PROGRESS OF DETRITAL ZIRCON CHRONOLOGY IN SEDIMENT PROVENANCE STUDIES IN THE YANGTZE RIVER BASIN

Evolution of the Yangtze River in East Asia is closely linked to the evolving topography following India-Eurasia collision and plays an important role in connecting the Tibetan plateau and the marginal sea, which is of great significance for understanding the evolution of modern Asian landform pattern and exploring the response of river development to tectonic uplift and monsoon evolution. Thus, many methods have been performed to reconstruct the evolution history of the Yangtze River, but there are still some disputes about the age of the Yangtze River, which has been strongly debated for over a century with estimates ranging from late Cretaceous to late Pleistocene. At present, sediment provenance tracing is one of the most important methods for studying the Yangtze River drainage evolution, for the provenance tracers could effectively represent the source area information and the various dating methods would provide reliable chronology framework. Previous studies showed that the zircon high closure temperature, wide distribution in fluvial sediment, and convenient sampling and analyzing made the zircon U-Pb dating a unique indicator recording the source area information. However, the Yangtze River drains a large basin and runs through different geological blocks with complicated lithology, as well as the abundant thermal historical events, leading to the zircon U-Pb dating a challenge work in tracing the sediment source within the Yangtze River Basin. In this study, based on the combination of previous research data and the "source to sink" system, the limitations and disadvantages of the detrital zircon U-Pb dating in the studies of sediment provenance tracing of the Yangtze River Basin were re-analyzed and re-discussed. Considering the evolving process of the large river system, some key areas and diagnostic information carrier, including bedrock and fluvial sediments deposited in present day or geo-history, would provide significant constraints on the evolution process. The former records the original information of the source region, and the latter reserves the practical information preserved in the downstream sink. As for the Yangtze River Basin, the limitation and disadvantages of the detrital zircon U-Pb dating in tracing sediment provenance are showed as follows:Firstly, six major tectonic units in the source region shows four similar age peaks, which closely corresponds to the previously identified synchronous major granitoid magmatic episodes. Five similar age peaks obviously exist in the sediment of the downstream sink both in the modern fluvial sediment and the geo-historical deposits such as outcrops and basin sediments. Thus, detrital zircon U-Pb chronology is indistinguishable from source to sink, making it unreliable in provenance tracing of the Yangtze River. Secondly, comparing with the detrital zircon spectra of tributary downstream and the upper reaches, all the tributaries below the Three Gores, the running-through of which is regarded as the symbol of the establishment of the modern Yangtze River system, could make up the similar spectra with the modern river sediments. Moreover, Sichuan Basin and Jianghan Basin, which is the last basin and first basin in western and eastern of the Three Gorges, are crucial basins for recording the incision information. However, sediment in these two basins show the similar spectra with five major age peaks from early Jurassic to late Cretaceous, which means the detrital zircon U-Pb chronology could not efficiently record the capture information no matter in spatial scale or time scale. In addition, the same results are also shown in Neogene gravel layer both in Jianghan Basin and Nanjing area. In summary, we propose that the similarity of the detrital zircon age spectra exists widely in Yangtze River system, and this greatly restricts the application of detrital zircon chronology in provenance tracing in the Yangtze River Basin, and the combination of multi-index and multi-method will shed new light in the future studies of provenance tracing within Yangtze River drainage system.     

Application and evaluation of multiple-centres ESR dating of Pliocene-Quaternary fluvial sediments: A case study from the Zhoulao core from the Jianghan Basin,middle Yangtze River basin,China

