Tributary Channels Research Articles

Patterns of incision and deformation on the southern flank of the Yellowstone hotspot from terraces and topography

Abstract Understanding the dynamics of the greater Yellowstone region requires constraints on deformation spanning million year to decadal timescales, but intermediate-scale (Quaternary) records of erosion and deformation are lacking. The Upper Snake River drainage crosses from the uplifting region that encompasses the Yellowstone Plateau into the subsiding Snake River Plain and provides an opportunity to investigate a transect across the trailing margin of the hotspot. Here, we present a new chronostratigraphy of fluvial terraces along the lower Hoback and Upper Snake Rivers and measure drainage characteristics through Alpine Canyon interpreted in the context of bedrock erodibility. We attempt to evaluate whether incision is driven by uplift of the Yellowstone system, subsidence of the Snake River Plain, or individual faults along the river's path. The Upper Snake River in our study area is incising at roughly 0.3 m/k.y. (300 m/m.y.), which is similar to estimates from drainages at the leading eastern margin of the Yellowstone system. The pattern of terrace incision, however, is not consistent with widely hypothesized headwater uplift from the hotspot but instead is consistent with downstream baselevel fall as well as localized deformation along normal faults. Both the Astoria and Hoback faults are documented as active in the late Quaternary, and an offset terrace indicates a slip rate of 0.25–0.5 m/k.y. (250–500 m/m.y.) for the Hoback fault. Although tributary channel steepness corresponds with bedrock strength, patterns of χ across divides support baselevel fall to the west. Subsidence of the Snake River Plain may be a source of this baselevel fall, but we suggest that the closer Grand Valley fault system could be more active than previously thought.

Improved thermal performance of new staggered double P-type minichannel heat exchangers

• New type of heat exchanger designs with three inlets and outlets are proposed. • The performance of the novel heat sinks are studied by numerically and experimentally. • The effect of geometric parameters on the cooling ability is studied numerically. • The numerical results agree well with the numerical results. In order to obtain better thermal management performance, two heat sinks are proposed, namely, the enhanced design and the staggered double P-type design. Firstly, the effect of the inlet and outlet layout on the heat transfer ability of the conventional straight design is studied numerically. The results show that the conventional straight design with staggered inlet and outlet layout has better heat transfer performance. Secondly, the cooling performance of the enhanced design is numerically investigated. The results show that the maximum temperature of the enhanced design can be reduced by 41.71% compared to the conventional straight heat sink design. Thirdly, the cooling capacity of the staggered double P-type design is examined numerically and experimentally. The simulated results agree well with experimental results. The minimum substrate temperature difference is only 9.65 K. The maximum temperature of the staggered double P-type design can be reduced by 6.99 K. Moreover, the staggered double P-type design has the best heat dissipation ability among the three heat sinks. Then, the heat transfer capacities of the staggered double P-type at different inclination angle β of the V-type shunt channel and that at different inclination angle α of the confluence channel are studied. The results show that with the decrease of β , the heat transfer capacity of the staggered double P-type design is decreased, and the change trend of the heat transfer capacity with α is the same as that with β. When β = 30° and α = 90°, the heat transfer effect of the staggered double P-type design is the best.

Swimming behavior of juvenile silver carp near the separation zone of a channel confluence

Knowledge of locomotion of fish near river confluences is important for prediction of fish distribution in a river network. The flow separation zone near the confluence of a river network is a favorite habitat and feeding place for silver carp, which is one of the four major species of Chinese carp and usually provides positive rheotaxis to water flow. In the current study, a series of laboratory experiments were done to determine the behavioral responses of juvenile silver carp to the hydrodynamic forces near the separation zone of a channel confluence. The locomotion and trajectory of juvenile silver carp were recorded by infrared thermal imaging, while the flow velocity field near the separation zone was measured by a Particle Image Velocimetry (PIV) system. A total of 60 juvenile silver carp were released near the separation zone among which 40 carp swam in the upstream direction. Amongst them, 24 carp swam to the tributary and the remaining 16 swam into the main channel. Almost all these 24 carp travelled initially along the boundary of the separation zone near the corner, where flow shear was strongest, and then swam to the tributary. Instead of avoiding zones of strong vorticity, they chose and followed a trajectory along which the flow vorticity was large. On encountering these vortical flows, they increased the tail-beat frequency and decreased the tail-beat amplitude to maintain body stability. These observations provide important knowledge on locomotion of fish near river confluences and are beneficial for the fish habitat protection.

