2020 Vol. 42, No. 5
Display Method:
2020, 42(5): 1-11.
doi: 10.3969/j.issn.0253-4193.2019.05.001
Abstract:
Boussinesq-type equation is one of the important tools for simulating the propagation and evolution of water waves. The theoretical derivation and numerical application of the Boussinesq-type water wave equation dating back to 1967 are reviewed with the hope of promoting its deep development and application in the fields of coastal and ocean engineering. From the theoretical point of view, the derivation of such equations mainly starts from Euler equations or Laplace equations. Under the conditions of certain nonlinearity and gentle slope assumptions, a variety of Boussinesq-type water wave equations have been proposed worldwide. Through the comparisons with the related theories of Stokes waves, these equations are investigated with respect to phase velocity, group velocity, linear shoaling gradient, second-order nonlinearity, third-order nonlinearity, dispersion characteristics due to amplitude dispersion, velocity distribution along the vertical column, sub- and super harmonics etc. The majority of Boussinesq-type equations in literature for waves are reviewed and grouped into two categories, namely horizontal two-dimensional type and three-dimensional type. The usage of Boussinesq-type equations involved with permeable media and the presence of fluid stratification are also briefly described and commented. Finally, the application of these equations is summarized and analyzed.
Boussinesq-type equation is one of the important tools for simulating the propagation and evolution of water waves. The theoretical derivation and numerical application of the Boussinesq-type water wave equation dating back to 1967 are reviewed with the hope of promoting its deep development and application in the fields of coastal and ocean engineering. From the theoretical point of view, the derivation of such equations mainly starts from Euler equations or Laplace equations. Under the conditions of certain nonlinearity and gentle slope assumptions, a variety of Boussinesq-type water wave equations have been proposed worldwide. Through the comparisons with the related theories of Stokes waves, these equations are investigated with respect to phase velocity, group velocity, linear shoaling gradient, second-order nonlinearity, third-order nonlinearity, dispersion characteristics due to amplitude dispersion, velocity distribution along the vertical column, sub- and super harmonics etc. The majority of Boussinesq-type equations in literature for waves are reviewed and grouped into two categories, namely horizontal two-dimensional type and three-dimensional type. The usage of Boussinesq-type equations involved with permeable media and the presence of fluid stratification are also briefly described and commented. Finally, the application of these equations is summarized and analyzed.
2020, 42(5): 128-138.
doi: 10.3969/j.issn.0253-4193.2020.05.012
Abstract:
Investigating the morphodynamic equilibrium of embayment is important to understand the evolution of coastal morphology. This study investigates the effect of embayment shape on equilibrium bottom profile of the embayment. Three typical embayments, rectangular, convergent and divergent types, are considered to examine their bottom equilibrium profiles analytically and numerically. The approximate analytic solutions for bottom equilibrium profile and mean sand concentration applicable to the three types of the embayments are established for the case of embayment’s length much smaller than tidal wave length. The two-dimensional depth-average model coupling hydrodynamics, sand transformation and bottom evolution is adopted to simulate the embayment equilibrium state of these three types of embayments, and the numerical result of surface elevation is then applied to determine the two parameters contained in the bottom analytic solution. The research results give the three different equilibrium bottom profiles: the plane slope for rectangular embayment; the downward convex form for convergent embayment and the upward concave form for divergent embayment. The good agreements between the theoretical and numerical results of tidal current, sand concentration and bottom profile are achieved.
Investigating the morphodynamic equilibrium of embayment is important to understand the evolution of coastal morphology. This study investigates the effect of embayment shape on equilibrium bottom profile of the embayment. Three typical embayments, rectangular, convergent and divergent types, are considered to examine their bottom equilibrium profiles analytically and numerically. The approximate analytic solutions for bottom equilibrium profile and mean sand concentration applicable to the three types of the embayments are established for the case of embayment’s length much smaller than tidal wave length. The two-dimensional depth-average model coupling hydrodynamics, sand transformation and bottom evolution is adopted to simulate the embayment equilibrium state of these three types of embayments, and the numerical result of surface elevation is then applied to determine the two parameters contained in the bottom analytic solution. The research results give the three different equilibrium bottom profiles: the plane slope for rectangular embayment; the downward convex form for convergent embayment and the upward concave form for divergent embayment. The good agreements between the theoretical and numerical results of tidal current, sand concentration and bottom profile are achieved.
