Improved method for quantifying how trees limit runoff into local waters

For Immediate Release

Contact: Kristen Peterson, The Hatcher Group, 410-990-0284, kristen@thehatchergroup.com

ELLICOTT CITY, Md. (Jan. 17, 2018) – The Center for Watershed Protection announced today it has developed a ground-breaking new method to account for the capacity of trees planted in urban areas to reduce runoff pollution.  The Center has used that model to develop two tree planting credits — a pollutant load reduction credit and a stormwater performance-based credit.

“Urban trees and forests improve water quality primarily by decreasing the amount of stormwater runoff and pollutants that reach our local waters,” said Karen Cappiella, director of research for the Center. “The use of trees as a stormwater best management practice (BMP) has been limited by the uncertainty of how to ‘credit’ trees for runoff and pollutant reduction to meet water quality requirements. In 2014, we began a study to address this gap by developing a science-based crediting system for urban tree planting and today, we are excited to announce two new national credits.”

Realizing that only a limited number of studies directly address the water quality benefits of urban trees, the Center’s project team developed a “water balance model” to provide an improved method for quantifying the stormwater benefits of urban tree canopy. The model estimates the mean annual runoff for a single tree at maturity planted over grass or impervious cover, compared to runoff from those same sites without trees.

The Center used the results of this water balance model to develop the two national credits. These credits can be adopted by regulatory agencies wishing to offer science-based credits that encourage greater use of tree planting. The pollutant load reduction credit applies to Total Maximum Daily Load (TMDL) requirements, while the stormwater performance-based credit applies to stormwater management requirements for new and redevelopment.

This project was funded through a grant from the U.S. Forest Service’s National Urban and Community Forestry Advisory Council.

For more information, visit https://www.cwp.org/making-urban-trees-count/