Meandering Research Articles

Assessment of Flood-Induced Geomorphic Changes in Sidere Creek of the Mountainous Basin Using Small UAV-Based Imagery

Floods often cause changes in the hydro-geomorphology of riverbeds and banks. These changes need to be closely monitored to find a balance and exchange between lateral and vertical erosion and deposition, upstream local sediment supply, and a stream’s transport capacity. Low-frequency cross-sectional field surveys cannot map hard-to-reach locations. Innovative techniques, such as small unmanned aerial vehicles (UAVs), must be employed to monitor these processes. This research compared historical data with a UAV survey and the Pix4DMapper structure-from-motion (SfM) program to assess the longitudinal, lateral, and vertical changes of Sidere Creek in the eastern Black Sea, Türkiye. Digitization was undertaken using 2011–2015–2017 Google Earth photographs, 1960s topographic maps, and 2023 orthomosaics. ArcGIS 10.6 was used to delineate the centerlines (thalweg), left/right banks, alluvial bars, active channel widths, and channel confinement layers. Channel Migration Toolbox and CloudCompare were utilized for analyzing lateral and vertical morphological changes, respectively. The active channel migrated 25.57 m during 1960–2011, 15.84 m during 2011–2015, 6.96 m during 2015–2017, and 5.79 m during 2017–2023. Left-bank channel confinement rose from 2.4% to 42% and right-bank channel confinement from 5.9% to 34.8% over 63 years. Neither stream meandering nor sinuosity index changed statistically. Active channel boundary widths varied from 149.79 m to 9.46 m, averaging 37.3 m. It can be concluded that UAV surveys can precisely measure and monitor the stream channel longitudinal, lateral, and vertical morphological changes at a lower cost and in less time than previous methods.

Modelling shear stress distribution in ice-covered streams

Abstract Distribution of bed shear stress is the critical factor in regulating the meandering of single-thread rivers. However, the impact of ice cover on bed shear stress is largely unknown. In this study, we develop a theoretical model of cross-stream momentum balance to examine the distribution of bed shear stresses in ice-covered meandering rivers. To validate the theoretical model, field surveys were carried out in a river reach of the Red River in Fargo, North Dakota. Data monitoring was completed using an Acoustic Doppler Current Profiler to obtain time-averaged velocity profiles. Our theoretical model indicates that an ice covering develops high-shear zones near both the inner and outer banks, which might exacerbate sediment transport and enhance bank erosion. Velocity measurements confirm the results of the proposed model and demonstrate a clear impact of meandering river banks on velocity profiles and secondary flow patterns under ice cover. Based on our results, we hypothesize that ice cover increases turbulent stresses near banks, which in turn lead to the enhancement of the bed shear stress. Our work provides new insights into the impact of ice cover on bed shear stress distribution, which could play an important role in driving sediment-transport processes and the long-term morphodynamic evolution of meandering rivers seasonally covered by ice.

Comparing turbulent flow and bank erosion with controlled experiments in a field-scale meandering channel

Abstract Bank erosion commonly occurs in alluvial rivers, shaping landscapes and riparian habitats and impacting water quality and infrastructure. Several models have been proposed that link shear stresses to bank erosion. However, data to test these hypotheses for characteristic geometries of meandering channels are sparse and technically challenging to acquire. Here we present results from a controlled experiment in a naturalistic channel to isolate the relationships between turbulent flow and nascent bank erosion. We ran the experiments at the Outdoor StreamLab (St Anthony Falls Laboratory, University of Minnesota) and gathered high-precision, contemporaneous measurements of the turbulent flow field and topography near a standardized, erodible bank at five locations along a single meander. The measurements show that the rate of bank erosion varied both along the channel and vertically and, local bank erosion was not correlated with any single hydrodynamic parameter. Upstream of the meander apex, erosion correlated with the near-bank time-averaged streamwise velocity magnitude while downstream of the apex, bank erosion correlated more strongly with near-bank turbulence parameters and depth. These results support field measurements that suggest that fluid shear contributions to outer bank erosion reflect multiple components of turbulent flow structure in river meanders.

