Resources for maintaining your stormwater management facility

Required maintenance after an inspection

If you received an inspection letter from Environmental Services, the required corrective actions and routine maintenance activities outlined in the letter are crucial for ensuring that your facility adheres to your operations and maintenance (O&M) plan.

The resources and information on this page may help guide you through the necessary actions and steps outlined in the letter. For specific questions related to an inspection at your location, contact the City Inspector listed on the inspection letter.

For general questions or inquiries about inspections or maintenance of stormwater management facilities, please contact the Stormwater Facility Inspection Team at StormwaterFIT@portlandoregon.gov or 503-823-5313.

Required maintenance thresholds

The following list describes typical required maintenance thresholds for vegetated stormwater management facilities. Structural or mechanical facilities may have manufacturer-specific guidance to follow. If you have questions about maintenance thresholds for structural or mechanical facilities, please contact your inspector or the Stormwater Facility Inspection Team.

• Beneficial vegetation covers at least 90% of the facility area
• Replace dead or stressed vegetation as needed
• Invasive, prohibited, and nuisance vegetation is routinely removed
• Inlets and overflows are maintained to no more than 50% blockages
• Sediment, debris, and trash are removed when more than 4 inches deep or blocks the flow of stormwater into or out of the facility
• Fill in eroded areas and flow-path rills when greater than 2 inches
• Loosen or amend compacted soils when standing water does not drain within 48 hours of the last significant rainfall
• Jet cleanouts and underdrains if water does not drain within 48 hours of the last significant rainfall

Standard operations and maintenance plans

The Stormwater Management Manual contains standard O&M plans. At a minimum, the standard O&M plans must be followed for these facility types:

• Ecoroofs
• Permeable Pavement
• Rain Gardens
• Basins
• Planters
• Filter Strips
• Drywells and Soakage Trenches
• Sand Filters
• Pollution & Flow-Control Manholes

View the Stormwater Management Manual

Approved plants

Select the right plants for your stormwater management facility. The plants in the Stormwater Management Manual Plant List are approved species for stormwater management facilities. This is not a complete list but rather a list of vetted plants that perform well in stormwater facilities. If you do not see plants on this list that you are interested in, please contact the Stormwater Facility Inspection Program for additional guidance.

Please note that invasive, prohibited, and nuisance vegetation, as defined in the Portland Plant List, are not permitted in vegetated stormwater facilities.

Plant maintenance and guidance

Seasonally appropriate maintenance is essential to ensure plant health and prevent conditions that reduce functionality, collect debris, and impede water flow. This section provides tips and best practices for maintaining your facility's vegetation.

All vegetated stormwater management facilities (planters, basins, rain gardens, ecoroofs, swales) are required to maintain 90% vegetated coverage across the facility. Dead or stressed vegetation should be replaced in early fall or spring to take advantage of cooler temperatures and wet weather to facilitate plant establishment. Sometimes, pruning may be necessary to remove dead growth, seed heads, damaged vegetation, blocked inlets or overflows, or for safety and visual clearance. When pruning, take extra care not to over-prune, especially during the rainy season.

Pruning should be minimal to promote the natural form and maintain structure throughout the facility. This helps to improve stormwater filtration, minimize bare areas where weeds can take over, and help prevent erosion across the facility. Use the following guidance when pruning vegetation within a stormwater facility:

• Rushes, sedges, and ferns should not be pruned but raked through to remove dead plant material
• When cutting back grasses, maintain a minimum height of 6 inches
• Trees and shrubs should only be pruned for dead or diseased branches or crossed branching
• Maintain structure and canopy of trees and shrubs
• If needed, ferns and sedges may be cut back in the early spring

Utilizing this guidance can help reduce maintenance and plant replacement costs and ensure optimal stormwater management and treatment performance.

Shrub pruning and maintenance

View full size image of A graphic that shows how to and how not to prune. The existing condition shows a shrub with many branches. The what not to do shows a heavily sheared shrub. The what to do shows a shrub that has selectively pruned back branches.

Rushes and sedges maintenance

View full size image of A graphic that shows how to and how not to trim rushes and sedges. The existing condition shows a sedge with many leaves. The what not to do shows a heavily sheared sedge. The what to do shows the intact sedge with dead leaves removed.

Weeds and invasives maintenance

View full size image of A graphic that shows how to and how not to remove invasives and weeds. The existing condition shows an invasive plant. The what not to do shows spraying the plant with herbicide. The what to do shows hand pulling the invasive.

Mulch maintenance

View full size image of A graphic that shows how to and how not to remove invasives and weeds. The existing condition shows a pile of mulch. The what not to do shows using bark chips as mulch. The what to do shows coarse yard debris and compost as the mulch.

View full size image of A side-by-side image of a stormwater planter. On the left is what not to do, with grass and other weeds taking over an empty stormwater planter. On the right is what to do, with multiple healthy shrubs occupying the same stormwater planter.

View full size image of A side-by-side image of a stormwater planter. On the left is what not to do, with plants pruned back heavily and a lot of exposed ground. On the right is what to do, with the same plants covering the entire planter and no exposed ground.

View full size image of A side-by-side image of a stormwater planter inlet. On the left is what not to do, with weeds and sediment blocking the inlet. On the right is what to do, with a clear inlet and approved plants.

Use of herbicides

Use of herbicides is strongly discouraged within vegetated stormwater management facilities. 

Herbicides are prohibited on ecoroofs.

If herbicides are used for weeds or invasive species management, utilize an ODA-licensed applicator and products approved for the site conditions. Always follow the herbicide product label for approved uses.

Vendors and contractors

The businesses listed below are vendors and contractors who specialize in stormwater management facility maintenance. The City of Portland does NOT hereby recommend, certify, or guarantee the work of independent contractors.

Vegetated Facility Contractors

Structural and Mechanical Facility Contractors

Related City Code

Property owners with stormwater planters are required to develop and adhere to an Operations and Maintenance (O&M) plan per City Code Section 17.38.041. Owners of development or redevelopment sites must comply with the standards of the Stormwater Management Manual or the Source Control Manual, submit an O&M plan, and complete an O&M form for the required stormwater management facilities.