Modeling the infilling process of an abandoned fluvial-deltaic distributary channel: An example from the Yellow River delta, China

Abstract

As an inevitable result of fluvial-deltaic avulsions, abandoned distributary channels and associated lobes form an important component of coastal marine systems, serving as a sediment source and sink for the adjacent delta region. The distinct differences between normal tidal flats and abandoned channel systems restrict the application of classic intertidal mud flat morphological theory to the study of the evolution of abandoned channels. Herein, a quantitative model based on the concept of mass conservation was proposed to describe the infilling processes for an abandoned channel. Sediment cores and elevation profiles from an abandoned channel of the Yellow River delta (China), along with hydrodynamic observational data, are used to constrain a numerical approach and test model performance. The modeled accumulation thicknesses are satisfyingly consistent with those derived from sediment cores. The model results indicate that the tide-delivered sediment flux and channel water depth are the dominant variables governing the variation in accumulation thickness in the abandoned channel, whereas the channel shortening rate largely impacts the depositional area rather than depositional thickness. By contributing to steady deposition on the mud flat, tide-associated landward sediment deposition formed a steep profile near the estuary, while the final four years of deposition represent only a quarter of the total deposition compared to that from the first five years owing to a decreasing depositional rate. The model-derived sediment volume indicates that shore-parallel flow is significant in shaping mudflat morphology, especially in the late stages, while the shortening of tidal channels leads to shrinking of the mud flat and sediment volumes. Despite its limitation to residual channels, our model presents a new approach for quantitative interpretation of the geomorphic evolution of an abandoned river channel with finite boundary conditions, providing a good reference to apply to other large deltaic systems.