The Bohai Sea(BS)is the unique semi-closed inland sea of China,characterized by degraded water quality due to significant terrestrial pollution input.In order to improve its water quality,a dedicated action named“Uph...The Bohai Sea(BS)is the unique semi-closed inland sea of China,characterized by degraded water quality due to significant terrestrial pollution input.In order to improve its water quality,a dedicated action named“Uphill Battles for Integrated Bohai Sea Management”(UBIBSM,2018–2020)was implemented by the Chinese government.To evaluate the action effectiveness toward water quality improvement,variability of the satelliteobserved water transparency(Secchi disk depth,Z_(SD))was explored,with special emphasis on the nearshore waters(within 20 km from the coastline)prone to terrestrial influence.(1)Compared to the status before the action began(2011–2017),majority(87.3%)of the nearshore waters turned clear during the action implementation period(2018–2020),characterized by the elevated Z_(SD)by 11.6%±12.1%.(2)Nevertheless,the improvement was not spatially uniform,with higher Z_(SD)improvement in provinces of Hebei,Liaoning,and Shandong(13.2%±16.5%,13.2%±11.6%,10.8%±10.2%,respectively)followed by Tianjin(6.2%±4.7%).(3)Bayesian trend analysis found the abrupt Z_(SD)improvement in April 2018,which coincided with the initiation of UBIBSM,implying the water quality response to pollution control.More importantly,the independent statistics of land-based pollutant discharge also indicated that the significant reduction of terrestrial pollutant input during the UBIBSM action was the main driver of observed Z_(SD)improvement.(4)Compared with previous pollution control actions in the BS,UBIBSM was found to be the most successful one during the past 20 years,in terms of transparency improvement over nearshore waters.The presented results proved the UBIBSM-achieved remarkable water quality improvement,taking the advantage of long-term consistent and objective data record from satellite ocean color observation.展开更多
A three-dimensional nearshore circulation model was developed by coupling CH3D, a three-dimensional hydrodynamic model and REF/DIF, a nearshore wave transformation model. The model solves the three-dimensional wave-av...A three-dimensional nearshore circulation model was developed by coupling CH3D, a three-dimensional hydrodynamic model and REF/DIF, a nearshore wave transformation model. The model solves the three-dimensional wave-averaged equations of motion. Wave-induced effects on circulation were introduced in the form of radiation stresses, wave-induced mass transport, wave-induced enhancement of bottom friction and wave-induced turbulent mixing. Effects of breaking waves were considered following Svendsen (1984a and 1984b) and Stive and Wind (1986). The model was successfully tested against the analytical solution of longshore currents by Longuet and Higgins (1970). The model successfully simulated the undertow as observed in a laboratory experiment by Stive and Wind (1982). In addition, the model was applied to a physical model by Mory and Hamm (1997) and successfully reproduced the eddy behind a detached breakwater as well as the longshore current on the open beach and the contiguous eddy in the open area of the wave tank. While the qualitative agreement between model results and experimental observations was very good, the quantitative agreement needs to be further improved. Albeit difficult to explain every discrepancy between the model results and observations, in general, sources of errors are attributed to the lack of understanding and comprehensive description of following processes: (1)the horizontal and vertical distribution of radiation stress, especially for breaking waves;(2)the detailed structure of turbulence;(3)Wave-current interaction (not included at this moment); and (4)the wave-current boundary layer and the resulting bottom shear stress.展开更多
The offshore turbine system was installed on a floating platform moored in Hakata Bay, offshore of Fukuoka, Japan. An identical turbine system was also installed at the adjacent waterfront. The separation of the two t...The offshore turbine system was installed on a floating platform moored in Hakata Bay, offshore of Fukuoka, Japan. An identical turbine system was also installed at the adjacent waterfront. The separation of the two turbines was 3.7 km. Wind flow tends to be more stable and the average wind speed is often larger in offshore areas than adjacent land areas at typical wind turbine hub height. This study focused on the wind condition of a nearshore area to clarify the advantages of nearshore wind farming. Prior to field experiment, wind conditions were predicted by using numerical simulation. It is useful for estimating topographical effect in nearshore areas. Next, field verification test was done by directly comparing wind data obtained from the identical wind turbine systems installed at an offshore location and the adjacent waterfront over the same extended period. The corresponding power output of these turbines was also compared. The data set exhibits 23% larger annual average wind speed at the offshore location and smaller turbulent intensity, resulting doubled annual power production.展开更多