2020, 42(5): 12-21.
doi: 10.3969/j.issn.0253-4193.2020.05.002
Abstract:
Lagrangian motion of fluid has important significance for studying material transport. Compared with the traditional Euler method, Lagrangian coherent structures (LCSs) as a new method to research current structures is more objective. This paper presents a new method to calculate LCSs bundles. Based on the average velocity fields of 25 years, climatological LCSs of the Kuroshio area are calculated by variational method. Then simplify and merge the LCSs to obtain climatological LCSs bundles. The LCSs bundles can show the typical current characteristics and transport patterns, represent the average Lagrangian circulation which has a strong constraint. Finally, the climatological flow structures for 12 months are obtained, revealing the periodic Lagrangian circulation rules in different months. Also, virtual particle transport, trajectories of drifters, temperature and salt anomalies distributions are used to verify the results, which are consistent with the transport patterns mentioned in this paper, proving the accuracy and reliability of the current Lagrangian coherent structures.
Lagrangian motion of fluid has important significance for studying material transport. Compared with the traditional Euler method, Lagrangian coherent structures (LCSs) as a new method to research current structures is more objective. This paper presents a new method to calculate LCSs bundles. Based on the average velocity fields of 25 years, climatological LCSs of the Kuroshio area are calculated by variational method. Then simplify and merge the LCSs to obtain climatological LCSs bundles. The LCSs bundles can show the typical current characteristics and transport patterns, represent the average Lagrangian circulation which has a strong constraint. Finally, the climatological flow structures for 12 months are obtained, revealing the periodic Lagrangian circulation rules in different months. Also, virtual particle transport, trajectories of drifters, temperature and salt anomalies distributions are used to verify the results, which are consistent with the transport patterns mentioned in this paper, proving the accuracy and reliability of the current Lagrangian coherent structures.
2020, 42(5): 22-30.
doi: 10.3969/j.issn.0253-4193.2020.05.003
Abstract:
The ocean mixing is one of the most important parameters in the global climate system. The simulation biases of the stratification and the ocean mixing are still open questions. Compared to observations, the simulated multi-model mean stratification during winter in the subtropical regions of both hemispheres shows week bias from 45 CMIP5 climate models. Our results from two numerical experiments using one of CMIP5 models, FIO-ESM v1.0, show that the non-breaking surface wave-induced vertical mixing can serve as a remedy. It increases the temperature of the upper ocean in winter which then stabilize the upper ocean and increase the stratification in subtropical regions. As a result, the stronger stratification restrains the ocean vertical mixing. The simulation of ocean mixing reduce from 227 cm/m2 to 178 cm/m2 in the north subtropical in winter, and from 189 cm/m2 to 165 cm/m2 in the south subtropical. They reduced by 21.6% and 12.7%, respectively. Further analysis indicated that the the surface wave-induced mixing strengthen the stratification by the increasing the upper ocean heat content and then improve the simulation of the ocean mixing.
The ocean mixing is one of the most important parameters in the global climate system. The simulation biases of the stratification and the ocean mixing are still open questions. Compared to observations, the simulated multi-model mean stratification during winter in the subtropical regions of both hemispheres shows week bias from 45 CMIP5 climate models. Our results from two numerical experiments using one of CMIP5 models, FIO-ESM v1.0, show that the non-breaking surface wave-induced vertical mixing can serve as a remedy. It increases the temperature of the upper ocean in winter which then stabilize the upper ocean and increase the stratification in subtropical regions. As a result, the stronger stratification restrains the ocean vertical mixing. The simulation of ocean mixing reduce from 227 cm/m2 to 178 cm/m2 in the north subtropical in winter, and from 189 cm/m2 to 165 cm/m2 in the south subtropical. They reduced by 21.6% and 12.7%, respectively. Further analysis indicated that the the surface wave-induced mixing strengthen the stratification by the increasing the upper ocean heat content and then improve the simulation of the ocean mixing.
2020, 42(5): 31-40.
doi: 10.3969/j.issn.0253-4193.2020.05.004
Abstract:
A total of 126 cases of storm surge along Tianjin coast from 1956 to 2016 were selected. Based on statistical data to study its occurrence, and classify these cases according to weather circulation situation. Extratropical storm surge induced by cold-front accounted for more than 60% of all cases, with an average of 1.28 times per year, and there is a significant increase in 2013−2016. Using Lamb-Jenkinson (L-J) objective typing method, extratropical storm surges induced by cold-front from 2003 to 2016 were objectively classified, and calculated five circulation indices. The results of objective typing showed that: except for one case which can not be classified, the other processes can be classified objectively. Among all 27 types of circulation, circulation situations of extratropical storm surges induced by cold-front are mainly concentrated in 12 types. Types of co-influence of anticyclone and eastward airflow, types of co-influence of anticyclone and northeaster airflow and types of influence of easterly airflow occurred many times, accounting for 58.8% of the total. These three types of objective circulation situation occur more frequently and increase more storm surge elevation. It can be concluded extratropical storm surges induced by cold-front can be subdivided into three types again according to objective classification. 80% of these three main circulation types are concentrated in autumn and winter. By comparing and analyzing the sea-level pressure field of typical processes, these results of objective circulation typing can be used to distinguish the direction of the cold front and the location of the center of the cold high in the circulation situation affecting the Bohai Sea. The strength of circulation index roughly indicates the strength of storm surge process. The objective circulation type and circulation index can provide objective basis for comparative analysis of storm surge cases.