Multiple-centres electron spin resonance (MC-ESR) dating of quartz grains has been commonly applied to fluvial and lacustrine deposits and can provide a precise chronological framework for depositional histories. However, the reliability of this method for quartz grains obtained from sediments of boreholes, which are usually deposited continuously and record information regarding basin evolution and climate change, has not yet been assessed. In this study, we have initially applied the MC-ESR dating method to borehole sediments from the Zhoulao core (ZLC), located in the depocenter of the Jianghan Basin, middle Yangtze River, China. Dating of quartz grains from the ZLC using MC-ESR yields estimated ages that are generally consistent with the established paleomagnetic chronological framework. For Middle Pleistocene samples (i.e., 0.7–0.3 Ma), the Ti–Li centre provides more accurate ages than those of Al centre, which are overestimated. For Early Pleistocene samples (i.e., 2.3–0.8 Ma), both the Al centre and Ti–Li centre give highly consistent estimate ages, indicating that this is a favorable dating range for MC-ESR. Overall, the Al centre shows promise for dating Pliocene samples, whereas the Ti–Li centre is more suitable for Middle-Early Pleistocene (2.3–0.3 Ma) sediments. In addition, the deposition rate of depth ＜170 m in the ZLC is greater than those of depth ＞170 m sediments; however, the specific tectonic, climatic, or geomorphic mechanism for this change in sedimentation rate is still unclear.     

第四纪沉积物ESR年代学研究进展

在缺少第四纪火山活动的区域,沉积物成为第四纪地质构造和地貌、环境演化等方面研究的主要年代学测量对象.对于老于200ka的沉积物,电子自旋共振(ESR)是潜在的测量方法之一.ESR信号中心会在光晒退或热事件的作用下衰减或"回零".对于第四纪沉积物而言,在最后一次埋藏事件发生之前,只存在阳光晒退作用,因此了解各ESR信号中...     

OSL dating of fine-grained quartz from Holocene Yangtze delta sediments

Holocene flood events in the Yangtze River are associated with variations in East Asian Summer Monsoon (EASM) precipitation, and so Yangtze delta sediments may preserve information about the frequency and magnitude of EASM precipitation. These flood/drought cycles of the EASM directly affect the living standards of East Asian population. However, despite its importance, little chronological control is available for the Yangtze Delta sediments; because biogenic carbonate only occurs sporadically, it has proved the difficulty to discuss sedimentation mechanisms and rates in any detail.In 2013 two sediment cores (YD13-G3 and H1) were taken from the Yangtze subaqueous delta to investigate precipitation history. In this study, we investigate the potential of quartz OSL dating of the fine silt fraction (fine-grained quartz; 4–11 μm) from these cores to estimate the depositional age of the sediments. We test whether: (1) Yangtze subaqueous delta sediments contain quartz with suitable characteristics for dating, and (2) quartz grains are well-bleached during/before the transportation process, by examining a modern analogue of suspended particulate matter, and by cross-checking with the doses derived from infrared stimulated luminescence (IRSL) signals (both IR₅₀ and pIRIR₁₆₀) from feldspar in polymineral fine grains. We find that both the quartz and feldspar luminescence characteristics are satisfactory (quartz dose recovery ratio 1.067 ± 0.004; n = 250, pIRIR₁₆₀ dose recovery ratio 1.01 ± 0.02; n = 151). Modern suspended particulate matter has measured quartz equivalent doses between 0.1 and 0.2 Gy, suggesting that this material was sufficiently bleached during/before transportation to allow dating of Holocene sediments (mean dose rates of ∼3 Gy ka⁻¹). OSL ages of 44 samples from the 2 cores show apparently rapid accumulation at ∼6 ka between 9.65 and 5.50 m in core H1 and ∼2 ka throughout core G3 and between 5.0 and 0.0 m in core H1. The pIRIR₁₆₀ signals suggest less light exposure of the core top sediments and of those from the transition layer between ∼6 ka to ∼2 ka, although there is no evidence for incomplete bleaching of quartz. The question remains as to whether significant deposition took place only at these two times, or whether the record has been disturbed by erosion/reworking.     

