scholarly journals Tidal Variation in Cohesive Sediment Distribution and Sensitivity to Flocculation and Bed Consolidation in An Idealized, Partially Mixed Estuary

2019 ◽  
Vol 7 (10) ◽  
pp. 334 ◽  
Author(s):  
Tarpley ◽  
Harris ◽  
Friedrichs ◽  
Sherwood
Keyword(s):  
Settling Velocity ◽  
Transport Model ◽  
Tidal Flow ◽  
Sediment Concentration ◽  
Tidal Variation ◽  
Model Framework ◽  
Sediment Distribution ◽  
Floc Size ◽  
Size Classes ◽  
Suspended Floc

Particle settling velocity and erodibility are key factors that govern the transport of sediment through coastal environments including estuaries. These are difficult to parameterize in models that represent mud, whose properties can change in response to many factors, including tidally varying suspended sediment concentration (SSC) and shear stress. Using the COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) model framework, we implemented bed consolidation, sediment-induced stratification, and flocculation formulations within an idealized two-dimensional domain that represented the longitudinal dimension of a micro-tidal, muddy, partially mixed estuary. Within the Estuarine Turbidity Maximum (ETM), SSC and median floc diameter varied by a factor of four over the tidal cycle. Downstream of the ETM, the median floc size and SSC were several times smaller and showed less tidal variation (~20% or less). The suspended floc distributions only reached an equilibrium size as a function of SSC and shear in the ETM at peak tidal flow. In general, flocculation increased particle size, which reduced SSC by half in the ETM through increased settling velocity. Consolidation also limited SSC by reduced resuspension, which then limited floc growth through reduced SSC by half outside of the ETM. Sediment-induced stratification had negligible effects in the parameter space examined. Efforts to lessen the computation cost of the flocculation routine by reducing the number of size classes proved difficult; floc size distribution and SSC were sensitive to specification of size classes by factors of 60% and 300%, respectively.

scholarly journals Investigating Suspended-Sediment Transport in a Shallow Lake Using a Three-Dimensional Model

2017 ◽  
Author(s):  
Hong-Ming Liu ◽  
Wen-cheng Liu ◽  
Chih-Yu Chiu
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Shallow Lake ◽  
Suspended Sediment Concentration ◽  
Transport Model ◽  
Three Dimensional ◽  
Sediment Concentration ◽  
Suspended Sediment Transport ◽  
Sediment Distribution ◽  
Mean Current

A three-dimensional, unstructured grid, hydrodynamic and suspended-sediment transport model (i.e., SELFE-SED) was developed to simulate temporal and spatial variations of suspended sediment and was applied to the subtropical subalpine Tsuei-Feng Lake (TFL) of Taiwan. The model was validated with measured water level and suspended‑sediment concentration in 2009, 2010, and 2011. The overall model simulation results are in quantitative agreement with the observational data. The validated model was then applied to explore the most important parameter that affects the suspended-sediment concentration and to investigate the effect of wind stress on the mean current and suspended‑sediment distribution in this shallow lake. Modeling results of sensitivity analysis reveal that the settling velocity is a crucial parameter and erosion rate is less important in the suspended-sediment transport model. Remarkable lake circulation was found based on the strength of wind speed and wind direction. Strong wind would result in higher mean current in the top layer and suspended-sediment distribution in the top and bottom layers. This study demonstrated that the wind stress played a significant influence on mean circulation and suspended-sediment transport in a shallow lake.

