Chronic detachment of the ‘Epilithic Biofilm’ (EB) was investigated by coupling experimental and numerical approaches focusing on EB-flow interactions during 65 days in an artificial rough open-channel flow. Local hydrodynamic conditions were measured by Laser Doppler Anemometry and numerical simulations of the EB biomass dynamics were performed with three models of chronic detachment that integrated successively as a descriptor of the flow conditions: the discharge Q, the friction velocity u and the roughness Reynolds number k+ = uks/ν (ν = water kinematic viscosity). Comparisons of numerical simulation results with experimental data showed that modelling the chronic detachment by taking k+ as the external variable of forcing gave the best fit. This suggests that description of the near bed turbulence by taking account of the evolution of both the friction velocity and the height of roughness seems to be the most relevant approach in studying the dynamics of EB in streams.