黄河小浪底水库区断层的ESR年龄测定

为了检验应用ESR方法测定断层运动年龄的可行性,在黄河小浪底水库区内的5个断层剖面上采集了13个样品进行ESR年龄测定。结果指出;研究区内的断层活动大致发生于距今0.154—0.183Ma及0.374—0.532Ma两个时期。并对一些有关问题作了讨论,指出这是一种很有希望的确定断层活动近似年龄的新方法,在地震地质及工程地质领域中具有良好的应用前景     

ANALYSIS OF SOIL EROSION CHARACTERISTICS AND SEDIMENT SOURCES FOR THE YANTZE THREE GORGES REGION

In this paper the researches made in 1981-1990 have identified that the annual soil loss in the Three Gorges region is 157 million t. and the annual incoming sediment load of the Three Gorges reservoir is 40 million t. Soil erosion increases with the destruction of vegetative cover and its subsequent evolution. The annual amounts of sediment erosion for forest land, shrub land, grassland and farmland make up respectively 6.19%, 10.76%, 23.05% and 60% of the total erosion of the Three Gorges region; the quantities of incoming sediment load to the Yangtze River from the above four types of land account for 5.95%, 12.42%, 35.46% and 46.1 % of the total amount of sediment transported to the reservoir. The farmland of offers the main source of sediment. Gravitational erosion produces more bed loads, which will present serious threat to the Three Gorges Project if entering the reservoir. Resettlement of people to the upper parts of the mountainous areas for agricultural production will increase the sediment yield of the Three Gorges region by 10-20 million t and increase the incoming sediment of the Yangtze River by 50-60 million t. Consequently, it is necessary to make a realistic assessment of the soil erosion in the Three Gorges region.     

ESR dating of late Cenozoic molassic deposits in the Jiuxi Basin

In the Hexi Corridor, foreland depression at the north periphery of the Tibetan Plateau, late Cenozoic sediments can be divided into the lacustrine to deltaic Red Bed. The unconformably overlying coarse fan-conglomerate was shed from the northern plateau. This remarkable alternation of sedimentary environment and discontinuity reflect intensive rise of the plateau. Moreover, this suite of coarse molasses is divided into two formations as the Yumen conglomerate and the Jiuquan Gravel by another angular discontinuity. Tentatively, we applied ESR dating on this suite of molassic deposits at the Laojunmiao Section in the Jiuxi Basin, west of the Hexi Corridor, which shows that the bottom of the Yumen conglomerate and the Jiuquan Gravel are about 3.4 and 0.9 Ma respectively, indicating that the northern plateau at least experienced two intensive tectonic movements at about 3.5 and 0.9 Ma.

     

Geomorphology of the Urümqi River Valley and the uplift of the Tianshan Mountains in Quaternary

The Shaerqiaoke Gravel, more than 400 m in thickness, on the north piedmont of the Tianshan Mountains, is located at the exit of the Urümqi River Valley and belongs to the Molasse construction of the Tianshan Mountains. Another uplift event with the tectonic boundary expansion ended the deposition of the Shaerqiaoke Gravel, and resulted in folding, faulting and down-erosion in the frontier of the deposit. The ESR dating indicates that the top of the Shaerqiaoke Gravel accumulated before 1148 kaBP, probably responding to the Kunlun-Huanghe movement of the Qinghai-Tibetan plateau. After that time, erosion-deposition cycle occurred and 9 terraces developed. The TL and ESR dating techniques were employed to date these terraces, and the results indicate that Terrace 3 was formed at MIS 6. Terrace 2 at Houxia also developed simultaneously. Terraces 5 and 6 were accumulated in 338 kaBP and 562-591 kaBP, respectively. The oldest glaciation, named Gao Wangfeng, correlates to MIS 12.     

ESR dating of fluvial quartz: Estimate of the minimal distance transport required for getting a maximum optical bleaching

An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.

In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated.     

PREDICTION OF IMPACT OF THE THREE GORGES PROJECT ON ESTUARY BEACH OF THE YANGTZE RIVER

ＰＲＥＤＩＣＴＩＯＮＯＦＩＭＰＡＣＴＯＦＴＨＥＴＨＲＥＥＧＯＲＧＥＳＰＲＯＪＥＣＴＯＮＥＳＴＵＡＲＹＢＥＡＣＨＯＦＴＨＥＹＡＮＧＴＺＥＲＩＶＥＲＷｅｉｂｉｎｇＦＥＮＧ１ＹｉｇａｎｇＷＡＮＧ２ａｎｄＸｉｕｃｈｅｎｇＺＨＯＮＧ３ＡＢＳＴＲＡＣＴＡｌｔｈｏ...     

