Green Stormwater Infrastructure Assessments in Santa Clara County, CA: An In-Situ Analysis of Select Bioretention Projects

Stormwater runoff, defined as rainwater that flows over impervious surfaces, is both an under-harnessed groundwater resource and the leading contributor to water body impairments due to the number of pollutants it can transport. One widely successful strategy to capture and treat stormwater runoff is to implement Green Stormwater Infrastructure (GSI): engineered green spaces to enhance the overall environmental quality of an urban landscape. GSI projects, particularly bioretention systems, capture and treat stormwater runoff through infiltration and plant absorption before it reaches receiving bodies of water. In order to operate efficiently, GSI systems require specific maintenance procedures. The purpose of this study is to evaluate the performance and maintenance processes of approximately fifty bioretention areas in Santa Clara County. The bioretention areas in this study were evaluated by observing current site conditions and measuring infiltration rates, as well as conducting interviews of municipal and facilities staff to determine the processes and challenges for GSI design, inspection, and maintenance. The results of this study showed that 26% of sites fell within the acceptable range of 5 to 10 inches per hour. Additionally, larger site designs and California native perennial bunch grasses were positively associated with acceptable infiltration rates. This research will help contribute to future GSI design and maintenance considerations for local municipal and facilities staff, such as the use of larger bioretention ponds over smaller designs, and planting more bunch grass vegetation