Structural Soil

Davis, CA (June 20, 2006)- The USDA Forest Service, Pacific Southwest Research Station’s Center for Urban Forest Research, is currently working on a project to quantify the benefits tree crowns have on runoff reduction. They also seek to build on that by studying how the use of structural soils can enhance the role that trees play in onsite storm water management. Developing green infrastructure technologies that protect water quality by reducing contaminants in urban runoff is gaining interest among regulators, developers, and consultants.


They are developing and evaluating a storm water management system that directs water to a reservoir of structural soil under pavement. Structural soils are engineered to support vigorous tree growth and reduce root and hardscape conflicts, as well as be load-bearing. Trees are an integral part of the system by first intercepting rainfall to reduce runoff rates, and then removing water from the reservoir with their root systems. Using these engineered soils as runoff treatment and storage sites is a new idea.
Key to the system is its ability to be used in ordinary situations with no additional land area required. All developers and municipalities should be delighted to have a beautiful, compact, shaded parking lot with plenty of parking spaces but no runoff—or a shady broad avenue with arching trees and little or no runoff. These ideals seem impossibly distant from most development today, which provides little space for trees. By integrating trees into the engineered storm water management system, this research will yield findings for how to increase space for trees, minimize conflicts, and make efficient use of valuable land.
Success will mean increased benefits from urban trees for those responsible for managing storm water, trees, streets, and utilities. Consequently, findings will be targeted for an array of constituencies, especially municipalities, engineers, landscape architects, planners and public works professionals. By demonstrating innovative ways to integrate trees into the infrastructure of cities, this research facilitates the development of greener cities.
Related Resources:
Green Streets Structural Soils
Center for Urban Forest Research