Tributary Channels Research Articles

How does landscape vegetation configuration regulate local channel initiation in a rapidly expanding micro-tidal system?

Tidal channels are essential morphological structures that mediate hydrological connectivity and maintain coastal resilience. Previous studies on vegetation-induced channel development primarily focused on the stages of initial establishment or later elaboration, characterized by slow and localized changes. However, the impact of rapid shifts in landscape vegetation on the initiation of tidal channels, such as main or tributary channels, remains poorly understood, particularly in micro-tidal system. In this study, we investigated this relationship through satellite imagery analysis and biogeomorphic modeling of a rapidly expanding micro-tidal marsh in the Yellow River Delta, China, which has experienced an invasion by Spartina alterniflora over the past decade. The satellite imagery demonstrated that Spartina alterniflora invasion has increased drainage density and reduced overland flow path length. Our modeling results showed that local flow acceleration between vegetation patches was insufficient to rapidly initiate channels under micro-tidal conditions. As the patchy marsh coalesced and expanded into a contiguously vegetated marsh, it altered landscape-scale flow patterns, diverting from homogenous platform flow to concentrated channel flow. This shift prominently promoted the initiation of tributary channels in the landward marsh zone. The simulated scenarios of vegetation removal highlighted a marked increase in flow divergence from adjacent platforms due to changes in landscape-scale vegetation configuration. This alteration in flow pattern amplified local hydrodynamics, consequently intensifying local channel incision. Our findings emphasize that the channel initiation is significantly influenced by landscape-scale vegetation configuration under micro-tidal conditions, beyond the localized interactions between plants and flow.

CSUPASZ LEJTŐK KARRJAINAK VIZSGÁLATA

This study deals with the karren formation of bare surfaces. The used methods are theoretical calculations, field mapping, laboratory experiments, and digital modelling. The denudation rate of karren surfaces on bare slopes and based on the data of measurements, the denudation rate of karren in different vegetation belts were given. Mostly, the development of rinnenkarren and meanderkarren was analysed. A function relation was determined between the density of rinnenkarren types and the slope angle. The effect of the main channel and tributary channels on each other was studied by computer modelling. The impact of the wind on the development of karren and the conditions for the development of tropical karren was also investigated.

Interaction between hydrodynamic and morphodynamic processes at the confluence of pipe and channel

Confluences between a pipeline and a channel are commonly found in urban drainage networks. The mechanisms of sediment transport and the coherent structure within the confluence zone remain ambiguous. The hydro-morpho-sedimentary processes at pipe and channel confluences, which are influenced by discharge ratios, are investigated using a laboratory-scale confluence. The pipe current compresses and diverts downstream upon entering the main channel, creating a scour hole that carries sediment downstream. Coarser sediment deposits first, forming the slope of the downstream boundary of the scour hole (D50 = 60.31 μm) and the inner bar (D50 = 62.67 μm). Finer sediments are then deposited in the outer bar (D50 = 53.12 μm), resulting in a bed morphology consisting of the scour hole, outer and inner bars, and corridor. The penetration of the pipe current causes redistribution of the main channel flow, creating two shear layers. The height of the bar is directly related to the intensity of turbulence. Within the range of discharge ratios from 0.06 to 0.09, the shear layers and bars are displaced toward the outer bank by a distance of approximately one pipe diameter (0.05 m). Turbulence in this area is not isotropic, with power-law relations for streamwise and lateral velocity having an exponent of approximately −5/3. Conversely, the separation zone deviates from this pattern. Overall, this study highlights the significant influence of the bed morphology in modifying the flow structure compared to channel confluences and jets into crossflow, which are important in drainage engineering designs and fluvial studies.

Replacive IOCG systems in the Ossa Morena Zone (SW Iberia): The role of pre-existing ironstones as a geochemical trap

