2015 Vol. 37, No. 9
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2015, 37(9): .
Abstract:
2015, 37(9): 1-9.
Abstract:
Experiments based on observational data and numerical simulation were carried out in this study to analyze the applicability of three different computational methods of wave power density in finite water depth. From the comparison we conclude that,the deterministic method fully considering the features of waves in finite depth yields the most accurate results,but it has a relatively narrow range of application because it strongly depends on the existence of wave spectrum; the experimental method only depends on regular wave parameters and is applicable for almost all of the basic data,but it yields the results a little lower than the deterministic method and cannot obviously describe the convergence effect of wave power density due to a uplift of the seabed; the correctional method considering the effects of finite depth can yield very accurate results if a proper parameter has been chosen,but it may overate those places with high values. Each one of the three methods has both merits and defects respectively,a proper choice is needed before taking into practice.
Experiments based on observational data and numerical simulation were carried out in this study to analyze the applicability of three different computational methods of wave power density in finite water depth. From the comparison we conclude that,the deterministic method fully considering the features of waves in finite depth yields the most accurate results,but it has a relatively narrow range of application because it strongly depends on the existence of wave spectrum; the experimental method only depends on regular wave parameters and is applicable for almost all of the basic data,but it yields the results a little lower than the deterministic method and cannot obviously describe the convergence effect of wave power density due to a uplift of the seabed; the correctional method considering the effects of finite depth can yield very accurate results if a proper parameter has been chosen,but it may overate those places with high values. Each one of the three methods has both merits and defects respectively,a proper choice is needed before taking into practice.
2015, 37(9): 10-16.
Abstract:
In the paper,a wave forecast system is established by running the wave model SWAN (Simulating Waves Nearshore). The forcing wind field in this system is reconstructed by the 51 members of EC ensemble weather forecast system. Then,a case study of the cold air during December 2013 to February 2014 is conducted to analysis the features of wave effected by the cold air using this system. Furthermore,using buoys data,the system forecasts are verified and compared. The main results are as follows: for the view of hourly mean bias,in 24 h forecast period the performance of ensemble mean is similar to control forecast,in 48 to 72 h forecast period the performance of ensemble mean is better than control forecast. The forecast of ensemble mean and control forecast are smaller than the reality. In both periods,the performance of ensemble statistics (75%,90% and extreme value) is better than control forecast and especially better in the long period of validity. Meanwhile,the forecast of ensemble extreme value is equal to or slightly larger than the reality; for the view of 24 hourly mean bias,the products of ensemble statistics (75%,90% and extreme value) are closer to the reality than the ensemble mean and control forecast value. To sum up,the products of ensemble statistics (75%,90% and extreme value) have higher accuracy of cold wave field. Conclusions show this system can improve the forecast level of wave influenced on cold air and have a good prospect of application.
In the paper,a wave forecast system is established by running the wave model SWAN (Simulating Waves Nearshore). The forcing wind field in this system is reconstructed by the 51 members of EC ensemble weather forecast system. Then,a case study of the cold air during December 2013 to February 2014 is conducted to analysis the features of wave effected by the cold air using this system. Furthermore,using buoys data,the system forecasts are verified and compared. The main results are as follows: for the view of hourly mean bias,in 24 h forecast period the performance of ensemble mean is similar to control forecast,in 48 to 72 h forecast period the performance of ensemble mean is better than control forecast. The forecast of ensemble mean and control forecast are smaller than the reality. In both periods,the performance of ensemble statistics (75%,90% and extreme value) is better than control forecast and especially better in the long period of validity. Meanwhile,the forecast of ensemble extreme value is equal to or slightly larger than the reality; for the view of 24 hourly mean bias,the products of ensemble statistics (75%,90% and extreme value) are closer to the reality than the ensemble mean and control forecast value. To sum up,the products of ensemble statistics (75%,90% and extreme value) have higher accuracy of cold wave field. Conclusions show this system can improve the forecast level of wave influenced on cold air and have a good prospect of application.
2015, 37(9): 17-28.