Short note. A new U-PB age for the Talampaya Formation: Stratigraphic and paleoclimatic implications

This paper presents a new U–Pb zircon age of 253.40 ± 1.06 Ma for the middle part of the Talampaya Formation, which is consistent with the previously reported dating of 252.38 ± 0.22 Ma at the top of the unit. The age herein presented was obtained from a tuff level intercalated into a fluvial sequence formed by finning-up cycles of massive conglomerates, cross-bedded sandstones, and laminated sandy mudstones interpreted as deposited by sandy meandering rivers with dominant sandy floodplains. In this context, a vitric tuff from a floodplain located 140 m from the base of the unit provided the zircons dated by the combination of LA-ICP-MS (Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry).The radiometric age of 253.40 ± 1.06 Ma confirms the relocation of the Talampaya Formation in the Late Permian and demonstrates that at least the upper half and probably the whole of this unit was deposited during the Lopingian, a time interval scarcely represented in South America. This assumption is consistent with the age of 249.66 ± 0.11 Ma (early Triassic) reported in the overlying La Veteada Formation.The new age presented has paleoclimatic implications regarding the worldwide climatic aridification event that occurred at the end of the Late Paleozoic since it gives a relatively precise approximation to the onset of the aridization in this part of Gondwana during the Lopingian (circa 252.38 Ma).

Stream power curve–loop–spiral conceptual method and an application to rivers of Taiwan

Study regionEighteen main rivers in Taiwan. Study focusThe concept of total stream power (TSP) or specific stream power (SSP) has been investigated previously as an index for assessing the status of a river channel. Here, we introduce a new diagram called the “stream power loop” to review variations in fluvial conditions, morphology, and sediment transport potential from river source to estuary. Because of its physical basis, the loop diagram reflects fluvial morphology and watershed conditions. Additionally, we present a spiral diagram that depicts variations in the spatial gradients of TSP and SSP. The gradient implied the sediment transport trend, which from upstream to downstream changes gradually from scouring to siltation in ideal conditions. The loop and spiral diagrams provide an overview of the fluvial system. New hydrological insights for the regionThe loop diagram applications in Taiwan categorized the rivers into three types: simple loop, maple-leaf loop, and complex loop. Diverse geology increases the likelihood of large tributaries and abrupt changes in terrain, both of which affect the components of stream power–discharge and slope. The scatter distribution of all the data aggregated from the 18 rivers showed a shrinking radius and a counter-clockwise spiral pathway, passing through the mountain river zone, the braided river zone, and finally to the straight & meandering river zone. The result supported the concept of stream power loop and indicated that stream power loop can interpret the status of the river systems.

What even is a meandering river? A philosophy-enhanced synthesis of multilevel causes and systemic interactions contributing to river meandering

Abstract Despite creating one of Earth's most iconic landforms, and having been studied since antiquity, river meandering is currently explained by several alternative models that remain debated. This is partly because observers have deconstructed meanders to a set of properties thought to be fundamental or significant for meandering, but each of these underpinning properties is itself complex and in turn requires analysis of its causes and mechanisms. This philosophical contribution aims to provide a perspective on the state of the science that makes a rigorous interrogation into what ‘causation’ actually means, and explores what a systems perspective can elucidate about meandering phenomena. We approach the problem through a discussion of the variety of ways in which previous researchers have tackled the problem of meandering, from a channel and floodplain perspective, on Earth and Mars, in the field and laboratory, and at the present day through to the ancient stratigraphic record. It is evident that river meandering has numerous causal pathways rather than a single set of necessary and sufficient conditions. A systemic view on the evolution of plant species shows that their feedbacks on river pattern likewise have several pathways. Employing the conceptual apparatus of the philosophy of science will move us towards a more consensual synthesis of river meandering.

