Yangtze River Channel Research Articles

Enhancing water depth inversion accuracy in the Yangtze River's Nantong Channel using random forest and coordinate attention mechanisms

Accurate bathymetry information is crucial for safe navigation and efficient management of the Yangtze River Channel, a vital shipping corridor in China. Traditional bathymetric surveying methods are time-consuming and labor-intensive, limiting their application in large-scale and real-time monitoring. This study proposes a novel approach for bathymetry inversion in the Yangtze River Nantong Channel by integrating geolocational features obtained from the ZY-1E satellite with high-resolution multibeam data using the random forest algorithm. Our approach incorporates geographical coordinates enhancing the predictive capabilities of conventional models. The random forest with longitude/latitude (RF-Lon./Lat.) model, which incorporates geographical information, outperformed conventional methods, achieving an R2 of 0.57, MAE of 1.99 m, and RMSE of 2.96 m. The successful application of the RF-Lon./Lat. model highlights the effectiveness of integrating geolocational features with machine learning algorithms for accurate bathymetry inversion in the complex and turbid waters of the Yangtze River Channel. This innovative approach offers a promising solution for precise and efficient water depth estimation, which is essential for various applications in the Yangtze River Basin, including channel management, waterway maintenance, and hydrological studies. The insights gained from this study contribute to the growing body of knowledge on the application of machine learning and remote sensing techniques for bathymetric mapping in complex river environments, particularly in the context of the Yangtze River Channel.

Enhancing ecological success in Yangtze River channel construction: A numerical modelling approach

AbstractChannel constructions significantly impact river hydrodynamics, subsequently influencing river ecosystems. To mitigate the negative influence of channel construction and protect fish habitat, it is essential to evaluate fish habitat suitability through the integration of hydrodynamic and habitat models. This study models channel constructions on both the left and right riverbanks to evaluate habitat suitability for Four Major Chinese Carps and the Chinese sturgeon. Initially, flow velocity, water depth and grain size are simulated, followed by an assessment of habitat conditions using the Habitat Suitability Index (HSI) for three distinct construction strategies. Results reveal that constructing channels on the left bank mitigates adverse effects on fish habitat, while constructions on the right bank and both riverbanks lead to habitat degradation. Long‐term effects on riverbed elevation and fish habitat suitability post‐construction were also investigated. Notably, the Four Major Chinese Carps consistently demonstrate greater suitability for the studied river, regardless of flow rate or construction strategies, in comparison to the Chinese sturgeon. These findings underscore diverse responses to channel construction, providing valuable insights for identifying critical habitat areas for endemic fish conservation. This research presents a robust framework for assessing fish ecology in river systems, offering support for conservation decision‐makers.

The inland waterway ship emission inventory modeling: The Yangtze River case

The estimation of inland waterway ship emission inventories through the Automated Information System (AIS) is associated with considerable uncertainty. A method for calculating the Inland Waterway Ship Emission Inventory Model (IWSEIM) was proposed, based on shipping material flow, to address this challenge. A comparison between CO2 emissions of inland ships calculated by the IWSEIM and the fuel consumption records revealed a relative error of 21.88%. The IWSEIM was applied to calculate the emission inventory of ships passing through a certain channel section on the Yangtze River channel during the whole voyage from 2017 to 2022. Cargo ships emerged as the primary CO2 emitters on the Yangtze River, accounting for 57.67%. CO2 emissions grew by 0.68% annually from 2017 to 2020. In 2018, SO2 and PM emissions decreased by 94.91% and 88.26% versus 2017. The emission intensity (g/t-cargo/km) of ships in the Yangtze River from 2017 to 2022 was calculated by integrating freight data and emission inventory results.

