scholarly journals Flume experiments on vegetated alternate bars

2018 ◽  
Vol 40 ◽  
pp. 02034 ◽  
Author(s):  
Giulio Calvani ◽  
Simona Francalanci ◽  
Luca Solari
Keyword(s):  
Hydrological Regime ◽  
Spatial Arrangement ◽  
Flume Experiments ◽  
Rigid Vegetation ◽  
Hydraulic Conditions ◽  
Laboratory Flume ◽  
Alternate Bars ◽  
River Reach ◽  
Bed Slope ◽  
And Migration

The planform morphology of a river reach is the result of the combined actions of sediment motion (erosion, transport and deposition), hydrological regime, development and growth of vegetation. However, the interactions among these processes are still poorly understood and rarely investigated in laboratory flume experiments. In these experiments and also in numerical modelling, vegetation is usually represented by rigid cylinders, although it is widely recognized that this schematization cannot reproduce the effects of root stabilization and binding on riverbed sediment. In this work, we focus on the effects of added vegetation on morphological dynamics of alternate bars in a straight channel by means of flume experiments. We performed laboratory experiments reproducing hydraulic conditions that are typical of gravel bed rivers, in terms of water depth, bed slope and bed load; these conditions led to the formation of freely migrating alternate bars. We then employed rigid vegetation that was deployed on the reproduced alternate bars according to field observations. Various vegetation scenarios, in terms of density and spatial arrangement, were deployed in the flume experiments such to mimic different maintenance strategies. Results show the effects of rigid vegetation on the alternate bar configuration on the overall topographic pattern, the main alternate bar characteristics (such as amplitude and wavelength) and migration rate.

Debris flow impact on a flexible barrier: laboratory flume experiments and force-based mechanical model validation

2021 ◽  
Vol 106 (1) ◽  
pp. 735-756
Author(s):  
R. Brighenti ◽  
L. Spaggiari ◽  
A. Segalini ◽  
R. Savi ◽  
G. Capparelli
Keyword(s):  
Debris Flow ◽  
Model Validation ◽  
Mechanical Model ◽  
Flume Experiments ◽  
Flexible Barrier ◽  
Laboratory Flume

scholarly journals Evaluating a Laboratory Flume Microbiome as a Window Into Natural Riverbed Biogeochemistry

2021 ◽  
Vol 3 ◽  
Author(s):  
Matthew H. Kaufman ◽  
John G. Warden ◽  
M. Bayani Cardenas ◽  
James C. Stegen ◽  
Emily B. Graham ◽  
...  
Keyword(s):  
16S Rrna Gene Sequencing ◽  
Spatiotemporal Variability ◽  
Rrna Gene ◽  
Natural Ecosystems ◽  
Flume Experiments ◽  
Riverbed Sediments ◽  
Laboratory Flume ◽  
Curtis Dissimilarity ◽  
The Common ◽  
Rrna Gene Sequencing

Riverbeds are hotspots for microbially-mediated reactions that exhibit pronounced variability in space and time. It is challenging to resolve biogeochemical mechanisms in natural riverbeds, as uncontrolled settings complicate data collection and interpretation. To overcome these challenges, laboratory flumes are often used as proxies for natural riverbed systems. Flumes capture spatiotemporal variability and thus allow for controlled investigations of riverbed biogeochemistry. These investigations implicitly rely on the assumption that the flume microbiome is similar to the microbiome of natural riverbeds. However, this assumption has not been tested and it is unknown how the microbiome of a flume compares to natural aquatic settings, including riverbeds. To evaluate the fundamental assumption that a flume hosts a microbiome similar to natural riverbed systems, we used 16s rRNA gene sequencing and publicly available data to compare the sediment microbiome of a single large laboratory flume to a wide variety of natural ecosystems including lake and marine sediments, river, lake, hyporheic, soil, and marine water, and bank and wetland soils. Richness and Shannon diversity metrics, analyses of variance, Bray-Curtis dissimilarity, and analysis of the common microbiomes between flume and river sediment all indicated that the flume microbiome more closely resembled natural riverbed sediments than other ecosystems, supporting the use of flume experiments for investigating natural microbially-mediated biogeochemical processes in riverbeds.

