Effect of Downward Seepage on Turbulence and Morphology in Mobile Boundary Sinuous Channel

The porous boundary of alluvial channels allows water to interact with the surrounding groundwater. With the reduction in groundwater level, the transfer of water from the main channel to the groundwater is significant and referred to as downward seepage. The action of downward seepage at the boundary zones of sinuous bend causes morphological alteration along the sinuous alluvial channel. Laboratory experiments were conducted for no-seepage and seepage conditions to study the effect of downward seepage on turbulence and bed morphology in rectangular and trapezoidal sinuous channels. The deformation along the streambed and bank of the sinuous channels showed remarkable alterations with seepage. The banks are eroded, and the bed elevation is lowered in the presence of downward seepage as observed from the cross-sectional profiles of the channel. This infers the excess sediment transport with downward seepage. With increased flow rate and downward seepage, prominent deposition zones near the inner region and erosion near the outer region of the bend were observed in the rectangular sinuous channel. The trapezoidal channel showed much less change as the side slope was near to the angle of repose of the sand. However, with the application of downward seepage, the streambed of the channel has lowered in elevation, indicating sediment movement. Streamwise velocity at the center of the bend showed an average percentage increase of 26% in the rectangular channel and about 20% in the trapezoidal channel. The Reynolds shear stress estimated with downward seepage has increased near the channel bed, indicating high momentum flux.