The central Ossa Morena Zone (SW Iberia) hosts a regionally extensive ironstone level interbedded with bimodal volcanic rocks, limestone and shale of Lower-Middle Cambrian age. The stratabound ironstone includes dominant magnetite and hematite with locally abundant chert and barite. It is interpreted as being (sub-)exhalative at or near the seafloor and formed during a rifting event that postdated the Cadomian orogeny. In some places, such as in the Las Herrerías deposit, the ironstone is irregularly replaced by a chalcopyrite-rich ore; the Cu-rich mineralization is accompanied by the pervasive phyllic alteration of the hosting siliciclastic sediments. The highest copper grades are found when the ironstone is crosscut by WNW-ESE-trending late-Variscan extensional brittle-ductile structures that are interpreted as the feeder channels for deep hydrothermal fluids. A similar nearby copper-rich mineralization (Pallares) is likely controlled by the tectonic contact between limestone and pyrite-rich black shale.Sr-Nd whole-rock isotope geochemistry data suggests that the Sr in the ironstone (87Sr/86Sri ≈ 0.7088) is close to isotopic equilibrium with the local exhalative barite (0.7084–0.7086) and Cambrian seawater. The ironstone has a significantly more crustal εNd initial signature (<-1.8) than the coeval volcanic rocks (+5.2 to + 7.9). The younger sulfide mineralization inherited the Nd isotope composition of the ironstone but shows a significant enrichment in 87Sr (87Sr/86Sr > 0.7091) that is interpreted as related with the input of genetically different and more crustally-derived hydrothermal fluids.39Ar-40Ar dating of the phyllic alteration suggest that the copper mineralization was formed at ca. 332–330 My. These ages are coeval with those of small peraluminous granite intrusions that host Cu-Au vein-like mineralization and dated at 331.8 ± 1.6 Ma (LA ICPMS U-Pb zircon). Our interpretation is that the copper-rich mineralization at the Las Herrerías area is the distal expression of an intrusion-related hydrothermal system.Numerical modelling shows that ironstone is an effective trap for copper precipitation due to the large changes in pH and fO2 that take place when copper-bearing acid and reduced fluids react with the brittle ironstone. The precipitation of chalcopyrite, however, is controlled by the amount of available reduced sulfur in the ore trap. The δ34S values of the sulfides (+12.6 to + 21.6 ‰) suggest that the most likely source for the reduced sulfur is the thermogenic reduction of aqueous sulfate equilibrated with the exhalative barite (δ34S, +31.4 to + 35 ‰) with some minor input of reduced sulfur leached from the metasediments.This system could be considered as a variant of the IOCG clan. The formation of the ironstone and the copper mineralization, however, are separated by more than 200 My. Probably, many IOCG systems have a similar origin as Las Herrerías, with an ironstone being just a passive geochemical trap for the copper–gold mineralization.

A modified Soil and Water Assessment Tool Plus (M-SWAT+) model for sediment yield estimation

ABSTRACT The Soil and Water Assessment Tool Plus (SWAT+) model depends on the Modified Universal Soil Loss Equation (MUSLE), which in turn depends on the peak runoff rate for the estimation of soil loss from a catchment. The SWAT+ model generates a random number for each day in the process of peak runoff rate estimation from the catchment. On the other hand, the model provides calibration parameters like the peak rate adjustment factor for sediment routing in the tributary channels and main channels. There is uncertainty that how likely the SWAT+ model estimates the actual peak runoff rates. An improved MUSLE does not depend on the peak runoff rate, and, therefore, it minimizes uncertainty related to the peak runoff rate when estimating soil loss from the catchment in the SWAT+ environment. On the other hand, the effect of the topographic factor of the MUSLE or improved MUSLE on soil erosion and sediment transport is not explicitly explained. Therefore, we modify the source code of the SWAT+ model for sediment yield estimation by replacing the improved MUSLE and the best-fitted equations of the topographic factor in the source code. The modified SWAT+ model showed better performance than the original SWAT+ model.

Source-to-sink processes and genetic mechanism of progradational and lateral accretion submarine fans in the Qiongdongnan Basin, South China Sea

Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary system analysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems.The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins.

Pressure Distributions in Glottal Geometries With Multichannel Airflows

Computer simulation of self-sustained oscillation of the vocal folds has been successful with application of simple Bernoulli-like driving pressures. As voice simulation is now applied to asymmetric vibration with complex mode structures that yield partial vocal fold contact, the driving pressures need refinement. Two independent approaches were used to obtain pressure distributions. The first was a high-fidelity immersed-boundary method computation and the second was a series of pressure tap measurements on scaled-up physical models. Glottal geometries were based on normal surface modes of vibration. Samples are chosen from a large inventory of measured and calculated profiles. Pressure distributions show the complexity that can exist in the driving forces on vocal fold surfaces. Qualitative similarity between computation and measurement was established for a variety of contact patterns, showing diverse pressure gradients in multiple directions. Simplified Bernoulli approaches to glottal pressure distributions are defensible when a single flow channel is preserved in vocal fold oscillation. However, when there are contact islands that produce confluence or difluence of multiple airflow channels, the pressure gradients vary profoundly. Small quantitative differences were observed between measurement and calculation, primarily due to spatial sampling.

