Suspended Sand Research Articles

Microplastics elutriation system: Part B: Insight of the next generation

Elutriation is an efficient process for extracting microplastics. The development of a numerical model has shown the need for optimizing aspects of the design of the actual elutriation protocol as well as the dimensioning of the column to increase its efficiency. The study aims to propose new dimensioning data and protocol elements for designing an efficient column. Using a numerical model, the filling velocity was calculated as a function of the size and the density of the particles to prevent sand suspension. The sieving protocol was adapted to increase the density limit for the extraction of plastic particles from 1460 to >1800 kg·m−3. The durations of the elutriation and the column height were calculated to improve the control of the particle suspension. These results contribute to the development of the next generation of elutriation system and will accelerate the study of plasticome in the context of sandy sediments.

Sands Escaping Haeundae Beach

Lee, H.J.; Do, J.-D.; Kim, S.S., and Lim, H.S., 2018. Sands Escaping Haeundae Beach. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1006–1010. Coconut Creek (Florida), ISSN 0749-0208.Haeundae Beach has been hypothesized to lose sands from the nearshore of the western extremity of its pocket-beach system with a tidal range of 0.5 – 1.2 m. To test the hypothesis, a measurement station was located in this area to observe a suspended transport of sands near the seabed. The hydrodynamic measurements included water level, wave, currents and suspended sediment concentration with a benthic tripod for longer than one month of the 2013–2014 winter. In addition, a Telemac-2D tide model was run to simulate tidal currents for the same period of time as the measurements. A total of 6 events of two tidal cycles each were selected and analyzed to represent a variety of combinations of tidal phase, wave energy and wave direction. The results show that the suspended sand transport occurred continuously and was controlled predominantly by ebb-dominant tidal currents. Thus it was always directed offshore. Waves higher than 1 m sporadically took place during the measurements. However, high waves could just reorient the offshore suspended sand transport from obliquely to normal to the shoreline. This is because they created residual currents flowing roughly parallel to the shoreline. Neither offshore wave direction nor tidal phase evidently influenced the characteristics of residual currents. Therefore, the escape of the Haeundae sand from the area of interest has been proven to occur year round intrinsically by tidal currents. Waves intermittently contribute much to enhancing the suspended sand flux offshore by vigorous resuspension processes.

Observational data set: Sand suspension and transport during barrier island inundation

Observational data set: Sand suspension and transport during barrier island inundation

Estimation of sand suspension in a secondary channel of an alpine river

In this paper, we present some first attempt to measure graded suspension of sands in an alpine river. It is a real challenge to measure gradedsuspensions of sands in such dynamic rivers. Specific measurements of the graded suspension in the middle of a secondary channel were attempted using a sampler that allows simultaneous sampling at three different elevations (5 cm, 10 cm, and 20 cm) above the bed. Very large concentrations (up to C = 40 g/l) of fine sediments in suspension were measured during a dam reservoir flushing event. It included large amounts of sand (from 10 to 60% of the measured concentration). A substantial graded suspension of sand was measured even for relatively low velocities. Sand fluxes estimates for varying bed shear stresses during the event are discussed. In particular, based on the measured bed shear stress, a semi-empirical formula developed for sand suspension is applied to test its ability to predict sand flux in alpine rivers. The sensibility of such formula to the grain size is very high whereas large uncertainties exist in the measurement (d50 varies from 0.1 to 0.3 mm depending on the sample), which makes its application difficult at the moment.

Principles of designing well separators

Vortex motion is effectively used in the development of wellbore filter designs. Further development of the principles of such design requires the development of some principles based on experimental observations and computer modeling. A constructive analogy between the wellbore filter and the Ranque vortex tube is shown. The results of experimental and theoretical studies of the vortex tube are applied as a basis for designing a well separator. Recommendations are formulated regarding the radius of the inner branch pipe of the downhole filter placed in the body. Approaches are discussed when choosing the length of the working section of the well separator, as well as the choice of the shape of the input cochlear, the size of the outlet diaphragm, and the shape of the sand suspension window.

