Currently, 17% of manholes are predicted to flood during the 3-month, 24-hour event under existing conditions. Installing bioretention at all possible locations reduces flooding by 88%; installing permeable pavement at all possible locations eliminates flooding altogether.
First, a detailed EPA Storm Water Management Model (SWMM) was developed to represent runoff generation and conveyance in the Johnson Street Basin. Second, three alternative green street designs were selected for further analysis. One of the selected designs added bioretention to the right-of-way, while two of the selected designs added permeable pavement. Third, the applicability of each design within the basin was determined. While there was sufficient space to place bioretention along 30 percent of local roads, permeable pavement could be installed along 80 percent of major roads and 90 percent of local roads. Fourth, each design was simulated in the SWMM model across a range implementation levels. Finally, cost data were integrated to yield cost effectiveness curves.