Downstream Channel Research Articles

Patterns of Mekong Mollusc Biodiversity: Identification of Emerging Threats and Importance to Management and Livelihoods in a Region of Globally Significant Biodiversity and Endemism

The Lower Mekong Basin (LMB) is a key biodiversity hotspot. To facilitate conservation and management, we examine mollusc biodiversity patterns and distribution along LMB’s longitudinal gradients, identify environmental drivers, and discuss the importance of these drivers to management. Cluster analysis, redundancy analysis (RDA), and variation partitioning were conducted using mollusc data collected from 63 sampling sites. Results indicated that species diversity is dominated by gastropods (61%) and bivalves (39%) and feeding trait diversity by scrapers (52%) and filter-collectors (37%). Only 48 species (49%) out of 98 taxa have been assessed by the International Union for Conservation of Nature (IUCN) including a growing number of invasive species. The lack of complete, up-to-date information highlights the need for more research on both native and alien species. Cluster analysis revealed a clear mollusc biodiversity structure along the LMB’s longitudinal segments. Diversity was lowest in upstream tributaries, increased in upstream main channels, and was highest in downstream channels and the Mekong delta, the exception being the observed high gastropod abundance in Chi-Mun river mouth and Luang Prabang areas. The RDA and variation partitioning demonstrated that combined physical–chemical and climatic conditions are the key drivers of biodiversity patterns. Given the potential spread of invasive alien species and increasing anthropogenic impacts, further ecological research, regular monitoring, and adaptive management are needed to sustain mollusc biodiversity and associated ecosystem services, which contribute to food security, nutrition, and livelihoods in the LMB.

Considerations for the design of swirl chambers for the cyclone cooling of turbine blades and for other applications with high swirl intensity

The focus of this study lies on turbulent incompressible swirling flows with high swirl intensity. A systematic parameter study is conducted to examine the sensitivity of the mean velocity field in a swirl chamber to changes in the Reynolds number, swirl intensity and channel outlet geometry. The investigated parameter range reflects the typical kinematic flow conditions found in heat transfer applications, such as the cooling of the turbine blade known as cyclone cooling. These applications require a swirl intensity, which is typically much higher than necessary for vortex breakdown. The resulting flows are known as flow regime II and III. In comparison to flow regime I, which denotes a swirling flow without vortex breakdown, these flow regimes are characterized by a subcritical behavior. In this context, subcritical means that the flow is affected by the downstream channel section. Based on mean velocity field measurements in various swirl chamber configurations, it is shown that flow regime III is particularly sensitive to these effects. The channel outlet geometry becomes a determining parameter and, therefore, small changes at the outlet can produce entirely different flow patterns in the swirl chamber. In contrast, flow regime II, as well as flow regime I and axial channel flows, are much less sensitive to changes at the channel outlet. The knowledge about the sensitivity of the flow in different flow regimes is highly relevant for the design of a cyclone cooling system. Cooling systems employing flow regime III can result in a weakly robust flow system that may change completely over the operating range. As a remedy, the swirl intensity needs to be decreased so that flow regime III cannot be reached, which, however, reduces the maximum achievable heat transfer in the cooling system. Alternatively, the flow has to transition back from flow regime III to flow regime II or I before the flow leaves the swirl chamber. Two practical methods are presented. These findings can be directly applied in the design processes of future cyclone cooling systems, and other applications of swirling flow.

