Keywords
rain garden, infiltration, richards, recharge, urbanisation
Start Date
1-7-2004 12:00 AM
Abstract
Traditional stormwater management does not mitigate groundwater depletion resulting from groundwater pumping and reduction in recharge. Infiltration practices, such as rain gardens, offer a potentially effective approach for addressing groundwater depletion. A rain garden is a landscaped garden in a shallow depression that receives the stormwater from nearby impervious surfaces, focusing recharge. We have developed a numerical model that can be applied in rain garden design and evaluation. Water flow through the rain garden soil is modeled over three layers- a root zone, a middle storage layer of high conductivity, and a subsoil lower layer. To continuously simulate recharge, runoff and evapotranspiration, the model couples the Richards Equation with a surface water balance. The model was applied to the climate of southern Wisconsin. Simulation results show that very high recharge rates are possible during the nonsnowfall season. A rain garden with an area of approximately 10-20% of the contributing impervious area maximizes groundwater recharge. An experimental rain garden was installed to gather quantitative data on the water budget terms in a continuous fashion. Sensors were installed to measure the water input, garden ponding, soil moisture and bottom drainage. To validate the Richards Equation model, we used data from three experiments resembling typical recharge events. The model results agree well with soil moisture data, but predicts a higher recharge than measured (15 to 37% more). This could be due to intermediate storage in the system, insufficient characterization of initial conditions, or limitations of the 1-D model.
Infiltration of Stormwater in a Rain Garden: Richards Equation Numerical Model and Field Experiment
Traditional stormwater management does not mitigate groundwater depletion resulting from groundwater pumping and reduction in recharge. Infiltration practices, such as rain gardens, offer a potentially effective approach for addressing groundwater depletion. A rain garden is a landscaped garden in a shallow depression that receives the stormwater from nearby impervious surfaces, focusing recharge. We have developed a numerical model that can be applied in rain garden design and evaluation. Water flow through the rain garden soil is modeled over three layers- a root zone, a middle storage layer of high conductivity, and a subsoil lower layer. To continuously simulate recharge, runoff and evapotranspiration, the model couples the Richards Equation with a surface water balance. The model was applied to the climate of southern Wisconsin. Simulation results show that very high recharge rates are possible during the nonsnowfall season. A rain garden with an area of approximately 10-20% of the contributing impervious area maximizes groundwater recharge. An experimental rain garden was installed to gather quantitative data on the water budget terms in a continuous fashion. Sensors were installed to measure the water input, garden ponding, soil moisture and bottom drainage. To validate the Richards Equation model, we used data from three experiments resembling typical recharge events. The model results agree well with soil moisture data, but predicts a higher recharge than measured (15 to 37% more). This could be due to intermediate storage in the system, insufficient characterization of initial conditions, or limitations of the 1-D model.
