Performance of Two Case Study Rain Gardens with Multilayers Native Soil

Increasing urbanization results in increased runoff, which elevates the demand for stormwater control measures (SCMs) to reduce the volume of storm runoff and restore pre-development conditions. Rain gardens, one of the most commonly used SCMs, rely mainly on infiltration to reduce the volume and peak flow of storm runoff. Ultimately, the infiltration rate is controlled by the native soil beneath the upper soil media of rain gardens. To investigate the influence of these native soils, the hydraulic performance of two rain gardens located at the headwaters of the Jenkintown Creek in Pennsylvania were monitored and modeled. The upstream rain garden has two native soil layers, while the downstream rain garden has four native soil layers. Due to the variable water level in the bowls of the two rain gardens before and during a storm event, it was required to use a variably saturated mathematical model, HYDRUS 2D. Thus, it was essential to classify the soil layers of the two rain gardens and obtain the soil water characteristic curves for each soil type. In addition, site observations and monitoring parameters, such as rain garden geometry, water level in the bowls, water content of the soils, and outflow from the underdrain structure, were extremely valuable for the model inputs and boundary and initial conditions. The model was used to examine several scenarios of different soil types after calibrating the observed and modeled outflow to identify any improvements in the performance of the two rain gardens.