Longitudinal Hillslope Shape Effects on Runoff and Sediment Loss: Laboratory Flume Experiments

2018 ◽  
Vol 144 (2) ◽  
pp. 04017097 ◽  
Author(s):  
João L. M. P. de Lima ◽  
Jorge M. G. P. Isidoro ◽  
M. Isabel P. de Lima ◽  
Vijay P. Singh
Keyword(s):  
Flume Experiments ◽  
Sediment Loss ◽  
Laboratory Flume ◽  
Shape Effects

scholarly journals Recalling Meyer-Peter and Müller Approach for Assessment of Bed-Load Sediment Transport

2019 ◽  
Author(s):  
Alban Kuriqi
Keyword(s):  
Sediment Transport ◽  
Bed Load ◽  
Initial Condition ◽  
Sediment Discharge ◽  
Mechanical Process ◽  
Natural Stream ◽  
Hydraulic Conditions ◽  
Bed Slope ◽  
Water Amount ◽  
Load Sediment

In this paper is discussed sediment transport as a mechanical process that characterises a natural stream or channel flow regime. The objective of experimental work presented in this paper is to recall and to give another prospect of well-known Meyer-Peter and Müller approach for estimation of Shield’s number (θ_c,θ) in laboratory conditions, and calibration of dimensionless MPM number (A). For this purpose two different experiments are conducted, during the first experiment water amount flushed on the flume and bed slope was changed simultaneously until equilibrium state is achieved, meanwhile is estimated the critical Shield’s number (θ_c). While, during the second experiment, water amount was kept constant, only bed slope of flume was continuously tilted, meanwhile sediment, discharge and Shield’s number (θ) was determined for given hydraulic conditions. In addition calibration of dimensionless MPM number (A) was performed, where several iteration were considered until for (A=3.42), sediment discharge measured become almost equal with sediment discharge computed by using MPM formula. After these experiments, is concluded that MPM formula can be used also for other certain initial condition and similar procedure may be adopted to calibrate the dimensionless MPM number (A) .

scholarly journals Observing and modeling bedload sediment transport at the grain-scale

2020 ◽  
Author(s):  
Eric Deal ◽  
Taylor Perron ◽  
Jeremy Venditti ◽  
Qiong Zhang ◽  
Santiago Benavides ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Particle Tracking ◽  
High Speed ◽  
Flume Experiments ◽  
Physical Mechanisms ◽  
Glass Spheres ◽  
Granular Dynamics ◽  
Image Velocimetry ◽  
Laboratory Flume ◽  
Bedload Sediment

<p>Empirical sediment transport models have common characteristics suggestive of the underlying physics, but mechanistic explanations for these characteristics are lacking due to an incomplete understanding of the fundamental physical mechanisms involved. Hydrodynamic interactions at the grain-scale are thought to be key, however, it is a major challenge to either observe or model these processes. In order to improve our understanding of grain-scale dynamics in sediment entrainment and transport we are studying the detailed mechanics of fluid-grain interactions using a combination of laboratory flume experiments, advanced numerical simulations, and granular mechanics theory. </p><p>The flume experiments are conducted with an emphasis on exploring differences and similarities in the behaviour of glass spheres, a common theoretical tool, to naturally sourced river gravel. Using high-speed cameras coupled with computer-vision based particle tracking, we tracked the majority of grains in the grain bed and water column, with 130,000 glass sphere track paths longer than 10 particle diameters. In particular, we introduce a newly developed a machine learning based particle tracking of the natural grains, with 30,000 gravel track paths longer than 10 mean particle diameters. Fluid flow fields are also observed using particle image velocimetry (PIV). We present the comparison of our detailed observations of granular dynamics between spheres and natural gravel, with a focus on how grain shape impacts fluid-grain and grain-grain interactions.</p><p>Using a discrete-element plus Lattice-Boltzmann fluid method (LBM-DEM) we simulate a small portion of the laboratory flume with high temporal and spatial resolution. This method tracks discrete particles interacting with each other through contact laws while mechanically coupled to a dynamic interstitial fluid. We discuss the ability of our simulations to emulate our experiments, the benefits of which are twofold. First, where the simulations work well, we use them to observe grain-scale dynamics that would be difficult or impossible to measure in a laboratory setting or in the field. Second, we learn from situations in which the experiments and simulations diverge, leading to improvements in both the simulations and our understanding of how fluid-grain interactions influence sediment transport.</p>

scholarly journals Predicting discharge capacity of vegetated compound channels: uncertainty and identifiability of 1D process-based models

2020 ◽  
Author(s):  
Adam Kiczko ◽  
Kaisa Västilä ◽  
Adam Kozioł ◽  
Janusz Kubrak ◽  
Elżbieta Kubrak ◽  
...  
Keyword(s):  
Discharge Capacity ◽  
Probabilistic Approach ◽  
River Channels ◽  
Compound Channels ◽  
Practical Applications ◽  
Rigid Vegetation ◽  
Dimensional Modeling ◽  
Output Uncertainty ◽  
Hydraulic Conditions ◽  
Flexible Vegetation

