The sediment discharge from the Yangtze River Basin has a stepwise decreasing trend in recent years. The impounding of the Three Gorges Reservoir exacerbated this de- creasing trend and affected the change of the susp...The sediment discharge from the Yangtze River Basin has a stepwise decreasing trend in recent years. The impounding of the Three Gorges Reservoir exacerbated this de- creasing trend and affected the change of the suspended sediment concentration （SSC） in the Yangtze River Estuary through the transmission effect. The SSC data of the Yangtze River Estuary during 1959-2012 showed that： （1） The SSC in the South Branch of the Yang- tze River in the estuary and in the off-shore sea area displayed decreasing trends and de- creased less towards the sea. At the same time, the difference in decreasing magnitude be- tween SSC and sediment discharge became bigger towards the sea. （2） For the North Branch the preferential flow did not change much but the SSC tended to decrease, which was mainly caused by the decrease of SSC in the South Branch and China East Sea. （3） Due to the de- creased runoff and the relatively strengthened tide, the peak area of the SSC in the bar shoal section in 2003-2012 moved inward for about 1/6 longitude unit compared with that in 1984-2002, and the inward-moving distance was in the order of flood season 〉 annual average 〉 dry season. （4） In the inlet of the South Passage, the SSC decreased mainly because the increase caused by resuspension and shore-groove exchange was less than the decrease caused by the sharp SSC decrease in the basin and the sea areas. The reverse was true in the middle section, where the SSC showed an increasing trend. （5） In the inlet of the North Passage, under the combined influence of decreased flow split and sediment split ratios, the decreased SSC in the basin and the sea area and decreased amount of resuspension, the SSC displayed a decreasing trend. In the middle section, because the increased amount caused by sediment going over the dyke was markedly more than the decreased amount caused by external environments, the SSC tended to increase. Holistically, the sharp decrease in sediment discharge caused synchronized SSC decreases in the Yangtze River Estuary. But there were still areas, where the SSC displayed increasing trends, indicatingsynchronicity and difference in the response of SSC to the sharp decrease in sediment discharge from the basin.展开更多
River basin reservoir construction affects water and sediment transport processes in downstream reaches. The downstream impact of the Three Gorges Projects （TGP） has started to become apparent： （1） reduction in f...River basin reservoir construction affects water and sediment transport processes in downstream reaches. The downstream impact of the Three Gorges Projects （TGP） has started to become apparent： （1） reduction in flood duration and discharge, and significant reduction in sediment load. Although there was some restoration in downstream sediment load, the total amount did not exceed the pre-impoundment annual average; （2） in 2003-2014 the d 〉 0.125 mm （coarse sand） load was restored to some degree, and to a maximum at Jianli Station, which was mainly at the pre-impoundment average. After restoration, erosion and deposition characteristics of the sediment was identical to that before impoundment. The degree of restoration during 2008-2014 was less than during 2003-2007; （3） after TGP im- poundment, there was some restoration in d 〈 0.125 mm （fine sand） sediment load, however, it was {ower than the pre-impoundment average; （4） due to riverbed compensation, the d 〉 0.125 mm sediment load recovered to a certain degree after impoundment, however, the total did not exceed 4400x104 t/y. This was mainly limited by flood duration and the average flow rate, and was less affected by upstream main stream, tributaries, or lakes. Restoration of d 〈 0.125 mm suspended sediment was largely controlled by upstream main stream, tributaries, and lakes, as well as by riverbed compensation. Due to bed armoring, riverbed fine suspended sediment compensation capability was weakened; （5） during 2003-2007 and 2008-2014, Yichang to Zhicheng and upper Jingjiang experienced coarse and fine erosion,lower Jingjiang experienced coarse deposition and fine erosion, Hankou to Datong had coarse deposition and fine erosion, and Chenglingji and Hankou was characterized by coarse deposition and fine sand erosion in 2003-2007, and coarse and fine erosion in 2008-2014. This difference was controlled by flood duration and number at Luoshan Station.展开更多
According to the mechanism of sediment suspension under waves, namely, the main reason of sediment suspension changes from the turbulent mixing in the bottom boundary layer to the periodic motion of the water particle...According to the mechanism of sediment suspension under waves, namely, the main reason of sediment suspension changes from the turbulent mixing in the bottom boundary layer to the periodic motion of the water particle near the free water surface, a three-layer model of sediment concentration distribution due to waves is presented along the whole water depth based on the concept of the finite mixing length. 1he determination of the parameters in the model is discussed and an empirical formula is suggested. Comparisons between the calculated results and the measurements indicate that the resuits of the model agree well with the data from both the large and small scale flume experiments.展开更多
In order to determine how the subaqueous delta evolution depends on the water and sediment processes in the Yangtze Estuary, the amounts of water and sediment discharged into the estuary were studied. The results show...In order to determine how the subaqueous delta evolution depends on the water and sediment processes in the Yangtze Estuary, the amounts of water and sediment discharged into the estuary were studied. The results show that, during the period from 1950 to 2010, there was no significant change in the annual water discharge, and the multi-annual mean water discharge increased in dry seasons and decreased in flood seasons. However, the annual sediment discharge and the multi-annual mean sediment discharge in flood and dry seasons took on a decreasing trend, and the intra-annual distribution of water and sediment discharges tended to be uniform. The evolution process from deposition to erosion occurred at the -10 m and -20 m isobaths of the subaqueous delta. The enhanced annual water and sediment discharges had a silting-up effect on the delta, and the effect of sediment was greater than that of water. Based on data analysis, empirical curves were built to present the relationships between the water and sediment discharges over a year or in dry and flood seasons and the erosion/deposition rates in typical regions of the suhaqueous delta, whose evolution followed the pattern of silting in flood seasons and scouring in dry seasons. Notably, the Three Gorges Dam has changed the distribution processes of water and sediment discharges, and the dam＇s regulating and reserving functions can benefit the subaqueous delta deposition when the annual water and sediment discharges are not affected.展开更多
Sediment distribution is important for morphodynamic evolution and shoreline changes in coastal zones and estuaries. In the study, the data of 230 surface sediment samples collected from the Xiamen Bay sea area in Sep...Sediment distribution is important for morphodynamic evolution and shoreline changes in coastal zones and estuaries. In the study, the data of 230 surface sediment samples collected from the Xiamen Bay sea area in September 2008 are used to investigate the spatial distribution and sediment transport pathway. The grain size distribution of surficial sediments in the Xiamen Bay area is shown distinctly in this study. In addition, the Grain Size Transport Analysis model is used for conveying trend analysis of the sediment in this area, particularly for determining the sediment movement trend. The results indicate that eight sediment types are present for samples, with clayey silt comprising the highest percentage in the study area at 65.22%. Moreover, in the different subareas, the characteristics of grain size parameters are obviously different owing to different sediment sources and hydrodynamic conditions. Furthermore, runoff, tides, and waves are the main forces dominating sediment dynamics on the seabed and tidal flats, and the sediment movement trend is closely related to hydrodynamic conditions.展开更多
Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary we...Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary were analyzed in depth, and the effects of natural mechanism and human activities were discussed. The results show that： （1） In recent years （2006-2013）, the median grain size of sediment and the distribution pattern of grouped sediments in the adjacent continental shelf area to the Yangtze Estuary have presented no obvious change compared with those before 2006; （2） The median diameter of the surface sediment in the continental shelf area displayed a coarsening trend with the decrease of sediment discharge from the basin and the drop in suspended sediment concentration in the shore area; （3） In 2004-2007, the sand-silt boundary in the north part （31 ~30＇N） of the continental shelf area presented no significant changes, while that in the south part （31~30＇S） moved inwards; In 2008-2013, both the sand-silt boundaries in the north and south parts of the continental shelf area moved inwards, mainly due to the fact that in the dry season, a relatively enhanced hydrodynamic force of the tides was generated in the Yangtze River, as well as a decreased suspended sediment concentration and a flow along the banks in North Jiangsu; （4） The mud area where the maximum deposition rate is found in the Yangtze Estuary, tends to shrink due to the drop in sediment discharge from the basin, and the decrease in suspended sediment concentration in the shore area and erosion in the delta. Moreover, it tended to shift to the south at the same time because the implement of the training works on the deep-water channel of the North Passage changed the split ratio between the North and South Passages with an increase in the power of the discharged runoff in the South Passage.展开更多
Coastal overwash is a natural phenomenon that commonly occurs during storm events and can cause considerable changes in nearshore morphology within a short time.In this study,a complete set of empirical overwash trans...Coastal overwash is a natural phenomenon that commonly occurs during storm events and can cause considerable changes in nearshore morphology within a short time.In this study,a complete set of empirical overwash transport algorithms is developed and introduced into a phase-averaged wave-current-sediment transport coupling model that integrates the Finite-Volume Community Ocean Model(FVCOM)and the Simulating Waves Nearshore(SWAN)model.The resulting morphological evolution model can simulate coastal overwash.Validation against the data obtained from multiple sets of laboratory overwash experiments demonstrates that the model performs relatively well in simulating morphological changes caused by runup overwash and inundation overwash under different hydrodynamic and beach profile conditions.The sensitivity of each empirical coefficient in the overwash transport algorithms is comprehensively analyzed.The effects of each coefficient on the output of the model are discussed,and a recommended value range is provided for each coefficient.展开更多
In this study, data measured from 1955–2016 were analysed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam（TGD） after the impoundment...In this study, data measured from 1955–2016 were analysed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam（TGD） after the impoundment of the dam. The results highlight the following facts：（1） for the same flow, the low water level decreased, flood water level changed little, lowest water level increased, and highest water level decreased at the hydrological stations in the downstream of the dam;（2） the distribution of erosion and deposition along the river channel changed from ＂erosion at channels and deposition at bankfulls＂ to ＂erosion at both channels and bankfulls;＂ the ratio of low-water channel erosion to bankfull channel erosion was 95.5% from October 2002 to October 2015, with variations between different impoundment stages;（3） the low water level decrease slowed down during the channel erosion in the Upper Jingjiang reach and reaches upstream but sped up in the Lower Jingjiang reach and reaches downstream; measures should be taken to prevent the decrease in the channel water level;（4） erosion was the basis for channel dimension upscaling in the middle reaches of the Yangtze River; the low water level decrease was smaller than the thalweg decline; both channel water depth and width increased under the combined effects of channel and waterway regulations; and（5） the geometry of the channels above bankfulls did not significantly change; however, the comprehensive channel resistance increased under the combined effects of riverbed coarsening, beach vegetation, and human activities; as a result, the flood water level increased markedly and moderate flood to high water level phenomena occurred, which should be considered. The Three Gorges Reservoir effectively enhances the flood defense capacity of the middle and lower reaches of the Yangtze River; however, the superposition effect of tributary floods cannot be ruled out.展开更多
Quarter circular breakwater （QCB） is a new-type breakwater developed from senti-circular breakwater （SCB）. The superstructure of QCB is composed of a quarter circular front wall, a horizontal base slab and a verti...Quarter circular breakwater （QCB） is a new-type breakwater developed from senti-circular breakwater （SCB）. The superstructure of QCB is composed of a quarter circular front wall, a horizontal base slab and a vertical rear wall. The width of QCB＇ s base slab is about half that of SCB, which makes QCB suitable to be used on relatively finn soil foundation. The numerical wave flume based on the Reynolds averaged Navier-Stokes equations for impressible viscosity fluid is adopted in this paper to simulate the hydraulic performances of QCB. Since the geometry of both breakwaters is similar and SCB has been studied in depth, the hydraulic performances of QCB are given in comparison with those of SCB.展开更多
The waterway in the middle and lower reaches of the Yangtze River has long been known as the Golden Waterway and has served as an important link in the construction of the Yangtze River Economic Belt.Therefore,expandi...The waterway in the middle and lower reaches of the Yangtze River has long been known as the Golden Waterway and has served as an important link in the construction of the Yangtze River Economic Belt.Therefore,expanding its dimensions is a significant goal,particularly given the long-range cumulative erosion occurring downstream of the Three Gorges Dam (TGD),which has been concentrated in the dry river channel.With the regulation of the volume from upstream reservoirs and the TGD,the minimum discharge and water level of the river downstream are increasing,and creating favorable conditions for the increase of the depth of the waterway.The discharge compensation effect during the dry season offsets the decline in the water level of the river channel caused by the down-cutting of part of the riverbed,but the minimum navigable water level of the segment near the dam still shows a declining trend.In recent years,several waterway remediation projects have been implemented in the downstream reaches of the TGD and although the waterway depth and width have been increased,the channel dimensions are still insufficient in the Yichang-Anqing reach (with a total length of 1026 km),as compared to the upstream reservoir area and the deep water channel in the downstream tidal reaches.A comprehensive analysis of the water depth and the number and length of shoals in the waterway indicates that its dimensions can be increased to 4.5 m ×200 m and 6.0 m×200 m in the Yichang-Wuhan and Wuhan-Anqing reaches,respectively.This is also feasible given the remediation technologies currently available,but remediation projects need to be coordinated with those for flood prevention and ecological protection.展开更多
