The city is spending billions of dollars to separate storm drains from dirtier sewer water, but at the same time, they're implementing much less expensive efforts to reduce urban runoff before it even gets to a drain: by subsidizing green roofs that absorb rainwater on top of buildings, and green streets that soak up water from the pavement before it goes down a storm drain.
Here are a few photos of Portland's NE Siskiyou "green street" project, courtesy of the project's designer, Kevin Robert Perry (as seen on Pruned):
Above: rainwater flowing along the curb enters a vegetated basin before it gets to a storm drain.
Plants inside the basin help aerate the soil, which in turn improves the basin's absorption capacity. Their root systems also support bacteria that can absorb and break down pollutants that flow off from the pavement.
The "green street" occupies what had been underutilized curbside parking on a neighborhood street. It's traffic calming, neighborhood green space, and inexpensive water treatment, all rolled into one elegant solution. This is the sort of thing that makes me want to become a landscape architect myself.