Low Impact Development Manual for Michigan - OSEH - University ...

Description and Function
Bioretention is a method of managing stormwater by
pooling water within a planting area and allowing the
water to infiltrate the garden. In addition to managing
runoff volume and reducing peak discharge rates, this
process filters suspended solids and related pollutants
from stormwater runoff. Bioretention can be implemented
in small, residential applications (Figure 7.3) or
as part of a management strategy in larger applications
(Figure 7.4).
Figure 7.3
Residential Rain Garden
Source: Rain Gardens of West Michigan
Figure 7.4
Commercial Rain Garden
Source: Rain Gardens of West Michigan
Bioretention is designed into a landscape as a typical
garden feature, to improve water quality while reducing
runoff quantity. Rain gardens can be integrated into a
site with a high degree of flexibility and can integrate
nicely with other structural management systems including
porous pavement parking lots, infiltration trenches,
and other non-structural stormwater BMPs.
Bioretention vegetation serves to filter (water quality)
and transpire (water quantity) runoff, and enhance
infiltration. Plants absorb pollutants while microbes
associated with the plant roots and soil break them
down. The soil medium filters out pollutants and
allows storage and infiltration of stormwater runoff,
providing volume control. In addition, engineered soil
media may serve as a bonding surface for nutrients to
enhance pollutant removal.
Properly designed bioretention techniques provide a
layer of compost that acts like a sponge to absorb and
hold runoff. Vegetation in the rain garden can be diverse,
through the use of many plant species and types, resulting
in a system tolerant to insects, diseases, pollution,
and climatic stresses.
The term “rain garden” is used
to refer to smaller-scale bioretention
facilities typically found on
residential properties.
Bioretention can Accomplish
the Following:
• Reduce runoff volume
• Filter pollutants, through both soil particles (which
trap pollutants) and plant material (which take up
pollutants)
• Provide habitat
• Recharge groundwater (if no underdrain is placed
underneath)
• Reduce stormwater temperature impacts
• Enhance site aesthetics
LID Manual for Michigan – Chapter 7 Page 133