Effect Of Sediment Size Research Articles

Sediment size effects on non-Darcy flow: insights from Izbash equation and Forchheimer inertial coefficient analysis

The transition from Darcy to non-Darcy flow regimes was investigated using column experiments. This revealed key relationships between sediment characteristics and critical thresholds for the onset of the non-Darcy flow regime, as well as inertial flow parameters. An exponential dependence of the critical Reynolds number (Rec) on hydraulic conductivity (K) and a linear dependence on sediment size (d50) was found. The analysis revealed a potentially universal relationship between the critical hydraulic gradient (Ic) and K, with a power-law exponent of –3/2, consistent with previous investigations. Additionally, Ic was found to be inversely proportional to the power law of the square root of d50. Novel relationships are derived for estimating the Izbash equation inertial exponent (n) and the Forchheimer inertial coefficient (β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document}) based on sediment characteristics. The exponent (n) was found to decrease with d50 and increase with K, following power-law relationships. A new equation is proposed, capable of predicting β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} with slightly improved accuracy, outperforming numerous and previously proposed empirical equations. Additionally, these data validate the works of Ergun and Irmay as an alternative for β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} estimation using porosity and sediment size. As the attainment of statistical significance in multiparameter curve fitting can be trivial, it has led to the proliferation of empirical equations for estimating β. This study highlights the limitations of existing empirical methods in determining β and emphasizes the necessity for a universal approach to predict this critical parameter, which will facilitate broader adoption of the Forchheimer equation.

Effects of sediment size and type on the tribological properties of NBR in water

Nitrile Butadiene Rubber (NBR) is widely used in ship water-lubricated stern tube bearings. Sediments in the water would cause a serious effect on friction and wear properties of the water-lubricated bearings. In this study, the tribological performance of water-lubricated rubber bearings under different sediment particle sizes and sand types were analyzed. Two sediment sand types are involved in the research, (i) SiO2 particles with sizes of 0–25 μm, 48–60 μm, 75–90 μm and 150–200 μm, respectively; (ii) Sediment particles collected from the Yangtze River with sizes of 48–60 μm, 75–90 μm and 120–150 μm, respectively. The friction coefficients and wear volumes as well as surface morphology were measured. It was found that NBR worn by SiO2 particles was worse than that by the sediment within a certain particle size range. On the other hand, the particle sizes exhibited significant effects on the tribological properties. As the particle size increased, the largest wear volume of NBR occurred at particle size of 75–90 μm, While the friction coefficient grew firstly and then fell down, and reached its maximum at particle size of 48–60 μm. Additionally, the friction coefficient demonstrated a negative correlation with sliding speed regardless of the sediment type and particle size. The particle sizes were prevented from flowing into the friction pair as applied load increased. In conclusion, this research offers a great insight for designing water-lubricated bearings.

Acoustic doppler velocimeter backscatter for suspended sediment measurements: Effects of sediment size and attenuation

Use of backscatter output from a 10-MHz acoustic Doppler velocimeter (ADV) for quantifying suspended sediment concentration was investigated in a laboratory setting. The ADV was immersed in a 125-liter solid polycarbonate circulation tank in which known concentrations of non-cohesive quartz sediments (63–500 µm size range) were mixed in freshwater to obtain homogeneous solutions. Six different size fractions under a wide range of concentration conditions up to 10 kgm−3 were used in the tests. Empirical relations between the acoustic backscatter strength and concentration for each sediment size fraction revealed that there are size-dependent upper and lower bounds on measurable concentrations. Above or below an optimum number of particles in suspension, the performance degrades due to insufficient scatterers which results in a lower bound, and high acoustic attenuation which results in an upper bound on concentration. Both upper and lower bounds increased with increasing sediment concentration, providing, in general, a wider applicability range for larger particles. The range of measurable conditions was broad enough to make the approach useful for sand sizes and concentrations commonly encountered in nature. Effect of sound attenuation was also examined in detail by correcting the acoustic backscatter for transmission losses due to spreading, absorption of energy by water and attenuation due to suspended sediments. The results showed that the effect of transmission losses varies significantly depending on sediment size and concentration, which especially becomes important at high concentrations. This is the first time this effect is quantified to show the direct impact of signal attenuation on suspended sediment measurements using an ADV.

