Bioswales: Benefit or Burden?

Jack Anderson and Thomas Meixner

Department of Hydrology and Atmospheric Sciences

The University of Arizona

Green infrastructure has been a tool used by cities to mitigate runoff and improve water quality. However there are dozens of guides, both official manuals and informal neighborhood workshops, leading to a wide variety of design choices. This lack of uniformity can be seen in Tucson with the recent advent of bioswales: vegetated basins intended to capture and clean street runoff during precipitation events. With the lack of comprehensive studies, it is unclear if the hundreds of bioswales, representing thousands of dollars and many of hours of maintenance each year, are performing as their original designers envisioned. In order to test performance, bioswales were subjected to a combination of qualitative and quantitative tests. Based on preliminary results there is evidence that supports the use of large boulders and coarse soil for maximizing infiltration, while basins with high organic matter content may actually reduce overall infiltration. When attempting to balance runoff mitigation with street aesthetics in the form of mature vegetation, there is no single “best” bioswale, but standardization of a few designs can lead to better use of city and neighborhood resources.