On the role of flocculation, hindered settling and sediment-induced damping of turbulence in trapping sediment in estuaries, with focus on the North Passage, Yangtze Estuary

2020 ◽  
Author(s):  
Chenjuan Jiang ◽  
Huib E. de Swart ◽  
Jianan Zhou ◽  
Jiufa Li
Keyword(s):  
Sediment Transport ◽  
Settling Velocity ◽  
Sediment Concentration ◽  
Yangtze Estuary ◽  
Fine Sediment ◽  
Sediment Distribution ◽  
Hindered Settling ◽  
Density Driven Flow ◽  
The North ◽  
Upstream Flow

<p>Many estuaries are characterized by one or more locations where the concentration of fine sediment attains a maximum. The locations and intensities of these estuarine turbidity maxima (ETM) are sensitive to river discharge, tides, depth and sediment properties. In this contribution, results are presented of a width-averaged process-based model that describes tides, residual currents and sediment transport in an estuarine channel. The aim is to quantify the sensitivity of location and intensity of ETM to 1) flocculation and hindered settling of fine sediment and 2) sediment-induced damping of turbulence. The model is applied to the North Passage of the Yangtze Estuary, which is a prototype estuary that undergoes strong variations in environmental conditions. The sediment settling velocity is allowed to vary along the channel due to the effects of flocculation and hindered settling, by parametrizing settling velocity as the function of the subtidal near-bed sediment concentration according to results obtained from laboratory experiments. Sediment-induced turbulence damping is taken into account by parametrizing eddy viscosity and eddy diffusivity coefficients as functions of bulk Richardson number.</p><p>In the flocculation (low concentration) regime, where the settling velocity increases with sediment concentration, the rapid settling of flocs induces larger landward sediment transport due to upstream flow in the lower layer of density-driven flow, leading to a landward shift and intensification of the ETM (with respect to the case of a constant settling velocity). In the hindered settling (high concentration) regime, the settling velocity decreases with bottom concentration. This induces a decrease in upstream sediment transport due to density-driven flow and an increase in seaward sediment transport due to river flow, leading to seaward migration and attenuation of the ETM. In both regimes, sediment-induced damping of turbulence results in stronger upstream flow in the bottom layer of density-driven flow and more vertically stratified sediment distribution, which significantly intensifies the landward sediment transport due to density driven flow, and hence causes a landward shift and intensification of the ETM.</p>

scholarly journals Settling Velocity of Microplastics Exposed to Wave Action

2021 ◽  
Vol 9 (2) ◽  
pp. 142
Author(s):  
Annalisa De Leo ◽  
Laura Cutroneo ◽  
Damien Sous ◽  
Alessandro Stocchino
Keyword(s):  
Laboratory Experiments ◽  
Settling Velocity ◽  
Transport Model ◽  
Stokes Drift ◽  
Inertial Effects ◽  
Sea Waves ◽  
Heavy Particles ◽  
Analytical Formulation ◽  
Simplified Approach ◽  
Remote Areas

Microplastic (MP) debris is recognized to be one of the most serious threats to marine environments. They are found in all seas and oceanic basins worldwide, even in the most remote areas. This is further proof that the transport of MPs is very efficient. In the present study, we focus our attention on MPs’ transport owing to the Stokes drift generated by sea waves. Recent studies have shown that the interaction between heavy particles and Stokes drift leads to unexpected phenomena mostly related to inertial effects. We perform a series of laboratory experiments with the aim to directly measure MPs’ trajectories under different wave conditions. The main objective is to quantify the inertial effect and, ultimately, suggest a new analytical formulation for the net settling velocity. The latter formula might be implemented in a larger scale transport model in order to account for inertial effects in a simplified approach.

Extending the integrated land-use and transport model framework

2014 ◽  
Author(s):  
Δημήτριος Ευθυμίου
Keyword(s):  
Land Use ◽  
Transport Model ◽  
Model Framework