A total of 126 cases of storm surge along Tianjin coast from 1956 to 2016 were selected. Based on statistical data to study its occurrence, and classify these cases according to weather circulation situation. Extratropical storm surge induced by cold-front accounted for more than 60% of all cases, with an average of 1.28 times per year, and there is a significant increase in 2013−2016. Using Lamb-Jenkinson (L-J) objective typing method, extratropical storm surges induced by cold-front from 2003 to 2016 were objectively classified, and calculated five circulation indices. The results of objective typing showed that: except for one case which can not be classified, the other processes can be classified objectively. Among all 27 types of circulation, circulation situations of extratropical storm surges induced by cold-front are mainly concentrated in 12 types. Types of co-influence of anticyclone and eastward airflow, types of co-influence of anticyclone and northeaster airflow and types of influence of easterly airflow occurred many times, accounting for 58.8% of the total. These three types of objective circulation situation occur more frequently and increase more storm surge elevation. It can be concluded extratropical storm surges induced by cold-front can be subdivided into three types again according to objective classification. 80% of these three main circulation types are concentrated in autumn and winter. By comparing and analyzing the sea-level pressure field of typical processes, these results of objective circulation typing can be used to distinguish the direction of the cold front and the location of the center of the cold high in the circulation situation affecting the Bohai Sea. The strength of circulation index roughly indicates the strength of storm surge process. The objective circulation type and circulation index can provide objective basis for comparative analysis of storm surge cases.
2020, 42(5): 41-48.
doi: 10.3969/j.issn.0253-4193.2020.05.005
Abstract:
Under the effects of global climate change and regional climate factors, marine heatwaves occur frequently, resulting in a decline of coral reefs over the Beibu Gulf. Understanding the mechanisms of strengthened marine heatwaves is critical for predicting the future evolution of local reef ecosystems. According to sea surface temperature recorded from four marine stations (Beihai, Weizhou, Haikou, Dongfang) in the eastern part of Beibu Gulf, we analyzed the sea surface temperature anomaly (SSTA), degree heating mouths (DHM), degree heating weeks (DHW) and degree heating days (DHD) which are typical proxies for identifying the marine heat waves (MHW) with its tendency and frequency during the past 58 years. The results show that: (1) The intensity and frequency of marine heat waves (MHW) in 1960−2017 displayed an increasing tendency; (2) The strengthened MHW is probably attributed to many factors, including the increase of El Niño events, regional high-pressure system enhancement, wind weakening; (3) MHW caused by global warming will adversely affect coral reef ecosystems over the Beibu Gulf.
Under the effects of global climate change and regional climate factors, marine heatwaves occur frequently, resulting in a decline of coral reefs over the Beibu Gulf. Understanding the mechanisms of strengthened marine heatwaves is critical for predicting the future evolution of local reef ecosystems. According to sea surface temperature recorded from four marine stations (Beihai, Weizhou, Haikou, Dongfang) in the eastern part of Beibu Gulf, we analyzed the sea surface temperature anomaly (SSTA), degree heating mouths (DHM), degree heating weeks (DHW) and degree heating days (DHD) which are typical proxies for identifying the marine heat waves (MHW) with its tendency and frequency during the past 58 years. The results show that: (1) The intensity and frequency of marine heat waves (MHW) in 1960−2017 displayed an increasing tendency; (2) The strengthened MHW is probably attributed to many factors, including the increase of El Niño events, regional high-pressure system enhancement, wind weakening; (3) MHW caused by global warming will adversely affect coral reef ecosystems over the Beibu Gulf.
