Decadal Morphological Evolution and Governance Measures of the South Branch, Changjiang Estuary

Estuaries and deltas possess significant socioeconomic importance and exhibit high ecological value because of their dynamic geomorphic processes and unique geographical advantages. However, delta recession and the instability of river regimes have become worldwide issues due to intensive human interventions in upstream river basins and local areas in recent decades. This study focuses on a typical example, the South Branch of the Changjiang Estuary, to explore its morphological evolution in the past decades and near future and propose suitable solutions to enhance the stability of the river regimes. Based on bathymetric data analysis, we find significant channel-shoal adjustment within the South Branch from 1958 to 2016, characterized by substantial erosion and deposition on decadal timescales. After 1997, the South Branch experienced overall erosion due to the reduced fluvial sediment supply. Disturbances on the Baimao Shoal and Biandan Shoal further aggravated the river regime’s stability. Numerical predictions for future evolution trends indicate continuous erosion in the South Branch over the next 20 years, with further adjustments to the channel-shoal pattern. Hydrodynamic modeling of the proposed measures demonstrates an increased ratio for the North Baimao Shoal Channel, leading to enhanced stability of the channel-shoal system. These integrated governance measures have been incorporated in the new round of renovation planning for the Changjiang Estuary. The findings provide valuable scientific guidance for the comprehensive management of the Changjiang Estuary and offer insights applicable to other large estuaries.