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[[File:Rake technique for bioretention.png|300px|thumb|alt=photo showing demonstration of the rake technique for bioretention|<font size=3>Demonstration of the rake technique with a bucket with teeth (top) and scoop technique using a bucket with a smooth blade (right). During the final pass of excavation, the rake technique should be used to break up the soil and promote exfiltration. Source: Dr. Robert Brown, ORISE Research Fellow, US EPA, Edison, NJ.</font size>]] | [[File:Rake technique for bioretention.png|300px|thumb|alt=photo showing demonstration of the rake technique for bioretention|<font size=3>Demonstration of the rake technique with a bucket with teeth (top) and scoop technique using a bucket with a smooth blade (right). During the final pass of excavation, the rake technique should be used to break up the soil and promote exfiltration. Source: Dr. Robert Brown, ORISE Research Fellow, US EPA, Edison, NJ.</font size>]] | ||
− | Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include | + | Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include the following. |
− | #Before construction begins | + | #'''Before construction begins''' |
##Ensure that the contributing drainage area is fully stabilized with vegetation prior to the beginning of construction. Also make sure that impervious areas in the contributing drainage area are clean. If this is not possible, use barriers or diversions to direct stormwater flows from the contributing drainage area away from the practice. See [[Sediment control practices]] for more information. | ##Ensure that the contributing drainage area is fully stabilized with vegetation prior to the beginning of construction. Also make sure that impervious areas in the contributing drainage area are clean. If this is not possible, use barriers or diversions to direct stormwater flows from the contributing drainage area away from the practice. See [[Sediment control practices]] for more information. | ||
##Install any needed erosion and sediment controls in your construction site and prepare a storm water pollution prevention plan (SWPPP). | ##Install any needed erosion and sediment controls in your construction site and prepare a storm water pollution prevention plan (SWPPP). | ||
##Designate a stormwater supervisor to make sure someone is responsible for erosion and sediment control. | ##Designate a stormwater supervisor to make sure someone is responsible for erosion and sediment control. | ||
##Hold a pre-construction meeting with the designer and the installer to review the construction plans and the sequencing of construction. | ##Hold a pre-construction meeting with the designer and the installer to review the construction plans and the sequencing of construction. | ||
− | #During construction | + | #'''During construction''' |
##Construct any pre-treatment devices before constructing the main bioretention or infiltration system. | ##Construct any pre-treatment devices before constructing the main bioretention or infiltration system. | ||
##Ensure heavy equipment does not enter the footprint of the practice to avoid compaction of the infiltration medium. | ##Ensure heavy equipment does not enter the footprint of the practice to avoid compaction of the infiltration medium. | ||
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##Inspect the practice during construction to ensure that the infiltration practice is built in accordance with the approved design and standards and specifications. This includes verification of the media composition and depths. Use a detailed inspection checklists that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. Example construction phase inspection checklists are provided further down below. | ##Inspect the practice during construction to ensure that the infiltration practice is built in accordance with the approved design and standards and specifications. This includes verification of the media composition and depths. Use a detailed inspection checklists that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. Example construction phase inspection checklists are provided further down below. | ||
##Ensure that the plant and vegetation mix conforms to the vegetation design plan, particularly if the vegetation was selected to provide ecological function (such as pollinator habitat). | ##Ensure that the plant and vegetation mix conforms to the vegetation design plan, particularly if the vegetation was selected to provide ecological function (such as pollinator habitat). | ||
− | #After construction | + | #'''After construction''' |
##Verify that the infiltration practice was built in accordance with the approved design and standards and specifications, including the pre-treatment devices as well as the main infiltration practice. | ##Verify that the infiltration practice was built in accordance with the approved design and standards and specifications, including the pre-treatment devices as well as the main infiltration practice. | ||
##Verify that the contributing drainage area is fully stabilized with vegetation prior to removing any barriers, diversions, or erosion and sediment control measures. | ##Verify that the contributing drainage area is fully stabilized with vegetation prior to removing any barriers, diversions, or erosion and sediment control measures. |
This page provides guidance for operation and maintenance (O&M) of bioretention and other stormwater infiltration practices, including above- and below-ground infiltration practices. This includes biofiltration, bioinfiltration, infiltration trenches, and infiltration basins.
