Experimentation on submerged flow over flexible vegetation patches with downward seepage

The present study addresses the change in flow characteristics of alluvial channel occupied by submerged vegetated patches of different spacing under downward seepage condition. Measurements show that velocity measured at upstream vegetation section is reduced in the range of 8-16% as the flow reaches the downstream vegetation section. An increase in the near bed velocity and Reynolds stresses has been observed with the application of downward seepage. Reynolds stress profiles show that the maximum value exists near the top of the patches. When the flow enters the vegetation section, more erosion takes place at the upstream vegetation section and then decreases along the downstream section. The maximum turbulence intensities lie near the vegetation top and the turbulence created at the upstream vegetation section is reduced in the range 4-9% as the flow reached the downstream vegetation section. The presence of vegetation induces a local effect which leads to occurrence of erosion and deposition in the vegetated section. Third order moments highlights the downward seepage effect on increasing the flux transport in downward direction and diffusion in the streamwise direction which is shown by the governance of sweep event over ejection event from quadrant analysis. Drag coefficient decreases with the application of downward seepage. The experiments have resulted that vegetation can provide considerable stability to channels by reducing channel erosion even with downward seepage.