Technical Abstract: Nearly half of the 10,000 small watershed dams constructed in the U.S. with the assistance of the NRCS will reach the end of their proposed service life in the next 10 years. While many of these structures were originally built to protect agricultural land from floods, urbanization around some of them has; thereby, changed the hazard classification of these dams. To meet current federal and state dam safety standards, rehabilitation of these structures are necessary. If ignored, these dams could place life and property at risk. The Georgia NRCS requested a specific model study for a proposed design of a converging roller compacted concrete (RCC) stepped spillway for the rehabilitation of Big Haynes Creek Watershed Dam Number 3 (H-3) in Gwinnett County, Georgia. The USDA-ARS Hydraulic Engineering Research Unit conducted a three-dimensional, 1:22 scale physical model study to evaluate the hydraulic performance of this structure. The results of the study indicated that the proposed height of the spillway training walls will be overtopped by the maximum expected discharge. Air entrainment was not shown to significantly influence the depth of flow at the highest tested flow rate based on the calculated and observed locations of the air entrainment inception point. However, complete interpretation and/or extrapolation of the data for the prediction of prototype behavior for similarly designed structures may require the addition of an appropriate scaling factor to account for air entrainment depending on the location of where air entrainment starts. Other significant design recommendations resulting from this study include the extension of the stilling basin downstream for added protection of the structure and downstream channel. The design recommendations and overall performance observations resulting from this model study are discussed in this report.