Modeling of flow and migration of subaerial and submarine meandering channels

Intensely meandering channels are commonly found on the surface of deep sea fans. Although formed, maintained and modified by density driven underflows, these channels demonstrate many similarities with meandering subaerial rivers. During this research, three analytical models were developed to study the flow field, bed topography and migration of sinuous channels in submarine and subaerial environments.; First, a linear model was developed to study the curvature effect on density driven flows in a sinuous channel. Both water entrainment from the ambient water and exchange of suspended sediment with the channel bed were considered. The perturbation method was utilized to linearize depth-averaged governing equations of particulate density currents by assuming steady flow in a straight channel as the base state. The resulting linear level equations were derived and numerically solved using the solution of the zero order equations i.e. the base state. The linear model was employed to examine the flow characteristics of conservative and non-conservative depositional and erosional density flow in meandering submarine channels. Compared to the depositional flow, it was found that the erosional flow had large lateral variation, which is more favorable for causing the growth and migration of sinuous channels. Also, the channel curvature effects on the flow field were investigated over a range of physical parameters such as channel curvature, sediment size, and bed slope.; Second, a nonlinear model was developed to study the flow field and bed topography of a meandering channel in both submarine and subaerial environments. In this model the base state was assumed as uniform flow in a straight channel. The linear and nonlinear level solutions were compared to investigate the nonlinear effects. The effect of nonlinearity was analyzed over a range of physical parameters such as channel curvature, water surface slope and sediment size. It was found that higher bed slope, finer sediment size and larger channel curvature caused the nonlinear solution to deviate more from the linear level solution. With similar channel geometry and flow conditions, the similarities and differences between the submarine and subaerial environment were studied. Comparisons between the subaerial and subaqueous environment showed that the superelevation of water depth in the submarine environment is much larger than that in the subaerial environment.; Third, a kinematic model of channel evolution was developed to study the migration patterns of meandering channels in the two environments. The migration pattern was calculated by relating the bank erosion rate to the computed flow field and bed level obtained using the second model. The influences of the nonlinear terms in the flow and sediment transport equations on the long term channel evolution were studied by comparing channel planforms obtained with linear and nonlinear level flow field solutions. Simulations starting from a straight channel with small and random perturbations were performed to demonstrate the meandering process of channels in both subaerial and subaqueous environments. Quantitative comparison between channel planforms obtained with the linear and nonlinear solutions indicated that the nonlinear terms do have noticeable effects on the long term channel evolution. In particular, the locations of cut-offs and point bars predicted using the linear and nonlinear level flow solutions were different.