In 1994,Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves.The method was extended to irregular waves b...In 1994,Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves.The method was extended to irregular waves by Cheon and Suh in 2016.In this study,this method is further extended to include the effect of future change in offshore wave height and the sea level rise.The relative changes in wavelength,refraction coefficient,shoaling coefficient,and wave height in nearshore area are presented as functions of the relative changes in water depth and offshore wave height.The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise and offshore wave height change on coastal structures by calculating the relative changes in wave run-up height,overtopping discharge,crest freeboard,and armor weight of the structures.The relative changes in wave characteristics and structure-related parameters are all expressed as a function of the relative water depth for various combinations of the relative changes in water depth and offshore wave height.展开更多
An offshore shoal or bar refracts ocean surface waves and causes wave focusing/defocusing on the adjacent beach. Wave focal patterns characterized by alongshore variations in wave height, wave angle, and breaking loca...An offshore shoal or bar refracts ocean surface waves and causes wave focusing/defocusing on the adjacent beach. Wave focal patterns characterized by alongshore variations in wave height, wave angle, and breaking location induce alongshore non-uniformities of wave setup and nearshore circulation, e.g., rip currents and alongshore currents, in the surfzone. A simplified analytic model for nearshore circulation generated by focused/defocused waves on a planar beach is developed and theoretical solutions are obtained using transport stream function and perturbations in alongshore distributions of wave height and wave angle at the breaker line. The analytic model suggests that alongshore currents are strongly affected by a pair of counter-rotating vortices generated shoreward of the wave focal zone. The vortices are persistent, and their strengths depend on the amplitudes of alongshore variations in wave height and wave angle. The alongshore gradient in wave height tends to intensify the vortices while the convergence of wave angle tends to weaken the vortices. Divergent flows associated with the vortices in the surfzone are intense, strengthening alongshore currents in the downstream of the wave focal zone and weakening alongshore currents or causing flows reversal in the upstream. Alongshore currents are modulated by rip currents associated with the wave focusing/defocusing patterns.展开更多
Wave formulae derived from the dispersion relation for cnoidal waves are used to find an analytical solution to the problem of nearshore wave height variation on a simple topography, i. e., with an incrementally const...Wave formulae derived from the dispersion relation for cnoidal waves are used to find an analytical solution to the problem of nearshore wave height variation on a simple topography, i. e., with an incrementally constant slope. The solution accounts for shoaling, frictional dissipation and will be sufficiently accurate for practical purposes considering the simplified assumptions which are necessary for the treatment of this problem by any method.展开更多
Detailed analyses of the monitored data provided by the Yantai Ocean Administration Office between 1989 and 1996 show that, the fluctuation regularities of content of the inorganic phosphorus are as follows: the conte...Detailed analyses of the monitored data provided by the Yantai Ocean Administration Office between 1989 and 1996 show that, the fluctuation regularities of content of the inorganic phosphorus are as follows: the content of inorganic phosphorus fluctuated near the class-1 standard line basically from 1989 to 1993, tended to increase rapidly from 1993, and increased continuously, causing water quality to be deteriorated from the class-2 to class-3 standard by 19%. Causes for increment of the content of inorganic phosphorus are also analyzed. The results show that, the flux of phosphorus entering Yantai nearshore sea area increases at an annual rate of 16.5 percent, in which the increment rates of the phosphorus contained in washing powder and in phosphate fertilizer are 12.9 and 17.5 percent respectively. Both of them kept a positive interrelationship with their fluxes into the sea. In addition, the migration and regeneration mechanism of the phosphorus within the nearshore area also lead to the展开更多
