Experimental and numerical analysis of velocity distribution in a compound meandering channel with double layered rigid vegetated flood plains

Abstract

Vegetation is one of the major topographic features that is encountered along and across the margins and flood plains of many rivers systems. This vegetation creates a most complex flow mechanism in the compound river bed channels; therefore, a detailed analysis is required to observe the flow and vegetation interactions to understand the hydrodynamic aspects in the river systems. This paper studies the effect of double-layered rigid vegetation in a meandering channel on the flow characteristics at two relative depth conditions, of 0.34, 0.45 which creates an alternate emergent and submerged flow situation. The three-dimensional velocity distribution was captured using micro-ADV. The concept of two relative depth conditions allowed us to capture record and classify the velocity zones between the short and tall vegetation. Compared to the flow in the main channel, flood plains registered relatively lower velocity values due to the resistance offered by the vegetation along the flood plains, which consequently led to the increase in main channel flow velocities. Velocities compared to the non-vegetated meandering channels; the highest velocity readings were recorded at the centerline of the main channel. Numerical analysis was also conducted using the CFD codes in fluent. The vegetation geometry is modelled as cylindrical dowels of diameter 10 mm and two-variable heights of 7.5 cm and 15 cm at two relative depth flow conditions. The experimental results were numerically compared using the k-ϵ model along with grid sensitivity tests. The final simulated numerical results were found to be close and in good agreement with experimental values.