Investigation the Effective Parameters on the Drag Coefficient in Rigid and Flexible Vegetation

Document Type : Research Paper


1 Ph.D candidate/, Hydraulic Structure Department,/ Faculty of Water and Environmental Engineering,/ Shahid Chamran University of Ahvaz, /Ahvaz/ Iran

2 Professor, Department of marine structures, Faculty of water and environmental engineering, Shahid chamran university of Ahvaz, Ahvaz , Iran

3 Associate Professor of Water Engineering and Environment Faculty, Shahid Chamran Univeristy of Ahvaz,Ahvaz, Iran.

4 Assistant Professor/Hydraulic Structures Department,/ Faculty of Water and Environmental Engineering,/ Shahid Chamran University of Ahvaz/, Ahvaz,/ Iran


The issue of resistance to flow in open channels with vegetation has attracted the attention of many researchers in recent decades. The presence of vegetation in flood-prone areas and along the banks of rivers has a significant effect on the distribution of energy and reduction of possible damages. In this paper, in order to investigate the effect of vegetation in waterways, rigid and flexible vegetation was modeled with artificial samples. In laboratory conditions, the drag force was measured directly by means of a dynamic load cell in the moving part of the flume. In this paper, a new index named "density index" of vegetation is introduced. The introduced index depends on the frontal area of each vegetation and the total number of vegetation in the area. The results showed that in both rigid and flexible models, with the increase of vegetation density index and relative depth, the drag force absorption increases. Investigating the effect of the vegetation density index showed that increasing this index has a significant effect on reduces the drag coefficient; thus, at the maximum increase in the density index, a decrease of 19.8% in the drag coefficient was observed. Increasing the relative depth of the flow until reaching to just-submerged condition, in rigid and flexible models, causes a decrease of the drag coefficient by 12.81% and 10.43%, respectively. Finally, two mathematical models with regression coefficients of 0.87 and 0.89 were presented to estimate the drag coefficient of rigid and flexible vegetation by considering the effective dimensionless parameters.


Main Subjects

  • Receive Date: 06 August 2022
  • Revise Date: 14 October 2022
  • Accept Date: 27 November 2022
  • First Publish Date: 27 November 2022