Geoinformation model of river meandering for predictive mapping

An algorithm for predictive monitoring of the development of "tortuosity" of riverbed, called the process of meandering, is proposed. The algorithm is based on the statement that the riverbed is displaced from its current position along the normal to the dynamic axis of the flow in the direction from the center of curvature in a given alignment, and the displacement is proportional to the curvature, but the proportionality coefficient is not known in advance and must be determined in the process of cartographic monitoring. When using the proposed algorithm, such a well-known phenomenon in hydrology as the emergence, formation and development of meanders, which give the rivebed bizarre shapes, naturally turns out. The numerical implementation of the proposed algorithm, supplemented by predictive mapping of the riverbed deformation in previous years, is able to predict the channel displacement for future periods of time.

Impact of morpho-sedimentary heterogeneities on the evolution of coastal meandering rivers (Brenta River, Italy)

Over time, alluvial coastal plains are formed as rivers evolve and alter the landscape by eroding and depositing various morpho-sedimentary bodies. These bodies contribute to creating morphological, lithological, and topographic heterogeneities in the floodplain, which can in turn influence river dynamics by providing preferential areas for erosion and river avulsion. While the influence of differential changes in floodplain elevation on river dynamics has been explored in relation to the interaction between rivers and tectonics, there is still a significant gap in understanding the effects of subtle elevation changes produced by the distribution and composition of buried sedimentary bodies.This study examines the response of an ancient river channel to morphological and sedimentological heterogeneities in the floodplain substrate. It focuses on a 14 km long paleo-channel belt located in the southern Venetian Plain (northeast Italy), using field analyses such as sediment coring and geophysical investigations, as well as remote sensing for morphometric analyses. The results indicate that the paleo-channel belt underwent changes as it crossed an ancient sandy beach ridge, which is still visible as a relative high point in the present-day floodplain. Variations in floodplain gradient and substrate erodibility brought about morphometric changes in the paleo-channel, with downstream impacts on the grain-size distribution. This study emphasizes how heterogeneous substrates in alluvial and coastal plains have the potential to induce significant alterations of river morpho-sedimentary processes.

Fish Assemblages as Ecological Indicators in the Büyük Menderes (Great Meander) River, Turkey

This research describes fish assemblages and associated aquatic ecosystem degradation patterns in the Büyük Menderes River, one of Turkey’s most important Anatolian basins. Using standard electrofishing, 44 river sites were sampled throughout the basin accounting for the distribution and abundance of 20 native and seven non-native species, totaling 13,535 fish specimens. At each sampling site, anthropogenic pressures were assessed, and information was gathered to determine the degree of human-induced degradation that may affect fish and their habitats; each site was scored on the basis of a site quality index (SQI). Using the best-available relatively less-degraded river sites, cluster analyses of the samples defined six fish assemblage river types. Further classification of all fish samples utilizing bipartite network analysis resulted in comparable assemblage groupings. The European Fish Index (EFI+) with minor adaptations was applied for assessing river ecological integrity at all sampled sites in order to explore the utility of this widely used index. The EFI+ index results correlated with scores of the SQI but provided a very narrow assessment range, thus failing to accurately and consistently assess the severity of anthropogenic degradation. We recommend a new multimetric index to be developed for the Western Anatolian Ecoregion, of which this basin is a part. The data and insights gained from this exercise may help continue fish-based indicator development for policy-relevant management and conservation in Turkey’s rivers.

