Graduate Thesis Or Dissertation
 

Debris flows and flood disturbance in small, mountain watersheds

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gf06g706q

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  • This study examined debris flows occurring in a 125 km² study area in the Blue River watershed in the western Cascade Mountains of Oregon over a 50-year period. Debris flow occurrence was found to be concentrated in a distinct zone of high activity occupying approximately half of the study area, characterized by weak rock, low elevation, and steep slopes. Three quarters of the total of 91 inventoried debris flows occurred during two seasons, in the winters of 1964-1965 and 1995-1996. Clearcutting appeared to increase debris flow initiation by 3-7 times relative to forest areas. Increases in initiation frequency from roads ranged from 11-50 times more frequent than forested areas. While land use activity was associated with an increase in debris flow frequency, it was not associated with changes in the elevation, slope steepness, and geologic site conditions of initiation. Stream network structure was a significant factor influencing the spatial distribution of debris flows and their disturbance of stream and riparian systems. Patterns of disturbance that were partially controlled by stream network structure were speculated to affect aquatic and riparian biota, perhaps influencing rates of recolonization following severe disturbance events.
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