Prospects for enhanced groundwater recharge via infiltration of urban storm water runoff: A case study

The rain garden is an urban storm water best management practice that is used to infiltrate runoff close to its source, thereby disconnecting impervious area while providing an avenue for groundwater recharge. Groundwater recharge may provide additional benefits to aquatic ecosystems via enhancement of stream base flow.Yet, soil conditions can impact on certain aspects of rain garden performance and its provision of ecosystem services. In the context of a watershed-level study to determine the effectiveness of decentralized storm water management, we performed an order 1 soil survey of the Shepherd Creek watershed (Cincinnati, Ohio) to delineate soils and identify and describe representative soil pedons, and then we assessed subsoil saturated hydraulic conductivity (K-sat) in each of the three dominant subsoils with qualitative estimation methods and directly with constant-head permeametry. We next simulated the effect of subsoil hydrology of a hypothetical implementation of a parcel-level rain garden on groundwater recharge in this watershed. Measured subsoil K-sat were overall very low with a mean of 0.01 cm hr(-1) (4 x 10(-3) in hr(-1)) for Eden soil and a mean of 0.2 cm hr(-1) (0.08 in hr(-1)) for both the fine-silty family and Switzerland soils. Compared with the measured values, qualitative measures overestimated K-sat and depth of recharge for Eden and fine-silty, and underestimated the same for Switzerland. Based on median parcel features and 2004 warm-season storm records, rain gardens in the fine-silty family and Switzerland subsoils would be expected to contribute about 6 cm (2.4 in) of recharge as compared to the 2 cm (0.8 in) expected in Eden soils. Our results also suggest the highest potential for abatement of storm water quantity abatement in Eden soils, with some partitioning of this water to recharge as an added benefit. Our approach and results form the basis for a comprehensive understanding of how storm water management decentralized at the watershed level may positively impact ecosystem services.