Flow velocity evolution through a floating rigid cylinder array under unidirectional flow

Floating canopies with unanchored roots are often distributed in streams and wetlands, which alters the evolution of the flow velocity inside the canopy interiors. Based on the flow continuity equation and layer-averaged momentum equations, an analytical model was proposed to predict the velocity evolution through floating canopies under unidirectional flow. Laboratory experiments showed that the velocity evolution within the canopy interior was impacted by the mean channel velocity, canopy density and ratio of the height of the free flow region below the floating canopy to the flow depth. Inside a floating canopy, the flow adjustment distance, XD, was defined as the distance from the canopy leading edge to the position at which the velocity decreased to a constant value. A new estimator of XD was proposed and validated for floating canopies. The shear parameter (C = 0.076 +/- 0.025) was determined and used to characterize the vertical momentum exchange between the incanopy and below-canopy flows. The velocities of the proposed model predicted using the new estimator (XD) and shear parameter (C) were in good agreement with fourteen groups of measurements from different sources. The vegetation rigidity and flexibility had a weak influence on the flow velocity evolution inside the floating canopy. This indicated that the proposed model was capable of accurately predicting the velocity evolution through floating canopies of vegetation. In addition, the proposed model can be applied to predict the velocity evolution inside the root zones of floating vegetation islands (FVIs). Compared to that of the drag of the root zones, the influence of the drag of the floating island on the velocity evolution inside the root zones was negligible.

Automated summary

An analytical model was proposed to predict the velocity evolution through floating canopies under unidirectional flow. Laboratory experiments showed that the velocity evolution within the canopy interior was influenced by the mean channel velocity, canopy density, and ratio of the height of the free flow region to the flow depth. The proposed model accurately predicted the velocity evolution in floating canopies and could be applied to predict the velocity evolution in the root zones of floating vegetation islands.