Operation and maintenance of bioretention and other stormwater infiltration practices

Overview of typical O&M issues

Bioretention practices and other stormwater infiltration practices like rain gardens and 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 that pollinate. Bioretention and other infiltration practices may be subject to higher 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. The most frequently cited O&M concerns for infiltration practices include:

Permanent standing water or flooding due to clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Clogging can occur at the surface, or in the inlet, outlet, or underdrain pipes.
Runoff bypasses the practice due to incorrect grading and slopes, or because the inlet is blocked.
Accumulation of trash and debris within the infiltration practice.
Insufficient/inadequate vegetation or overcrowded vegetation .
Inadequate pollutant removal due to improper soil media selection.

The sections below describe best practices to prevent or minimize these common problems.

Design Phase O&M Considerations

Designers should design bioretention and infiltration practices in ways that prevent or minimize O&M issues. Examples include:

Limiting the contributing drainage area and sizing the practice in accordance to its contributing drainage area to prevent flooding issues.
Providing pre-treatment and trash racks to prevent clogging or trash accumulation.
Providing a vegetation design plan, emphasizing native plantings (see Plants for Stormwater Design) to enhance pollinator and wildlife habitat, improve infiltration and evapotranspiration, reduce urban heat island effect, provide optimized carbon sequestration, and provide climate adaptation.
Specifying the optimized soil media composition and depth to effectively trap or sequester nutrients (phosphorus in particular), and that can also support the desired vegetation.
Providing educational signage to increase public awareness.
Installing measures like low fencing to prevent damage from pedestrian foot traffic .

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:

Incorporating multiple and easy site access points
Installing observation wells
Providing recommendations of vegetation appropriate to the location

The designer should also provide a site-specific O&M plan that includes the following:

Construction inspection schedule and checklists
Post-construction routine maintenance schedule and checklists
Operating instructions for the practice (if applicable)

Example O&M plans are provided further down.

For more design information and criteria for individual infiltration practices, see the “design criteria for bioretention” or “design criteria for infiltration practices” pages.

Construction Phase O&M Considerations Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include:

Before construction begins:
1. 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.
2. Install any needed erosion and sediment controls in your construction site and prepare a storm water pollution prevention plan (SWPPP).
3. Designate a stormwater supervisor to make sure someone is responsible for erosion and sediment control.
4. Hold a pre-construction meeting with the designer and the installer to review the construction plans and the sequencing of construction.
During construction:
1. Construct any pre-treatment devices before constructing the main bioretention or infiltration system.
2. Ensure heavy equipment does not enter the footprint of the practice to avoid compaction of the infiltration medium.
3. Store any soil or gravel media downstream of the practice footprint to avoid clogging the infiltration medium. If this is not possible, store soil or gravel media in some type of covered or contained structure.
4. 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.
5. 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:
1. 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.
2. Verify that the contributing drainage area is fully stabilized with vegetation prior to removing any barriers, diversions, or erosion and sediment control measures.
3. Verify that the practice actually captures and infiltrates runoff. Conduct a full inundation test to inspect the underdrain and outflow function.
4. Verify that the practice reduces nutrient loads. Collect inflow and outflow storm water samples and have them analyzed for nutrient concentrations.
5. Use a detailed inspection checklist that includes sign-offs by qualified individuals at the completion 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.

Post-Construction Phase O&M

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.

A site-specific Operations and Maintenance Plan should be prepared by the designer prior to putting the stormwater practice into operation. This plan should provide any operating procedures related to the practices. The plan should also provide clear maintenance expectations, activities, and schedules. The O&M plan should also include an example O&M inspection checklist and an example maintenance report. Example O&M plans and inspection checklists are provided further down below.
A legally binding and enforceable maintenance agreement should be executed between the practice owner and the local review authority. Example maintenance agreements are provided further down below.
Maintenance activities should be careful not to cause compaction or damage to the vegetation. No vehicles or stockpiling should be allowed within the footprint of the practice. Foot traffic should be kept to a minimum.
Maintenance activities should apply to all parts of the bioretention or infiltration practices, including the pre-treatment devices, the main bioretention/infiltration area, the vegetation, the media, and any conveyance or discharge pipes.
BMP areas generally should not be used as dedicated snow storage areas. Click here for additional snow and salt considerations.

Overview and schedule of general maintenance activities for bioretention and infiltration practices

Common problems and how to troubleshoot them for bioretention and infiltration practices

Maintenance Costs

Maintenance costs will vary depending on the size of the practice, its contributing drainage area, type of plantings, and whether it is part of a larger GI effort. 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. Maintenance may be higher the first few years, while plants are being established.

Useful Resources

Additional Detailed O&M Information

https://docs.google.com/document/d/1ZtzA923zvt_unapGb6U8ggQLTH4U5fH9Q1ejStyao6Y/edit?usp=sharing (this captures everything that was on the original MPCA BR O&M page but that is not captured in this document)

Case Studies

None identified that specifically include maintenance considerations.

Maintenance Training Documents and Videos

Chesapeake Stormwater Network TECHNICAL BULLETIN No. 10. Bioretention Illustrated: A Visual Guide for Constructing, Inspecting, Maintaining and Verifying the Bioretention Practice
Archived webcast from Chesapeake Stormwater Network - TRUST BUT VERIFY: Urban BMP Verification in the Chesapeake Bay
Archived webcast from Chesapeake Stormwater Network - Bioretention Maintenance: In the Trenches
MSD Rain Garden and Planter Box Maintenance video
DOEE RiverSmart Rain Garden Maintenance video

O&M Resource Catalog

MPCA has compiled publicly available O&M resources related to green infrastructure. This non-exhaustive catalog is intended as a resource to practitioners.

Example O&M Plans, Checklists, Reports, and Maintenance Agreements

Operation & Maintenance Plan
- County of Napa, CA, Example Stormwater Treatment Facilities Operations and Maintenance Plan for a Commercial Project
- County of Napa, CA, Example Stormwater Treatment Facilities Operations and Maintenance Plan for a Residential Project
Construction phase inspection checklist
O&M inspection checklist
- Bioretention - operation and maintenance checklist (link to table)
- Infiltration trench basin operation maintenance checklist (link to table)
O&M example report
- MSD Example
Maintenance Agreements

Related pages

Supplemental guidance

Contents