Sand dynamics in the Mekong River channel and export to the coastal ocean

Two field campaigns were conducted in the tidal and estuarine reach of the Sông Hậu distributary of the Mekong River to explore the dynamics of sand transport and export to the coastal ocean. This study examines variations in suspended sand concentration and net flux of suspended and bedload sand with respect to changes in discharge between the October 2014 high discharge and March 2015 low discharge season. Isokinetic measurements of suspended sand were used to calibrate a larger dataset of LISST profiles to report suspended sand mass concentrations. During the high discharge season, ebb and flood currents are a primary control on suspended sand concentrations. Ebb tidal flows are more capable of sand transport than flooding flows, due to river discharge augmenting tidal currents. Sand in suspension is primarily derived locally from bed material sand. Bedform transport estimates were limited, but suggest that bedload sand transport is less than 10% of net suspended sand flux. Very low concentrations of suspended sand sediment are found during the low discharge season. These low concentrations are likely caused by (1) a reduction in maximum ebb tide shear stresses associated with less freshwater input, and (2) mud mantling in the bed associated with upstream migration of estuarine circulation, that inhibits local sourcing (resuspension) of bed sand. Results of the observational study were used to calibrate a numerical model of annual sand flux to the ocean from all distributaries of the Mekong River. Annual sand export is estimated at 6.5 ± 1.6Mtyr−1. The Định An subdistributary accounts for 32% of this total while the smaller Trần Đề subdistributary accounts for only 9%.

Analysis and numerical modeling of the flow and sand dynamics in the lower Song Hau channel, Mekong Delta

Two- and three-dimensional Delft3D Flow and Morphology models were constructed for the lower Song Hau distributary channel of the Mekong River in Vietnam to provide insights into the hydrodynamics and sand transport of the channel system. The models were calibrated and validated with data for observed water level, water discharge, velocity, and suspended-sand concentration during the high- and low-flow seasons of 2014 and 2015. The water and sand budgets of the Dinh An and Tran De channels, the two sub-distributaries of the lower Song Hau channel, were calculated, showing that ~73% of the fluvial water discharge and ~90% of suspended sand were transported through the Dinh An channel, while the rest was transported through the Tran De channel in the high-flow season. In the low-flow season, the total fluvial water discharge was < 20% of that in the high-flow season; and ~96% of it was transported through the Dinh An channel and the rest was transported through the Tran De channel. Sand was transported from channels into the ocean in both the Dinh An and Tran De channels during the high-flow season, but from the ocean into the two channels during the low-flow season. The reversed sand flux from ocean into river channels during low-flow season was not observed in field studies. The different behaviors between models and field observations might be caused by the absence of baroclinic effects in the model set up. The Dinh An channel was found to be dominated by ebb tide, in favor of transporting water and sediment to the ocean, and the Tran De channel was dominated by flood tide. In the high-flow season, the residual currents were directed toward the ocean for both the Dinh An and Tran De channels. In the low-flow season, the magnitude of the residual currents decreased in the river channels. Under these conditions, the residual-current direction changed to be ambiguous in the Tran De channel, but remained seaward in the Dinh An channel. The low fluvial discharge combined with strong tides under very low-flow conditions can probably generate a net clockwise water circulation between the Dinh An and Tran De channels, which transports water from the ocean to the river through the Tran De channel, then back into the ocean through the Dinh An channel. The clockwise circulation pattern is likely to influence the channel evolution and impact saltwater intrusion issue in the lower Song Hau channel.

Enhanced Fenton-like degradation of TCE in sand suspensions with magnetite by NTA/EDTA at circumneutral pH.