Evolution of a Late Miocene Deep-Water Depositional System in the Southern Taranaki Basin, New Zealand

A long-standing problem in the understanding of deep-water turbidite reservoirs relates to how the three-dimensional evolution of deep-water channel systems evolve in response to channel filling on spatiotemporal scales, and how depositional environments affect channel architecture. The 3-D structure and temporal evolution of late Miocene deep-water channel complexes in the southern Taranaki Basin, New Zealand is investigated, and the geometry, distribution, and stacking patterns of the channel complexes are analyzed. Two recently acquired 3-D seismic datasets, the Pipeline-3D (proximal) and Hector-3D (distal) are analyzed. These surveys provide detailed imaging of late Miocene deep-water channel systems, allowing for the assessment of the intricate geometry and seismic geomorphology of the systems. Seismic attributes resolve the channel bodies and the associated architectural elements. Spectral decomposition, amplitude curvature, and coherence attributes reveal NW-trending straight to low-sinuosity channels and less prominent NE-trending high-sinuosity feeder channels. Stratal slices across the seismic datasets better characterize the architectural elements. The mapped turbidite systems transition from low-sinuosity to meandering high-sinuosity patterns, likely caused by a change in the shelf-slope gradient due to localized structural relief. Stacking facies patterns within the channel systems reveal the temporal variation from a depositional environment characterized by sediment bypass to vertically aggrading channel systems.

Research on the impact of ship traffic flow on the restricted channel segment of the middle Yangtze River based on traffic wave theory

On the basis of the influence of dry season on ship traffic flow, the gathering and dissipating process of ship traffic flow was researched with Greenshields linear flow—density relationship model, the intrinsic relationship between the ship traffic congestion state and traffic wave in the unclosed restricted channel segment was emphatically explored when the ship traffic flow in a tributary channel inflows, and the influence law of multiple traffic waves on the ship traffic flow characteristics in unclosed restricted segment is revealed. On this basis, the expressions of traffic wave speed and direction, dissipation time of queued ships and the number of ships affected were provided, and combined with Monte Carlo method, the ship traffic flow simulation model in the restricted channel segment was built. The simulation results show that in closed restricted channel segment the dissipation time of ships queued is mainly related to the ship traffic flow rate of segments A and C, and the total number of ships affected to the ship traffic flow rate of segment A. And in unclosed restricted channel segment, the dissipation time and the total number of ships affected are also determined by the meeting time of the traffic waves in addition to the ship traffic flow rate of segments. The research results can provide the theoretical support for further studying the ship traffic flow in unclosed restricted channel segment with multiple tributariesArticle HighlightsThe inflow of tributaries' ship traffic flows has an obvious impact on the traffic conditions in the unenclosed restrictedchannel segment.The interaction and influence between multiple ship traffic waves and the mechanism of generating new traffic waves are explained.The expression of both dissipation time of queued ships and the total number of ships affected in the closed and unclosed restricted channel segment are given.

Recognizing a lost nesting ground: First unambiguous Testudines eggshells from the Eocene, associated with the pleurodiran Eocenochelus (Huesca, Northern Spain)

The Eocene record of turtle eggshells is scarce, with a single unconfirmed report from France. This scarcity contrasts with the great abundance of osteological remains, distributed over a wide palaeogeographical range as a result of climatic warmth. In this paper, we describe the first definitive Eocene Testudoolithidae eggshell fragments attributable to Testudines, most likely pleurodiran turtles, from the Eocene Sobrarbe Formation at the Castejón de Sobrarbe fossil site (CS-41) in northern Spain. The eggshells were found in association with osteological remains of at least four individuals of Eocenochelus eremberti (Pleurodira, Erymnochelyini) in an otherwise sirenian-dominated bonebed. Analysis of eggshell ultra- and microstructure allows comparison with eggshells from fossil and extant turtles. The eggshells are highly recrystallized but preserve relics of their original aragonitic radial ultrastructure as crystal phantoms. The barrel-shaped shell units, which are taller than wide, with compactituberculate ornamentation and funnel-shaped pore openings are similar to those of the Palaeocene ootaxon Haininchelys curiosa, whose holotype and paratype have been lost. The CS-41 eggshells are most similar to those of the pleurodiran Erymnochelys madagascariensis from Madagascar, the closest living relative to Eocenochelus, further supporting our attribution. Sedimentological and taphonomic analysis of the assemblage supports the hypothesis that the CS-41 fossil site was formed as the infilling of an abandoned tributary channel in the deltaic plain by an overbank or debris-flow deposit associated with a storm event. This storm resulted in the exhumation and subsequent re-sedimetation of the remains of a nesting ground of Eocenochelus eremberti, an otherwise coastal turtle, which would have entered inland streams to nest in the sand bars at the mouth of the Sobrarbe Deltaic Complex.

