Tributary Channels Research Articles

Experimental field study on the formation process of debris flow dam at channel confluence: Implications for early identification of river blockage

Experimental field study on the formation process of debris flow dam at channel confluence: Implications for early identification of river blockage

Scour pattern at zero-degree confluent channels

Scour pattern at zero-degree confluent channels

The Early Pre-Pottery Neolithic B Site of Aḥihud (Western Galilee, Israel)

Abstract. The recent excavations at the site of Aḥihud uncovered the remains of an Early Pre-Pottery Neolithic B village on the bank of Nahal Ḥilazon (Acre valley, Israel) tributary channel. The site is in an ecotone between the western Galilee hills and the northern coastal plain. The lithic assemblage from the site includes typical PPNB arrowheads (about a third are El-Khiam and Helwan types) as well as hundreds of sickle blades. The fauna include evidence to the hunting of large and small game as well as small predators. The flora from the site shows evidence for an intensive legume crop agriculture. Thousands of legume seeds were concentrated in two silos. The vast majority are broad beans (Vicia faba) that predate the earliest evidence for an established cultivation of legumes in the Southern Levant. Other finds attest to the acquisition of exotic goods such as various green stones and obsidian from the Northern Levant or shells from the Red Sea.

Non-invasive (georadar) investigation of groundhog (Marmota monax) burrows, Pennsylvania, USA

Zoogenic impact plays a critical role in stream processes, especially bank stability and resulting channel dynamics. This study focuses on bioturbation by groundhogs (Marmota monax) along the riparian zone of Mill Creek (Bucks County, Pennsylvania, USA). Several complexes comprising at least 32 active burrows (average diameter: 25.9 cm) were geolocated, with morphometric measurements obtained at selected sites. Two networks were imaged using high-frequency 800 MHz ground-penetrating radar (GPR) and included: 1) a grid of parallel 3-m-long transects on the south bank, and 2) an 11-m-long profile on the north bank. Post-processed electromagnetic signal traces (A-scans) comprising 2D radargrams (B-scans) revealed voids as reverse-polarity anomalies (hollow inclined shafts and tunnels), allowing for a general assessment of burrow depth and orientation. At the southern cutbank site, a large burrow had an entrance diameter of 0.3 m and a westerly dip. A sloping tunnel section was detected at ~0.5 m depth, based on the geometry of point-source (transverse) hyperbolic diffractions corresponding to the roof and a floor ‘pull-up’. The second locality traversed three open burrow entrances adjacent to large tree roots. This survey along a tributary channel shows multiple hyperbolics below adjacent openings, with the latter showing the characteristic signal ‘breakout’. GPR data show hyperbolic signatures ~0.3–0.4 m below the ground surface. Along this transect, burrowing activity appears to increase with proximity to the northern bank of Mill Creek. An example of a depth slice (bedding-plane view) from a nearby riverbank demonstrates the potential for 3D visualization (C-scans) of burrow networks using a grid of closely spaced GPR profiles. Groundhog burrows constrain maximum long-term level of the groundwater table and serve as important zoogeomorphic structures in diverse ecotones, including developed landscapes. Abundant evidence of bank slumping, incision, and treefall suggests that burrowing activity likely weakens root systems and enhances groundwater flow, thereby initiating or accelerating geomorphic cascades leading to slope failure.

Numerical Simulation of Confluence Flow in a Degraded Bed

The fluid dynamics of channel confluences are highly complex due to flow separation and secondary currents. Although numerous studies in the past few decades have focused on the numerical simulation of confluence flow, deformed beds were rarely used. This study attempts to address this issue through numerical simulation of the flow behavior in an open-channel confluence flume with an equilibrium degraded bed in OpenFOAM (version 6.0) to compare the results with a flatbed. In the present study, different turbulence models, including Reynolds-Averaged Navier–Stokes (RANS), large-eddy simulation (LES), and detached eddy simulation (DES) models were performed using rigid-lid and volume-of-fluid (VoF) methods. The accuracy of the models was statistically analyzed by comparing them with observation data. The results demonstrated that the LES model had the best performance, with a minimum average normalized root-mean-square error (NRMSE) of 3% under the VoF assumption. The investigation also further illuminated the intricate interplay of vortical structures within the confluence zone. Notably, the number and behavior of vortices were found to be influenced by channel geometry and size, as well as interactions between separated shear layers. Circulation within the separation zone near the inner bank differed in rotation between the degraded and flatbed cases.

