Restoring sediment continuity in large regulated rivers: a 2D-informed 1D morphodynamic framework applied to the Hungarian Danube

Sustainable sediment management in large, regulated rivers requires modelling tools that can reliably predict long-term morphological trends while remaining computationally efficient for scenario testing. This study presents a simplified one-dimensional (1D) morphodynamic framework parameterized using effective flow conveyance and sediment transport widths extracted from a calibrated two-dimensional (2D) hydrodynamic model. The approach corrects a key limitation of conventional 1D models, which implicitly assumes that the entire cross-section is hydraulically and morphologically active. The method was applied to a 100-km gravel-bed reach of the Hungarian Danube, where sediment deficit caused by the upstream hydropower-plant impoundment and extensive training works have caused persistent bed degradation, reaching 5 m erosion at places. The model was validated against measured water levels, two multi-year bathymetric datasets, and a bedload rating curve derived from direct field measurements. Using total or constant channel widths substantially distorted predicted erosion–deposition patterns, whereas the 2D-derived effective widths reproduced both the magnitude and spatial distribution of observed bed changes. Long-term simulations (2005–2035) show continuing riverbed incision of ∼0.8 m in the most active 20 km. A widening scenario (1.5× effective width), modelling the removal of river training works, reduced incision by ∼50%, while targeted sediment feeding (10,000 m 3 /yr) produced local mitigation with weaker downstream propagation. The study demonstrates that 2D-informed 1D morphodynamic modelling provides a transparent and computationally light decision-support tool suitable for evaluating sediment management strategies in large, engineered rivers.