Design Specifications and Schematics for Typical Tree-Based Stormwater Installations
Multiple Practices: Delta Institute has developed a plan book which includes sketch designs, downloadable CAD files, pictures and specifications for most common green infrastructure practices, including tree planting.
Green Streets: Montgomery County, Maryland has implemented comprehensive green infrastructure programs and policies. This handbook details the type of residential site designs promoted by the county.
Tree Pits: The most common tree-planting technique along roads and rights-of-way, tree pits often offer too little room for root growth, inadequate and/or highly-compacted soil, and reduced water flow to roots. When surrounded by impervious pavement, all these issues are exacerbated. One common solution deploys permeable pavement over soil cells which supply adequate room for soil or engineered soil compounds. And, as always, size matters.
Stormwater Planter: Often elevated above grade, large planters can recover and filter significant amounts of rainfall. When stacked up a building’s side, it’s often possible to direct roof runoff into a cascaded series of planters.
Tree Trenches: Trenches, running parallel to or perpendicular to rights-of-way, allow series of trees to be planted and interspersed with other features, including public art. When adjacent to roadways, curb cuts can divert significant amounts of runoff — reducing flow and increasing pollutant reduction. Design, soil volumes, and surrounding pavement conditions will affect how well the system works.
Parking Lot Enhancements: Adding trees to strategic spots in a parking lot, along with careful direction of flow, can absorb significant levels of precipitation as well as reduce heat island effects by shading asphalt. Permeable pavement maximizes impact. Effective systems require adequate rooting space and appropriate soil type and volume. Most successful projects tend to favor engineered soil. Take a look at this experimental project by Davey.
Rain Gardens with Trees and Shrubs: Rain gardens without trees don’t perform nearly as well as those that include them. Recent research at the Morton Arboretum showed that tree transpiration accounted for 46-72% of the water inputs into parking lot bioswales during summer months, confirming the significant potential of trees to maximize the performance of BMPs.
Bioswales: Bioswales are modestly effective for redirecting sheet flow but they have little impact on flow reduction.