ERT investigation of mud volcanoes: detection of mud fluid migration pathways from 2D and 3D synthetic modelling

Mud volcanoes are geological structures observed throughout the world that arise from the upwelling of deep fluids along discontinuities in the subsoil. The detection of mud fluid migration pathways can be challenging, even when using Electrical Resistivity Tomography (ERT) as detectability issues may arise from complex geological settings. This paper presents new results from 2D and 3D ERT synthetic modelling for the investigation of the shallow, internal structure of terrestrial mud volcanoes. This study revealed the internal structure of the ‘Cenerone-Pineto’ mud volcano (Central Italy) and provided further clues as to its internal structure. The main results of the study are: the presence of a mud chamber, which represents the last phase of mud accumulation before final emission, not located beneath the crater but laterally offset, as well as the presence of a narrow, shallow feeder channel; these findings represent evidence of a much more complex structure than one would expect. This means that the mud volcano is not supplied with mud fluids directly from below as would be the case with an uprising of deep fluid along a near-vertical open fracture and that the shallow mud fluid reservoir is not correlated to the distribution of any mud volcano observed on the surface. Findings from this study are consistent with the observed structural features already noted in ERT and seismic field data collected at the ‘Cenerone-Pineto’ mud volcano and may be helpful in explaining the mechanisms and processes involved in mud volcanism in similar geological settings.

Experimental Study on Depth-Averaged Velocity and Bed Profile in a Braided Channel with a Mid-Bar

Braided alluvial rivers with a mid-bar are common features occurred in alluvial river that consists of bifurcation and confluence channels. The formation of the mid-bar will affect the hydraulics of river systems in terms of velocity and bed morphology. The studies corresponding to the typical braided river with a mid-bar are still ongoing. This paper is to present the finding of depth-averaged velocity, Ud and bed profile at the bifurcation and confluence channel. A channel with a mid-bar and erodible bed was used in this research. The experimental work was carried out in the Hydraulic Laboratory at Universiti Teknologi Malaysia, (UTM). In the experiment, two types of flow which are low flow and high flow rates were considered. The study found that depth-averaged velocity distributions are influenced by flow discharge and varied at the braided channel. The highest Ud velocity is 0.35 m/s occurred at the bifurcation area and the lowest Ud is 0.2 m/s that was occurred at the confluence area. This genesis to more erosion occurred at the bifurcation area compared to the confluence area.

The submerged Palaeo-Ems River in the Quaternary stratigraphic context of the German North Sea

During the Late Pleistocene, the Palaeo-Ems system (PES) was one of the major tributary channels feeding the Elbe Palaeovalley (EPV) and formed an important part of the drainage system of the continental northwestern Europe unglaciated hinterland. In this study, a detailed interpretation of high-resolution 2D sub-bottom profiler and Boomer grids were used to map the overall course of the submerged PES channel, as well as its spatial and stratigraphic relationships with other Quaternary geological units in the German North Sea. Mapping of buried tunnel valleys, a lacustrine-fill unit, straight channel structures was also carried out. The sedimentary record of the PES is represented by a low gradient and meandering channel which branched into two major pathways as it approached the EPV western flank. Its upstream to downstream trends, coupled with seaward decreasing gradient and sinuosity, are similar to those visible in present-day river deltas. Both the PES and EPV subsequently formed a combined depositional system, which was successively drowned due to the fast-rising relative sea level that overwhelmed the adaptation capabilities of the joint drainage system. For the first time, this study sheds light onto the PES/EPV morpho-stratigraphic relationships which played a key role in the coastal landscape architecture of the German North Sea since the Late Pleistocene.

