Rain gardens are flat-bottomed depressions in the ground which are used to capture excess water and pollutants, such as storm runoff from rooftops, driveways, sidewalks, parking lots, and streets, from reaching streams and oceans.

The purpose of these rain gardens is to mimic natural forest and meadow conditions to act as an infiltration system from hard surfaces. They are beneficial because they reduce flooding by absorbing rain water; they filter oil, grease and other toxic materials before polluting water bodies; they allow groundwater aquifers to be recharged because of more pervious surfaces; and they provide habitat for wildlife.

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. View the time-lapse video of the Heʻeia State Park rain garden construction.

He'eia Rain Garden Build 3/25/2011 from Hui o Ko'olaupoko on Vimeo.

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