Effect of sediment size on damage caused by cavitation erosion and abrasive wear in sediment-water mixture

Damage caused by cavitation erosion and abrasive wear is a significant problem for hydraulic machinery in rivers with high concentrations of sediment. In this study, experiments are performed using a vibratory apparatus and a custom-made particle-moving device. The specimens are ASTM 1045 carbon steel, and sediment particles with mean diameters of 0.026–0.531mm are mixed in water at concentrations of 25kg/m3, 50kg/m3, and 85kg/m3. Experimental results demonstrate that damage is indeed exacerbated with increasing sediment sizes. However, when the size of sediment particles is smaller than a critical number (Dc), the damage caused by the sediment-water mixture is slightly less than the cavitation damage caused by sediment-free water; furthermore, for this small sediment, the damage decreases as the concentration increases. The critical size for the cases in this study is approximately 0.035–0.048mm. The viscosity of the mixture is likely a key factor to this phenomenon because the viscosities of mixtures with sediment smaller than the critical size increase as the sediment size decreases or the concentration increases. Experiments with mixtures with two sediment sizes further demonstrate that smaller sediment can inhibit the damage by cavitation.

Sediment Size Effects in Acoustic Doppler Velocimeter-Derived Estimates of Suspended Sediment Concentration

Backscatter output from a 10 MHz acoustic Doppler velocimeter (ADV) was used to quantify suspended sediment concentrations in a laboratory setting using sand-sized particles. The experiments included (a) well-sorted sand samples ranging in size from 0.112 to 0.420 mm, obtained by the sieving of construction sand, (b) different, known mixtures of these well-sorted fractions, and (c) sieved natural beach sand with median sizes ranging from 0.112 to 0.325 mm. The tested concentrations ranged from 25 to 3000 mg•L−1. The backscatter output was empirically related to concentration and sediment size, and when non-dimensionalized by acoustic wavelength, a dimensionless sediment size gradation coefficient. Size-dependent upper and lower bounds on measurable concentrations were also established empirically. The range of measurable conditions is broad enough to make the approach useful for sand sizes and concentrations commonly encountered in nature. A new method is proposed to determine concentrations in cases of mixed-size sediment suspensions when only calibration data for well-sorted constituent sands are available. This approach could potentially allow better estimates when the suspended load is derived from but is not fully representative of the bed material, and when the size characteristics of the suspended material are varying in time over the period of interest. Differences in results between the construction and beach sands suggest that sediment shape may also need to be considered, and point to the importance of calibrating to sediments encountered at the site of interest.

Numerical Study for Near-Bed Variables in Velocity-Skewed Oscillatory Sheet Flow Transport

The near-bed sediment concentration and vertical sediment flux are important in sediment transport mechanics, but they are known much less than the horizontal sediment flux, especially for fine sediment in unsteady flows. A developed two-phase model is applied to study the near-bed sediment concentration, vertical sediment flux, and the relevant total sediment amount for the velocity-skewed oscillatory sheet flow transport. With the sediment concentration hindered fall velocity, the classical reference concentration formulas conducted by Engelund and Fredsoe (1976) and Zyserman and Fredsoe (1994) are utilized for the comparison with the two-phase model and illustration of the phase-lag and sediment size effects in near-bed sediment concentration and vertical sediment flux. The concentration and vertical flux predicted by the two-phase model agree well with experimental data and are better than empirical formulas. Furthermore, the sediment size effect for pick-up flux function over starved bed is shown to be quite different from that containing sufficient sediment in oscillatory flows.

