As a part of our green infrastructure in the urban environment, trees provide significant and measurable benefits. One of these benefits is the interception of rainwater in our cities and towns.
Urban stormwater runoff is a major source of pollution entering our waterways. As municipalities struggle with managing stormwater, healthy urban trees and green infrastructure are part of the solution.
Federal Clean Water Act regulations aimed at addressing this challenge require municipalities to obtain a permit for managing stormwater. Each city’s program must identify the Best Management Practices (BMPs) it will implement to reduce its pollutant discharge. Many cities have the challenge of legacy structures with combined sewer outflow systems allowing excess runoff to mix with raw sewage during rainfall events. Rainfall interception by trees can reduce the magnitude of this problem. According to the U.S. Forest Service, one hundred mature tree crowns intercept roughly 100,000 gallons of rainfall per year.
Trees provide the opportunity to control runoff at the source, which is especially important in our urban settings, which are often characterized by multiple impervious surfaces in close proximity to valuable waterways.
Healthy urban trees can play a role in three primary ways:
- Leaf and branch surfaces intercept and store rainfall, reducing runoff volumes and delaying the onset of peak flows.
- Root growth and decomposition increase the capacity and rate of soil infiltration by rainfall and reduce overland flow.
- Tree canopies reduce soil erosion and surface transport by diminishing the impact of raindrops on barren surfaces.
We often work with municipalities to create proactive planting programs with a focus on addressing the stormwater challenge. Ongoing management and maintenance of tree assets is equally important because healthy, vigorous trees can play a larger role in intercepting excess runoff and reducing the impact on stormwater management systems.