Investigation on Logarithmic and Coles Laws under Different Emergent Vegetation Patches

Document Type : Research Article


1 Professor, Faculty of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

2 M.Sc. Graduate, College of Agricultural Engineering, Isfahan University of Technology, Isfahan, Iran


Vegetation can be divided into two groups in terms of height and water depth as the submerged vegetation and the emergent vegetation. This paper investigates the emergent vegetation, using reedy rods. The presence of vegetation cover in rivers and open channels calls for better understanding the effect of this significant factor in application of the boundary-layer laws, including the logarithmic law and the Coles’ law. The results show that the logarithmic law can be applied in the presence of vegetation cover with different densities as well as the gravel-bed streams. However, this law deviates in the outer layer where the empirical Coles’ law is not valid in the presence of vegetation cover. The more vegetation density, the more deviation of data from the Coles’ law. The reason for invalidity of Coles’ law in the outer layer is due to irregular velocity distribution and turbulence intensity in the presence of vegetation, leading to augmentation of the deviation with vegetation density.


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