design elements - San Jacinto Texas Historic District

Volunteer installation of a parking lot bioretention swale.
Parking lot bioretention swale, early season growth.
Parking lot bioretention swale, later season growth.
IMAGE: CONSERVATION DESIGN FORUM IMAGE: CONSERVATION DESIGN FORUM IMAGE: CONSERVATION DESIGN FORUM
Design Considerations
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Impermeable liners should be installed
to prevent infi ltration of stormwater into
underlying soils where contaminated
soils are present, or where rain gardens
are immediately adjacent to buildings
with basements.
Bioretention practices must be sized and
designed to account for drainage area and
soils and to convey the design runoff rate
(typically the 10-year storm).
A gravel trench with underdrain should
be used to allow excess fl ow to drain into
storm sewer system.
Protect bioretention practices from
construction site runoff to prevent sealing
of amended topsoil.
A minimum 12 inch layer of planting
soil containing approximately 50%
organic compost, and 50% sand will
enhance fi ltration. Planting soil thickness
should be increased to 18 to 24 inches to
accommodate trees.
Cross section of a bioretention swale.
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Provide adequate side slopes and
underdrains to prevent ponding of water
for greater than 48-72 hours.
Filtration benefi ts can be improved by
planting native deep-rooted grasses and
forbs and minimizing side slopes. Plants
can include a combination of native shrubs,
grasses, and fl owering perennials. Plants
should be selected for low maintenance
and to tolerate winter salt.
Maintenance Considerations
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Similar to typical gardens requiring
occasional
plantings.
weeding and additional
Periodic sediment removal may be needed
to maintain function.
Bioretention practices may need to be
replaced periodically (every 20 years or
more) due to sediment accumulation
SAN JACINTO TEXAS HISTORIC DISTRICT CORRIDOR STANDARDS │ 143
IMAGE: CONSERVATION DESIGN FORUM