Measurement of soil aggregate settling velocities. 1. A modified bottom withdrawal tube method

Soil Research ◽  
1988 ◽  
Vol 26 (1) ◽  
pp. 55 ◽  
Author(s):  
CJ Lovell ◽  
CW Rose
Keyword(s):  
Entire Range ◽  
Settling Velocity ◽  
Soil Aggregates ◽  
Soil Aggregate ◽  
Natural Sediment ◽  
Polydisperse Suspension ◽  
Modified Method ◽  
Sediment Types ◽  
Settling Velocity Distribution ◽  
Sediment Settling

Sediment eroded by water consists largely of soil aggregates. The settling velocity of such aggregates and primary soil particles is of fundamental importance to the processes of sediment transport and deposition in water. A modified bottom withdrawal tube method is presented for the direct measurement of the settling velocity distribution of soil aggregates or particles of different sizes that settle together in a polydisperse suspension. The modified method overcomes experimental error and analytical deficiencies present in the initial method and is suitable for measuring settling velocities up to 0.5 m s-1. The method employs the bottom withdrawal principle; new exact theory is presented for interpretation of sedimentation data thus measured. By complementing the pipette or hydrometer methods which measure settling velocities less than 10-3 ms-1, this modified method allows analysis of the entire range of settling velocities encountered in natural sediment. Settling velocity distributions measured for a variety of sediment types are illustrated.

Polydisperse particle-driven gravity currents

2002 ◽  
Vol 472 ◽  
pp. 333-371 ◽  
Author(s):  
THOMAS C. HARRIS ◽  
ANDREW J. HOGG ◽  
HERBERT E. HUPPERT
Keyword(s):  
Shallow Water ◽  
Numerical Integration ◽  
Shallow Water Equations ◽  
Settling Velocity ◽  
Continuous Distribution ◽  
Flow Speed ◽  
Asymptotic Results ◽  
Rigid Boundary ◽  
Polydisperse Suspension ◽  
Settling Velocity Distribution

The intrusion of a polydisperse suspension of particles over a horizontal, rigid boundary is investigated theoretically using both an integral (‘box’) model and the shallow-water equations. The flow is driven by the horizontal pressure gradient associated with the density difference between the intrusion and the surrounding fluid, which is progressively diminished as suspended particles sediment from the flow to the underlying boundary. Each class of particles in a polydisperse suspension has a different settling velocity. The effects of both a discrete and continuous distribution of settling velocities on the propagation of the current are analysed and the results are compared in detail with results obtained by treating the suspension as monodisperse with an average settling velocity. For both models we demonstrate that in many regimes it is insufficient to deduce the behaviour of the suspension from this average, but rather one can characterize the flow using the variance of the settling velocity distribution as well. The shallow-water equations are studied analytically using a novel asymptotic technique, which obviates the need for numerical integration of the governing equations. For a bidisperse suspension we explicitly calculate the flow speed, runout length and the distribution of the deposit, to reveal how the flow naturally leads to a vertical and streamwise segregation of particles even from an initially well-mixed suspension. The asymptotic results are confirmed by comparison with numerical integration of the shallow-water equations and the predictions of this study are discussed in the light of recent experimental results and field observations.

Methodology of Calculation the Terminal Settling Velocity Distribution of Irregular Particles for High Values of the Reynold’s Number/Metodologia Wyliczania Rozkładu Granicznej Prędkości Opadania Ziaren Nieregularnych Dla Wysokich Wartości Liczb Reynoldsa

2014 ◽  
Vol 59 (2) ◽  
pp. 553-562 ◽  
Author(s):  
Agnieszka Surowiak ◽  
Marian Brożek
Keyword(s):  
Velocity Distribution ◽  
Settling Velocity ◽  
Random Variables ◽  
Independent Random Variables ◽  
Calculation Algorithm ◽  
Shape Coefficient ◽  
Geometrical Properties ◽  
Size And Shape ◽  
Physical Density ◽  
Settling Velocity Distribution

Abstract Settling velocity of particles, which is the main parameter of jig separation, is affected by physical (density) and the geometrical properties (size and shape) of particles. The authors worked out a calculation algorithm of particles settling velocity distribution for irregular particles assuming that the density of particles, their size and shape constitute independent random variables of fixed distributions. Applying theorems of probability, concerning distributions function of random variables, the authors present general formula of probability density function of settling velocity irregular particles for the turbulent motion. The distributions of settling velocity of irregular particles were calculated utilizing industrial sample. The measurements were executed and the histograms of distributions of volume and dynamic shape coefficient, were drawn. The separation accuracy was measured by the change of process imperfection of irregular particles in relation to spherical ones, resulting from the distribution of particles settling velocity.

scholarly journals Dynamics of Soil Organic Carbon and Labile Carbon Fractions in Soil Aggregates Affected by Different Tillage Managements

2021 ◽  
Vol 13 (3) ◽  
pp. 1541
Author(s):  
Xiaolin Shen ◽  
Lili Wang ◽  
Qichen Yang ◽  
Weiming Xiu ◽  
Gang Li ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Aggregates ◽  
Aggregate Stability ◽  
Soil Aggregate ◽  
No Tillage ◽  
Labile Carbon ◽  
Carbon Fractions ◽  
Soil Aggregate Stability ◽  
Positive Effects