Τα Ολοκληρωμένα Μοντέλα Χρήσεων-γης και Μεταφορών (ΟΜΧΓΜ)συνδυάζουν πρότυπα επιλογής τοποθεσίας κατοικίας/εργασίας, αξιώνακινήτων και κυκλοφοριακά μοντέλα, για την εκτίμηση και πρόβλεψη τωνεπιπτώσεων συγκοινωνιακών έργων και πολιτικών χρήσεων – γης στοπεριβάλλον, την κοινωνία και την οικονομία των αστικών περιοχών. Για τηναναπαράσταση των πολύπλοκων αστικών συστημάτων απαιτούνταιπολυσύνθετες μεθοδολογίες και λεπτομερή δεδομένα. Η πρόβλεψη κρίσιμωνστοιχείων της αστικής δομής και η έλλειψη ικανοτήτων πρόβλεψης τουμοντέλου, οδηγεί σε λανθασμένες εκτιμήσεις, που σε περιπτώσειςσυγκοινωνιακών επενδύσεων μεταφράζεται σε απώλειες εκατομμυρίων ευρώκαι κοινωνική ανισότητα. Ως εκ τούτου, τα ΟΜΧΓΜ αξιοποιούνται ακόμαδιστακτικά, ενώ τα τελευταία χρόνια το ενδιαφέρον της επιστημονικής κοινότητας αυξάνεται διαρκώς. Αντικείμενο της παρούσας έρευνας είναι να διερευνήσει, αναπτύξει καιπροτείνει μεθοδολογίες συλλογής δεδομένων, μοντελοποίησης καιαξιολόγησης πολιτικών για ολοκληρωμένα Μοντέλα Χρήσεων-Γης καιΜεταφορών. Οι προτεινόμενες προσεγγίσεις αποσκοπούν στη μείωση τουκόστους και την αύξηση της ικανότητας πρόβλεψης, εκμεταλλευόμενες ταπλεονεκτήματα της μικρό- προσομοίωσης σε τρείς διαστάσεις: άτομο, χώροκαι χρόνο.Η παρούσα διδακτορική έρευνα συμβάλλει με τα ακόλουθα στη διεύρυνσητου μεθοδολογικού πλαισίου των ΟΜΧΗΜ:- Διερευνάται η προοπτική χρήσης δεδομένων συλλεγμένων από τα πλήθη(crowd-sourced) στην ανάπτυξη ΟΜΧΓΜ. Ηλεκτρονικά δεδομέναακινήτων συλλέχθηκαν και χρησιμοποιήθηκαν για την ανάπτυξηπροτύπων. Δεδομένα χρήσεων-γης /κάλυψης εξάχθηκαν από δορυφορικέςαπεικονίσεις με μεθόδους τηλεπισκόπισης, με σκοπό να χρησιμοποιηθούνγια την ανάπτυξη μοντέλων. Σκοπεύοντας στη μείωση της εξάρτησης απόβάσεις δεδομένων υψηλού κόστους, προτείνεται μια γράφο-θεωρητική προσέγγιση για δημιουργία συσχετίσεων σε συνθετικό πληθυσμό.- Προτείνεται ένα πλαίσιο ενσωμάτωσης χωρικών οικονομετρικών μοντέλωνσε ΟΜΧΓΜ. Πιο συγκεκριμένα:o Με τη χρήση χωρικών οικονομετρικών μοντέλων μοντελοποιήθηκανοι αξίες των ακινήτων. Τα μοντέλα αυτά οδηγούν σε καλύτερηακρίβεια συγκριτικά με τη μέθοδο των ελαχίστων τετραγώνων, καιαπαλείφουν αποτελεσματικά τη χωρική αυτοσυσχέτιση.Αποσκοπώντας στη μέτρηση των επιπτώσεων των συγκοινωνιακώνυποδομών και πολιτικών στις αξίες αγοράς και ενοικίασης,αναπτύχθηκαν δυο περιπτωσιακές μελέτες στην Ελλάδα, για τηνΑθήνα και τη Θεσσαλονίκηo Nγινε προτυποποίηση της αλλαγής χρήσεων-γης/κάλυψης με τηχρήση χωρικού μοντέλου διακριτών επιλογών, επιτυγχάνονταςκαλύτερη εφαρμογή από τη γενικευμένη γραμμική παρεμβολή.Διερευνήθηκαν οι επιπτώσεις συγκοινωνιακών υποδομών μεγάληςέκτασης στην αλλαγή χρήσεων γης στην Αθήνα.Αναπτύχθηκε μεθοδολογία για τη χωρική κατανομήσυγκοινωνιακών υποδομών (σταθμών φόρτισης ηλεκτρικώναυτοκινήτων, μοιραζόμενων/κοινόχρηστων αυτοκινήτων καιποδηλάτων) που βασίζεται σε χωρικά οικονομετρικά μοντέλα και πολύ-κριτηριακή ανάλυση.- Αναπτύχθηκε μεθοδολογία για ποιοτική και ποσοτική αξιολόγησηπολιτικών που βασίζεται σε δείκτες, εκμεταλλευόμενη τα οφέλη της μικρό-προσομοίωσης σε τρείς διαστάσεις (άτομο, χώρο και χρόνο). Διερευνάται ηχρήση άτομο-βασικών δεικτών για την προσβασιμότητα, ανισότητα,οικονομία/επενδύσεις και κοινωνική ποιότητα. Η προτεινόμενημεθοδολογία βασίζεται σε χωρικές κατανομές και όχι σε μοναδικέςγενικευμένες μετρήσεις- Διερευνήθηκαν οι συνέπειες της χρηματοοικονομικής κρίσης στηναντίληψη των μετακινούμενων για την ποιότητα των συγκοινωνιακώνυποδομών/πολιτικών, και στις αξίες ακινήτων.

