2015 Vol. 37, No. 3
Display Method:
2015, 37(3): .
Abstract:
2015, 37(3): 1-14.
doi: 10.3969/j.issn.0253-4193.2015.03.001
Abstract:
Lateral circulation,which can be generated in estuarine systems by a variety of mechanisms,plays an important role in the momentum balance and mass transport in estuaries. A three-dimensional hydrodynamic model (EFDC),combined with field measurement data in 1989 and 2002,is used to investigate the lateral circulation in the Lingding Estuary. The model have successfully reproduced the hydrodynamics and salinity distribution during the flood and dry seasons. Two cross-sectional profiles in two different regions are chosen to examine the lateral circulation and salinity dynamics in different periods. The results show that lateral circulation is poorly developed in the Lingding Estuary and features more local characteristics because of its special bathymetry and hydrodynamic conditions. The lateral circulation in the Lingding Estuary is generated by the interaction among river flow,tidal currents and bathymetry,and the mechanisms in two sections are different. In this study,we conclude that lateral circulation is not significant for the dynamics of Lingding Estuary.
Lateral circulation,which can be generated in estuarine systems by a variety of mechanisms,plays an important role in the momentum balance and mass transport in estuaries. A three-dimensional hydrodynamic model (EFDC),combined with field measurement data in 1989 and 2002,is used to investigate the lateral circulation in the Lingding Estuary. The model have successfully reproduced the hydrodynamics and salinity distribution during the flood and dry seasons. Two cross-sectional profiles in two different regions are chosen to examine the lateral circulation and salinity dynamics in different periods. The results show that lateral circulation is poorly developed in the Lingding Estuary and features more local characteristics because of its special bathymetry and hydrodynamic conditions. The lateral circulation in the Lingding Estuary is generated by the interaction among river flow,tidal currents and bathymetry,and the mechanisms in two sections are different. In this study,we conclude that lateral circulation is not significant for the dynamics of Lingding Estuary.
2015, 37(3): 15-24.
doi: 10.3969/j.issn.0253-4193.2015.03.002
Abstract:
Since 1945,thousands of nuclear experiments have been carried outin many countries. Those experiments,performed either in atmosphere or under seawater,have posed a significant distribution to the radionuclide contamination on the world oceans. The distribution and evolution process of radioactive materials in the ocean have to be studied based on the long-term pollution characters,which requires a marine radionuclides model to be established. Thus in this paper,we have established a quasi-global marine radionuclides model to study the transport,distribution and evolution of the 137Cs in the China seas,resulting from the nuclear experiments since 1945. The 137Cs is introduced into seawaters not only from the sub-water experiments but also from the global fallout due to atmospheric nuclear experiments. The simulated vertical and horizontal distribution of the 137Cs agrees well with the observation. The decaying process of the 137Cs is also presented in the simulation. The 137Cs from nuclear experiments entered in China seas since the 1940s. In the early 1960s,the concentration of 137Cs in China seas reached its maximum and then reduced gradually due to the decay of the 137Cs and the dilution from sea waters. By 2011,the concentration of 137Cs in China seas is less than 2 Bq/m3 and the concentration of 137Cs is higher in the South China Sea than in the other seas.
Since 1945,thousands of nuclear experiments have been carried outin many countries. Those experiments,performed either in atmosphere or under seawater,have posed a significant distribution to the radionuclide contamination on the world oceans. The distribution and evolution process of radioactive materials in the ocean have to be studied based on the long-term pollution characters,which requires a marine radionuclides model to be established. Thus in this paper,we have established a quasi-global marine radionuclides model to study the transport,distribution and evolution of the 137Cs in the China seas,resulting from the nuclear experiments since 1945. The 137Cs is introduced into seawaters not only from the sub-water experiments but also from the global fallout due to atmospheric nuclear experiments. The simulated vertical and horizontal distribution of the 137Cs agrees well with the observation. The decaying process of the 137Cs is also presented in the simulation. The 137Cs from nuclear experiments entered in China seas since the 1940s. In the early 1960s,the concentration of 137Cs in China seas reached its maximum and then reduced gradually due to the decay of the 137Cs and the dilution from sea waters. By 2011,the concentration of 137Cs in China seas is less than 2 Bq/m3 and the concentration of 137Cs is higher in the South China Sea than in the other seas.