Entrance effect of curved endwall on heat transfer and flow structure in a confluent channel with pin fins

In advanced turbine blade internal cooling channels, the majority of the remaining coolant converges into the trailing edge and constitutes a confluent flow before the slot entrance. The entrance effects of curved endwalls (convex, concave) for confluent internal cooling channel are numerically investigated in this paper. The overall heat transfer performances and flow structures are compared in the slot channel with pin fin cooling at the five momentum ratios (M = 0.1–2.1). Among all the cases studied, the higher momentum inflow not only enhance heat transfer but also reduce pressure loss in the slot channel with concave endwalls. In particular, the substantial comprehensive heat transfer factor (η) increase reaches 29.4% higher than the flat endwalls at the given relative curvature height ratio of 1.83. For the models with convex endwalls, the jet-like flow improves the η at the most by 12.1% compared to the flat endwalls. As the curvature height ratio increases, the effects of curved endwalls diminish eventually. In addition, the momentum ratio determines the formation and specified impact of the above flow characteristics in the confluent flow. The curved endwalls exhibit more increase in the η at lower M.

Effect of channel confluence on the dynamics of debris flow in the Niutang Gully

Effect of channel confluence on the dynamics of debris flow in the Niutang Gully

Sedimentary Characteristics and Evolution of the Late Miocene to Quaternary Tributary Channels in the Head of Bounty Channel, New Zealand

The Bounty Channel is a large-scale submarine channel system located in the eastern continental margin of New Zealand. Extending along the axis of the Bounty Trough, the channel system comprises three main tributaries (C1–C3) at its head, which merge downstream into a trunk channel leading to a terminal submarine fan. In this study, we use high-quality two-dimensional multichannel seismic data to investigate the formation and evolution of tributary channels C1 and C2. Four types of seismic facies are identified in the tributary channels: fill-type, mounded divergent, wavy, and subparallel facies. These seismic facies are correspondingly interpreted as topographic depression or channel fills, levees, sediment waves, and hemipelagic deposits. The Late Miocene tributary channels were developed above a pre-existing NE–SW-oriented depression. The Pliocene to Quaternary tributary channels are characterized by preferential development of higher levees on their left hand, and the presence of sediment waves on the lower levees of their right-hand, signaling an effect of the Coriolis force. The formation and evolution of the tributaries are primarily linked to regional tectonics, including increased convergence rate between the Pacific and Australian plates along the Alpine Fault in the Late Miocene and enhanced uplift and erosion at the Southern Alps during the Pliocene.

The influence of density difference, discharge ratio and wind on the mixing at large river confluence

Numerical simulations for a large river confluence were conducted to comprehend the influences of three factors: density difference, discharge ratio, and wind shear on tributary flow dispersion. The present study focused on the confluence channel of the Nakdong River and the Yangsan Stream in South Korea, with simulation conditions selected based on realistic conditions. Numerical results revealed that tributary flow can disperse upstream under high discharge ratio conditions, which becomes stronger with density stratification. In particular, when the tributary flow is denser than the mainstream, bathymetry around the junction determines the flowing direction of the density current. Thus, understanding tributary flow dispersion under varying conditions is vital due to its influence not only downstream but also upstream of the confluence. Additionally, wind shear impact on the mixing between mainstream and tributary flow is notable but less significant than density difference or discharge ratio.

