Exploratory morphodynamic hindcast of the evolution of the abandoned Yellow River delta, 1578-1855

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The Abandoned Yellow River Delta (AYD), which formed when the Yellow River flowed into the Southern Yellow Sea between 1128 and 1855 AD, is a representative example of the sensitivity of deltas to modifications in their environments. In this study, we established a process-based morphodynamic model to explore the morphological evolution of one such largescale fine-grained delta (the AYD before 1855). The uncertainties in the model settings, which are inevitable when historical data are insufficient, were assessed together with the corresponding influences on the evolution of the deltaic system by considering a series of scenarios. The results indicate that the strength of local tidal forcing is the key factor that determines the shape and evolutionary trend of the delta. Sediment input discharge and the slope of the initial coastal profile have a considerable effect on the overall size of the delta and the relative ratio between subaerial and subaqueous parts of the delta, respectively. Based on the evaluation of the uncertainties and a comparison with historical maps, the simulated AYD was evaluated to be reliable. Through an analysis of the temporal delta evolution and residual sediment transport, the morphological evolution of the AYD before 1855 AD was investigated. The southern delta grew as the shoals merged with the mainland, which is in agreement with an existing hypothesis (Zhang, 1984), whereas the accretion of the northern delta was independent from the shoals in the northern part. Additionally, suggestions are made regarding the distribution of the AYD at the end of its progradation stage, which provides fundamental information for analyzing subsequent erosion processes since 1855 AD. This study differs from existing studies on the AYD, which are all based on geological approaches. It provides insight into the evolution of the AYD through an alternative means, viz. a process-based morphodynamic-modeling approach.