A PHYSICAL HYDRAULIC MODEL TEST TO SOLVE THE PROBLEM ON SPILLWAY DAM

This research studies about the hydraulic performance and and the problem solving alternativesof spillway design at Fila Tukutaha Dam, Alor District Indonesia. Flow water passing over the spillway of adam typically has a large amount of energy, must be dissipated safely before the floodwaters rejoin to thenatural river system. Therefore, energy dissipation takes place at the downstream end of the chuteway. Thestilling basin at the end of the chute way is commonly used to dissipate energy from the spillway and slow thewater velocity to protect the downstream river channel from erosion and damage. The methodology ofexperiment consists of physical modeling in the Hydraulic and Coastal Engineering Laboratory of CivilDepartement, Sepuluh Nopember Institute of Technology. The discharge design was analyzed by hydrologicalrouting formula over the spillway. The methods include Bernoulli’s formula equation for the steeply slopedchannel, the standard step formula for calculating the energy equation on the transition channel, and the USBRtype 2 for designing the stilling basin. From the experimental result, cross-flow was reduced by adding thehexagonal baffle block on the transition channel, and the effectiveness of stilling basin was occurred by placingthe abrupt rise in the downstream area.

Comparative study on the dynamic calculation method of river ecological water demand

In order to maximize the seasonal ecological hydrological demand of the river, this paper introduces three improved dynamic calculation methods. Taking the downstream channel of the Jilintai-I Hydropower Station on the Kashi River in Xinjiang as an example, three methods are applied to calculate the ecological water demand of the channel. Meanwhile, it is compared with the improved classification standard of Tennant method, and a method that is more suitable for the calculation of the ecological water demand of the river in this basin is selected, so that the calculation results can meet the seasonal dynamic demand of runoff while ensuring the basic ecological and hydrological demand of the basin, and benefit to the sustainable development of the river habitat. And reduce the losses caused by hydrological disasters, and achieve the coordinated development of economy and ecology.

Effects of recent morphological change on the redistribution of flow discharge in the Yangtze River Delta

Morphological evolution in tidally influenced estuarine channel networks has strong influence on the redistribution of fluvial discharge and tidal motion. Based on channel bathymetry and hydrological data observed in 2002 and 2016, this study investigated the influence of morphological evolution on subtidal flow division in the Yangtze River Delta. Experiments using a 2D hydrodynamic model revealed the subtidal discharge was allocated more equally to the downstream channels at the main bifurcation in 2016. The bathymetric variation results in reduction of the discharge asymmetry index by reducing the effect of tidal motion. The decreased channel volume and cross-sectional area of the North Branch has been responsible for the reduction of the tidal flow intrusion into this channel. Allocation of the subtidal discharge to the North Branch has increased because of the reduction of tidal motion in this channel, induced by accretion in this channel during 2002–2016.

1.28 and 5.12 Gbps multi-channel twinax cable receiver ASICs for the ATLAS Inner Tracker Pixel Detector upgrade

We present two prototypes of a gigabit transceiver ASIC, GBCR1 and GBCR2, both designed in a 65-nm CMOS technology for the ATLAS Inner Tracker Pixel Detector readout upgrade.The first prototype, GBCR1, has four upstream receiver channels and one downstream transmitter channel with pre-emphasis. Each upstream channel receives the data at 5.12 Gbps through a 5 m AWG34 Twinax cable from an ASIC driver located on the pixel module and restores the signal from the high frequency loss due to the low mass cable. The signal is retimed by a recovered clock before it is sent to the optical transmitter VTRx+. The downstream driver is designed to transmit the 2.56 Gbps signal from lpGBT to the electronics on the pixel module over the same cable. The peak–peak jitter (throughout the paper jitter is always peak–peak unless specified) of the restored signal is 35.4 ps at the output of GBCR1, and 138 ps for the downstream channel at the cable ends. GBCR1 consumes 318 mW and is tested.The second prototype, GBCR2, has seven upstream channels and two downstream channels. Each upstream channel works at 1.28 Gbps to recover the data directly from the RD53B ASIC through a 1 m custom FLEX cable followed by a 6 m AWG34 Twinax cable. The equalized signal of each upstream channel is retimed by an input 1.28 GHz phase programmable clock. Compared with the signal at the FLEX input, the additional jitter of the equalized signal is about 80 ps when the retiming logic is off. When the retiming logic is on, the jitter is 50 ps at GBCR2 output, assuming the 1.28 GHz retiming clock is from lpGBT. The downstream is designed to transmit the 160 Mbps signal from lpGBT through the same cable connection to RD53B and the jitter is about 157 ps at the cable ends. GBCR2 consumes about 150 mW when the retiming logic is off. This design was submitted in November 2019.

