Studies on emergent flow over vegetative channel bed with downward seepage

Experimental observations in a tilting flume having a bed covered with rice plants (Oryza sativa) are used to analyse the flow characteristics of flexible emergent vegetation with downward seepage. The flow velocity for no-seepage and with seepage is reduced by, on average, 52% and 33%, respectively, as the flow reaches the downstream end with vegetation. Higher Reynolds stress occurs at the start of the vegetation zone; hence, bed material transport occurs in this region. The results indicate that the bed is no longer the primary source of turbulence generation in vegetated flow; rather it is dominated by turbulence generated by the vegetation stems. The local effect of the presence of vegetation causes variations in the hydrodynamic characteristics along the vegetated portion of the channel, which leads to erosion and deposition in the vegetation zone. The experiments show that vegetation can provide considerable stability to channels by reducing channel erosion even with downward seepage.