City of Portland Bureau of Environmental Service
Date of Award
Master of Environmental Management (MEM)
Environmental Science and Management
The riparian areas adjacent to streams are sensitive and important environments that have a great deal of influence on the overall health of the streams they border. In cities, riparian areas are routinely impacted and degraded by property developments, urban infrastructure, and other alterations to the natural environment. In this study, I worked with the City of Portland to determine how a wide range of landscape features occurring in riparian areas affect the overall health of streams at multiple scales. Data were collected from buffer areas of widths ranging from 15 ft to 500 ft that were digitally generated around 1-km reaches upstream of 59 long term monitoring stations. In these buffer areas, I aggregated information on 20 variables relating to land use, impervious surfaces, transportation, vegetation, and hydrologic control structures. Using a random forest variable selection algorithm and regression analysis tools, I created models that described the health of the urban streams (represented by macroinvertebrate IBI) as a function of the urban landscape variables in the multiple riparian buffer areas surrounding the 59 study reaches. In the process of model refinement and analysis, I determined that the 50 ft and 500 ft buffer models were sufficient at describing the spatial variability in the datasets. I found that the length of piped stream in both of the buffer areas was negatively correlated with stream health but that it had an especially strong influence in the 50 ft buffer areas. In these same buffer areas, the mean canopy height was positively correlated with stream health, but its effect was much more pronounced in 50 ft buffer areas. Additionally, my analysis showed that impervious surfaces in riparian areas within 50 ft of streams had a strong, negative impact on the health of the 59 stream reaches studied. These findings suggest that health of streams in the study area could be improved by planting more trees in riparian zones, daylighting piped waterways, and by removing impervious surfaces from areas within 50 ft of streams.
© 2020 Dylan Esmonde
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Esmonde, Dylan, "A Multi-Scale Assessment of the Relationship Between the Riparian Landscape and the Health of Streams in Portland, Oregon" (2020). Environmental Science and Management Professional Master's Project Reports. 75.