How was the rain garden constructed?
(Conservation Currents, Northern Virginia Soil and Water Conservation District)
Elements of a Rain Garden
In this engineered rain garden, the hole was dug 4 feet deep with a 600 square foot surface area.
Across the bottom of the ponding area, on top of a 6 inch base of gravel (VDOT #57), lay a perforated drain pipe (not visible). Over the horizontal pipe is 6 more inches of gravel (VDOT #57), and then a 6 inch layer of pea gravel. On top of the gravel layers is a manufactured soil (Biofilter ®) with 25 percent organic material.
The soil is covered with mulch. The mulch is held down by netting to reduce the likelihood of it floating away after a storm. The last element are the plants, all native to the area and tolerant of moist soil. The plant roots and mulch are responsible for pollutant removal.
A vertical pipe allows visual access to the underdrain, and, if necessary, an entry point for cleaning out debris in the drain.