Vorticity preference of the Yangtze finless porpoise (Neophocaena asiaeorientalis) during the dry season at the Wanhe River Estuary confluence

The Yangtze finless porpoise (Neophocaena asiaeorientalis) is critically endangered. Finless porpoises rely on small fish as their primary food source. Fish distribution is impacted by topography and vorticity (i.e., water flow patterns), which are markedly more complex in river channel confluences than in other aquatic habitats. Thus, the hydrodynamic conditions imposed by confluences may influence habitat selection by fish and the subsequent behavior and predation strategies of porpoises. However, hydrodynamic effects and driving mechanisms for porpoise occurrence, distribution, and feeding strategies remain unclear. Based on survey data and hydrologic measurements, we created a hydrodynamic model to investigate the driving mechanism of porpoise clustering in a confluence of the Wanhe River Estuary, China. We showed a preference for vorticity in the range 0.001 s−1–0.0015 s−1. Our multivariate logarithmic linear model revealed a fit of R2 = 0.792, indicating consistency between theoretical and actual occurrence values. Certain patch parameter effects suggest that vorticity fragmentation affects porpoise habitat selection and utilization. Our study provides a new perspective on the ecological impact of the Yangtze River wading project and the habitat protection of aquatic animals in rivers and aids future research examining hydrodynamic effects on the feeding behavior of freshwater cetaceans.

Morphologies, patterns, and filling architectures at the confluence zones of the cretaceous shallow-water delta in the Songliao Basin, NE China

Confluences are particular locations within distributary channel networks that undergo notable changes in hydraulic and morphological features, leading to distinct erosional and sedimentary characteristics. However, our understanding of the filling architecture of river confluences remains incomplete. To address this gap, it is necessary to explore typical deposits at ancient channel confluences. This study conducts a detailed analysis of parasequence set 4 (PSS4) from 36,886 wells that penetrated the Cretaceous shallow-water Daqing Changyuan delta, Songliao Basin, NE China. Based on the composition, fabric, texture, particle size, and sedimentary structures of cores, seven lithofacies, ten lithofacies associations, and two facies associations were identifed. The interpretation of the sedimentary environment indicated that Daqing Changyuan delta mainly comprises delta plain and delta front in the study area, and we provided a precise description of the distributary channel system covering 690 km2. The distributary channels in the delta show three confluence patterns: asymmetric confluence, symmetric confluence with a low angle, and asymmetric confluence with a high angle. The patterns give rise to varied three-dimensional reservoir architecture units, including a tributary mouth-bar, an upstream junction bar, a separation zone bar, a confluence scour bar, a fine-grained deposition wing, and a post-confluence mid-channel bar. Each confluence pattern has its own unit compositions and distributions, resulting in varying reservoir potentials.

Modeling Steady Grain Sorting in River Bifurcations

AbstractA striking feature of rivers is their ability to sort the sediments composing them. One of the chief causes for grain sorting consists in the selective transport of different sizes moving downstream. This process can be substantially influenced by the presence of lateral topographic variations, as those produced by channel bifurcations, in which water and sediment are diverted between two smaller anabranches. In particular, field and laboratory observations have shown that the asymmetric flux distribution commonly observed in actual bifurcations is associated with a coarsening of the most‐carrying branch. Here, equilibrium sorting in river bifurcations is addressed through a quasi‐2D model. Differently from previous works, a fully physically based description of the processes tied to a heterogeneous sediment mixture is introduced. The main mechanisms consist in the lateral pull of sediment due to a sloping bed upstream the bifurcation, and the variation of transport capacity in downstream branches. The model indicates that grain sorting tends to reduce the degree of flux asymmetry between branches for increasing heterogeneity of the mixture. Moreover, the uneven discharge distribution is associated with a different bed surface composition, with bed coarsening of the dominating channel and fining of the other branch. The reduced sediment transport asymmetry and bed surface fining enhance the transport of fine material in the less‐carrying branch, thus contributing to keep it morphologically active. Finally, the model predicts an overall fining of bed surface material with respect to the feeder channel.