Alluvial channel has always adjusted itself to the equilibrium state of sediment transport after it was artificially or naturally disturbed. How to maintain the equilibrium state of sediment transport and keep the riv...Alluvial channel has always adjusted itself to the equilibrium state of sediment transport after it was artificially or naturally disturbed. How to maintain the equilibrium state of sediment transport and keep the river regime stable has always been the concerns of fluvial geomorphologists. The channel in the middle and lower reaches of the Yangtze River is characterized by the staggered distribution of the bifurcated river and the single-thread river. The change of river regime is more violently in the bifurcated river than in the single-thread river. Whether the adjustment of the river regime in the bifurcated river can pass through the single-thread river and propagate to the downstream reaches affects the stabilities of the overall river regime. Studies show that the barrier river reach can block the upstream channel adjustment from propagating to the downstream reaches; therefore, it plays a key role in stabilizing the river regime. This study investigates 34 single-thread river reaches in the mid- dle and lower reaches of the Yangtze River. On the basis of the systematic summarization of the fluvial process of the middle and lower reaches of the Yangtze River, the control factors of barrier river reach are summarized and extracted： the planar morphology of single-thread and meandering; with no flow deflecting node distributed in the upper or middle part of the river reach; the hydraulic geometric coefficient is less than 4; the longitudinal gradient is greater than 12‰, the clay content of the concave bank is greater than 9.5%, and the median diameter of the bed sediment is greater than 0.158 mm. From the Navier-Stokes equation ,the calculation formula of the bending radius of flow dynamic axis is deduced and then the roles of these control factors on restricting the migration of the flow dynamic axis and the formation of the barrier river reach are analyzed. The barrier river reach is considered Such. When the ratio of the migration force of the flow dynamic boundary is less than 1 under different flow levels axis to the constraint force of the channel boundary is less than 1 under different flow levels.The mechanism of the barrier river reach is such that even when the upstream river regime adjusts, the channel boundary of this reach can always constrain the migration amplitude of the flow dynamic axis and centralize the planar position of the main stream line under different upstream river regime conditions, pro- viding a relatively stable incoming flow conditions for the downstream reaches, thereby blocking the upstream river regime adjustment from propagating to the downstream reaches.展开更多
The characteristics of three-dimensional （3-D） tidal current in the Oujiang Estuary are investigated according to in situ observations. The Oujiang Estuary has features of irregular coastline, complex topography, ma...The characteristics of three-dimensional （3-D） tidal current in the Oujiang Estuary are investigated according to in situ observations. The Oujiang Estuary has features of irregular coastline, complex topography, many islands, moveable boundary, and submerged dyke, therefore, σ 3-D numerical model oil an unstructured triangular grid has been degeloped. The σ coordinate transforination, the moveable boundary and submerged dyke treatment techniques were employed in the model so it is suitable for the tidal simulations in the Oujing Estuary with submerged dyke and moveable boundary problems. The model is evaluated with the in situ data, and the results show that the calculated water elevations at 19 stations and currents at 19 profiler stations are in good agreement with measured data both in magnitude and phase. This numerical model is applied to the 3-D tidal circulation simulations of experiments in stopping flow transport through the South Branch of the Oujiang Estuary, and the feasibility to cutoff the flow in the South Branch of the Oujiang Estuary is demonstrated by numerical simulation experiments. The developed numerical model simulated the 3-D tidal current circulations in complicated coastal and estuarine waters very well.展开更多
A process-based 3D numerical model for surfzone hydrodynamics and beach evolution was established. Comparisons between the experimental data and model results proved that the model could effectively describe the hydro...A process-based 3D numerical model for surfzone hydrodynamics and beach evolution was established. Comparisons between the experimental data and model results proved that the model could effectively describe the hydrodynamics, sediment transport feature and sandbar migration process in the surfzone with satisfactory precision. A series of numerical simulations on the wave breaking and shoaling up to a barred beach were carried out based on the model system. Analyzed from the model results, the wave-induced current system in the surfzone consists of two major processes, which are the phase-averaged undertow caused by wave breaking and the net drift caused by both of the nonlinear wave motion and surface roller effect. When storm waves come to the barred beach, the strong offshore undertow along the beach suppresses the onshore net drift, making the initial sandbar migrate to the seaside. Under the condition of calm wave environment, both the undertow and net drift flow to the shoreline at the offshore side of the sandbar, and then push the initial sandbar to the shoreline. The consideration of surface roller has significant impact on the modeling results of the sandbar migration. As the roller transfer rate increases, the sandbar moves onshore especially under the storm wave condition.展开更多
The operation of large-scale reservoirs have modified water and sediment transport processes,resulting in adjustments to the river topography and water levels.The polynomial fitting method was applied to analyze the v...The operation of large-scale reservoirs have modified water and sediment transport processes,resulting in adjustments to the river topography and water levels.The polynomial fitting method was applied to analyze the variation characteristics of water levels under different water discharge values in the Jingjiang reach of the Yangtze River from 1991–2016.The segregation variable method was used to estimate the contributions of the varied riverbed evaluation,the downstream-controlled water level,and the comprehensive roughness on the altered water level at an identical flow.We find that low water levels in the Jingjiang reach of the Yangtze River from 1991–2016 are characterized by a significant downward trend,which has intensified since 2009.Riverbed scouring has been the dominate factor causing the reduced low water level while increased roughness alleviated this reduction.From 1991–2016,there was first a decrease followed by an increase in the high water level.The variation characteristic in terms of the'high flood discharge at a high water level'before 2003 transformed into a'middle flood discharge at a high water level'since 2009.The increased comprehensive roughness was the main reason for the increased high water level,where river scouring alleviated this rise.For navigation conditions and flood control,intensified riverbed scouring of the sandy reaches downstream from dams enhanced the effects that the downstream water level has on the upstream water level.This has led to an insufficient water depth in the reaches below the dams,which should receive immediate attention.The alteredvariation characteristics of the high water level have also increased the flood pressure in the middle reaches of the Yangtze River.展开更多
