The Influence of Submerged and Floating Vegetation on Manning’s Roughness Coefficient: An Experimental Analysis

The Manning Equation is widely used in hydraulic engineering to estimate mean velocity and discharge in open channels. This equation is based on various parameters, with the roughness coefficient being the most crucial factor. The nature of the channel is the primary factor in estimating this roughness coefficient. In vegetated channels, several factors affect the roughness coefficient, including water depth, velocity, friction slope, type, height, and density of the vegetation. In this research, an experimental investigation is conducted to analyze the roughness coefficient caused by submerged and floating vegetation. Artificial flexible elements made of perspex are used to simulate submerged vegetation, while foam integrated with aluminum wires is utilized to represent floating vegetation. The roughness coefficient values are estimated for various discharges (25.0, 30.0, 35.0, and 40.0 l/sec), flow depths (0.25, 0.30, and 0.35 m), and friction slopes in both non-vegetated and vegetated channels with various bed slopes (0.0010, 0.0020, 0.0023, 0.0049, and 0.0062). An analysis of the relationship between the roughness coefficient and the Froude number reveals that this coefficient exhibits a power function relationship with the Froude number. The roughness coefficient increases with higher friction slopes and decreases as the Froude number rises. Additionally, the presence of vegetation significantly increases the roughness coefficient from 0.032 to 0.098 when the submerged ratio is 0.94, the bed slope is 0.0062, and the Froude number is 0.19. The roughness coefficient further escalates with higher submerged ratios. New empirical equations have been developed to estimate the roughness coefficient.