ORIGINAL ARTICLE Theoretical modeling of suspended grain-size distribution in fluvial environment by stratification and secondary current approaches Debasish Pal 1,2 • Koeli Ghoshal 1 Received: 24 January 2016 / Accepted: 5 January 2017 Ó Springer Science+Business Media Dordrecht 2017 Abstract Here we propose a theoretical model to compute the suspended grain-size distri- bution in fluvial environment. We derive the model based on the Reynolds averaged Navier– Stokes equation and the continuity equation of sediment phase. The model includes the effects of secondary current and stratification which are the cause of complex interaction between turbulence and grain-size distribution in the sediment-laden flow. Due to an immense importance of particle–particle and particle-turbulence interactions near the channel bed, we include their impacts in the boundary condition of the model. The present model has note- worthy contribution to demonstrate the phenomena of suspended grain-size distribution in the real world. Reported experimental data in literature shows well agreement with the numerical solution computed from the suggested model. The better computational accuracy of the present model is ascertained when the upper bound of calculated error between observed experimental data and computed values is found to be lowest for our model in comparison to a large number of existing models developed from different mathematical viewpoints. Keywords Grain-size distribution  Stratification  Secondary current  Turbulent flow  Open channel 1 Introduction Transport of sediment in fluvial environment has a crucial effect on several aspects which are economic development, water resources management, environmental safety and others which are essentially connected with our life. For the immeasurable importance of & Debasish Pal bestdebasish@gmail.com 1 Department of Mathematics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India 2 Present Address: Pillar of Engineering Systems and Design, Singapore University of Technology and Design, 8 Somapah Road, Singapore 487372, Singapore 123 Environ Fluid Mech DOI 10.1007/s10652-017-9510-7