Ponding and compartmentalization of a giant Paleogene slope fan by mass transport complexes, offshore Newfoundland, Canada

The Ephesus fan is a giant channel-lobe complex that extends across 460 km2 in the lower structured slope of the West Orphan Basin, offshore Newfoundland, Canada. Based on biostratigraphic dating of offset wells, the fan was likely deposited during the Oligocene. High resolution 3D seismic data reveal that the fan overlies a succession of mass transport deposits that initially created a flatter topographic surface, with later slumping events building elongated ridges. Subsequent high density turbidity currents coursed into the area through a single feeder channel, depositing as lobes onto the flatter area via a network of distributary channels. The lobes were circumferentially ponded and internally compartmentalized by the slump ridges, and the ponding forced the fan to assume its unique, 46 km-wide shape. Distributary channels were initially directed to the south side of the fan, due to the higher relief of the mass transport deposits to the north. After the infill of the accommodation space to the south, subsequent sediment input levelled the remaining rugose topography, and some distributary channels were able to avulse north. Throughout deposition of the fan, distributary channels also continued down-dip from the lobe complex, indicating some sediment bypass continuing down the lower slope. Overlying laminated mudrock displays pervasive polygonal faulting, signaling dewatering processes and the end of deposition by muddy submarine landslides and high density turbidity currents.

3D model of the El Hornito pluton, Sierras Pampeanas of Argentina: Evidence of hybridization in the re-used feeder channels for emplacement in the ductile-brittle level

A comprehensive structural, petrological, and geophysical study of the 385 ± 2 Ma Devonian El Hornito Pluton (EHP) in the Sierra Grande de San Luis, Argentina, is presented. We establish that the EHP results from the intrusion of three main magma batches. The three-dimensional shape of the pluton was modeled using stochastic litho-constrained gravity data inversion and was complemented with a field geology survey. Results suggest a shallow-rooted, irregularly shaped pluton with a mean depth of 1.5 km, 16 km long and 4 km deep with a volume of 217 km³. Two areas of negative residual Bouguer anomaly reveal the existence of two root zones interpreted to indicate feeder channels. One of the feeders does not have a surface expression, but the other coincides with the central part of the pluton. A hot mafic magma intruded into and rejuvenated a crystallizing granite mush and the thermal perturbations triggered local convection with the development of an ascending magma plume developing mixing/mingling structures. Pluton emplacement was controlled by a shear zone at the boundary between two major metamorphic units. Emplacement is evidenced by the location of the two root zones along the interpreted contacts of the metamorphic zones, and the shear zone along this basement anisotropy provided the space into which magma batches were emplaced. Internal and external structures indicate that space for pluton emplacement was generated by a combination of tectonism with ballooning and stoping assisted by floor depression, which were the most effective processes during the final emplacement of the magma. This was possible due to the contrasting rheological responses of the host rocks.

Microbial community structure and metabolic profile of anthropized freshwater tributary channels from La Plata River, Argentina, to develop sustainable remediation strategies.

Microbial communities from freshwater sediments are involved in biogeochemical cycles and they can be modified by physical and chemical changes in the environment. Linking the microbial community structure (MCS) with physicochemistry of freshwater courses allows a better understanding of its ecology and can be useful to assess the ecological impact generated by human activity. The MCS of tributary channels from La Plata River affected by oil refinery (C, D, and E) and one also by urban discharges (C) was studied. For this purpose, 16S rRNA metabarcoding analysis, in silico metagenome functional prediction, and the hydrocarbon degradation potential (in silico predictions of hydrocarbon-degrading genes and their quantification by qPCR) of the MCS were studied. Principal coordinate analysis revealed that the MCS was different between sites, and it was not structured by the hydrocarbon content. Site C showed physicochemical characteristics, bacterial taxa, and an in silico functional prediction related to fermentative/heterotrophic metabolism. Site D, despite having higher concentration of hydrocarbon, presented autotrophic, syntrophic, and methanogenic pathways commonly involved in natural processes in anoxic sediments. Site E showed and intermediate autotrophic/heterotrophic behavior. The hydrocarbon degradation potential showed no positive correlation between the hydrocarbon-degrading genes quantified and predicted. The results suggest that the hydrocarbon concentration in the sites was not enough selection pressure to structure the bacterial community composition. Understanding which is the variable that structures the bacterial community composition is essential for monitoring and designing of sustainable management strategies for contaminated freshwater ecosystems.