To get the accurate wave loads on wharf composite structure,the wave force on small-scale piles and the uplift force on lower surface of caisson must be considered.Based on the Reynolds averaged Navier-Stokes (RANS)eq...To get the accurate wave loads on wharf composite structure,the wave force on small-scale piles and the uplift force on lower surface of caisson must be considered.Based on the Reynolds averaged Navier-Stokes (RANS)equations,the pore media theory and the volume of fluid(VoF)method,a three-dimensional numerical model is established.The model has been developed to simulate wave interaction with a composite structure including caisson,piles and deck.The numerical results agree very well with the experimental data on total force.The spatial distributions of the non-dimensional wave height and the maximum of wave pressure on surface of composite structure are presented and discussed.The effects of relative caisson length,relative wave height and relative caisson height on horizontal wave force are given.The result indicates that the horizontal wave force achieves maximum value at the relative caisson length of 0.18 and increases linearly with the increase of the relative caisson and wave height.It is proved that the model is an accurate and effcient numerical tool to investigate different problems of wave-structure interaction.展开更多
In order to accurately simulate strong three-dimensional （3-D） free surface flows and sediment transport, the fully 3- D non-hydrostatic pressure models are developed based on the incompressible Navier-Stokes equati...In order to accurately simulate strong three-dimensional （3-D） free surface flows and sediment transport, the fully 3- D non-hydrostatic pressure models are developed based on the incompressible Navier-Stokes equations and convection-diffusion equation of sediment concentration with the mixing triangle and quadrilateral grids. The governing equations are discretized with the unstructured finite volume method in order to provide conservation properties of mass and momentum, and flexibility with practical application. It is shown that it is first-order accurate on nonuniform plane two-dimensional （2-D） grids and second-order accurate on uniform plane grids. A third-order approximation of the vertical velocity at the top-layer is applied. In such a way, free surface zero stress boundary condition is satisfied maturely, and very few vertical layers are needed to give an accurate solution even for complex discontinuous flow and short wave simulation. The model is applied to four examples to simulate strong 3-D free surface flows and sediment transport where non-hydrostatic pressures have a considerable effect on the velocity field. The newly developed model is verified against analytical solutions with an excellent agreement.展开更多
The sea level variabilities, especially the atmosphere-driven sea level variabilities, which are diff erent in studies on diverse areas and timescales, need to be further documented in the Bohai Bay. Coastal sea level...The sea level variabilities, especially the atmosphere-driven sea level variabilities, which are diff erent in studies on diverse areas and timescales, need to be further documented in the Bohai Bay. Coastal sea level data and coincident meteorological data collected hourly at two observation stations (E1 and E2) in the Bohai Bay, which is a typical semi-enclosed coastal sea in China, are analyzed for the period from 19 August 2014 to 18 November 2014. The sub-sampled low-pass (<0.8 cpd) sea levels (SLSLs) at E1 and E2 are almost the same as each other, while the winds are not. On the whole, SLSLs at E1 and E2 are dominantly influenced by the across-shore wind;in detail, the dominant wind orientation at E1 is 65° measured clockwise from north, and SLSL at E2 is significantly influenced by the sub-sampled wind (SW) at 55°. Regression of SLSL onto the corresponding SW in dominant orientation and the atmospheric pressure is used to predict SLSL, which make the frequency of occurrences when the predicted total sea level is within 0.15 m from the observed values increase to 66.03% and 58.08% at E1 and E2 from original 36.71% and 34.80% without using it, respectively. The results indicate that for the prediction of the total sea level variability in the coastal shallow waters, the SLSL influenced by the atmospheric forcing, including local wind and atmospheric pressure, can be predicted using the multivariable linear regression model.展开更多
A staggered finite-volume technique for non-hydrostatic, small amplitude free surface flow governed by the incompressible Navier-Stokes equations is presented there is a proper balance between accuracy and computing t...A staggered finite-volume technique for non-hydrostatic, small amplitude free surface flow governed by the incompressible Navier-Stokes equations is presented there is a proper balance between accuracy and computing time. The advection and horizontal diffusion terms in the momentum equation are discretized by an integral interpolation method on the orthogonal unstructured staggered mesh and, while it has the attractive property of being conservative. The pressure-correction algorithm is employed for the non-hydrostatic pressure in order to achieve second-order temporal accuracy. A conservative scalar transport algorithm is also applied to discretize k - c equations in this model. The eddy viscosity is calculated from the k-c turbulent model. The resulting model is mass and momentum conservative. The model is verified by two examples to simulate unsteady small amplitude free surface flows where non-hydrostatic pressures have a considerable effect on the velocity field, and then applied to simulate the tidal flow in the Bohai Sea.展开更多
With the advantages on rapid construction,no limitation of extent,less influence on environment, the VLFS has been turned into the focus of coastal and offshore engineering studying.As the platform,VLFS was built as a...With the advantages on rapid construction,no limitation of extent,less influence on environment, the VLFS has been turned into the focus of coastal and offshore engineering studying.As the platform,VLFS was built as airport,huge oil house etc,and would play the role of ocean economics,politics and military.The restrictive condition of VLFS is strong wave by monsoon,seismic,serious bomb etc.The floating breakwater should be put forward to shelter VLFS.The analysis of wave condition including typhoon route,archipelago and water depth is performed in this paper.The advantage and disadvantage are compared between VLFS and the marine structure from land.展开更多
基金Fund from the Ministry of Science and Technology of China,No.2010CB429002National Natural Science Foundation of China,No.51209112No.41331174
文摘The sediment discharge from the Yangtze River Basin has a stepwise decreasing trend in recent years. The impounding of the Three Gorges Reservoir exacerbated this de- creasing trend and affected the change of the suspended sediment concentration （SSC） in the Yangtze River Estuary through the transmission effect. The SSC data of the Yangtze River Estuary during 1959-2012 showed that： （1） The SSC in the South Branch of the Yang- tze River in the estuary and in the off-shore sea area displayed decreasing trends and de- creased less towards the sea. At the same time, the difference in decreasing magnitude be- tween SSC and sediment discharge became bigger towards the sea. （2） For the North Branch the preferential flow did not change much but the SSC tended to decrease, which was mainly caused by the decrease of SSC in the South Branch and China East Sea. （3） Due to the de- creased runoff and the relatively strengthened tide, the peak area of the SSC in the bar shoal section in 2003-2012 moved inward for about 1/6 longitude unit compared with that in 1984-2002, and the inward-moving distance was in the order of flood season 〉 annual average 〉 dry season. （4） In the inlet of the South Passage, the SSC decreased mainly because the increase caused by resuspension and shore-groove exchange was less than the decrease caused by the sharp SSC decrease in the basin and the sea areas. The reverse was true in the middle section, where the SSC showed an increasing trend. （5） In the inlet of the North Passage, under the combined influence of decreased flow split and sediment split ratios, the decreased SSC in the basin and the sea area and decreased amount of resuspension, the SSC displayed a decreasing trend. In the middle section, because the increased amount caused by sediment going over the dyke was markedly more than the decreased amount caused by external environments, the SSC tended to increase. Holistically, the sharp decrease in sediment discharge caused synchronized SSC decreases in the Yangtze River Estuary. But there were still areas, where the SSC displayed increasing trends, indicatingsynchronicity and difference in the response of SSC to the sharp decrease in sediment discharge from the basin.