Effects of grain size on quartz ESR dating of Ti–Li center in fluvial and lacustrine sediments

The electron spin resonance (ESR) dating method has been introduced into the Quaternary chronology for nearly 40 years and has been successfully used for dating of fluvial and lacustrine sediments. In order to evaluate the possible effect of the sediment grain size on the dating estimate, the parallel ESR dating testing was carried out on quartz grains of five different size fractions ranging from 50 to 450 μm extracted from the same fluvial and lacustrine sediment collected close to the M/B boundary at the Donggutuo section, Nihewan Basin, China. The results show that equivalent doses and associated ages vary significantly. However the beta irradiation dose rate of the grains with different sizes accounts for only about 6% of the total deviation of the dating results. At the same time, the sensitivity of quartz Ti–Li center was calculated based on the additional irradiation. It shows that the larger grains are more sensitive than the smaller ones, which can leads to higher saturate ESR intensity and less equivalent dose. The variations of the sensitivity of quartz Ti–Li center of the grains with different sizes are responsible for the primary deviation of the dating results. The results also suggest that 100–150 μm grain size fraction would be priority size for the ESR dating of quartz Ti–Li center on fluvial and lacustrine sediments.     

长江三峡地区地球物理异常带的地表地质特征

通过对长江三峡地区（巴东－宜昌段）野外地质调查获得的实际资料研究,认为沿长江北西西向地球物理异常带在地不存在着相应的断层破碎带及裂隙密集带。地下深处与地球物理异常带相对应的基底断裂已切穿中、新生代沉积盖层,在地不形成一组北西西向断裂带,现代地震活动与这组断裂带有密切的关系。     

On the interest of using the multiple center approach in ESR dating of optically bleached quartz grains: Some examples from the Early Pleistocene terraces of the Alcanadre River (Ebro basin,Spain)

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula.Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.     

Luminescence dating of the late Quaternary sediments in Hangzhou Bay,China

Coastal plain of Hangzhou Bay, to the south of the present Yangtze Estuary, is closely linked to the evolution of the Yangtze River delta. However, absolute age of Pre-Holocene sediments is limited, which hinders the understanding of this area's environmental evolution. In this study, using optically stimulated luminescence (OSL), single aliquots and single grains of quartz and K-feldspar were used to date the late Quaternary sediments in coastal plain on the southern Hangzhou Bay. The vertical difference in particle size composition render either silt- or sand-sized quartz for dating. Cross-checking of multiple OSL dating methods indicated that the upper ∼65 m recorded the Holocene part of the succession; sediment from a depth of 136.6 m was dated to ∼180 ka. It was found that the single-grain method was more reliable in comparison to single-aliquot age, the former minimized the effect of signal components. Single-grain quartz and K-feldspar luminescence yielded consistent ages at sample depth of 136.6 m (∼160–180 ka), while the latter gave robust age at depth of 115.5 m (∼150 ka). This chronology is in general in accordance with neighbouring cores and can constrain paleomagnetic dating results in those cores. Taking together, the study site has thickest Holocene deposits in comparison to the highland centered around Taihu Lake on the southern Yangtze delta. Moreover, the luminescence characteristics of quartz from different sample depths, behaved differently with respect to luminescence sensitivity, signal components and saturation level, perhaps reflecting varied provenance and weathering characteristics caused by climate change.     

Shrinking of Dongting Lake and its weakening connection with the Yangtze River:Analysis of the impact on flooding