Abstract:
The authors evaluated the performance of a regional ocean-atmosphere coupled model (FROALS) in the simulation of the surface circulation and its interannual variability during 1984-2007 over the northwestern Pacific. FROALS well reproduced the mean state of sea surface temperature but with an obvious cold bias. The climatology of surface currents and its inter-annual variability are reproduced reasonably for both summer and winter. The bias of simulated surface circulation is mainly associated with the sea surface height bias. Due to stronger heat transport by Kuroshio in FROALS,the warm bias of simulated sea surface temperature was found along Kuroshio path. For inter-annual variability of surface currents,the ENSO-related inter-annual signal was well reproduced in FROALS. During El Niño years,North Equatorial Current (NEC) and Mindanao Current (MC) were stronger,while sea surface height of low-latitude western Pacific were lower than normal years; during La Niña years it showed opposite pattern. The discrepancy was that the inter-annual signal in FROALS is stronger than observation.
The authors evaluated the performance of a regional ocean-atmosphere coupled model (FROALS) in the simulation of the surface circulation and its interannual variability during 1984-2007 over the northwestern Pacific. FROALS well reproduced the mean state of sea surface temperature but with an obvious cold bias. The climatology of surface currents and its inter-annual variability are reproduced reasonably for both summer and winter. The bias of simulated surface circulation is mainly associated with the sea surface height bias. Due to stronger heat transport by Kuroshio in FROALS,the warm bias of simulated sea surface temperature was found along Kuroshio path. For inter-annual variability of surface currents,the ENSO-related inter-annual signal was well reproduced in FROALS. During El Niño years,North Equatorial Current (NEC) and Mindanao Current (MC) were stronger,while sea surface height of low-latitude western Pacific were lower than normal years; during La Niña years it showed opposite pattern. The discrepancy was that the inter-annual signal in FROALS is stronger than observation.
2015, 37(9): 29-38.
Abstract:
Via WRF numerical simulation experiments,this paper discusses the relationship between tropical cyclone(TC) size and intensity,and diagnose the possible mechanism of how TC inner core and outer size influence TC intensity. Results show that: (1) while TC has large inner core,the balance of angular momentum explains that why changing of inner core will course TC intensifying or weakening. (2) While TC has small inner core,the reason why zoom out(zoom in)of inner core leads to TC weakening (intensifying) might be the damage of secondary circulation. (3) the changing of humidity supply and convergence area in low level may be the mechanism for that outer size increment(decrease) helps TC intensifying(weakening).
Via WRF numerical simulation experiments,this paper discusses the relationship between tropical cyclone(TC) size and intensity,and diagnose the possible mechanism of how TC inner core and outer size influence TC intensity. Results show that: (1) while TC has large inner core,the balance of angular momentum explains that why changing of inner core will course TC intensifying or weakening. (2) While TC has small inner core,the reason why zoom out(zoom in)of inner core leads to TC weakening (intensifying) might be the damage of secondary circulation. (3) the changing of humidity supply and convergence area in low level may be the mechanism for that outer size increment(decrease) helps TC intensifying(weakening).
2015, 37(9): 39-50.
Abstract:
An ENSO forecast system based on the Community Earth System Model (CESM) released by the National Center for Atmospheric Research (NCAR) is developed. We use a simple sub-surface sea temperature nudging scheme to generate realistic SST distribution. Hindcast results for the period 1982-2011 show a high predictability of ENSO. All past El Niño and La Niña events,including the strong 1997/1998 warm episode,are successfully predicted with SST,zonal wind and precipitation matching well with GODAS and NCEP datasets. The correlation coefficient of Niño3 index scores 0.88,0.81 and 0.70 at the 1-,3-and 6-month lead time respectively. However,the model shows a "spring prediction barrier" with the best predictability in autumn and the worst in spring. The comparisons of zonal wind,heat flux,SST anomaly,wind stress and sub-surface temperature of 1982/1983 and 1997/1999 demonstrate that the atmospheric response is latter than that of the ocean,which is in contrast with observing and reanalysis data. This is due to the ocean-only data assimilation scheme,which forces a delayed atmospheric response.
An ENSO forecast system based on the Community Earth System Model (CESM) released by the National Center for Atmospheric Research (NCAR) is developed. We use a simple sub-surface sea temperature nudging scheme to generate realistic SST distribution. Hindcast results for the period 1982-2011 show a high predictability of ENSO. All past El Niño and La Niña events,including the strong 1997/1998 warm episode,are successfully predicted with SST,zonal wind and precipitation matching well with GODAS and NCEP datasets. The correlation coefficient of Niño3 index scores 0.88,0.81 and 0.70 at the 1-,3-and 6-month lead time respectively. However,the model shows a "spring prediction barrier" with the best predictability in autumn and the worst in spring. The comparisons of zonal wind,heat flux,SST anomaly,wind stress and sub-surface temperature of 1982/1983 and 1997/1999 demonstrate that the atmospheric response is latter than that of the ocean,which is in contrast with observing and reanalysis data. This is due to the ocean-only data assimilation scheme,which forces a delayed atmospheric response.