Upland river planform morphodynamics and associated riverbank erosion: Insights from channel migration of the upper Yarlung Tsangpo river

River meandering and lateral migration, caused by riverbank erosion, is a major global threat to soil, sediment, lands, and habitats. However, compared to the densely populated lowland floodplains, the upland channel morphodynamics of free-flowing rivers in a complex high-elevation alluvial setting have received less attention. In this study, we quantitatively investigated channel morphodynamics and associated frozen bank migration in the upper Yarlung Tsangpo River in the Himalayan headwater basin from the 1980s to the 2010s. By combining remote sensing analysis with field investigations, we found mean migration rates of 244 gravel-bed river bends ranging from 1.63 m/yr in the 1980s to 2.76 m/yr in the 2010s, with a maximum rate of 18.61 m/yr. The highest migration rates were associated with bends that had a width-normalised curvature radius between 3.0 and 5.0 and a sinuosity between 1.2 and 1.5. A ∼69% increase in river-bend migration and 30% more frequent bend cutoffs coincided nicely with the rapid expansion of glacial lakes due to a ∼1 °C increase in mean annual air temperature over the past four decades. Positive correlations were observed between channel migration rate and temperature, mean glacial lake area, and runoff. These results highlight the importance of the unique channel morphodynamics and the intense lateral movements of upland rivers. The close link between these dynamics and climate change suggests that a warmer world may significantly influence bank erosion and associated ecosystem processes of upland alluvial systems, which are essential for comprehending frozen channel dynamics and developing strategies for habitat protection in uplands worldwide.

The delta-fluvial evolution of a lacustrine basin with gentle slope and low sedimentation rate: A case study of the Fudong Slope, Junggar Basin, Northwest China

Gentle slope belts of lacustrine basins are important areas for the generation of stratigraphic petroleum reservoirs controlled by sedimentary systems. Based on coring, well logging, 3D seismic and analytical test data, the sedimentary system and sandbody distribution characteristics of the Jurassic Toutunhe Formation (J2t) in the Fudong slope of the Junggar Basin were analysed. The results indicated that the Fudong slope showed the characteristics of low sediment input. Sediments mainly originated from the Shaqi uplift, and the sediment input gradually weakened from the early to the late J2t stages. The sedimentary system evolved from a delta to a meandering river, resulting in a delta front facies in the 1st member (J2t1) and a meandering river facies in the 2nd (J2t2) and 3rd (J2t3) members of the Toutunhe Formation. A sedimentary evolution pattern for the gentle slope with low sediment input was established. Thick deltaic sandbodies developed locally in the J2t1 stage. However, meandering rivers with high sinuosities predominantly developed and resulted in a striped geometry in the J2t2 and J2t3 members. Moreover, the meandering sandbodies exhibited an anastomosing morphology after multistage superposition. The channel and point bar facies in J2t2 were more developed than those in J2t3 because of sediment input differences. Under low-sediment input conditions, the sedimentary environment of the gentle slope belt in the lacustrine basin was controlled by changes in the palaeoclimate, palaeogeomorphology, gradient (slope) and base level. Palaeoclimate was the main factor controlling the evolution of the sedimentary environment. Palaeogeomorphology and slope controlled the distribution of sedimentary microfacies, channel sinuosity and sandbodies. Base-level change restricted the sandbody superimposition style. Under the low sediment input conditions of the Fudong slope, the subaqueous distributary channels of the delta environment and the point bars of the meandering river environment in the transitional belt of the Fudong slope are the main potential targets for stratigraphic petroleum reservoirs, whilst the 2nd member of the Toutunhe Formation (J2t2) is the main favourable interval for stratigraphic reservoir exploration.

Photonic snake states in two-dimensional frequency combs

Taming the instabilities inherent to many nonlinear optical phenomena is of paramount importance for modern photonics. In particular, the so-called snake instability is universally known to severely distort localized wave stripes, leading to the occurrence of transient, short-lived dynamical states that eventually decay. This phenomenon is ubiquitous in nonlinear science—from river meandering to superfluids—and so far it apparently remains uncontrollable; however, here we show that optical snake instabilities can be harnessed by a process that leads to the formation of stationary and robust two-dimensional zigzag states. We find that such a new type of nonlinear waves exists in the hyperbolic regime of cylindrical microresonators, and that it naturally corresponds to two-dimensional frequency combs featuring spectral heterogeneity and intrinsic synchronization. We uncover the conditions of the existence of such spatiotemporal photonic snakes and confirm their remarkable robustness against perturbations. Our findings represent a new paradigm for frequency comb generation, thus opening the door to a whole range of applications in communications, metrology and spectroscopy. By tuning the spatial width, the strength and the frequency of a pump beam in two-dimensional cylindrical microcavities supporting stable, robust photonic snake states, a set of broadband and perfectly synchronized two-dimensional frequency combs can be realized.