2015, 37(3): 25-36.
doi: 10.3969/j.issn.0253-4193.2015.03.003
Abstract:
The impact of assimilating radar radial velocity data on the analysis and forecasting of the super typhoon "Saomai" (2006) is investigated in this study. The pre-processing and quality control are performed on radar radial velocity observations,which are further assimilated every 30 minutes into the framework of Weather Research and Forecasting (WRF) V3.5 and its three-dimensional variational data assimilation system WRF-3DVAR developed by the U.S. National Center for Atmospheric Research (NCAR). The results show that assimilating Doppler radar radial velocity can improve the typhoon initialization for wind and temperature fields,producing more meticulous mesoscale structure information. Furthermore,radial velocity data assimilation have improved the forecasting of typhoon track,minimum sea level pressure,maximum wind speed,and precipitation. The analysis and forecasting performances can be further improved by reducing the background length-scale.
The impact of assimilating radar radial velocity data on the analysis and forecasting of the super typhoon "Saomai" (2006) is investigated in this study. The pre-processing and quality control are performed on radar radial velocity observations,which are further assimilated every 30 minutes into the framework of Weather Research and Forecasting (WRF) V3.5 and its three-dimensional variational data assimilation system WRF-3DVAR developed by the U.S. National Center for Atmospheric Research (NCAR). The results show that assimilating Doppler radar radial velocity can improve the typhoon initialization for wind and temperature fields,producing more meticulous mesoscale structure information. Furthermore,radial velocity data assimilation have improved the forecasting of typhoon track,minimum sea level pressure,maximum wind speed,and precipitation. The analysis and forecasting performances can be further improved by reducing the background length-scale.
2015, 37(3): 37-45.
doi: 10.3969/j.issn.0253-4193.2015.03.004
Abstract:
A three-layer tsunami model was established utilizing COMCOT numerical model to simulate the generation and propagation of 2011 Tohoku-Oki earthquake tsunami event. The numerical results show that the errors between the computed arrive time and wave height and the observations at the DARTs near earthquake source and the tide gauge stations along Zhejiang coast are less than 15%. Studies show that Japan Nankai Trough,Okinawa Trough and South Ryukyu Trench would be the major potential regional tsunami sources which may threaten Zhejiang coast. Three hypothetical events of the above sources with Mw9.1,Mw8.0 and Mw8.7 earthquakes were studied by the model to assess their impacts on Zhejiang coast. The numerical results show that the tsunami waves generated by three hypothetical events would take 3 to 8 hours to reach the Zhejiang coast area,and the amplitude could vary between 1 and 3 m,with the maximum wave up to 4 m. The simulation indicates that the study area would face the tsunami hazards with level Ⅲ or level Ⅳ,which can cause inundation or serious inundation risk.
A three-layer tsunami model was established utilizing COMCOT numerical model to simulate the generation and propagation of 2011 Tohoku-Oki earthquake tsunami event. The numerical results show that the errors between the computed arrive time and wave height and the observations at the DARTs near earthquake source and the tide gauge stations along Zhejiang coast are less than 15%. Studies show that Japan Nankai Trough,Okinawa Trough and South Ryukyu Trench would be the major potential regional tsunami sources which may threaten Zhejiang coast. Three hypothetical events of the above sources with Mw9.1,Mw8.0 and Mw8.7 earthquakes were studied by the model to assess their impacts on Zhejiang coast. The numerical results show that the tsunami waves generated by three hypothetical events would take 3 to 8 hours to reach the Zhejiang coast area,and the amplitude could vary between 1 and 3 m,with the maximum wave up to 4 m. The simulation indicates that the study area would face the tsunami hazards with level Ⅲ or level Ⅳ,which can cause inundation or serious inundation risk.
