Large scale implementation of green infrastructure, such as bioretention, has become increasingly common. The goal of these installations moves beyond just reducing downstream peak flows, these efforts also aim to provide more natural hydrology in local streams. As such, the performance of controls such as bioretention in small events; the extent to which these systems partition runoff to infiltration, drainage, and overflow; and the timing of these hydrologic pathways becomes critical to holistically evaluating implementations. Recent advances in bioretention hydrologic modeling have allowed better representation of the hydrographs leaving these systems via drainage and overflow. However, scaling these advanced models to the watershed scale has not been widespread. In this study, DRAINMOD-Urban (a robust drainage model) is coupled with SWMM to provide a watershed scale model that can also perform fine scale modeling of bioretention. This combined model is tested in a watershed in Columbus, Ohio, (which has been retrofitted with multiple bioretention areas) to evaluate its performance. Initial results indicate that the combined model performs well for modeling the test watershed (NSE = 0.66 for hydrograph representation). Further, the performance for hydrograph representation, mean flow, and volume was found to exceed that of a model representing the system using SWMM LID tools. The results suggest that the model chosen for site scale representation of green infrastructure can make a difference in modeling watershed scale performance.