scholarly journals ANALISIS KECEPATAN JATUH SEDIMEN PADA SUNGAI CIBEET, JAWA BARAT

2021 ◽  
Vol 5 (1) ◽  
pp. 45
Author(s):  
Kevin Wijaya Warsito ◽  
Wati Astriningsih Pranoto
Keyword(s):  
Conceptual Understanding ◽  
Settling Velocity ◽  
Soil Mechanics ◽  
River Estuary ◽  
Sediment Concentration ◽  
Water And Sediment ◽  
Sediment Research ◽  
Hydraulics Laboratory ◽  
The Relationship ◽  
Optimum Salinity

Cibeet River is one of the branch of the Citarum river in West Java province with a length of 101 km. Cibeet River is one of the rivers supplying water and sediment to the West Tarum irrigation channel or known as the Kalimalang. In this research, the sample used was in the form of mud taken at the Cibeet River Estuary. This research is focused on settling velocity which is a parameter for sedimentation in order to improve numerical modeling and conceptual understanding of sediment dynamics, especially mud. Sediment research is carried out in the Soil Mechanics laboratory and Hydraulics laboratory. Bottom withdrawal tube experiments were carried out using 5 types of salinity and 6 kinds of sediment concentrations. The purpose of the study was to obtain settling velocity and compare laboratory results with the Stokes law approach and compare the relationship between settling velocity with sediment concentration and salinity. The optimum salinity is obtained at 15 ‰, and the optimum sediment concentration at 4700 ppm with an average fall speed of 37,28 mm / s. The results from the laboratory are not in accordance with the Stokes law due to the influence of flocculation from the cohesive nature of the mud sediment, so that using the Stokes law approach cannot calculate the velocity of falling sediment on the mud. Keywords: concentration; salinity; sediment; settling velocity AbstrakSungai Cibeet merupakan salah satu anak sungai dari sungai Citarum di provinsi Jawa Barat dengan panjang 101 km. Sungai Cibeet merupakan salah satu sungai pemasok air dan sedimen ke saluran irigasi Tarum Barat atau dikenal sebagai Kalimalang. Pada penelitian ini, sampel yang digunakan berupa lumpur yang diambil di Muara Sungai Cibeet. Penelitian ini difokuskan pada kecepatan jatuh sedimen yang merupakan parameter untuk sedimentasi demi meningkatkan permodelan numerik dan pemahaman konsep dari dinamika sedimen terutama lumpur.  Penelitian ini dilakukan di laboratorium Mekanika Tanah dan laboratorium Hidrolika, memakai bottom withdrawal tube, dilakukan dengan menggunakan 5 macam jenis salinitas dan 6 macam konsentrasi sedimen.  Penelitian ini membandingkan antara hasil laboratorium dengan pendekatan yaitu hukum Stokes serta membandingkan hubungan antara konsentrasi sedimen dengan salinitas. Untuk salinitas didapat optimum pada saat 15‰, dan konsentrasi sedimen yang optimum pada saat 4700 ppm dengan kecepatan jatuh rata-rata 37,28 mm/s. Hasil dari laboratorium tidak sesuai dengan pendekatan hukum stokes dikarenakan adanya pengaruh flokulasi dari sifat sedimen lumpur yang kohesif, sehingga menggunakan pendekatan hukum stokes tidak bisa untuk menghitung kecepatan jatuh sedimen pada lumpur.

