A diffusive 1D model for the evolution of a braided network subject to varying sediment supply

The impact of human activity on the morphological evolution of braided rivers produces serious problems for the river management and consequently a wide range of questions to the research community. In this work we explore the response of a braided network to variations in the sediment supply which can be induced by river interventions like dam construction or sediment mining. We have focused in particular on the simple case of a confined braided network with constant discharge and well-sorted, cohesiveless bed material. It is well known that within the context of a one-dimensional formulation the governing hyperbolic system can be readily reduced to a simple diffusive scheme when the hypothesis of local equilibrium is satisfied. The main objective of the work is to asses the suitability of such simple model to investigate the time evolution of bed profile in a braided network. Theoretical findings are tested with the results of two long-term runs in a 23 m long and 1 m wide sand-bed flume, starting from an equilibrium configuration and varying the sediment supply. This analysis reveals that the bed morphology eventually reaches an equilibrium status and, consequently, the long-term variation of the bed elevation can be predicted with the simple diffusive scheme. Further investigations are needed to study the response of the braided network in the early stages of the experiments, when the morphology is clearly in a non-equilibrium state. In these conditions the complete hyperbolic model could serve as an useful tool to model the channel response to varying conditions.