The processes that determine the morphology of rivers, estuaries and coastal regions involve the displacement of sediment, i.e. granular material of several sizes and provenance. There is no universal description of the motion and of the causes of motion of granular material within a fluid flow. The common idealisation is that of a discrete granular phase moving together with or as an effect of the action of a continuum phase. Research on kinematics and dynamics of granular media has led to outstanding achievements, mostly at “engineering” scales. However, these advances have seldom resulted from the integration of processes occurring at a grain-scale. In fact, the vast amount of research work carried out at the grain-scale has yet to be harmonized to match results obtained at macroscale into a consistent theoretical body.
Addressing the open research questions, topics of interest include (but are not restricted to):
- grain-scale mechanics of particle entrainment and disentrainment;
- upscaling and averaging techniques for stochastic processes related to granular processes;
- bed surface dynamics, including interaction among grain sizes in a poorly sorted mixture, and grain segregation;
- interaction between fluid flow and grain motion, including turbulence over granular smooth or rough beds, dense mixtures of fluid and granular material;
- momentum transfer within the granular;
- formulation and solution of the equations governing bed morphology and the motion of granular material.

Currently, the description of the motion and causes of motion of the discrete phase still encounters difficulties at fundamental levels. These include the identification of the scales at which an Eulerian-continuum approach is justified, the articulation between the probabilistic definition of sediment discharge, the stochastic nature of the (turbulent) near-bed flow and the development of bed forms or the relation between Lagrangian and Eulerian quantities describing sediment fluxes.
The session is co-organised within the two EU projects "HYTECH" (ITN-Marie Curie FP7-PEOPLE-2013-ITN-316546) and "SEDITRANS (ITN-Marie Curie FP7-PEOPLE-2013-ITN- 607394) by a working group formed to promote fundamental research on mechanics of sediment transport which, in addition to the convenors of the session, includes Claudia Adduce, Christophe Ancey, Robert Bialik, Philippe Frey, Andrea Marion, Vladimir Nikora, Athanasios Papanicolaou, Alessio Radice and Simon Tait.