USING X-RAY COMPUTED TOMOGRAPHY AND GRAIN-SIZE ANALYSIS OF OXBOW LAKE SEDIMENTS TO REVEAL A CENTENNIAL-SCALE PALEOFLOOD HISTORY OF THE PEE DEE RIVER, SOUTH CAROLINA

A warming climate is expected to increase frequency and intensity of heavy precipitation and consequently, extreme floods. Unfortunately, instrumental flood records are relatively short (often <100 years) and overlap with major anthropogenic changes to river systems, which limits the reliability of accrediting changes in extreme flooding to climate forcing. This study aims to identify signals of extreme floods in oxbow lake sediments and establish a timeline of past flooding events to evaluate possible change(s) in flood hazard near the Pee Dee River (PDR), South Carolina. Oxbow lakes, ubiquitous in the floodplains of alluvial rivers, may preserve an archive of extreme flood as they capture coarser channel sediments transported by intensified river flows.

A 2-m long piston core (SBL2) was scanned by X-ray computed tomography (CT) and sub-sampled for laser grain-size analysis to identify event layers of extreme floods. SBL2 will be dated using a combination of ¹⁴C, optically stimulated luminescence, and ²¹⁰Pb methods. A preliminary radiocarbon age of 142±127 cal. yr BP at the base of the core (195 cm), suggests that SBL2 likely preserves a flood record for multiple centuries. CT images reveal laminations interpreted as flood event layers; and a major shift in sedimentation at ~75 cm depth is probably representing an abrupt change in the PDR’s hydrological and sedimentary processes.

Preliminary interpretations reveal that a multi-decadal trend in extreme flood frequency may be present in the PDR system, likely controlled by climate mode variability. This study may reveal a broad range of flood conditions that the PDR has experienced in the past, potentially leading to an understanding of the effects of climate change and natural variability on extreme flooding in this region.