Reconstructing the dynamics of a meandering river in an intensively managed landscape through analysis of floodplain deposits

Keywords: Lateral migration, meandering river, intensive management, floodplain coring, floodplain geomorphology, fluvial sedimentology, paleohydrology, chronology
Session Type: Virtual Poster Abstract
Day: Saturday
Session Start / End Time: 2/26/2022 09:40 AM (Eastern Time (US & Canada)) - 2/26/2022 11:00 AM (Eastern Time (US & Canada))
Room: Virtual 37

Abstract

Human activities influence river dynamics by disturbing natural rates of fluvial processes. Throughout the Central Lowlands of the Midwest, increases in rates of overbank deposition associated with agricultural development have been well-documented, but the influence of agricultural transformation of landscapes on rates of lateral migration is poorly understood. The purpose of this research is to investigate lateral movement of a meandering river over long timescales by identifying lateral-accretion deposits in cores obtained from floodplain scrolls and by dating these deposits to determine the rate at which the river moved laterally from scroll to scroll. The study site is the floodplain of the Sangamon River within Allerton Park in east-central Illinois. Historical aerial photography shows that rates of lateral migration of this river over the past 80 to 90 years are nearly zero. Despite these low rates, prominent scroll bars on the floodplain suggest that lateral migration has been substantial in the past. Eleven cores have been obtained across the valley bottom at a bend in the river, including several cores located on scrolls. Descriptions of the cores reveal that sandy lateral accretion deposits underlie fine-grained overbank deposits, including post-settlement alluvium. Particle-size analysis of the lateral-accretion deposits indicates that texturally these deposits are similar to contemporary lateral accretion deposits on active point bars. Dating of wood samples (radiocarbon dating) and of sands (OSL dating) will provide the basis for comparing contemporary rates of migration under intensive agricultural management to long-term rates prior to agricultural development.