KAJIAN EFEKTIFITAS GULLY PLUG DALAM PENGENDALIAN RUN OFF DI KAWASAN HULU DAS PULISAN

The flood problem in Pulisan village that occurred in 2019 is one of the problems that needs to be addressed immediately because it causes losses to residents living around the river, and disrupts vehicle traffic. One of the causes of flooding in the Pulisan river is the magnitude of the run off and the large flow rate so that potential flooding events can occur. Therefore, run-off control is needed in the upstream area of the Pulisan river. Pulisan watershed has a total watershed area of 3.25 km2 and has 9 tributary channels. The location reviewed is in the Pulisan river channel with selected sections is the channel of 5 Pulisan rivers which has a watershed area of 0.2512 Km2. The Araren-Pigrandma MRG rain post and the Maen Climatology rain post are sources of maximum daily rainfall data used with a time span of 2002 to 2021. HEC-HMS software is used to obtain the parameters needed to obtain a peak discharge of 2.2 m3 / second and a planned flood discharge. HEC-RAS software to analyze water level and flow rate when using gully plug. The simulation results show that from several types of gully plugs, a significant reduction in flow speed is in type 60 gully plugs, namely the flow speed to 0.6 – 1 m / second, the flow speed does not cause deposits in the channel.

Dendritic ridges in Antoniadi basin, Mars: Fluvial or volcanic landforms?

Antoniadi basin displays dark-toned dendritic ridges previously interpreted as inverted fluvial channels. Detailed observations of these dark-toned ridges as well as the geological units in the central region of Antoniadi basin are provided emphasizing images from the Colour and Stereo Surface Imaging System (CaSSIS), the High Resolution Stereo Camera (HRSC) and the High Resolution Imaging Science Experiment (HiRISE) instruments. Results show that the dark-toned ridges are part of the most recent geological unit as they overlie, and thus postdate all plains of the central Antoniadi basin, which is Early Amazonian based on its crater size-frequency distribution. Our observations of the dark-toned ridges are not consistent with inverted fluvial channels: they do not widen in the expected downstream direction, they display a rubbly texture and lack layering at high resolution, and have lobes with local levees in place of channel heads. In addition, the branched ridges are more mafic in composition and display a relatively higher thermal inertia than their surroundings. This suite of characteristics is better explained by volcanic flows developed as distributary channels rather than fluvial tributary channels. The occurrence of dikes in the east and west of the studied region supports that these flows were formed by lava, perhaps a'a like flows as suggested by the rubbly texture, but with an unusually high degree of digitation. Alternatively, such a geometry could be explained by the emplacement of the lava along pre-existing fluvial valleys, but neither the underlying topography, nor two nearby older craters, exhibit signs of fluvial erosion.

Evolution of the main channel of the Yangtze River

AbstractThe construction and operation of the Three Gorges Reservoir and the cascade reservoirs upstream have significantly altered the processes of flow and sediment in the main and tributary channels of the Yangtze River. This has led to substantial adjustments in the riverbed through erosion and deposition, thereby impacting flood protection, water resource utilization, navigation, and the aquatic environment in the Yangtze River basin. In this study, prototype measurements were used to analyze the variations in runoff and sediment load in the main channel of the Yangtze River, as well as the changes and evolution of the riverbed. Mathematical modeling was done to predict the trends in reservoir sedimentation and riverbed adjustments. The results indicate that, apart from the significantly increased runoff and sediment load in the river source region (Zhimenda station) over the past two decades, there is no clear unidirectional trend of increasing or decreasing in the main and tributary annual runoff of the Yangtze River. However, the release of reservoir outflows undergoes significant changes throughout the year due to reservoir regulation. Suspended sediment load in the upper Yangtze River has been decreasing since the 1990s, especially after the operation of the Three Gorges Reservoir and the four cascade reservoirs in the lower reach of the Jinsha River. The factors influencing flow and sediment variations include mainly climate change and human activities such as reservoir operation and soil and water conservation. The significant changes in flow and sediment conditions have disrupted the original relative equilibrium state of the main channel of the Yangtze River, leading to riverbed adjustments. The river sections in the upper reach, located within reservoir areas, have shifted from erosional state under natural conditions to accumulative state, while the middle and lower reaches have transitioned from a relatively equilibrium state to a process dominated by erosion and reconstruction. Overall, the river regime in the reservoir area and downstream of the Three Gorges Dam remains relatively stable, but there have been adjustments in some local river sections, for example, in the curved sections, particularly in the sharply curved sections downstream of the Three Gorges Dam, where gradual or abrupt chute cutoff has occurred. In the foreseeable future, the river channel downstream of the Three Gorges Dam will remain in an unsaturated state regarding sediment transport. The process of river channel erosion will persist for a long time and have far‐reaching consequences. Some long straight sections, multiple bifurcation sections, and sections with large curvature are expected to undergo certain adjustments in the river regime, necessitating continuous observation, long‐term monitoring, and timely river management and channel governance.

