Analysis of the Hydrologic Performance in a Lined Bioretention Basin and Implications for Monitoring and Design

Lined bioretention basins can be an optimal solution for urban stormwater runoff problems in regions with karst geology or high-density urban environments. In this study, inflows and outflows of a lined bioretention basin in central Pennsylvania were monitored for a year from June 2020 to June 2021. These data were used to generate hydrologic performance metrics, such as peak flow ratio, peak delay ratio, and runoff reduction. The basin displayed an impressive capacity in total volumetric runoff reduction, achieving an overall efficiency of 94%. This exceptional performance was primarily attributed to the basin’s effectiveness in capturing and managing smaller storm events. The basin’s performance declined when dealing with larger and more intense rainfall events, with a decrease in runoff reduction to as low as 64%. There was excellent control of peak outflow rates from the basin, with nearly 97% of events meeting the target peak flow reduction threshold. The basin did not perform well in delaying its peak outflow, which is likely due to the location of an underdrain very close to the inlet. When evaluating contributions to runoff reduction, the total evapotranspiration, overflow, and storage could not match this reduction volume, indicating leakage and exfiltration from the system. Although there are potential sources of error in this water budget, this indicates possible issues with the integrity of the basin’s lining and the importance of proper construction and maintenance. Overall, this study demonstrates the hydrologic benefits that lined bioretention basins can provide but also highlights important monitoring and design considerations. For monitoring, this includes the challenge of closing the water budget and assessing liner leakage. For design, this includes the need to ensure liner integrity and appropriately place underdrains for increased peak flow delay.