Large eddy simulation of compound open-channel flows with emergent vegetation near the floodplain edge

Trees and shrubs observed in floodplain edge in natural rivers have significant impacts on hydrodynamic characteristics. In particular, spanwise profile of streamwise velocity component is influenced by the drag force of the trees, and consequently, the streamwise velocity decreases locally behind trees and near the junction between the main-channel and the floodplain. Furthermore, concentration exchanges such as nutrients between the main-channel and the floodplain differ from those observed in the non-tree compound open-channel flows. It is of essential importance to reveal how emergent trees influences these mass transfers. However, it is very difficult to evaluate time and space variations of the concentration by laboratory measurements. So, in the present study, a 3-D LES is used to overcome this difficulty, and we reveal the relation between the tree-alignment density and the exchange-rate of the concentration.