Supplemental information can be found on the page called Operation and maintenance of bioretention and other stormwater infiltration practices - supplemental information. Supplemental information includes the following.
Bioretention practices and other stormwater infiltration practices (e.g. rain gardens, infiltration trenches) are vegetated landscape practices that capture, filter, and infiltrate stormwater runoff. In addition, these practices can provide ecosystem services such as nutrient cycling and storage, carbon sequestration, reduction in heat island effect, climate adaptation, and habitat for bees, butterflies, and other insects and small animals, including pollinators. Bioretention and other infiltration practices may be subject to high public visibility, greater trash loads, pedestrian traffic, vandalism, and vehicular loads, particularly in urban areas.
These practices require dedicated and regular maintenance to ensure proper and long-lasting operation and ecosystem benefits. Estimated bioretention lifespans range from 10 to 40 years (Drescher, 2012). The most frequently cited O&M concerns for infiltration practices include the following.
The sections below describe best practices to prevent or minimize these common problems.
Designers should design bioretention and infiltration practices in ways that prevent or minimize O&M issues. Examples include the following.
Designers should consult and include any local requirements regarding green infrastructure. O&M considerations often depend on whether the practice is located on public land, private land, or in the public right of way. For example, plantings in the public right of way that conflict with any traffic safety considerations could require increased O&M, such as pruning or complete removal.
Designers should also recognize the need to perform frequent landscaping maintenance to remove trash, check for clogging, and maintain vigorous and healthy vegetation. Designers can incorporate design solutions to facilitate maintenance activities. Examples include
The designer should also provide a site-specific O&M plan that includes
Example O&M plans are provided below.
For more design information and criteria for individual infiltration practices, see the Design criteria for bioretention or Design criteria for infiltration practices pages.
Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include the following.
For information on construction specifications, see the links below.
Effective short and long-term operation of bioretention and infiltration practices requires dedicated and routine maintenance. Proper maintenance will not only increase the expected lifespan of the facility but will improve ecological function, aesthetics, and property value. Important post-construction considerations are provided below.
Overview and schedule of general maintenance activities for bioretention and infiltration practices.
Link to this table
First Year of Operation | ||||
---|---|---|---|---|
Activity | Frequency | Time period | Level of effort | O&M benefita |
Check that there is no ponding in the pretreatment device and/or in the main treatment area. | At least twice after storm events > 0.5 inches | Within the first 6 months | < 1 hour | 1 |
Check for evidence of clogging in the pretreatment device and/or in the main treatment area. | At least twice after storm events > 0.5 inches | Within the first 6 months | < 1 hour | 1 |
Check for evidence of clogging or failing of the inlet, outlet, and bypass pipes. | At least twice after storm events > 0.5 inches | Within the first 6 months | < 1 hour | 1 |
Remove any stormwater diversion or barriers once seedlings are established. | Once | When plants are sufficiently established | 1-2 hours | 1,2,3,4,5 |
Supplemental watering during drier periods, particularly if keeping stormwater offline until plant seedlings are established. | 1/week initially | During first 2 months | 1-2 hours | 2,3,4,5,6 |
As needed | First growing season | 1-2 hours | 2,3,4,5,6 | |
Remove and replace dead plants | As needed | First growing season | 2-4 hours | 2,3,4,5,6 |
Spot reseeding of bare patches and eroding areas | As needed | First growing season | 2-4 hours | 1,2,3,4,5,6 |
After First Year of Operation | ||||
Activity | Frequency | Time period | Level of effort | O&M benefita |
Check that there is no ponding in the pretreatment device and/or in the main treatment area | Semi-annually | 48 hours after a rain event and when ground is not frozen. Note that deep sumps can have ponding | 1-2 | 1 |
