The Jingjiang Sandbank (JJS) is located on the bank of the tidal reach in the Yangtze River. It experiences a periodic evolution process of increase, split, migration, and dissipation, which affects the current direction, fish habitat, navigation safety, etc. In this paper, the periodic evolution of the JJS is investigated based on 17 field bathymetric measurements of the river from 1999 to 2017. Firstly, six cycles of the evolution process of the sandbank are described, and the evolution pattern of the split detached bar and the main body of the sandbank are analyzed according to the migration tracks of the detached bars and the historical volume-change of the JJS, respectively. Then an empirical orthogonal function (EOF) is conducted on the historical measurements of the bathymetry. The first four eigenfunctions correspond to the time-averaged bathymetry, the long-term change of the pattern of bathymetry, the periodic change of the JJS, and the downstream migration of the split detached bar, and the periodic change of the rip at the back of JJS. It is pointed out that the construction of two waterway regulation projects might have changed the evolution pattern of the JJS permanently.

Large marginal sandbanks in tidal rivers experience periodic splitting processes. In this paper, the morphodynamic evolution of Jingjiang Beach, a sandbank on the Yangtze tidal river, has been investigated based on measured data. The results show that the duration of the splitting process in the middle and lower sections of Jingjiang Beach is 4–6 years. The periodical evolution occurred both in flood season and dry season, with a slight difference in the initial stage of splitting. This paper focuses on the evolution characteristics related to strong human activities since 2003. Ever since the second stage of the 12.5 m Deepwater Channel Project (DCP), the volumes above the 10 m and 12.5 m isobaths of Jingjiang Beach have been generally decreasing. The elevation data in recent years have demonstrated that the upper section, and nearshore side of the middle section, of Jingjiang Beach have tended to be stable. Moreover, the migration distance for a splitting sand body at the tail of Jingjiang Beach appears to have shortened. With the operation of the Three Gorges Reservoir, the number of days with discharge less than 15,000 m³/s has shown a decreasing trend; thus, the development scale of Jingjiang Beach could decline in the future.

Under the background of the construction of cascade reservoir group in the main stream of the Yangtze River, the lower reaches of the Yangtze River are faced with new water and sediment situation, which leads to the increased risk of bank collapse in the lower reaches of the Yangtze River. Therefore, the purpose of this study is to have a certain supporting significance for the prevention and control of riverbank collapse disasters. The study takes the Jiangsu section of the lower reaches of the Yangtze River as the research object. Firstly, according to the measured data over the years, the macroscopic characteristics of the collapsed bank in the Jiangsu section are analyzed, and the temporal and spatial distribution characteristics are mainly analyzed. The research results show that the collapse of the Jiangsu section of the Yangtze River is dominated by Ω-collapse, which mostly occurs in the flood season and the post-flood receding water period. The frequency of bank collapse in the Yangzhong Reach is relatively the highest among all river segments, and there are more bank collapses on the north bank than the south bank. According to statistics, the average collapse width of the collapse in the Jiangsu section can reach 130 m, the depth of the collapse can reach 60 m, and the ratio of the average bank collapse to the depth can reach 2.15. Then, aiming at the characteristics of the main bank collapse type in the Jiangsu section is the Ω-collapse, the experimental investigation and numerical calculation are used to conduct in-depth research, combined with the measured data, probability and statistical analysis and theoretical analysis. Three-dimensional hydrodynamic analysis is carried out on the mainstream area near the collapse area and outside the collapse area, focusing on the analysis of its nearshore velocity and shear stress and other factors. Combined with the water tank test, the water flow in the inner surface, middle and bottom layers of the Ω-type nest was studied under different flow levels, and it was concluded that the water flow in the nest had a counterclockwise backflow, and the backflow intensity gradually weakened from the side wall to the center. And the phenomenon that the surface layer and the bottom water flow are separated, and this phenomenon becomes more prominent with the increase of the flow rate.

The Ma’anshan section of the lower Yangtze River features a complex multi-anabranching system, where the river divides into several branches around mid-channel sandbars, with distinct point bars alternately developing along both banks. Within this morphologically active system, Zhengpu Harbor suffered severe operational disruptions by accelerated siltation at its approach channel, primarily due to its vulnerable location downstream of the expanding Niutun River point-bar on the left bank. To systematically diagnose the mechanisms of siltation, this study integrates multi-method investigations: decadal-scale morphodynamic analysis using long-term bathymetric surveys, numerical modeling to quantify engineering impacts on flow dynamics, and multiple linear regression analysis for the contributions of key influencing factors. The result identifies three primary drivers of siltation, collectively responsible for 70% of the sediment accumulation, including the rightward shift of the thalweg in the Ma’anshan left branch, reduced flow diversion of the left Branch of Central bar, and the expansion of the Niutun River point bar. River engineering structures, such as bridges, contribute approximately 12%, while changes in upstream flow-sediment supply account for approximately 18%. To mitigate siltation at Zhengpu Harbor’s approach channel, this study proposes targeted engineering interventions to enhance local hydrodynamic conditions. The spur dikes were designed to enhance the morphological stabilization of the Central bar head to regulate flow distribution. A diversion channel could also be excavated at the tail of the Niutun River shoal, and emergency dredging was recommended at the harbor front. Numerical modeling indicates that these measures will increase flow velocity by over 0.1 m/s at the harbor front, mitigating the siltation situation. The study concludes that the proposed engineering measures can reduce annual siltation by approximately 30% under normal-year hydrological conditions, demonstrating their feasibility in mitigating siltation trends in multi-anabranching river systems. This research provides a reference for addressing siltation issues in harbors within complex anabranching river systems.

Accurately quantifying vertical sediment transport rates in large seaward rivers is vital for estimating basin-scale water and sediment fluxes and assessing riverbed evolution. Traditional multi-point velocity and suspended sediment concentration (SSC) measurements are costly and slow, hindering long-term online monitoring. Bidirectional flows in tidal reaches further exacerbate this challenge. We propose a physics-constrained support vector machine (SVM) inversion method to estimate vertical sediment transport rates from single-point measurements. Constrained by modified logarithmic velocity and Rouse suspended sediment concentration profiles, it quantitatively relates single-point hydraulic variables to key parameters governing vertical distributions. Lower Yangtze River tidal reach field data validate the hybrid model’s successful reconstruction of vertical distributions. It accurately captures transient sediment responses across maximum flood and ebb. Inverted transport rates match measurements closely (RMSE = 0.085, NSE = 0.969, PBIAS = 2.50%) and exhibit strong cross-site generalization. Sensitivity analysis identifies 0.4 times the water depth above the riverbed as the optimal single-point sensor position. Although currently validated only in the lower Yangtze River, this low-cost, reliable method supports local basin management, flood control, and disaster mitigation by enabling continuous sediment flux monitoring. However, applying it to other river or estuarine systems may require recalibration or retraining to adapt to different local conditions.