Three-dimensional numerical study of submerged spatial hydraulic jumps

Abstract A three-dimensional numerical model was applied to simulate submerged spatial hydraulic jumps (SSHJ) downstream of a symmetric vent that discharges into a wider channel. Simulations were carried out for different aspect ratios of the vent, expansion ratios of vent width to downstream channel width, tailwater depth, and inlet Froude number. Depending on these factors, simulations indicated the formation of steady asymmetric SSHJ, oscillatory asymmetric SSHJ, and steady symmetric SSHJ, consistent with results of previous experimental studies. The model reproduced observed depth downstream of vent, jump length, and velocity profiles along channel centerline for steady symmetric SSHJ. For oscillatory asymmetric SSHJ, simulated oscillation frequencies had Strouhal numbers that varied with expansion ratio and ranged between 0.003 and 0.015. With piers downstream of the vent, oscillatory SSHJ continued to exhibit jet deflections when pier length was relatively short ( ≲ 0.2 of jump length) but became steady asymmetric for longer piers.

Effect of water-sediment regulation operation on sediment grain size and nutrient content in the lower Yellow River

The Yellow River (YR) is famous for its high sediment concentration. The Xiaolangdi dam (XLD), the most downstream dam on the mainstream of the YR, plays an integral role in siltation mitigation, flood defence, agriculture, and hydropower generation. To alleviate siltation of the Xiaolangdi Reservoir (XLDR) and riverbed uplift of the lower reaches of the YR and strengthen flood control safety downstream, the XLDR began to implement water-sediment regulation in 2002. Water-sediment regulation (WSR) has significantly changed the hydrological processes, erosion and deposition, and sediment transport in the downstream channel, and the downstream water environmental conditions have also changed. In this study, 10 sections in the Lower Yellow River (LYR, from the XLDR to the Lijin section) and 4 sections in the soft floodplain area were sampled in the field to analyse their surface sediment grain size composition and nutrient content. At the same time, data on the average annual median particle sizes (D50) of channel sediments and suspended particles in 7 typical sections in the LYR from 2004 to 2015 were statistically analysed. The results show that the channel sediment grain size in the LYR decreased along the river course, and the D50 ranged from 0.20 mm in the HYK section to 0.08 mm in the LJ section. Moreover the D50 of the suspended sediment was less than 0.05 mm. The D50 of the channel and suspended sediment were both ranked as follows: non-flood season > flood season > WSR period. After WSR, fine silt particles with diameters of 0.01–0.05 mm were deposited on the soft floodplain. The channel sediment size was mainly coarse particles with diameters of 0.05–0.20 mm due to channel erosion. The suspension of fine silt particles due to flood scouring led to the total organic carbon (TOC) and total nitrogen (TN) absorbed in the particles to also be resuspended in the water. As a result, the TOC and TN contents in the channel sediments decreased by approximately 40% after WSR.

Research progress and ideas of Influence of hydrological regimes on river primary productivity of algae

The algae, as the primary producer of the water ecosystem, are the basic part of food chain in aquatic ecosystem. The flow pattern and hydrological process of the river have been significantly changed by the construction of the high dams. Not only the natural hydrological characteristics and physical and chemical conditions of the river were changed by the obstacle of the dams, but also the habitat environment on which the phytoplankton live, and its community structure, biomass and primary productivity of the water further were affected. In this paper, the research on the effect of river hydrological regime change on the primary productivity of water body were summarized and summarized. In the future, further research can be carried out in these aspects: (i) the analysis of the key factors affecting the primary productivity; (ii) clarifying the mechanism of the influence of hydrological situation change on the primary productivity and its distribution of algae in the reservoir area and downstream channel; (iii) establishing the coupling relationship between the change of hydrological regime and the primary productivity of phytoplankton.

