Date of Award
Urban runoff -- Management -- Oregon -- Portland, Green roofs (Gardening) -- Effect of high precipitation on, Evapotranspiration -- Measurement
Greens roofs, also known as ecoroofs or living roofs, provide numerous ecosystem services and are becoming widely integrated into urban stormwater management systems. Despite a long and robust history of green roof projects in Portland, Oregon, there is a distinct lack of research on in situ performance. This thesis addressed this gap by investigating the hydrologic performance of five green roofs in Portland for a time period spanning November through February. Despite difficulty with the sensor calibrations, our analysis of moisture content data from these roofs revealed variation in: (1) total evapotranspiration, which serves as a proxy for total stormwater retention, and (2) storage capacity, which was defined as the difference between average maximum and minimum substrate volumetric water content measured under field conditions. Evapotranspiration was predicted by storage capacity following first order growth using non-linear regression analysis, suggesting that increasing storage capacity should correspond with increases in evapotranspiration and retention up until an inflection point of possibly 8-9mm beyond which the effect diminishes. Storage capacity was further shown to be correlated with substrate properties such as organic matter content and coefficient of curvature. Finally, retention values of 13.4% - 32.8% for Portland’s rainy season in 2015-2016 were found to be substantially lower than optimal annual values reported in other studies in Portland as well as cities around the world. This suggests that Portland’s green roofs may not perform as well as expected during months of high precipitation, which are the times when hydrologic performance is most critical. Further research should consider seasonal green roof performance in the Pacific Northwest and also revisit storage capacity as a parameter to include in future design standards.
Estrella, Melecio J., "Variation in Green Roof Storage Capacity, Associated Drivers, and Implications for Stormwater Management in Portland, Oregon" (2016). University Honors Theses. Paper 351.