scholarly journals Sand and Gravel Bed Cored from the Bottom of the Suruga Bay

1962 ◽  
Vol 68 (806) ◽  
pp. 609-617 ◽  
Author(s):  
Takahiro SATO
Keyword(s):  
Suruga Bay ◽  
Gravel Bed ◽  
Sand And Gravel

scholarly journals Comparison of flow turbulence over a sand bed and gravel bed channel

2021 ◽  
Author(s):  
Anurag Sharma ◽  
Bimlesh Kumar
Keyword(s):  
Reynolds Shear Stress ◽  
Longitudinal Velocity ◽  
Boundary Surface ◽  
Vertical Direction ◽  
Gravel Bed ◽  
Flow Energy ◽  
Bed Materials ◽  
Flow Turbulence ◽  
Sand And Gravel ◽  
Flow Anisotropy

Abstract Experiments were performed to examine the variations in flow turbulence with respect to sand and gravel bed channel. The 3D instantaneous velocity of water is measured by acoustic doppler velocimeter (ADV) at the test section which will provide an important data related to the flow turbulence. The parameters of turbulence measured that the vertical profiles of longitudinal velocity in flows with sand bed channel at the vicinity of bed surface are higher by 2–6% than flow subjected to gravel bed channel, while away from the boundary surface, it decreases by 5–10%. The variations of Reynolds shear stress increases by 35–50% with gravel bed channel, indicating higher exchange of flow energy towards the boundary and vice versa. The higher value is obtained for shear velocities by 58.5% and the von Karman's constant with gravel bed channel. The gravel bed channel influenced the turbulence intensities with higher magnitude in the streamwise and vertical direction. The present study also analysed the flow anisotropy, correlations coefficient and turbulence diffusivity and compared the results. The outcomes of the current work are beneficial for civil and hydraulic engineers, since the data of turbulence will advance the management of bed materials present in the river.

Multiband (X, C, L) radar amplitude analysis for a mixed sand- and gravel-bed river in the eastern central Andes

2020 ◽  
Author(s):  
Benjamin Purinton ◽  
Bodo Bookhagen
Keyword(s):  
Power Spectrum ◽  
Spatial Scales ◽  
High Mountain ◽  
Amplitude Analysis ◽  
Gravel Bed ◽  
Fourier Frequency ◽  
Mountain Environments ◽  
Tectonically Active ◽  
L Band ◽  
Sand And Gravel

<p>Synthetic Aperture Radar (SAR) amplitude measurements from spaceborne sensors are sensitive to surface roughness conditions near their radar wavelength. These data can be exploited to measure gravel-to-sand transitions and downstream gradients in grain size related to geomorphic setting in tectonically active high mountain environments at large spatial scales. The bedload of mixed sand- and gravel-bed rivers can be considered mixed smooth (compacted sand) and rough (gravel) surfaces. Here, we assess backscatter gradients over a large high-mountain alluvial river with aerially exposed sand and gravel bedload using X-band TerraSAR-X/TanDEM-X, C-band Sentinel-1, and L-band ALOS-2 PALSAR-2 radar scenes. In a first step, we compare backscatter response over vegetation-free endmember surfaces within the dry channel bed to assess expected responses and limitations of SAR roughness measurements. We then develop methods to extract smoothed backscatter gradients downstream along the channel using kernel density estimates. In a final step, the presence of sand and gravel bars is analyzed using Fourier frequency analysis, by fitting stretched exponential and power-law models to the power spectrum. We find a large range in backscatter depending on the heterogeneity of contiguous smooth- and rough-patches of bedload material. The SAR signal responds primarily to the fraction of smooth-sand bedload, but is further modified by gravel elements. The sensitivity to gravel is more apparent in longer wavelength (L-band) radar. Because the spatial extent of smooth sand bars is typically < 50 m, only higher resolution sensors (e.g., TerraSAR-X/TanDEM-X) are useful for power spectrum analysis. Our results show the potential for mapping sand-gravel transitions and local geomorphic complexity using SAR amplitude at the scale of large high mountain catchments with aerially exposed bedload.</p>

XII.—On some Waxed Tablets said to have been found at Cambridge

Archaeologia ◽  
1897 ◽  
Vol 55 (2) ◽  
pp. 257-282 ◽  
Author(s):  
T. McKenny Hughes
Keyword(s):  
Gravel Bed ◽  
Sand And Gravel

Close to the inner margin of the King's Ditch at Cambridge, which until quite recently was the only ditch known to exist, excavations were lately made for the foundations of Messrs. Fosters' new bank. The ditch which runs along Hobson Street was only just touched, but there was at this spot a large quantity of sand and gravel. This had apparently been thrown out of the ditch, which here skirted the edge of an extensive gravel bed. No water passed through this dry subsoil from any side, and the area was soon built over, so that no rain fell into it. These were, therefore, conditions very favourable for the preservation of perishable materials

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