Rip Currents Off Rocky‐Shore Surge Channels

AbstractMore than half the world's coastlines are rocky, but rip‐current dynamics on these topographically complex shores have not been studied. Field experiments on a typical rocky shore using video, drifters, and in‐situ current meters and pressure sensors reveal that incoming narrow‐banded swells result in incident wave groups that force breakpoint low‐frequency (LF) waves, which act in phase inside the surf zone to generate set‐up, run‐up, overtopping, and mass flux, pooling water atop the shore. Set‐up is enhanced by the change in momentum of the LF waves owing to dissipation by bottom friction over the rough seafloor, and by depth‐limited breaking, evidenced by low reflection. A 1D momentum balance results in a mean bottom‐drag coefficient of 1 owing to the rough bottom and vegetation. During wave‐group minima, the hydraulic head of the pooled water forces a return flow through a network of incised feeder channels that converge to a primary surge channel, directing flow offshore. The rip current extends three surf‐zone widths offshore with a maximum velocity of 1 m/s, and (in contrast to sandy shores) flow exits the surf zone, augmenting cross‐shore transport. Rip current strength is a function of channel hypsometry, overtopping, and exit constriction, factors that vary with the tide. As the tide rises, the mean flow decreases as the hydraulic head decreases and the constriction diminishes. Similar to rip currents on sandy beaches, rip currents on rocky shores are modulated by tides and sea‐swell, but they differ in geometric scale and forcing mechanism.

Characterizing the supra- and subsolidus processes that generated the Current PGE-Cu-Ni deposit, Thunder Bay North Intrusive Complex, Canada: insights from trace elements and multiple S isotopes of sulfides.

The online version contains supplementary material available at 10.1007/s00126-023-01193-9.

Stratigraphic architecture and distribution patterns of submarine fan-reservoir elements: insights derived from the Pliocene and Pleistocene Bengal Fan

ABSTRACT 3-D seismic data from the Bengal Fan along with spectral decomposition and RGB color blending techniques display stratigraphic architectures and spatiotemporal distribution patterns of submarine fan-reservoir elements in stark detail. Seven reservoir elements are recognized in Pliocene and Pleistocene channel–lobe complexes (i.e., subfans) developed on the northeastern fringe of the Bengal Fan. Among them, crevasse, overbank, and avulsion splays are not well acknowledged by standard models of submarine fan-reservoir elements. Crevasse splays decrease in thicknesses towards ancestral channels, and are capped by overlying levees, whereas overbank and avulsion splays increase in thicknesses towards ancestral channels and cap underlying levees. Crevasse and avulsion splays exhibit lobate planform morphology and are linked updip to ancestral channels by feeder channels, whereas overbank splays display tongue-like planform morphology and lack feeder channels. Fills of laterally migrated channel-complex sets (CCSs) appear only in early stage of subfan evolution, whereas fills of vertically stacked CCSs can appear either in middle or late stages of subfan evolution. The inner segment of the documented subfans fostered infills of both laterally migrated and vertically stacked CCSs, whereas the outer segment of the studied subfans contains terminal lobe complexes and distributary-channel fills. Crevasse, overbank, and avulsion splays can appear either in middle or late stages of subfan evolution, and mainly occur in overbank environments of middle segments of the documented subfans, which are dominated by muddy facies as predicted by the standard model of submarine fan-reservoir elements. Pliocene and Pleistocene subfans demonstrate the importance of splay processes in submarine-fan evolution, and this has implications for understanding the evolution of the volumetrically largest sediment accumulations on Earth and the distribution of submarine fan-reservoir components. The downlap of subsequent levees onto crevasse splays and overbank splays created stratigraphic traps with the potential for large hydrocarbon accumulations.