2015, 37(9): 51-58.
Abstract:
Suaeda salsa and tamarisk are the typical vegetation in Yellow River Estuary,and also a key habitat for many kinds of rare birds. Suaeda salsa and tamarix,whose landscape scale usually small,widely distributed and often mixed with each other or other vegetation or bare soil in remote sensing images,are difficult to obtain the vegetation fractional cover efficiently,thereby affecting biomass monitoring and ecological assessment. In this study,we acquired the end-members in two ways,the first is measure the vegetation spectrum through field work,and the second way is extract them from the hyperspectral remote sensing image with the SAMCC method. Then we use the two kinds of end-members in the pixel spectral un-mixing process with 5 different algorithms,which are: LUS,OSP,MF,CEM and ACE. At last we evaluate the two kinds of end-members coverage inversion capability of the salsa and Tamarix through correlation analysis with the real coverage which measured in the field work.
Suaeda salsa and tamarisk are the typical vegetation in Yellow River Estuary,and also a key habitat for many kinds of rare birds. Suaeda salsa and tamarix,whose landscape scale usually small,widely distributed and often mixed with each other or other vegetation or bare soil in remote sensing images,are difficult to obtain the vegetation fractional cover efficiently,thereby affecting biomass monitoring and ecological assessment. In this study,we acquired the end-members in two ways,the first is measure the vegetation spectrum through field work,and the second way is extract them from the hyperspectral remote sensing image with the SAMCC method. Then we use the two kinds of end-members in the pixel spectral un-mixing process with 5 different algorithms,which are: LUS,OSP,MF,CEM and ACE. At last we evaluate the two kinds of end-members coverage inversion capability of the salsa and Tamarix through correlation analysis with the real coverage which measured in the field work.
2015, 37(9): 59-70.
Abstract:
In this paper,seabed morphology features related to submarine slide and mud volcanism activities are presented and analyzed,their impacts to gas hydrate formation and decomposition are discussed,and two models of slide driven and slide-mud volcano driven are proposed. Dataset used in this paper including seismic lines,sub-bottom profiler lines and bathymetry data obtained from seabed reflection picking. The study area consists of two main landforms: "regular slide region",and "mud volcanism activities affected region". We identify characteristic features such as mud volcano,mud volcano ridge,groove and pit from the bathymetry map. Submarine slide and mud volcanism activities play significant roles in affecting the morphology of the gas hydrate distribution region on the northeastern slope of South China Sea. Combining the analyses of BSR(Bottom Simulating Reflector) and mud volcanoes' distribution,relations between BSR discontinuity and mud volcano occurrence,we know that BSRs are continuous and gas hydrate reservoir is almost complete one in the regular slide region,while there is less and local destruction for the gas hydrate reservoir in the mud volcanism affected region slide and mud volcanism activities are important for long-term natural gas releasing process in the studied area.
In this paper,seabed morphology features related to submarine slide and mud volcanism activities are presented and analyzed,their impacts to gas hydrate formation and decomposition are discussed,and two models of slide driven and slide-mud volcano driven are proposed. Dataset used in this paper including seismic lines,sub-bottom profiler lines and bathymetry data obtained from seabed reflection picking. The study area consists of two main landforms: "regular slide region",and "mud volcanism activities affected region". We identify characteristic features such as mud volcano,mud volcano ridge,groove and pit from the bathymetry map. Submarine slide and mud volcanism activities play significant roles in affecting the morphology of the gas hydrate distribution region on the northeastern slope of South China Sea. Combining the analyses of BSR(Bottom Simulating Reflector) and mud volcanoes' distribution,relations between BSR discontinuity and mud volcano occurrence,we know that BSRs are continuous and gas hydrate reservoir is almost complete one in the regular slide region,while there is less and local destruction for the gas hydrate reservoir in the mud volcanism affected region slide and mud volcanism activities are important for long-term natural gas releasing process in the studied area.
2015, 37(9): 71-83.