The present study investigated the degradation of trichloroethylene (TCE) in sand suspensions by Fenton-like reaction with magnetite (Fe3O4) in the presence of various chelators at circumneutral pH. The results showed that ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) greatly improved the rate of TCE degradation, while [S,S]-ethylenediaminedisuccinic acid (s,s-EDDS), malonate, citrate, and phytic acid (IP6) have minimal effects on TCE degradation. Quenching tests suggested that TCE was mainly degraded by hydroxyl radical (HO·) attack, with about 90% inhibition on TCE degradation by the addition of HO· scavenger 2-propanol. The presence of 0.1-0.5% Fe3O4/sand (w/w) contributed to 40% increase in TCE degradation rates. In particular, the use of chelators can avoid high concentrations of H2O2 required for the Fenton-like reaction with Fe3O4, and moreover improve the stoichiometric efficiencies of TCE degradation to H2O2 consumption. The suitable concentrations of chelators (EDTA and NTA) and H2O2 were suggested to be 0.5 and 20mM, respectively. Under the given conditions, degradation rate constants of TCE were obtained at 0.360h-1 with EDTA and 0.526h-1 with NTA, respectively. Enhanced degradation of TCE and decreased usage of H2O2 in this investigation suggested that Fenton-like reaction of Fe3O4 together with NTA (or EDTA) may be a promising process for remediation of TCE-contaminated groundwater.

The effect of sand particle concentrations on the vibratory cavitation erosion

Comparisons between the cavitation erosion (CE) in pure water and cavitation-silt erosion (CSE) in sand suspensions were carried out experimentally on 304 stainless steel. The damage was evaluated by mass loss, scanning electron microscopy, roughness and surface residual stress. The effects of the particles and the sand concentrations on the CSE were analyzed. The results show that cumulative mass loss decreases with increasing sand concentration until the sand concentration exceeds 3wt%. A center region and the periphery of the test surface are dominated by particles erosion wear and CE respectively at lower sand concentrations. While the entire surface is covered by the particles erosion wear at higher sand concentrations. However, the roughness declines with increasing sand concentration in both regions. The damage mechanism is also proposed based on the comprehensive analyses.

Numerical simulation of sand load applied on high-speed train in sand environment

High-speed train running in the sand environment is different from the general environment. In the former situation, there will be sand load applied on high-speed train(SLAHT) caused by sand particles hitting train surface. This will have a great impact on the train stability, running drag and surface corrosion. Numerical simulation method of SLAHT in sand environment is studied. The velocity and mass flow rate models of saltation and suspension sand particles and the calculation model of SLAHT caused by sand particles hitting train surface are established. The discrete phase method is adopted for numerical simulating the process of saltation and suspension sand particles moving to train surface and generating sand load. By comparison with the field tests, the numerical simulation reliability is analysed. The theoretical formula of SLAHT changing with cross-wind and train speed is proposed. SLAHT changing law is analyzed. Research results indicate that SLAHT changing with cross-wind and train speed is a quadratic relationship. When train speed is constant, SLAHT increases quadratically with cross-wind speed improvement. When cross-wind speed is constant, SLAHT increases quadratically with train speed improvement.

Effect of Sediment Suspensions on Seawater Salinity Assessments

The absolute salinity of seawater can be assessed by conductivity measurements and the calculation of a practical salinity, or by density measurements. The effect of low concentrations of suspended particulate matter on these measurements has never been documented, but the theories developed to explain and predict the conductivity of sediments show clearly that, under an electrical field, they interact with the ionic composition of seawater. Moreover, it can be easily shown that adding any quantity of particles has an effect on the measured density of a seawater sample. This publication describes a measurement method settled to measure the effect of sediment particles on seawater conductivity and proposes relations for explaining and predicting the observed phenomena. It also describes the effects of particles on density measurements. The results obtained show that the errors on the measured conductivities (and practical salinities) caused by sand in suspensions, are less than 0.001 mS cm^-1 (on average) with concentrations encountered in oceans fields, but that these cannot be neglected in some coastal areas. The amplitude of the measurement noise leaded by particles circulation in the conductivity cell exceeds 0.002 in salinity beyond 200 mg l^-1. For density measurements, the threshold for keeping the error inferior to the uncertainty of 0.004 kg m^-3 usually obtained with vibrating tube densimeters, is much lower, 9 mg l^-1, and close to the concentrations encountered in the open ocean.