Evolution of the Chenglingji–Datong Channel in the Middle and Lower Reaches of the Yangtze River and Its Drivers

In recent years, the water–sand composition of the Yangtze River channel has changed due to the influence of human factors, especially the construction of water reservoirs such as the Three Gorges Project. Changing water–sand conditions have a long-term impact on the shaping of the river channel morphology in the middle and lower reaches of the Yangtze River, and the erosion retreat of local river sections has caused great harm to embankment projects. This paper focuses on the river evolution mechanism of the river channel from Chenglingji to Datong in the middle and lower reaches of the Yangtze River over the past 31 years. Landsat remote sensing images from 1989–2019 were used to extract and interpret water bodies, river shorelines, and central bars in the study area using the Modified Normalized Difference Water Index (MNDWI) combined with visual interpretation. We used near analysis to study the morphological evolution characteristics of the river, the channel, and selected typical river reaches for comparative analysis. We found out that the overall change in river morphology between 1989 and 2019 was small in the horizontal direction, but the local area changed significantly. Considerable scouring occurred in the vertical direction. Combining hydrological and meteorological data, we investigated the effects of the Three Gorges Dam, instream sand mining, boundary conditions, vegetation cover on both sides of the riverbanks, and aspects of storm flooding in the watershed on the evolution of the river. The study indicated that the geological conditions on both sides of the river, the implementation of the bank protection project, and the improvement of vegetation cover on both sides of the river have made the riverbanks more resistant to scouring. However, heavy rainfall floods, the operation of the Three Gorges Reservoir, and sand mining activities in the river channel make the river channel more susceptible to scouring. Based on the calculation of the slope change rate of the accumulated volume, it was found that the runoff is mainly influenced by precipitations, while the sand transport is mainly affected by human activities. This study shows that natural and anthropogenic activities affect the equilibrium state of the river’s water and sediment to varying degree.

A preliminary study on the mechanism of the Liangzhu culture’s migration across the Yangtze river

The Liangzhu culture (5300–4200 cal BP) was the most famous Neolithic culture of who settled near the lower reaches of the Yangtze River in China. The core and initial distribution area of Liangzhu originated around Taihu Lake, located on the south bank of the Yangtze River delta. Recently, archaeological studies believe that the Jianghuai area and Huanghuai area north of the Yangtze River are also important distribution areas of Liangzhu culture. The route for Liangzhu culture migrating across the Yangtze River is inferred as follows: One would have crossed the Yangtze River from Nanjing-Zhenjiang belt and continued to migrate northward; while the other would have crossed the River near the estuary before moving north along the ancient coastline to the Jianghuai during the late period of Liangzhu, or crossed the Yangtze River from the east of the present Beijing-Hangzhou Grand Canal to Jianghuai and Huanghuai. According to the formation of the Yangtze River delta during the Holocene and the evolution of the estuarine sand bar, it is believed that there were large shoals in the Yangtze River channel in the middle-Holocene. The Liangzhu ancestors around 5000 cal BP had the ability of making canoes over 8 m. Based on the archaeological research of the Neolithic period, the evolution of the Yangtze River channel in the Holocene, the history of ancient Chinese shipbuilding, and the modern examples of crossing the Yangtze River with boat, it can be concluded that the present Changzhou–Jiangyin–Zhangjiagang line should be the main and reasonable route for the Liangzhu culture migrating across the Yangtze River.

