Effect of Geotechnical Parameters on the Percolation Performance of an Established Rain Garden in Pennsylvania

摘要

Rain gardens are an effective type of stormwater control measure (SCM) used in developed areas to reduce runoff and replicate pre-development conditions by restoring the hydrologic cycle. The volume of water is controlled by infiltration and evapotranspiration. Percolation, which is sometimes referred to as deep infiltration, occurs deeper within the subgrade or underlying soil and is affected by the presence/absence, location, and design details of an underdrain; the thickness of soil media (typically imported engineered media); and the type and thickness of the native soils. Underdrains, when used, consist of a perforated pipe surrounded by coarse aggregate; they are often wrapped by a geotextile to prevent clogging. To investigate the influence of these factors, the hydraulic performance of a rain garden located at the headwaters of the Jenkintown Creek in Pennsylvania was monitored and modeled by using HYDRUS 2D. The rain garden, which has an underdrain, was installed in 2015 at the Abington Friends School in Abington, Pennsylvania. After construction, the rain garden was instrumented with a weather station, bubblers to measure the water level inside the bowl, soil moisture sensors, and a pressure transducer to measure outflow from the underdrain orifice. The water level from the bubbler and the local soil properties were used as inputs in the HYDRUS 2D model. The measured outflow was used to calibrate the model. The calibrated model was used to examine several scenarios such as the optimal size and location of the underdrain and the need for using a bio retention mix as opposed to the native soils.