Temperature and salinity data,obtained by two snapshot surveys during 19-20 May 2019 and 12-25 September 2019 across the East China Sea(ECS)shelf,revealed that the Kuroshio intrusion to the north of 28°N comprise...Temperature and salinity data,obtained by two snapshot surveys during 19-20 May 2019 and 12-25 September 2019 across the East China Sea(ECS)shelf,revealed that the Kuroshio intrusion to the north of 28°N comprised the Nearshore Kuroshio Branch Current(NKBC)and the Off shore Kuroshio Branch Current(OKBC)at the bottom of the ECS during spring 2019,and that the NKBC was weak during autumn 2019.The Regional Ocean Model System was used to reproduce the distribution of water masses and the current structure over the continental shelf of the ECS during 2019.Analyses of the momentum balances indicated that the cross-shore range and the intensity of the NKBC were determined by the combination of the geostrophic fl ow and bottom Ekman current.In comparison with that in May 2019,a weakened shoreward bottom Ekman current and an increased off shoreward geostrophic fl ow caused the disappearance of cross-shore range of the NKBC in September 2019.Meanwhile,a diminished northeastward alongshore geostrophic fl ow in September 2019 also weakened the intensity of the NKBC.Sensitivity experiments indicated that a strong southwestward wind can push the western(eastern)boundary of the NKBC further off shoreward(shoreward)by increasing(decreasing)the off shore geostrophic fl ow(bottom Ekman current).A weak Taiwan Warm Current(TWC)can move the eastern boundary of the NKBC shoreward by decreasing the onshore bottom Ekman current.A weak Kuroshio Current(KC)can move the eastern boundary of the NKBC shoreward by increasing the off shoreward geostrophic fl ow.Furthermore,a strong(weak)southwestward wind,weak(strong)TWC,and strong(weak)KC can diminish(enhance)the intensity of the NKBC.Of the three factors,the wind plays the major role in infl uencing the NKBC.展开更多
Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact,causing complicated genesis and distribution of argillaceous sediments,as well as other i...Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact,causing complicated genesis and distribution of argillaceous sediments,as well as other issues.This paper investigates the spatial configuration of sand and mud in the sand bar reservoir,and analyzes its internal structure.Modern sand bar deposits in the Xiashan Lake,Shandong Province,China,were analyzed and compared with the sand bar reservoirs of the Member 2 of the Paleogene Shahejie Formation in the Banqiao Sag,China.The configurational mode of sand bar deposits was explored from the perspective of the spatial distribution and composition relationships between sand and mud.Based on the alternate deposition characteristics of sand and mud in the longitudinal direction,lacustrine nearshore sand bars can be divided into three sedimentary combination patterns:thin-sand and thin-mud interbed pattern,thick-mud thick-sand pattern,and thin-mud thick-sand pattern.Their mud components manifest as the deposition of fine-grained lithofacies of multiple genetic types.These include(semi-)deep lacustrine mud,sand and mud interbedded beach,argillaceous sediments in the water retention area behind the bar,and fall-silt seams that resulted from flood discharge.By summarizing the specific developmental locations and sequential relationships of each fine-grained argillaceous facies in modern sand bar deposits,a depositional process-based argillaceous sediment composition model is proposed.Based on this,this paper discusses the spatial configuration of sand bodies and argillaceous sediments in sand bar reservoirs,and introduces the typical stratigraphic structures of sand bars in two environments,i.e.,vertical superposition and lateral migration.In lacustrine nearshore sand bar reservoirs,the deposition and preservation degrees of mud mainly depend on three factors:accommodation space change,frequency of base-level cycles,and exposure-erosion time.These in turn influence the continuity and relative contents of sand and mud in reservoirs.The distribution of argillaceous sediments forms different orders of interlayers,which affects the heterogeneity and fluid percolation of sand bar reservoirs.Clarifying the space-matching relationship of sand and mud in sand bar deposits provides geological models and information parameters for the refined characterization and modeling of the internal configuration of sand bar reservoirs.Furthermore,this work offers guidance for the optimal adjustment of reservoir development strategies or the optimization of reservoir development plans.展开更多
