Calculating stormwater volume and total suspended solids reduction under urban tree canopy in Wisconsin using available research
Current research has shown that urban trees can contribute significantly to stormwater volume control by retaining rainfall in the canopy of trees and increasing infiltration. The potential role of urban trees for stormwater design was evaluated at a proof-of-concept level for a planning study of part of the University of Wisconsin (UW)—Madison campus in 2016. There is currently no regulatory stormwater performance credit for trees in Wisconsin, and the effects of urban trees are not simulated by WinSLAMM or other common design models. The purpose of this project is to demonstrate a simple method of quantifying tree canopy rainfall interception and stormwater volume reduction based on data from published research, which was used to better inform a WinSLAMM model of the benefits of tree canopy cover over a parking lot. The model predicted that tree canopy coverage over a parking lot improved the bioretention performance for both runoff volume and total suspended solids (TSS) load reduction by 15% to 17%, depending on the design of the bioretention facility. Urban forest systems should be considered as one option for sustainable stormwater management, and this model demonstrates that tree canopy interception can have a substantial stormwater runoff reduction benefit.