Stormwater management features such as bioretention systems, rain gardens and other green infrastructure provide valuable ecosystem services. These features are used increasingly to capture and treat stormwater runoff before entering aging combined sewer overflow systems. However, despite significant investments in green infrastructure, little data exists on long term condition, performance, and maintenance. A rapid visual assessment method for stormwater management features was developed utilizing physical characteristics, plant species present (including weedy and invasive species), surrounding land use, and the identified level of need for routine maintenance to determine overall condition. Initial site visits were conducted in June 2015 for 164 bioretention, bioswales, and rain gardens in Greater Cleveland, Ohio to test the protocol. Second site visits were conducted in August 2015 for final plant surveys.
Results/Conclusions
A mean number of 17.5 total plants per site were found, this included plants that were established and assumed to be planted as target species. The average number of weedy and invasive plant species found at all sites was 7.1. Four maintenance proxy variables; the presence of excess leaf litter, and sediment inside the basin, excess leaf litter and sediment blocking either the inlet and/or the outlet, and the degree of weedy vegetation present, were used to determine overall condition. Five percent of sites were in excellent condition, 34% in very good, 35% in good, 25% in fair, and 1% in poor. A multivariate conical correspondence analysis compared plant species data with environmental variables. The presence of invasive and weedy plant species was associated with a bare soil bottom substrate and the presences of buildings as surrounding land use. Preliminary results suggest a bare soil bottom substrate is correlated with fair or poor feature condition, and lower plant species richness. Bare soil substrate and lower species richness can lead to erosion or compaction in the system, affecting stormwater infiltration. Inadequate and unqualified maintenance of stormwater management features can impact long term function. This study emphasizes an urgent need for the development of conclusive maintenance and design guidelines, including follow up care and research after installation.