This paper investigates the periodic bulk eddy generation mechanism in the surface rollers of hydraulic jumps through analysis of the surface fluctuation at the downstream end of jumps based on the fact that the released large eddies may interact with the free surface hence leaving their characteristic signatures. A simple model for estimating the generation frequency of the surface roller based on the excursion time of a fluid parcel traveling around the surface roller is presented. It is examined experimentally by analyzing the water surface fluctuation downstream of 21 hydraulic jumps with upstream Froude numbers lying between 1.37 and 3.04. Energy spectra of the surface measurements show bands of approximately normal distributed energy centering at particular frequencies exist when the upstream Froude numbers are 1.53 and larger. These identified center frequencies are found to match the estimated surface roller generation frequencies well hence indirectly verifying the periodic surface roller formation-advection process. © 2004 International Association of Hydraulic Engineering and Research.