Page 36 - Green Builder March-April 2016 Issue
P. 36
LET’S SAY YOU WANT TO DESIGN a rain gardens, bioswales, permeable pavement,
garden, but the heavy clay soil won’t allow “green” parking areas, trees and disconnected
water to infiltrate effectively. Or you want downspouts. Designers must always choose
to direct roof runoff into a swale, but from this menu of practices, selecting those
you’re dealing with a tiny lot. best suited to the site. However, sometimes
“Green infrastructure” refers to the host of restrictive site conditions can be addressed—
techniques and strategies that slow stormwater and the options widened. Here are the most
runoff, clean and filter stormwater and enhance common issues, along with the solutions that
groundwater recharge. These include rain will help you design around them.
1. SLOW SOILS Amend soils. Adding compost or other organic matter can increase
soil infiltration rates, while improving the soil’s fertility and its ability
Soils that are dominated by clay and/or glacial till often have low to remove pollutants (see Sidebar).
infiltration rates, and stormwater may run off before it can be
captured on the site. But it is still possible to design infiltration-based Go deep. Enhance soil infiltration rates by planting deep-
stormwater controls, such as rain gardens and swales, for sites with rooted vegetation. The roots create small conduits for water to
these soils. Take these steps to ensure your plan succeeds: infiltrate and increase biological activity in the soil. The U.S.
Geologic Survey found that the median infiltration rate of a clay
Measure infiltration rates. This should be done before designing soil planted with prairie species was more than three times the
stormwater controls. A generally accepted guideline is that the rate of a clay soil planted in turf (0.88 inches/hour compared to
infiltration rate of native soils beneath swales and rain gardens 0.28 inches/hour).
should be greater than 0.25 to 0.5 inches/hour.
CREDIT: U.S. BOTANIC GARDEN
Below the Surface. The roots of native prairie plants penetrate five to 15 feet into the soil. In contrast, shallow-rooted turfgrasses don’t
penetrate beyond a few inches.
34 GREEN BUILDER March/April 2016 www.greenbuildermedia.com