Analysis of the influence of reservoir regulation on the multi-scale periodic effect of runoff time series

The periodic effect of runoff time series is a basic characteristic that reflects the change law of river hydrological situation. In order to reveal the influence of power station regulation on the periodic change of runoff process, the Gangkouwan Station, the controlling reservoir of the Shuiyangjiang River, was taken as the object in this article, based on the Morlet wavelet analysis technique, the influence of the reservoir on the periodic characteristics of natural runoff was analyzed and the influence of the reservoir on the periodic effect of runoff process of downstream channel on different time scales was revealed. The results show that the Gangkouwan Station significantly affects the periodic change of runoff on the 1-year, 4-month and 1-day scales, and among them, periodic change on the 1-day scale shows change law of day night alternative wetness-dryness.

Efficiency of the Drawdown Flushing and Partition Desilting of a Reservoir in Taiwan

Sedimentation limits the benefits of storage reservoirs, especially in areas with higher sediment yields, such as Agongdian Reservoir in southern Taiwan. Although drawdown flushing is a known strategy that releases large amounts of fine sediment into a downstream channel, there is limited information on the long-term monitoring and multiple metrics being used to evaluate flushing efficiency. The objectives of this study were three-fold: (1) to continue collecting valuable long-term observed data, since Agongdian Reservoir is one of the few reservoirs currently conducting sediment flushing operations; (2) to evaluate and identify the hydrological parameters that are highly related to the flushing efficiency; (3) to execute numerical simulations of different reservoir flushing scenarios at multiple water levels to discuss potential strategies to improve the flushing efficiency. The findings of this study revealed that long-term monitoring data was valuable for identifying factors highly related to the flushing efficiency, which included the initial water level; average water level; average velocity. Based on simulations, compartmentalizing the reservoir is a proposed strategy that has demonstrated high levels of improvement in terms of the flushing efficiency, depending on particular scenarios involving partition desilting, empty flushing, or a combination of both. Recommendations to increase the flushing efficiency include lowering the initial water level, creating a narrower gorge-like geometry by partitioning, and further considering to modify the operation rules.

Impact of human intervention on assessing downstream channel behaviour of Ichamati River on the lower Gangetic Plain of West Bengal, India

Since the period of human civilization, the hydrological and morphological characteristics of most of the rivers have been intensively modified by human interferences. In this context, the Ichamati River is one of the worst affected distributary channels flowing on the lower Gangetic delta of South Bengal. This tidally active river is streaming on the most densely inhabited district (North 24 Parganas) of West Bengal. The river is gradually decaying over time due to direct and indirect human activities on and along the river. Therefore, the prime aim of this research study is to explain the temporal change of the channel behaviour, especially fluvio-morphological characteristics of the river during 1976–2016. The present study also highlights location-specific causal factors liable for the downstream modification of the channel behaviour. In this research study, channel migration, erosion rate, bank vulnerability zone and channel planform pattern have been assessed using Landsat images of 1976, 1996 and 2016 in remote sensing and GIS environment. Besides, an intensive field survey was conducted for cross-sectional survey of the river. Primary data were gathered from brick kilns through a questionnaire survey for the estimation of sediment extraction rate from the river to prepare the sediment-water budget of the river. This study reveals that the morphological characteristics of Ichamati River have been modified at the human–nature interface and continuous siltation causes gradual upliftment of the riverbed. The channel is gradually narrowing and decaying over time. This study is helpful to understand the current status of the river and helps river scientists for its restoration as well as management planning.

