Abstract
AbstractPredicting sediment transport and river morphodynamics is a challenging task in gravel-bed rivers where sediment mixtures have various particle sizes. In this study, we derive a binary pack...
Highlights
The interactions between water flow and riverbed sediment in gravel-bed rivers must be determined to prevent or mitigate the damage from sediment-flood disasters and to create or preserve aquatic habitats
The active layer concept itself is not restricted to a constant porosity condition, many models for river morphodynamics have assumed a constant porosity condition because no reliable method for determining changes in the porosity of natural river sediment is available to be applied to the calculations
This study considers the bimodal sphere packing problem to formulate the available porosity for fine particles in an aggregation of coarse particles
Summary
The interactions between water flow and riverbed sediment in gravel-bed rivers must be determined to prevent or mitigate the damage from sediment-flood disasters and to create or preserve aquatic habitats. The rootmean square (RMS) of the difference between the calculated and measured porosities with the natural sediment increases gradually with the increasing particle diameter ratio, while the RMS of those for spheres with a large diameter ratio is not so high (Fig. 8) The reason for this difference is the difficulty in experimentally achieving the closest packing condition because in actual experiments, the pore structure of the larger particles. The sediment samples with wide range of medium diameter d50 and standard deviation d50=d84 were collected in October 2018 at six places in the Noro River Dam reservoir, Japan, for porosity measurements in natural deposition conditions and the closest packing experiment (Table 2, Fig. 10). These advantages mean that the present model is suitable for coupling with fluid dynamics models that can calculate the flow and turbulence in the roughness layer (e.g., Olsen and Stokseth 1995; Lane et al 2004; Carney et al 2006; Nikora 2008; Rameshwaran et al 2011; Dey and Das 2012; Uchida et al 2016; Uchida and Fukuoka 2019); this can help evaluate the driving forces acting on the sediment, and variations in the sediment porosity and aquatic habitat in the vicinity of the bed in gravel-bed rivers
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