Flow in multi-layered vegetated compound channels with different bank slopes

Abstract

Bank angle and floodplain vegetation emergence determine the flow nature in a compound channel. Two sets of 45° and 90° bank angle compound channel is considered in the present work. Each set considers three cases of vegetation arrangements: no vegetation, multi-layered fully submerged, and multi-layered partially emergent. The flow characteristics like velocity, Reynolds shear stress (RSS), and turbulent kinetic energy (TKE) do not vary much in the cross section in the absence of vegetation. However, with vegetation, the slopes and nearby region are affected the most as it acts as an intermediary region between the main channel and floodplain. An analysis of the anisotropic invariant map shows the dominance of the transverse component in the slopes compared to the main channel and floodplain. The velocity in and around the slopes is higher for steep slopes (90°) compared to a gradual slope (45°) compound channel. The streamwise RSS and bursting events also show higher magnitude near the channel bed in and around the sloping region. This indicates the instability of the steep banks compared to gradual bank slopes. The increase in floodplain vegetation emergence also affects the slopes. The magnitude of RSS and TKE in the slopes is higher with greater vegetation emergence in the floodplain. This shows the higher vulnerability of the slopes in the presence of higher vegetation emergence. From the hydraulic engineering perspective, this study will be helpful in the field of understanding the failure of banks and ways to maintain their stability.