Experimental studies on initiation of current-induced movement of mud

•A new method to determine the initiation movement of mud in laboratory is provided (i.e., the method of relative grey value of water’s image in the flume).•The PIV velocimeter is used to measure velocity profile in order to more precisely determine the friction velocity.•The grey value of water’s image has a good correlation with weak erosion and chunk erosion.•The empirical formula between deposit density and critical flow velocity for initiation movement of mud was provided.