There are many ways to handle rainwater runoff from parking lots and roofs, etc. One way is to do nothing. Another way to handle the runoff is to just let it pour into drainage ponds. Still yet another, more efficient use of the rainwater is to plant and maintain a rainwater garden.
The American Society of Landscape Architects did a project at a school in Portland.
The Mount Tabor Middle School Rain Garden transformed a parking lot courtyard from a “gray space” into a “green space” that manages stormwater, helps cool the school’s adjacent classrooms, and provides a canvas for environmental education for the students, staff, and overall community.