design elements - San Jacinto Texas Historic District

Bioretention Practices
Defi nition
Rain gardens, tree wells, and planter boxes
can be designed as vegetated stormwater
bioretention features that convey, retain,
cool, and cleanse stormwater before being
discharged to sewer systems. They are
installed in parkways, medians, and parking
lot islands, and along the sides of buildings
to capture roof runoff . These practices are
typically designed to allow stormwater to
pond slightly and infi ltrate into the ground,
or to be absorbed and evaporated into the
atmosphere by vegetation. Impermeable
liners should be used to prevent water from
infi ltrating into the underlying soils where
contaminated soils are present. Excess water
is collected by a drain and discharged to
storm sewers.
Applicability
Bioretention practices are appropriate for
most new and retrofi t projects on individual
lots and rights-of-way to accept runoff from
roof downspouts, streets, driveways, alleys,
sidewalks, and parking lots.
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Benefi ts
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Reduces impervious surface runoff
volumes (up to 15%) and rates (50% or
more).
Reduces sediments and metals (30 to 70%),
nutrients (10 to 30%), and other pollutants
from runoff .
Provides stormwater detention depending
on the thickness of the gravel layer and
depth of basin.
Provides limited habitat for birds,
butt erfl ies, and benefi cial insects such as
dragonfl ies, which eat mosquitoes.
Can increase aesthetic value of
properties.
Cost Considerations
Costs range from $3 to $4 per square foot for
very simple designs and from $10 to $40 per
square foot for complex designs, depending
on the plants, drainage structures, and curb
designs.
Bioretention / infi ltration tree wells.
Parkway bioretention / infi ltration planters.
Bioretention planters within a curb bumpout.
IMAGE: CONSERVATION DESIGN FORUM
IMAGE: ENVIRONMENTAL SERVICES, PORTLAND, OR IMAGE: ENVIRONMENTAL SERVICES, PORTLAND, OR