The Jing River–Dongting Lake (DTL), a critical river–lake complex system in the Middle Yangtze River, China, plays a vital role in flood regulation and ecological sustainability. Recent decades have experienced significant morphology adjustments due to upstream reservoir operations; however, the long-term high-resolution hydro-morphodynamic evolution and its impacts on river–lake interactions remain insufficiently quantified. To address this gap, a two-dimensional hydro-morphodynamic model based on HEC-RAS was employed to simulate three decades of hydro-morphology evolution under projected flow–sediment conditions. The model was validated against observed data and reproduced erosion–deposition trends consistent with previous numerical studies. The results indicate sustained channel incision in the Jing River, with a cumulative erosion volume of 462 million m³, in contrast to net deposition in the DTL area totaling 276 million m³ over three decades. A comparison of results under a sediment reduction regulation shows that the overall spatial pattern of erosion and deposition remains largely consistent, although local areas, particularly the confluence of the three major inlets feeding the lake, exhibit pronounced sensitivity to sediment variations. Furthermore, continuous mainstream incision intensifies a draining effect on the lake during dry seasons, leading to declines in both water levels and surface area in the DTL. This effect is most pronounced in the eastern lake area, with reductions being markedly greater in dry periods than in wet periods. Finally, the lake’s storage capacity progressively decreases, with an average annual loss of approximately 36.5 million m³ in the wet periods, underscoring significant impairment of its flood-regulation function. This study provides a validated modeling framework and critical insights for predicting morphological evolution and informing adaptive management in large river–lake systems.

Turbidity currents transport fine sediment through reservoirs, with their propagation influenced by changing inflow conditions and sediment exchange with the bed. This study investigated the first turbidity-current event during the 2004 Xiaolangdi water–sediment regulation operation using a two-dimensional layer-averaged model calibrated against field observations. Calibration against observed front positions yielded a root-mean-square error of approximately $1.8\mathrm{km}$ and a Nash–Sutcliffe efficiency of $0.90$. The simulated current evolved from an initial erosion-dominated stage to downstream deceleration, deposition, and attenuation. Stronger hydraulic forcing, higher sediment concentration, and longer high-intensity inflow generally promoted downstream advancement. Varying the distribution of inflow altered the propagation process and endpoint advancement under equal cumulative water volume and sediment mass, identifying input timing as a control alongside total supply. The two stratified beds comprised equal-thickness layers in opposite vertical orders and shared the same combined grain-size composition as the uniform reference. These configurations changed $24\mathrm{h}$ front advancement by less than $2\%$ relative to the reference and modified local velocity and response timing. Simulated grain-size distributions revealed spatial variations in sediment sorting. Together, these findings support joint evaluation of inflow forcing, bed-sediment availability, and sediment-exchange parameters in reservoir-scale modelling and process-based assessments of sediment routing.