ABSTRACT:

A shapefile of the watersheds included in a meta-analysis of post-settlement alluvium in the Central Lowlands/Midwest USA is included as a zipped archive. A data table with PSA thickness, landscape, climate and soils data from the watersheds is provided as a text file.
Accelerated floodplain sedimentation related to agricultural development of uplands has produced post-settlement alluvium (PSA) along rivers throughout the upper Midwest, U.S.A. Landscape characteristics in the region vary geographically in relation to differences in geologic history, yet the extent to which this geographic variability influences PSA accumulation remains unexplored. This study uses existing data to assess how non-dimensional PSA thickness varies with landscape characteristics and climate. Geographic variability is associated with three subregions: 1) areas glaciated during the Late Wisconsin Episode (LWE), 2) areas glaciated during Pre-Illinois and Illinois Episodes (PI&IE), and 3) the Paleozoic Plateau (PP), an area where evidence of Quaternary glaciation is highly localized and does not influence geomorphic characteristics of the landscape. These subregions differ significantly in average geomorphic characteristics, including mean watershed slope (WS), mean local relief (LR), fraction of non-contributing area (NCA), pre-settlement drainage density (DD), and mean normalized river steepness (KSN). Non-dimensional PSA thickness also differs significantly among the subregions, increasing systematically with landscape age; it also is significantly positively correlated with LR, KSN and WS, and significantly negatively correlated with NCA. Non-visibly distinct PSA is present in some LWE watersheds characterized by significantly lower KSN and WS relative to other LWE watersheds in which PSA is visibly distinct. These results indicate that PSA thickness and visibility reflect inherited landscape characteristics, emphasizing the importance of geographic setting, geological history, and geomorphic context for understanding historical river sediment dynamics. Spatial variability in PSA thickness also serves as an indicator of river system sensitivity to human-induced land-use change, which informs river management strategies.