Simple structured and highly efficient passive T‐type micromixer with circumferential in‐step at entry

AbstractMany micromixing applications require simple structured passive mixers rather than complex structured passive or expensive active mixers. However, mixing quality in a typical simple structured passive mixer remains poor. In the present work, simple T‐type micromixer is modified with a circumferential in‐step at the entry of inlet channels to generate velocity components oblique to the mainstream inlet flow. The performance of T and T–T mixers with and without circumferential in‐step has been estimated for various Re (0 to 700). Results showed that inlet sample flow achieved velocity components of three‐dimensional nature with circumferential in‐step, leading to a momentous degree of intertwinement and entanglement of samples during the collision at the confluence of inlet channels. As a result, a remarkable improvement in mixing is obtained in the presence of in‐step for sufficiently higher flow rates of Re above 100 by T‐mixer and Re above 300 by T–T mixer. In particular, T‐mixer offers better advantage with in‐step compared to T–T mixer; marking an improvement for Re as low as 100 and above, as well as exhibiting shorter mixing lengths. Therefore, the present design of simple structured T‐mixer with in‐step at entry can be an effective device for various micromixing applications.

Deep-water sedimentation controlled by interaction between bottom current and gravity flow: A case study of Rovuma Basin, East Africa

By using 3D seismic dataset recently acquired in offshore Mozambique, we address the distribution pattern of an Upper Eocene channel-levee-lobe complex in deep-water of Rovuma Basin. The unique levee of this complex asymmetrically developed only on one side of the channel course. We attribute this asymmetric levee development to the interaction between the western slope bottom current from south to north and the gravity flow from west down slope. Due to the winnowing and sorting by the western slope bottom current, the sorted fine grain sediments of the gravity flow was blew and deposited to aside remaining clean sand from the gravity flow deposited within the channel as quality reservoir. The stacking and expanding of the levee forced the channels windward migrated to the south forming channel-1 to 6 from north to south.The corresponding lobe did not keep its feeder channel's axis direction, but bended from northeast to east or southeast, forming a U-turn from the channel to lobe. We believe that in addition to the paleotopography effect, the bottom current in Querimbus Graben might also lead to the bending of the lobe. The Querimbus Graben bottom current in this region flows from north to the south driven by the southward-drifting eddy. We suppose that a southward bottom current also existed at the Eocene time in this region and contributed to the southward bending of the lobes.

An Experimental Study on the Influence of Drastically Varying Discharge Ratios on Bed Topography and Flow Structure at Urban Channel Confluences

The confluences of rivers are important nodes for energy conversion and material transport in the river network. A slight morphological alteration of the confluences may trigger the “butterfly effect”, which will bring about changes in the ecology and environment of the entire river network. During the transition period of the wet and dry seasons, the variation of discharge ratio will make the originally balanced river bed change again, which will bring a series of follow-up effects. This research mainly studied the features of water flow itself and results showed that the variation of discharge ratio caused secondary erosion of the balanced bed surface and transported the sediment downstream. Thus, the zone of maximum velocity was enlarged and the maximum flow velocity at the equal discharge was reduced, and more intense vortex and turbulence were generated. The lateral velocity, vertical velocity, and turbulent structure were mainly controlled by the quantity and ratio of the discharge, and the varying topography only played a minor role in local areas. Nowadays, some scholars have been studying the combination of flow field features and various environmental substances and biological habitats, and the basic work done in this article has laid the foundation for these studies.

Investigation of red blood cell partitioning in an in vitro microvascular bifurcation.

