Atlanta's Flood: Changing What the Rain Falls On

The floods that devastated Atlanta and surrounding areas recently looked like the aftermath of a powerful hurricane or tropical storm. In fact, they had a more routine source: plain old rain. A low-pressure system parked over Georgia, and for eight days, it released several inches of rain.

Water at that volume would be hard for any region to handle, but the Atlanta metro area had a disadvantage: miles and miles of asphalt. When the rains came, water rushed over the blacktop--where it picks up speed--got squeezed into overflowing drainage systems and then dumped into rising creeks and rivers.

One meteorologist explained, "There used to be a lot more earth and soil to help absorb this stuff. But the rain really fell on the concrete jungle.

While rainfalls like this may seem like the proverbial act of God, there is something cities can do to lessen or prevent the damage.

We may not be able to stop the rain, but we can change what it falls on to. Instead of rain hitting huge swaths of concrete in our cities, we can use things like porous pavement, planted swales around parking lots, rain gardens planted along sidewalks, green roofs, and additional trees to help absorb the water like sponges.

These forms of green infrastructure mimic nature's own hydrology. Trees, gardens, and parks let rain infiltrate where it falls. Under natural conditions, the amount of rain that is converted to runoff is less than 10 percent of rainfall volume.

In contrast, water quality in the lakes and creeks that receive stormwater runoff--which often picks up toxic pollution and bacteria as it travels across streets and parking lots--starts getting degraded sometimes when just 3-5 percent of a watershed is paved.

Clearly most metropolitan areas in America have paved more than 10 percent of their watersheds. But more and more cities are also taking steps to let rain fall on soil instead of concrete.

The Sunday before last the Philadelphia Inquirer ran a front page story about the city's $1.6 billion plan to use green infrastructure to cut down on its stormwater problem.

In a recent report, Rooftops to Rivers, NRDC described how nine different cities, from Milwaukee to Pittsburgh, are applying these same techniques. Most found that not only were they a cost-effective way to manage stormwater, but they were also welcomed by residents who enjoyed the added green space.

Green infrastructure alone would not have saved Atlanta from its deadly floods, but it could have softened the blow in some neighborhoods, and it might have bought the city more time before creeks breached their banks.

The region, still recovering from a punishing drought, is not accustomed to such intense rain events. But climate change promises to make these uncommon events more common. Green infrastructure gives cities a powerful tool for coping with what could become the new normal.