This study aimed to advance watershed-scale scenario testing by coupling the site-scale bioretention model, DRAINMOD-Urban (DMU), with the Stormwater Management Model (SWMM) to enhance bioretention representation at the catchment scale. The objectives included calibrating and validating the coupled SWMM-DMU model using field data, exploring different model calibration scenarios, and evaluating if including bioretention contributes to improved representation of outfall flows at the watershed scale. Field monitoring data from a stormwater sewer system with three bioretention cells in Columbus, Ohio, was used for SWMM-DMU model calibration and validation. The SWMM-DMU model performed well for representing hydrographs during calibration (NSE =0.55) and validation (NSE = 0.67), with simultaneous calibration of SWMM and DRAINMOD-Urban yielding the best performance. Further, a substantial improvement in model performance was observed when bioretention cells were included in the catchment-scale model. These findings suggest that better representation of site scale bioretention hydrology can improve modeling of watershed-scale interventions