基金National Natural Science Foundation of China,No.51479146,No.51579123,No.51509012Fundamental Research Funds for Central Welfare Research Institutes,No.TKS160103+2 种基金No.TKS150102The National Key Research&Development Programs,No.2013BAB12B01National Key Research Program of China,No.2016YFC0402106
文摘River basin reservoir construction affects water and sediment transport processes in downstream reaches. The downstream impact of the Three Gorges Projects （TGP） has started to become apparent： （1） reduction in flood duration and discharge, and significant reduction in sediment load. Although there was some restoration in downstream sediment load, the total amount did not exceed the pre-impoundment annual average; （2） in 2003-2014 the d 〉 0.125 mm （coarse sand） load was restored to some degree, and to a maximum at Jianli Station, which was mainly at the pre-impoundment average. After restoration, erosion and deposition characteristics of the sediment was identical to that before impoundment. The degree of restoration during 2008-2014 was less than during 2003-2007; （3） after TGP im- poundment, there was some restoration in d 〈 0.125 mm （fine sand） sediment load, however, it was {ower than the pre-impoundment average; （4） due to riverbed compensation, the d 〉 0.125 mm sediment load recovered to a certain degree after impoundment, however, the total did not exceed 4400x104 t/y. This was mainly limited by flood duration and the average flow rate, and was less affected by upstream main stream, tributaries, or lakes. Restoration of d 〈 0.125 mm suspended sediment was largely controlled by upstream main stream, tributaries, and lakes, as well as by riverbed compensation. Due to bed armoring, riverbed fine suspended sediment compensation capability was weakened; （5） during 2003-2007 and 2008-2014, Yichang to Zhicheng and upper Jingjiang experienced coarse and fine erosion,lower Jingjiang experienced coarse deposition and fine erosion, Hankou to Datong had coarse deposition and fine erosion, and Chenglingji and Hankou was characterized by coarse deposition and fine sand erosion in 2003-2007, and coarse and fine erosion in 2008-2014. This difference was controlled by flood duration and number at Luoshan Station.
基金supported by the National Natural Science Foundation of China (Grant No.50279029)
文摘According to the mechanism of sediment suspension under waves, namely, the main reason of sediment suspension changes from the turbulent mixing in the bottom boundary layer to the periodic motion of the water particle near the free water surface, a three-layer model of sediment concentration distribution due to waves is presented along the whole water depth based on the concept of the finite mixing length. 1he determination of the parameters in the model is discussed and an empirical formula is suggested. Comparisons between the calculated results and the measurements indicate that the resuits of the model agree well with the data from both the large and small scale flume experiments.
基金supported by the National Basic Research Program of China(the 973 Program,Grant No.2010CB429002)
文摘In order to determine how the subaqueous delta evolution depends on the water and sediment processes in the Yangtze Estuary, the amounts of water and sediment discharged into the estuary were studied. The results show that, during the period from 1950 to 2010, there was no significant change in the annual water discharge, and the multi-annual mean water discharge increased in dry seasons and decreased in flood seasons. However, the annual sediment discharge and the multi-annual mean sediment discharge in flood and dry seasons took on a decreasing trend, and the intra-annual distribution of water and sediment discharges tended to be uniform. The evolution process from deposition to erosion occurred at the -10 m and -20 m isobaths of the subaqueous delta. The enhanced annual water and sediment discharges had a silting-up effect on the delta, and the effect of sediment was greater than that of water. Based on data analysis, empirical curves were built to present the relationships between the water and sediment discharges over a year or in dry and flood seasons and the erosion/deposition rates in typical regions of the suhaqueous delta, whose evolution followed the pattern of silting in flood seasons and scouring in dry seasons. Notably, the Three Gorges Dam has changed the distribution processes of water and sediment discharges, and the dam＇s regulating and reserving functions can benefit the subaqueous delta deposition when the annual water and sediment discharges are not affected.
基金The Open Research Fund of State Key Laboratory of Estuarine and Coastal Research under contract No.SKLEC-KF201508the Western Traffic Construction Technology Projects of the Ministry of Transport of China under contract No.2007-353-X02-160the National Natural Science Foundation of China under contract No.41306033
文摘Sediment distribution is important for morphodynamic evolution and shoreline changes in coastal zones and estuaries. In the study, the data of 230 surface sediment samples collected from the Xiamen Bay sea area in September 2008 are used to investigate the spatial distribution and sediment transport pathway. The grain size distribution of surficial sediments in the Xiamen Bay area is shown distinctly in this study. In addition, the Grain Size Transport Analysis model is used for conveying trend analysis of the sediment in this area, particularly for determining the sediment movement trend. The results indicate that eight sediment types are present for samples, with clayey silt comprising the highest percentage in the study area at 65.22%. Moreover, in the different subareas, the characteristics of grain size parameters are obviously different owing to different sediment sources and hydrodynamic conditions. Furthermore, runoff, tides, and waves are the main forces dominating sediment dynamics on the seabed and tidal flats, and the sediment movement trend is closely related to hydrodynamic conditions.
