A rain garden is a shallow, flat-bottom garden bed designed to serve as a collection and treatment site for storm water runoff from rooftops, driveways, walkways, streets, or parking lots. Through the process of infiltration and phytoremediation, rain gardens can remove pollutants from runoff before water recharges aquifers or flows into our streams and ocean.
On March 25, 2011, a demonstration rain garden was constructed at Heʻeia State Park as a joint effort between HOK, Kamaʻāina Kids, University of Hawaiʻi Sea Grant Program and Oregon State University Sea Grant Program. With the help of a number of volunteers, the rain garden was constructed and planted in just one day. The site is open to the public and was constructed to provide an example what rain gardens look like and how they function.