Morphological evolution of bifurcations in tide-influenced deltas

Abstract. In river-dominated deltas, bifurcations often develop an asymmetrical morphology; i.e. one of the downstream channels silts up, while the other becomes the dominant one. In tide-influenced systems, bifurcations are thought to be less asymmetric and both downstream channels of the bifurcation remain open. The main aim of this study is to understand how tides influence the morphological development of bifurcations. By using a depth-averaged (2DH, two-dimensional horizontal) morphodynamic model (Delft3D), we simulated the morphological development of tide-influenced bifurcations on millennial timescales. The schematized bifurcation consists of an upstream channel forced by river discharge and two downstream channels forced by tides. Two different cases were examined. In the first case, the downstream channels started with unequal depth or length but had equal tidal forcing, while in the second case the morphology was initially symmetric but the downstream channels were forced with unequal tides. Furthermore, we studied the sensitivity of results to the relative role of river flow and tides. We find that with increasing influence of tides over river, the morphology of the downstream channels becomes less asymmetric. Increasing tidal influence can be achieved by either reduced river flow with respect to the tidal flow or by asymmetrical tidal forcing of the downstream channels. The main reason for this behaviour is that tidal flows tend to be less unequal than river flows when geometry is asymmetric. For increasing tidal influence, this causes less asymmetric sediment mobility and therefore transport in both downstream channels. Furthermore, our results show that bedload tends to divide less asymmetrically compared to suspended load and confirm the stabilizing effect of lateral bed slopes on morphological evolution as was also found in previous studies. We show that the more tide-dominated systems tend to have a larger ratio of bedload-to-suspended-load transport due to periodic low sediment mobility conditions during a transition between ebb and flood. Our results explain why distributary channel networks on deltas with strong tidal influence are more stable than river-dominated ones.

Electro-elastic flow instabilities of viscoelastic fluids in contraction/expansion micro-geometries

Electro-elastic instabilities in electro-osmotic contraction/expansion flows (EOF) of viscoelastic fluids are experimentally investigated in this work. Several microchannel configurations are used, including the cases with hyperbolic-shaped contractions followed by an abrupt expansion, or abrupt contractions followed by a hyperbolic-shaped expansion. Such cases were selected to assist in the understanding of the EOF instability mechanisms and at which conditions they occur. A reference Newtonian fluid was also used in the experiments, and a wide range of electric fields were imposed to drive the flow. Flow visualizations for a Newtonian fluid allowed to assess the impact of dielectrophoresis on the velocity field of the seeding particles. For each geometry, depending on the polymer concentration, the flow was found to be quasi-Newtonian below a critical electric potential difference, characterized by smooth parallel steady flow patterns in the upstream and downstream channels. Above the critical voltage difference two types of electro-elastic instabilities were found to occur, leading to an unsteady symmetric flow, and to time-dependent irregular flow.

SAT-LB97 MiRNA-99a and mTOR2 Mediate Enhanced Endothelial Mineralocorticoid Receptor Signaling-Induced Activation of Sodium Channel and Endothelium Stiffness

In diet induced obesity enhanced endothelial cell (EC) mineralocorticoid receptor (MR) (ECMR) and downstream sodium channel (EnNaC) activity increases oxidative stress and inflammation, thereby promoting vascular stiffness and associated impaired endothelial mediated relaxation. For example, consumption of a Western diet (WD) containing excess fat (46%) and fructose (17.5%) for 16 weeks elevated plasma aldosterone levels and increased vascular MR expression in conjunction with increased endothelial and vascular stiffness in female mice. EC specific deletion of either the ECMR or EnNaC significantly attenuated this diet induced endothelial/vascular stiffness. Emerging information suggests that abnormal expression of miR-99a may be involved in these processes. To this point, we recently observed that aldosterone (10-7 mol/L) causes a reduction in miR-99a that was prevented by the MR antagonist, spironolactone (10µM) in in vitro ECs. By using RNA sequencing, we also demonstrated that ECMR activation reduced arterial miR-99a expression in diet induced obesity. Since the mammalian target of rapamycin (mTOR2)/SGK1 signaling pathway is involved in aldosterone activation of ENaC we then explored the effects of miR-99a on mTOR2 expression. Indeed, miR-99a reduced mTOR2. We further observed that inhibition of mTOR2 with PP242 inhibited EnNaC activity as determined by patch clamping of ECs. Collectively these data suggest that consumption of a WD induced ECMR activation and increased EnNaC activity and endothelial stiffness, in part, by reducing the tonic inhibitory effects exerted by miR-99a on mTOR2 mediated EnNaC activation.