Pseudotolithus typus is one of the two commercially important Sciaenids off Benin nearshore waters mainly fished by beach seining. Unfortunately, since 1994, the production of this species has been decreasing, and inc...Pseudotolithus typus is one of the two commercially important Sciaenids off Benin nearshore waters mainly fished by beach seining. Unfortunately, since 1994, the production of this species has been decreasing, and increasingly more small-sized fishes are regularly harvested, while little is known about the species’ population structure and its life history. Therefore, population structure, probability of capture and size at first capture were investigated using length-frequency data of 1144 specimens sampled from beach seine hauls over a period of 18 months. A total of 54.3% of this population was immature, confirming the domination of smallsized fishes in the catches. Gonad maturation stages were also examined. Frequency distribution of oocyte size exhibited two cohorts of mature oocytes suggesting two spawning periods per year. Monthly averages of gonado-somatic index confirmed that P. typus spawned twice a year during the major warm season (March - May) and during the transition minor warm to minor cold season in October - November. Length at first capture (L75 = 22.76 cm) was smaller than the length at first sexual maturation (L50% = 23.6 cm) indicating a heavy pressure of the beach seine on this resource. To give each fish the chance of reproducing at least once in its lifetime to recruit into the stock, necessary measures such as the size-limit regulation by gradually increasing beach seine mesh size should be developed. Community-based management of the nearshore fishery could contribute to reducing fishing effort during the reproductive periods from February to May and from October to December each year.展开更多
Ⅰ.INTRODUCTION The Republic of Maldives is an archipelago of some 1200 coral islands which clustered in 26 atolls in the central Indian Ocean (Figure 1). The total area of the county is 10,800 km^2, however its land ...Ⅰ.INTRODUCTION The Republic of Maldives is an archipelago of some 1200 coral islands which clustered in 26 atolls in the central Indian Ocean (Figure 1). The total area of the county is 10,800 km^2, however its land area accounts for only 3% (298 km^2). Thus, the most of its resources are hidden in underwater. For a few thousands years tuna fishing has been the traditional industrial of the Maldives. Tourism becomes important in the national income only in the recent 20 years. Due to the coplexity of the underwater topography in the coral reef area, the investigation of the natural resources using conventional methods is difficult. To evaluate the potential applications of remote展开更多
As the increasing number of wind energy is integrated into the national power grid,analyses of wind energy are becoming increasingly more crucial.The interaction between the topography and the northeast(NE)monsoon bri...As the increasing number of wind energy is integrated into the national power grid,analyses of wind energy are becoming increasingly more crucial.The interaction between the topography and the northeast(NE)monsoon brings abundant wind resources to the Taiwan Strait in autumn and winter.The offshore area has stronger and more stable wind resources,so deployment of offshore wind power is also actively being carried out.However,development of offshore wind power systems requires stricter evaluation and decision-making.Therefore,this study implements a multi-site measurement verification to establish the relationship between the wind resources of the nearshore wind turbine system and a potential offshore power site in Chanbin.In the absence of a wind turbine at a specific location,potential of offshore wind energy is analyzed through wind resources.The findings showed that although the distance between these two sites is substantial,the nearshore and offshore areas at Chanbin experience similar wind conditions,and nearshore wind turbine can respond well to changes in wind speed and generate power accordingly.Afterwards,on this basis,the offshore power potential was evaluated and compared with the nearshore wind turbine systems.The results suggested the advantages of offshore wind power.A further analysis of the differences between power generation on a monthly basis was carried out to determine the distribution of wind turbine operation modes and illustrate the influence of the NE monsoon.展开更多
The severity of lightning strikes on offshore wind turbines built along coastal and nearshore regions can pose safety concerns that are often overlooked.In this research study the behavior of electrical discharges for...The severity of lightning strikes on offshore wind turbines built along coastal and nearshore regions can pose safety concerns that are often overlooked.In this research study the behavior of electrical discharges for wind turbines that might be located in the nearshore regions along the East Coast of China and Sea of Japan were characterized using a physics-based model that accounted for a total of eleven different geometrical and lightning parameters.Utilizing the electrical potential field predicted using this model it was then possible to estimate the frequency of lightning strikes and the distribution of electrical loads utilizing established semi-empirical relationships and available data.The total number of annual lightning strikes on an offshore wind turbine was found to vary with hub elevation,extent of cloud cover,season