The anomalous variation in the diversion of flow and sediment at the
major bifurcation nodes of the Pearl River network in recent years has
been generally recognised and accepted, yet the underlying mechanisms
have not been revealed. In this study, a large-scale two-dimensional
flow-sediment numerical model of the Pearl River estuary was constructed
using the TELEMAC-MASCARET modelling system. Additionally, synchronous
field surveys from the dry season of 2016 and wet season of 2017 were
used to validate the model. The complex branches system of the Pearl
River network was generalised. The theoretical models for calculating
the water diversion ratio of complex estuarine river networks were
proposed. The water diversion ratio at each river network node is
related to the Manning's roughness coefficient, the average
cross-sectional water depth, the water surface slope, the length of the
branches, and the average cross-sectional area from the river network
nodes to the main estuary outlets. Specifically, the average
cross-sectional water depth is the main driver of the formation of the
water diversion ratios at the nodes in the Pearl River network. The
sediment diversion ratios at the primary and secondary lateral branching
nodes, are significantly higher than the water diversion ratios in the
dry season, which explains the uneven distribution of flow and sediment.
Sediment mining and reclamation are the main factors that have affected
the variation in flow and sediment diversion ratios in the Pearl River
network over recent decades.