Investigation of the Effect of Roughness Coefficient of Kashafrud River on the Water Surface Level Focusing on Vegetation

Abstract

The roughness coefficient is one of the important parameters in the hydraulics of open channels, which is a function of various factors; therefore, its exact determination is of great importance. In practical studies such as the determination of riverbed limits or river management plans, the roughness coefficient is generally determined by field observations and based on engineering judgments. In this study, the Cowan, Jarvela, and Velzen methods have been used to calculate the vegetation roughness, in addition, the exact roughness coefficient of the Kashafrud River was determined using field observations and experimental results. Finally, the total roughness coefficient was used as input data in the HEC-RAS software to calculate the water level. It was revealed that vegetation density and water level were the most important factors in determining the roughness coefficient, and factors like flow velocity or vegetation height were less effective in comparison with the afore-mentioned factors. It was also found that the Jarvela and Velzen methods had the lowest and highest roughness coefficients, respectively; in other words, the Jarvela and Velzen methods provided an underestimate and an overestimate of vegetation roughness, respectively.