2015, 37(3): 46-53.
doi: 10.3969/j.issn.0253-4193.2015.03.005
Abstract:
Aquarius is a spaceborne L-band radiometer whose mission focuses on the measurement of sea surface salinity from space. Aquarius was successfully launched on June 2011 and has been working operationally for more than two years. This research shows the preliminary results of quality assessment of Aquarius salinity data product based on the Argo buoy data for 2012. The results reveal that the standard deviation of the error of the Aquarius L2 data is about 0.7,with a negative mean bias of -0.1. There is little difference between ascending and descending orbits data. The data quality degrades in coastal region because of the impact of land contamination and RFI. Because that the brightness temperature sensitivity is affected by the sea surface temperature,larger errors are observed in the region of low SST and higher latitude. The performance of sea surface emissivity model with wind-induced roughness in current salinity retrieval algorithm degrades under high wind speed,so large discrepancies are observed with the standard deviation of more than 1.
Aquarius is a spaceborne L-band radiometer whose mission focuses on the measurement of sea surface salinity from space. Aquarius was successfully launched on June 2011 and has been working operationally for more than two years. This research shows the preliminary results of quality assessment of Aquarius salinity data product based on the Argo buoy data for 2012. The results reveal that the standard deviation of the error of the Aquarius L2 data is about 0.7,with a negative mean bias of -0.1. There is little difference between ascending and descending orbits data. The data quality degrades in coastal region because of the impact of land contamination and RFI. Because that the brightness temperature sensitivity is affected by the sea surface temperature,larger errors are observed in the region of low SST and higher latitude. The performance of sea surface emissivity model with wind-induced roughness in current salinity retrieval algorithm degrades under high wind speed,so large discrepancies are observed with the standard deviation of more than 1.
2015, 37(3): 54-69.
doi: 10.3969/j.issn.0253-4193.2015.03.006
Abstract:
The lagoon,one of the most important types of coastal wetlands,provides abundant natural resources and unique ecological functions. In recent years,coastal lagoons in China have been greatly damaged. Therefore,remote sensing monitoring and analysis of it is of great significance. According to a total of 102 scenes of multi-temporal remote sensing image data in 1979,1990,2000 and 2010,the paper monitored the coastal lagoons in the mainland of China with remote sensing and geographical information system techniques. The name,quantity,distribution,shoreline length and area information of coastal lagoons were surveyed for the first time. Also,the evolutions of coastal lagoons in mainland China in recent 31 years were analyzed. The results showed that,there were 251 coastal lagoons in mainland China in 1979,but a total of 19 lagoons disappeared in the last 31 years,among which are 15 of Liaoning province,3 of Guangdong Province and 1 of the Guangxi Autonomous Region; the total length of the shoreline and the area of the lagoons were 2 692.26 km and 1 092.805 5 km2 respectively in 1979,but both of them reduced by 337.80 km and 204.103 0 km2 during the period; the shoreline length and the lagoon area of China mainland were in decline overall,and the 5 provinces were basically in accordance with this law; from 1979 to 2010,most of the coastal lagoons in the mainland of China were in the old phase,and there were 19 lagoons lost in the death phase in the last 31 years.
