Drag Coefficient for Rigid Vegetation in Subcritical Open Channel

Abstract

Vegetation in fluvial systems plays an important role in environmental and ecological aspects. Vegetation can cause energy dissipation via drag force due to the interaction between vegetation and flow, and the dimensionless drag coefficient (Cd) is of great importance for understanding and predicting the drag force. Currently Cd was determined through model experiments and mass literature about subcritical open channel flow with rigid vegetation can be obtained. A data processing method was introduced to seek an empirical prediction for Cd. Firstly, the influencing factors of Cd was determined by dimensional analysis method. Then based on the collected data, we used multi-parameter regression analysis to obtain an empirical expression of Cd with those dimensionless influencing factors. It is interesting to find that drag coefficients for subcritical and supercritical flows have opposite trends with varied vegetation density, and Cd remains almost constant with high Froude number for subcritical flow, or the Froude number has little impact on Cd; while for subcritical flow with low Froude number, the effect of Froude number cannot be ignored.