Abstract:
Based on island survey and the existing literature,15 kinds of geological disasters were found in the typical islands of China,they are landslides,coastal erosion,saltwater intrusion,wetland degradation,soil and water loss,land subsidence,aeolian disaster,fault,harbor siltation,beach surface erosion,beach mudding,shallow gas,sand soil liquefaction,earthquake and soft soil foundation. The most frequent disasters is landslide,it can occur on the land,shore,seabed of rocky islands; followed by coastal erosion,it mainly occurs on the shore of rocky islands and sandy islands; seawater intrusion (include saltwater intrusion) is thirdly,it occurs on the shore of rocky islands and sandy islands; wetland degradation also occurs on the shore of rocky islands and sandy islands; other types of disaster is relatively rare occurrence. Through the genetic mechanism analysis of geological disasters,we found that all kinds of geological disasters are the combined result of natural factors and human activities,the impact of human activity gradually increased,and there is a link between the causes of the island geological disasters.
Based on island survey and the existing literature,15 kinds of geological disasters were found in the typical islands of China,they are landslides,coastal erosion,saltwater intrusion,wetland degradation,soil and water loss,land subsidence,aeolian disaster,fault,harbor siltation,beach surface erosion,beach mudding,shallow gas,sand soil liquefaction,earthquake and soft soil foundation. The most frequent disasters is landslide,it can occur on the land,shore,seabed of rocky islands; followed by coastal erosion,it mainly occurs on the shore of rocky islands and sandy islands; seawater intrusion (include saltwater intrusion) is thirdly,it occurs on the shore of rocky islands and sandy islands; wetland degradation also occurs on the shore of rocky islands and sandy islands; other types of disaster is relatively rare occurrence. Through the genetic mechanism analysis of geological disasters,we found that all kinds of geological disasters are the combined result of natural factors and human activities,the impact of human activity gradually increased,and there is a link between the causes of the island geological disasters.
2015, 37(9): 84-94.
Abstract:
Coastal lagoon deposits may provide evidence for the history of past intense tropical cyclones activities. In the present study, sediment cores from two coastal lagoons (Li'an Lagoon and Xincun Lagoon) of southeastern Hainan Island have been analyzed to address this issue. Storm-induced deposits were identified on the basis of detailed core descriptions, loss-on-ignition (LOI) and grain size analysis. Storm layers associated with 35 typhoon events have been identified from two short cores. The age of storm events calculated using 210Pb dating method with the CRS model is in agreement with historical documents. On such a basis, a 350 year history of local typhoon activities is reconstructed by incorporating the 210Pb dating results, typhoon-induced sediment records and the historical documents. A comparison of the frequency of typhoon occurrence with the regional climate records indicates that storm activity patterns may be related to EI Niño, Pacific Decadal Oscillation (PDO), sunspot, and other potential climate drivers that affect the tropical cyclone variability. Thus, our study shows that storm events can be obtained from coastal lagoon deposits, which would provide meaningful information on past storm activities in long-term scales.
Coastal lagoon deposits may provide evidence for the history of past intense tropical cyclones activities. In the present study, sediment cores from two coastal lagoons (Li'an Lagoon and Xincun Lagoon) of southeastern Hainan Island have been analyzed to address this issue. Storm-induced deposits were identified on the basis of detailed core descriptions, loss-on-ignition (LOI) and grain size analysis. Storm layers associated with 35 typhoon events have been identified from two short cores. The age of storm events calculated using 210Pb dating method with the CRS model is in agreement with historical documents. On such a basis, a 350 year history of local typhoon activities is reconstructed by incorporating the 210Pb dating results, typhoon-induced sediment records and the historical documents. A comparison of the frequency of typhoon occurrence with the regional climate records indicates that storm activity patterns may be related to EI Niño, Pacific Decadal Oscillation (PDO), sunspot, and other potential climate drivers that affect the tropical cyclone variability. Thus, our study shows that storm events can be obtained from coastal lagoon deposits, which would provide meaningful information on past storm activities in long-term scales.
2015, 37(9): 95-105.
Abstract:
Bathymetric data surveyed from 1958 to 2013 were analyzed using ArcGIS and DSAS software to investigate the evolution of the tidal flats in the bar area of the Yangtze Estuary. And driving factors such as the declined riverine sediment supply and the major engineering works constructed in the Yangtze Estuary were discussed in this study. The results demonstrated that: (1) the amount of tidal flat resources has experienced slight decrease since 1958; but it comes to be stable, with amount of 2 350 km2 in recent decade. (2) the area deeper than 5 m has begun to experience erosion since 1997, and the averaged vertical erosion rate was 7.3 cm/a. (3) the dramatic sediment decline from Yangtze River in recent decade has brought negative impact on the progradation of the tidal flat deeper than 0 m. Nevertheless, the area shallower than 0 m was continued to accretion due to the influence of the engineering works in the estuary.