At what scales does a river meander? Scale-specific sinuosity (S3) metric for quantifying stream meander size distribution

Stream bend geometry is linked to terrain features, hydrologic and ecologic conditions, and anthropogenic forces. Knowledge of the distributions of geometric properties of streams advances understanding of changing landscape conditions and associated processes that operate over a range of spatial scales. Statistical decomposition of sinuosity in natural linear features has proven a longstanding challenge and a particular impediment to automated analysis. This paper demonstrates that sinuosity can vary with the magnitude of units at which it is measured (measurement scales). The paper derives a scale-specific sinuosity (S3) metric intended to measure stream bend geometry across a range of measurement scales. The metric is warranted for analysis and modeling at measurement scales equal or similar to the spatial process and landscape conditions under investigation. Derived from the Richardson (1961) plot, the S3 metric quantifies a frequency signature of planform bend sizes spanning a range of measurement units, enabling visual and quantitative analysis of bend geometry in linear stream features. Derivation of the metric makes evident a systematic relationship between stream bend size, sinuosity, and measurement scale, formalizing a relationship between sinuosity and fractal dimension. The paper shows the utility of the S3 metric in examining bend patterns for synthetic and real-world linear stream data.

Experimental study on velocity distribution and bed load transport in compound channels: Effect of the floodplain’s wall parallel with the meandering main channel

In this study, the effect of the floodplain’s parallel wall with a compound meandering main channel over the hydraulics flow has been analyzed experimentally. A constant sinuosity factor of 1.3 and relative flow depths of 0.3 to 0.55 were considered to illustrate the effect of the hydraulic parameters on the variations of the velocity components. Velocity components were measured by ADV velocimeter at seven cross sections with angles of zero, 30, and 60 degrees and mesh size of 2 cm × 2 cm. Furthermore, a laser meter measured the topographies of the sediment bed in the 33 cross-sections with an angle difference of 5 degrees to the bend apex. The results showed that in lower relative depths, due to vortexes and high turbulence intensity, the ability of flood damage will be more eminent. The CS04 section with the least longitudinal and transverse changes in the water level is the best position for hydraulic investigation of the meandering rivers. The left bank in sections CS03 to CS07 will be the place of deposit of sediment in nature with the formation of the stagnation area. The velocity of (Ud(fp-inner)) is 3 to 5 times higher than (Ud(fp-outer)). For this cause, the flow in the outer bank, unlike the inner bank, has a reduced effect on the flow velocity in the main channel. Increasing the relative depth, the ratio (Ud(mc)/Ud(T)) and (Ud(fp)/Ud(T)) decreased and increased, respectively. Therefore, the average velocity values in the main channel and the floodplains reached the average velocity of the whole section. The flow velocity in the main channel is always higher than in the floodplains, and the ratio (Ud(fp)/Ud(mc)) is less than one. The variation trend in the average values of bed shear stress, turbulence kinetic energy (TKE) and average kinetic energy (MKE) was decreased with increasing relative flow depth. Both factors of relative depth and Froude number will affect the location of the occurrence of the maximum values of velocity, bed shear stress, maximum depth hole and the peak of the sedimentary hill.

