Flow characteristics in a partly vegetated channel with emergent vegetation and seepage

摘要

The flow characteristic in a partly vegetated channel with emergent condition is studied by covering a finite length of the channel with natural Oryza sativa (rice) stems with downward seepage. Spatial study of velocity profiles shows that vegetation reduces the flow velocity lengthways of vegetation zone even with the presence of downward seepage. Reynolds stress increases at the downstream end of the interface section because of higher velocity fluctuations between vegetated and un-vegetated zone. The increase in Reynolds stress at the downstream of interface section is attributed to higher lateral flow and momentum exchange in this transition zone between vegetated and un-vegetated area. For the vegetated section, vegetation serves as a barrier for the vegetated section in reducing the maximum Reynolds stress in the range of 17-20% along the flow direction. It is also observed that downward seepage increases the Reynolds stress as well as turbulence intensities. Integral scales increase with increase in percentage of downward seepage resulting in higher Reynolds stresses with downward seepage. Presented work will help in analyzing the changes in flow field with partially emergent vegetation in alluvial channel subjected to downward seepage. The overall results of this study may enhance the comprehensive understanding of the vegetation effects on flow characteristics in partly emerged vegetated channel and may also provide some guidance for the practice of river ecological restoration on river bed or banks. (C) 2018 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.