Bathymetric data surveyed from 1958 to 2013 were analyzed using ArcGIS and DSAS software to investigate the evolution of the tidal flats in the bar area of the Yangtze Estuary. And driving factors such as the declined riverine sediment supply and the major engineering works constructed in the Yangtze Estuary were discussed in this study. The results demonstrated that: (1) the amount of tidal flat resources has experienced slight decrease since 1958; but it comes to be stable, with amount of 2 350 km2 in recent decade. (2) the area deeper than 5 m has begun to experience erosion since 1997, and the averaged vertical erosion rate was 7.3 cm/a. (3) the dramatic sediment decline from Yangtze River in recent decade has brought negative impact on the progradation of the tidal flat deeper than 0 m. Nevertheless, the area shallower than 0 m was continued to accretion due to the influence of the engineering works in the estuary.
2015, 37(9): 106-112.
Abstract:
133 high density sediment samples were collected from Qianhu Bay coastal section to analyze their grain size which showed a variety of the frequency curves indicated the changes of sedimentary environment. Some samples of beach,shallow,estuary,seamarsh and dunes around the section were also collected to analyze grain size. Their parameters of mean particle size (Mz),the standard deviation (σ),kurtosis (Kg) were set as criterion to calculate the minimum distance between the section samples and the criterion samples. Samples with minimum distance were classified to the similar of criterion sample so that to known their paleo-environment. We use this method to analyze 133 coastal samples and known their environmental evolution from estuaries shallow,estuaries,dunes,seamarsh to beach. The silt sample under the bottom of the coastal section was dating of 14 C=(32 815±170)a BP and known the ages of environmental changes of Qianhu Bay. Referring the sealevel changes in Fujian coastal during that time we know it was climate and sealevel changes that cause the environmental changes in Qianhu Bay.
133 high density sediment samples were collected from Qianhu Bay coastal section to analyze their grain size which showed a variety of the frequency curves indicated the changes of sedimentary environment. Some samples of beach,shallow,estuary,seamarsh and dunes around the section were also collected to analyze grain size. Their parameters of mean particle size (Mz),the standard deviation (σ),kurtosis (Kg) were set as criterion to calculate the minimum distance between the section samples and the criterion samples. Samples with minimum distance were classified to the similar of criterion sample so that to known their paleo-environment. We use this method to analyze 133 coastal samples and known their environmental evolution from estuaries shallow,estuaries,dunes,seamarsh to beach. The silt sample under the bottom of the coastal section was dating of 14 C=(32 815±170)a BP and known the ages of environmental changes of Qianhu Bay. Referring the sealevel changes in Fujian coastal during that time we know it was climate and sealevel changes that cause the environmental changes in Qianhu Bay.
2015, 37(9): 113-125.
Abstract:
The erosion-accretion evolution pattern and mechanism within the Jinshan Trough is analyzed using GIS technology,aiming to imply the sediment transport characteristics in a complex hydrodynamic condition from a spatial-temporal view. Data during 1972-2013 was collected. Analysis results show that: (1) In the long term,the evolution in areas deeper than 15 m is dominated by erosion,accounting for 88.05% of the total trough area,and the erosion amount (120.35×106 m3) is larger than that of accretion (3.76×106 m3),with the average net erosion rate reaching up to 7.46 cm/a. Generally,for the Jinshan Trough as a whole,it is extending lengthwise and broadening southward obviously. The maximum length of it increased by 7.34 km; the maximum width has also nearly 1 km. Nevertheless,the anti-scouring deposit layer in the Jinshan Trough has somehow promoted a rough equilibrium of erosion and accretion even with continuing effects of the strong tidal currents during the last four decades. Besides,the average depth ranges from 21.0 to 23.59 m with a slight fluctuating amplitude,and the maximum depth from 46.90 to 51.00 m and are spatially aggregated. (2) With a basis of specific topography,the short-term erosion-accretion pattern are drastically affected by the water and sediment condition changes due to human activities. During 2002 to 2012,the net erosion rate is as high as 22.14 cm/a. On the whole,the erosion and accretion pattern in the Jinshan Trough keeps balanced during 2012 to 2013. (3) By analyzing the swinging values of the central axis in areas deeper than 15 m,20 m and 25 m respectively,it is revealed that most parts of the Jinshan Trough are in a stable state,which accounts for more than 65% of the whole trough. However,unstable areas are distributed at the west of the Sixth Coastal Levee and the city beach,where the water depth fluctuates with a larger amplitude. As a proposal provided by our research,intent hydrographic monitoring and accurate evaluation of seawalls' safety are required for the near future.
