An annular flume combined with a microscopic system is used to explore local erosion mechanisms of transparent cohesive beds (yield stress fluids) under shear-induced flowing liquid. The observations at a microscopic scale for erosion flume experiments are the originality of this work. Our first results reveal that the deformation and erosion dynamics of bed material mainly depends on its miscible state with the flume fluid, its structural organization being associated with mechanical properties and the measurement section. Shear localization within the bed is also observed. Moreover, the erosion rate and the local bed shear stress can vary with time even for an imposed constant global hydrodynamic flow as they result from the coupling between the fluid flow and cohesive bed conditions at the bottom. We also try to link the local resistance to erosion to the local cohesive strength estimated from rheometric microscopic data for the same sample conditions with homogeneous properties.