Modelling of Sediment Grains Size Distribution in River Bend Using Generalized Additive Model

Sediment grains size have always been considered as one of the crucial issues in the case of sediment dynamics. This seems necessary as it significantly affects sediment transport, bed roughness, and river environmental conditions. Since the geometric factors and characteristics of hydraulic flow in river bends are very complex, the analysis of sediment grain size distribution becoming an essential issue in bends that has been studied less so far. In this research, the distribution of the sizes of sediment grains in natural river bends having gravel beds was taken into consideration using field data. To achieve such a goal, 180 sedimentary samples from upper layers and other hydraulic flow parameters, including the velocity and depth of the flow and the characteristics of geometric beds, were gathered from nine different river bends. After determining the grain sizes of the sediments in the laboratory and calculating other required parameters, the P-Buckingham theory was applied to identify both the effective non-dimensional parameters and the characteristic equation. Then, the Generalized Additive Model (GAM) was used to determine the relationship between variables. Also, to avoid errors in the results, variables with a correlation coefficient greater than 0.5 and a probability value (p-value) greater than 0.05 were removed from the modeling process. Finally, a mathematical model for the distribution of sediment particle sizes based on the geometric parameters of the bends and the flow characteristics was developed. The obtained equation, with a coefficient of determination (R^2) equal to 0.76, shows that Froude Number (F_r), Shields parameter (θ_Shields), and the proportion of curvature radius to the top width section (R_c/T) affect on the median sizes of sediments in the gravel river bends.