Portland State University. Department of Geography
Date of Award
Master of Science (M.S.) in Geography
River sediments -- Fanno Creek (Multnomah County and Washington County Or.) -- Effect of beavers on, Urban hydrology -- Oregon -- Beaverton
Beaver activities can cause drastic changes to hydrogeomorphic processes by impounding waterways through the construction of dams, trapping sediments and reducing the downstream sediment load. The presence of beaver is increasing in urban areas. Urban streams exhibit hydrogeomorphic processes distinct from natural systems because of changes in land cover that alter hydrology. This case study was developed as part of an effort to understand the sedimentation patterns of a beaver impounded urban stream in Beaverton, Oregon. Twelve sediment samples were collected and processed for organic matter content and particle size and sediment depths were calculated using GIS software from data collected through bathymetric and depth-to-resistance surveys. Spatial variability of and correlations between sample composition and depth were examined through visual analysis and descriptive statistics for in-channel/floodplain and upstream/downstream comparisons. Sediment depth and organic matter were found to be highest immediately upstream of the dams and in the floodplain pond, which exhibited decreasing depth with distance downstream. Floodplain organic matter and particle sizes did not display distinct spatial patterns. Moderate correlations were identified between composition and sediment depth for both floodplain and in-channel samples. Opposite correlations were identified between organic matter and particle size for floodplain versus in-channel samples. These results provide an understanding of baseline conditions for the study area under beaver impoundment. Future research should work towards collecting more robust datasets at a variety of sites and spatial scales to understand the full spectrum of the influence of beaver in urban basins.
Santora, Alexandra Joan, "Stream Sedimentation Patterns in an Urban Beaver System: Fanno Creek, Oregon" (2017). Geography Masters Research Papers. 21.