scholarly journals Apparent roughness coefficient in overbank flows

2021 ◽  
Vol 3 (7) ◽  
Author(s):  
João N. Fernandes
Keyword(s):  
Shear Stress ◽  
Channel Flow ◽  
Isotropic Turbulence ◽  
Single Channel ◽  
Main Channel ◽  
Roughness Coefficient ◽  
Compound Channel ◽  
Secondary Currents ◽  
Flow Mechanisms ◽  
Overbank Flows

AbstractOverbank flows occur in alluvial valleys during flood events when the conveyance of main channel of rivers is exceeded. Once floodplains are inundated and the so-called compound channel flow is observed, the faster flow in the main channel interacts with the slower flow in the floodplain featuring a much more pronounced 3D flow structure compared to single channel flow. These flow mechanisms comprise a shear layer near the interface, lateral momentum transfer and strong secondary currents due to the non-isotropic turbulence. This paper starts by giving an overview of the main flow mechanisms in compound channels pointing out the importance of taking into account the apparent shear stress generated between the main channel and the floodplain flows due to the interaction of these flows. A new simple model was developed to include the apparent shear stress concept as a correction of the Manning roughness coefficient of main channel and floodplains. The proposed method for predicting stage–discharge relationships was calibrated and validated by experimental data from several compound channel facilities. A significant improvement in prediction of the compound channel conveyance in comparison with the traditional methods was achieved.

scholarly journals Prediction of Boundary Shear Stress Distribution in Converging Compound Channel Using Gene Expression Programming

2022 ◽  
Author(s):  
Bandita Naik ◽  
Vijay Kaushik ◽  
Munendra Kumar
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Shear Force ◽  
Gene Expression Programming ◽  
Main Channel ◽  
Shear Stress Distribution ◽  
Force Distribution ◽  
Compound Channel ◽  
Boundary Shear ◽  
Boundary Shear Stress

Abstract The computation of the boundary shear stress distribution in an open channel flow is required for a variety of applications, including the flow resistance relationship and the construction of stable channels. The river breaches the main channel and spills across the floodplain during overbank flow conditions on both sides. Due to the momentum shift between the primary channel and adjacent floodplains, the flow structure in such compound channels becomes complicated. This has a profound impact on the shear stress distribution in the floodplain and main channel subsections. In addition, agriculture and development activities have occurred in floodplain parts of a river system. As a consequence, the geometry of the floodplain changes over the length of the flow, resulting in a converging compound channel. Traditional formulas, which rely heavily on empirical approaches, are ineffective in predicting shear force distribution with high precision. As a result, innovative and precise approaches are still in great demand. The boundary shear force carried by floodplains is estimated by gene expression programming (GEP) in this paper. In terms of non-dimensional geometric and flow variables, a novel equation is constructed to forecast boundary shear force distribution. The proposed GEP-based method is found to be best when compared to conventional methods. The findings indicate that the predicted percentage shear force carried by floodplains determined using GEP is in good agreement with the experimental data compared to the conventional formulas (R2 = 0.96 and RMSE = 3.395 for the training data and R2 = 0.95 and RMSE = 4.022 for the testing data).

Maximum and mean velocity relationships in laboratory flumes with different cross-sectional shapes

2005 ◽  
Vol 32 (2) ◽  
pp. 413-419 ◽  
Author(s):  
Galip Seckin
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Single Channel ◽  
Maximum Velocity ◽  
Open Channel Flow ◽  
Compound Channel ◽  
Velocity Data ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Series Of Experiments

A series of experiments was conducted to measure velocity distributions in a straight compound-channel flume. Additional velocity data measured in flumes with single rectangular and V-shaped channels were also collected from the work of other researchers to compare the relation between cross-sectional mean and maximum velocities in different shaped flumes with different bed slopes and flow regimes. The results showed that there is a significant linear relationship between the maximum velocity and the cross-sectional mean velocity in flumes with both compound and single rectangular and V-shaped channels. An attempt was also made to determine the relation between cross-sectional mean and maximum velocities in both compound- and single-channel flumes. Key words: mean velocity, maximum velocity, open channel flow.

Modelling floodplain conveyance in compound channel flows

1995 ◽  
Vol 22 (4) ◽  
pp. 660-667 ◽  
Author(s):  
Jean G. Chatila ◽  
Ron D. Townsend
Keyword(s):  
Field Data ◽  
Single Channel ◽  
Laboratory Data ◽  
Main Channel ◽  
Channel Flows ◽  
Interface Plane ◽  
Data Sets ◽  
Compound Channel ◽  
Dynamic Flow ◽  
Composite Flow

Floodplain conveyance in compound channel flows is examined through applications of the dynamic flow routing model DWOPER to both laboratory and field data sets. Three different approaches regarding the modelling of off-channel storage are considered, namely, the single-channel approach and two interface-plane methods, which artificially separate main channel flows from floodplain flows, using (i) vertical and (ii) diagonal interface planes. The single-channel method, which views composite flow fields as single units without storage, produced significant differences between simulated and observed stage and discharge hydrographs. The vertical interface method gave generally good results in the case of the laboratory data, but was less successful when applied to the field data. The diagonal interface method, which in this instance applied outward-facing diagonal interface planes at the junctions of the main channel and floodplain zones, produced superior results overall. Key words: floodplain, conveyance, unsteady flow, compound channels, off-channel storage, interface planes.

scholarly journals Modeling effects of bank friction and woody bank vegetation on channel flow and boundary shear stress in the Rio Puerco, New Mexico

2005 ◽  
Vol 110 (F4) ◽  
pp. n/a-n/a ◽  
Author(s):  
E. R. Griffin ◽  
J. W. Kean ◽  
K. R. Vincent ◽  
J. D. Smith ◽  
J. M. Friedman
Keyword(s):  
Shear Stress ◽  
New Mexico ◽  
Channel Flow ◽  
Boundary Shear ◽  
Boundary Shear Stress
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