Free surface flow of concentrated suspensions of small particles in a viscous fluid differs from that of a homogeneous medium. It exhibits surface roughness that results from the counteraction shear-induced migration of particles and restoring surface tension forces. For a layer of suspension that is bounded between two horizontal free surfaces and is uniformly sheared by side walls, the corrugation of the upper free surface exhibits characteristics of a homogeneous turbulent interface with a relatively wide spectrum of frequencies. When the flow of the concentrated suspension is driven by gravity in an open inclined rectangular channel, the roughness intensity is affected by the stationary boundaries and varies locally with the shear strength. Coherent macrostructures, with scale larger than the particle size, develop in the flowing layer in the form of large vortices that are advected downstream. The presentation will present experiments showing these phenomena, and documentation of flow patterns and surface corrugation via video, LDV and PIV techniques. Characteristic velocity profiles, fluctuations and power spectra and their dependence on particle concentration and shear intensity will be depicted.