WASTING AWAY IN WESTERN OREGON: GEOLOGIC AND PHYSIOGRAPHIC CONTROLS ON BED-MATERIAL YIELD, TRANSPORT, AND CHANNEL MORPHOLOGY FOR ALLUVIAL AND BEDROCK RIVERS

We relate differences in channel morphology of Western Oregon rivers to bed-material transport rates as derived from a coupled regional analysis of empirical sediment yield measurements and physical experiments of clast attrition during transport. This sediment supply analysis shows that overall bed-material transport rates are chiefly controlled by (1) lithology and basin slope, which are the key factors for bed-material supply into the stream network, and (2) lithologic control of bed-material attrition from in-transport abrasion and disintegration. Bed-material comminution strongly affects bed-material transport in the study area, reducing transport rates by 50-90% along the length of the larger rivers in the study area. Comparing the bed-material transport estimates with analyses of channel and bed-material characteristics shows that alluvial gravel-bed channels have systematic and bounding relations between bed-material transport rate and attributes such as bar area and local transport capacity. By contrast, few such relations are evident for non-alluvial rivers with bedrock or mixed-bed substrates, which are apparently more influenced by local controls on channel geometry and sediment supply. At the scale of western Oregon, the physiographic and lithologic controls on the balance between bed-material supply and transport capacity exert far-reaching influence on the distribution of alluvial and non-alluvial channels and their consequently distinctive morphologies and behaviors—differences germane for understanding river response to tectonics and environmental perturbations, as well as for implementing effective restoration and monitoring strategies.