Biological Systems Engineering


Date of this Version



Written for presentation at the 2012 ASABE Annual International Meeting Sponsored by ASABE Hilton Anatole Dallas, Texas July 29 – August 1, 2012.


Increased urbanization has resulted in water quality and flooding problems for many receiving waters in the United States. Rain gardens are one type of best management practice commonly used in low impact development (LID). Many studies have evaluated large engineered bioretention cells in research settings. There is little information on the effectiveness of homeowner-maintained rain gardens that rely on deep percolation as the method for water exfiltration. Repeatable controlled experiments are very rare in hydrologic studies due to the inherent variability of weather data. The objective of this study was to evaluate the hydrologic properties of twelve established rain gardens using a stormwater runoff simulator. A volume-based design storm of 1.2 inches, the “water quality volume” storm, was applied as a synthetic SCS-type II 30-minute runoff hydrograph to each garden based on its respective catchment characteristics. Every rain garden tested drained in 30 h or less, with six gardens draining in less than one hour. Results of the study indicate that these 2-4 year old rain gardens are limited not by infiltration rate, which often met or exceeded performance standards, but rather by inadequate surface storage characteristics. Overall, rain garden storage capacity was poor with only two gardens able to store and infiltrate the water quality volume. On average, rain gardens studied were able to store and infiltrate only 40% of the design storm volume. Focus on accurate construction and berm grading should be a high priority for rain garden installers. Use of a stormwater runoff simulator to assess post-construction performance is feasible and can provide repeatable data on hydrologic effectiveness.