A Four-Stage Morphodynamic Model for the Abandoned Subaqueous Diaokou Lobe of the Yellow River Delta (1976–2026): Semi-Quantitative Assessment of Natural and Anthropogenic Forcing Factors

Abstract

Abandoned delta lobes worldwide face severe net erosion driven by chronic sediment starvation and intensifying marine hydrodynamic forcing, which poses pervasive threats to nearshore and offshore engineering infrastructure, particularly delta zones with dense subsea energy facilities. This study investigates the multi-scale morphodynamic evolution of the abandoned subaqueous Diaokou Lobe (Yellow River Delta) over a 50-year period (1976–2026), combining multi-source bathymetric mapping, sediment sampling, and year-round hydrodynamic monitoring to assess natural and human-driven geomorphic changes. Four sequential evolutionary stages with falling erosion rates are identified following the 1976 river avulsion: rapid erosion (>0.6 m yr−1, 1976–1986), gradual erosion (0.2–0.3 m yr−1, 1986–1996), erosional adjustment (<0.1 m yr−1, 1996–2016), and dynamic equilibrium (<0.05 m yr−1, 2016–2026). Monsoons trigger annual seabed fluctuations of up to 1 m in shallow zones, while winter cold surge storms dominate short-term erosion and make a disproportionate contribution to annual sediment transport. Natural marine processes are the dominant long-term driver of the morphological evolution, whereas anthropogenic activities—most notably the Chengdao oilfield facilities—create growing localized erosion hotspots and become increasingly important as natural erosion rates decline. The four-stage sequence is proposed as a conceptual framework for the reworking of fine-grained abandoned deltas, providing targeted risk evaluation for the Chengdao offshore oilfield with hundreds of platforms and thousands of kilometers of subsea pipelines, as well as general technical references for erosion control and sustainable coastal management across sediment-starved muddy deltas worldwide.