Anthropogenic disturbances drive stepwise geomorphic changes of shoal-channel systems in a tide-dominated estuary

The shoal-channel system, a fundamental geomorphic feature in estuaries globally, plays a crucial role in ensuring navigational safety and sustaining estuarine-deltaic ecosystem services. However, in the Anthropocene, this system has undergone significant transformations, challenging its stability and functional integrity. To investigate these changes, we applied a Digital Elevation Model (DEM) and Morphological Shannon Entropy (MSE) to quantify the stepwise evolution of the shoal-channel system in the Shiziyang (SZY) Tidal Channel, a tide-dominated reach of the Pearl River Estuary (PRE). Our findings reveal that anthropogenic disturbances triggered a systematic eastward channel migration, progressive shoal expansion, and peak erosion of 2.37 × 10⁶ m³/yr during Period III (1989–2000), exceeding concurrent deposition by 50 %. These changes culminated in a systemic reconfiguration from a V-shaped to a W-shaped channel profile. Sequential dredging emerged as the principal driver, accounting for a 17 m incision and contributing up to 68.45 % of the total scouring in Period III. Additional factors, including port construction (which reduced channel width by 20.39 %), diminished sediment flux (causing a 27.65 % decrease in depositional bank extent), and intensified hydrodynamics (reflected by a tidal range increase of 4.56 mm/yr), acted synergistically to amplify the regime shift. By elucidating the key drivers and consequences of this geomorphic evolution, our study provides critical insights for the sustainable management of heavily engineered coastal systems in the Anthropocene.