Evaluation of maintenance efficiency for multiple green infrastructure designs based on water quality performance and economic costs

Green infrastructure (GI) systems have been employed as an environmentally sustainable alternative to treat stormwater in urban areas, and many previous studies indicated GI practices are effective at reducing stormwater runoff flows to watersheds by rerouting flows through vegetation and soil. However, little is known about the effects of maintenance on GI performance. This study evaluated the maintenance efficiency for four GI designs (bioretention, grass channel, compost-amended grass channel, and bioswale) receiving the same weather conditions and pollutants along Lorton Road, Fairfax County, VA, USA., based on water-quality performance and economic costs. Seven regular maintenance events and a forebay restoration were monitored from 2018 to 2022. Stormwater quality performance among these four GI practices before and after these in-field maintenance activities was assessed on the load reduction of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total suspended solids (TSS), and runoff over four years. The average runoff reductions over all monitored storms were 74%, 85%,63%, and 68% for bioretention, grass channel, compost-amended grass channel, and bioswale, respectively. Over these maintenance events, the mean runoff reduction of all monitored GI designs improved by 3% after maintenance, DOC mass load reduction increased by 41%, TDN mass load reduction improved by 21%, and TSS mass load reduction increased by 2%. All the pollutant and runoff reductions for swales improved after spring maintenance events, and monitored GI systems generally performed better after spring maintenance events, potentially due more to the vegetation growth than the maintenance work. Bioretention and compost-amended grass channel DOC load reductions were the only statistically significant GI performance improvements attributable to maintenance.