Civil and Environmental Engineering - Master Calendar

Abstract
Intensive agriculture has altered water and sediment fluxes to and through rivers in the US Midwest. Accelerated floodplain sedimentation in response to agriculture, referred to as post-settlement alluvium (PSA), has been observed in North America since the early 19th century. In the unglaciated Paleozoic Plateau region of southwest Wisconsin, floodplain sedimentation was particularly pronounced and was followed by channel incision and widening. In East-central Illinois, PSA is less easily recognized, but still widespread. We use fly ash from coal combustion as a marker for historic sedimentation. I present our records of PSA in the Upper Sangamon River, the Middle Fork Vermillion River, and their tributaries and compare the thickness and grain size of this material to that in the Paleozoic Plateau. PSA is thinner in Illinois with variable grain size reflecting sediment sources. A broader meta-analysis of records of PSA across the Midwest indicates that the non-dimensional thickness of PSA (PSA thickness / valley width) varies with the relief and slope of watersheds, the fraction of non-contributing area, and the slope of river networks.  Intensive study of the floodplain of the Sangamon River at Allerton Park has documented spatially-variable deposition during individual flood events.  Secondary channels on this floodplain experience flow conditions consistent with floodplain erosion and trees rooted in and near these channels have exposed roots, indicating erosion within the trees' lifetimes. The channels also show profiles of fly ash that appear to be truncated. These two lines of evidence suggest that the secondary channels have formed and/or deepened within the last ~50 years. Will the streams of central Illinois experience the entrenchment seen in Wisconsin as the impact of historic land use change continues to play out

Bio
Alison Anders is an Associate Professor in the Department of Earth Science and Environmental Change. She's a geomorphologist with research interests in the glacial and post-glacial evolution of the landscape and critical zone of US Midwest and the impact of spatial and temporal variability in climate and rock hardness on long-term landscape evolution.