Abstract. Despite the development of advanced process-based methods for estimating the discharge capacity of vegetated river channels, most of the practical one-dimensional modeling is based on a relatively simple divided channel method (DCM) with the Manning's flow resistance formula. This study is motivated by the need to improve the reliability of modeling in practical applications while acknowledging the limitations on the availability of data on vegetation distributions and densities required by the process-based methods. We investigate whether the advanced methods can be applied to modeling vegetated compound channels by identifying the missing characteristics as parameters through the formulation of an inverse problem. We developed a new probabilistic approach for comparing six models of channel discharge capacity in respect of their uncertainty, with the model with the lowest uncertainty considered the most favorable. Calculations were performed for flume and field settings varying in floodplain vegetation submergence, density, and flexibility, and in hydraulic conditions. The output uncertainty, estimated on the basis of a quasi-Bayes approach, was analyzed for a varying number of observation points, demonstrating the significance of the parameter equifinality. The results showed that very reliable predictions with low uncertainties can be obtained for process-based methods with a large number of parameters. The equifinality affects the parameter identification but not the uncertainty of a model. The best performance for sparse, unsubmerged, rigid vegetation was obtained with the Mertens method and for dense, flexible vegetation with the generalized two-layer method combined with a description of the flexibility-induced reconfiguration. We found that the process-based methods are superior when applied for vegetative conditions they were developed for while the Manning based DCM seems to be the most flexible technique.

scholarly journals Turbulent Flow through Random Vegetation on a Rough Bed

Water ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 2564
Author(s):  
Francesco Coscarella ◽  
Nadia Penna ◽  
Aldo Pedro Ferrante ◽  
Paola Gualtieri ◽  
Roberto Gaudio
Keyword(s):  
Flow Field ◽  
Flow Conditions ◽  
Bed Sediments ◽  
Turbulence Characteristics ◽  
Rigid Vegetation ◽  
Laboratory Flume ◽  
Rough Bed ◽  
Flow Through ◽  
Bed Roughness

River vegetation radically modifies the flow field and turbulence characteristics. To analyze the vegetation effects on the flow, most scientific studies are based on laboratory tests or numerical simulations with vegetation stems on smooth beds. Nevertheless, in this manner, the effects of bed sediments are neglected. The aim of this paper is to experimentally investigate the effects of bed sediments in a vegetated channel and, in consideration of that, comparative experiments of velocity measures, performed with an Acoustic Doppler Velocimeter (ADV) profiler, were carried out in a laboratory flume with different uniform bed sediment sizes and the same pattern of randomly arranged emergent rigid vegetation. To better comprehend the time-averaged flow conditions, the time-averaged velocity was explored. Subsequently, the analysis was focused on the energetic characteristics of the flow field with the determination of the Turbulent Kinetic Energy (TKE) and its components, as well as of the energy spectra of the velocity components immediately downstream of a vegetation element. The results show that both the vegetation and bed roughness surface deeply affect the turbulence characteristics. Furthermore, it was revealed that the roughness influence becomes predominant as the grain size becomes larger.

scholarly journals Laboratory Flume Experiments on the Formation of Spanwise Large Wood Accumulations: Part II-Effect on local scour

2019 ◽  
Vol 55 (6) ◽  
pp. 4871-4885 ◽  
Author(s):  
I. Schalko ◽  
C. Lageder ◽  
L. Schmocker ◽  
V. Weitbrecht ◽  
R. M. Boes
Keyword(s):  
Local Scour ◽  
Large Wood ◽  
Flume Experiments ◽  
Laboratory Flume

scholarly journals Morphometric properties of alternate bars and water discharge: a laboratory investigation

2020 ◽  
Author(s):  
Marco Redolfi ◽  
Matilde Welber ◽  
Mattia Carlin ◽  
Marco Tubino ◽  
Walter Bertoldi
Keyword(s):  
Water Discharge ◽  
Hydrological Regime ◽  
Theoretical Models ◽  
Quantitative Information ◽  
Quantitative Agreement ◽  
Critical Threshold ◽  
Morphological Variations ◽  
Theoretical Predictions ◽  
Alternate Bars ◽  
Harmonic Composition

Abstract. The formation of alternate bars in straightened river reaches represents a fundamental process of river morphodynamics that has received great attention in the last decades. It is well-established that migrating alternate bars arise from an autogenic, instability mechanism occurring when the channel width-to-depth ratio is sufficiently large. While several empirical and theoretical relations for predicting how bar height and length depend on the key dimensionless parameters are available, there is a lack of direct, quantitative information about the dependence of bar properties on flow discharge. We performed a series of experiments in a long, mobile-bed flume with fixed and straight banks, at different discharges. The self-formed bed topography was surveyed, different metrics were analysed to obtain quantitative information about bar height and shape, and results were interpreted in the light of existing theoretical models. The analysis reveals that the shape of alternate bars highly depends on their formative discharge, with remarkable variations in the harmonic composition and a strong decreasing trend of the skewness of the bed elevation. Similarly, the height of alternate bars clearly decreases with the water discharge, in quantitative agreement with theoretical predictions. However, the disappearance of bars when discharge exceeds a critical threshold is not as sharp as expected, due to the formation of so-called diagonal bars. This work provides basic information for modelling and interpreting short-term morphological variations during individual flood events and long-term trajectories due to alterations of the hydrological regime.

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