160-4 Compound Impacts of a Natural Lake and Navigation Dams on Suspended Sediment Dynamics in the Upper Mississippi River

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

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Suspended sediment transport is a key driver of riverine geomorphology, water quality, and ecosystem health. However, this process is often disrupted by dams and natural lakes that act as sediment traps. In this study, we examine how a compound impoundment system—Lock & Dam 3, Lake Pepin, and Lock & Dam 4—alters sediment dynamics in the Upper Mississippi River’s Pool 4 reach, as a test case for understanding sediment recovery in a dam–lake–dam configuration.We analyze 34 years (1984–2018) of satellite-derived suspended sediment concentration (SSC) data from the RivSed database, integrating it with topographic, bathymetric, hydrologic, and watershed modeling (particularly using the InVEST Sediment Delivery Ratio), to assess spatial and temporal patterns of sediment recovery along the longitudinal profile of the river. Our findings show that Lake Pepin acts as a highly efficient sediment sink, causing a substantial SSC drop and an unusually long downstream recovery length, averaging ~100 km—nearly twice the national average below single dams. Recovery distances also vary by season, reaching over 100 km in spring and nearly zero in winter. Interestingly, despite declining upstream SSC in recent decades, downstream recovery distances have increased, indicating growing sediment starvation. Within Lake Pepin, SSC is inversely related to water depth, confirming stratified sedimentation. While SSC shows a weak correlation with watershed sediment yield (r ≈ 0.16), the discharge-weighted sediment flux shows a much stronger relationship, highlighting the importance of transport capacity. Sediment contributions from major upstream sub-watersheds appear to be uniformly mixed across the lake, emphasizing the need for coordinated, basin-wide sediment management. These findings offer valuable insights into the compounded effects of sediment disruption and provide guidance for maintaining sediment continuity in regulated river systems.

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

doi: 10.1130/abs/2025AM-5857

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