2020, 42(5): 49-64.
doi: 10.3969/j.issn.0253-4193.2020.05.006
Abstract:
In this paper, the simulation performance of the sea ice concentration, ice extent/area, and ice thickness of the Arctic is compared based on the results of the climate system model of Beijing Climate Center (BCC_CSM) in the recent two coupling model comparison programs (CMIP5 and CMIP6). The results show that, compared with the results in the CMIP5, the CMIP6 historical experiment recently released has different degrees of improvement in the Arctic sea ice extent seasonal cycle and sea ice thickness, which are shown as follows: (1) In the CMIP6 experiment, the simulated sea ice extent in summer is larger, while the sea ice extent in winter is smaller, which is generally closer to the observation result than the CMIP5. (2) The sea ice thickness simulated by BCC_CSM in the two CMIP is relatively small, but the CMIP6 experiment slightly improves the problem of excessively thin sea ice thickness. Through the analysis of the variables (such as SST, air temperature and radiation flux, turbulent heat flux, ocean heat flux) in different spheres of the climate system affecting the sea ice process, we discuss the causes of the above simulation errors and the improvement of CMIP6 simulation results. The analysis shows that the Arctic sea ice extent simulated by BCC_CSM model in CMIP5 from August to September is small, which is mainly caused by greater ocean heat flux, larger downward short-wave radiation and smaller albedo, while CMIP6 experiment has a great improvement in these aspects. From December to February, the Arctic sea ice extent simulated by CMIP5 is relatively large mainly because of the low ocean heat flux, and the ocean heat flux simulated by CMIP6 is larger than that of CMIP5. However, the improvement of the north Atlantic regional ocean surface current is the main reason for the improvement of the sea ice extent in this region, especially the sea ice edge in the Baffin Bay. The thinner summer sea ice thickness simulated by CMIP5 is mainly due to the larger ocean heat flux and ice surface heat budget from June to August, while the improvement of sea ice thickness simulated by CMIP6 is mainly due to the improvement of ocean heat flux and net short-wave radiation. The improvement of sea ice simulation has direct and indirect relationship with CMIP6 sea ice module and atmospheric module parameterization. By changing short-wave radiation, ice surface albedo and ocean heat flux, the performance of BCC_CSM mode on Arctic sea ice has been effectively improved.
In this paper, the simulation performance of the sea ice concentration, ice extent/area, and ice thickness of the Arctic is compared based on the results of the climate system model of Beijing Climate Center (BCC_CSM) in the recent two coupling model comparison programs (CMIP5 and CMIP6). The results show that, compared with the results in the CMIP5, the CMIP6 historical experiment recently released has different degrees of improvement in the Arctic sea ice extent seasonal cycle and sea ice thickness, which are shown as follows: (1) In the CMIP6 experiment, the simulated sea ice extent in summer is larger, while the sea ice extent in winter is smaller, which is generally closer to the observation result than the CMIP5. (2) The sea ice thickness simulated by BCC_CSM in the two CMIP is relatively small, but the CMIP6 experiment slightly improves the problem of excessively thin sea ice thickness. Through the analysis of the variables (such as SST, air temperature and radiation flux, turbulent heat flux, ocean heat flux) in different spheres of the climate system affecting the sea ice process, we discuss the causes of the above simulation errors and the improvement of CMIP6 simulation results. The analysis shows that the Arctic sea ice extent simulated by BCC_CSM model in CMIP5 from August to September is small, which is mainly caused by greater ocean heat flux, larger downward short-wave radiation and smaller albedo, while CMIP6 experiment has a great improvement in these aspects. From December to February, the Arctic sea ice extent simulated by CMIP5 is relatively large mainly because of the low ocean heat flux, and the ocean heat flux simulated by CMIP6 is larger than that of CMIP5. However, the improvement of the north Atlantic regional ocean surface current is the main reason for the improvement of the sea ice extent in this region, especially the sea ice edge in the Baffin Bay. The thinner summer sea ice thickness simulated by CMIP5 is mainly due to the larger ocean heat flux and ice surface heat budget from June to August, while the improvement of sea ice thickness simulated by CMIP6 is mainly due to the improvement of ocean heat flux and net short-wave radiation. The improvement of sea ice simulation has direct and indirect relationship with CMIP6 sea ice module and atmospheric module parameterization. By changing short-wave radiation, ice surface albedo and ocean heat flux, the performance of BCC_CSM mode on Arctic sea ice has been effectively improved.