Oxidation of petrogenic organic carbon in a large river-dominated estuary

Riverine export of petrogenic organic carbon (OCpetro) from continents to coastal oceans is a dynamic component of the global carbon budget and affects the long-term atmospheric carbon reservoir. In large fluvial systems, oxidation of OCpetro during transit releases a large flux of carbon dioxide to the atmosphere, influencing climate changes; however, the transport and fate of OCpetro and their controls along the fluvial–marine transition remain poorly constrained. Here, we combined Raman spectral, radiocarbon activity (F14C), mineralogical, and sedimentological techniques with multiple geochemical analyses to characterize the dynamics of OCpetro in the water column and sediment particles from the Yangtze River channel–estuary–shelf continuum systems.Our data show that much of the OCpetro present in suspended sediment (POCpetro) exported by the Yangtze River is “labile” fractions (mostly disordered materials) that can be degraded or lost during transport across the estuarine continuum, whereas the OCpetro deposited in seabed sediment are characterized by highly recalcitrant, unreactive, and graphitic carbon phases. As discrete “free” particles, coarse plant debris (>63 μm) with ages of several thousand years observed in the proximal delta of the Yangtze River exhibit nearly identical characteristics of disordered materials, and the presence of aged vascular plant detritus (carbon-rich and 14C-depleted materials) may lead to an overestimate of OCpetro in marine sediments. Using a Bayesian endmember mixing approach, a binary mixing model, and the ratio of fraction modern carbon (F14C) to Al/OC, we found a large decrease in POCpetro concentration and loading from the suspended sediments to seabed sediments, suggesting a loss of mineral-bound OCpetro fraction during sediment transport through the estuary and deposition on the shelf. We estimated that, on average, 46 ± 35 % of the POCpetro initially present in suspended sediments delivered to the Yangtze River Estuary during a flood event was primarily oxidized at the sediment–water interface, leaving the most graphitic carbon components transported laterally and efficiently reburied in shelf sediments. We found that during estuarine mixing, flocculation process-induced microaggregates may provide transient physical protection for POCpetro in the form of inclusions/aggregates with carbonate minerals; however, when POCpetro is physically and chemically separated from its mineral matrix via disaggregation and dissolution, it may be easily oxidized by microbial activity. In contrast, OC-phyllosilicates interactions exert a first-order control on the preservation of OCpetro in marine sediments. Our findings suggest that the importance of POCpetro oxidation and loss in carbon cycling and budget assessments of estuaries may be underestimated.

Beneficial utilization of ultra-fine dredged sand from Yangtze River channel as a concrete material based on the minimum paste theory

Ultra-fine sands are dredged periodically in order to maintain the normal activities of the Yangtze River Channel. Finding a new solution for managing these ultra-fine dredged sand becomes a challenge for channel managers. In this study, ultra-fine dredged sand and manufactured sand were used as the concrete fine aggregates. The concrete mix ratio was obtained based on the minimum paste theory by setting different target strengths, Average Paste Thickness (APT) between aggregates and dredged sand contents. The feasibility of applying the minimum paste theory in the design of ultra-fine dredged sand concrete mix ratio was verified by compressive strength tests. The influences of APT and dredged sand content on the mechanical properties and workability of concrete were analyzed. The results showed that with the increase of the APT, the compressive strength initially was increased and then decreased and the workability was improved. The workability of the concrete was improved with more content of ultra-fine dredged sand through the analysis of the microstructure of the fine aggregates. The concrete with a mass ratio 25% ultra-fine dredged sand had a lower harmful porosity which was verified by mercury intrusion porosimetry (MIP) and SEM, and has a compressive strength value of 43.8 MPa at 28 days which was 11.4% and 10.61% higher than that of the control group with the content ratio of 0% and 50%, respectively. The test results proved that the use of the minimum paste theory in the design of the ultra-fine dredged sand concrete mix ratio is expected to obtain concrete with fewer paste content and proper working performance.

Provenance Shift during the Plio-Pleistocene in the Vertex of Yangtze Delta and Its Geomorphological Implications

One of the key issues of the Source-to-Sink process is revealing the geomorphological evolutions of large rivers from the perspective of river sink areas. This study aims to reveal the provenance change near the vertex of the Yangtze delta during the late Cenozoic and provide insight into the Yangtze channelization into the sea due to regional tectonic subsidence. Heavy minerals and zircon geochronology in the Plio-Pleistocene sediments of the vertex of the modern Yangtze delta (core RGK15) reveal that a significant provenance shift occurred at ~2.6 Ma (the beginning of the Pleistocene). During the Pliocene, ultra-stable heavy minerals and pre-Mesozoic zircon grains predominated in the sediments, probably derived from contemporary outcrops of sedimentary rock that were widely distributed in the delta and its surrounding area. They are completely different from those in the Pliocene sediments of the south delta, indicating that decentralized, local, small watersheds dominated the Yangtze delta during the Pliocene. This resulted from the relatively elevated terrain of this region due to the adjacent ancient Zhejiang–Fujian Uplift (ZFU) at that time. However, diversified heavy minerals and zircon geochronology similar to those of the modern upper Yangtze fingerprints occur in the Pleistocene sediments of core RGK15, implying that a significant provenance shift to the Yangtze River occurred here at ~2.6 Ma. The provenance shift recorded by the cores in the south delta mainly occurred at ~1.2 Ma, indicating that the Yangtze River channel was dragged southward with the further subsidence of the ancient Zhejiang–Fujian Uplift. This study reveals the southward migration process of the Yangtze River channel with the regional tectonic subsidence from the perspective of provenance evolution, which contributes to an understanding of when the Yangtze River channelized into the sea.