The lagoon,one of the most important types of coastal wetlands,provides abundant natural resources and unique ecological functions. In recent years,coastal lagoons in China have been greatly damaged. Therefore,remote sensing monitoring and analysis of it is of great significance. According to a total of 102 scenes of multi-temporal remote sensing image data in 1979,1990,2000 and 2010,the paper monitored the coastal lagoons in the mainland of China with remote sensing and geographical information system techniques. The name,quantity,distribution,shoreline length and area information of coastal lagoons were surveyed for the first time. Also,the evolutions of coastal lagoons in mainland China in recent 31 years were analyzed. The results showed that,there were 251 coastal lagoons in mainland China in 1979,but a total of 19 lagoons disappeared in the last 31 years,among which are 15 of Liaoning province,3 of Guangdong Province and 1 of the Guangxi Autonomous Region; the total length of the shoreline and the area of the lagoons were 2 692.26 km and 1 092.805 5 km2 respectively in 1979,but both of them reduced by 337.80 km and 204.103 0 km2 during the period; the shoreline length and the lagoon area of China mainland were in decline overall,and the 5 provinces were basically in accordance with this law; from 1979 to 2010,most of the coastal lagoons in the mainland of China were in the old phase,and there were 19 lagoons lost in the death phase in the last 31 years.
2015, 37(3): 70-76.
doi: 10.3969/j.issn.0253-4193.2015.03.007
Abstract:
This study analyzed the stratigraphic correlation among several cores collected from the Guangxi coastline,and discussed the spatial discrepancy of transgression since Holocene. And,using the East Asia seal level fluctuation curve as a reference,this study also estimated the rate of vertical tectonic movement in main bays offshore Guangxi Province. The results show that since Holocene the initiation time for transgression in different local regions along Guangxi coastline are different,which is due to regional differences in tectonic sinking movement among these main bays. The tectonics in the eastern part of the Lianzhou Bay is stable,and that in the western part of the bay is unstable with a sinking speed of 1 to 3 mm/a. The tectonic sinking process resulted in regional differences in the sea level fluctuation curves,and thereby influenced the development of stratigraphy. For example,the salt mash face can only be found in the area west to Lianzhou Bay,where experienced a relative slow local sea level rising speed.
This study analyzed the stratigraphic correlation among several cores collected from the Guangxi coastline,and discussed the spatial discrepancy of transgression since Holocene. And,using the East Asia seal level fluctuation curve as a reference,this study also estimated the rate of vertical tectonic movement in main bays offshore Guangxi Province. The results show that since Holocene the initiation time for transgression in different local regions along Guangxi coastline are different,which is due to regional differences in tectonic sinking movement among these main bays. The tectonics in the eastern part of the Lianzhou Bay is stable,and that in the western part of the bay is unstable with a sinking speed of 1 to 3 mm/a. The tectonic sinking process resulted in regional differences in the sea level fluctuation curves,and thereby influenced the development of stratigraphy. For example,the salt mash face can only be found in the area west to Lianzhou Bay,where experienced a relative slow local sea level rising speed.
2015, 37(3): 77-85.
doi: 10.3969/j.issn.0253-4193.2015.03.008
Abstract:
Mangrove evolution is the long time-scale process under the condition of climate change and human activity,and is clearly recorded by the surrounding sediments. It is a new palaeoecological approach to trace mangrove evolution using organic carbon isotopes and mangrove pollen from sedimentary records. In the study,a sediment core was collected from a mangrove swamp of the Qinzhou Bay,Guangxi. Based on the three end-number model,δ13C and C/N analysis were used to calculate the contribution of mangrove-derived organic carbon. Compared with mangrove pollen assemblage and 210Pb dating,it revealed the temporal evolution of mangrove development and its community succession in the recent 150 years. The mangrove evolution could be divided into three major stages: flourish (1864-1918 A.D.),degradation (1918-1968 A.D.) and low-level period (1968-2007 A.D.),which was consistent with the previous reports. An significantly degradation in mangrove ecosystem recently corresponded to the increase of reclamation area (especially for the shrimp-pond reclamation) and artificial seawalls,rather than the climate change as recorded in the region.