Sediment size effects on rip channel dynamics

Field observations indicate that both wave conditions and sediment characteristics exert the controlling effects on the beach states and determine the development of rip channel system. Although the role of wave conditions on the rip channel dynamics has been extensively studied, little attention has been paid to the effects of sediment characteristics. In this paper, we use a nonlinear morphodynamic model, XBeach, to investigate the impact of grain size on the formation and nonlinear evolution of rip channels under the condition of uniform sediments. We find that the grain size can affect a number of aspects of rip channel dynamics. With increasing grain size, both longshore migration speed and growth rate decrease significantly, while the response and saturation times increase. On the other hand, the influence of grain size on the geometrical properties of the rip channel seems to be much less pronounced, as the wavelength of the channels hardly changes and the three-dimensionality features only vary slightly. The “global analysis” method is applied to investigate the mechanism underlying the variations of growth rate and migration speed for varying sediment size. The calculations reveal that these variations are mainly caused by the amount of sea bed sediments being stirred up which is clearly grain-size-dependent. Quantitative relationships between predicted rip channel characteristics, sediment grain size and the hydrodynamic conditions are tentatively established, which is amendable to improvement by extending the analysis to other or more general situations.

Effect of sediment size on bioleaching of heavy metals from contaminated sediments of Izmir Inner Bay

The effect of sediment size on metals bioleaching from bay sediments was investigated by using fine (< 45 μm), medium (45–300 μm), and coarse (300–2000 μm) size fractions of a sediment sample contaminated with Cr, Cu, Pb, and Zn. Chemical speciation of the metals in bulk and size fractions of sediment were studied before and after bioleaching. Microbial activity was provided with mixed cultures of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. The bioleaching process was carried out in flask experiments for 48 days, by using 5% (W/V) of solid concentration in suspension. Bioleaching was found to be efficient for the removal of selected heavy metals from every size fraction of sediments, where the experiments with the smaller particles resulted in the highest solubilization ratios. At the end of the experimental period, Cr, Cu, Pb and Zn were solubilized to the ratios of 68%, 88%, 72%, and 91% from the fine sediment, respectively. Higher removal efficiencies can be explained by the larger surface area provided by the smaller particles. The changes in the chemical forms of metals were determined and most of the metal releases were observed from the reducible and organic fractions independent from grain size. Higher concentrations were monitored in the residual fraction after bioleaching period, suggesting they are trapped in this fraction, and cannot be solubilized under natural conditions.

Hysteresis in suspended sediment to turbidity relations due to changing particle size distributions

[1] Turbidity (T) is the most ubiquitous of surrogate technologies used to estimate suspended-sediment concentration (SSC). The effects of sediment size on turbidity are well documented; however, effects from changes in particle size distributions (PSD) are rarely evaluated. Hysteresis in relations of SSC-to-turbidity (SSC∼T) for single stormflow events was observed and quantified for a dataset of 195 concurrent measurements of SSC, turbidity, discharge, velocity, and volumetric PSD collected during five stormflows in 2009–2010 on Yellow River at Gees Mill Road in metropolitan Atlanta, Georgia. Regressions of SSC-normalized turbidity (T/SSC) on concurrently measured PSD percentiles show an inverse, exponential influence of particle size on turbidity that is not constant across the size range of the PSD. The majority of the influence of PSD on T/SSC is from particles of fine silt and smaller sizes (finer than 16 µm). This study shows that small changes in the often assumed stability of the PSD are significant to SSC∼T relations. Changes of only 5 µm in the fine silt and smaller size fractions of suspended sediment PSD can produce hysteresis in the SSC∼T rating that can increase error and produce bias. Observed SSC∼T hysteresis may be an indicator of changes in sediment properties during stormflows and of potential changes in sediment sources. Trends in the PSD time series indicate that sediment transport is capacity limited for sand-sized sediment in the channel and supply limited for fine silt and smaller sediment from the hillslope.