Olfactory marker protein directly buffers cAMP to avoid depolarization-induced silencing of olfactory receptor neurons

Olfactory receptor neurons (ORNs) use odour-induced intracellular cAMP surge to gate cyclic nucleotide-gated nonselective cation (CNG) channels in cilia. Prolonged exposure to cAMP causes calmodulin-dependent feedback-adaptation of CNG channels and attenuates neural responses. On the other hand, the odour-source searching behaviour requires ORNs to be sensitive to odours when approaching targets. How ORNs accommodate these conflicting aspects of cAMP responses remains unknown. Here, we discover that olfactory marker protein (OMP) is a major cAMP buffer that maintains the sensitivity of ORNs. Upon the application of sensory stimuli, OMP directly captured and swiftly reduced freely available cAMP, which transiently uncoupled downstream CNG channel activity and prevented persistent depolarization. Under repetitive stimulation, OMP-/- ORNs were immediately silenced after burst firing due to sustained depolarization and inactivated firing machinery. Consequently, OMP-/- mice showed serious impairment in odour-source searching tasks. Therefore, cAMP buffering by OMP maintains the resilient firing of ORNs.

Impact of human intervention on channel shrinkage and restoration in the Huanghe Estuary

Human intervention has become a globally dominant factor in the morphological evolution of estuary channels in recent decades. This paper analyzes seasonal morphological changes in the Huanghe estuarine channel for a 37-year period from 1976 to 2012 as a measure of estuarine shrinkage and restoration. The results show that the channel underwent four stages of development: enlargement (1976–1985), a gradual decreased area (1986–1994), shrinkage (1995–2001), and restoration (2002–2012). Generally, changes in the channel transect geometry during the first stage are regulated by natural fluctuations in water and sediment discharges, but the other three stages are impacted mainly by human intervention. The decreased runoff and sediment discharge caused by dam construction and water and soil conservation are the main reasons for the decrease and shrinkage of the channel transect. During the fourth stage, the increased ratio between water and sediment due to new reservoir construction and the water–sediment regulation scheme (WSRS) progressively affects runoff discharge, producing remarkable impacts on channel morphology during restoration. Human intervention has varying influences on different channel transects. The upstream channel section is more stable than the downstream channel, and human intervention in the downstream unstable channel has a 50% greater effect than that in the upstream stable channel. The WSRS has greater effects on the downstream unstable channel than on the upstream stable channel; however, a higher water–sediment ratio during the restoration stage results in greater impacts on the upstream stable channel than on the downstream unstable channel. Seasonal changes in the channel geometry indicate that seasonal adjustment is important for channel self-adjustment and that human intervention enhances variations in seasonal transect areas and impacts channel morphology.

Hydrodynamic and geomorphic adjustments of channel bars in the Yichang-Chenglingji Reach of the Middle Yangtze River in response to the Three Gorges Dam operation

