INTERACTION OF POST-GLACIAL LANDFORMS AND HISTORICAL HUMAN ALTERATIONS ON BEHAVIOR, RESPONSE, AND EVOLUTION OF FLUVIAL SYSTEMS IN THE GREAT LAKES AND UPPER MISSISSIPPI RIVER BASINS (Invited Presentation)

Historical evolution of fluvial systems in the Great Lakes and Upper Mississippi River Basins reflects the interaction of spatially variable post-glacial landforms with historical human alterations in land cover and drainage networks across landscapes generally less than 30,000 to 10,000 years old. These features have affected longitudinal connectivity and patterns in fluvial sediment erosion, transport, and deposition that are different from older landscapes with well-developed drainage networks and valleys. One primary difference is that stream slopes and bottom substrates are directly related to the proximity of post-glacial landforms, resulting in the potential for relatively gentle slopes and fine-grained sediment (silts and clays) in the headwaters compared to relatively steep slopes and coarse sediment (boulders, cobbles, and gravel) in the middle of drainage networks. In addition, many streams intersect discontinuous erosion-resistant bedrock units that affect slope, bottom sediment, and channel morphology and floodplain interactions. The distribution of stream power, as defined by streamflow and slope, is also affected by the topography of post-glacial landforms rather than only drainage area. Channel hydraulic geometry characteristics reflect not only modern flood hydrology related to regional climate patterns, but they also reflect the topography and sediment characteristics of intersected post-glacial landforms. Many channels are surrounded by post-glacial deposits and not alluvium. These variations will be shown in examples from fluvial systems dominated by forested, agricultural, and urban land cover across the northern Great Lakes and Upper Mississippi River Basins. Stream characteristics from the older, greater than 2-million-year-old landscape associated with the Driftless Area of southwest Wisconsin will be included. Implications for aquatic and riparian rehabilitation and restoration will be discussed.