Triple Bottom Line of Green Infrastructure

18 11 2009

Before and After of Green Infrastructure Improvements
(Source:“Green Cities Clean Waters” Plan)

In an earlier post titled “Making Green Infrastructure Common Place” we discussed the recent release of Philadelphia’s $1.6 billion dollar “Green Cities Clean Waters” Plan. Its thrust is to transform over 4,000 acres of impervious areas within the City’s Combined Sewer System to green space over the next 20 years through the use of green infrastructure strategies. This would involve converting over 34% of all existing impervious areas. Of this, the conversion will primarily be made on public property and right-of-ways. Green streets, the most widely used management tool, will comprise nearly 38% of these improvements (see graphic). The report claims this is “the largest green stormwater infrastructure program ever envisioned in this country”. While green infrastructure has been utilized and proven in many parts of the country, the sheer magnitude and commitment of the city is a radical departure from the conventional approach to stormwater management practices.

Map of Green Street Locations
(Source:“Green Cities Clean Waters” Plan)

So why did Philadelphia decide to rely so heavily on green infrastructure as a means of reducing overflows in their CSO system? Quite simply it was cheaper, significantly cheaper. The plan estimates over the next 20 years the plan is to be implemented, the “triple bottom line” benefits (social, environments, economic) of the plan alone will add up to a present value of $2.2 billion dollars. The following is a breakdown of the benefits that comprise this figure.

  • Heat Stress Mortality Reduction (35%)
  • Recreation (22%)
  • Property Value Added (18%)
  • Water Quality and Habitat (14.5%)
  • Air Quality (4.6%)
  • Avoided Social Costs from Green Jobs (3.7%)
  • Energy Savings (1.0%)
  • Carbon Footprint Reduction (0.6%)
  • Reduction in Construction- Related Disruptions (0.2%)

So instead of employing conventional underground infrastructure that is one-dimensional, and is estimated to cost $16 billion, the city has decided that implementing a multi-dimensional strategy with multiple benefits made more sense. But not only is it more desirable, it is politically easier to implement because it makes the city a more beautiful and healthy place. So if you are going to have to spend the money anyway, why not make it count.

The shortcomings of the conventional “tanks and tunnels” approach were not only that it exceeded the EPA’s affordability standard for stormwater management (2% of median household income), but it also did not address water quality issues and could require green infrastructure tools anyway to meet these requirements. In addition, the report points out that the conventional solution isn’t aligned with the EPA’s broader goals of sustainability, reduces streams baseflow thereby damaging the resources that is designed to protect, and doesn’t offer any secondary triple bottom line benefits. Furthermore, since the conventional solution is not delivered incrementally it is not flexible and does not offer any benefits immediately.

Green infrastructure on the other hand offered the city the opportunity to revitalize and restore the city’s streams and rivers, enhance the quality of the built environment throughout the city, improve air quality, reduce the heat island effect, and sequester carbon. While accumulating these benefits, the approach was more flexible, offered immediate benefits, and, most importantly, the cost of implementation was offset by the dollar value of the benefits. (see Volume 2: Triple Bottom Line Analysis of the plan for specifics)

While conventional infrastructure has its place, the combination of the two can play a significant role in addressing many of the issues facing our cities. It is critical that we continue to move toward making these strategies common place. By doing so we can make our cities healthier and more beautiful for all of us to enjoy, while at the same time responsibly managing our stormwater.

-Brian Phelps



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