Rosgen stream types as a tool for predicting bedload and suspended sediment export in low-order Lake Superior watersheds

D.L. Taylor, N.E. Detenbeck, C.M. Elonen, T.M. Jicha, and L.E. Anderson. U.S. Environmental Protection Agency, Mid-Continent Ecology Division, Duluth, MN 55804

Bedload samples were collected from 48 second and third order Lake Superior tributaries during snowmelt in 1998 and 1999. Suspended sediment samples were collected over a three-year period during baseflow, rain events, and snowmelt. This work was part of a comparative watershed study evaluating the effects of hydrogeomorphic region, and instream, riparian, and watershed features on stream water quality, habitat, and biota. To explain differences in sediment export Rosgen's hierarchical stream type classification system was introduced as an integrator of stream geomorphological characteristics such as bedrock geology, width to depth ratio, entrenchment, and channel slope. Rosgen stream types and stream power accounted for 71 per cent of the variation in bedload mass exported. Watershed area and observable bank erosion were also significant predictors of bedload in stream types with flatter gradients, low bankful width to depth ratios, wide floodplains, and smaller median stream bottom particle sizes. Suspended sediment results suggest that suspended sediment export increased with greater proportions of fine sediments in the streambeds, and with increased discharge, bank erosion, and watershed land uses such as agriculture and road/stream intersection density. Overall, bedload appears to be power-limited, while suspended sediment is more supply-limited. Abstract does not necessarily reflect EPA policy.