Topic
Point bar
About: Point bar is a research topic. Over the lifetime, 461 publications have been published within this topic receiving 13492 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this paper, the effect of topographically induced velocity changes on the cross-stream flow pattern was analyzed in a channel with a constant bottom topology, where the velocity component near the bed and the pattern of boundary shear stress can be estimated by assuming fluid acceleration to be small.
Abstract: In a channel with bed topography that does not vary in the downstream direction, a secondary circulation composed of outward flow at the surface and inward flow near the bottom extends across the entire width. If the curvature is constant, the cross-stream velocity component near the bed and the pattern of boundary shear stress can be estimated by assuming fluid accelerations to be small. Unfortunately, this procedure cannot be used in analyzing the flow through natural river meanders, or through channels with downstream constant bottom topography but with rapidly changing curvature. In these latter cases, effects arising from bed- and bank-induced momentum changes must be accounted for. Evidence for a substantial topographically induced alteration in the cross-stream flow pattern relative to that for the analogous constant bottom topography case is provided through new analyses of several sets of laboratory and field data. Shoaling over the point bar in the upstream part of the bend is shown to force the high-velocity core of the flow toward the pool. This is accomplished by a convective acceleration-caused decrease in the cross-stream water surface slope and a resulting dominance of the vertically averaged centrifugal force. The primary effect is a velocity component toward the outside or concave bank throughout the flow depth over the upstream, shallow part of the point bar and an outward component of boundary shear stress in this region. The channel curvature-induced inward component of boundary shear stress consequently is confined to 20 or 30% of the channel width at the pool. Outward transfer of momentum over the point bar, as manifested by a rapid crossing of the high-velocity core from the inside bank to the outside one, contributes to an enhanced decrease in boundary shear stress along the convex side of the stream as the top of the bar is approached. Forces arising from topographically induced spatial accelerations are of the same order of magnitude as the downstream boundary shear stress and water surface slope force components, so they must be modeled as zero-order, not first- or second-order, effects.
461 citations
TL;DR: In this paper, a linear analysis of the water and sediment motion for the steady state of a curved flume with fixed banks is presented, where the deformation is explained in terms of wave length and damping.
Abstract: Recent research activities at the Delft Hydraulics Laboratory and the Delft University of Technology have increased the understanding of the large-scale bed deformation in alluvial rivers with relatively stable banks. In this paper the most important results of these activities are given. First bed deformation in river bends is explained in the light of the results of some laboratory experiments in curved flumes with fixed banks. The deformation is then explained in terms of wave length and damping with a linear analysis of the water and sediment motion for the steady state. From this analysis the conclusion is drawn that the point bar height and pool depth in bends cannot be predicted solely from local conditions. A significant part of the lateral bed slope is due to an overshoot effect induced by the redistribution of the water and sediment motion in the first part of the bend. Finally the results of computations with a non-linear two-dimensional model, simulating three curved flume experiments, are dis...
432 citations
TL;DR: In this article, a series of laboratory experiments demonstrates that riparian vegetation can cause a braided channel to self-organize to, and maintain, a dynamic, single-thread channel.
Abstract: A series of laboratory experiments demonstrates that riparian vegetation can cause a braided channel to self-organize to, and maintain, a dynamic, single-thread channel. The initial condition for the experiments was steady-state braiding in non-cohesive sand under uniform discharge. From here, an experiment consisted of repeated cycles alternating a short duration high flow with a long duration low flow, and uniform dispersal of alfalfa seeds over the bed at the end of each high flow. Plants established on freshly deposited bars and areas of braidplain that were unoccupied during low flow. The presence of the plants had the effect of progressively focusing the high flow so that a single dominant channel developed. The single-thread channel self-adjusted to carry the high flow. Vegetation also slowed the rate of bank erosion. Matching of deposition along the point bar with erosion along the outer bend enabled the channel to develop sinuosity and migrate laterally while suppressing channel splitting and the creation of new channel width. The experimental channels spontaneously reproduced many of the mechanisms by which natural meandering channels migrate and maintain a single dominant channel, in particular bend growth and channel cutoff. In contrast with the braided system, where channel switching is a nearly continuous process, vegetation maintained a coherent channel until wholesale diversion of flow via cutoff and/or avulsion occurred, by which point the previous channel tended to be highly unfavorable for flow. Thus vegetation discouraged the coexistence of multiple channels. Varying discharge was key to allowing expression of feedbacks between the plants and the flow and promoting the transition from braiding to a single-thread channel that was then dynamically maintained. Copyright © 2010 John Wiley & Sons, Ltd.