2020, 42(5): 65-76.
doi: 10.3969/j.issn.0253-4193.2020.05.007
Abstract:
As the active part of gravitational potential energy (GPE), available gravitational potential energy (AGPE) can participate in ocean energy cycle. In this paper, we calculated the AGPE in the upper 2 000 m in the global ocean and the mesoscale AGPE within the depth range of 200−500 m from the outputs of 9 CMIP5 models. The results are compared with those calculated from BOA_Argo observational data. The results show that the basin scale AGPE calculated from model outputs are mostly larger than those obtained by Argo observations. In the areas with strong dynamic activities (especially the Kuroshio, gulf stream, the Antarctic Circumpolar Current), the AGPE calculated from model outputs show obvious difference from those obtained via the Argo observation, and the difference mainly comes from the density perturbation. The eddy kinetic energy (EKE) and the mesoscale AGPE have a remarkable temporal correlation in the Kuroshio and the Southern Ocean regions, but their correlation coefficient is low in the gulf stream region of North Atlantic. The power spectrum analysis shows that both the mesoscale AGPE and EKE have significant semi-annual and annual variablilities.
As the active part of gravitational potential energy (GPE), available gravitational potential energy (AGPE) can participate in ocean energy cycle. In this paper, we calculated the AGPE in the upper 2 000 m in the global ocean and the mesoscale AGPE within the depth range of 200−500 m from the outputs of 9 CMIP5 models. The results are compared with those calculated from BOA_Argo observational data. The results show that the basin scale AGPE calculated from model outputs are mostly larger than those obtained by Argo observations. In the areas with strong dynamic activities (especially the Kuroshio, gulf stream, the Antarctic Circumpolar Current), the AGPE calculated from model outputs show obvious difference from those obtained via the Argo observation, and the difference mainly comes from the density perturbation. The eddy kinetic energy (EKE) and the mesoscale AGPE have a remarkable temporal correlation in the Kuroshio and the Southern Ocean regions, but their correlation coefficient is low in the gulf stream region of North Atlantic. The power spectrum analysis shows that both the mesoscale AGPE and EKE have significant semi-annual and annual variablilities.
2020, 42(5): 77-94.
doi: 10.3969/j.issn.0253-4193.2020.05.008
Abstract:
Submarine hydrothermal fields in the vicinity of slow- and ultraslow-spreading oceanic ridges reveal a variety of altered rocks, recording the interaction between the deep crust fluid and the surrounding rock, and providing evidence of the characteristics of the deep hydrothermal fluid and associated cyclic processes. We studied samples of metabasalt, metagabbro, altered pyroxenite, and serpentinite collected by TV-grab during Chinese cruises of DY30, DY34, and DY40 at the Longqi hydrothermal field (areas A, B and C) at the ultraslow-spreading Southwest Indian Ridge. The petrography and mineral chemistry of the rock samples were examined under optical microscope and with an electron microprobe analyzer. The petrographic results show that ～95% of the altered rock samples in the Longqi hydrothermal field exhibited brittle deformation and therefore were probably formed in the upper crust. The remaining 5% of samples, from a deep source close to the Longqi-1 hydrothermal hydrothermal field (Area A) were variable, with brittle and plastic-brittle deformation. The altered rock in the Longqi hydrothermal field exhibited medium-low temperature metamorphism, and was mainly composed of chlorite, epidote, albite, actinolite, and sphene of low green-schist facies. In addition, the chlorite formation temperature (201–341°C) in the altered rocks in Area A, and the Fe content (17.5%–27.5%) of the altered minerals such as serpentine, actinolite and chlorite, were both higher than those for Longqi hydrothermal field areas B and C, where chlorite formation temperature was 239–303°C and the Fe content was 16.8%–26.5%. This is consistent with the high temperature hydrothermal vents observed in Area A. We consider that the detachment fault developed by the ridge section of the Longqi hydrothermal field provides a channel for the upward migration of hydrothermal fluids. The small-scale magmatic intrusion or eruption activity of the magma melt in the axial portion of the shaft during expansion may provide a heat source for the hydrothermal circulation.
Submarine hydrothermal fields in the vicinity of slow- and ultraslow-spreading oceanic ridges reveal a variety of altered rocks, recording the interaction between the deep crust fluid and the surrounding rock, and providing evidence of the characteristics of the deep hydrothermal fluid and associated cyclic processes. We studied samples of metabasalt, metagabbro, altered pyroxenite, and serpentinite collected by TV-grab during Chinese cruises of DY30, DY34, and DY40 at the Longqi hydrothermal field (areas A, B and C) at the ultraslow-spreading Southwest Indian Ridge. The petrography and mineral chemistry of the rock samples were examined under optical microscope and with an electron microprobe analyzer. The petrographic results show that ～95% of the altered rock samples in the Longqi hydrothermal field exhibited brittle deformation and therefore were probably formed in the upper crust. The remaining 5% of samples, from a deep source close to the Longqi-1 hydrothermal hydrothermal field (Area A) were variable, with brittle and plastic-brittle deformation. The altered rock in the Longqi hydrothermal field exhibited medium-low temperature metamorphism, and was mainly composed of chlorite, epidote, albite, actinolite, and sphene of low green-schist facies. In addition, the chlorite formation temperature (201–341°C) in the altered rocks in Area A, and the Fe content (17.5%–27.5%) of the altered minerals such as serpentine, actinolite and chlorite, were both higher than those for Longqi hydrothermal field areas B and C, where chlorite formation temperature was 239–303°C and the Fe content was 16.8%–26.5%. This is consistent with the high temperature hydrothermal vents observed in Area A. We consider that the detachment fault developed by the ridge section of the Longqi hydrothermal field provides a channel for the upward migration of hydrothermal fluids. The small-scale magmatic intrusion or eruption activity of the magma melt in the axial portion of the shaft during expansion may provide a heat source for the hydrothermal circulation.
