I have just finished making a Power Point Presentation on Rain Gardens. It was a huge endeavor. I will be presenting it to a Garden Club up here in NH in a few weeks. Then I will present it again at ILEAD, which is the Institute for Lifelong Education At Dartmouth. Perhaps I should put it on this site, a bit at a time. I think you'd find it interesting.
To define a rain garden, it is an attractive, low maintenance garden planted with native plants that are able to survive in both wet and dry conditions. It allows polluted storm runoff to seep into the ground instead of running off into the curb, and from there into ponds and streams.
Since water runoff from roofs, driveways, patios, walkways, sump pumps, etc. are a main source of polluted water, a rain garden can reduce pollution going into the ground by as much as 30%. That's a BIG number!