Exploration of Volume Reduction via Infiltration and Evapotranspiration for Different Soil Types in Rain Garden Lysimeters

Abstract

Rain gardens are a commonly utilized stormwater control measure (SCM) that depend on infiltration and evapotranspiration (ET) for runoff reduction. Altering soil media, media depth, and flow path results in shorter or longer hydraulic retention times that promote either infiltration or ET, respectively. Often, rain gardens are not considered for cases in which the underlying conditions do not allow for deep infiltration (e.g., poorly infiltrating or contaminated native soils, karst topography, or areas with a high water table). It is common to import media to replace native soils and often soil mixes other than sandy soils are not considered. Designing for deep infiltration and ET in different proportions through design modifications based on site and soil characteristics can maximize runoff reduction. Discrete weighing rain garden lysimeters were used to perform a preliminary investigation of the impact of soil type and flow pattern on infiltration and ET from daily, seasonal, and event perspectives. It was found that one-dimensional (vertical flow) systems are deep infiltration dominated, while two-dimensional systems (horizontal flow) had nearly equal volume reduction from deep infiltration and ET. Five soil types (sandy loam, loamy sand, loam, silt loam, and clay loam) showed no statistical differences or slight statistical differences in ET rates and total volume reduction; there were, however, some statistical differences between soil types at the seasonal and event scales. Overall, all soil types except clay loam appeared to provide sufficient volume reduction in rain gardens, although the balance between deep infiltration and ET varied. This preliminary study showed that these soils could potentially be used in a rain garden design.