Traditional stormwater management does not mitigate groundwater depletion resulting from pumping and loss of recharge. There has been an increasing interest in the use of alternative practices, such as raingardens, that enhance infiltration of stormwater. We develop a simple numerical model for their design and evaluation. Water flow through the soil is modelled over three layers: a root zone; a middle storage layer; and the site subsoil. To continuously simulate recharge, runoff and evapotranspiration, a Green-Ampt equation coupled with a surface water balance is used. For the humid climate of Madison, Wisconsin, USA, results show very high recharge rates in the rainy season, where a raingarden with an area of 10–20% of the contributing impervious area maximizes recharge. For the semiarid climate of Santiago, Chile, the optimum ratio was 10–20%, and for the arid climate of Reno, Nevada, USA, it was closer to 5%.

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