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Historical and recent floodplain sedimentation rates along Big River, southeast Missouri Ozarks

Authors: Robert Pavlowsky*, Missouri State University, Miranda Jordan, Missouri State University, Marc Owen, Missouri State University, Derek Martin, Appalachian State University, Scott Lecce, East Carolina University
Topics: Geomorphology, Water Resources and Hydrology, Anthropocene
Keywords: fluvial geomorphology, floodplain, legacy deposits, Ozarks, mining contamination
Session Type: Paper
Presentation File: No File Uploaded

Floodplain sedimentation rates vary though time due to the influence of geomorphic, climate, and land use factors. Understanding the relative importance of these factors in regulating sediment budgets in watersheds in critical for assessing channel changes and planning management practices, particularly in rivers affected by sediment quantity or quality problems. This study focuses on understanding the downstream patterns of floodplain sedimentation since the middle 1880s along 170 km of lower Big River focusing on early legacy deposits prior to 1930 and more recent deposits since 1960. Big River drains the Old Lead Belt which was a global leader in lead production from 1895 to 1972. Mining metal profiles were used to date the older deposits since the production history of the mining district correlated well with contamination profiles in over-bank floodplain deposits. The younger deposits were dated with Cesium-137 profiles. In general, legacy sedimentation rates ranged from 1 to 7 cm/yr. These deposits were heavily contaminated with lead indicating that soil disturbance and related flooding due to settlement land clearing in the watershed was a driver of mining waste storage in floodplain deposits. Post-1960 sedimentation rates were <1 cm/yr indicating that soil erosion and, to a lesser degree, over-bank flood frequency has moderated in the present-day. However, recent trends with more extreme floods due to climate change may result in the release of stored lead from floodplains by bank erosion and potentially increase floodplain contamination rates downstream.

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