and geographical location.The annual lightning strike rate on a wind turbine along the nearshore region on the Sea of Japan during the winter season was shown to be moderately larger compared to the lightning strike frequency on a turbine structure on the East Coast of China.Short duration electrical discharges,represented using marginal probability functions,were found to vary with season and geographical location,exhibiting trends consistent with the distribution of the electrical peak current.It was demonstrated that electrical discharges of moderately long duration typically occur in the winter months on the East Coast of China and the summer season along the Sea of Japan.In contrast,severe electrical discharges are typical of summer thunderstorms on the East Coast of China and winter frontal storm systems along the West Coast of Japan.The electrical charge and specific energy dissipated during lightning discharges on an offshore wind turbine was found to vary stochastically,with severe electrical discharges corresponding to large electrical currents of long duration.展开更多
Al-Nakheel beach is located northwest of Alexandria city,Egypt,along the Mediterranean coast.During the period from 1998 to 2003,seven detached breakwaters were constructed along Al-Nakheel beach to create a sheltered...Al-Nakheel beach is located northwest of Alexandria city,Egypt,along the Mediterranean coast.During the period from 1998 to 2003,seven detached breakwaters were constructed along Al-Nakheel beach to create a sheltered area for swimming.Unfortunately,the structures amplify rip currents,shoreline accretions,and erosions.The aim of this research is to track the variations of the rip currents within the study area and show the effects of the breakwaters on the shoreline.The research is based on the hydrodynamic and morphological data of the study area and uses the Delft3D hydrodynamical model combined with other data analysis tools to serve the model input.The data include measured sea-level observations in 2013,the ERA-interim wave datasets from 2015 to 2018 and wind data in 2018,bed morphologies,and Google Earth satellite images from 2010 to 2020.The model is calibrated on the basis of the available current measurements within the nearshore zone.Results show that the shoreline eroded at an average rate of about 0.9 m/yr.Moreover,pairs of vortices are formed behind the breakwaters with an average current velocity of 0.6 m/s.The predominant northwest waves induce rip currents on the leeside of the structures with velocities reaching 1.2 m/s,associated with the rip pulsation that extends offshore.The problem solution decision recommends the removal of the sand deposition on the leeside of the breakwaters by an average amount of 100000 m3/yr and the fencing of the safe area for swimming by a floating fence of 1000 m length and 65 m average width.展开更多
基金The fund supported by Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) under contract No. SML2021SP313the fundamental research funds for the Central Universities of Sun Yat-Sen University under contract No.23xkjc019the fund supported by China-Korea Joint Ocean Research Center of China under contract No. PI-2022-1-01
文摘The Bohai Sea(BS)is the unique semi-closed inland sea of China,characterized by degraded water quality due to significant terrestrial pollution input.In order to improve its water quality,a dedicated action named“Uphill Battles for Integrated Bohai Sea Management”(UBIBSM,2018–2020)was implemented by the Chinese government.To evaluate the action effectiveness toward water quality improvement,variability of the satelliteobserved water transparency(Secchi disk depth,Z_(SD))was explored,with special emphasis on the nearshore waters(within 20 km from the coastline)prone to terrestrial influence.(1)Compared to the status before the action began(2011–2017),majority(87.3%)of the nearshore waters turned clear during the action implementation period(2018–2020),characterized by the elevated Z_(SD)by 11.6%±12.1%.(2)Nevertheless,the improvement was not spatially uniform,with higher Z_(SD)improvement in provinces of Hebei,Liaoning,and Shandong(13.2%±16.5%,13.2%±11.6%,10.8%±10.2%,respectively)followed by Tianjin(6.2%±4.7%).(3)Bayesian trend analysis found the abrupt Z_(SD)improvement in April 2018,which coincided with the initiation of UBIBSM,implying the water quality response to pollution control.More importantly,the independent statistics of land-based pollutant discharge also indicated that the significant reduction of terrestrial pollutant input during the UBIBSM action was the main driver of observed Z_(SD)improvement.(4)Compared with previous pollution control actions in the BS,UBIBSM was found to be the most successful one during the past 20 years,in terms of transparency improvement over nearshore waters.The presented results proved the UBIBSM-achieved remarkable water quality improvement,taking the advantage of long-term consistent and objective data record from satellite ocean color observation.
