A Novel Framework for Simulating Flow and Transport Processes during Bedforms Movement

Most current models for predicting flow and transport processes in bedforms do not consider that sandy streambeds occasionally move. In addition, models that consider bedform movement have used a moving reference frame, typically corresponding to an individual moving bedform. However, the latter approach cannot simulate the accumulation of fine particles at a given location over time as a modeling outcome or any other process influenced by the passage of multiple bedforms. We present a novel simulation framework that models periodic mobile bedforms within a stationary reference frame. This approach is combined with particle tracking to successfully reproduce clay deposition observations in sand beds and the resulting development of a low-conductivity layer near the scour zone. Passage of successive bedforms is represented by varying the shape of the top boundary of the domain. Simulation results successfully reproduce experimental observations of the development of the low-conductivity layer near the scour zone. We found that increased bedform celerity and filtration both lead to a shallower depth of clay deposition and a more compact deposition layer. While increased filtration causes more clay to deposit, increased celerity reduces deposition by flattening hyporheic exchange flow paths. Adopting this novel modeling approach creates opportunities to study realistic situations such as the influence of the passage of bedforms with changing sizes and shapes on flow and transport processes in sandy streams.