Page 418 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

378 Cha pte r T e n

Rain Gardens
Rain gardens or bioretention cells or swales are becoming common landscape features
which serve the dual purposes of landscaping and low-impact development stormwater
management. They are usually specially designed landscaped beds which have some
similar characteristics. They usually have a concave shape, instead of the convex or
mounded landscape beds which were popular in the past. This concave shape serves to
aid in water storage to allow for stormwater infiltration into the ground. There are
usually many separate rain gardens distributed throughout a site. Figures 10.1.9 and
10.1.10 are photographs of some of the rain gardens distributed throughout a middle
school yard in Tacoma, WA.
The design of rain gardens usually includes several layers of material to allow for
enhanced water storage, infiltration, and contaminant removal. The plantings are
chosen for the appropriate saturation levels found in the various portions of the rain
garden and the local climate. Some designs include nonvegetative media also for
aesthetics, especially in arid regions or when flows would damage vegetation. Rain
gardens can be very small or much larger, but generally are not as large as the typical
stormwater ponds. They can have a more centralized ponding area or be arranged
along channels or within sidewalk and other linear shoulders. Figure 10.1.11 is a
photograph of an open conveyance feature in a low-impact development project in
Central Washington that has little or no vegetation, while Figs. 10.1.12 and 10.1.13 are
photographs of a rain garden along a walkway in its first year, and its third year as the
planted vegetation becomes established.

FIGURE 10.1.9 A Gray Middle School rain garden. (Photograph courtesy Coughlin Porter
Lundeen taken November 2009.)