Experimental data on bed friction and solids transport in an open-channel flow at high bed shear are presented in this paper together with a discussion using analytical developments. Experiments were carried out using plastic particles transported in water above an erodible bed in a tilting flume. They confirmed that bed friction is affected by transport of solids for large bed shear stresses in the upper plane bed regime. Similarities in flow conditions were also observed between open-channel flows in steep slopes with intense solids transport, and stratified flows in slurry pipes. Furthermore, the experiments revealed two different sub-regimes for the upper plane bed regime in open channels. Formulae for the friction coefficient and the solids flowrate were proposed for an erodible bed with a developed shear layer. Measured velocity distribution indicated a linear velocity profile across a major part of the shear layer.