The catchment surface is the main source of sediments composing the river bed in a given reach, and of bedload and suspended load through a given cross-section. . Several processes act as drivers of sediment supply to the river network and also play a fundamental role in the dynamics defining the size of sediments supplied to the rivers. These processes operate and interact on an extremely wide range of spatial and temporal scales. Models exist to reproduce these processes, mainly aiming at the quantification of the sediment yield of a catchment or at the analysis of the sediment sources in a heterogeneous catchment. However there still exist a large gap to (1) estimate the grain size distribution of sediments supplied from the hillslopes to the river; (2) model their effects on river fish habitat; (3) model the impacts of changing uphill processes on the grain size distribution.