Rain Garden Performance as a Function of Native Soil Parameters

Green infrastructure has been widely studied as a means of runoff reduction in urban areas, but the performance of such infrastructure installations is dependent on local environmental conditions. Rain gardens in particular are affected not only by precipitation but also by the native soil within which a garden is situated. In this study, we quantified the likelihood that a rain garden would overflow under different storm conditions based on installation in various native soils. Using the US Environmental Protection Agency's Storm Water Management Model (EPA-SWMM) (v. 5.1), we simulated different environmental conditions; the output overflow results were used to create linear regressions of overflow quantity as a function of soil parameters. These empirical relationships give insight into which parameters are most significant for runoff reduction under different conditions. In particular, planting media thickness and soil porosity in a rain garden were significant indicators of overflow in native soils with lower seepage rates. We used results from the regressions to create fragility curves using the Finite-Element Reliability Using Matlab (FERUM) software tool to create a visual representation of the probability of failure for a rain garden with increasing precipitation intensity when installed in different native soil types. This study helps describe the spatial variability of rain garden performance, and insights from this study can be used to inform planners of the feasibility of implementing a rain garden in terms of the local soils and typical precipitation conditions.