Flume experiments on alternate bars in unsteady flow

1991 ◽  
pp. 103-117 ◽  
Author(s):  
Marco Tubino
Keyword(s):  
Unsteady Flow ◽  
Flume Experiments ◽  
Alternate Bars

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.

Growth of alternate bars in unsteady flow

1991 ◽  
Vol 27 (1) ◽  
pp. 37-52 ◽  
Author(s):  
Marco Tubino
Keyword(s):  
Unsteady Flow ◽  
Alternate Bars

scholarly journals DEVELOPMENT AND TRANSFORMATION OF ALTERNATE BARS UNDER UNSTEADY FLOW CONDITIONS

2003 ◽  
Vol 47 ◽  
pp. 619-624
Author(s):  
Hiroshi MIWA ◽  
Atsuyuki DAIDO ◽  
Jun YOKOGAWA
Keyword(s):  
Unsteady Flow ◽  
Flow Conditions ◽  
Alternate Bars

scholarly journals Effect of unsteady flows on the development and magnitude of bed forms

2021 ◽  
Author(s):  
Le Wang ◽  
Alan Cuthbertson ◽  
Gareth Pender ◽  
Zhixian Cao
Keyword(s):  
Unsteady Flow ◽  
Morphological Changes ◽  
Unsteady Flows ◽  
Coarse Sand ◽  
Total Water ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Bed Forms ◽  
Bed Form ◽  
Water Work

<p>Sediment transport and associated morphological changes in alluvial rivers occur primarily under unsteady flow conditions that are manifested as well-defined flood hydrograph events. At present, typical bed forms generated by such unsteady flows is far less studied and, thus, more poorly understood, than equivalent bed forms generated under steady flow conditions. In view of this, the objective of this work is to investigate the development of morphological bed features, and specifically variability in the length, height and steepness of bed forms that develop in a mobile coarse-sand bed layer under unsteady flow hydrographs under zero sediment feed conditions. A series of laboratory flume experiments is conducted within which different flow hydrograph events are simulated physically by controlling their shape, unsteadiness and magnitude. Experimental results indicate that different categories of bed forms such as dunes, alternate bars or transitional dune-bar structures develop within the erodible bed layer when subject to varying hydrograph flow conditions. Examination of relative importance of three parameters used to describe the hydrograph characteristics (i.e. asymmetry, unsteadiness and total water work) on bed form dimensional descriptors (i.e. wavelength, height and steepness) reveals that hydrograph unsteadiness and total water work are the primary and second-order controls on bed deformations or corresponding bed form dimensions. By contrast, hydrograph asymmetry appears to have minimal or negligible influence on bed form development in terms of their type and magnitude. Based on these findings, a physical model was developed and tested to describe the effect of unsteady flow hydrographs with varying unsteadiness and total water work on the nature and size of resulting bed forms that are generated in sand-bed layers. </p>

Primary Study on Overtopping Erosion of Non-Viscous Embankment and Assessment of Discharge through Breach

2011 ◽  
Vol 383-390 ◽  
pp. 3909-3916
Author(s):  
Ming Hui Yu ◽  
Yan Jie Liang
Keyword(s):  
Numerical Model ◽  
Unsteady Flow ◽  
Water Level ◽  
Scientific Basis ◽  
Flow Coefficient ◽  
Primary Study ◽  
Flow Rule ◽  
Flume Experiments ◽  
Discharge Variation ◽  
Variation Process

Combined with the flume experiments and 1D unsteady flow numerical model, the paper has investigated the overtopping breach process of the non-viscous embankment. The breach expansion and the variation process of water level above the breach gate have been studied by series of experiments. Considering the difficulty to monitor the discharge through the breach, 1D unsteady flow numerical model has been applied to simulate discharge variation process. It is found that the width of breach gate and water level above the breach gate are the two key factors which influence the discharge through the breach significantly. Discharge variation process through the breach gate is consistent with the flow rule of side weir. The calibrated flow coefficient is from 0.389 to 0.696. The investigation results can provide scientific basis for disaster prevention and evaluation of embankment burst.

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

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