Science Inventory

Factors contributing to the hydrologic effectiveness of a rain garden network (Cincinnati OH USA)

Citation:

Shuster, W., R. Darner, L. Schifman, AND D. Herrmann. Factors contributing to the hydrologic effectiveness of a rain garden network (Cincinnati OH USA). Infrastructures. MDPI, Basel, Switzerland, 2(3):11, (2017). https://doi.org/10.3390/infrastructures2030011

Impact/Purpose:

Rain gardens can be used as a green infrastructure control mechanism to help reduce stormwater runoff. However, little data is available to gauge the effectiveness of rain gardens. The purpose of this project was to determine rain garden effectiveness in controlling stormwater runoff by monitoring a field test site over a four-year period. This work shows that effectiveness depends on rainfall depth, event intensity, and soil properties. Communities, states, planners, and regulators who are interested in installing green infrastructure would find this research relevant.

Description:

Infiltrative rain gardens add retention capacity to sewersheds, yet, their capacity for detention and redistribution of stormwater runoff is dynamic and often unverified by monitoring. Over a 4-year period, we tracked whole system water fluxes in a two-tier rain garden network, and assessed near-surface hydrology and soil development across construction and operational phases. The monitoring data provided a quantitative basis for determining network effectiveness with implications for return-on-investment. Based on 233 monitored warm-season rainfall events, at least 50 percent of total inflow volume was detained, with 90 percent of all events producing no flow to the combined sewer. For the larger events that did result in flow to the combined sewer into the local combined sewer system, the rain gardens delayed flows for an average of 5.5 hours. Multivariate analysis of hydrologic fluxes showed that total event rainfall depth was the predominant hydrologic driver for network out flow during both phases, with average event intensity and daily evapotranspiration as additional, independent factors in regulating retention in the operational phase. Despite lower-than-design infiltration rates, tradeoffs among soil profile development and hydrology, and resilience to sediment loading contributed to maintaining hydrologic effectiveness. We suggest that a monitoring framework to evaluate effectiveness is useful in guiding adaptation of stormwater control measures toward functional green infrastructures.