Do rain gardens stand up to scrutiny when they are put through a cradle-to-grave life cycle assessment? In a word, absolutely!
Rain gardens out-performed gray infrastructure in Cincinnati, Ohio.
A recent study comparing the life cycle costs and environmental impacts of rain gardens and gray infrastructure in Cincinnati, Ohio, found significant advantages to the green approach. Net-net, rain gardens were more favorable in terms of cost and the environment: about a 42% cost reduction and from 62%-98% less environmental impact.
“Wastewater utilities may find significant life cycle cost and environmental impact reductions in implementing a rain garden plan,” say the multidisciplinary team of researchers from Ohio and California. About 13.1% of the studied watershed, Shepherd’s Creek catchment, is impervious or semi-pervious.
Cincinnati must eliminate 85% of its combined sewer overflow (CSO) volume to comply with the Clean Water Act (CWA). Rather than constructing a $250 million wastewater storage tunnel with a 40-million gal. capacity, the city is pursuing green stormwater solutions. The life cycle assessment took a look at 81 rain gardens designed to store a 2 in. rain event that were installed on residential property in Shepherd’s Creek in 2007. The average rain garden in the assessment detains 4.28 cu m of water (1,650 cu m over 35-year lifetime).
There’s a lot of detail in the paper that shows the lack of comparable studies in both green and gray infrastructure. The authors detail their assumptions, which likely underestimates the performance of rain gardens. They either assumed no maintenance costs with property owners providing the maintenance or high maintenance costs with four visits by a landscape maintenance crew annually. They also determined that gray infrastructure required higher skilled labor for all aspects—installation, operations and decommissioning–than green infrastructure, which further points out the steep learning curve of economists and engineers in understanding how live, vegetated systems really work.
Comparing green and gray infrastructure using life cycle cost and environmental impact: A rain garden case study in Cincinnati, OH (2015)
Comparing green and gray infrastructure using life cycle cost and environmental impact: A rain garden case study in Cincinnati, OH. Vineyard, Donald, Wesley W. Ingwersen, Troy R. Hawkins, Xiaobo Xue, Bayou Demeke, and William Shuster, 2015. Journal of the American Water Resources Association (JAWRA) 1–19. DOI: 10.1111/1752-1688.12320. http://onlinelibrary.wiley.com/doi/10.1111/1752-1688.12320/abstract