The erosion-accretion evolution pattern and mechanism within the Jinshan Trough is analyzed using GIS technology,aiming to imply the sediment transport characteristics in a complex hydrodynamic condition from a spatial-temporal view. Data during 1972-2013 was collected. Analysis results show that: (1) In the long term,the evolution in areas deeper than 15 m is dominated by erosion,accounting for 88.05% of the total trough area,and the erosion amount (120.35×106 m3) is larger than that of accretion (3.76×106 m3),with the average net erosion rate reaching up to 7.46 cm/a. Generally,for the Jinshan Trough as a whole,it is extending lengthwise and broadening southward obviously. The maximum length of it increased by 7.34 km; the maximum width has also nearly 1 km. Nevertheless,the anti-scouring deposit layer in the Jinshan Trough has somehow promoted a rough equilibrium of erosion and accretion even with continuing effects of the strong tidal currents during the last four decades. Besides,the average depth ranges from 21.0 to 23.59 m with a slight fluctuating amplitude,and the maximum depth from 46.90 to 51.00 m and are spatially aggregated. (2) With a basis of specific topography,the short-term erosion-accretion pattern are drastically affected by the water and sediment condition changes due to human activities. During 2002 to 2012,the net erosion rate is as high as 22.14 cm/a. On the whole,the erosion and accretion pattern in the Jinshan Trough keeps balanced during 2012 to 2013. (3) By analyzing the swinging values of the central axis in areas deeper than 15 m,20 m and 25 m respectively,it is revealed that most parts of the Jinshan Trough are in a stable state,which accounts for more than 65% of the whole trough. However,unstable areas are distributed at the west of the Sixth Coastal Levee and the city beach,where the water depth fluctuates with a larger amplitude. As a proposal provided by our research,intent hydrographic monitoring and accurate evaluation of seawalls' safety are required for the near future.
2015, 37(9): 126-137.
Abstract:
In this paper,various history datum,such as meteorological data,tidal data,and storm surge data,etc,are collected and analyzed. Highest tidal levels of multiyear return periods are calculated using the Gumbel curve method,and the related inundation areas are also showed. It is revealed that the worsening beach erosion of the southwestern Weizhou Island is mainly due to the frequently occurrence of the extreme high tide in recent years. In addition,a coupled storm surge-wave numerical model is used to present the inundation process by storm surge during the 0312 typhoon. Impacts of storm surge and spring tide on the beach erosion is analyzed and elaborated,which is of certain directive significance to the local beach restoration and protection.
In this paper,various history datum,such as meteorological data,tidal data,and storm surge data,etc,are collected and analyzed. Highest tidal levels of multiyear return periods are calculated using the Gumbel curve method,and the related inundation areas are also showed. It is revealed that the worsening beach erosion of the southwestern Weizhou Island is mainly due to the frequently occurrence of the extreme high tide in recent years. In addition,a coupled storm surge-wave numerical model is used to present the inundation process by storm surge during the 0312 typhoon. Impacts of storm surge and spring tide on the beach erosion is analyzed and elaborated,which is of certain directive significance to the local beach restoration and protection.
2015, 37(9): 138-151.
Abstract:
Based on 4 synchronous hydrological measurements in flood and dry seasons,this paper researches the variations in suspended sediment concentration (SSC) in a tidal cycle,the vertical distribution of SSC,the longitudinal distribution of SSC,the suspended sediment transport,and their temporal and spatial differences in the North Branch of the Yangtze Estuary. The results indicate that the process of variations in SSC in a tidal cycle mainly presents M pattern (two peaks) during spring and medium tides. However,in the main channel of the lower reach mostly V pattern occurs during spring tide,and in the upper reach one-peak during flood pattern could occur in dry season. During neap tide,no-peak,one-peak,or two-peak patterns could occur. About the maximum and average SSC during flood and ebb,they are usually larger during flood in dry season,in flood season more likely larger during ebb in medium and neap tides particularly in neap tide. In the main channel of the lower reach they are more likely larger during ebb in spring tide. The vertical distribution of SSC and its variations in a tidal cycle are related to the variational pattern of SSC during spring and medium tides. For M-pattern SSC it has obvious difference between flood season and dry season. Longitudinally,the maximum SSC occurs nearby the reach between Lingdiangang and Sanhegang in the middle reach during dry season,however around Santiaogang in the lower reach during flood season. Regarding the net suspended sediment transport in a tidal cycle,it is usually landward in dry season particularly during spring and medium tides,in flood season mostly seaward in the middle and upper reaches,mostly landward during spring tide and likely seaward during medium and neap tides in the lower reach. In the main channel of the lower reach it is likely seaward during spring tide.