基金supported by the Fundamental Research Funds for Central Welfare Research Institutes(Grant No.TKS160103)the National Key Research and Development Program of China(Grant No.2016YFC0402106)the National Natural Science Foundation of China(Grant Nos.51579123 and 41331174)
文摘Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary were analyzed in depth, and the effects of natural mechanism and human activities were discussed. The results show that： （1） In recent years （2006-2013）, the median grain size of sediment and the distribution pattern of grouped sediments in the adjacent continental shelf area to the Yangtze Estuary have presented no obvious change compared with those before 2006; （2） The median diameter of the surface sediment in the continental shelf area displayed a coarsening trend with the decrease of sediment discharge from the basin and the drop in suspended sediment concentration in the shore area; （3） In 2004-2007, the sand-silt boundary in the north part （31 ~30＇N） of the continental shelf area presented no significant changes, while that in the south part （31~30＇S） moved inwards; In 2008-2013, both the sand-silt boundaries in the north and south parts of the continental shelf area moved inwards, mainly due to the fact that in the dry season, a relatively enhanced hydrodynamic force of the tides was generated in the Yangtze River, as well as a decreased suspended sediment concentration and a flow along the banks in North Jiangsu; （4） The mud area where the maximum deposition rate is found in the Yangtze Estuary, tends to shrink due to the drop in sediment discharge from the basin, and the decrease in suspended sediment concentration in the shore area and erosion in the delta. Moreover, it tended to shift to the south at the same time because the implement of the training works on the deep-water channel of the North Passage changed the split ratio between the North and South Passages with an increase in the power of the discharged runoff in the South Passage.
基金This study is financially supported by the National Natural Science Foundation of China(Grant Nos.U1906231 and 51509183)the Tianjin Transportation Science and Technology Development Plan Project(Grant No.2020-12)the Fundamental Research Funds for the Central Public Welfare Research Institutes(Grant No.TKS20200410).
文摘Coastal overwash is a natural phenomenon that commonly occurs during storm events and can cause considerable changes in nearshore morphology within a short time.In this study,a complete set of empirical overwash transport algorithms is developed and introduced into a phase-averaged wave-current-sediment transport coupling model that integrates the Finite-Volume Community Ocean Model(FVCOM)and the Simulating Waves Nearshore(SWAN)model.The resulting morphological evolution model can simulate coastal overwash.Validation against the data obtained from multiple sets of laboratory overwash experiments demonstrates that the model performs relatively well in simulating morphological changes caused by runup overwash and inundation overwash under different hydrodynamic and beach profile conditions.The sensitivity of each empirical coefficient in the overwash transport algorithms is comprehensively analyzed.The effects of each coefficient on the output of the model are discussed,and a recommended value range is provided for each coefficient.
基金National Key Research and Development Program of China,No.2016YFC0402106National Natural Science Foundation of China,No.51579123,No.51579185,No.51339001+1 种基金Supported by the Open Research Fund Program of State Key Laboratory of Water Resources and Hydropower Engineering Science,No.2016HLG02Fundamental Research Funds for Central Welfare Research Institutes,No.TKS160103
文摘In this study, data measured from 1955–2016 were analysed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam（TGD） after the impoundment of the dam. The results highlight the following facts：（1） for the same flow, the low water level decreased, flood water level changed little, lowest water level increased, and highest water level decreased at the hydrological stations in the downstream of the dam;（2） the distribution of erosion and deposition along the river channel changed from ＂erosion at channels and deposition at bankfulls＂ to ＂erosion at both channels and bankfulls;＂ the ratio of low-water channel erosion to bankfull channel erosion was 95.5% from October 2002 to October 2015, with variations between different impoundment stages;（3） the low water level decrease slowed down during the channel erosion in the Upper Jingjiang reach and reaches upstream but sped up in the Lower Jingjiang reach and reaches downstream; measures should be taken to prevent the decrease in the channel water level;（4） erosion was the basis for channel dimension upscaling in the middle reaches of the Yangtze River; the low water level decrease was smaller than the thalweg decline; both channel water depth and width increased under the combined effects of channel and waterway regulations; and（5） the geometry of the channels above bankfulls did not significantly change; however, the comprehensive channel resistance increased under the combined effects of riverbed coarsening, beach vegetation, and human activities; as a result, the flood water level increased markedly and moderate flood to high water level phenomena occurred, which should be considered. The Three Gorges Reservoir effectively enhances the flood defense capacity of the middle and lower reaches of the Yangtze River; however, the superposition effect of tributary floods cannot be ruled out.
基金supported by the National Natural Science Foundation of China(Grant No.50779045)
文摘Quarter circular breakwater （QCB） is a new-type breakwater developed from senti-circular breakwater （SCB）. The superstructure of QCB is composed of a quarter circular front wall, a horizontal base slab and a vertical rear wall. The width of QCB＇ s base slab is about half that of SCB, which makes QCB suitable to be used on relatively finn soil foundation. The numerical wave flume based on the Reynolds averaged Navier-Stokes equations for impressible viscosity fluid is adopted in this paper to simulate the hydraulic performances of QCB. Since the geometry of both breakwaters is similar and SCB has been studied in depth, the hydraulic performances of QCB are given in comparison with those of SCB.