2020, 42(5): 95-103.
doi: 10.3969/j.issn.0253-4193.2020.05.009
Abstract:
The evolution of large tidal flat in estuaries is related to smooth navigation, ecological protection and safety of offshore engineering. It is also a hot topic in geomorphology and engineering. A single beam bathymetric system was used to monitor the Chongming Eastern Beach in the Changjiang River Estuary. The scouring and silting pattern was analyzed based on the environmental factors in recent years. The results are as follows: (1) Chongming Eastern Beach and the north inlet of the North Channel are mainly deposited in 2011−2017 years, and the northern sand terrain of the North Channel is greater than that of the Chongming Eastern Beach, and the central part of the North Branch of the North Channel is −2 m deep in the central area, which is a silt up situation, and the envelope area of the −5 m contour in the study area is basically stable, and the whole pattern is "long height and no growth". (2) Marine sediment is the main source of silting, and the main circulation of the two large circulation formed by the time and space of the rising and falling of the three branches in the study area is the main reason. (3) The reclamation project in the south of the Chongming Eastern Beach and the North Branch is the main factor causing the North Branch atrophy and the silt of the Chongming Eastern Beach, and the ebb tidal diversion of the cross sand channel. As a result, the curvature of the North Channel is a key factor leading to the deposition of North Sand in the North Channel. The siltation of the two beaches directly squeezed the development of the North Branch of the North Channel, which was the main cause of its transition from the tidal trough to the ebb trough, and the siltation situation in the North Branch of the North Channel may cause the next two large sand bodies.
The evolution of large tidal flat in estuaries is related to smooth navigation, ecological protection and safety of offshore engineering. It is also a hot topic in geomorphology and engineering. A single beam bathymetric system was used to monitor the Chongming Eastern Beach in the Changjiang River Estuary. The scouring and silting pattern was analyzed based on the environmental factors in recent years. The results are as follows: (1) Chongming Eastern Beach and the north inlet of the North Channel are mainly deposited in 2011−2017 years, and the northern sand terrain of the North Channel is greater than that of the Chongming Eastern Beach, and the central part of the North Branch of the North Channel is −2 m deep in the central area, which is a silt up situation, and the envelope area of the −5 m contour in the study area is basically stable, and the whole pattern is "long height and no growth". (2) Marine sediment is the main source of silting, and the main circulation of the two large circulation formed by the time and space of the rising and falling of the three branches in the study area is the main reason. (3) The reclamation project in the south of the Chongming Eastern Beach and the North Branch is the main factor causing the North Branch atrophy and the silt of the Chongming Eastern Beach, and the ebb tidal diversion of the cross sand channel. As a result, the curvature of the North Channel is a key factor leading to the deposition of North Sand in the North Channel. The siltation of the two beaches directly squeezed the development of the North Branch of the North Channel, which was the main cause of its transition from the tidal trough to the ebb trough, and the siltation situation in the North Branch of the North Channel may cause the next two large sand bodies.
2020, 42(5): 104-116.