In this article,the shrinking of Dongting Lake and its progressively weakening connection with the Yangtze River and their impact on flooding before and after the implementation of the Three Gorges Project are analyzed.In recent decades,human activity combined with natural processes has altered the flow of the middle reach channel of the Yangtze River and interfered with its connection with Dongting Lake.This has resulted in progressively more frequent flooding in the area.This study uses hydrological data to analyze the annual maximum discharge and annual maximum stage development of the middle reach of the Yangtze River and Dongting Lake.In recent decades before the Three Gorges Project became operational in 2003,the annual maximum discharge and the maximum stage recorded in the middle reach of the river downstream of Dongting Lake had increased,a result of the weakening of the flood regulation function of Dongting Lake;the annual maximum stage at Luoshan station(downstream,close to the confluence of the Yangtze River and Dongting Lake) had risen by about 2.0 m during 1955-2005,(1.5 m attributed to annual maximum discharge and 0.5 m to river channel deposition).Observational data recorded after the Three Gorges Project was put into operation in 2003,it can be seen that deposition in the Dongting Lake has nearly ceased and the lake's connection with the Yangtze River is stable.It is evident that the flood regulation function of Dongting Lake will continue,and that during the lifetime of the Three Gorges Project,the flood situation in the middle reach of the Yangtze River and Dongting Lake will remain stable.     

基于树形结构的地震数据库系统设计方法

地震观测数据的大量增长给数据管理提出了新的要求. 本文将树形结构引入到数据库设计中, 提出了基于树形结构设计关系数据库的方法. 该方法简单、 直观、 易于数据的组织, 可以简化数据库的设计过程. 在ldquo;长江三峡工程诱发地震监测系统地震监测总站数据库rdquo;设计中应用了该方法, 并取得了良好的效果.      

DISCUSSION ON THE TIMING AND ITS TECTONIC SIGNIFICANCE OF ANGULAR UNCONFORMITY IN HETAO BASIN IN THE LATE QUATERNARY SEDIMENTS

The interaction between the continental-continental collision of the Indian-Eurasian plate and the westward underthrusting of Pacific plate is generally considered to be the cause of the destruction of North China Craton. At present, there are still doubts in the researches worldwide about the dynamic mechanism of the formation and evolution of the Ordos peripheral fault-depression system and the contemporary tectonic stress field.
The Hetao Basin is a Cenozoic fault basin located between the Ordos block and the Yinshan Mountains. Due to the effect of uplift of the Tibet Plateau and the continuous subduction of the Pacific plate, graben faulting of different intensities occurred in different periods of Cenozoic around the Ordos block. Late Quaternary lacustrine facies sedimentary strata are widely developed in Hetao Basin. The Haolaigou profile, Bianqianhao profile and the Langshan profile in this study are all located in Hetao Basin. According to the lithology and structural analysis of the upper Pleistocene series in the three profiles, angular unconformities of phase 1-2 are recorded in the lacustrine facies sediments with a thickness of about 10m. The dating results of the Haolaigou profile, Bianqianhao profile and Langshan profile show that the formation time of both unconformities is 80ka BP.
Using the tectonic geology, Quaternary geology, stratigraphy, sedimentology and a variety of dating methods, we also carry out a comprehensive study and obtain the following results:
(1)The analysis of lithological and structural features of Haolaigou profile, Bianqianghao profile and Langshan profile in the Hetao Basin shows that multi-phase angular unconformities events are recorded in the lacustrine strata of a thickness of nearly 10m. These unconformities represent the tectonic movement in the late Pleistocene period since the 80ka BP and they may be widely distributed in the North China region. They are probably the direct products of the latest tectonic movement in the Quaternary period.
(2)The present tectonic movement initiates at about 80ka BP. It not only causes multiple angular unconformity events, but also leads to the disappearance of the Hetao ancient lake. The rapid regional epeirogenetic uplifting of the Ordos block since 76.4ka BP should also be the specific manifestation of this tectonic movement. Because of the influence of the accelerated uplifting and eastward spreading of the Qinghai-Tibet plateau in the late Quaternary, the NEE thrusting effect of the Ordos block is enhanced and affected.     