The evolution of channel bars in response to upstream damming has significant impacts on channel stability, navigation, and aquatic habitats. Here, the effects of the Three Gorges Dam (TGD) operation on downstream channel bars in the Yichang-Chenglingji Reach (YCR) were comprehensively analyzed using remote sensing images, cross-sectional profiles, and hydrological datasets. The morphodynamic adjustments of channel bars in the YCR were significantly different during the pre- and post-TGD periods (i.e., before and after the construction of the TGD). Specifically, the total area of channel bars did not exhibit any significant trend in the pre-TGD period, but displayed a significant reduction following the construction of the TGD, although the morphodynamic response of each sub-reach was different. The channel bars in the YCR were relatively stable in the pre-TGD period, but became more erodible in the post-TGD period. The length/width ratio (LWR) of the bars showed an overall increase trend during the whole period from 1992 to 2017, not changing before and after the dam construction. The water discharge that led to the greatest channel bars adjustment was 27,000–30,000 m3/s (corresponding to bankfull discharge) in the pre-TGD period and 15,000–18,000 m3/s (corresponding to the medium discharge that can submerge the surface of the bars) in the post-TGD period. In addition, the grain size of non-uniform sediment with the highest replenishment degree gradually reduced downstream; these finer sediments were the main sources of material for the channel bars in the YCR. Quantitative relationships between bars area, the most effective bar-forming discharge and suspended sediment load with the highest replenishment degree, were proposed based on the improved Delayed Response Model (DRM). Results indicate that geomorphic adjustments of channel bars in the YCR are closely related to the previous four-year flow and sediment regimes, implying a delayed response of the fluvial system to damming.

From Neural Tube Formation Through the Differentiation of Spinal Cord Neurons: Ion Channels in Action During Neural Development.

Ion channels are expressed throughout nervous system development. The type and diversity of conductances and gating mechanisms vary at different developmental stages and with the progressive maturational status of neural cells. The variety of ion channels allows for distinct signaling mechanisms in developing neural cells that in turn regulate the needed cellular processes taking place during each developmental period. These include neural cell proliferation and neuronal differentiation, which are crucial for developmental events ranging from the earliest steps of morphogenesis of the neural tube through the establishment of neuronal circuits. Here, we compile studies assessing the ontogeny of ionic currents in the developing nervous system. We then review work demonstrating a role for ion channels in neural tube formation, to underscore the necessity of the signaling downstream ion channels even at the earliest stages of neural development. We discuss the function of ion channels in neural cell proliferation and neuronal differentiation and conclude with how the regulation of all these morphogenetic and cellular processes by electrical activity enables the appropriate development of the nervous system and the establishment of functional circuits adapted to respond to a changing environment.

Density Effects at a Concordant Bed Natural River Confluence

AbstractConfluences are locations of complex hydrodynamic conditions within river systems. The effects on hydrodynamics and mixing of temperature‐induced density differences between incoming flows are investigated at a small‐size, concordant bed confluence. To evaluate density effects, results of eddy‐resolving simulations for a densimetric Froude number Fr = 4.9 (weak‐density‐effects cases) and Fr = 1.6 (strong‐density‐effects cases) are compared to results of simulations in which the densities of the incoming flows do not differ (no‐density‐effects cases). Flow patterns predicted for both weak‐ and strong‐density‐effects cases show that secondary flow develops with increasing distance from the confluence apex. The pattern of secondary flow is characterized by denser fluid on one side of the confluence moving near the bed toward the side of the downstream channel corresponding to the less dense fluid and the less dense fluid moving near the free surface in the opposite direction. This pattern of fluid motion is similar to a spatially evolving lock‐exchange cross flow. In the strong‐density‐effects simulations, a cross‐stream cell of secondary flow develops at the density interface between the flows, similar to interfacial billows generated in classical lock‐exchange flows. Density effects increase global mixing with respect to corresponding no‐density‐effects cases regardless of whether the high‐momentum stream contains the higher‐density fluid or the lower‐density fluid. When density effects are weak, the lock‐exchange mechanism either reinforces the pattern of mixing associated with secondary flow induced by inertial forces, particularly helical motion, or opposes this pattern of mixing, depending on which tributary contains the denser fluid. When density effects are strong, flow from the upstream channel with the denser fluid moves under the flow from the upstream channel with the less dense fluid.