Modeling the Cross‐Sectional Dynamics of Tidal Sandbanks in Sediment‐Scarce Conditions

Tidal sandbanks are large-scale dynamic bedforms that consist of sandy sediment. They have been observed in shallow seas with varying sediment supply, including sediment-scarce environments like the Flemish Banks, Zeeland Banks, and Norfolk Banks. However, we do not yet understand how scarcity affects sandbank evolution. Therefore, we have developed an idealized nonlinear process-based model with the aim of studying cross-sectional shape and migration under sediment-scarce conditions. Scarcity is included through a non-erodible layer from which no sediment can be entrained. Our results show that bank height and width decrease when the sediment budget decreases. The bank height is more sensitive to scarcity than bank width. Furthermore, sand scarcity decreases (and may even reverse) bank asymmetry and increases migration rate when a residual current is present. The migration rate attains a maximum for a specific sediment budget, which is controlled by the ratio of the cross-sectional area of the sandbank and the tide-averaged sediment flux. Our findings show that sandbank dynamics are strongly affected by scarcity, which is critical for seas with receding sediment stocks (e.g., through extraction).