Research on Ship Exhaust Gas Accounting in Yangtze River

Based on the comparison and analysis of existing ship exhaust emission accounting methods, and combined with the characteristics of ship exhaust emissions in the Yangtze River channel, this paper selects the appropriate calculation idea, and revises the basic accounting method of ship exhaust emissions according to the calculation accuracy requirements in this paper. Finally, a calculation model for the emissions of ships in the Yangtze River channel is established, and its reliability and accuracy have been confirmed by model tests of the model data. In this paper, the Yangtze River ships are divided into sea-going ships and inland river ships, and their corresponding parameters are calculated respectively, in order to make sure that the accounting results have higher accuracy. The model has strong applicability to the exhaust emission of ships in the Yangtze River, and its calculation results are relatively accurate, and the calculation process is simple and efficient. This paper has a very high social significance and practical value for the analysis and model optimization study of the Yangtze River’s exhaust emission accounting.

Structural Design of the Waterway Regulation Project of Dongbei Waterway in the Lower Reaches of Yangtze River

In view of the navigation problem of Dongbei Waterway in the lower reaches of the Yangtze River, the evolution of riverbed and the characteristics of the obstacles are analyzed. The engineering layout scheme is determined by various methods such as model test. In the design of engineering structure, the geological conditions of the project area are analyzed through geological exploration. The applicable engineering structure form is determining, the advanced and mature bank protection and beach protection structure is adopted in the regulation of the Yangtze River channel, and the optimized structural design is adopted to strengthen the stability of project and deal with problems such as geology and strong erosion. The environmental design material and the green structure type are adopted in the structural design to meet the ecological benefits of the project, which can provide reference for the engineering design of similar channel improvement project.

Accumulation and transformation of heavy metals in surface sediments from the Yangtze River estuary to the East China Sea shelf

The concentration and speciation of heavy metals (Cu, Co, Ni, Zn, Cr, Pb and Cd) were studied in surface sediment from the Yangtze River(YR)to the East China Sea (ECS) shelf. The results showed that high contents of metals were found in the YR estuary (YRE) and in the nearshore muddy area, while lower concentrations were found in the YR channel and the ECS shelf. However, after standardization, the total content of most heavy metals from the YR showed little change or slightly increased during the transport process from the river to the estuary but decreased significantly outside the estuary, especially in the sediments of the ECS shelf. The residual fraction is the dominant fraction for all the metals, while the oxidizable and reducible fractions are the most important forms of the nonlithogenic fractions. The total amount of heavy metals from the YR to the continental shelf is mainly affected by the filtration of the estuary and the barrier impacts of the coastal current in the ECS. The environmental physicochemical conditions that vary significantly in the turbidity zone greatly influence the associated forms of metals. The metals in the acid-soluble fraction are mostly affected by the pH change in the sediment and the discharge of human activities, while the reducible fraction is significantly affected by the bottom water DO. The oxidizable fraction was affected by oxidation-reduction potential (ORP), primary productivity, as well as OM content. Therefore, with changes in the physicochemical conditions of the environment, the metals have undergone significant changes in their speciation from the YR to the ECS shelf. Various complex effects in the estuary area have not only a large filtration effect on the total amount of metals but also a major impact on the geochemical forms of the metals.