Check for evidence of clogging in the pretreatment device, the inlets/outlets/bypass pipes, and in the main treatment area. Look for evidence of short circuiting or low spots that cause flow path issues. | Semi-annually | n spring and fall | 1-2 | 1 |
Supplemental watering | As needed during extended dry periods | During dry periods | 1-2 hours | 2,3,4,5,6 |
Remove trash and debris from the pretreatment device and/or in the main treatment area. | Monthly during rainy season | All year long. Cleaning may need to be done more frequently during the summer storm season and less during the drier winter season | 1-2 hours | 1,5 |
Inspect for and remove excess sediment in the pretreatment device and/or in the main treatment area. | Monthly | All year long | 4 hours if removal is needed | 1 |
Check and repair eroded areas | Annually | In fall or spring when vegetation has died down | 4 hours if repair is needed | 1,2,3,4,5 |
Mow grass filter strips and bioretention turf cover | Seasonally, but outside of the main pollinator or wildlife nesting season | During growing season | 1-2 hours | 2,3,4,5 |
Weed and remove invasive plants | Twice during growing season | During growing season | 1-2 hours | 2,3,4,5 |
Inspect plant composition and health and replace as needed | Annually | In fall or spring | 4 hours if plant replacement is needed | 2,3,4,5,6 |
Prune trees and shrubs | Annually | In fall or spring | 2-4 hours | 2,3,4,5 |
Inspect for and repair broken inlets or pipes | As needed | Any time | 2 hours, more if repairs are needed | 1 |
Renew mulchb | As needed | In fall or spring | 1-2 hours | 4,5 |
Spring cleanup (cut back and remove last year’s material) | Annually | In spring | 2-4 hours | 2,3,4,5 |
Fall cleanup (removed excessive leaf litter, particularly in areas with lots of trees) | Annually | In fall | 2-4 hours | 2,3,4,5 |
After 5+ Years of Operation (non-routine maintenance) | ||||
Activity | Frequency | Time period | Level of effort | O&M benefita |
After long term operation of the practice, some occasional and infrequent maintenance activities might be required, such as bigger repairs, soil regeneration, or redesign of key elements of the practice. | As neede | As needed | Could be significant depending on the activity | 1,2,3,4,5,6 |
aKey to Maintenance Benefits:
|
Common problems and how to troubleshoot them for bioretention and infiltration practices
Link to this table
Symptom | Possible causes | Solution |
---|---|---|
Standing water within the infiltration area for more than 48 hours | The surface of the ponding area may become clogged with fine sediment over time. This might be because the pretreatment is no longer working, or there are excessive sediment loads due to erosion or high sediment loads from the contributing area. |
|
Rainwater does not appear to flow to the infiltration area | Leaves, sediment, trash, or plant debris may be blocking the flow path. | Remove these materials on a regular basis |
Vegetation is not able to establish | Plant selection is inappropriate for the site | Consult with a landscaper or horticulturist. Check that plants are suited to the local conditions. Make sure BMP is protected from snow storage or salt application. |
Erosion or scouring around the inlet | Flow is obstructed by debris or improper grading | Correct for drainage and flow path issues to make sure flows are evenly distributed. Make sure the flow paths are unobstructed. |
Maintenance costs will vary on a number of factors, including but not limited to:
Preventative maintenance is key to minimizing major costs associated with repairs. A general rule of thumb to estimate maintenance costs is 3%-6% of the installation costs, but can run higher. Maintenance may be higher the first few years, while plants are being established. Maintenance costs should account for the number of hours of labor, the cost for different types of labor expertise required, and any equipment needed to successfully complete the maintenance activities.
A study published in 2017 by ASCE shows the median annual maintenance cost of bioretention devices was estimated at $0.687/sq ft with lower and higher costs of $0.13/sq ft and $2.30/sq ft, respectively. The survey also provides average annual reported maintenance costs, which range from $250 to $3880 with a median of $850 (Clary, 2017).
More detailed information regarding specific maintenance activities are provided here. Topics discussed include:
MPCA has compiled publicly available O&M resources related to green infrastructure. This non-exhaustive catalog is intended as a resource to practitioners.
Supplemental guidance