Sources of per- and polyfluoroalkyl substances in an arid, urban, wastewater-dominated watershed

Per- and polyfluoroalkyl substances (PFAS) enter surface waters from various sources such as wastewater treatment plants, fire-fighting sites, and PFAS-producing and PFAS-using industries. The Las Vegas Wash in Southern Nevada of the United States (U.S.) conveys wastewater effluent from the Las Vegas metropolitan area to Lake Mead, a drinking water source for millions of people in the U.S. Southwest. PFAS have previously been detected in the Las Vegas Wash, but PFAS sources were not identified. In this study, upstream wash tributaries, wastewater treatment effluents, and shallow groundwater wells were sampled in multiple campaigns during dry-weather conditions to investigate possible PFAS sources. Out of 19 PFAS, two short-chain PFAS—perfluoropentanoic acid (48 % of the total molar concentration) and perfluorohexanoic acid (32 %)—comprised the majority of PFAS loading measured in the Las Vegas Wash, followed by perfluorooctanoic acid (9 %). On a mass loading basis, the majority of total measured PFAS (approximately 90 %) and at least 48 % of each specific PFAS in the Las Vegas Wash likely entered via municipal wastewater effluents, of which the main source was likely residential wastewater. One of the drainage areas with a major civilian airport was identified as a potential source of relatively enriched perfluorosulfonic acids to a small wash tributary and shallow groundwater samples. Nonetheless, that tributary contributed at most 15 % of any specific PFAS to the mainstem of the Las Vegas Wash. Total PFAS concentrations were relatively low for the small tributary associated with an urban smaller airport and the lack of flow in the tributary channel immediately downgradient of an Air Force base indicates the smaller airport and base were unlikely significant PFAS sources to the Las Vegas Wash. Overall, this study demonstrated effective PFAS source investigation methodology and the importance of wastewater effluent as a PFAS environmental pathway.

Limited effect of the confluence angle and tributary gradient on Alpine confluence morphodynamics under intense sediment loads

Abstract. Confluences are dynamic morphological nodes that are found in all river networks. In mountain regions, they are influenced by hydraulic and sedimentary processes that occur in steep channels during extreme events in small watersheds. Sediment transport in the tributary channel and aggradation in the confluence can be massive, potentially causing overbank flooding and sedimentation into adjacent settlement areas. Previous works dealing with confluences have mainly focused on lowland regions, and those that have focused on mountain areas have used sediment concentrations and channel gradients that are largely under-representative of mountain river conditions. The presented work contributes to filling this research gap with 45 experiments that use a large-scale physical model. Geometric model parameters, the applied grain size distribution, and the considered discharges represent the conditions at 135 confluences in South Tyrol (Italy) and Tyrol (Austria). The experimental program allowed for a comprehensive analysis of the effects of (i) the confluence angle, (ii) the tributary gradient, (iii) the channel discharges, and (iv) the tributary sediment concentration. In contrast to most research dealing with confluences, results indicate that, in the presence of an intense tributary sediment supply and a small tributary-to-main-channel discharge ratio (0.1), the confluence angle does not have a decisive effect on confluence morphology. Adjustments to the tributary channel gradient yielded the same results. A reoccurring range of depositional geomorphic units was observed in which a deposition cone transitioned to a bank-attached bar. The confluence morphology and tributary channel gradient rapidly adjusted, tending towards an equilibrium state to accommodate both water discharges and the sediment load from the tributary. Statistical analyses demonstrated that the confluence morphology was controlled by the combined channel discharge and the depositional or erosional extent was controlled by the sediment concentration. Applying conclusions drawn from lowland confluence dynamics could misrepresent depositional and erosional patterns and the related flood hazard at mountain river confluences.

Where are the feeder channels for platinum reefs in the Bushveld Complex?

AbstractThe Bushveld Complex in South Africa hosts the lion’s share of the world’s noble metal resources in platinum reefs – thin layers of silicate/chromite rocks containing platinum-rich sulphides. The reefs are widely attributed to multiple replenishments by ore-forming magmas that have been entering the evolving Bushveld chamber through numerous feeder conduits. The replenishment events are marked by regional and local disconformities/unconformities, significant isotopic shifts, and notable reversals in the whole-rock and mineral compositions. Surprisingly, however, so far no single feeder conduit for platinum reefs has been found despite extensive surface and underground mining for over a century. Feeder conduits appear entirely absent from the Bushveld Complex. This paradox has long been known but has never been specifically addressed. Here, we suggest that the absence of feeder channels is a natural consequence of the magma chamber replenishment through a cumulate pile. The fossilization of the feeder channels in the cumulate pile is likely impeded by two principal factors: (a) a cumulate pile is too hot to enable efficient cooling and crystallization of magma flowing through the channels, and (b) the channels are closed by an adjacent elastically deformable pile immediately after cessation of the magma emplacement. The feeding dykes are thus absent because there is little chance for the conduits to get preserved in a hot and deformable cumulate pile of layered intrusions.