Air quality in the middle and lower reaches of the Yangtze River channel: a cruise campaign

Abstract. The Yangtze River is the longest river in China; nearly one-third of the national population lives along the river. Air quality over the Yangtze River is important as it may have significant influences on the aquatic ecosystem, the health of everyone living along the Yangtze River, and regional climate change. Chemical compositions of ambient aerosol were determined during a comprehensive cruise campaign carried out along the mid–lower reaches of the Yangtze River (MLYR) in winter of 2015. The total average concentration of PM2.5 was 119.29±33.67 µg m−3, and the dominant ionic composition in PM2.5 was SO42- with an average concentration of 15.21±6.69 µg m−3, followed by NO3- (13.76±4.99 µg m−3), NH4+ (9.38±4.35 µg m−3), and Ca2+ (2.23±1.24 µg m−3) in this cruise. Based on the filter samples, the concentration and chemical composition of PM2.5 were remarkably varied or fluctuated from coastal areas to inland over the MLYR region. Crustal elements (Ca, Mg, Al, and K) from floating dust showed peak concentrations in the Yangtze River Delta (YRD) region, while secondary inorganic species (SO42-, NO3-, and NH4+) and some of the most enriched elements (Pb, As, Se, and Cd) presented high levels in central China (Wuhan region). The significant correlation between Se and SO42- suggested that coal combustion may play an important role in secondary inorganic aerosol formation. The relatively high enrichment factors (EFs) of Ca (EFs >100) suggested the crustal elements may derive from anthropogenic sources. Furthermore, the concentration of levoglucosan in PM2.5 and the CO column level from satellite observation were greatly enhanced in the rural areas (Anhui and Jiangxi), indicating that biomass burning may make a remarkable contribution to rural areas. The concentrations of typical tracer for heavy oil (V and Ni) significantly increased in the Shanghai port, which was mainly ascribed to ship emissions, based on the air mass source analysis and the relatively high ratio of V ∕ Ni as well. The results shown herein portray a good picture of air pollution along the Yangtze River.

Remote Sensing of Hydrological Changes in Tian-e-Zhou Oxbow Lake, an Ungauged Area of the Yangtze River Basin

The hydrological pattern changes have a great influence on the wetland environment. However, some important wetland areas often lack historical observations due to economic and physical conditions. The Tian-e-Zhou oxbow lake wetland is an important habitat for two endangered species and also has very little historical hydrological data. Remote sensing images can be used to explore the historical water area fluctuation of lakes. In addition, remote sensing can also be used to obtain historical water levels based on the water boundary elevation integrated with a topographic data (WBET) method or the level-surface area relationship curve (LRC) method. In order to minimize the uncertainty of the derived results, both methods were introduced in the extraction of the water level of Tian-e-Zhou during 1992–2015. The results reveal that the hydrological regime of the oxbow lake has experienced a significant change after the Shatanzi Levee construction in 1998. With the impact of the levee, the mean annual water surface area of the lake was reduced by 5.8 km2 during the flood season, but, during the non-flood season, it was increased by 1.35 km2. For the same period, the water level of the lake during the flood season also showed a 1.47 m (WBET method) or 3.21 m (LRC method) decrease. The mean annual water level increased by 1.12 m (WBET method) or 0.75 m (LRC method). Both results had a good accuracy with RMSE (root-mean-square errors) of less than 0.4 m. Furthermore, the water level differences between the Yangtze River channel and the oxbow lake increased by at least 0.5 m. It is found that the hydrological pattern of the oxbow lake changed significantly after the levee construction, which could bring some disadvantages to the habitats of the two endangered species.

Study on Sinking-Sliding Failure Mechanism of Perilous Rock at Wangxia in Three Gorges of the Yangtze River, China

