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.

The flow pattern of the water with vegetation is complex. For the micro-bend channel which has compound cross-sections and has vegetation on the slope, the situation is more complex. This paper measures and analyses the hydraulic characteristics of the micro-bend channel with trapezoidal cross-sections and with vegetation on the slope,by using the ACM2-RS electromagnetic flow meter. The influence of vegetation structure changes on the hydraulic characteristics are further analysed, which includes flow velocity distribution, turbulence intensity and channel roughness. Studies have shown that, with the decrease of the rigidity of vegetation density, the sinuosity of the hydrodynamic axis increases, the longitudinal velocity of each section in the main channel has an obvious trend of decrease. Besides, the longitudinal and lateral turbulence intensity keeps constant in the main channel, have obvious decreasing trends on the slopes. In addition, river manning roughness coefficient increases with the increase of rigid vegetation density.

Many subways, light rails, and trains travel through urban flood retention regions via tunnels, viaducts, and roadbeds; however, less is known about the flood influence laws of rail transportation by the crossing ways. Rail transit projects were chosen as research objects for the ordinary subway, light rail, and railway passing through urban flood detention areas in Wuhan, and the flood influence characteristics were systematically compared for the three crossing ways. The study revealed that crossing ways primarily affected the flood storage volume occupied per unit length of lines and that the flood influence of rail projects on flood detention areas was proportionate to the flood storage volume occupied per unit length of lines. Specifically, the flood storage volume occupied per unit length of tunnels was about 1/8.9 that of viaducts and 1/19.7 that of roadbeds. Moreover, the tunnel way had the least influence on the main aspects, such as flood control, floods on engineering, and engineering-related aspects; the roadbed-based way had the largest; and the viaduct way was in the middle. These findings may provide technical support for the decision-making, engineering planning, construction, and management of rail transit and other projects in urban flood detention areas.

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.

Estuaries and deltas hold significant socioeconomic importance and immense ecological value due to their dynamic geomorphic processes and unique geographical advantages. However, in recent decades, delta recession and the instability of river regimes have become global challenges, driven by intensive human interventions in upstream river basins and local regions. This study examines the South Branch of the Changjiang Estuary as a typical case to investigate its morphological evolution over the past decades and project future trends, offering suitable solutions to enhance the river regime stability. Analysis of bathymetric data reveals substantial channel–shoal adjustments in the South Branch from 1958 to 2016, characterized by significant erosion and deposition on a decadal scale. After 1997, reduced fluvial sediment supply has led to widespread erosion in the South Branch. Further disturbances at the Baimao Shoal and Biandan Shoal have exacerbated the instability of the river regime. Numerical predictions indicate continued erosion in the South Branch over the next 20 years, accompanied by further channel–shoal pattern adjustments. Hydrodynamic modeling of proposed measures demonstrates an improved flow ratio for the North Baimao Shoal Channel, contributing to enhanced channel–shoal system stability. These integrated governance measures have been incorporated into the latest renovation plan 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 facing similar challenges.