scholarly journals Flocculation of Clay Suspensions by Anionic and Cationic Polyelectrolytes: A Systematic Analysis

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 999
Author(s):  
Ahmad Shakeel ◽  
Zeinab Safar ◽  
Maria Ibanez ◽  
Leon van Paassen ◽  
Claire Chassagne
Keyword(s):  
Light Scattering ◽  
Shear Rate ◽  
Settling Velocity ◽  
Rheological Analysis ◽  
Floc Size ◽  
Clay Concentration ◽  
History Of ◽  
Settling Column ◽  
Cationic Polyelectrolytes ◽  
Shear History

The characteristics of clayey suspensions, majorly composed of quartz microparticles, in the presence of anionic and cationic polyelectrolytes were investigated using different techniques. A wide range of clay concentrations was used, i.e., from 0.07 to 1000 g/L for different experimental techniques, based on the fact that the clay concentration possible to analyze with selected experimental methods was significantly different. The optimum flocculant to clay ratio was defined as the ratio that gives the fastest initial floc growth by static light scattering or fastest initial settling velocity by settling column experiments. In case of anionic polyelectrolyte, it was observed that the optimum flocculant dose depends on the amount of cations present in the system. For suspensions made with demi-water, a lower optimum flocculant dose (<1 mg/g) than for suspensions prepared in tap water (2.28 mg/g) was observed. At these lower salinities, the supernatant remained turbid in all the experiments and was, therefore, not a good measure for optimal anionic based flocculation. The equilibrium floc size at a given shear rate was found to be independent on the shear history of the floc and only dependent on the current applied shear. This was confirmed by both light scattering and rheological analysis. In case of cationic polyelectrolyte, the optimum flocculant ratio (5–6 mg/g) corresponded to the ratio that gives the lowest electrophoretic mobility for each clay concentration and to the ratio that gives the fastest settling velocity for the highest clay concentrations (12–15 g/L), where static light scattering measurements were not possible. All investigation techniques, therefore, proved to be good indicators for predicting the optimum flocculant to clay ratio. For the lowest concentrations (1.75–8.7 g/L) studied by settling column measurements, the optimum flocculant ratio was observed to increase with decreasing clay concentration, for fixed mixing conditions. The optimum flocculant to clay ratio was not always corresponding to the clearest supernatant and the size of flocs at optimum dosage was dependent on the mixing efficiency. The equilibrium floc size at a given shear rate was found to be dependent on the shear history of the floc and the current applied shear. This was confirmed by both light scattering and rheological analysis.

scholarly journals Association of Cryptosporidium with bovine faecal particles and implications for risk reduction by settling within water supply reservoirs

2006 ◽  
Vol 4 (1) ◽  
pp. 87-98 ◽  
Author(s):  
Justin D. Brookes ◽  
Cheryl M. Davies ◽  
Matthew R. Hipsey ◽  
Jason P. Antenucci
Keyword(s):  
Particle Size ◽  
Water Supply ◽  
Risk Reduction ◽  
Settling Velocity ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Particle Size Fractions ◽  
Size Classes ◽  
Large Particles ◽  
Water Supply Reservoirs

