The relation between vegetation and storm-water runoff in Portland, Oregon
Geoffrey Donovan, David Butry
Past research has examined the effect of urban trees on storm-water runoff using hydrological models or small-scale experiments. However, there has been no statistical analysis of the influence of trees on runoff in an intact urban watershed. We address this gap in the literature by quantifying the effect of trees, and other vegetation, on storm-water runoff for a summer (June 15-16, 2010) and a winter (December 18-19, 2010) storm in Portland, Oregon. We found that additional tree canopy cover was associated with lower runoff in the summer storm but not the winter storm. In addition, we found that additional ground cover (grass and shrubs) was associated with lower peak flow in the summer but not the winter storm. Results suggest that trees and other vegetation can be effective at moderating storm-water runoff. However, vegetation is not as effective in the winter, which is consistent with past modeling and experimental studies.