Brandee Carlson, Jeffrey Nittrouer, Andrew Moodie, Gail C. Kineke, Lisa L. Kumpf, Hongbo Ma, Dan Parsons

Upon avulsion, abandoned deltaic distributary channels receives water and sediment delivered by a tie channel, overbank flow, and by tidal inundation from the receiving basin. The transport and deposition of sediment arising from this latter input have important impacts on delta development, yet are not well-constrained from field observations or numerical models. Herein, the Huanghe (Yellow River) delta of China is used as a case study to evaluate how marine sourced sediment impacts abandoned channel morphology. For this system, artificial deltaic avulsions occur approximately decadally; the abandoned channels are inundated by tides, and deposition of sediment transforms the channel and adjacent lobe into a mudflat. Field data were collected from a channel abandoned twenty years ago, and included cores that penetrated the tidally deposited mud and antecedent fluvial channel sediment, topography and bathymetry surveys, and detailed time-series monitoring of hydrodynamic conditions within the tidal channel and adjacent mudflat. These data are used to validate a model that constrains material exchange between the channel and flat. The thickness of the marine-sourced mud differs spatially by an order of magnitude, and is primarily impacted by antecedent channel topography, rather than spatial variability in mud deposition, as has been observed in other mudflat environments. The system is nearing its limit of fill potential, which is set by the spring tide water elevation. As this elevation is below antecedent levees, assuming stationary sea level, the abandoned channel will remain a topographic low on the delta landscape and is therefore susceptible to reoccupation with future avulsions.