Mitigating impervious surface hydrology at a large commercial store using green infrastructure retrofits

Large directly connected impervious parking areas are a common feature of commercial developments. Despite their prevalence in the United States and beyond, limited research has investigated the potential for green stormwater control measures (SCMs) to mitigate runoff from these areas. To address this konwledge gap, a paired watershed study was performed to evaluate the impacts of SCM retrofits in a commercial parking lot in Reynoldsburg, Ohio, USA. Hydrological responses of the existing parking lot were studied during a 12-month monitoring period. Following this, a bioretention cell and permeable pavement were installed and received runoff from 0.60 ha and 0.42 ha of the parking area, respectively; the SCMs were monitored for an additional 20 months post-construction. Despite poorly infiltrating underlying soils, the bioretention cell provided substantial reductions in runoff volume (by 83%) and peak flow rates (by 86%). Analysis of drawdown rates revealed the influence of urban karst features, as subsurface infrastructure (i.e., a gravel trench around a nearby sewer pipe) provided preferential pathways for exfiltration from the cell. The permeable pavement provided no hydrologic benefits, primarly due to extensive clogging which occurred rapidly after construction. It was concluded that the loading ratio (27.6:1) of the permeable pavement was much too large and should be avoided in future retrofit efforts. Overall, the systems resulted in signficant runoff mitigation at the site, demonstrating SCM effectiveness in highly connected, highly impervious commercial catchments.