A predictive model of velocity for local hydrokinetic power assessment based on remote sensing data

Hydrokinetic power is a small-scale, zero-head form of hydropower with the potential to address renewable energy needs for many communities, including those in the Arctic. An impediment to its wide deployment is the ability to screen suitable stream reaches for adequate power generation. Remote resource assessment of streams, particularly the estimation of mean velocity, is valuable for assessing the potential of new locations prior to field visits. Many studies have investigated remote sensing techniques for stream velocity prediction through machine learning and empirical relations, but most of these studies relied at least partly on in-situ data and were not suitable for small width streams. This study addresses these gaps with a Random Forest machine learning model that uses only remotely sensible data to estimate velocities of small and large streams at locations across Alaska. The developed model, validated by velocity gage readings, had a mean prediction error of 24%, at the lower end of error rates (20–30%) found for large channel widths. Novel geometric and temporal parameters were developed and found to importantly influence predictive accuracy (e.g. slope, stream meanders). Remotely sensible data enables future model expansion by those interested in assessing new sites for community energy planning.

Analysis of Oil-Water Distribution Law and Main Controlling Factors of Meandering River Facies Reservoir Based on the Single Sand Body: A Case Study from the Yan 932 Layer of Y Oil Area in Dingbian, Ordos Basin

After the oilfield development enters the medium and high water cut stage, the fine three-dimensional description of the single sand body, the distribution rules of the remaining oil, and its main controlling factors have become the focus of research. The premise is to understand the original oil and water distribution characteristics and the important influencing factors of the reservoir. Taking the Yan 932 reservoir of Y oil area in Dingbian as an example, combined with the meandering river sedimentary model, this paper uses dense well pattern logging data to dissect single sand body on the foundation of the core and logging results. The conclusion shows that, first, Yan 932 layer is divided into two stages: Yan 932-1 and Yan 932-2, which constitute four single sand body superposition configuration modes, namely, type I, type II, type I & II, and type I/II. Second, type I & II is mainly developed in the sand body of the main channel. In the west of the main channel sand body, type I, type II, and type I/II are developed. Only type II is developed in the east of the main channel sand body. Thirdly, sedimentary microfacies, sand body thickness, sand body configuration, and structural characteristics are the key factors influencing the oil-water distribution law of the Yan 932 reservoir.

Meandering river evolution in an unvegetated permafrost environment

Meandering river sedimentary facies are associated with the rise of terrestrial vegetation in the rock record, but modern examples of highly sinuous, single-threaded streams are also found in many modern non-vegetated environments. Prior workers have speculated that permafrost or ice-cemented sediment could provide the cohesion needed to generate single-threaded, meandering channels, however, the presence of bank vegetation in the overwhelming majority of terrestrial permafrost sites in which meandering rivers are present has made it impossible to disentangle the relative impact of bank cohesion provided by frozen sediments from that provided by roots. Here, we examine topographic change over 13 years at the Onyx River, an unvegetated, permafrost-affected, sand-and-gravel-bottomed river in the McMurdo Dry Valleys (MDV) of Antarctica, supported by ∼40 years of image data. On the basis of lidar change detection and satellite/airborne image analysis, we find that meandering river processes (cut bank erosion, point bar growth, and meander migration) can occur in this ice-cemented, unvegetated permafrost river system. We find that the Onyx River's upper, single-threaded reach is meandering, and that bank cohesion is provided by ice-cemented permafrost. Meander migration rates within the Onyx's meandering reach are extremely close to values predicted based on observations of meander migration rates in other unvegetated rivers, however, the short (∼70 day) duration of Onyx River discharge suggests these migration rates should be considered low estimates, which could be up to ∼5 times greater during the short, summer erosion season. Together, these observations suggest that ice-cemented permafrost is a weak form of bank cohesion that can result in rapid landscape change in response to thermokarstic fluvial erosion, producing dynamic river channels, especially where warm meltwater encounters ice-rich permafrost deposits.

