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The existence of rapids may seriously threaten the safety and ease of ship navigation in mountainous rivers due to its high flow velocity and water surface gradient. Whether a ship can ascend rapids is normally assessed by the navigable hydraulic index (NHI), a pair of parameters composed of flow velocity and water surface gradient. In this study, five approaches for determining the NHI were reviewed and discussed, namely, (1) empirical method, (2) semi-theoretical method, (3) full-scale field ship test method, (4) small-scale ship test method and (5) ship mathematical model method. Some rapids on Lancang River were selected as typical cases to demonstrate these five methods. The results show that the NHI obtained by all methods can be matched well with each other; while method (2) is the most widely used method, method (3) is the most reliable method, and method (5) is the most flexible approach. In addition, Hekuan Rapids were selected as a case study to conduct seaworthiness simulations based on the model of ships ascending inland waterways. The ships in upper reach of Hekuan Rapids can ascend rapids successfully but could not ascend the lower reach, which is consistent with the NHI results obtained by method (3). • Five approaches for determine the Navigable Hydraulic Index have been reviewed. • Some rapids in Lancang River were selected for demonstrating these five methods. • The reliability of each method was comparatively analysed and discussed. • The ship mathematical model suited for mountainous river was well calibrated. • Well seaworthiness simulation of the ship model was put into the typical rapids. [ABSTRACT FROM AUTHOR]

Oil spills occurring either in oceans or inland waterways may cause serious economic losses and ecological damage. Previous studies pertaining to oil spills and their consequences are primarily based on marine environments, whereas few have focused on oil spills occurring in inland waterways characterised by pronounced flow advection transport effects, which differ from the marine environment. A generalised flume experiment is performed to investigate the spread and transport of oil spills, and the relationships between the area and thickness of oil slick over time are analysed parametrically. An oil spill model combined with a depth–integrated two–dimensional non–uniform flow model, which is suitable for modelling inland waterways based on the Lagrangian method, is established; it is calibrated and verified using measured data from the flume experiment. The model is applied to three scenarios on the Luoqi reach of the Yangtze River, and spilled oil drifting trajectory maps are obtained and analysed considering the field wind parameters. The results show that the drift distance of the oil slick in the inland waterway is primarily controlled by the flow velocity with effects of advection transport; however, the oil spill trajectory spreads toward the wind direction when the flow velocity is relatively small compared with the wind speed. The results of this study serve as a reference for predicting the spread and transport of oil spills in inland waterways. [Display omitted] • A generalised flume experiment of spread and transport of oil spill was carried out. • Relationships between area and thickness of oil slick with time were analysed. • An oil spill model suited for inland waterways was established. • Verifying the oil model by using the measured data from the flume experiment. • Well application of the oil model was put into the typical inland waterways. A generalised flume experiment is performed and relative parameters are quantitatively analysed; an oil model suitable for inland waterways is established and applied to the typical reach of the Yangtze River. [ABSTRACT FROM AUTHOR]

Sailing attitude would experience many changes when ship entering shallow water, due to the hydrodynamic interaction between ship hull and seabed or riverbed which can be expressed in a significant increase in resistance, sinkage and trim and can engender the safety of ships. A numerical model of ship maneuvering motion that takes account of the shallow water effect is proposed based on the Maneuvering Mathematical Modeling Group (MMG) model. Flow field data solved based on a numerical model of non – uniform flow serves as the basis for calculating hydrodynamic forces of the ship model. Simulations of straightforward, turning and zig-zag motions are performed on a cargo ship using various empirical methods and the fourth-order Runge – Kutta method. Ship trajectories for varying depth-draft ratio, rudder angle and flow velocity are compared, indicating that shallow water effect would increase ship sailing resistance and decrease maneuverability. Result shows that ship maneuverability would be reduced as the depth-draft ratio decrease when ship sailing in shallow water. Application of the model in a typical mountainous river reveals that the model can reasonably simulate the shallow water effect. The study could be a valuable reference for further investigation on shallow water effect, as well as providing guidance on ship maneuvering in shallow waterways. [ABSTRACT FROM AUTHOR]

Ships navigating inland waterways, especially mountainous waterways, may encounter complex navigation environments. Under these circumstances, the force of the ship is extremely complex, the attitude of the ship may be unstable, and the control performance may decrease, possibly resulting in marine accidents. In this study, a modular-type manoeuvring model (MMG) is used to develop a ship manoeuvring model that comprehensively considers multiple factors. Based on this model, numerical simulations are conducted on the ship Seiun Maru , and Esso Osaka ; the simulation results are found to be in good agreement with the results of real ship motions. Then, numerical simulations are conducted on the navigation of a 500-ton ship in a typical mountainous waterway, the Suoluo Rapids in the Lancang River, and the impact of the complex environment in this area on the safety of ship navigation is explored. The results reveal that ignoring the influence of environmental factors may put ships in dangerous situations when navigating mountain waterways. In addition, the model can effectively simulate the manoeuvring motion of a ship in a typical mountain waterway, and the calculation cost is negligible. This study provides valuable suggestions for long-distance ship manoeuvring in complex inland river environments. • Ship maneuverability in mountainous rivers is discussed via MMG model. • A more efficient non-uniform flow model. • It is more realistic to consider the impact of multiple factors on ship maneuvering. • Environmental factors' impact on ship safety in mountainous rivers is studied. • Guidance for long-distance ship maneuvering in complex inland rivers. [ABSTRACT FROM AUTHOR]

Phosphorus is the primary eutrophication cause of river, lake, reservoir and estuary and it may be one of the principal pollutants for the agricultural watershed with middle and small cities. The sediment and phosphorus loads, related migration paths and contribution of source regions to receiving waters at different sections of a river basin are not clear. The modified Soil and Water Assessment Tool (SWAT) model was utilized to investigate the phosphorus loads and the relationships among water resources, sediment, and phosphorus loads in one of the important tributaries of the Three Gorge Reservoir (TGR) of China, and to investigate the retention dynamics of phosphorus in the river continuum and the influencing factors. It showed that under the scenario of rice terraces and ponds, the annual sediment loss and total phosphorus load were 125t and 2.5t, being reduced by 40%–80% compared to the natural slope scenario; the daily peak value of suspended sediment load was reduced by 30%–75%, and the relationship between the rainfall and runoff was weakened slightly; the retention rate of phosphorus sources reached 40%–78%. The results confirm that the rice terraces and ponds have altered local hydrological conditions, enhanced a substantial water, sediment, and phosphorus retention capacity that is highly consistent over time and space scales, thereby altering the predominant forms of phosphorus and improving the environmental resilience in soil and nutrition loss for the hilly watershed of the TGR. • Phosphorus and sediment loads are quantitative analyzed in a typical hilly watershed of TGR. • Rice terraces and ponds reduce the particle phosphorus concentration and flux up to 80%. • Response relationship among the flow, sediment and TP in different land use are altered at different degree. • Rice terraces and ponds improved the local environment residence at moderate and relative heavy rainfall. [ABSTRACT FROM AUTHOR]