The goal of this paper is to set up a framework designed to take into account
the characteristics of sediment particles when transported by water. Our
protocol consists in describing the characteristics of sediment particles via
an additional variable, and to build operators involving this new variable,
modeling the evolution of the particle characteristics. Several such operators
are proposed, some based on principles of relaxation toward an equilibrium, and
others on a description of the particles' aggregation and fragmentation
process. A discrete version of the latter is also offered for numerical
settings
