Analyzing the performance of a rain garden over 15 years

The Bioinfiltration Traffic Island (BTI) is a bioinfiltration rain garden that was retrofitted off an existing traffic island located at Villanova University, USA in 2001. Having been monitored since 2003, the BTI has quantitative hydrological data collected for the approximately two decades, making it a very valuable dataset for an in-depth analysis of the performance of the site.

The initial analysis comprises of a high-resolution analysis of rainfall event frequency along with resulting performance at the bioinfiltration rain garden. All rainfall events within the 15 years of collected data was discretized in to 2.5 mm, 2-hour bins. The binned rain events were then analyzed using a mass balance approach to understand how the different hydrological elements contribute to the ability of the site to treat incoming stormwater runoff. The second part of the analysis focuses on assessing the intensities of each of the recorded storms to understand its influence on the performance of the rain garden.

The third part of this analysis will comprise of studying the site’s ability to manage incoming runoff with the rain garden’s development over the fifteen years. The main focus will be to assess the performance of the site in the earlier stages and compare it to the performance seen in the latter stages with established vegetation. The binned rainfall events will be used to compare the performance of the BTI for storms with similar characteristics (similar precipitation amount and event duration) occurring in different stages of the timeline. The extensive dataset will additionally give insight to internal mechanisms such as evapotranspiration and infiltration occurring at the site and indicate how their contribution changes with the evolution of the site.

The overall analysis provides lessons into system components and aims to understand the interaction of the different hydrological elements within the rain garden. The objective is to use the findings in designing Green Infrastructure systems that can be optimized in their ability to manage incoming stormwater.