The aim of this study is to determine the erosion rate of the cohesive sediments when the critical condition of putting back in suspension is exceeded. We are specially interested in relationships between the hydrodynamic actions and the behavior laws of the cohesive sediments. Five series of tests have been canied out in laboratory for five different concentrations of a mud of the Loire estuary. For each concentration, we have realized three experiences in order to examine statistically the results.