Abstract
In gravel-bed rivers, monitoring porosity is vital for fluvial geomorphology assessment as well as in river ecosystem management. Conventional porosity prediction methods are restricting in terms of the number of considered factors and are also time-consuming. We present a framework, the combination of the Discrete Element Method (DEM) and Artificial Neural Network (ANN), to study the relationship between porosity and the grain size distribution. DEM was applied to simulate the 3D structure of the packing gravel-bed and fine sediment infiltration processes under various forces. The results of the DEM simulations were verified with the experimental data of porosity and fine sediment distribution. Further, an algorithm was developed for calculating high-resolution results of porosity and grain size distribution in vertical and horizontal directions from the DEM results, which were applied to develop a Feed Forward Neural Network (FNN) to predict bed porosity based on grain size distribution. The reliable results of DEM simulation and FNN prediction confirm that our framework is successful in predicting porosity change of gravel-bed.
Highlights
The significantly different size of fine sediment and coarse bed material is the reason for the change in the void space of gravel-bed rivers
If finer sediments are supplied at a small rate to a riverbed covered by a completely developed armor coat, the fine sediments can infiltrate into the interstitial spaces of the coarser bed material and move into void spaces
The void of bed material plays an important role in fluvial geomorphology, exchange processes between river and groundwater and river ecosystem
Summary
The significantly different size of fine sediment and coarse bed material is the reason for the change in the void space of gravel-bed rivers. If finer sediments are supplied at a small rate to a riverbed covered by a completely developed armor coat, the fine sediments can infiltrate into the interstitial spaces of the coarser bed material and move into void spaces. From a river management point of view, the amount of fine sediment stored in the void space of the gravel-bed up to 22% may be neglected and porosity can be considered constant [1]. The impact the void spaces of gravel-bed have on habitats for fish and aquatic species are substantial, and are of important considerations in assessing changes in the void structure of bed materials [3]. The variation of the bed porosity should be considered in hydromorphological models for gravel-bed rivers and in defining hydrological conductivity of modeling of ground water [7,8]
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