Comparison of Velocity and Reynolds Stress Distributions in a Straight Rectangular Channel with Submerged and Emergent Vegetation
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Comparison of Velocity Distributions for Submerged and Emergent Vegetation Covers
3.2. Comparison of Reynolds Shear Stress for Submerged and Emergent Vegetation
4. Discussion
5. Conclusions
- In emergent vegetation, the velocity distribution is influenced by a small aspect ratio (W/h < 5) forcing the maximum velocity to move towards the bed. However, in the submerged vegetation, the velocity distribution is less influenced by the aspect ratio, showing the location of maximum velocity far from the bed.
- The log law is valid up to y/h = 0.23 for the flow over submerged vegetation in different aspect ratios. However, for emergent vegetation, the validation zone depends on the distance from the vegetation bank; at small aspect ratio and the central axis of the flume, this law is valid up to y/h = 0.75.
- Reynolds stress (RS) distributions show a convex form for submerged and emergent vegetation covers at different aspect ratios. However, approaching the bank vegetation (emergent case), the power of secondary currents increases, forcing the maximum RS shifts towards the bed.
- For the aspect ratio of W/h = 4 and flow over submerged vegetation, the location of zero shear stress superposes that of maximum velocity. However, in emergent vegetation, such a superposition is not considered. Further, approaching the bank vegetation and shifting the maximum velocity towards the bed, the location of zero shear stress approaches the bed.
- The results of this research show that estimation of key parameters of fluvial projects, velocity and Reynolds stress is influenced by the vegetation arrangements, submerged or emergent. Therefore, a better estimation of these parameters influences drag coefficient and sediment determinations, improving bank stability with reasonable channel design, reducing the cost of project and modifying the input data for hydraulic models.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Abbreviations
d50 | Median diameter of sediment particles |
C | Constant of the log law |
D | Distance from the wall |
yp | Plant height (for run 1 and 2) |
h | Water depth above the vegetation (for run 1 and run 2) and water depth over gravel bed (for run 3 and run 4) |
W | Flume width |
ks | Roughness scale (equivalent sand roughness) |
Q | Flow discharge |
u | Mean point velocity |
uave | Average velocity at a section; |
umax | Maximum velocity |
u’ | Turbulence intensity in longitudinal direction |
w’ | Turbulence intensity in vertical direction |
u* | Shear velocity |
y | Distance from top of gravel or vegetation cover |
Y | Distance from the bed |
κ | von Karman constant |
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Exp. | Q (m3/s) | h (cm) | W (cm) | Uavg (m/s) | W/h | Covered Area |
---|---|---|---|---|---|---|
Run 1 | 0.037 | 11 | 60 | 0.56 | 5.45 | Bed |
Run 2 | 0.055 | 15 | 60 | 0.61 | 4 | Bed |
Run 3 | 0.037 | 11 | 60 | 0.56 | 5.45 | Bank |
Run 4 | 0.055 | 15 | 60 | 0.61 | 4 | Bank |
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Mofrad, M.R.T.; Afzalimehr, H.; Parvizi, P.; Ahmad, S. Comparison of Velocity and Reynolds Stress Distributions in a Straight Rectangular Channel with Submerged and Emergent Vegetation. Water 2023, 15, 2435. https://doi.org/10.3390/w15132435
Mofrad MRT, Afzalimehr H, Parvizi P, Ahmad S. Comparison of Velocity and Reynolds Stress Distributions in a Straight Rectangular Channel with Submerged and Emergent Vegetation. Water. 2023; 15(13):2435. https://doi.org/10.3390/w15132435
Chicago/Turabian StyleMofrad, Mohammad Reza Tabesh, Hossein Afzalimehr, Parsa Parvizi, and Sajjad Ahmad. 2023. "Comparison of Velocity and Reynolds Stress Distributions in a Straight Rectangular Channel with Submerged and Emergent Vegetation" Water 15, no. 13: 2435. https://doi.org/10.3390/w15132435