04/17/2012 06:15 pm ET Updated Jun 17, 2012

April Showers: The Tale of Two Cities

Two sides of the country and two different discussions about sewage and stormwater: Why is San Francisco a decade behind east coast cities in the adoption of green infrastructure?

At around 8 a.m. on April 12th, San Francisco experienced an April Shower that overwhelmed the sewage system and flooded large parts of the Mission District. This was not a storm of the century or anything approaching it; only one half inch of rain fell but during a short amount of time. This is exactly the kind of storm event that shows the tremendous benefits of green infrastructure and green roofs in particular. Green roofs mimic the natural environment -- that has been replaced by impervious streets, roofs, sidewalks, and parking lots -- by absorbing harmful runoff. These vegetated roof areas reduce, filter, and slow stormwater runoff, dramatically reducing the burden on the overtaxed and limited combined sewer system.

The SF Chronicle quoted Tyrone Jue, spokesman for the city's Public Utilities Commission (the body in charge of stormwater management.) "This is the third time the area has flooded since 2004.

A large volume of rainfall over a short time frame can overwhelm even the best designed sewers," Jue said.

This failure of the system occurred even though improvements were made to the sewer capacity as recently as 2009. It happens in many major cities, especially older cities on the east coast (cities built before 1900, which is why San Francisco is the rare major west coast city with combined sewers.)

I'm sure it is just a matter of time before S.F. takes seriously the adoption of green infrastructure and I know there are city officials who "get it" but it's striking that one of the most environmentally progressive cities on the planet falls behind Philadelphia, Baltimore, Washington D.C. , and New York City in their support of green infrastructure

In the case of green roofs I've heard the argument that due to water constraints in California green roofs -- by requiring a limited amount of additional irrigation -- are an impractical and wasteful technology. I argue that green roofs in particular are an excellent use of our limited water resources. By slowly releasing rainwater and evaporating absorbed water into the atmosphere green roofs are more likely to recharge aquifers and return to earth as rain, cleaning the air while they're at it and preventing harmful pathogens and heavy metals from reaching California's bays, rivers, creeks and lakes.

Green roofs insulate in ways beyond the public health benefits above: From the heat in summer and the cold in winter (maybe the inverse for San Francisco), to the damaging UV rays that eventually break the roof membrane down.

On the other coast, Philadelphia announced this week that they -- in partnership with EPA -- are putting a major investment into green infrastructure, called the Green City Clean Waters Plan. Two billion dollars will be invested over the next 25 years.

EPA Administrator Lisa P. Jackson said: "The Green City, Clean Waters Partnership promises to lead the way for communities across the nation, which can use the lessons learned through this long-term project to protect their health, safeguard their waters and boost their economies."

"The Green City Clean Waters Plan is our proposal to revitalize our rivers and streams by managing stormwater in a way that provides multiple benefits. It will result in clean and beautiful waterways, a healthier environment and increased community value. The assistance of our many and diverse regulatory and public partners makes it the most cost effective investment of its kind in the country," said Philly's Mayor Nutter. "Where other cities are challenged by very expensive commitments for tunnels, tanks and other gray infrastructure, we have worked with the state and the EPA to take this greener, more fiscally prudent approach that will realize multiple benefits."

Congratulation to Philadelphia for seeing the stormwater through the storm!

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