Sediment transport in an active erodible channel bend of Brahmaputra river

Abstract

Spatial variation of sediment transport in an alluvial sand-bed river bend needs to be understood with its influencing factors such as bank erosion, secondary current formation, land spur and bed-material characteristics. In this study, detailed hydrographic surveys with Acoustic Doppler Current Profiler (ADCP) were conducted at an active erodible river bend to measure suspended load, velocity, bathymetric profile and characteristics of the bed material. Study indicates the presence of multi-thread flow in the channel bend. Local variation of sediment transport is primarily controlled by active bank erosion, land spur and sand bar formation. Vertical distribution of suspended sediment concentration follows a power function with normalized depth. Average bed-material concentration at the reach level is computed from observed sediment profiles, and is compared against various sediment transport functions. Results show that the sediment transport function suggested by Yang gives better predictions for this reach. Transverse bed slopes at critical survey transects were computed from the bathymetric data and evaluated with analytical approaches. Out of three analytical approaches used, Odgaard’s approach estimates the bed slopes fairly close to the observed one. These two functions are suitable in the Brahmaputra river for further morphological studies.