Alluvial rivers exhibit diverse forms that represent adjustments to the prevailing and past water and sediment supply. Rivers in historically glaciated and intensively managed landscapes of the United States Midwest generally have single-channel meandering forms but locally can have multiple channels either as anabranches or incipient secondary channels perched on the floodplain surface – features that have not been extensively documented in the US Midwest. This dissertation uses GIS analysis, fieldwork, and numerical modeling to 1) quantify the abundance, planform morphology and stream power domain of anabranching reaches in the US Midwest, 2) investigate fluvial processes of secondary channels along meandering reaches and their role in anabranch development, and 3) examine the consequences of anabranch development within meandering rivers with respect to river stability.
Results indicate that anabranching is a rare but important phenomenon in the US Midwest and while generally having low stream powers relative to rivers across the globe, is locally associated with higher stream powers relative to adjacent meandering reaches. Further, secondary channels studied on the floodplain of Sangamon River at Allerton Park, IL are active conveyors of cohesive bed material when flooded and may be important in anabranch development. Modeling indicates that abrupt change in channel planform between meandering and anabranching exhibited in the Sangamon River at Sangamon Park does not cause excessive sedimentation or erosion and is a stable configuration.
These results provide insights into morphologically diverse fluvial elements and thus have implications for the restoration of lowland rivers in the agricultural Midwest.