Confinement width and inflow-to-sediment discharge ratio control the morphology and braiding intensity of submarine channels: insights from physical experiments and reduced-complexity models

Abstract. Submarine channels conveying sediment gravity flows are often topographically confined, but the effect of confinement width on channel morphodynamics is incompletely understood. We use physical experiments and a reduced-complexity model to investigate the effects of confinement width (B) and the inflow-to-sediment discharge ratio (Qin/Qs) on the evolution of submarine braided channels. The results show that a larger confinement width results in increased active braiding intensity (BIA) and that BIA takes longer to stabilize (i.e., a longer critical time; tc). At a fixed confinement width, a higher Qin/Qs slightly decreases the BIA. Digital elevation models of difference (DoD) of the experiments allow measurement of the morphological active width (Wa) of the submarine channels and the bulk morphological change (Vbulk) within an experiment, defined as the sum of total erosion and deposition. We find that Wa and Vbulk are proportional to B. We further confirm that BIA is proportional to both dimensionless sediment–stream power (ω**) and dimensionless stream power (ω*). These trends are consistent for submarine braided channels both with and without confinement width effects. Furthermore, we built a reduced-complexity model (RCM) that can simulate flow bifurcation and confluence of submarine braided channels. The simulated flow distribution provides reliable predictions of flow depth and sediment transport rate in the experiments. Using kernel density estimation (KDE) to forecast the probability and trends of cross-sectional flow distribution and corresponding BIA under extreme events, we find that skewness of the flow distribution decreases as discharge increases. The development of braided submarine channels, shown here to extend to conditions of topographic confinement, suggests that factors not modeled here (e.g., fine sediment) may be necessary to explain the abundance of single-thread submarine channels in nature.

Extrinsic controls on turbidity fan lobes spatial distribution and potential reservoir presence prediction in half-graben lacustrine basin during early syn-rift: Insights from stratigraphic forward modelling

Turbidite strata are common along faulted margins of half-graben lacustrine basins, but complex lobe evolution may cause significant variability and uncertainty in the spatial distribution of turbidite sand bodies. This study integrates core samples, seismic and well log data from the Dongying Depression lacustrine basin in East China, and uses these data as inputs to a reduced-complexity stratigraphic forward model of turbidite fan lobe evolution. Data-unconstrained sensitivity analysis is used to investigate sensitivity of fan-lobe spatial distribution to fault-related subsidence rate, basin-margin slope, sediment input volume, and sediment input volume oscillation period. A data-constrained multiple-scenario approach then varied parameters within defined uncertainty ranges to generate a series of best-fit models to predict optimal reservoir presence locations. Results indicate that syn-rift segmentation of the Shengbei fault leads to spatial and temporal variation of fault-related subsidence in the hanging wall basin. External controls exert systematic impact on the spatial distribution of both smaller-scale flow beds and larger-scale fans on basin floor. Higher rates of fault-related subsidence and smaller sediment input volume produce more laterally confined fan lobe distribution. Higher basin-margin slope gradient produces more laterally clustered turbidites, but does not change fan lobe location, indicating break of slope is a more significant control on fan location. Multiple scenario reservoir presence probability maps suggest that bypass-dominated middle and inner fan areas, and smaller lengths of retrogradation-dominated feeder channels are most promising reservoir locations.

Avulsion dynamics determine fluvial fan morphology in a cellular model

Abstract Fluvial fans are large, low-gradient depositional systems that occur in sedimentary basins worldwide. Fluvial fans can represent much of the geologic record of foreland basins, create hazards, and record paleoclimate and tectonic signals. However, we lack an understanding of how fluvial fans grow into the variety of shapes observed around the world. We explored this aspect using a cellular model of foreland basin landscape evolution with rules for sediment transport, river avulsion, and floodplain processes. We tested the hypothesis that avulsion dynamics, namely, avulsion trigger period and abandoned channel dynamics, are a primary control on fluvial fan development. We found that shorter trigger periods lead to rounder planform fluvial fan shapes because, between avulsions, channel aggradation (and thus avulsion setup) propagates shorter distances from the upstream boundary along channel pathways. This prioritizes lateral sediment dispersion, creating shorter, rounder fans, over sediment delivery further into the basin, which would create elongated fans. Modeled fans with abandoned channel attraction (but not repulsion) generated a commonly observed abrupt fan boundary marked by a transition from distributary to tributary channel patterns. While fluvial fans are thought to be linked to climate, they can occur anywhere that rivers aggrade, lose lateral confinement, and preserve alluvial topography. Instead, fluvial fans might be more recognizable in environments that frequently trigger avulsions and preserve abandoned channels that capture future avulsions.