Large Wood Transport and Accumulation Near the Separation Zone of a Channel Confluence

AbstractFallen trees enter the adjacent stream and are carried away downstream by the current. As the stream joins another one, the complex hydrodynamics near their confluence make the movement of wood hard to predict. These woods may accumulate near the confluence resulting in backwater and subsequent potential flooding. A laboratory study was conducted to investigate the movement and accumulation behavior of individual pieces of wood near the confluence. The characteristics of wood (i.e., the length, diameter, and density) and the hydraulic conditions (i.e., the discharge ratio and the release distance) were varied in this investigation. It was found that the wooden pieces released from the tributary got occasionally trapped in the flow separation zone of the confluence, whereupon they were mainly trapped by a clockwise vortex and continued to stay driven by a reverse cluster of currents within this zone. The accumulation probability of wood was mainly related to its length, the discharge ratio and the release distance. The effect of wood diameter and density within the tested parameters was negligible. The probability increased with an increase in the discharge ratio as well as a decrease in the release distance. The longer pieces had a higher probability of being trapped, whereas for those exceeding some critical value, the probability was nearly the same, or dropped sharply. A generalized model for wood accumulation near the confluence was developed for practical application. These findings carry significant implications for river management, particularly in preventing the risk of flooding caused by wood blockage.

Effect of hydrological variability on suspended sediment load at a river junction: a case study

Abstract Confluences act as crucial intersection in a fluvial system as they regulate the flow, sediment, and geomorphological stability. Two of the natural occurrences that have an effect on hydro-morphological processes that characterize the channel are sediment movement and stream discharge. However, assessments of suspended sediment distribution patterns across channel confluences and functions of tributaries on sediment transfer in downstream streams are still inadequately explored. To fulfil this, a year-long field investigation was conducted around river confluence at various time scales during the hydrological season. The bathymetry of the confluence was performed using digital echo-sounding equipment, electro-magnetic current meter, and differential global positioning equipment. This study uses in situ measurement and empirical techniques to quantify the spatiotemporal distribution of suspended sediment particles. Furthermore, Yang's formula was used to analyze the sediment concentration, and several statistical standards were employed to establish a differentiation between predicted and observed data. The results illustrated that a good agreement has been achieved among the calculated and measured statistics based on the correlation coefficient value. According to the findings, 8% fewer errors in the quantification of suspended sediment were induced in the tributary than in the main river because of the very low flow of the tributary. The present ramifications can help increase our database and understanding of the dynamics of major river confluences.

Estimation of river discharge using Monte Carlo simulations and a 1D hydraulic model based on the artificial multi-segmented rating curves at the confluence of two rivers

During extreme floods caused by climate change, reliable flow discharge data are essential for successful reservoir operation to mitigate downstream flood damage. Generally, the flow discharge is computed using the rating curve (RC) established from the relationship between the flow rate and water stage level. Determining the parameters of rating curves is subject to uncertainties related to the difficulties and limitations of flow monitoring in covering a wide range of flow variations. Especially at river confluences, the uncertainties are pronounced when floods occur owing to several factors such as roughness change, backwaters, and levee overflow. The Seomjin River Basin in Korea suffered from flood inundation that occurred at the tributary confluence during an extreme flood in 2020. To identify a reliable flow rate of the main stream and tributary, this study proposes an indirect flow assessment scheme using a 1D hydrodynamic simulation model to find the best simulated water level in an iterative manner based on Monte Carlo (MC) simulations. With a large amount of discharge data generated from random-number combinations, it is possible to obtain the best results automatically by specifying the reliability limitation considering the uncertainty of the predetermined RC parameters associated with the roughness coefficient. Nash Sutcliffe Efficiency (NSE) was incorporated to evaluate the reproduced water level to meet the threshold specified for NSE ≥ 0.75. The simulated flowrates computed from the revised RC and roughness coefficients revealed an error range of 8%–36.6% compared with the design flood. The approach proposed in this study is applicable for determining the valid parameters necessary to create a revised RC at an existing water level gauge station, where the uncertainties of the RC are pronounced, particularly in the vicinity of the channel confluence.