Reliability-Based Approach to Investigating Long-Term Clogging in Green Stormwater Infrastructure

Green stormwater infrastructure (GSI) is defined by the integration of natural processes into the built environment to provide important ecosystem services. While GSI has multiple benefits, its hydrologic performance can be highly variable. One of the factors driving GSI performance is age and maintenance. Physical clogging as a result of fine sediments carried by influent stormwater is a particularly important issue for many forms of infiltration-based GSI. The authors propose a probabilistic method to determine optimal maintenance timeframes to mitigate the impact of clogging for rain gardens under short duration storms, thereby filling an important gap in the literature. A test rain garden is modeled in the EPA's Stormwater Management Model (EPA-SWMM) and calibrated using USGS data from a 9.3-m2 site in Wisconsin surrounded by clay loam native soils. The results suggest that in a humid continental climate similar to that of Urbana, Illinois, a three-year window should be used to monitor rain gardens for clogging, and to ensure optimal performance for larger storms. Model results also reveal that pretreatment to reduce total suspended sediment loading is useful in ensuring the long-term performance of rain gardens, and highlight a need for more long-term data collection from existing GSI. These findings caution against using a single monitoring parameter, such as saturated hydraulic conductivity, for stormwater management, and instead suggest a holistic consideration in future monitoring and evaluation of GSI.