文摘A three-dimensional nearshore circulation model was developed by coupling CH3D, a three-dimensional hydrodynamic model and REF/DIF, a nearshore wave transformation model. The model solves the three-dimensional wave-averaged equations of motion. Wave-induced effects on circulation were introduced in the form of radiation stresses, wave-induced mass transport, wave-induced enhancement of bottom friction and wave-induced turbulent mixing. Effects of breaking waves were considered following Svendsen (1984a and 1984b) and Stive and Wind (1986). The model was successfully tested against the analytical solution of longshore currents by Longuet and Higgins (1970). The model successfully simulated the undertow as observed in a laboratory experiment by Stive and Wind (1982). In addition, the model was applied to a physical model by Mory and Hamm (1997) and successfully reproduced the eddy behind a detached breakwater as well as the longshore current on the open beach and the contiguous eddy in the open area of the wave tank. While the qualitative agreement between model results and experimental observations was very good, the quantitative agreement needs to be further improved. Albeit difficult to explain every discrepancy between the model results and observations, in general, sources of errors are attributed to the lack of understanding and comprehensive description of following processes: (1)the horizontal and vertical distribution of radiation stress, especially for breaking waves;(2)the detailed structure of turbulence;(3)Wave-current interaction (not included at this moment); and (4)the wave-current boundary layer and the resulting bottom shear stress.
文摘The offshore turbine system was installed on a floating platform moored in Hakata Bay, offshore of Fukuoka, Japan. An identical turbine system was also installed at the adjacent waterfront. The separation of the two turbines was 3.7 km. Wind flow tends to be more stable and the average wind speed is often larger in offshore areas than adjacent land areas at typical wind turbine hub height. This study focused on the wind condition of a nearshore area to clarify the advantages of nearshore wind farming. Prior to field experiment, wind conditions were predicted by using numerical simulation. It is useful for estimating topographical effect in nearshore areas. Next, field verification test was done by directly comparing wind data obtained from the identical wind turbine systems installed at an offshore location and the adjacent waterfront over the same extended period. The corresponding power output of these turbines was also compared. The data set exhibits 23% larger annual average wind speed at the offshore location and smaller turbulent intensity, resulting doubled annual power production.
基金National Research Foundation of Korea(NRF)funded by Korea Ministry of Science,ICT and Future Planning(NRF-2014R1A2A2A01007921)
文摘In 1994,Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves.The method was extended to irregular waves by Cheon and Suh in 2016.In this study,this method is further extended to include the effect of future change in offshore wave height and the sea level rise.The relative changes in wavelength,refraction coefficient,shoaling coefficient,and wave height in nearshore area are presented as functions of the relative changes in water depth and offshore wave height.The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise and offshore wave height change on coastal structures by calculating the relative changes in wave run-up height,overtopping discharge,crest freeboard,and armor weight of the structures.The relative changes in wave characteristics and structure-related parameters are all expressed as a function of the relative water depth for various combinations of the relative changes in water depth and offshore wave height.