Based on 4 synchronous hydrological measurements in flood and dry seasons,this paper researches the variations in suspended sediment concentration (SSC) in a tidal cycle,the vertical distribution of SSC,the longitudinal distribution of SSC,the suspended sediment transport,and their temporal and spatial differences in the North Branch of the Yangtze Estuary. The results indicate that the process of variations in SSC in a tidal cycle mainly presents M pattern (two peaks) during spring and medium tides. However,in the main channel of the lower reach mostly V pattern occurs during spring tide,and in the upper reach one-peak during flood pattern could occur in dry season. During neap tide,no-peak,one-peak,or two-peak patterns could occur. About the maximum and average SSC during flood and ebb,they are usually larger during flood in dry season,in flood season more likely larger during ebb in medium and neap tides particularly in neap tide. In the main channel of the lower reach they are more likely larger during ebb in spring tide. The vertical distribution of SSC and its variations in a tidal cycle are related to the variational pattern of SSC during spring and medium tides. For M-pattern SSC it has obvious difference between flood season and dry season. Longitudinally,the maximum SSC occurs nearby the reach between Lingdiangang and Sanhegang in the middle reach during dry season,however around Santiaogang in the lower reach during flood season. Regarding the net suspended sediment transport in a tidal cycle,it is usually landward in dry season particularly during spring and medium tides,in flood season mostly seaward in the middle and upper reaches,mostly landward during spring tide and likely seaward during medium and neap tides in the lower reach. In the main channel of the lower reach it is likely seaward during spring tide.
2015, 37(9): 152-161.
Abstract:
The Laser In Situ Scattering and Transmissometry-100(LISST-100)was used to the field observation in the Modaomen Estuary of the Pearl River during the July 2013(flood season). Based on the in situ data,we get some flocculation information: the dispersion of suspended sediment particle size is about 27.9 μm,the measured floccules mean diameter is about 91.6 μm,it indicated that suspended sediment flocculation phenomenon significantly. The in situ mean diameter of floc varied from 13.0 to 273.8 μm,the neap tidal floc was larger than spring tide. The variation of floc particle size was decreases at first,and then increases. The relationship between floc diameter and volume concentration,settling velocity were vary from case to case. The volume concentration and particle size of the floccules had positive correlation in surface and middle layer,floccules settling velocity increases with the increase of particle size in spring time. Comprehensive analysis of the factors affecting flocculation,the results show that the salinity have no significant relationship with floccules size,the influence of velocity to floccules had two kinds of circumstances,large flow motion will hinder the development of the floc size. These knowledge will contributes to a further understanding of fine sediment transport characteristics and biochemical process in the Pearl River Estuary.
The Laser In Situ Scattering and Transmissometry-100(LISST-100)was used to the field observation in the Modaomen Estuary of the Pearl River during the July 2013(flood season). Based on the in situ data,we get some flocculation information: the dispersion of suspended sediment particle size is about 27.9 μm,the measured floccules mean diameter is about 91.6 μm,it indicated that suspended sediment flocculation phenomenon significantly. The in situ mean diameter of floc varied from 13.0 to 273.8 μm,the neap tidal floc was larger than spring tide. The variation of floc particle size was decreases at first,and then increases. The relationship between floc diameter and volume concentration,settling velocity were vary from case to case. The volume concentration and particle size of the floccules had positive correlation in surface and middle layer,floccules settling velocity increases with the increase of particle size in spring time. Comprehensive analysis of the factors affecting flocculation,the results show that the salinity have no significant relationship with floccules size,the influence of velocity to floccules had two kinds of circumstances,large flow motion will hinder the development of the floc size. These knowledge will contributes to a further understanding of fine sediment transport characteristics and biochemical process in the Pearl River Estuary.
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