Intrawave sand suspension in the shoaling and surf zone of a field‐scale laboratory beach

AbstractShort‐wave sand transport in morphodynamic models is often based solely on the near‐bed wave‐orbital motion, thereby neglecting the effect of ripple‐induced and surface‐induced turbulence on sand transport processes. Here sand stirring was studied using measurements of the wave‐orbital motion, turbulence, ripple characteristics, and sand concentration collected on a field‐scale laboratory beach under conditions ranging from irregular nonbreaking waves above vortex ripples to plunging waves and bores above subdued bed forms. Turbulence and sand concentration were analyzed as individual events and in a wave phase‐averaged sense. The fraction of turbulence events related to suspension events is relatively high (∼50%), especially beneath plunging waves. Beneath nonbreaking waves with vortex ripples, the sand concentration close to the bed peaks right after the maximum positive wave‐orbital motion and shows a marked phase lag in the vertical, although the peak in concentration at higher elevations does not shift to beyond the positive to negative flow reversal. Under plunging waves, concentration peaks beneath the wavefront without any notable phase lags in the vertical. In the inner‐surf zone (bores), the sand concentration remains phase coupled to positive wave‐orbital motion, but the concentration decreases with distance toward the shoreline. On the whole, our observations demonstrate that the wave‐driven suspended load transport is onshore and largest beneath plunging waves, while it is small and can also be offshore beneath shoaling waves. To accurately predict wave‐driven sand transport in morphodynamic models, the effect of surface‐induced turbulence beneath plunging waves should thus be included.

Large‐eddy simulation of wave‐breaking induced turbulent coherent structures and suspended sediment transport on a barred beach

AbstractTo understand the interaction between wave‐breaking induced turbulent coherent structures and suspended sediment transport, we report a Large‐Eddy Simulation (LES) study of wave‐breaking processes over a near‐prototype scale barred beach. The numerical model is implemented using the open‐source CFD toolbox, OpenFOAM®, in which the incompressible three‐dimensional filtered Navier‐Stokes equations for the water and air phases are solved with a finite volume scheme. A volume of fluid (VOF) method is used to capture the evolution of the water‐air interface. The numerical model is validated with measured free surface elevation, turbulence‐averaged flow velocity, turbulent intensity, and for the first time, the intermittency of breaking wave turbulence. Simulation results confirm that as the obliquely descending eddies (ODEs) approach the bottom, significant bottom shear stress is generated. Remarkably, the collapse of ODEs onto the bed can also cause drastic spatial and temporal changes of dynamic pressure on the bottom. By allowing sediment to be suspended from the bar crest, intermittently high sediment suspension events and their correlation with high turbulence and/or high bottom shear stress events are investigated. The simulated intermittency of sediment suspension is similar to previous field and large wave flume observations. Coherent suspension events account for only 10% of the record but account for about 50% of the sediment load. Model results suggest that about 60%∼70% of coherent bottom stress events are associated with surface‐generated turbulence. Nearly all the coherent sand suspension events are associated with coherent turbulence events due to wave‐breaking turbulence approaching the bed.

Cross-shore sand transport by infragravity waves as a function of beach steepness

Two field data sets of near-bed velocity, pressure, and sediment concentration are analyzed to study the influence of infragravity waves on sand suspension and cross-shore transport. On the moderately sloping Sand Motor beach (≈1:35), the local ratio of infragravity wave height to sea-swell wave height is relatively small (HIG/HSW 0.4), most sand is suspended during negative infragravity velocities, and qIG is offshore directed. The infragravity contribution to the total sand flux is considerably larger and reaches up to ≈60% during energetic conditions. On the whole, HIG/HSW is a good indicator for the infragravity-related sand suspension mechanism and the resulting infragravity sand transport direction and relative importance.

