Hydrologic impacts of retrofitted low impact development in a commercial parking lot

Abstract

This paired watershed study investigated the hydrologic impacts of low impact development (LID) stormwater control measures (SCMs) receiving runoff from a highly impervious, highly connected commercial parking area located in Reynoldsburg, Ohio, USA. The site was retrofitted with a bioretention cell and permeable pavement, treating 0.60 ha and 0.42 ha of the parking lot, respectively, following a 12-month monitoring period of the existing parking lot hydrology (i.e., calibration period). Monitoring continued for an additional 20 months after construction (i.e., treatment period). The bioretention cell significantly reduced runoff depths and peak flow rates from the catchment, reducing mean values by 83% and 86%, respectively. Subsurface infrastructure (i.e., a gravel trench enclosing an adjacent sewer pipe and a nearby curb drain) was suspected to provide preferential pathways which resulted in substantial exfiltration from the cell despite poorly infiltrating underlying soils. Conversely, no significant differences in catchment hydrology were observed following the installation of the permeable pavement. The median surface infiltration rate decreased by 96% during the study, indicating that surface clogging occurred in the upper layers of the permeable pavement. Clogging was attributed to concentrated sediment loading delivered from the impervious catchment, along with lack of routine maintenance and snow plowing activities. It was concluded the loading ratio (27.6:1) of the permeable pavement was much too high, and this level of run-on should be avoided in future retrofits. Despite this, the combined effects of the bioretention cell and the permeable pavement led to significant runoff mitigation from the parking lot, reducing both runoff depths (47%) and peak flow rates (56%). Results were similar to previous studies of LID implemented in commercial catchments with lower levels of directly connected impervious cover than those herein. This study demonstrates the effectiveness of SCMs in highly impervious, highly connected catchments and their ability to mitigate runoff in commercial settings when properly sized and maintained.