Mangrove evolution is the long time-scale process under the condition of climate change and human activity,and is clearly recorded by the surrounding sediments. It is a new palaeoecological approach to trace mangrove evolution using organic carbon isotopes and mangrove pollen from sedimentary records. In the study,a sediment core was collected from a mangrove swamp of the Qinzhou Bay,Guangxi. Based on the three end-number model,δ13C and C/N analysis were used to calculate the contribution of mangrove-derived organic carbon. Compared with mangrove pollen assemblage and 210Pb dating,it revealed the temporal evolution of mangrove development and its community succession in the recent 150 years. The mangrove evolution could be divided into three major stages: flourish (1864-1918 A.D.),degradation (1918-1968 A.D.) and low-level period (1968-2007 A.D.),which was consistent with the previous reports. An significantly degradation in mangrove ecosystem recently corresponded to the increase of reclamation area (especially for the shrimp-pond reclamation) and artificial seawalls,rather than the climate change as recorded in the region.
2015, 37(3): 86-98.
doi: 10.3969/j.issn.0253-4193.2015.03.009
Abstract:
Cohesive sediment meter was used to measure sediment critical shear stress along the measuring line perpendicular to coastal line in different sedimentary lobes in the modern Yellow River delta. These obtained sediment critical shear stress,combined with the test results of sediment physical and mechanical properties and granularity composition,then were used to study on the distribution of sediment erodibility in the modern Yellow River Delta and its relationship with the influencing factors. This study indicated that,(1) high tidal flat was hard to be eroded with high critical shear stress ranging from 1.1 to 4.02 Pa,which was due to the following factors including the low water content,high dry bulk density,high content of silt and clay particles,small average particle diameter,and high undrained shear strength; (2) middle tidal flat was characterized with obviously different critical shear stress ranging from 0.10 to 1.90 Pa,which was mainly influenced by biological activities in different sedimentary lobes including biodisturbation,biological waste,remains and remnants with different amounts and degree; and (3) low tidal flat can be easily eroded with low critical shear stress ranging from 0.08 to 0.80 Pa,which was induced by the high water content,low dry bulk density,high sand content,gentle average particle diameter,and low undrained shear strength. For the whole modern Yellow River Delta,low,middle and high the critical shear stress occur in the northern part,middle part and the southern part of the delta,respectively. The discrepancy of particle compositions can be considered as the critical factor for causing the variety of sediment critical shear stress in different areas. Compared with other main estuarine deltas in the world,non-uniform degree of sediment erodibility was higher and anti-erosion strength was lower in the modern Yellow River Delta.
Cohesive sediment meter was used to measure sediment critical shear stress along the measuring line perpendicular to coastal line in different sedimentary lobes in the modern Yellow River delta. These obtained sediment critical shear stress,combined with the test results of sediment physical and mechanical properties and granularity composition,then were used to study on the distribution of sediment erodibility in the modern Yellow River Delta and its relationship with the influencing factors. This study indicated that,(1) high tidal flat was hard to be eroded with high critical shear stress ranging from 1.1 to 4.02 Pa,which was due to the following factors including the low water content,high dry bulk density,high content of silt and clay particles,small average particle diameter,and high undrained shear strength; (2) middle tidal flat was characterized with obviously different critical shear stress ranging from 0.10 to 1.90 Pa,which was mainly influenced by biological activities in different sedimentary lobes including biodisturbation,biological waste,remains and remnants with different amounts and degree; and (3) low tidal flat can be easily eroded with low critical shear stress ranging from 0.08 to 0.80 Pa,which was induced by the high water content,low dry bulk density,high sand content,gentle average particle diameter,and low undrained shear strength. For the whole modern Yellow River Delta,low,middle and high the critical shear stress occur in the northern part,middle part and the southern part of the delta,respectively. The discrepancy of particle compositions can be considered as the critical factor for causing the variety of sediment critical shear stress in different areas. Compared with other main estuarine deltas in the world,non-uniform degree of sediment erodibility was higher and anti-erosion strength was lower in the modern Yellow River Delta.