Effect of Sediment Size in Hydraulic Turbine Material: A Case Study of Roshi Khola in Nepal

Siltation problem in Nepal is major and challenging in hydropower development. It degrades the reservoir capacity and hydraulic turbines’ efficiency. Many researches have been carried out in this field and have proven sand as major substance that erodes the turbine material, but only few researches have accounted every parameters of sand on degradation of hydraulic turbines. This paper accounts size of sediments important parameter that has direct impact on turbine material. Sediment size impact has been studied firstly by characterizing size into six layered using sieve analyzer and testing its impact using high velocity test rig at Kathmandu University. Sand samples from 20 different stations of Roshi river were collected and tested on turbine material 18Cr4Ni. It found that greater micron sizes of sediments have great impact was than relatively smaller ones. It is depicted that 300-400 micron size sediment, have highest impact with weight loss of 0.022 milligram, 212-300 micron size has 0.013 milligram weight loss, 90-212 micron size has 0.012 and below 90 micron sizes have 0.0075 milligram of weight loss. Nepal Journal of Science and Technology Vol. 13, No. 2 (2012) 129-132 DOI: http://dx.doi.org/10.3126/njst.v13i2.7725

Preliminary Results: Release of Metals from Acid-Mine Drainage Contaminated Streambed Sediments under Anaerobic Conditions

Many miles of streams in the western U.S are contaminated with acidmine drainage (AMD) from abandoned metal mines. Treatment of these streams may include removal of the existing sediments, with subsequent burial (e.g. in a repository). Burial of previously aerobic sediments may result in release of metals through multiple processes, including reductive-dissolution of metal oxyhydroxides, with concurrent release of previously sorbed metals. This paper discusses preliminary results from a laboratory study examining the release of Cd, Cu, Fe, Mn, and Zn from aerobic streambed sediments collected from an AMDimpacted stream (North Fork Clear Creek, CO). The pH, Eh, and metal release were monitored over twenty-eight days in an anaerobic chamber from sediment slurries prepared using filtered stream water. Additionally, the effect of sediment size was examined by using two size fractions: 2 mm to 63 μm and less than 63 μm. Dissolved Cd, Cu, Fe, and Mn were released and re-sequestered over time from both sediment size fractions. Dissolved Zn, however, demonstrated a continual decrease in concentration over time, relative to the concentration present in the stream water used to prepare the slurries. Releases of Cd, Cu, Fe, and Mn varied for each of the size fractions over time. In the case of Cd and Cu, no further release was observed in either size fraction after one week. Releases of Fe and Mn declined after the first week in the smaller size fraction and after the second week in the larger size fraction. Because of the presence of SO4 in the stream water, it is hypothesized that the metals were re-sequestered as sulfide precipitates. Future studies will include replication, measurement of sulfur species, and the use of surface chemical techniques to examine the solids for the presence of metal oxides and sulfides. Additional

BURROWING AND SWASH BEHAVIOR OF THE PACIFIC MOLE CRAB HIPPA PACIFICA (ANOMURA, HIPPIDAE) IN TROPICAL SANDY BEACHES

To investigate factors associated with the distribution of an intertidal crab, Hippa pacifica Dana, which is common in the swash zones of reflective subtropical and tropical sandy beaches, we examined the effect of sediment size on burrowing rates of a wide size range of individuals. We also examined aspects of swash behavior in field conditions, including drift time, distance and velocity of individual crabs. Hippa pacifica burrowed very rapidly (in 0.3 to 2.7 s) in laboratory and field conditions. Burrowing time increased significantly with increasing crab size in all sediments tested but did not differ between male and female crabs nor between ovigerous and non-ovigerous crabs. There were no significant differences in burrowing times among five sediments ranging from very fine sand to gravel, suggesting that this species is a sediment generalist whose distribution is not limited by sediment size. Individual crabs released in the swash zone of a reflective beach oriented, swam and/or drifted for 1.2 to 3.8 seconds before contacting substrate and burrowing. Drift times were similar for all sizes of crabs. However, drift distance (ranging 0.10 m to 1.16 m) and drift velocity (ranging 0.11 m/s to 0.45 m/s), decreased with increasing crab size, suggesting a possible mechanism for size-specific zonation patterns reported in this species. Burrowing times observed in H. pacifica in this study were faster than reported for other sandy beach macrofauna, including tropical forms. This burrowing ability, in combination with the characteristics of substrate generalist and well-oriented swash behavior, appear to be a key to the ability of H. pacifica to inhabit reflective coarse sand beaches.

