Trees can be used to mitigate for ground level impervious surfaces due to their ability to intercept stormwater and allow it to evaporate, as well as dissipating the energy of runoff. They also provide shade, which helps keep surface temperatures lower, and they facilitate stormwater infiltration and groundwater recharge.
Credit is given for new trees that are planted within 30 feet of ground-level impervious surfaces. For each new deciduous tree that is planted, credit for 100 square feet will be given. 200 square feet of credit is given for new evergreen trees. Stormwater management credit equal to one-half of the existing tree canopy is also available to existing trees on the site, if the canopies are within 30 feet of ground-level impervious surfaces. Trees planted for other stormwater facility planting requirements do not qualify for tree credit. For project areas with greater than 1,000 square feet of impervious area, tree credits may only be used to mitigate for 10% of the area.
Trees selected for credit should be long-lived species, and suitable for site conditions. New deciduous trees must be at least 7 feet in height or 1 ½ caliper inches. Bare root deciduous trees are acceptable during the dormant season; trees must otherwise be balled and burlapped. New evergreen trees must be at least 5 feet tall. Existing trees used for credit must be 4 caliper inches or larger, and shown on site plans are protected. Credit for existing trees is based on one-half of the square footage of the canopy, measured within the drip line. Trees that die or are removed must be replaced within 6 months.
For more information on required tree planting for new construction and redevelopment, please refer to the Sandy Municipal Code, Title 17 - Development Code. The City of Sandy Planning Department maintains a "Street Tree List" showing all of the different species of trees that have been pre-approved for planting within city limits. Others may be substituted by approval upon written request to Public Works.
- Water trees until established and able to withstand drought
- Provide protection for tree trunk and roots to ensure survival
- Remove fallen leaves and debris from around the tree
- Remove any nuisance and prohibited vegetation (as listed in the Portland Plant list) from around the tree
- Prune dead vegetation
- Inspect tree for damage and disease, and treat as appropriate
- Replace dead trees or trees removed for any other reason
- City of Gresham Department of Environmental Services Stormwater Division. Water Quality Manual. Summer 2003.
- City of Oregon City. City of Oregon City Stormwater and Grading Design Standard; Chapter 5 of City Code.
- City of Portland Bureau of Environmental Services. Stormwater Management Manual. July 1, 1999; Revised 2004
- Clean Water Services. Design and Construction Standards for Sanitary Sewer and Surface Water Management. March 2004.
- Additional information and resources are available on the City of Portland Bureau of Environmental Services web page