Long-term morphodynamic evolution in the Modaomen Estuary of the Pearl River Delta, South China

Anthropogenic activities and natural disturbances will cause large-scale changes in the morphology of estuarine systems. Studies of estuarine morphology tended to focus on a single driving factor, however, the intertwined ef-fects (e.g., land reclamation, sand excavation, tides, waves, runoff) are rarely mentioned in the literature. This work characterizes and conceptualizes the morphodynamics of the Modaomen Estuary (ME), the largest estuary in the Pearl River Delta (PRD), China, based on Landsat satellite imagery, high-resolution bathymetry survey data, and in situ hydrographic measurements. The morphodynamic evolution of the ME since the 1970s-2010s is analyzed with respect to planform configuration and bathymetry. Quantification of estuarine hydrodynamic and sediment parameters for the most recent years indicates that the ME has transformed from a traditional fluvial-and tide-dominated estuary into a fluvial-and wave-dominated estuary. Ocean currents intrude along the eastern channel and draw down along the western channel, in which estuarine flow deflection is induced by the combined effect of upstream runoff, coastal waves, and littoral currents. Furthermore, a life-cycle model of the morphological migration of the ME is presented by synthesizing hydrodynamics and sediment dynamics. This conceptual model of three geomorphological states clearly shows that the main channel experiences a life cycle covering several decades, from the origin of the main channel to its bifurcation into two distributaries, and finally a recovery and westward deflection of the main channel. The cognition of the appearance and disappearance with one sandbar and two channels will be helpful in numerical modeling of estuary evolution, and it also has important implications for the regulation of estuarine regions, hazard prevention and channel navigability.(c) 2021 Published by Elsevier B.V.