2015, 37(3): 99-105.
doi: 10.3969/j.issn.0253-4193.2015.03.010
Abstract:
For wave-induced stability analysis on submarine infinite slopes,the limit equilibrium method generally ignores horizontal stresses acting in the soil deposit. On basis of describing the characteristics of the submarine infinite slope under wave action and considering the soil stress state at the slip surface,this study proposed a stress analysis method to analyze sliding stability of the submarine infinite slope,and discussed the applicable prospect of the method. A case study of a submarine infinite slope has been conducted by both of the limit equilibrium method and the proposed stress analysis method. The results have shown that the factor of safety by the stress analysis method is greater than that of the limit equilibrium method,and the differences of factors obtained by the two methods become larger with increasing depth of the slip surface,Poisson ratio of the soil deposit and dip angle of the infinite slope. For a submarine infinite slope with gentle dip angle under wave action,it may slide along a slip zone rather than a single slip surface under unstable state,and the depth for the maximum shear stress does not generally indicate the most instability location of the infinite slope.
For wave-induced stability analysis on submarine infinite slopes,the limit equilibrium method generally ignores horizontal stresses acting in the soil deposit. On basis of describing the characteristics of the submarine infinite slope under wave action and considering the soil stress state at the slip surface,this study proposed a stress analysis method to analyze sliding stability of the submarine infinite slope,and discussed the applicable prospect of the method. A case study of a submarine infinite slope has been conducted by both of the limit equilibrium method and the proposed stress analysis method. The results have shown that the factor of safety by the stress analysis method is greater than that of the limit equilibrium method,and the differences of factors obtained by the two methods become larger with increasing depth of the slip surface,Poisson ratio of the soil deposit and dip angle of the infinite slope. For a submarine infinite slope with gentle dip angle under wave action,it may slide along a slip zone rather than a single slip surface under unstable state,and the depth for the maximum shear stress does not generally indicate the most instability location of the infinite slope.
2015, 37(3): 106-113.
doi: 10.3969/j.issn.0253-4193.2015.03.011
Abstract:
A set of 2D wave flume experiments on a sandy beach were performed to investigate the morphological response of sandy beach to the wave dynamic factors causing sea-level changes. The initial 1/10 simplex beach slope was exposed to the following different wave actions,i.e.,cnoidal waves,irregular waves,regular waves and solitary waves actions,and three different experimental water depths were used to simulate the sea-level change. This study measured a series of free surface elevations for different waves at the time of wave propagation,wave breaking,uprush and backwash,and cross-shore beach profiles after undergoing wave actions. The results showed that the equilibrium beach profile showed wide high berm topography after undergoing cnoidal waves,irregular waves and regular waves,and yet it became sandbar form topography after undergoing solitary wave action. The equilibrium profile shapes were essentially unchanged but moved shoreward under sea-level rise,and the position of berm,trough,sandbar and the retrograde distance of shoreline show good correlations under the four different wave actions.
A set of 2D wave flume experiments on a sandy beach were performed to investigate the morphological response of sandy beach to the wave dynamic factors causing sea-level changes. The initial 1/10 simplex beach slope was exposed to the following different wave actions,i.e.,cnoidal waves,irregular waves,regular waves and solitary waves actions,and three different experimental water depths were used to simulate the sea-level change. This study measured a series of free surface elevations for different waves at the time of wave propagation,wave breaking,uprush and backwash,and cross-shore beach profiles after undergoing wave actions. The results showed that the equilibrium beach profile showed wide high berm topography after undergoing cnoidal waves,irregular waves and regular waves,and yet it became sandbar form topography after undergoing solitary wave action. The equilibrium profile shapes were essentially unchanged but moved shoreward under sea-level rise,and the position of berm,trough,sandbar and the retrograde distance of shoreline show good correlations under the four different wave actions.