doi: 10.3969/j.issn.0253-4193.2020.05.010
Abstract:
Estuary shoal not only provides valuable wetland resources for humans, and also plays an important role in adjusting evolution of river regime. It is of vital significance to understand the morphodynamic evolution of estuary shoal for channel regulation, wetland development and dike protection. Therefore, based on historical chart for 150 years, bathymetric data, hydrology and sediment data, the morphodynamic processes and associated evolution mechanism of the Biandan Shoal, the biggest shoal in the South Branch were analyzed. The main results show that: (1) During 1860−2016, the Biandan Shoal has experienced the process of “deposition-erosion-deposition” repetitively; and its morphodynamic status was formed from original submerged shoal to spindle-shaped configuration above water surface; subsequently, the appearance was evolved to be relatively slim shoulder pole morphology with tail which was broken into a claw-like status; the lower part was gradually accreted due to the filled tidal creek among the claw-like configuration. (2) There is upward trend in both area and volume of the Biandan Shoal above −2 m, −5 m, respectively. The average annual increased rate of area above −2 m and −5 m is 0.88 km2/a and 0.81 km2/a, and corresponding increased volume rate is 1.3×106 m3/a and 5×106 m3/a, respectively. Meanwhile, extremely erosion occurred in 1998 with average thickness of 1.4 m. (3) While yearly sediment discharge from upstream has insignificant impact on the Biandan Shoal, water discharge could be responsible for the erosion/accretion of the Biandan Shoal; (4) The hydrology condition of strong south and weak north of the Baimao Shoal, the project of distributary reach of south and north channels, and the Dongfengxisha Reservoir directly caused the Biandan Shoal to move northward.
Estuary shoal not only provides valuable wetland resources for humans, and also plays an important role in adjusting evolution of river regime. It is of vital significance to understand the morphodynamic evolution of estuary shoal for channel regulation, wetland development and dike protection. Therefore, based on historical chart for 150 years, bathymetric data, hydrology and sediment data, the morphodynamic processes and associated evolution mechanism of the Biandan Shoal, the biggest shoal in the South Branch were analyzed. The main results show that: (1) During 1860−2016, the Biandan Shoal has experienced the process of “deposition-erosion-deposition” repetitively; and its morphodynamic status was formed from original submerged shoal to spindle-shaped configuration above water surface; subsequently, the appearance was evolved to be relatively slim shoulder pole morphology with tail which was broken into a claw-like status; the lower part was gradually accreted due to the filled tidal creek among the claw-like configuration. (2) There is upward trend in both area and volume of the Biandan Shoal above −2 m, −5 m, respectively. The average annual increased rate of area above −2 m and −5 m is 0.88 km2/a and 0.81 km2/a, and corresponding increased volume rate is 1.3×106 m3/a and 5×106 m3/a, respectively. Meanwhile, extremely erosion occurred in 1998 with average thickness of 1.4 m. (3) While yearly sediment discharge from upstream has insignificant impact on the Biandan Shoal, water discharge could be responsible for the erosion/accretion of the Biandan Shoal; (4) The hydrology condition of strong south and weak north of the Baimao Shoal, the project of distributary reach of south and north channels, and the Dongfengxisha Reservoir directly caused the Biandan Shoal to move northward.
2020, 42(5): 117-127.
doi: 10.3969/j.issn.0253-4193.2020.05.011
Abstract:
Six representative Landsat remote sensing images from 1985 to 2018 are selected in this paper. Using the digital coastline analysis system to quantitatively analyze the shoreline changes in the Haizhou Bay by using the area method and the baseline method, and to classify and the driving force analysis. The results show that the coastline of the Haizhou Bay moving towards the sea for more than 30 years, and the proportion of the growth shoreline is generally in a growing trend, except for a brief decrease in 2005−2009. From 1985 to 2018, the shoreline length increased by 10.40 km and the land area increased by 52.84 km2. The artificial coastline is the dominant type in the Haizhou Bay, and its proportion is increasing. From 47.90% in 1985 to 70.88% in 2018, coastal cofferdam farming in the early and mid-term and post-sea reclamation are the main driving forces for coastline change. The endpoint change rate was 26.09 m/a, the net coastline change was 155.12 m, and the recorded total cross-section was greater than 50% in each period. The most severe area of the coastline change was from the Xinshu Estuary to Gaogong Island. In the island section, the growth of land area lies in the construction of Ganyu City, Lianyun New City and Lianyungang Port.
Six representative Landsat remote sensing images from 1985 to 2018 are selected in this paper. Using the digital coastline analysis system to quantitatively analyze the shoreline changes in the Haizhou Bay by using the area method and the baseline method, and to classify and the driving force analysis. The results show that the coastline of the Haizhou Bay moving towards the sea for more than 30 years, and the proportion of the growth shoreline is generally in a growing trend, except for a brief decrease in 2005−2009. From 1985 to 2018, the shoreline length increased by 10.40 km and the land area increased by 52.84 km2. The artificial coastline is the dominant type in the Haizhou Bay, and its proportion is increasing. From 47.90% in 1985 to 70.88% in 2018, coastal cofferdam farming in the early and mid-term and post-sea reclamation are the main driving forces for coastline change. The endpoint change rate was 26.09 m/a, the net coastline change was 155.12 m, and the recorded total cross-section was greater than 50% in each period. The most severe area of the coastline change was from the Xinshu Estuary to Gaogong Island. In the island section, the growth of land area lies in the construction of Ganyu City, Lianyun New City and Lianyungang Port.
