There is great interest among urban designers regarding the use of tree pits to harvest and make use of stormwater.
The basic concepts are sound, and when designed intelligently, the system can deliver a true Win-Win situation.
Stormwater discharge is delayed and/or reduced, and trees get the benefit of rainwater delivered to the root system.
Arborgreen Landscape Products is currently involved with several projects, where enterprising clients are incorporating these W.S.U.D. (Water Sensitive Urban Design) philosophies by various methods as shown below.
Permeable pavements over Rootcell zone
By creating grades, surface runoff can be directed to areas of permeable pavement directly over the extended Rootcell zone for infiltration.
There are some fundamental engineering principles to be observed, including adequate provision for drainage, and protection of adjacent subgrades.
Surface drainage grating systems
Surface water can also be captured through drainage grades, and directed to the root zone using perforated piping within or above the Rootcell matrix.
Heel Safe grates can be positioned to take advantage of grades in foot paths or malls and plazas. Another alternative is to integrate drainage pits into the kerb and gutter; however, designers often hesitate to use this method because of the presence of pollutants on road surfaces.
Roof water discharge method
Arborgreen Landscape Products also has gained experience with the design of tree-pit systems that harvest roof water from nearby buildings.
This water is typically cleaner than road runoff, and pipes can deliver this precious resource to Rootcell zones below pavements.
Designs must take into consideration many factors, including inlet level, drainage levels, tree-pit volume, surrounding services, depth of road base, surface load etc.
While this application is relatively young, it is growing rapidly, due to the desire for trees in the built environments, and the increasing value of water.