A new era of flood control strategies from the perspective of managing the 2020 Yangtze River flood

Flood control of the Yangtze River is an important part of China’s national water security.In July 2020,due to continuous heavy rainfall,the water levels along the middle-lower reaches of the Yangtze River and major lakes constantly exceeded the warning levels,in which Taihu Lake exceeded its highest safety water level and some stations of Poyang Lake reached their highest water levels in its history.In August 2020,another huge flood occurred in the Minjiang River and the Jialing River in the upper Yangtze River,and some areas of Chongqing Municipality and other cities along the rivers were inundated,resulting in great pressure on flood control and high disaster losses.The 2020 Yangtze River flood has received extensive media coverage and raised concerns on the roles of the Three Gorges Dam and other large reservoirs in flood control.Here we analyze the changes in the pattern of the Yangtze River flood control by comparing the strategies to tackle the three heavy floods occurring in 1954,1998,and 2020.We propose that the overall strategy of the Yangtze River flood control in the new era should adhere to the principle of"Integration of storage and drainage over the entire Yangtze River Basin,with draining floods downstream as the first priority"by using both engineering and non-engineering measures.On the basis of embankments,the engineering measures should use the Three Gorges Dam and other large reservoirs as the major regulatory means,promote the construction of key flood detention areas,keep the floodways clear,and maintain the ecosystem services of wetlands and shoals.In terms of non-engineering measures,we should strengthen adaptive flood risk management under climate change,standardize the use of lands in flood detention areas,give space to floods,and promote the implementation of flood risk maps and flood insurance policies.The ultimate goal of this new flood control system is to enhance the adaptability to frequent floods and increase the resilience to extreme flood disasters.     

Deciphering the Holocene evolution of the St. Lawrence River drainage system using luminescence and radiocarbon dating

The St. Lawrence River is an important drainage route for eastern North American fresh waters. Following Late Pleistocene deglaciation, several fluctuations in base level have fine-tuned the evolution of the ancestral St. Lawrence. These fluctuations are hereby dated using K-feldspar infrared stimulated luminescence (IRSL) and radiocarbon. The accuracy of the individual IRSL dates was achieved by properly correcting for thermal transfer and anomalous fading. For each site investigated, widely used statistical approaches in equivalent dose data have been used to establish which age model, the central or the minimum model, would be appropriate to define the “true” depositional age. The chronology of the succession of regional lake levels is based on careful mapping and dating of the regional dunes, beaches and deltaic sediments. A relative time-space evolution history could be drawn, from ca. 8000 years BP to the present time period. Three major fluctuations are documented for the middle to late Holocene. An unexpected finding, from the ages cluster diagram, is that there have been times in the recent past (ca. 1000–4000 years BP) when the river level was lower or at the same elevation as today. The potential for K-feldspar IRSL to accurately date the Holocene lacustrine evolution is critical in the St. Lawrence River modern drainage basin, an environment that might be negatively impacted over the next century.     

FLUVIAL PROCESSES IN THE LOWER JINGJIANG RIVER：IMPACT OF THE THREE GORGES RESERVOIR IMPOUNDMENT

Sediment supply to the lower Jingjiang River will be subject to substantial reduction after the impoundment of the Three Gorges Reservoir, which could result in an excess of carrying capacity and serious bank erosions in the downstream alluvial channel, threatening the bank protection works and the safety of the Jingjiang Dyke. This paper presents a summary of research works concerning the fluvial processes in the lower Jingjiang River and the possible impact of the Three Gorges Reservoir impoundment on the variation of its channel pattern. Three different predictions have been put forward by researchers: 1) the Jingjiang River will evolve towards a more sinuous, meandering channel pattern, with extensive bank erosion taking place along the river; 2) the river channel will be straightened and broadened because no point bar can be formed due to reduced sediment supply while bank erosion develops in the concave bank, and 3) this river reach will maintain its present channel pattern without significant change, although the sinuosity may be slightly reduced, since: a) the Three Gorges Reservoir mainly intercept sediment particles with sizes larger than 0.025mm, and b) the complex interaction between the Yangtze River and the Dongting Lake helps to reduce the negative effect of channel erosion through certain self-adjusting mechanism in fluvial processes. Discrepancy between these predictions shows that further research efforts are needed to understand the impact of Three Gorges Reservoir operation on the downstream fluvial processes. Meanwhile, there is an urgent need to closely monitor future development in the fluvial processes of the Jingjiang River and its influence on the safety of the Jingjiang Dykes.