A street tree trench is a linear stormwater management feature, typically placed along sidewalks, that combines tree pits with an underground stormwater management system. A tree trench is a type of bioretention system, but does not currently appear in the NJ BMP manual.
Although street tree trenches may appear like conventional tree pits, they are designed with piped connections and underground stormwater storage systems that capture runoff, provide additional storage and allow slow release of stormwater. Street tree trenches can be used effectively in tight spaces such as along footways and parking lots due to their small above ground footprints.
Most tree trenches incorporate infiltration through a soil layer. Stormwater runoff is diverted to the trench by a curb cut, storm drain or permeable concrete sidewalk pavers. The soils typically provide treatment for the runoff before it enters a storage area, where the water is available to the tree roots for uptake. Tree trenches can position trees below grade, as pictured here, or at grade, like the rendering below.