Effect of lift on bed‐surface sediment size distribution in channel bend

Sediments were collected from four slow vegetation recovery plots, six fast vegetation recovery plots and five unburned plots at a post-fire site on a rainfall event basis and sorted for size distribution. The aim was to evaluate the effects of vegetation cover, soil aggregate stability, slope and rainfall intensity on sediment size distribution, transport selectivity and erosion processes between the burned and unburned treatment plots. Sediment detachment and transport mechanisms and the particle size transport selectivity of the eroded sediment were assessed based on enrichment ratios (ER) and mean weighted diameter (MWD) methods. The most eroded particle size class in all treatment plots was the 125–250μm class and, generally, the percentage of eroded particle sizes did not increase with slope and rainfall intensity. Higher MWD of the eroded sediment was related to a higher percentage of bare soil exposed and gravel content associated with high soil burn severity and soil disaggregation in the slow vegetation recovery plots. The enrichment of finer clay silt particle sizes increased with varying maximum 30-min rainfall intensity (I30) in the slow vegetation recovery plots, and reflected increased aggregate breakdown and transport selectivity, whereas no good relationship was found in the fast vegetation recovery and unburned plots with varying I30. A minimum I30 of <3.56mmh–1 and a maximum of 10.9mmh–1 were found to be the threshold rainfall intensity values necessary for aggregate breakdown and transport of finer particles by both rainsplash and rainflow in the slow vegetation recovery plots, whereas the response was weak in the fast vegetation recovery and unburned plots following varying I30 dominated only by rainsplash transport closer to the plot sediment collector. The results show that higher vegetation cover in the fast vegetation recovery and unburned plots reduces erosive rainfall energy by 5.6- and 17.7-fold respectively, and runoff energy by 6.3- and 21.3-fold respectively, limiting aggregate breakdown and transport selectivity of finer particles compared with the slow vegetation recovery plots.

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Ablation Capability Infection of Hydraulic Turbine Material by Sediment Size Distribution

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.48-49.131 ◽

2011 ◽

Vol 48-49 ◽

pp. 131-134

Author(s):

Yan Ren ◽

Yan Pin Li ◽

De Xin Chen

Keyword(s):

Size Distribution ◽

Yellow River ◽

Hydraulic Turbine ◽

Critical Parameters ◽

The Yellow River ◽

Size Distributions ◽

Direct Relation ◽

Scientific Methods ◽

Sediment Size ◽

The Common

So far, the research about sediment ablation characteristic of the Yellow River is very insufficiency. For preventing and alleviating sediment ablation of the Yellow River stations by more scientific methods, it is very necessary to research ablation characteristic of hydraulic turbine systematically. The ablation characteristic of hydraulic turbine has direct relation with sediment size distribution. By research ablation of hydraulic turbine material under different sediment size distributions, the common rules are summarized between material ablation and sediment size distribution, and the key data and critical parameters are found out, which provides evidence for sediment ablation defend of hydraulic turbine.

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Sediment size on talus slopes correlates with fracture spacing on bedrock cliffs: Implications for predicting initial sediment size distributions on hillslopes

10.5194/esurf-2020-54 ◽

2020 ◽

Author(s):

Joseph P. Verdian ◽

Leonard S. Sklar ◽

Clifford S. Riebe ◽

Jeffrey R. Moore

Keyword(s):

Particle Size ◽

Size Distribution ◽

Characteristic Size ◽

Residence Times ◽

Size Distributions ◽

Initial Size ◽

Fracture Spacing ◽

Rock Fragments ◽

Sediment Size ◽

Wide Range

Abstract. The detachment of rock fragments from fractured bedrock on hillslopes creates sediment with an initial size distribution that sets the upper limits on particle size for all subsequent stages in the life of sediment in landscapes. We hypothesize that the initial size distribution should depend on the size distribution of latent sediment (i.e., blocks defined by through-going fractures) and weathering of sediment before or during detachment (e.g., disintegration along crystal grain boundaries). However, the initial size distribution is difficult to measure, because the interface across which sediment is produced is often shielded from view by overlying soil. Here we overcome this limitation by comparing fracture spacings measured from exposed bedrock on cliff faces with particle size distributions in adjacent talus deposits at 15 talus-cliff pairs spanning a wide range of climates and lithologies in California. Median fracture spacing and particle size vary by more than tenfold and correlate strongly with lithology. Fracture spacing and talus size distributions are also closely correlated in central tendency, spread, and shape, with b-axis diameters showing the closest correspondence with fracture spacing at most sites. This suggests that weathering has not modified latent sediment either before or during detachment from the cliff face. In addition, talus has not undergone much weathering after deposition and is slightly coarser than the latent sizes, suggesting that it contains some fractures inherited from bedrock. We introduce a new conceptual framework for understanding the relative importance of latent size and weathering in setting initial sediment size distributions in mountain landscapes. In this framework, hillslopes exist on a spectrum defined by the ratio of two characteristic timescales: the residence time in saprolite and weathered bedrock, and the time required to detach a particle of a characteristic size. At one end of the spectrum, where weathering residence times are negligible, the latent size distribution can be used to predict the initial size distribution. At the other end of the spectrum, where weathering residence times are long, the latent size distribution can be erased by weathering in the critical zone.

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Effects of Spur Dyke’s Orientation on Bed Variation in Channel Bend

Hydro Science & Marine Engineering ◽

10.30564/hsme.v3i2.3834 ◽

2021 ◽

Vol 3 (2) ◽

Author(s):

Mohammad Athar ◽

Talib Mansoor ◽

Nishank Aggarwal

Keyword(s):

Angular Displacement ◽

Velocity Shear ◽

Bridge Piers ◽

Geometrical Parameters ◽

Meandering Channel ◽

Sediment Size ◽

Channel Bend ◽

Outer Bank ◽

Main Emphasis ◽

Present Thesis

Spur dykes also known as Groynes are often used to either divert or attract the flow from the main structure to safeguard their life. Those structures may be bridge piers, abutments or any similar hydraulics structures. Spur dykes are also used to save the cutting of banks on concave side of stream. Lots of work have been done in recent past on spur dykes by many investigators in which various hydraulic and geometrical parameters of spur dykes such as discharge, sediment size, flow velocity, shear stress, spur dykes shape, size and submergence etc. are studied in detail. But mostly all the studies were pointed out in straight open channels. Very few studies were done in curved channel and only their similar effects were studied. In present thesis main emphasis is given to study the effect of orientation and location of spur dykes in meandering channel on the bed of downstream side. In the present study experimental work has been carried out in 80° bend and constant discharge (Q = 4.5 l/s) is allowed to pass in channel without spur dyke. It is found that maximum scouring occurs at angular displacement θ = 60° to 80° in the vicinity of outer bank. To minimize this scouring, spur dyke has been installed at angular displacement θ = 20°, 40° & 60° by changing the dyke angle α = 60°, 90° & 120° respectively. It is found that scouring at θ = 60° is reduced by installing spur dyke at angular displacement θ = 40° which is oriented at α = 60° and scouring at θ = 80° is reduced by installing spur dyke at angular displacement θ = 60° which is oriented at α = 60°.

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