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REGIONAL, BASIN, AND LOCAL FACTORS INFLUENCING THE USE OF SYNOPTIC SURVEY DATA TO ASSESS ANTHROPOGENIC CHANGES IN STREAMBED STABILITY AND FINE SEDIMENT
Citation:
Faustini, J. M. AND P R. Kaufmann. REGIONAL, BASIN, AND LOCAL FACTORS INFLUENCING THE USE OF SYNOPTIC SURVEY DATA TO ASSESS ANTHROPOGENIC CHANGES IN STREAMBED STABILITY AND FINE SEDIMENT. Presented at American Geophysical Union fall meeting, San Francisco, CA, December 8-12, 2003.
Description:
To evaluate anthropogenic changes in stream bed stability or texture from synoptic stream surveys, we calculated relative bed stability RBS* as the ratio of the geometric mean bed surface substrate diameter to the estimated bankfull critical diameter. RBS* decreased with increasing watershed and riparian disturbance in a previous survey of Oregon and Washington coastal streams, but showed a greater apparent response in streams draining basins underlain by weak sedimentary rock than in those underlain by more resistant volcanic rocks. Systematic natural variation in RBS* (e.g., downstream trends, local variation due to channel morphology, regional differences due to geology or climate) might affect its utility as a routine assessment tool by leading to differences in the relationship between RBS* and land disturbance. To explore these issues, we sampled streams over a wide range of disturbance intensity and geologic erodibility in the northern Oregon Coast Range, eastern Oregon, and mid-Atlantic USA. In each of 17 watersheds we sampled 3 closely-spaced main stem reaches (25-50 km2 drainages in the Oregon Coast Range and mid-Atlantic USA, 250-400 km2 in eastern Oregon) and 3 reaches each in 1 to 3 smaller tributaries to assess local variability and within-basin longitudinal trends in RBS* relative to variation between watersheds with different land use intensity. Detailed aerial photo analysis of land cover and watershed and riparian disturbance in the study basins is currently in progress.
Preliminary results show significant regional differences in RBS*. The northern Oregon coastal streams had higher average RBS* than the other two regions, but also a greater range and lower values. These streams also showed the strongest (inverse) relationship between RBS* and anthropogenic disturbance. Contrary to expectations, RBS* generally increased with watershed area in this part of Coast Range, although the downstream pattern of RBS* values within individual watersheds was quite variable.