Fluvial reservoir characterization through channel belt dimension and petrophysical analysis

The dimensions and connectivity of fluvial reservoirs vary greatly, making it challenging to characterize them using conventional approaches. In this study integrated channel belt dimension analysis from seismic geomorphology and empirical equations, well log facies, and petrophysical analysis were performed to characterize the fluvial reservoirs. The study interval consists of fluvial deposits and is divided into three reservoir zones, which are defined by four key regional markers (B, D, K, O). In these intervals, six (6) fluvial facies have been identified. Based on the log facies proportions and their stacking relationships, it is interpreted that the reservoirs in Zone 1 (B to D) were deposited in a proximal reach of a meandering system, Zone 2 (D to K) in a marginal marine setting, and Zone 3 (K) in a distal reach of a meandering system. The dimensions of fluvial channels and channel belts were determined using empirical equations. The results were compared with the observed dimensions of fluvial channels and channel belts from the seismic horizon and stratal slices of the same intervals. Zone 1 and 3 are characterized by broad meander belts (1000–4000 m) compared to zone 2 (600–1300m). Petrophysical analysis showed zone 1 and 3 have the better petrophysical properties compared to zone 2. Though zone 3 has the most well-developed sand bodies the best reservoir interval is zone 1 because of its higher porosity. Although channel belt dimensions have a significant influence on reservoir connectivity, they do not seem to have control on reservoir properties. The channel belt dimensions obtained from the empirical equations and interpreted from the seismic geomorphology analysis were found to be strikingly similar. Since three-dimensional seismic data is not available everywhere and seismic imaging quality decreases with depth, empirical equations can be used to analyze fluvial reservoir parameters and their connectivity at greater depths.

Refining the Bank Stability and Toe Erosion Model: Improving the timestep, the top of toe selection and the iteration routine

AbstractRiverbank failure is an essential source of river sediment and a major cause of river meandering. The Bank Stability and Toe Erosion Model (BSTEM) is a widely used simulation tool owing to its simplicity and clear presentation of results. However, the three core issues in the simulation by the software, time‐step determination, top‐of‐toe (TT) selection, and the iterative algorithm, still lack an in‐depth discussion to ensure the rationality and stability of the simulation results. In this study, the Jing‐150 cross‐section of the Jingjiang River was chosen as an example to illustrate these three problems. For the first problem, which is the choice of the time step, the simulation results become stable and close to the measured value as the time‐step decreases. After determining a suitable time step, the difference between adopting and modifying the default TT of the BSTEM was analysed. The results show that adopting the default TT causes chaos in the distribution of profile nodes, leading to an overly large bank failure width, whereas the modified TT node distribution is normal and the bank failure width is close to the measured value. For the third problem, the original iteration routine (OR) may cause the output bank profile to be unstable and cause a deviation between the bank width and measured value. The negative impact of unstable bank profiles diminishes as the time‐step decreases. However, the workload for reducing the time step is enormous. Therefore, an improved routine (IR) was proposed. With IR, the relative error between the simulated and measured values of the failure width was within 15% when the SD of the water stage was reduced to 0.2478. A similar result could only be obtained when the SD of the water stage was less than 0.099 for OR. This means that to obtain the same simulation accuracy for the failure width, IR can use a larger time step than OR, thereby reducing the workload of the simulation.

Experimental comparison of flow pattern around convergent-vertical and divergent-vertical pier groups located in a 180 degree sharp bend with streamwise direction

ABSTRACT The flow pattern at the meandering rivers changes to a helical flow. The installation of bridge piers on the meandering river and collision of the flow with pier geometry creates a far more complicated flow. The experiments were performed in a 180-degree bend channel and a radius to curvature ratio of two. The pier groups were installed in convergent-vertical in streamwise direction (CVS) and divergent-vertical in streamwise direction (DVS). The results show that the earliest eddy flows in the convergent-vertical pier groups were formed at near water surface level. According to the findings, the formation of return flow from a 77.5 degree angle and at a distance of 35 to 45 percent of the width of the channel from the inner bank happened. However, the return flows were initiated from the 87.5 degree and at a distance of 60% to 70% of the width of the channel from the inner bank in the divergent-vertical pier group. The power of secondary flow in convergent-vertical and divergent-vertical pier groups occurred at 85 and 87.5 degree sections respectively, and equal to 3.5 and 1.25 times the pier diameter from the center of the piers’ location upstream.