There is a long history of research examining red blood cell (RBC) partitioning in microvasculature bifurcations. These studies commonly report results describing partitioning that exists as either regular partitioning, which occurs when the RBC flux ratio is greater than the bulk fluid flowrate ratio, or reverse partitioning when the RBC flux ratio is less than or equal to that of the bulk fluid flowrate. This paper presents a study of RBC partitioning in a single bifurcating microchannel with dimensions of 6 to 16μm, investigating the effects of hematocrit, channel width, daughter channel flowrate ratio, and bifurcation angle. The erythrocyte flux ratio, N*, manifests itself as either regular or reverse partitioning, and time-dependent partitioning is much more dynamic, occurring as both regular and reverse partitioning. We report a significant reduction in the well-known sigmoidal variation of the erythrocyte flux ratio (N*) versus the volumetric flowrate ratio (Q*), partitioning behavior with increasing hematocrit in microchannels when the channel dimensions are comparable with cell size. RBCs "lingering" or jamming at the bifurcation were also observed and quantified in vitro. Results from trajectory analyses suggest that the RBC position in the feeder channel strongly affects both partitioning and lingering frequency of RBCs, with both being significantly reduced when RBCs flow on streamlines near the edge of the channel as opposed to the center of the channel. Furthermore, our experiments suggest that even at low Reynolds number, partitioning is affected by the bifurcation angle by increasing cell-cell interactions. The presented results provide further insight into RBC partitioning as well as perfusion throughout the microvasculature.

Alluvial fans of Trans-Himalayan cold desert (Pin valley, India): quantitative morphology and controlling factors

ABSTRACT Pin valley is an ideal area for alluvial fans’ development. Being least disturbed and devoid of vegetation, fans of this area provide exquisite information and extraordinary opportunity to understand different factors that affect their morphology. Despite aforesaid advantages these fans are hitherto not studied. Thus, the present study is an attempt to understand the morphology of these fans and explore factors affecting fan morphology, primarily through morphometry. Data were derived from various satellite imageries, topographical sheets, DEM and field observations. Various parameters of 51 fans and of their basins were measured and relationships among different parameters were examined. The results of the study are generally comparable to literature though these fans are much steeper than their counterparts in similar environmental settings. Multi-proxy approach was used to explore controlling factors. Fan Conicality Index (FCI) and sweep angle of fan (SA ) suggest confinement imposed by surrounding environment has considerably reduced the size of these fans. Further, valley-floor width to height ratio (Vf ), feeder channel and geological group-wise analyses reveal that active tectonic attitude, order of feeder channel, lithology and characteristics of contributing basin along with associated depositional processes exercise significant control on morphology of these fans.

An investigation of the characteristics of dam-break flood in a confluence channel based on the lattice Boltzmann method

In this study, we use a lattice Boltzmann method with a multi-relaxation-time model to simulate dam-break flooding in confluence channels with four confluence angles. Compared with physical experiment, the simulation proves reliable. We analyze the influence of the confluence angle on the propagation of dam-break flood. The stage hydrograph at the confluence area can be divided into four stages: before the wavefront reaches—rising rapidly—falling gradually—planarization with periodic fluctuation. The water depth of the measuring points in the confluence area is influenced by two factors: the confluence angle and the distance from the measuring point to the first impact point. The results demonstrate that the backwater effect of the confluence is enhanced at higher confluence angles. As the confluence angle increases, the first impact point moves upstream. Moreover, there is a strong backwater effect close to the first impact point, resulting in superelevation mainly occurring in the confluence area.

Elucidating suspended sediment dynamics in a glacierized catchment after an exceptional erosion event: The Djankuat catchment, Caucasus Mountains, Russia

Suspended sediment yields from glacierized catchments are often among the highest in the world, and their sediment dynamics can be highly variable. This study was undertaken in the 9.1 km2 glacierized catchment of the Djankuat River located in the Russian part of the Northern Caucasus. The outlet of the study catchment is a hydrological gauging station located at an altitude of 2635 m a.m.s.l. (‘N43°12′31.71″, E42°44′05.93″). The catchment includes a temperate valley glacier (area = 2.42 km2) and three smaller hanging glaciers, several moraine deposits, rock walls, and a large and expanding proglacial area. The main goal of our study was to assess the impact of an exceptional erosion event on 1st July 2015 (with an annual exceedance probability of less than 0.1%) on suspended sediment yields and the relative contributions of various sediment sources The work combined direct suspended sediment discharge measurements at the gauging station during five ablation seasons (2015–2019) with geomorphic mapping techniques based on detailed field observations and sediment source fingerprinting. Results show that mean annual suspended sediment yields reached 1118 t km−2 year−1 which is one of the highest measured estimates for any of the glacierized mountain rivers globally. About half of the annual suspended sediment flux was exported during a limited number (1–12% of the annual events) of extreme hydrological events. The sediments mobilized by bank and riverbed erosion within the new lower reach of a tributary channel which appeared after the breakthrough of a lateral moraine became the primary sediment source. It contributed over 50% of the suspended sediment on days with extreme rainfall. Contributions to the suspended sediment load from the glacier source were event-dependent and were only dominant (c. 60–70%) in the upper reaches of the proglacial area (first 800 m). The proglacial part of the study catchment with buried ice was the main sediment source (79%) during non-rain days.