基金supported by the National Key Research and Development Program of China(Grants No.2016YFC0402306 and 2016YFC0402106)the National Natural Science Foundation of China(Grant No.51809131)+1 种基金the Key Laboratory of Yellow River Sediment Research,Ministry of Water Resources of China(Grant No.2016002)the Fundamental Research Funds for Central Public Welfare Research Institutes(Grants No.TKS160103,TKS180201,and TKS180411)
文摘The waterway in the middle and lower reaches of the Yangtze River has long been known as the Golden Waterway and has served as an important link in the construction of the Yangtze River Economic Belt.Therefore,expanding its dimensions is a significant goal,particularly given the long-range cumulative erosion occurring downstream of the Three Gorges Dam (TGD),which has been concentrated in the dry river channel.With the regulation of the volume from upstream reservoirs and the TGD,the minimum discharge and water level of the river downstream are increasing,and creating favorable conditions for the increase of the depth of the waterway.The discharge compensation effect during the dry season offsets the decline in the water level of the river channel caused by the down-cutting of part of the riverbed,but the minimum navigable water level of the segment near the dam still shows a declining trend.In recent years,several waterway remediation projects have been implemented in the downstream reaches of the TGD and although the waterway depth and width have been increased,the channel dimensions are still insufficient in the Yichang-Anqing reach (with a total length of 1026 km),as compared to the upstream reservoir area and the deep water channel in the downstream tidal reaches.A comprehensive analysis of the water depth and the number and length of shoals in the waterway indicates that its dimensions can be increased to 4.5 m ×200 m and 6.0 m×200 m in the Yichang-Wuhan and Wuhan-Anqing reaches,respectively.This is also feasible given the remediation technologies currently available,but remediation projects need to be coordinated with those for flood prevention and ecological protection.
基金National Natural Science Foundation of China, No.51379155, No.51339001, No.51579185 National Key Research Program of China, No.2016YFC0402306, No.2016YFC04022310, No.2016YFC0402106 CentraI Public Research Institutes Fundamental Research, No.TKS 160103
文摘Alluvial channel has always adjusted itself to the equilibrium state of sediment transport after it was artificially or naturally disturbed. How to maintain the equilibrium state of sediment transport and keep the river regime stable has always been the concerns of fluvial geomorphologists. The channel in the middle and lower reaches of the Yangtze River is characterized by the staggered distribution of the bifurcated river and the single-thread river. The change of river regime is more violently in the bifurcated river than in the single-thread river. Whether the adjustment of the river regime in the bifurcated river can pass through the single-thread river and propagate to the downstream reaches affects the stabilities of the overall river regime. Studies show that the barrier river reach can block the upstream channel adjustment from propagating to the downstream reaches; therefore, it plays a key role in stabilizing the river regime. This study investigates 34 single-thread river reaches in the mid- dle and lower reaches of the Yangtze River. On the basis of the systematic summarization of the fluvial process of the middle and lower reaches of the Yangtze River, the control factors of barrier river reach are summarized and extracted： the planar morphology of single-thread and meandering; with no flow deflecting node distributed in the upper or middle part of the river reach; the hydraulic geometric coefficient is less than 4; the longitudinal gradient is greater than 12‰, the clay content of the concave bank is greater than 9.5%, and the median diameter of the bed sediment is greater than 0.158 mm. From the Navier-Stokes equation ,the calculation formula of the bending radius of flow dynamic axis is deduced and then the roles of these control factors on restricting the migration of the flow dynamic axis and the formation of the barrier river reach are analyzed. The barrier river reach is considered Such. When the ratio of the migration force of the flow dynamic boundary is less than 1 under different flow levels axis to the constraint force of the channel boundary is less than 1 under different flow levels.The mechanism of the barrier river reach is such that even when the upstream river regime adjusts, the channel boundary of this reach can always constrain the migration amplitude of the flow dynamic axis and centralize the planar position of the main stream line under different upstream river regime conditions, pro- viding a relatively stable incoming flow conditions for the downstream reaches, thereby blocking the upstream river regime adjustment from propagating to the downstream reaches.
基金The Natural Science Foundation of Tianjin, China under contract No.08JCZDZT00200
文摘The characteristics of three-dimensional （3-D） tidal current in the Oujiang Estuary are investigated according to in situ observations. The Oujiang Estuary has features of irregular coastline, complex topography, many islands, moveable boundary, and submerged dyke, therefore, σ 3-D numerical model oil an unstructured triangular grid has been degeloped. The σ coordinate transforination, the moveable boundary and submerged dyke treatment techniques were employed in the model so it is suitable for the tidal simulations in the Oujing Estuary with submerged dyke and moveable boundary problems. The model is evaluated with the in situ data, and the results show that the calculated water elevations at 19 stations and currents at 19 profiler stations are in good agreement with measured data both in magnitude and phase. This numerical model is applied to the 3-D tidal circulation simulations of experiments in stopping flow transport through the South Branch of the Oujiang Estuary, and the feasibility to cutoff the flow in the South Branch of the Oujiang Estuary is demonstrated by numerical simulation experiments. The developed numerical model simulated the 3-D tidal current circulations in complicated coastal and estuarine waters very well.
基金financially supported by the National Key Research and Development Program of China(Grant No.2016YFC0402603)the National Natural Science Foundation of China(Grant Nos.51779112,51509119,and 51609029)+2 种基金the Project of Tianjin Natural Science Foundation(Grant No.16JCQNJC06900)the Open Project of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering(Grant No.2014492211)the Fundamental Research Funds for the Central Public Welfare Research Institutes(Grant Nos.TKS170101and TKS170202)
文摘A process-based 3D numerical model for surfzone hydrodynamics and beach evolution was established. Comparisons between the experimental data and model results proved that the model could effectively describe the hydrodynamics, sediment transport feature and sandbar migration process in the surfzone with satisfactory precision. A series of numerical simulations on the wave breaking and shoaling up to a barred beach were carried out based on the model system. Analyzed from the model results, the wave-induced current system in the surfzone consists of two major processes, which are the phase-averaged undertow caused by wave breaking and the net drift caused by both of the nonlinear wave motion and surface roller effect. When storm waves come to the barred beach, the strong offshore undertow along the beach suppresses the onshore net drift, making the initial sandbar migrate to the seaside. Under the condition of calm wave environment, both the undertow and net drift flow to the shoreline at the offshore side of the sandbar, and then push the initial sandbar to the shoreline. The consideration of surface roller has significant impact on the modeling results of the sandbar migration. As the roller transfer rate increases, the sandbar moves onshore especially under the storm wave condition.
