Abstract
Understanding the alterations of gravel bed structures, sediment transport, and the effects on aquatic habitat play an essential role in eco-hydraulic and sediment transport management. In recent years, the evaluation of changes of void in bed materials has attracted more concern. However, analyzing the morphological changes and grain size distribution that are associated with the porosity variations in gravel-bed rivers are still challenging. This study develops a new model using a multi-layer’s concept to simulate morphological changes and grain size distribution, taking into account the porosity variabilities in a gravel-bed river based on the mass conservation for each size fraction and the exchange of fine sediments between the surface and subsurface layers. The Discrete Element Method (DEM) is applied to model infiltration processes and to confirm the effects of the relative size of fine sediment to gravel on the infiltration depth. Further, the exchange rate and the bed porosity are estimated while using empirical formulae. The new model was tested on three straight channels. Analyzing the calculated results and comparing with the observed data show that the new model can successfully simulate sediment transport, grain sorting processes, and bed change in gravel-bed rivers.
Highlights
Sediment transport processes that are due to flowing water in gravel-bed rivers can be formed from bed load, suspended load, and movement inside the bed layer
The flow module interacts with sediment transport and bed variation module that is based on the mechanism of quasi-steady morphodynamic time-stepping, in which the interaction between the flow and bed profile is considered in two different times
Due to the complexity of the structure of the river bed and the mechanism of particles movements, most of conventional models simulate sediment transport and bed variation, but they are still limited by various assumptions
Summary
Sediment transport processes that are due to flowing water in gravel-bed rivers can be formed from bed load, suspended load, and movement inside the bed layer. In the same hydraulics condition, the transport rate of coarse size fraction may be different from the rate of fine size fraction. These reasons lead to the distinct forms of gravel-bed rivers. Under low-flow conditions, sediment transport can cause the extensive infiltration of fine sediment into void spaces in coarse bed material [3,4], which is known as clogging or colmation [5,6] (see Figure 1)
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