2015, 37(3): 114-125.
doi: 10.3969/j.issn.0253-4193.2015.03.012
Abstract:
The water and sediment change of the bifurcation mouth is one of the key parts to influence the estuarine delta formation,which is a determinative controlled factor on the stability of the downstream river situations. Here,based on the flood season water and sediment data observed synchronously in the bifurcation mouth between North and South Passage (BMNSP) during the operations of the second and third phases of the Deep Water Channel Project (DWCP) in the Yangtze Estuary,impacts of DWCP on hydrodynamics and sediment dynamics of the BMNSP were discussed. The results can be summarized as follows: (1) There had been almost no changes for the situation of both the ebb flow and ebb sediment dominance located at the BMNSP,even though the operations of DWCP had experienced time span from the second to the post-third phase. However,the coefficients of both the ebb flow and ebb sediment dominance of the upstream mouth in the South Passage showed an obvious change from low values in the second DWCP to high values in the third DWCP during the flood season. The corresponding coefficients of both the ebb flow and ebb sediment dominance in the North Passage showed inverse changes comparing with those in the South Passage. (2) The Euler residual flow in the flood season could directly determine the flow transport of the BMNSP. During the second and third phase of the DWCP,average transport discharge of the BMNSP was enhanced except the upstream of the North Passage where the average transport discharge still remained low. The change of the Lagrange residual flow of the BMNSP was similar to that of the Euler residual flow. However,the Stokes residual flow of the BMNSP has remained minor changes. (3) Due to the decreased ebb current velocities,increased suspended sediment concentrations,decreased flow transportation and weaken sediment transport rate of the upstream mouth of the North Passage from the second to the post-third DWCP,it could be the main reasons to induce the aggravation of accretions in the upstream mouth of the North Passage.
The water and sediment change of the bifurcation mouth is one of the key parts to influence the estuarine delta formation,which is a determinative controlled factor on the stability of the downstream river situations. Here,based on the flood season water and sediment data observed synchronously in the bifurcation mouth between North and South Passage (BMNSP) during the operations of the second and third phases of the Deep Water Channel Project (DWCP) in the Yangtze Estuary,impacts of DWCP on hydrodynamics and sediment dynamics of the BMNSP were discussed. The results can be summarized as follows: (1) There had been almost no changes for the situation of both the ebb flow and ebb sediment dominance located at the BMNSP,even though the operations of DWCP had experienced time span from the second to the post-third phase. However,the coefficients of both the ebb flow and ebb sediment dominance of the upstream mouth in the South Passage showed an obvious change from low values in the second DWCP to high values in the third DWCP during the flood season. The corresponding coefficients of both the ebb flow and ebb sediment dominance in the North Passage showed inverse changes comparing with those in the South Passage. (2) The Euler residual flow in the flood season could directly determine the flow transport of the BMNSP. During the second and third phase of the DWCP,average transport discharge of the BMNSP was enhanced except the upstream of the North Passage where the average transport discharge still remained low. The change of the Lagrange residual flow of the BMNSP was similar to that of the Euler residual flow. However,the Stokes residual flow of the BMNSP has remained minor changes. (3) Due to the decreased ebb current velocities,increased suspended sediment concentrations,decreased flow transportation and weaken sediment transport rate of the upstream mouth of the North Passage from the second to the post-third DWCP,it could be the main reasons to induce the aggravation of accretions in the upstream mouth of the North Passage.
2015, 37(3): 126-133.
doi: 10.3969/j.issn.0253-4193.2015.03.013
Abstract:
Based on wave generation technique by a inner-domain source,a two-dimensional nonlinear numerical wave flume over time is developed to investigate the fluid resonance induced by the interaction between wave and multi-objects with narrow gaps. In the numerical model,the fully nonlinear kinematic and dynamic boundary conditions are set for the instantaneous free surface; the artificial damping is introduced into the gap to simulate the viscous dissipation due to vortex motion and flow separation; the computational domain is discretized using higher-order boundary elements. The proposed model is validated by the published experimental and numerical data of the relative wave height at two narrow gaps of three boxes.Numerical experiments are performed to study the following: the effects of the number of the boxes on the resonant frequency,wave height at various gaps and the reflected and transmitted wave heights of the objects.
