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Bioretention - Maintenance
The primary maintenance requirement for bioretention cells (rain gardens) is that of
inspection and repair or replacement of the treatment area's components. Generally,
this involves nothing more than the routine periodic maintenance that is required of
any landscaped area. Native plant species should have been selected for use in the
bioretention cell, reducing fertilizer, pesticide, water, and overall maintenance
requirements. Bioretention system components should blend over time through plant and
root growth, organic decomposition, and the development of a natural soil horizon.
These biologic and physical processes over time will lengthen the facility's life span
and reduce the need for extensive maintenance.
New Jersey's Department of Environmental Protection states in their bioretention
systems standards that accumulated sediment and debris removal (especially at the
inflow point) will normally be the primary maintenance function. Other potential tasks
include replacement of dead vegetation, soil pH regulation, erosion repair at inflow
points, mulch replenishment, unclogging the underdrain, and repairing overflow
structures. There is also the possibility that the cation exchange capacity of the
soils in the cell will be significantly reduced over time. Depending on pollutant
loads, soils may need to be replaced within 5-10 years of
construction.1
In general, however, a routine maintenance schedule can be followed. An example is
presented here, as adapted from the Prince George's County
Bioretention Manual.2 For rain gardens in low density residential
developments, these maintenance responsibilities are often transferred to the
individual property owner. Experience has shown that the economic incentive of
maintaining property values ensures that most homeowners will maintain their LID
landscape. For rain gardens in common areas, Homeowner Associations may assume upkeep
responsibility. In commercial and industrial settings, the standard on-site facility
maintenance agreement can be used for the bioretention cell with modifications as
necessary.
Example Maintenance Schedule
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Soil
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Visually inspect and repair erosion monthly. Use small stones to stabilize
erosion along drainage paths.
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Check the pH once or twice a year. Apply an alkaline product, such as
limestone, if needed.
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Mulch
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Re-mulch any void areas by hand as needed.
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Every 6 months, in the spring and fall, add a fresh mulch layer.
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Once every 2 to 3 years, in the spring, remove old mulch layer before
applying new one.
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Plants
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Immediately after the completion of cell construction, water plant material
for 14 consecutive days unless there is sufficient natural rainfall.
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When trees have taken root, or at least by 6 months, remove stakes and wires.
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Once a month (more frequently in the summer), visually inspect vegetation
for disease or pest problems.
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If treatment is warranted, use the least toxic approach.
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Twice a year, from March 15th to April 30th and October 1st to November 30th,
remove and replace all dead and diseased vegetation considered beyond treatment.
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During times of extended drought, look for physical features of stress
(unrevived wilting, yellow, spotted or brown leaves, loss of leaves, etc.).
Water in the early morning as needed.
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Weed regularly, if needed.
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Prune excess growth annually or more often, if desired. Trimmed materials
may be recycled back in with replenished mulch or land filled if there is a
concern of heavy metals accumulation.
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General
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After rainstorms, inspect the cell and make sure that drainage paths are
clear and that ponding water dissipates over 4-6 hours. (Water may pond for longer
times during the winter and early spring.)
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KEEP IN MIND, THE BIORETENTION CELL IS NOT A POND. IT SHOULD NOT PROVIDE A
BREEDING GROUND FOR MOSQUITOES. MOSQUITOES NEED AT LEAST 4 DAYS OF STANDING WATER
TO DEVELOP AS LARVA.
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1 Low Impact Development (LID): A Literature Review. United States
Environmental Protection Agency Office of Water. EPA-841-B-00-005. October 2000.
2 The Bioretention Manual, Prince George's County Department of
Environmental Resources Programs and Planning Division, Maryland, 2001. |
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