Turbulence in a compound channel with the combination of submerged and emergent vegetation

Abstract

Floodplain vegetation is heterogeneous with varying heights and spacing. Laboratory studies concerning compound channels with mixed submerged and emergent vegetation are scarce. This paper attempts to address the difference in flow behavior when it encounters single-layered submerged or emergent vegetation or a combination of both. Two different sets of uniform and non-uniform vegetation setups are considered. Vegetation cases with submerged, emergent, and mixed vegetation are considered for each set. The velocity in the floodplain region of fully emergent cases is higher than that in combined vegetation because of the less frontal area provided by the emergent vegetation. The Reynolds shear stress is also higher in the lower depth of the main channel in combined vegetation compared to uniform height vegetation, especially in the uniform vegetation setup. Turbulent anisotropy and octant analysis are studied in detail to get further insight into flow behavior in different vegetation setups. The anisotropic invariant map and invariant function F reveal that the main channel section of 67% emergent vegetation case has a greater tendency to approach two-dimensional turbulence than other non-uniform vegetation setups. Octant analysis study shows that internal sweep in the main channel is highest in 34% emergent uniform vegetation setup and lowest in 100% emergent non-uniform vegetation setup.