399 citations
TL;DR: This paper examined the morphology, sedimentology and genesis of the point bars and floodplain of the Beatton River and found that the formation of point bars occurs in distinct stages, and the most rapid is for surfaces less than 50 years old, although sediment accumulation still persists on surfaces up to 250 years in age.
Abstract: This study examines the morphology, sedimentology and genesis of the point bars and floodplain of the Beatton River. The formation of point bars occurs in distinct stages. An initial point bar platform composed mainly of coarse sediment is formed adjacent to the convex bank of a migrating meander bend, and is the base on which develops a single scroll bar of fine traction and suspended load. With continued sedimentation, the scroll bar grows, eventually supporting vegetation and becoming a floodplain ridge. Scroll bars form with greatest size and frequency in rapidly migrating bends, and the shape of the meander bend appears to determine both the location of the initial bar deposit, and its direction of growth up or downstream. Approximately one-half of the floodplain sediment is derived from suspended load, and the initiation of a scroll bar appears to be due to excessive deposition of suspended load in a zone of flow separation over a point bar platform. The critical flow condition for the initiation of a scroll bar does not occur with the same recurrence interval on different shaped meander bends, however, the average recurrence interval within the study reach is approximately every 30 years. Sedimentation rates on point bars and on the floodplain indicate two relatively distinct stages of floodplain alluviation. The most rapid is for surfaces less than 50 years old, although sediment accumulation still persists on surfaces up to 250 years in age. Although frequently flooded, surfaces older than this accumulate very little sediment. Despite 2–3 m of overbank deposition, the amplitude of floodplain ridges is maintained by secondary currents which sweep sediment from the swales towards the ridge crests.
337 citations
TL;DR: In this article, the authors compare an empirical stream power-based classification and a physics-based bar pattern predictor to understand general causes of different river channel patterns, finding that increasing potential-specific stream power implies more energy to erode banks and indeed correlates to channels with high width-depth ratio.
Abstract: Our objective is to understand general causes of different river channel patterns. In this paper we compare an empirical stream power-based classification and a physics-based bar pattern predictor. We present a careful selection of data from the literature that contains rivers with discharge and median bed particle size ranging over several orders of magnitude with various channel patterns and bar types, but no obvious eroding or aggrading tendency. Empirically a continuum is found for increasing specific stream power, here calculated with pattern-independent variables: mean annual flood, valley gradient and channel width predicted with a hydraulic geometry relation. ‘Thresholds’, above which certain patterns emerge, were identified as a function of bed sediment size. Bar theory predicts nature and presence of bars and bar mode, here converted to active braiding index (Bi). The most important variables are actual width–depth ratio and nonlinearity of bed sediment transport. Results agree reasonably well with data. Empirical predictions are somewhat better than bar theory predictions, because the bank strength is indirectly included in the empirical prediction. In combination, empirical and theoretical prediction provide partial explanations for bar and channel patterns. Increasing potential-specific stream power implies more energy to erode banks and indeed correlates to channels with high width–depth ratio. Bar theory predicts that such rivers develop more bars across the width (higher Bi). At the transition from meandering to braiding, weakly braided rivers and meandering rivers with chutes are found. Rivers with extremely low stream power and width–depth ratios hardly develop bars or dynamic meandering and may be straight or sinuous or, in case of disequilibrium sediment feed, anastomosing. Copyright © 2010 John Wiley & Sons, Ltd.
315 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2025 | 5 |
| 2024 | 9 |
| 2023 | 18 |
| 2022 | 44 |
| 2021 | 21 |
| 2020 | 22 |