基金National Key Research and Development Program of China,No.2018YFB1600400Open Foundation of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering,No.2017491211Fundamental Research Funds for Central Welfare Research Institutes,No.TKS20200312。
文摘The operation of large-scale reservoirs have modified water and sediment transport processes,resulting in adjustments to the river topography and water levels.The polynomial fitting method was applied to analyze the variation characteristics of water levels under different water discharge values in the Jingjiang reach of the Yangtze River from 1991–2016.The segregation variable method was used to estimate the contributions of the varied riverbed evaluation,the downstream-controlled water level,and the comprehensive roughness on the altered water level at an identical flow.We find that low water levels in the Jingjiang reach of the Yangtze River from 1991–2016 are characterized by a significant downward trend,which has intensified since 2009.Riverbed scouring has been the dominate factor causing the reduced low water level while increased roughness alleviated this reduction.From 1991–2016,there was first a decrease followed by an increase in the high water level.The variation characteristic in terms of the'high flood discharge at a high water level'before 2003 transformed into a'middle flood discharge at a high water level'since 2009.The increased comprehensive roughness was the main reason for the increased high water level,where river scouring alleviated this rise.For navigation conditions and flood control,intensified riverbed scouring of the sandy reaches downstream from dams enhanced the effects that the downstream water level has on the upstream water level.This has led to an insufficient water depth in the reaches below the dams,which should receive immediate attention.The alteredvariation characteristics of the high water level have also increased the flood pressure in the middle reaches of the Yangtze River.
基金the National Natural Science Foundation of China(Nos.51079025 and 51009022)
文摘To get the accurate wave loads on wharf composite structure,the wave force on small-scale piles and the uplift force on lower surface of caisson must be considered.Based on the Reynolds averaged Navier-Stokes (RANS)equations,the pore media theory and the volume of fluid(VoF)method,a three-dimensional numerical model is established.The model has been developed to simulate wave interaction with a composite structure including caisson,piles and deck.The numerical results agree very well with the experimental data on total force.The spatial distributions of the non-dimensional wave height and the maximum of wave pressure on surface of composite structure are presented and discussed.The effects of relative caisson length,relative wave height and relative caisson height on horizontal wave force are given.The result indicates that the horizontal wave force achieves maximum value at the relative caisson length of 0.18 and increases linearly with the increase of the relative caisson and wave height.It is proved that the model is an accurate and effcient numerical tool to investigate different problems of wave-structure interaction.
基金financially supported by the Science and Technology Project of the Ministry of Transport(Grant No.2013328352570)
文摘In order to accurately simulate strong three-dimensional （3-D） free surface flows and sediment transport, the fully 3- D non-hydrostatic pressure models are developed based on the incompressible Navier-Stokes equations and convection-diffusion equation of sediment concentration with the mixing triangle and quadrilateral grids. The governing equations are discretized with the unstructured finite volume method in order to provide conservation properties of mass and momentum, and flexibility with practical application. It is shown that it is first-order accurate on nonuniform plane two-dimensional （2-D） grids and second-order accurate on uniform plane grids. A third-order approximation of the vertical velocity at the top-layer is applied. In such a way, free surface zero stress boundary condition is satisfied maturely, and very few vertical layers are needed to give an accurate solution even for complex discontinuous flow and short wave simulation. The model is applied to four examples to simulate strong 3-D free surface flows and sediment transport where non-hydrostatic pressures have a considerable effect on the velocity field. The newly developed model is verified against analytical solutions with an excellent agreement.
基金Supported by the Fundamental Research Funds for the Central Public Welfare Research Institutes(No.TKS160224)the Key Research and Development Program of Shandong Province(No.2016ZDJS09A02)+2 种基金the National Key Research and Development Program of China(No.2016YFC1402304)the National Natural Science Foundation of China(No.41606006)the Open Fund of Key Laboratory of Engineering Sediment of the Ministry of Transport,Tianjin Research Institute for Water Transport Engineering,M.O.T
文摘The sea level variabilities, especially the atmosphere-driven sea level variabilities, which are diff erent in studies on diverse areas and timescales, need to be further documented in the Bohai Bay. Coastal sea level data and coincident meteorological data collected hourly at two observation stations (E1 and E2) in the Bohai Bay, which is a typical semi-enclosed coastal sea in China, are analyzed for the period from 19 August 2014 to 18 November 2014. The sub-sampled low-pass (<0.8 cpd) sea levels (SLSLs) at E1 and E2 are almost the same as each other, while the winds are not. On the whole, SLSLs at E1 and E2 are dominantly influenced by the across-shore wind;in detail, the dominant wind orientation at E1 is 65° measured clockwise from north, and SLSL at E2 is significantly influenced by the sub-sampled wind (SW) at 55°. Regression of SLSL onto the corresponding SW in dominant orientation and the atmospheric pressure is used to predict SLSL, which make the frequency of occurrences when the predicted total sea level is within 0.15 m from the observed values increase to 66.03% and 58.08% at E1 and E2 from original 36.71% and 34.80% without using it, respectively. The results indicate that for the prediction of the total sea level variability in the coastal shallow waters, the SLSL influenced by the atmospheric forcing, including local wind and atmospheric pressure, can be predicted using the multivariable linear regression model.
基金financially supported by the Science and Technology Project of the Ministry of Transport (Grant No. 2011329224170)
文摘A staggered finite-volume technique for non-hydrostatic, small amplitude free surface flow governed by the incompressible Navier-Stokes equations is presented there is a proper balance between accuracy and computing time. The advection and horizontal diffusion terms in the momentum equation are discretized by an integral interpolation method on the orthogonal unstructured staggered mesh and, while it has the attractive property of being conservative. The pressure-correction algorithm is employed for the non-hydrostatic pressure in order to achieve second-order temporal accuracy. A conservative scalar transport algorithm is also applied to discretize k - c equations in this model. The eddy viscosity is calculated from the k-c turbulent model. The resulting model is mass and momentum conservative. The model is verified by two examples to simulate unsteady small amplitude free surface flows where non-hydrostatic pressures have a considerable effect on the velocity field, and then applied to simulate the tidal flow in the Bohai Sea.
文摘With the advantages on rapid construction,no limitation of extent,less influence on environment, the VLFS has been turned into the focus of coastal and offshore engineering studying.As the platform,VLFS was built as airport,huge oil house etc,and would play the role of ocean economics,politics and military.The restrictive condition of VLFS is strong wave by monsoon,seismic,serious bomb etc.The floating breakwater should be put forward to shelter VLFS.The analysis of wave condition including typhoon route,archipelago and water depth is performed in this paper.The advantage and disadvantage are compared between VLFS and the marine structure from land.
