following exposure to these different prethreshold conditions, the flow was increased then to reach actual critical conditions, within a period of 2·5 min. The critical condition for the initiation of sediment movement was established using visual observation (supplemented by video recordings), according to the Yalin criterion. The results show that if the exposure duration to prethreshold velocities remains constant, then the critical shear velocity increases with increasing prethreshold velocity. Likewise, if the prethreshold velocity remains constant, then the critical shear velocity increases with increasing exposure duration. In some circumstances, the critical shear velocity was found to increase by as much as 27%. An empirical formula is proposed to account for the exposure correction to be applied to the critical shear velocities of sand-sized sediment beds; this is prior to their inclusion into bedload transport formulae, for an improved prediction of the magnitude and nature of transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.2005.00710.x
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  • 5
    Electronic Resource
    Electronic Resource
    Settling velocities and entrainment thresholds of biogenic sands (shell fragments) under unidirectional flow (2002)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 49 (2002), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Settling velocities and entrainment thresholds of biogenic sedimentary particles, under unidirectional flow conditions, are derived on the basis of settling tower and laboratory flume experiments. Material consisting predominantly of equant blocks (shell fragments of Cerastoderma edule, density, ρs=2800 kg m−3) or of mica-like flakes and elongate rods (Mytilus edulis fragments, ρs=2720 kg m−3) are used in separate series of experiments. Differences in the measured settling and threshold properties are related primarily to particle shape. The selection of a characteristic length scale for non-spherical grains is investigated by comparing two approaches used to define the grain size (D) of the sediment samples: grain settling and sieve analysis that are used to derive data for the threshold criteria, in terms of the Shields and Movability diagrams. The empirical curves effectively predict the threshold conditions for any grain shape, provided that grain size is defined in terms of grain settling velocity. However, a functional distinction is made between the characteristic `hydraulic' grain size, defined by grain settling for grain transport applications, and the actual (physical) grain size defined by sieve analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2002.00446.x
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  • 6
    Electronic Resource
    Electronic Resource
    On the threshold of transport of sand-sized sediment under the combined influence of unidirectional and oscillatory flow (1979)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 26 (1979), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: While the transport of sediment by unidirectional currents or by oscillatory (wave-induced) currents has been investigated, very little attention has been paid to the problem of the threshold of transport under the two mechanisms combined. Studies were carried out using cohesionless sand-sized (mean diameters: 142, 363, 771 and 1134 μm) quartz grains in a unidirectional flume, within which an oscillatory carriage had been installed. The experiments were carried out under unidirectional velocities ranging between 0 and 27 cm s-1, combined with simulated wave-induced currents (at periods of 5 and 15 s) ranging from 0 to 35 cm s-1. The threshold of transport was assessed, by visual observation, using the Yalin Criterion for unidirectional flow. This criterion permitted critical conditions to be estimated subjectively by observation of incipient transport from the flat beds. The results indicated the dependence of the critical threshold velocity combination on grain size and wave period. Thresholds tend to increase with increasing grain size or decreasing period. The grain-size dependence is predictable from existing empirical relationships for the separate mechanisms; statistical fluctuations in near-bed stress (bursting) however, are invoked to explain the wave period dependence. The latter effect acts in a reverse manner for wave and current combinations than for waves alone. Graphs are presented, relating grain size to critical threshold velocity combinations, to aid in the sedimentological interpretation of field data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1979.tb00973.x
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  • 7
    Electronic Resource
    Electronic Resource
    Laboratory investigations into the threshold of movement of natural sand-sized sediments under unidirectional, oscillatory and combined flows (2001)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 48 (2001), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The threshold of movement of sediment obtained from sandbanks within the Bristol Channel (UK) is investigated under unidirectional, oscillatory and combined flows. The experiments were undertaken in a recirculating, unidirectional laboratory flume containing an oscillating plate to simulate wave action, with movement along the same axis as the unidirectional flows. The sand samples consisted of cohesionless quartz grains with median grain sizes between 0·315 and 0·513 mm. The experiments were performed under flow velocities (measured at 2 cm above the bed) ranging between 0 and 24 cm s–1 and oscillatory currents (wave periods of 5, 12 and 15 s) ranging from 0 to 28 cm s–1. The critical conditions for the initiation of sediment movement were assessed, by visual observation, using the Yalin criterion. The results show that, under unidirectional flow, there is a slight overestimation of the threshold of naturally graded sediments derived on the basis of empirically derived threshold curves for artificially prepared sediments under similar flow conditions. In the case of oscillatory flows, the threshold for the natural sands is found to be higher than that predicted by previously derived empirical curves. Under combined flows, wave period is shown to control threshold conditions, with the unidirectional and oscillatory flow components combining in a linear fashion for long-period (12 s and 15 s) waves. In contrast, in the presence of short-period (5 s) waves, the unidirectional and oscillatory components of the flow appear to ‘decouple’. For high orbital velocities, in both cases, the effect of the wave period on threshold diminishes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2001.00385.x
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  • 8
    Electronic Resource
    Electronic Resource
    Hydrodynamics and sediment dynamics of The Wash embayment, eastern England (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 43 (1996), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Water and sediment movement in The Wash embayment has been determined from an extensive set of data, consisting of tidal current readings and suspended sediment concentration measurements. Instantaneous and residual currents in the embayment show a distinct lateral inhomogeneity, whereas vertically the water column is almost homogenous. The central deep water area (30–40 m) of the embayment is dominated by a residual landward water movement, whilst on the margins, the residual movement is seaward. Sediment is supplied predominantly in suspension from the north, through the northern extremity of Boston Deep. Suspended sediment pathways are coincident with the spring tide water movements and the subtidal channels act as the main conduits. Approximately 6·8 × 106 tonnes yr−1 of suspended sediments are supplied to the embayment from offshore areas. Bedload sediment supply is of lesser importance, ∼ 1·4 × 104 tonnes yr−1. Whereas suspended sediment movement appears to be the dominant mode of transport throughout the embayment, bedload transport is important in reforming the sea bed into a variety of bedforms which are particularly well developed on the margins of channels and shoals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1996.tb01465.x
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  • 9
    Electronic Resource
    Electronic Resource
    Threshold studies of gravel size particles under the co-linear combined action of waves and currents (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 41 (1994), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Gravel size sediment beds are tested under the combined influence of simulated wave action and co-linear currents in a laboratory flume. Critical current speed, at threshold, increases with increasing size. Superimposed wave energy causes a small reduction in the unidirectional current energy. For low values of wave-induced near bed current velocities, the resistance to erosion increases when the wave period decreases from 10 to 6 s. Finally, combined critical shear stresses are found to be lower than those predicted using the Shields curve, as modified for oscillatory flow. Grain protrusion is suggested as a mechanism to explain this divergence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1994.tb01434.x
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  • 10
    Electronic Resource
    Electronic Resource
    The use of settling velocity in defining the initiation of motion of heavy mineral grains, under unidirectional flow (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 29 (1982), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The results of critical threshold experiments on four commonly occurring heavy minerals are described. The data are presented, in conjunction with comparable quartz data, using the non-dimensional Shields’ Curve and the Movability Number (U*/ws). The results indicate that critical shear stress for material of high density is overestimated by use of Shields’ Curve, under smooth boundary conditions. Grain settling velocity is found to be a good indicator for the critical shear stress for grains of a wide density range. A physical explanation for the results is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1982.tb01804.x
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