Influences of focused recharge from rain gardens on groundwater level and water quality

As a low impact development (LID) practice, rain gardens may increase groundwater recharge in urban areas through focused infiltration of the storm runoff. This paper explored the impact of focused recharge through rain gardens on groundwater level and water quality based on a field monitoring study; the observed groundwater level and water quality metrics between the recharge point and a reference well were compared for both long-term (3 years) and short-term (3 days after the rain) periods. The results showed that the groundwater level in the rain garden recharge area was significantly higher the reference point (confidence level α=0.01, same hereafter). The groundwater quality observations showed that, the average concentrations of NH₄-N at the recharge point were significantly lower than that at the reference point for both long-term and short-term values; the TN concentrations increased in 3 days after storms, but the average concentration in 3 years did not increase significantly; the NO₃-N concentrations at the recharge points slightly increased, but not significantly different from the reference point. The TP concentrations was observed with both increased and decreased values during the long-term and the short-term periods. Findings from this research indicate that rain gardens may produce effective recharge to groundwater, limited influence on P, and significant influence on nitrogen concentration in groundwater for areas that water table depth is greater than 2-3 m.