Artificial cow pats were seeded with Cryptosporidium oocysts and subjected to a simulated rainfall event. The runoff from the faecal pat was collected and different particle size fractions were collected within settling columns by exploiting the size-dependent settling velocities. Particle size and Cryptosporidium concentration distribution at 10 cm below the surface was measured at regular intervals over 24 h. Initially a large proportion of the total volume of particles belonged to the larger size classes (&gt;17 μm). However, throughout the course of the experiment, there was a sequential loss of the larger size classes from the sampling depth and a predominance of smaller particles (&lt;17 μm). The Cryptosporidium concentration at 10 cm depth did not change throughout the experiment. In the second experiment samples were taken from different depths within the settling column. Initially 26% of particles were in the size range 124–492 μm. However, as these large particles settled there was an enrichment at 30 cm after one hour (36.5–49.3%). There was a concomitant enrichment of smaller particles near the surface after 1 h and 24 h. For Pat 1 there was no difference in Cryptosporidium concentration with depth after 1 h and 24 h. In Pat 2 there was a difference in concentration between the surface and 30 cm after 24 h. However, this could be explained by the settling velocity of a single oocyst. The results suggested that oocysts are not associated with large particles, but exist in faecal runoff as single oocysts and hence have a low (0.1 m d−1) settling velocity. The implications of this low settling velocity on Cryptosporidium risk reduction within water supply reservoirs was investigated through the application of a three-dimensional model of oocyst fate and transport to a moderately sized reservoir (26 GL). The model indicated that the role of settling on oocyst concentration reduction within the water column is between one and three orders of magnitude less than that caused by advection and dilution, depending on the strength of hydrodynamic forcing.

scholarly journals Decadal changes in anthropogenic source contribution of PM<sub>2.5</sub> pollution and related health impacts in China, 1990–2015

2019 ◽  
Author(s):  
Jun Liu ◽  
Yixuan Zheng ◽  
Guannan Geng ◽  
Chaopeng Hong ◽  
Meng Li ◽  
...  
Keyword(s):  
Transport Model ◽  
Rapid Development ◽  
Premature Mortality ◽  
Control Measures ◽  
Health Impacts ◽  
Noncommunicable Diseases ◽  
Anthropogenic Source ◽  
Model Framework ◽  
Source Contribution ◽  
Residential Sector

Abstract. Air quality in China has changed dramatically in response to rapid development of economy and policies. In this work, we investigate the changes of anthropogenic source contribution to ambient fine particulate matter (PM2.5) air pollution and related health impacts in China during 1990–2015 and elucidate the drivers behind the decadal transition. We estimate the contribution of five anthropogenic emitting sectors to ambient PM2.5 exposure and related premature mortality over China during 1990–2015 with 5-yr intervals, by using an integrated model framework of bottom-up emission inventory, chemical transport model, and the Global Exposure Mortality Model (GEMM). The national anthropogenic PM2.5-related premature mortality estimated with GEMM for the nonaccidental deaths due to noncommunicable diseases and lower respiratory infections rose from 1.26 million (95 % CI: 1.05, 1.46) in 1990 to 2.18 million (95 % CI: 1.84, 2.50) in 2005; then, it decreased to 2.10 million (95 % CI: 1.76, 2.42) in 2015. In 1990, the residential sector was the leading source of the PM2.5-related premature mortality [559,000 (95 % CI: 467,000, 645,900), 44 % of total] in China, followed by industry (29 %), power (13 %), agriculture (9 %) and transportation (5 %). In 2015, the industrial sector became the largest contributor of PM2.5-related premature mortality [734,000 (95 % CI: 615,500, 844,900), 35 % of total], followed by residential (25 %), agriculture (23 %), transportation (10 %) and power (6 %). The decadal changes in source contribution to PM2.5-related premature mortality in China represents a combined impact of socioeconomic development and clean air policy. For example, active control measures have successfully reduced pollution from power sector, while contribution from industrial and transportation sector continuously increased due to more prominent growth of activity rates. Transition in fuel consumption dominated the decrease of contribution from residential sector. In the meanwhile, contribution from agriculture sector continuously increased due to persistent NH3 emissions and enhanced formation of secondary inorganic aerosols under a NH3 rich environment.

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