Coupling Genomics and Hydraulic Information to Predict the Nitrogen Dynamics in a Channel Confluence.

The simulation of nitrogen dynamics in urban channel confluences is essential for the evaluation and improvement of water quality. The omics-based modeling approaches that have been rapidly developed have been increasingly applied to characterize metabolisms of the microbial community and transformation of the associated materials. However, the transport of microorganisms and chemicals within and among different phases, which could be the rate-limiting step for the nitrogen dynamics, are always neglected or oversimplified in omics-based models. Therefore, this study proposes a novel simulation system coupling genomic and hydraulic information to simulate transport and transformation processes and provide predictions of nitrogen dynamics in a confluence. The proposed model was able to capture multiphase mass transport, microbial population dynamics, and nitrogen transformation and accurately predict gene abundances and nitrogen concentrations in both water and sediment; the mean relative errors were all lower than 40%. The model emphasized the importance of transport processes, which contributed more than 90% to gene abundances and chemical concentrations. Moreover, the simulation of reaction rates exhibited the specific nitrogen transformation processes in the confluence. The sulfide oxidation and the nitrate reduction and anaerobic ammonium oxidation, with the participation of the genes nap and hzo, respectively, were promoted as the main processes of nitrate and nitrite reduction.

Formation of undulating topography and gravel beds at the bases of incised valleys: Last Glacial Maximum examples beneath the lowlands facing Tokyo Bay

Recent studies using well density distributed borehole logs have revealed undulating topography at the bases of incised valleys formed during the Last Glacial Maximum (LGM). In this study, from analysis of 4702 borehole logs, undulating topography forming a series of pits 1–2 km long, < 1 km wide, 5–10 m deep, and spaced at 1–2-km intervals was discovered at the bases of LGM incised valleys beneath the Tama River Lowland on the west coast of Tokyo Bay. This undulating topography can be attributed to scouring at braided river channel confluences. In the study area, single borehole logs are available within each 187 m × 187 m grid cell, and the logs sample both the bottom and marginal portions of the scouring, which suggests that this undulating topography is not an artifact of erroneous values arising from mathematical interpolation. The morphologies and incision depths of two incised valleys in the study area show a cover effect of the gravel bed at the base of the post-LGM incised-valley fills. The basal age of this basal gravel bed (BG) is confirmed at < 30 ka because the LGM incised valleys dissect the MIS 3 Tachikawa buried terrace overlain by the AT tephra dated 30.0 ka. This means that the BG, which represents braided-river sediments, is interpreted as resulting from the LGM sea-level lowstand after 30 ka.

Rinnenkarren systems and the development of their main channels

In this study, the development of rinnenkarren systems is analyzed. During the field studies, 36 rinnenkarren systems were investigated. The width and depth were measured at every 10 cm on the main channels and then shape was calculated to these places (the quotient of channel width and depth). Water flow was performed on artificial rinnenkarren system. A relation was looked for between the density of tributary channels and the average shape of the main channel, between the distance of tributary channels from each other and the shape of a given place of the main channel. The density and total length of the tributary channels on the lower and upper sections of the main channels being narrow at their lower end (11 pieces) and being wide at their lower end (10 pieces) of the rinnenkarren systems were calculated as well as their average proportional distance from the lower end of the main channel. The number of channel hollows was determined on the lower and upper sections of these main channels. It can be stated that the average shape of the main channel calculated to its total length depends on the density of the tributary channels and on the distance of tributary channels from each other. The main channel shape is smaller if less water flows on the floor for a long time because of the small density of the tributary channels and the great distance between the tributary channels. In this case, the channel deepens, but it does not widen. The width of the main channel depends on the number and location of the rivulets developing on channel-free relief. The main channel becomes narrow towards its lower end if the tributary rivulets are denser and longer on the upper part of the main rivulet developing on the channel-free, plain terrain and their distance is larger compared to the lower end. The channel hollows develop mainly at those places where the later developing tributary channels are hanging above the floor of the main channel. Thus, the former ones are younger than the latter ones. It can be stated that the morphology of the main channels (shape, channel hollows, and width changes of the main channel) is determined by the tributary channels (their number, location and age).