Our study aimed to provide a scientific basis for an appropriate tillage management of wheat-maize rotation system, which is beneficial to the sustainable development of agriculture in the fluvo-aquic soil areas in China. Four tillage treatments were investigated after maize harvest, including rotary tillage with straw returning (RT), deep ploughing with straw returning (DP), subsoiling with straw returning (SS), and no tillage with straw mulching (NT). We evaluated soil organic carbon (SOC), dissolved organic carbon (DOC), permanganate oxidizable carbon (POXC), microbial biomass carbon (MBC), and particulate organic carbon (POC) in bulk soil and soil aggregates with five particle sizes (>5 mm, 5–2 mm, 2–1 mm, 1–0.25 mm, and <0.25 mm) under different tillage managements. Results showed that compared with RT treatment, NT treatment not only increased soil aggregate stability, but also enhanced SOC, DOC, and POC contents, especially those in large size macroaggregates. DP treatment also showed positive effects on soil aggregate stability and labile carbon fractions (DOC and POXC). Consequently, we suggest that no tillage or deep ploughing, rather than rotary tillage, could be better tillage management considering carbon storage. Meanwhile, we implied that mass fractal dimension (Dm) and POXC could be effective indicators of soil quality, as affected by tillage managements.

scholarly journals Nutrient and Stoichiometric Characteristics of Aggregates in a Sloping Farmland Area under Different Tillage Practices

2021 ◽  
Vol 13 (2) ◽  
pp. 890
Author(s):  
Jie Zhang ◽  
Yaojun Liu ◽  
Taihui Zheng ◽  
Xiaomin Zhao ◽  
Hongguang Liu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Size Distribution ◽  
Soil Aggregates ◽  
Soil Aggregate ◽  
Elemental Content ◽  
Stoichiometric Ratio ◽  
Longitudinal Ridge ◽  
Stoichiometric Ratios ◽  
Sloping Farmland ◽  
Ridge Tillage

Sloping farmland is prevalent in hilly red soil areas of South China. Improper tillage patterns induce decreased soil organic matter, soil aggregate breakdown, and nutrient imbalance, thereby restricting crop production. However, the stoichiometric characteristics could reflect the nutrient availability which was mostly studied on bulk soil. The stoichiometric characteristics of soil aggregates with multiple functions in farmlands has rarely been studied. The study was to reveal the impact of tillage patterns on the size distribution, nutrient levels, and stoichiometric ratios of soil aggregates after 20 years’ cultivation. Soil samples of 0–20 cm and 20–40 cm from five tillage patterns, bare-land control (BL), longitudinal-ridge tillage (LR), conventional tillage + straw mulching (CS), cross-ridge tillage (CR), and longitudinal-ridge tillage + hedgerows (LH) were collected. The elemental content (C, N and P) and soil aggregate size distribution were determined, and the stoichiometric ratios were subsequently calculated. Through our analysis and study, it was found that the nutrient content of >2 mm soil aggregates in all plots was the highest. In the hedgerow plots, >2 mm water-stable soil aggregate content was increased. Therefore, LH plots have the highest content of organic matter and nutrients. After 20 years of cultivation, stoichiometric ratio of each plot showed different changes on soil aggregates at different levels. the C:N, C:P, and N:P ratios are lower than the national average of cultivated land. Among of them, the stoichiometric ratio in the LH plot is closer to the mean and showed better water-stable aggregate enhancement. Therefore, longitudinal-ridge tillage + hedgerows can be recommended as a cultivation measure. This study provides a reference for determining appropriate tillage measures, balancing nutrient ratios, and implementing rational fertilization.

Study on the Formula of Settling Velocity of Sediment Particle Cloud in the Water

2012 ◽  
Vol 212-213 ◽  
pp. 225-229
Author(s):  
Jie Gu ◽  
Dan Qing Ma ◽  
Wei Chen ◽  
Xin Qin ◽  
Xiao Li Wang
Keyword(s):  
Experimental Data ◽  
Particle Size ◽  
Settling Velocity ◽  
Sediment Particle ◽  
Particle Cloud ◽  
Characteristic Particle ◽  
Experimental Values ◽  
New Formula ◽  
Sediment Settling

Based on the experimental data of sediment particle cloud during the settlement process in the water and combined with the existed sediment settling velocity formulae, a new formula for calculation of the settling velocity of sediment particle cloud is proposed by the introduction of the characteristic particle size of sediment particle cloud ( D' ). By using experimentally measured settling velocity values of sediment particle cloud to verify the settling velocity values of sediment particle cloud which calculated by using this new formula, the results show that the calculated settling velocity values using this new formula are closer to the experimental values.

