160-12 Curvature as a Driver of Floodplain Contaminant Sequestration in Meandering Rivers

Session: Advances in Fluvial Processes and Sediment Transport, Part I

Presenting Author:

José Constantine

Authors:

Hugo, Emily¹, Blau, Emmett², Alagar, Jayalakshmi³, Constantine, José Antonio⁴, Thoman, Jay⁵, Dethier, David P.⁶, Racela, Jay⁷

(1) Geosciences, Williams College, Williamstown, MA, USA, (2) Geosciences, Williams College, Williamstown, MA, USA, (3) Chemistry, Williams College, Williamstown, MA, USA, (4) Geosciences, Williams College, Williamstown, MA, USA, (5) Chemistry, Williams College, Williamstown, MA, USA, (6) Geosciences, Williams College, Williamstown, MA, USA, (7) Environmental Studies, Williams College, Williamstown, MA, USA,

Abstract:

The role of curvature in controlling in-channel hydraulics is well established, but its influence on floodplain sedimentation, and specifically on the fate of sediment-associated contaminants, has received far less attention. Drawing on over 9,000 sediment samples collected along the Housatonic River in western Massachusetts, we examine how planform curvature governs the delivery and deposition of polychlorinated biphenyls (PCBs) across the floodplain of a meandering, contaminated system. Our findings show that regions of high bend curvature coincide with localized superelevation and overbank flow, producing repeated deposition of fine-grained, PCB-laden sediment along outer banks. This pattern is reflected in measured PCB concentrations and in the spatial coincidence of high-curvature zones with observed areas of contaminant accumulation. Additional analysis reveals that oxbows and floodplain depressions store significantly higher PCB concentrations than adjacent floodplain surfaces at similar distances from the channel, highlighting the role of geomorphic complexity in contaminant sequestration. Together, these results suggest that channel curvature can serve as a first-order control on the spatial distribution and long-term fate of legacy pollutants. To test the mechanistic basis of this relationship, we are developing a numerical experiment designed to isolate and quantify the role of curvature in driving overbank flow and contaminant delivery to the floodplain. This work provides a framework for anticipating floodplain risk and evaluating how geomorphic restoration might support natural attenuation processes in contaminated river systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9493

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