QUANTIFYING MODERN OVERBANK DEPOSIT CHARACTERISTICS OF THE LOWER MISSISSIPPI RIVER AT SHIPLAND WMA, MISSISSIPPI, USA

The Mississippi River’s economic and cultural significance has yielded a legacy of human settlement and development along its floodplains since the 1700s. Coincident to these sustained settlements is the potential risk of flood hazards, the largest of which occurred in 1927. Following the 1928 Flood Control Act, flood-navigation control structures were implemented to reduce the severity of floods. This study examines overbank deposits of “major” floods along the Lower Mississippi River from 1927 to present, to understand the impacts these control structures have had on the floods’ magnitudes. Our study area is located on the Shipland Wildlife Management Area (SWMA), ~70 km upstream of Vicksburg, MS. Using geological, geophysical, and geochemical characteristics of floodplain deposits at SWMA, we aim to identify and correlate overbank deposits to the 1927, 1937, 1973, 2008, 2011, and 2018-2020 floods, and to quantify their thicknesses, volumes, and sedimentation rates. To accomplish these objectives, nine sediment cores and 4,400 meters of ground penetrating radar (GPR) data were collected and analyzed. Grain-size properties and distributions from sediment cores measured at centimeter to decimeter-scale intervals were used for stratigraphic correlation to radar surfaces. Organic carbon samples were also taken for radiocarbon dating and used to calculate sedimentation rates, which range from ~0.22 to ~0.58 cm/yr. Composition of the cores was dominantly medium sand with some silt and clay deeper down section. Preliminary GPR analysis indicated clear dipping strata in the upper ~1.5 m. The significance of this project is the opportunity to use overbank thicknesses and sedimentation rates for SWMA to document historical trends in flood magnitudes, and to compare them to previous research further up or down river.