(HE-22620)
Richards Equation Model of a Rain Garden
Alejandro R. Dussaillant (ASCE associate member) 1, Chin H. Wu (ASCE associate member)2 & Kenneth W. Potter3
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
non-snowfall season. (The model does not handle snowmelt). A rain garden with an area of
approximately 10-20% of the contributing impervious area maximizes groundwater recharge.
Increasing the depression depth increases recharge and saturation times, affecting plant survival.
Rain garden feasibility also depends on the subsoil hydraulic conductivity.
KEYWORDS: rain garden, stormwater, infiltration, Richards, groundwater, recharge, urbanization, retention
1
Assistant Professor, Dept. Ingeniería Hidráulica y Ambiental, P. Universidad Católica, Av. Vicuña Mackenna
4860, Santiago, Chile. Phone: 56-2-3545873, Fax: 56-2-3545876, adussa@ing.puc.cl
2
Assistant Professor, Dept. Civil and Environmental Engineering, University of Wisconsin-Madison, 1415
Engineering Dr., Madison, WI 53703, U.S.A. Phone: 608-2633078, Fax: 608-2625199, chinwu@engr.wisc.edu
3
Professor, Dept. Civil and Environmental Engineering, University of Wisconsin-Madison, 1415 Engineering Dr.,
Madison, WI 53703, U.S.A. Phone: 608/262-0040, Fax: 608-2625199, kwpotter@facstaff.wisc.edu
1