Can bed load transport drive varying depositional behaviour in river delta environments?

• Channel kinematics increases with increased bed load or non-cohesive sediment load
• Similar deposits can originate from non-unique depositional controls and events
• Channel kinematics have less impact on delta front and prodelta deposits
• More bed load transport lead to more frequent but smaller autogenic reorganisations
• Suspended load increases the risk of misinterpreting autogenic events as allogenic

Understanding the processes and conditions at the time of deposition is key to the development of robust geological models which adequately approximate the heterogeneous delta morphology and stratigraphy they represent. We show how the mechanism of sediment transport (the proportion of the sediment supply transported as bed load vs. suspended load) impacts channel kinematics, delta morphology and stratigraphy, to at least the same extent as the proportion of cohesive sediment supply. This finding is derived from 15 synthetic delta analogues generated by processes-based simulations in Delft3D. The model parameter space varies sediment transport mechanism against proportions of cohesive sediment whilst keeping the total sediment mass input constant. Proximal morphology and kinematics previously associated with sediment cohesivity are also produced by decreasing the proportion of bed load sediment transport. However, distal depositional patterns are different for changes in sediment transport and sediment load cohesivity. Changes in sediment transport mechanisms are also shown to impact clinoform geometry as well as the spatiotemporal scale of autogenic reorganisation through channel avulsions. We conclude that improving insight into the ratio of bed load to suspended load is crucial to predicting the geometric evolution of a delta.