The sediment transport driven by a river or a channel flow is a phenomenon that operates at different scales. At the smallest scales, the coherent structures of the turbulent boundary layer are the mechanisms that govern the entrainment. At a greater scale, observed now from a particle ensemble point of view, the entrainment is part of a diffusive system, where transitions between anomalous and Fickian regimes occur. The understanding of the interaction between these scales has a great impact in engineering and geophysical sciences. However, this understanding is incomplete. There are crucial aspects of the sediment transport that are still not fully understood nor characterized, e.g. the transport at the first stages of the entrainment or the physical mechanisms that underlie the transition of diffusive regimes. This thesis aims to shed lights on the sediment transport dynamics by addressing these issues through a characterization of its statistical behavior. To reach the objective, Direct Numerical Simulations (DNS) of a flow in a rectangular flat-bed channel at a Reynolds number Re ≈ 3600, coupled with a Discrete Element Method (DEM) to simulate the dynamics of spherical particles near the bed, were carried out. These Lagrangian simulations were two-way coupled and included colliding sediment particles, with fixed particles at the bottom to account for bed roughness. The simulations considered eight different values of the non-dimensional Shields parameter, spanning θ ≈ 0.03 − 0.85. Different values of θ were obtained by varying the particles density. Additionally, the diffusive regimes of sediment transport observed through the DNS-DEM simulations were explored by implementing statistical models: a linear and a non-linear advection-diffusion equations, and autorregresive Markov models with correlated/non-correlated versions and Gaussian/non-Gaussian distributions. When observing the first stages of the entrainment, the sediment flux was intermittent, becoming a continuos transport as the Shields number increased. With respect to the diffusive behavior of sediment transport, it went from a ballistic regime to a close-Fickian regime when the time scale of the observation increased. Although subdifussion was also observed, specially at low Shields numbers. As a conclusion, the sediment transport is highly intermittent during its first stages, presenting a multifractal behavior which varies with the Shields number. This multifractality also characterizes the widespread range of sediment transport event magnitudes. Regarding the diffusive character of the sediment transport, it is concluded that the correlated particles motion governs the transitions between the different diffusive regimes, where this relation was quantified.The sediment transport driven by a river or a channel flow is a phenomenon that operates at different scales. At the smallest scales, the coherent structures of the turbulent boundary layer are the mechanisms that govern the entrainment. At a greater scale, observed now from a particle ensemble point of view, the entrainment is part of a diffusive system, where transitions between anomalous and Fickian regimes occur. The understanding of the interaction between these scales has a great impact in engineering and geophysical sciences. However, this understanding is incomplete. There are crucial aspects of the sediment transport that are still not fully understood nor characterized, e.g. the transport at the first stages of the entrainment or the physical mechanisms that underlie the transition of diffusive regimes. This thesis aims to shed lights on the sediment transport dynamics by addressing these issues through a characterization of its statistical behavior. To reach the objective, Direct Numerical Simulations (DNS) of a flow in a rectangular flat-bed channel at a Reynolds number Re ≈ 3600, coupled with a Discrete Element Method (DEM) to simulate the dynamics of spherical particles near the bed, were carried out. These Lagrangian simulations were two-way coupled and included colliding sediment particles, with fixed particles at the bottom to account for bed roughness. The simulations considered eight different values of the non-dimensional Shields parameter, spanning θ ≈ 0.03 − 0.85. Different values of θ were obtained by varying the particles density. Additionally, the diffusive regimes of sediment transport observed through the DNS-DEM simulations were explored by implementing statistical models: a linear and a non-linear advection-diffusion equations, and autorregresive Markov models with correlated/non-correlated versions and Gaussian/non-Gaussian distributions. When observing the first stages of the entrainment, the sediment flux was intermittent, becoming a continuos transport as the Shields number increased. With respect to the diffusive behavior of sediment transport, it went from a ballistic regime to a close-Fickian regime when the time scale of the observation increased. Although subdifussion was also observed, specially at low Shields numbers. As a conclusion, the sediment transport is highly intermittent during its first stages, presenting a multifractal behavior which varies with the Shields number. This multifractality also characterizes the widespread range of sediment transport event magnitudes. Regarding the diffusive character of the sediment transport, it is concluded that the correlated particles motion governs the transitions between the different diffusive regimes, where this relation was quantified.PFCHA-BecasLa tesis contiene información que actualmente se está preparando para publicar en revistas del área.PFCHA-Becas