This thesis proposes a method for modeling urban site-scale Low Impact Development (LID) features at the watershed-scale to evaluate the as-yet unknown performance of LID in a high intensity rainfall region. Increased impervious cover from urban development causes increased peak flows and shorter peak timing at the watershed outlet during rainfall events. Although LID features have been constructed across the U.S. to address these issues, their performance has not been evaluated in a high-intensity rainfall region or cumulatively throughout a large watershed. Using a fully-distributed Vflo® hydrologic model of the White Oak Bayou Watershed in Houston, TX, as opposed to conventional lumped-area models, two common urban retrofit LID features were modeled (rain gardens and green roofs) using a simple parameter-averaging method for various size storms. Findings indicate that although unable to significantly control the 100-year storm event, a combination of LID features can effectively reduce outlet discharges during smaller storms when fully implemented across a large watershed.