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A commonly held view is that a tree's root system will be similar to it's visible crown. For many trees, this is not the case, as roots will more often spread much more widely, but to a shallower depth <ref>Crow, P. (2005). The Influence of Soils and Species on Tree Root Depth. Edinburgh. Retrieved from https://www.forestry.gov.uk/pdf/FCIN078.pdf/$FILE/FCIN078.pdf</ref>. For more detailed information on planning (site) considerations see [[Bioretention]].
A commonly held view is that a tree's root system will be similar to it's visible crown. For many trees, this is not the case, as roots will more often spread much more widely, but to a shallower depth <ref>Crow, P. (2005). The Influence of Soils and Species on Tree Root Depth. Edinburgh. Retrieved from https://www.forestry.gov.uk/pdf/FCIN078.pdf/$FILE/FCIN078.pdf</ref>. For more detailed information on planning (site) considerations see [[Bioretention]].
==Site Topography==
===Site Topography===
Contributing slopes should be between 1-5%. The bottom of the trench and distribution pipes should be graded flat to allow water to spread out.
Contributing slopes should be between 1-5%. The bottom of the trench and distribution pipes should be graded flat to allow water to spread out.
===Soil===
===Soil===
Tree trenches can be constructed over any soil type, but hydrologic soil group A and B are best for achieving water balance objectives. Facilities designed to infiltrate water should be located on portions of the site with the highest infiltration rates. Native soil infiltration rate at the proposed location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions
Tree trenches can be constructed over any soil type, but hydrologic soil group A and B are best for achieving water balance objectives. Facilities designed to infiltrate water should be located on portions of the site with the highest infiltration rates. Native soil infiltration rate at the proposed location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions.
===Drainage Area===
Typical contributing drainage areas are between 150-300 m2 per tree, with a maximum of 450 m2 per tree.
===Setback from Buildings===
Tree trenches should be set back from the building far enough to allow for the tree canopy to grow to a healthy, mature size, depending on the species selected. A minimum setback of 4 m from buildings is recommended.
===Overhead Wires===
Tree trenches should be implemented with caution under overhead wires. If overhead wires conflict with proposed tree trench locations, check the height of existing wires, and choose small form trees that will not grow tall enough to interfere with wires.
===Pollution Hot Spot Runoff===
Tree trenches receiving road or parking lot runoff are not recommended in these areas.
===Proximity to Underground Utilities===
Designers should consult local utility design guidance for the horizontal and vertical clearances required.
===Karst===
Tree trenches designed to drain primarily by infiltration are unsuitable in areas of known or implied karst topography.
==Design==
==Design==