The transfer of uranium from sediment to water along Jucar River, Spain

The effect of sediment size, pH, temperature and conductivity on the transfer of uranium from sediment to water has been studied. The uranium concentration and the234U/238U,235U/238U activity ratios were measured in water, sediments and suspended matter sampled from Jucar River, using low level alpha-spectrometry. Distribution factors were obtained from these measurements. A more detailed sampling was done in the neighbourhood of the Cofrentes Nuclear Plant (Valencia, Spain). Total uranium activity,234U/238U activity ratio and distribution factors for234U and238U were found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes.

Effect of sediment size on area of influence during groundwater remediation by air sparging: a laboratory approach

Air sparging is a groundwater remediation technique, in which organic contaminants volatilize into air as it rises from the saturated to vadose zone. An unknown has been the relationship between sediment size and area affected by air. Laboratory experiments were performed on sediments to determine the area affected by air as a function of grain size. For average grain sizes of 1.1 and 1.3-mm diameter, air flow occurs in discrete meandering channels, with a maximum area of sediment column affected of 13%/m2 for 1.1-mm and 14%/m2 for 1.3-mm sediments. For average grain sizes of 1.84, 2.61 and 4.38-mm diameter, air flow is pervasive, forming a symmetrical cone of influence around the injection point. Maximum areas affected are15%/m2 for 1.84-mm, 25%/m2 for 2.61-mm, and 9%/m2 for 4.38-mm sediments. Optimal sites for air sparging, may be those with grain diameters between about 2–3 mm.

Effect of Texture, Rainfall and Slope on Rainfall Interrill Sediment Transport

Experiments were conducted with rainfall intensities of 45.0 and 140.0 mm/hr at slopes of 2, 9 and 20 per cent to separate the dominant effect of rainfall intensity on sediment transport capacity. The effect of sediment size on rainintensity contribution to unit sediment transport capacity was also investigated. Regression models for rain-intensity contribution to unit sediment transport capacity Y were developed including median particle diameter X of sediment as an additional independent variable. The constants of power relationships of the form Y ≡ aXb were found to vary with the median particle diameter of the soil.

EFFECT OF TEXTURE, FLOW, AND SLOPE ON INTERRLLL SEDIMENT TRANSPORT

ABSTRACT Experiments were conducted on a uniform interrill flow produced without rainfall to study the sediment transport capacity of flow. The effects of sediment size on interrill sediment transport capacity was investigated. The coefficients of a power relationship of the form Y=aX*^ were observed to vary with median particle diameter of soil. Regression model was developed including the sediment size as additional independent variable.

Depositional process and alluvial fan‐drainage basin morphometric relationships near banff, Alberta, Canada

AbstractTwo distinct types of alluvial fans occur in the Bow River Valley, Alberta, Canada: fluvially dominated and debris flow dominated. Large, gently sloping fans dominated by fluvial processes are associated with large and less rugged drainage basins, and small rugged basins have produced small, steep fans dominated by debris flow processes. Quantitative analysis demonstrates that strong fan‐basin morphometric relationships occur despite a short fan history.Statistical analysis of fan area‐basin area relationships indicate that debris flow fan areas do not increase in size as quickly as contributing basins. The relationship of fluvial fan area to basin area is not statistically significant. However, this relationship is probably affected by fan erosion. Examination of fan slope to basin ruggedness relationships indicates that fan slope increases more rapidly than basin ruggedness for both fan types. This is likely related to non‐linear discharge and sediment size effects on fluvial fans, and reworking of larger fan surfaces by fluvial processes on debris flow fans.

THE VORTEX SCOUR MECHANISM AT BRIDGE PIERS.

The paper examines the problem of localised scour by analysing the cause of the scouring process itself. The scouring vortex which develops because of an upstream flow separation ahead of the pier, and which is considered to be the basic mechanism operating at bridge piers, is subjected to detailed experimental analysis. The scour criterion is experimentally hypothesized, the scour depth is related to some of the basic characteristics of the scouring vortex and the effect of sediment size is discussed. The data of other investigators are analysed on the basis of the criterion established in the study. Many of the available field data are also analysed. (TRRL)