Estimating the Benefits of Trees in Storm Water Management

Urbanization has drastically changed the hydrologic cycle and has negatively impacted water quality. Best Management Practices (BMP) are designed to reduce the effects of pollutants in water and reduce the risk of flooding by controlling the storm water entering the river system. Current green storm water practices focus on herbaceous vegetation. Trees are superior at storm water management since they have an increased ability to capture and store rainfall in their canopy, facilitate evapotranspiration, and improve storm water quality by taking up and transforming pollutants through extensive root systems. The overarching objective of this work was to quantify the performance benefits of incorporating trees in bioretention systems. Two storm water tools were used in this project: (i) EPA National Storm Water Calculator and (ii) Green Values National Storm Water Calculator. The EPA calculator represented annual rainfall, annual runoff, days per year with runoff, rainfall retained. The Green Values Calculator represented volume capture, coefficient and runoff, land use, cost benefits. Both the tools demonstrated that trees in bioretention systems can capture more runoff volume than having only bioretention systems without trees. iv The literature suggests that evapotranspiration and interception together could address between 0.1% and 11% of annual rainfall in Northwest Ohio. However, neither tool had the capacity to quantify interception and evapotranspiration. More research is needed for effective usage of trees in storm water management. Storm water management decision making tools should be expanded by providing tree details like tree canopy size, leaf size, trunk diameter to incorporate the benefits associated with trees.