CHARACTERIZING LATE PLEISTOCENE AND HOLOCENE FLOOD DEPOSITS IN EASTERN CONNECTICUT

Establishing a record of Late Pleistocene and Holocene fluvial processes is crucial for developing a long-term context for modern extreme events and future climate change. There is still much evidence lacking in southern New England when comparing the paleo-flood record to modern flood records. This study examines paleo-floods through modeling and sedimentary analysis of kettle pond sediments in eastern Connecticut. Only floods large enough to overtop the topography surrounding the kettle pond is preserved at these sites, providing context for the magnitude of flood that deposited the sediment.

We focus on three sites within the Thames River watershed, specifically along the Mount Hope, Willimantic, and Quinebaug Rivers. Kettle ponds at these sites were established during post-glacial times ~20-17 ka. We collected one vibracore at the deepest point at each site (assessed by probing) and recovered 320cm, 194cm, and 245 cm of sediment from Mount Hope, Willimantic, and Quinebaug sites, respectively. We obtained age models for each core from C¹⁴ dating. Sediment cores were scanned for bulk density, magnetic susceptibility, XRF elemental analysis and sampled for LOI and grain size analysis. Ancient high stage floods were identified by vertically plotting bulk density and D50 of grains greater than 63µm. We use Manning Equation’s to model paleo-flood depth required for the D50 of flood layers to be fully suspended and be deposited in the kettle. Modern stream channel slope and roughness were found from 1 m LIDAR DEMs and field surveys. Comparing the modeled flood sizes to models based on modern overbank deposits provides insight into the climatic changes of New England as it adjusted to post-glacial conditions. The broader interpretations from this study include using these sites to address the amount of river incision during and after deglaciation as the late Pleistocene-Holocene climate stabilized.