The giant perilous rock at Wangxia (named Wangxia perilous rock) is representative in Three Gorges of the Yangtze River, China, has threatened badly the navigation of the Yangtze River channel for a long period. The giant perilous rock is composed of siliceous limestone and argillaceous limestone, and includes two elements marking by W1 and W2, respectively. The W1 is an isolated pillar while the W2 is in clintheriform. The linking segment of dominant fissure in the W2 is composed by moniliform solution funnels at its back, and the locked segment of the dominant fissure at the base of the W2 is composed by two parts. For the locked part of the dominant fissure of the W2, the upper segment shows the same lithology with the perilous rock and it can be simplified as an elastic medium, for the lower segment composed by argillaceous shale and mudstone can be simplified as a strain-softening medium. Introducing the water-softened function, the constitutive curves with two kinds of medium materials for the locked segment in the dominant fissure of the W2 have been proposed. Based on energy principle, the cusp catastrophe model for perilous rock rupture is built and formulas for the transient elastic and impulsive acceleration and the elastic-impulsive velocity of perilous rock catastrophe rupture have been established. By the calculation, the elastic-impulsive acceleration for the catastrophe rupture of the W2 is 531.4 m/s2, while the average elastic-impulsive velocity is 2.608 m/s. Further, it is deduced that the elastic-impulsive velocity at the base of the W2 is about 5.2 m/s. For the transient ruture of the W2, there is a greater speed difference between the top and the base of the W2, which impels the giant perilous rock to be retroverted sliding rupture, coinciding with the fact. Undoubtedly, studies in this paper must play an important role to analyze the catastrophe rupture mechanism of giant perilous rocks at both banks in Three Gorges of the Yangtze River, China.

Research on the Strength and Space-time Distribution of Sedimentation of Yi-Zheng Segment in Phase- II Project of Deep Water Channel Construction of Yangtze River

Phase-II Project of Deep Water Channel Construction of Yangtze River(2014-2015), including the Yi-Zheng Segment, enables the water depth of Yangtze River Channel between Nanjing and Nantong arrive 12.5 meters. This thesis analyzes the sedimentation movement of Yi-Zheng Segment with mathematical model, makes prediction of the sediment's strength and space-time distribution. The simulation results indicate that the yearly dredging quantity of 1998 and 2010, two typical hydrological years, are 1.528 million m3 and 0.499 million m3 separately. The main maintenance months are October, November and December during the dry season, while the main maintenance parts are the channel from Dadaohe to Majiakou, the channel from Majiakou to Qibaidu, the channel from Qibaidu to Longmenkou in the right branch of Shiyezhou. These results could be helped to provide support of later dredging operation for keeping deep water Channel of Yi-Zheng Segment.

Assessing the potential for change in the middle Yangtze River channel following impoundment of the Three Gorges Dam

The geomorphic impacts of dams on downstream river channels are complex, not readily predictable for specific cases, but widely reported in the literature. For the Three Gorges Dam on the Yangtze (Changjiang) River in China, no studies of the impact of the changed flow and sediment conditions below the dam on the behaviour of the channel were included in the pre-dam feasibility report. We have assembled a database of flow and sediment data for the middle Yangtze River from Yichang to Hankou and used this to analyse changes following the closure of the dam. While total flow is little affected, the operating strategy for the dam that provides for storage of part of the summer high flows to maintain hydroelectric power generation in winter (the low flow season) is reflected in changes to the seasonal distribution of flow below the dam. We calculated potential sediment carrying capacity and compared it with measured sediment concentrations for both pre- and post-dam conditions. While channel sedimentation is indicated along the middle Yangtze for pre-dam conditions, scour is indicated for post-dam conditions, highest at Yichang immediately below the dam and decreasing downstream.

Shanghai Yangtze River Bridge–The Longest Road-cum-Rail Bridge in China

The Shanghai Yangtze River Bridge, which is 10 km long crossing the north Yangtze River Channel, is built to serve both highway and light-rail transit line. This paper describes the following three main problems: (1) The structure restriction system and the specialty of separate type steel box girder of the main navigation channel cable-stayed bridge. (2) The scheme conformation, structure characteristics and construction methods of the composite girder in deep water area, specially the optimization design of structure and construction step based on the condition that the whole span hoisting construction method should be used. (3) The security of light-rail train on a bridge serves both highway and light-rail transit line, mainly the feasibility and relevant research results on the problem that the light-railway is set on the cantilever of the girder.

Numerical Model for Sediment Transport and Bed Degradation in the Yangtze River Channel Downstream of Three Gorges Reservoir

This paper presents a two-dimensional morphological model for unsteady flow and both suspended-load and bed-load transport of multiple grain size to simulate transport of graded sediments downstream from the Three Gorges Reservoir. The model system includes a hydrodynamic module and a sediment module. The hydrodynamic module is based on the depth-averaged shallow water equations in orthogonal curvilinear coordinates. The sediment module describing nonuniform sediment transport is developed to include nonequilibrium transport processes, bed deformation, and bed material sorting. The model was calibrated using field observations through application to a 63-km-long alluvial river channel on the middle Yangtze River in China. A total of 16 size groups and a loose layer method of three sublayers were considered for the transport of the nonuniform bed materials in a long-term simulation. Predictions are compared with preliminary results of field observations and factors affecting the reliability of the simulated results are discussed. The results may be helpful to the development of more accurate simulation models in the future.