Fluxes of nutrients and trace metals across the sediment-water interface controlled by sediment-capping agents: bentonite and sand.

The effect of bentonite and sand, as natural capping agents, on the fluxes of nutrients and trace metals across the sediment-water interface was studied through sediment incubation, and the ecotoxicological impact was assessed by using Daphnia magna. Bentonite and sand were layered on the sediment at 15, 75, and 225mgcm(-2), and the concentration of cations, nutrients, and trace metals was measured. Sediment incubation showed that bentonite reduced the N flux but increased the P flux as a result of dissolution of non-crystalline P from bentonite, while sand slightly decreased the N fluxes but not the P flux. The concentration of Na increased in the overlying water with increasing application rates of bentonite, while that of Ca decreased. However, regardless of the rate of sand application, concentrations of all cation species remained unchanged. The concentration of As and Cr increased with bentonite application rate but decreased with sand. Both capping materials suppressed fluxes of Cd, Cu, Ni, and Zn compared to control, and the extent of suppression was different depending on the trace metal species and capping agents used. During sediment incubation, the survival rate of D. magna significantly decreased in bentonite suspension but began to decrease at the end in sand suspension. Sediment capping of mildly polluted sediments by using bentonite and sand lowered the level of nutrients and trace metals. However, unexpected or undesirable side effects, such as influxes of P and As from bentonite to the overlying water and a possibility of toxic impacts to aquatic ecosystems, were observed, suggesting that capping agents with an adequate assessment of their side effects and toxicity should be predetermined for site-specific sediment management strategies.

Rheological characteristics of mixed kaolin–sand slurry, impacts of pH, temperature, solid concentration and kaolin–sand mixing ratio

Significant amount of slurry waste is produced from mineral processing plants globally constituting high levels of both kaolin and sand in aqueous suspension. Large quantities of slurry and mine tailings require efficient handling, transportation and storage system. The transportation and treatment of kaolin–sand slurry is dependent on its rheological behaviour which is a function of temperature, total solid concentration and pH. In this study, the effects of total solid concentration, pH and temperature on rheological behaviour of kaolin–sand mixture were investigated. These parameters were varied to analyse the viscosity, yield stress, flow index and shear force requirements of the mixed kaolin–sand suspension as a function of these varying parameters. Experimental rheological investigation conducted on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system showed that the kaolin–sand mixture suspension is shear thickening in nature. The shear stress-rate rheograms for the kaolin–sand suspension can be modelled by the Herschel–Bulkley model with high levels of accuracy for pH range of 4–11, temperature range of 20–50 °C and solid concentration of 5–50 %. Solid concentration of the suspension was found to significantly affect the rheological behaviour of the mixture where higher kaolin–sand slurry concentration resulted in greater viscosity and the trend becoming less predictable for solid concentration greater than 50 % by weight. pH was another factor affecting the rheological behaviour of kaolin–sand slurry. pH of 3 or less resulted in the dramatic increase of viscosity of the suspension possibly due to the isoelectric point of the mixture system found between pH of 3 and 4.

Effect of phase composition of natural quartz raw material on characterization of microfiltration ceramic membranes

The results of development of multi-layer ceramic membranes on the basis of natural quartz raw material from Mongolia are presented. The influence of the phase composition and temperature of calcination on the porosity, morphology and mechanical strength of large-porous ceramic support obtained by the method of isostatic pressing was studied. It was established that multi-layer ceramic membranes obtained by the application of water suspension of high-disperse quartz sand of Mongolia and alumosilicate binder with the addition of 15–35wt% of quartz are characterized by optimal properties. The developed tubular ceramic membranes with the average pore size 5.3µm, coefficient of air permeability (4.17–4.41)×10−13m2, productivity by water 46.3–48.0m3/(h×m2×bar) and mechanical strength 2.27–2.53MPa are perspective for wide use in microfiltration processes.