Based on wave generation technique by a inner-domain source,a two-dimensional nonlinear numerical wave flume over time is developed to investigate the fluid resonance induced by the interaction between wave and multi-objects with narrow gaps. In the numerical model,the fully nonlinear kinematic and dynamic boundary conditions are set for the instantaneous free surface; the artificial damping is introduced into the gap to simulate the viscous dissipation due to vortex motion and flow separation; the computational domain is discretized using higher-order boundary elements. The proposed model is validated by the published experimental and numerical data of the relative wave height at two narrow gaps of three boxes.Numerical experiments are performed to study the following: the effects of the number of the boxes on the resonant frequency,wave height at various gaps and the reflected and transmitted wave heights of the objects.
2015, 37(3): 134-143.
doi: 10.3969/j.issn.0253-4193.2015.03.014
Abstract:
Based on the digital nautical charts since 1997 and recent hydrologic field observations,the variations of erosion and siltation in Yangtze River Estuary under the influence of artificial regulation engineerings and basin reservoirs are analyzed. The results indicate that since 1997,(1) the morphological features have been undergone by slightly erosion in upper estuary,(2) the mouth bar crest still received deposition and moved seaward,and (3) the nearshore seabed have been increasingly eroded. And the dominant cause on those phenomena has been changed from the original nature factors to recent intensive human activities. Firstly,the riverbed in South Branch (SB),South Channel (SC) and the upper and middle reaches of North Channel (NC) has been eroded overall. The sediment above bed was very active and surface sediment was coarsened. Bed surface sand wave was becoming more distinct,and the nearshore seabed outside river mouth is being eroded slightly. These variations mentioned above are attributed to river runoff and sediment load. Secondly,there was a sediment deposition in the reaches of North Brach (NB),the mouth of NC and the mouth bars of North Passage (NP) and South Passage (SP),especially for the main channel of NP,which matches a big quantity of back silting after the Deep Waterway Project. The reasons why caused these variations are not only changes in the dynamic structure in estuarine mouth bars,but also variations for the supply of sediment resuspension in local area and offshore area. In addition,the severe erosion and siltation in some reaches is closely related to those estuarine engineering constructions. In a word,the Yangtze River Estuary is in slow adjustment and adaptation under changing natural factors and intensive human activities recently.
Based on the digital nautical charts since 1997 and recent hydrologic field observations,the variations of erosion and siltation in Yangtze River Estuary under the influence of artificial regulation engineerings and basin reservoirs are analyzed. The results indicate that since 1997,(1) the morphological features have been undergone by slightly erosion in upper estuary,(2) the mouth bar crest still received deposition and moved seaward,and (3) the nearshore seabed have been increasingly eroded. And the dominant cause on those phenomena has been changed from the original nature factors to recent intensive human activities. Firstly,the riverbed in South Branch (SB),South Channel (SC) and the upper and middle reaches of North Channel (NC) has been eroded overall. The sediment above bed was very active and surface sediment was coarsened. Bed surface sand wave was becoming more distinct,and the nearshore seabed outside river mouth is being eroded slightly. These variations mentioned above are attributed to river runoff and sediment load. Secondly,there was a sediment deposition in the reaches of North Brach (NB),the mouth of NC and the mouth bars of North Passage (NP) and South Passage (SP),especially for the main channel of NP,which matches a big quantity of back silting after the Deep Waterway Project. The reasons why caused these variations are not only changes in the dynamic structure in estuarine mouth bars,but also variations for the supply of sediment resuspension in local area and offshore area. In addition,the severe erosion and siltation in some reaches is closely related to those estuarine engineering constructions. In a word,the Yangtze River Estuary is in slow adjustment and adaptation under changing natural factors and intensive human activities recently.
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