One of the design precedents that has been suggested for Design Week '08 is Tanner Springs Park in Portland OR. This urban park, filling one block of the Pearl District, was conceived by Peter Walker & Assoc and designed by Atelier Dreiseitl and GreenWorks. Built on the site of an old springs, this very urban park celebrates the natural processes that used to flourish in this low area near the Willamette River. The official web site from Portland Parks offers a little more background.
These photos are from the summer of 2006.