Highstand shelf fans: The role of buoyancy reversal in the deposition of a new type of shelf sand body

Although sea-level highstands are typically associated with sediment-starved continental shelves, high sea level does not hinder major river floods. Turbidity currents generated by plunging of sediment-laden rivers at the fluvial-marine interface, known as hyperpycnal flows, allow for cross-shelf transport of suspended sand beyond the coastline. Hyperpycnal flows in southern California have deposited six subaqueous fans on the shelf of the northern Santa Barbara Channel in the Holocene. Using eight cores and nine grab samples, we describe the deposits, age, and stratigraphic architecture of two fans in the Santa Barbara Channel. Fan lobes have up to 3 m of relief and are composed of multiple hyperpycnite beds ∼5 cm to 40 cm thick. Deposit architecture and geometry suggest the hyperpycnal flows became positively buoyant and lifted off the seabed, resulting in well-sorted, structureless, elongate sand lobes. Contrary to conventional sequence stratigraphic models, the presence of these features on the continental shelf suggests that active-margin shelves may locally develop high-quality reservoir sand bodies during sea-level highstands, and that such shelves need not be solely the site of sediment bypass. These deposits may provide a Quaternary analogue to many well-sorted sand bodies in the rock record that are interpreted as turbidites but lack typical Bouma-type features.

Conversion of electro-optical signals to sediment concentration in a silt–sand suspension environment

The Optical Backscatter Sensor (OBS) has been widely used to measure suspended sediment concentration in both field and laboratory conditions, even though it is very sensitive to many factors. The most significant factor suggested is the grain size. In order to enhance the quality of OBS data, an improved approach is proposed, based on the “mixture of linear component response” method (Green and Boon III, 1993) to account for the effect of grain size. In addition to an original sediment sample, which commonly serves as a single calibration material, an accompanying sediment sample is necessary to calibrate OBS sensors. A multi-fraction sediment model is used to predict the grain size distribution in suspension. Compared with existing methods, the improved approach does not require a sieving procedure nor the assumption that the sediment fractions of the calibrated sediment sample exhibit the same sensitivities as those of the suspended sediments. The applicability of our method has been verified by a series of laboratory experiments over silt–sand mixtures. The results show that this method successfully yields continuous concentration profiles, which agree well with the measurements using a suction method. The converted concentrations of the time-averaged OBS measurements by traditional method and by the improved method, respectively, are compared with the suction measurements. The results of linear regression analyses show that the coefficient of determination increases (e.g. from 0.55 to 0.92 for wave–current conditions) and the Root Mean Square Error decreases (e.g. from 0.97 to 0.39 for wave–current conditions). It demonstrates that improved method enhances the quality of OBS conversion. Furthermore, suggestions on selecting the accompanying sediment sample (i.e. on grain size and composition) are given.

Tailoring of wormlike micelles as hydrodynamic drag reducers for gravel-pack in oil field operations

This paper describes a systematic investigation to verify the potential of wormlike micelles (WLMs) as additives to improve gravel-pack operations. This is an important step of the completion operations, in which a sand core along of an oil well is created. WLMs have high potential to reduce the hydrodynamic drag of sand suspensions during the gravel-pack operation. The capability of WLMs to survive in aqueous solution with high salt content and at the temperature of the reservoir was investigated. The screening of the best formulation was carried out in a rheometer under turbulent conditions. Based on the rheological results the best formulations were used to investigate the levels of hydrodynamic drag reduction (HDR) in circuits. The more appropriated WLMs were formed by the combination of commercial surfactants Ethoquad O/12 with Arquad 12–50 and sodium salicylate (NaSal). We also checked the effect of the presence of WLMs on the transportation of sand grains in conditions close to the ones used in gravel-pack operations.