Analysis of vegetation resistance based on two typical distribution types in ecological channel

This paper studied the potential mechanism of form drag for emergent vegetation by combining experiments and numerical simulation. Rigid cylindrical sticks arranged in an open channel were used to simulate vegetation and experiments on flow velocity distribution near the vegetation under different vegetation density and arrangement were carried out. The new expression of hydraulic radius indicated that form drag was closely related to vortex structure near the vegetation. The relationship between vortex volume caused by vegetation and form drag was proposed and verified under different experimental conditions. The results showed that resistance form in vegetated open channels could be divided into K- and D-type resistance based on different stick arrangements within one vegetation patch. The calculated and measured form drag values were in a good agreement under different experimental conditions. Meanwhile, the numerical simulation results fit well with the experimental values and more complex experimental conditions were replicated using numerical simulation. The results provided important information for vegetation layout in open channels.