Deposition pattern of stony and muddy debris flow at the confluence area

Debris flow fan affects the river profile and landscape evolution. The propagation of multiple debris flows along a river can cause inundation and breaching risk, which can be exemplified by the Min River after the Wenchuan earthquake, Sichuan province, China. In this work, large flume tests were conducted to examine the interactions between debris flows and water current with the fan geometry, momentum, runout distance, deposited width, the relative water level upstream and dominated stress. The results reveal that stony flow commonly travels at a high speed and forms a long rectangle shape fan, while the muddy flow generally travels at a low speed and forms a fan-shaped depositional area. The stony flow can block a river even when the momentum is close to the water current; the muddy flow can block a river when the momentum is lower than that of water current. In case of complete river damming, the relative water level upstream indicates that the inundation risk from the muddy flow damming river would be higher than the inundation risk of stony flow. The diversion ratio of muddy flow decreases as damming ratio. Comparison of dimensionless numbers reveals that stony flow is dominated by grain collision stress combined with turbulent mixing stress, while the muddy flow is dominated by viscous shear stress over friction stress. The fan geometry, damming ratio, diversion ratio, and the dominated stress all together indicate that stony flow strongly interacts with water current while the muddy flow does not. The results can be helpful for understanding the physical interactions between water current and various debris flows, and debris flow dynamics at the channel confluence area.

Turbulent Flow Structure in a Confluence: Influence of Tributaries Width and Discharge Ratios

River channel confluences are rather important interfaces where intense changes in physical, mixing and sediment transport processes occur. Following an experimental campaign, the main flow mechanisms in confluences and the development of the shear layer formed between the two tributary flows are presented. As the experimental flow cases comprised changes in the flow discharge and channel widths of the tributaries, the influence of width and discharge ratios on the turbulent flow structure and shear layer is also evaluated. Main findings indicate that changes in the difference between momentum ratio in the tributaries have a significant effect on the magnitude and location of flow mechanisms.

Distribution and release of perfluorinated compounds (PFCs) in water-sediment systems: The effect of confluence channels

Perfluorinated compounds (PFCs) released from sediment contribute to pollution in rivers. Considerable research has been conducted on submerged bottom sediment in long, straight channels. However, less attention has been paid to the junction of a plain river network where the hydrodynamic disturbance of confluence dominates. To date, the release mechanism of PFCs in confluence channels has not been revealed quantitatively. In this study, we carried out a series of flume experiments to evaluate the effect of varied discharge ratios of mainstream and tributary waters on the efflux of PFCs from sediment. The results demonstrate that the convergence of tributary water can affect the mainstream water significantly. The two most obvious features are the separation zone and the maximum velocity zone. The release of PFCs in sediment is correlated with the flow velocity. The discharge in the separation zone is low, and the discharge in the maximum velocity zone is high. The release of PFCs in water bodies, including the true soluble phase, colloid phase, and particle phase, increase with an increase to the discharge ratio. Perfluorooctanoic acid (PFOA) is more widely distributed in the true dissolved phase, and perfluorooctane sulfonate (PFOS) dominates in the colloid and particle phases. Our results indicate that the variation of PFCs in sediment is strongly correlated with the hydrodynamic partition. This study provides a scientific basis for regulating PFC transport at river channel confluences.

Concentration profiles of ions and particles under hydrodynamic focusing in Y-shaped square microchannel

Three-dimensional ion and particle concentrations under hydrodynamic focusing in a Y-shaped square microchannel are numerically simulated to clarify the decrease of the ion concentration along the flow direction within the focused particle stream. The simulation model is theoretically governed by the laminar flow and advection–diffusion equations. The governing equations are solved by the finite volume method. The ion and particle concentration distributions at five cross sections after the confluence of the branch channels are analyzed in 30 cases in which the sheath to sample flow rate ratio Qsh/Qsam and the Reynolds number Re are varied as parameters. The results show that the decrease of the cross-sectional average ion concentration along the flow direction within the particle stream overline{c}_{i} is described by the diffusion length during the residence time with a characteristic velocity scale. In addition, the deformation of the particle stream due to inertial effects is described by a scaled Reynolds number that is a function of the flow rate ratio. The simulated particle stream thicknesses are validated by theory and a simple experiment. This paper reveals the relationship between the ion and particle concentrations and the dimensionless parameters for hydrodynamic focusing in the Y-shaped square microchannel under typical conditions.