Modelling of Fine Sediment Infiltration into Static Gravel Bed: Binary Mixture Packing Model

Sediment flushing (dam removal) is a standard practice to recover the reservoir capacity. Often, the flushed fine sediment gets infiltrated into the gravel bed while being transported, which negatively affects several fluvial processes in river and river ecosystem. In this paper, we employed the Unresolved CFD-DEM method to simulate the process of fine sediment infiltration into static gravel bed. The system is simplified by considering a binary mixture to represent gravel and fine sediment. Theoretical packing limits, based on geometrical considerations of binary mixture for tetrahedral and cubical packings, are considered. The theoretical packing limits are based on size ratio (d/D); where d and D represent sizes of fine sediment and gravel, respectively. When the size ratio 0.154, filling of fine sediment occurs from bottom to top onwards (so-called unimpeded static percolation), resulting in densely packed bed. When the size ratio = 0.414, fine sediment gets clogged at the top surface layer (so-called bridging or clogging), precluding further infiltration, resulting in relatively loosely packed bed. For the considered size ratios, pure DEM simulations are also performed to facilitate the comparison of infiltration processes with and without water flow. Our results and subsequent discussion suggest that fine sediment infiltration process in fluvial deposits is gravity-dominated, supporting Cui’s hypothesis that fine sediment infiltration through intra-gravel flow is similar to infiltration process driven by gravity.