CIVIL ENGINEERING 365 ALL ABOUT CIVIL ENGINEERING



AbstractAccounting for seasonal effects on rain garden performance can be challenging in colder regions. Changes in temperature cause changes in the viscosity of water, infiltration rates, and evapotranspiration rates. A variably saturated hydrologic model (HYDRUS-1D) was calibrated and validated using observed ponding depth and soil moisture data from two different storm events for a rain garden owned and operated by the Philadelphia Water Department (PWD). Warm and cold seasons were simulated with typical meteorological data and temperature-adjusted saturated hydraulic conductivity values. Design storm simulations confirmed that the rain garden is over-performing. By increasing the loading ratio (i.e., the ratio of drainage area to rain garden footprint) in the model, the maximum capacity of the rain garden was estimated to be 43% more than the design in the cold season, and 110% more than that in the warm season. If the maximum allowable ponding was raised to accommodate more water depth, the rain garden could have a maximum capacity 205% larger than the design while still meeting the PWD’s 24-h drain down requirement. This study demonstrates (1) how to develop a simple one-dimensional (1D) model that can reasonably account for seasonal effects on rain garden performance; and (2) the use of this model to quantify system capacity year-round and ultimately inform regulations and design.



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