First Advisor

Heejun Chang

Term of Graduation

January 2021

Date of Publication

Summer 8-29-2019

Document Type


Degree Name

Master of Science (M.S.) in Geography






Green roofs (Gardening), Storm water retention basins, Runoff, Rainwater



Physical Description

1 online resource (vi, 34 pages)


It is essential that cities adopt new approaches to stormwater management in the face of changing precipitation regime. In some locations, ecoroofs have been incorporated into city plans as a stormwater control measure, and thus their real-world performance under current conditions can assist with adequate planning. In this study rainfall retention data collected during a three year period, between 2014-2017, is analyzed for 75mm and 125mm ecoroof plots in Portland, Oregon, USA. There is no difference in annual rainfall retention performance between the shallower and deeper plots. However, the 36% mean annual retention of the ecoroof plots is a significant improvement over the conventional rooftop. The two ecoroof plots exhibit similar performance, despite their difference in substrate depth, under high, medium, or low precipitation events, as defined by local meteorological conditions. Additionally, the 125mm ecoroof plot exhibits significantly greater performance during low intensity versus high intensity storms. The range of rainfall retention for the 125mm ecoroof under a precipitation event of low intensity ranges from 32% to 100%, with an average retention of 81%, while the high intensity events see a mean retention of 26%. The general trend of ecoroof behavior indicates that rainfall retention capacity shows a negative correlation (rho = -0.37, p=0.00) with increasing precipitation intensity for the 125mm plot. Overall, these findings indicate that extensive ecoroofs of shallower depths are capable of retaining a substantial amount of stormwater. However, their performance is at its worst during the high intensity events that have the potential to overload sewer systems. Further investigation into rainfall retention capabilities of these ecoroofs is warranted to provide more information about design principles, such as vegetation type and diversity, which could also be impactful.


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