2020, 42(5): 139-149.
doi: 10.3969/j.issn.0253-4193.2020.05.013
Abstract:
Under the influence of buoyancy and static or dynamic pressure, submarine shallow gas stored on high penetrability soil aggregates and migrates in uprightness and horizontal direction, which inducing stratum deformation and failure. For the purpose of real-time monitoring geological hazard induced by gas as well as early warning, a new type of in situ gas migration monitoring technology is discussed. Two resistivity probes with point-shaped electrode and ring-shaped electrode were respectively designed and manufactured based on the electrostatic field measurement principle. On the basis of detection accuracy analysis, continuous gas diffusion monitoring experiments in sand with three dissimilar gas injection rate are performed. As a result, both resistivity measurement error of two probes are less than 0.1%. With a high measuring sensitivity, the point-shaped electrode probe is capable of monitoring the variation of gas content, gas accumulation, gas dispersing and corresponding rate. The ring-shaped electrode probe has a relatively low sensitivity measurement, while it could monitor the spatio-temporal gas migration in sand soil. Understanding the pros and cons, each probe is able to implement effectively monitoring gas migration.
Under the influence of buoyancy and static or dynamic pressure, submarine shallow gas stored on high penetrability soil aggregates and migrates in uprightness and horizontal direction, which inducing stratum deformation and failure. For the purpose of real-time monitoring geological hazard induced by gas as well as early warning, a new type of in situ gas migration monitoring technology is discussed. Two resistivity probes with point-shaped electrode and ring-shaped electrode were respectively designed and manufactured based on the electrostatic field measurement principle. On the basis of detection accuracy analysis, continuous gas diffusion monitoring experiments in sand with three dissimilar gas injection rate are performed. As a result, both resistivity measurement error of two probes are less than 0.1%. With a high measuring sensitivity, the point-shaped electrode probe is capable of monitoring the variation of gas content, gas accumulation, gas dispersing and corresponding rate. The ring-shaped electrode probe has a relatively low sensitivity measurement, while it could monitor the spatio-temporal gas migration in sand soil. Understanding the pros and cons, each probe is able to implement effectively monitoring gas migration.
An experimental study on parametric scheme of lateral melting rate of ice layer based on temperature
2020, 42(5): 150-158.
doi: 10.3969/j.issn.0253-4193.2020.05.014
Abstract:
In order to quantitatively explore the main factors that affect the lateral melting of the ice layer and simplify the parametric scheme of the lateral melting rate of the ice layer, the melting process of pure water ice under the conditions of no wind, still water, no radiation and pure thermodynamics was simulated in the laboratory, the lateral melting amount of the ice layer was measured, and the laboratory air temperature, ice skin temperature, water temperature, ice temperature and other factors during melting were recorded. The observation results show that under the pure thermodynamic condition of no radiation, the ice layer melts uniformly in the lateral, and the melting rate of the upper and lower layers is faster than that of the middle layer. The results of correlation analysis show that there is a good linear correlation between air temperature and water temperature, ice temperature and ice skin temperature. Information flow results show that air temperature is the most important factor affecting the lateral melting of ice. Finally, a parametric model between the lateral melting rate and the air temperature is established by fitting, and is compared with previous parametric schemes. The results show that the parametric model in this study has a better simulation effect, and the standard deviation is the smallest, which is 0.08 mm/h, thus achieving the purpose of simplifying the parameters.
In order to quantitatively explore the main factors that affect the lateral melting of the ice layer and simplify the parametric scheme of the lateral melting rate of the ice layer, the melting process of pure water ice under the conditions of no wind, still water, no radiation and pure thermodynamics was simulated in the laboratory, the lateral melting amount of the ice layer was measured, and the laboratory air temperature, ice skin temperature, water temperature, ice temperature and other factors during melting were recorded. The observation results show that under the pure thermodynamic condition of no radiation, the ice layer melts uniformly in the lateral, and the melting rate of the upper and lower layers is faster than that of the middle layer. The results of correlation analysis show that there is a good linear correlation between air temperature and water temperature, ice temperature and ice skin temperature. Information flow results show that air temperature is the most important factor affecting the lateral melting of ice. Finally, a parametric model between the lateral melting rate and the air temperature is established by fitting, and is compared with previous parametric schemes. The results show that the parametric model in this study has a better simulation effect, and the standard deviation is the smallest, which is 0.08 mm/h, thus achieving the purpose of simplifying the parameters.
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