EFFECT OF SEDIMENT SUPPLY ON SUBSURFACE CONNECTIVITY IN FLUVIAL AND DELTAIC SEDIMENTARY ENVIRONMENTS

We examine the movement of river and delta channels, which transport sediment, nutrients and pollutants across Earth’s surface. Understanding how river and delta processes influence the size, spatial distribution, and connectedness of subsurface deposits is important for supporting United Nations Sustainable Development Goals (UNSDGs) in: Good Health and Well Being, Clean Water and Sustainability, Climate Action, and Life Below Water. To help address this need, we used numerical models to simulate river deposition and compared how model design and input parameters influence subsurface reservoir architecture. Channel migration processes can produce coarse-grained channel deposits surrounded by fine-grained floodplain sediments that seal fluids in a reservoir. The total amount of coarse and fine sediment supplied to a river network influences the movement and migration of channels and, in turn, the reservoir characteristics.

We used two process-simulating numerical models — Flumy and DeltaRCM — to compare how sediment supply influenced the scale and connectedness of subsurface channel deposits. Flumy relies on prescribed rules to simulate river meandering, avulsion, and floodplain deposition. DeltaRCM builds channel networks by routing sediment and water using slope-dependent flow partitioning and deposits sediment based on flow strength throughout the model domain. In both models, high mud supply results in higher total floodplain deposition and isolated, coarse channel deposits. In DeltaRCM, high mud supply also causes channels to migrate more slowly and develop more unevenly distributed channel deposits. We estimate static connectivity of each model to evaluate how sediment supply and channel movement change the interconnectedness of buried channel deposits. Preliminary results indicate sediment supply determines maximum connected volume of models. This work demonstrates how exploratory modeling can be used to understand the distribution of subsurface resources and explore the sensitivity of rivers to changing sediment supply. This work highlights the need for understanding complex feedbacks in rivers and deltas to help achieve UNSDGs.