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Inspection and Maintenance: Bioretention & Bioswales (view source)
Revision as of 20:20, 7 April 2022
, 2 years agono edit summary
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==Rehabilitation & Repair==
{|class="wikitable"
|+'''Bioretention/Swales: Key Components, Typical Issues and Rehabilitation Requirements'''
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!Component
!Problem
!Rehabilitation Tasks
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|'''[[Inlets]]'''
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Inlet is producing concentrated flow and causing filter bed erosion.
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*Add [[Level spreaders|flow spreading device]] or re-grade existing device back to level. Rake to regrade damaged portion of the filter bed and replant or restore [[mulch]]/[[stone]] cover. If problem persists, replace some mulch cover with stone.
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|'''[[Bioretention: Construction checklist|Filter Bed]]'''
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Local or average sediment accumulation ≥ 5 cm in depth.
Surface ponding remains for > 48 hours or surface infiltration rate is <25 mm/h.
Damage to filter bed or slide slope is present (e.g., [[erosion]] rills, animal burrows, sink holes, ruts)
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*At [[inlets]] remove [[stone]] and use vacuum equipment or rake and shovel to remove sediment. For large areas or BMPs, use of a small excavator may be preferable. Restore grades with filter media that meets design specifications. Test surface infiltration rate (one test for every 25 m2 of filter bed area) to confirm it is > 25 mm/h. Replace [[stone]], [[mulch]] and [[vegetation]] coverage (re-use/transplant where possible). If problem persists, add [[pretreatment]] device(s) or investigate the source(s).
*Remove sediment as described above. Core aerate (for sodded bioretention); or remove stone, sediment, mulch, and plant cover and till the exposed filter media to a depth of 20 cm; or remove and replace the uppermost 15 cm of material with filter media that meets specifications. Test surface infiltration rate (one test for every 25 m2 of filter bed area) to confirm it is > 25 mm/h. Replace stone, mulch and plants (re-use/ transplant where possible).
*Regrade damaged portion by raking and replant or restore [[mulch]]/[[stone]] cover. Animal burrows, sink holes and compacted areas should be tilled to 20 cm depth prior to re-grading. If problems persist, consider adding flow spreading device to prevent [[erosion]] or barriers to discourage foot or vehicular traffic.
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|'''[[Vegetation]]'''
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A mixture of deep rooting perennial plants, tolerant to both wet and dry conditions and salt (if receiving pavement runoff); can include grasses, flowers, shrubs and trees; roots uptake water and return it to the atmosphere; provide habitat for organisms that break down trapped pollutants and help maintain soil structure and permeability.
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*Routine maintenance is the same as a conventional perennial garden bed;
*In the first 2 months water plantings frequently (biweekly in the absence or rain) and as needed (e.g., bimonthly) over the remainder of the first growing season;
*Remove weeds and undesirable plants biannually to quarterly;
*Replace dead plantings annually to achieve 80% cover by the third growing season;
*Do not apply chemical fertilizers.
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|'''[[Overflow|Overflow Outlet]]'''
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Structures that convey overflows to another BMP or municipal storm sewer.
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*Keep free of obstructions;
*Remove trash, debris and sediment biannually to quarterly.
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|'''[[Underdrain|Sub-drain]]'''
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Optional component; [[Pipes|perforated pipe(s)]] surrounded by [[gravel]] and may be wrapped in [[Geotextile|geotextile filter fabric]]; installed below the [[filter media]] [[soil]] layer to collect and convey treated water to an adjacent drainage system; may also include a flow restrictor.
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*Include [[Bioretention: Sizing|standpipes]] or access points to provide means of flushing the [[perforated pipe]];
*Keep pipe and flow restrictor free of obstructions by flushing annually;
*Inspect flow restrictor frequently (e.g., biannually to quarterly).
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|'''[[Monitoring well]]'''
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[[Wells|Perforated standpipe]] that extends from the bottom of the BMP to above the invert of the [[Overflow|overflow outlet]]. Allows [[Digital technologies|measurement of subsurface water level]] to track drainage performance over time.
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*[[Wells|Standpipes]] should be securely capped on both ends and remain undamaged.
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==References==
==References==