Variations in downstream grain-sizes to interpret sediment transport in the middle-lower Yangtze River, China: A pre-study of Three-Gorges Dam

In 2000 and 2003 before the closure of 3-Gorges Dam, numerous sediment samples were taken from the middle-lower Yangtze River channel to examine sediment transport processes and associated hydromorphological nature of the river. Analytical results show that the riverbeds consist mostly of medium to coarse sands and gravelly sands, and fine sand occurs locally, especially near the river coast. The results further indicate a downstream fining trend in riverbed sediment from Yichang to the river mouth, totaling about 1900 km long with 12 sediment zones (I-XII). These were identified as alternate coarse- and fine-grained sediment on the riverbed, although the zonation of I–III below Three-Gorges Dam site is weaker. The mode of sediment transport in the river is dominated by saltation (20–80%), followed by bed-load transport with 3–15%; transport by suspension is quite low. Grain-sizes associated with hydrological parameters have greater values in the Jingjiang Reaches (from Yichang to Chenglingji; unit stream power: 5–18 N m − 1 s − 1 , boundary shear stress: 14 Nm − 2 and mean flow velocity: 2–3.2 ms − 1 ), whereas the values obtained from Chenglingji downstream are considerably low (< 5 N m − 1 s − 1 , 1–4 Nm − 2 and < 0.7–1.5 ms − 1 ). These values, when compared with on-site measured velocity of the ADP flow column, revealed the erosive riverbed sediment transport in the Jingjiang Reaches, and the accumulative riverbed transport downstream, from Wuhan to the river coast. Hydrological parameters together with distribution of grain-sizes indicate a coarsening riverbed in the Jingjiang river, largely because damming peaked since the last half-century. This corroborates the weakening sediment zonation in the Jingjiang Reaches, which is expected to extend further downstream towards the river coast in response to the potential impact of 3-Gorges Dam in the coming decades.

Impact on the Yangtze (Changjiang) Estuary from its drainage basin: Sediment load and discharge

This paper focuses on the sediment transport and freshwater discharging from upper Yangtze drainage basin downstream, primarily on the basis of multiyear hydrological data collected from three major hydrological gauge stations (Yichang, Hankou and Datong). Data indicate highest sediment load in Yichang (5.6 × 108 t/a), lowest in Hankou (5.1× 108 t) and second highest in Datong (5.4 ×108 t). This fluctuations are identical with what has been observed from the annual flood season. About one thirds of the sediment load are trapped in the middle Yangtze River course, where meandering river pattern prevails; rest of them are directly transported to the river mouth area via lower Yangtze River channel, where the river is typically confined by the exposed base rock and almost none is being trapped, instead, minor being drained to the mainstream from the local tributaries. To recognize this sediment delivery and river flow media is vital, because it can highlight morphologic/topographic correlation between the upper drainage basin and the estuary and the erosion and siltation in the river mouth area, where extensive coast has been exclaimed and or being exclaimed, and new navigation channel and port is being constructed. It is particularly crucial for monitoring the impact on estuarine change after 3-Gorges dam being closed in 2009. Data also indicate an increase in freshwater discharging downstream (>7.7 × 1111 m3/a), of which ∼50% derived from the upstream and another half concentrated from the local tributaries. The result shows that this numerous freshwater has constantly flowed into the river mouth area to support the estuarine aquaculture and ecosystem, where it is confronted with huge amount of tidal prism (>10 times more than that of the annual runoff) transforming from offshore. Thus, a great concern for saltwater intrusion especially during the dry season is aroused, largely due to the intense upstream agriculture irrigation and large water transfer project, such as the well-planned South-North Water Transfer project.