More Study Needed: How to Make Green Streets Work
"Surprisingly, there are very few peer-reviewed research papers that have evaluated Green Streets on a stormwater control and treatment basis," according to an article by Jonathan Page, who looks at some of the existing data and also makes recommendations for tailoring green streets to the specific needs of the natural and built characteristics of different cities.
According to Page, the “newness” of the green streets movement and the difficulty in monitoring and instrumenting green street projects contribute to a lack of data and research about the effectiveness of green streets.
Projects in Seattle and Portland have provided some non-peer reviewed dataset, "but the study and evaluation is typically not as rigorous as those found in a peer-reviewed journal."
Moreover, the "excellent" results in downstream water quality protection and combined sewer overflow (CSO) reductions from those examples can't be expected in all parts of the country (or world), according to Page. Portland, Seattle, and other communities in the Pacific Northwest are perfect locations for green streets because "[r]ainfall patterns and storms in that ecoregion are characterized by low rainfall intensities and long durations." In other ecoregions, like the Southeast, "storms tend to have a much higher rainfall intensity and shorter duration, which means a lot of above ground storage is needed to temporarily retain runoff for infiltration and treatment after the storm has passed."