Aggregate size distribution and stability of an oxisol under legume-based and pure grass pastures in the eastern Colombian savannas

Soil Research ◽  
1995 ◽  
Vol 33 (1) ◽  
pp. 153 ◽  
Author(s):  
AJ Gijsman ◽  
RJ Thomas
Keyword(s):  
Size Distribution ◽  
Soil Aggregates ◽  
Aggregate Stability ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Hot Water ◽  
Aggregate Size Distribution ◽  
Carbohydrate Concentration ◽  
Stability Measurement ◽  
Water Extractable

This study evaluated soil aggregate size distribution and stability of an Oxisol under improved grass-only or grass-legume pastures, established in previously native savanna. Three grass-legume combinations were included at various stocking rates. In all treatments and soil layers, soils were well aggregated, having more than 90% of their weight in macroaggregates (>250 �m). The addition of legumes to pastures did not affect the soil aggregate size distribution, although aggregates showed somewhat more stability against slaking. An increase in stocking rate negatively affected both average aggregate size and aggregate stability. Aggregates showed little or no dispersion of clay particles in any treatment. A positive correlation was found between wet aggregate stability and hot-water extractable carbohydrate concentration, supporting the hypothesis that these carbohydrates equate with plant-derived or microbial polysaccharides which glue soil aggregates together. It is suggested that determination of hot-water extractable carbohydrates may serve as a useful indicator of small differences in aggregate stability, even when these differences are not evident in the stability measurement itself.

A test of the ADV-based Reynolds flux method for in situ estimation of sediment settling velocity in a muddy estuary

2013 ◽  
Vol 33 (6) ◽  
pp. 477-484 ◽  
Author(s):  
Grace M. Cartwright ◽  
Carl T. Friedrichs ◽  
S. Jarrell Smith
Keyword(s):  
Settling Velocity ◽  
Flux Method ◽  
Sediment Settling

scholarly journals Factors Determining Soil Water Repellency in Two Coniferous Plantations on a Hillslope

Forests ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 730 ◽  
Author(s):  
Moein Farahnak ◽  
Keiji Mitsuyasu ◽  
Kyoichi Otsuki ◽  
Kuniyoshi Shimizu ◽  
Atsushi Kume
Keyword(s):  
Soil Water ◽  
Overland Flow ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Water Repellency ◽  
Soil Aggregate ◽  
Water Infiltration ◽  
Soil Water Repellency ◽  
Tree Cutting ◽  
Coniferous Plantations

Soil water repellency (SWR) is a cause of low water infiltration, overland flow and soil erosion in mountainous coniferous plantations in Japan. The factors determining SWR intensity were investigated in two coniferous plantations of Chamaecyparis obtusa (Siebold et Zucc.) Endl. and Cryptomeria japonica (L.f.) D. Don, using intact tree plots and cut tree plots on the same hillslope. The SWR of Ch. obtusa plots was stronger than that of Cr. japonica plots. SWR intensity decreased after tree cutting. There were no significant differences in SWR upslope and downslope of individual trees/stumps for both tree species, though areas downslope of individual Ch. obtusa trees had higher SWR intensity than those upslope. SWR intensity and soil aggregate stability were positively correlated in the Ch. obtusa intact tree plot (r = 0.88, p < 0.01), whereas in the cut tree plot, this correlation was weak with no significance (r = 0.29, p = 0.41). Soil aggregate size had a non-significant influence on SWR intensity. These findings suggest that SWR intensity was not related to the soil aggregate size, but SWR intensity seemed have a role in soil aggregation in the Ch. obtusa intact tree plot. Destruction of soil aggregates could occur after tree cutting because of physical disturbances or increased input of different types of organic matter from other vegetation into soil. The presence of Ch. obtusa introduces a source of SWR, although uncertainty remains about how water repellency is distributed around soil aggregates. The distribution pattern of soil water content and soil hydraulic conductivity around Cr. japonica was related to other factors such as the litter layer and non-water-repellant soil.

Distribution of Weed Seed Among Soil Structural Units

Weed Science ◽  
1985 ◽  
Vol 33 (2) ◽  
pp. 182-189 ◽  
Author(s):  
Mario R. Pareja ◽  
David W. Staniforth ◽  
Gilda P. Pareja
Keyword(s):  
Depth Distribution ◽  
Soil Depth ◽  
Soil Aggregates ◽  
Conventional Tillage ◽  
Soil Aggregate ◽  
Soil Samples ◽  
Reduced Tillage ◽  
Weed Seed ◽  
Structural Units ◽  
Seed Distribution

The depth distribution of weed seed, their location in relation to soil aggregates, and the size distribution of soil aggregates were determined in fields that had been under continual conventional or reduced tillage for more than 12 years. Soil samples were taken at three depths in the spring and fall of 1982, and soil aggregates were classified into seven size classes by dry, rotary sieving. Subsamples were deflocculated and washed through sieves to recover weed seed. In the spring, 85% of all seed in the reduced-tillage and 28% of those in the conventional-tillage soil were in the 0- to 5-cm-depth layer. Conventional tillage incorporated weed seed uniformly into various soil aggregate classes, whereas with reduced tillage more seed accumulated in the unaggregated fraction of the soil. In the fall, weed seed distribution in relation to soil depth and among soil aggregate classes was similar for both tillage regimes.

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