基金financially supported by the Tianjin Municipal Science and Technology Commission(Grant No.19JCYBJC22000)
文摘An offshore shoal or bar refracts ocean surface waves and causes wave focusing/defocusing on the adjacent beach. Wave focal patterns characterized by alongshore variations in wave height, wave angle, and breaking location induce alongshore non-uniformities of wave setup and nearshore circulation, e.g., rip currents and alongshore currents, in the surfzone. A simplified analytic model for nearshore circulation generated by focused/defocused waves on a planar beach is developed and theoretical solutions are obtained using transport stream function and perturbations in alongshore distributions of wave height and wave angle at the breaker line. The analytic model suggests that alongshore currents are strongly affected by a pair of counter-rotating vortices generated shoreward of the wave focal zone. The vortices are persistent, and their strengths depend on the amplitudes of alongshore variations in wave height and wave angle. The alongshore gradient in wave height tends to intensify the vortices while the convergence of wave angle tends to weaken the vortices. Divergent flows associated with the vortices in the surfzone are intense, strengthening alongshore currents in the downstream of the wave focal zone and weakening alongshore currents or causing flows reversal in the upstream. Alongshore currents are modulated by rip currents associated with the wave focusing/defocusing patterns.
文摘Wave formulae derived from the dispersion relation for cnoidal waves are used to find an analytical solution to the problem of nearshore wave height variation on a simple topography, i. e., with an incrementally constant slope. The solution accounts for shoaling, frictional dissipation and will be sufficiently accurate for practical purposes considering the simplified assumptions which are necessary for the treatment of this problem by any method.
文摘Detailed analyses of the monitored data provided by the Yantai Ocean Administration Office between 1989 and 1996 show that, the fluctuation regularities of content of the inorganic phosphorus are as follows: the content of inorganic phosphorus fluctuated near the class-1 standard line basically from 1989 to 1993, tended to increase rapidly from 1993, and increased continuously, causing water quality to be deteriorated from the class-2 to class-3 standard by 19%. Causes for increment of the content of inorganic phosphorus are also analyzed. The results show that, the flux of phosphorus entering Yantai nearshore sea area increases at an annual rate of 16.5 percent, in which the increment rates of the phosphorus contained in washing powder and in phosphate fertilizer are 12.9 and 17.5 percent respectively. Both of them kept a positive interrelationship with their fluxes into the sea. In addition, the migration and regeneration mechanism of the phosphorus within the nearshore area also lead to the
基金Supported by the National Natural Science Foundation of China(Nos.41630967,41776020)。
文摘Temperature and salinity data,obtained by two snapshot surveys during 19-20 May 2019 and 12-25 September 2019 across the East China Sea(ECS)shelf,revealed that the Kuroshio intrusion to the north of 28°N comprised the Nearshore Kuroshio Branch Current(NKBC)and the Off shore Kuroshio Branch Current(OKBC)at the bottom of the ECS during spring 2019,and that the NKBC was weak during autumn 2019.The Regional Ocean Model System was used to reproduce the distribution of water masses and the current structure over the continental shelf of the ECS during 2019.Analyses of the momentum balances indicated that the cross-shore range and the intensity of the NKBC were determined by the combination of the geostrophic fl ow and bottom Ekman current.In comparison with that in May 2019,a weakened shoreward bottom Ekman current and an increased off shoreward geostrophic fl ow caused the disappearance of cross-shore range of the NKBC in September 2019.Meanwhile,a diminished northeastward alongshore geostrophic fl ow in September 2019 also weakened the intensity of the NKBC.Sensitivity experiments indicated that a strong southwestward wind can push the western(eastern)boundary of the NKBC further off shoreward(shoreward)by increasing(decreasing)the off shore geostrophic fl ow(bottom Ekman current).A weak Taiwan Warm Current(TWC)can move the eastern boundary of the NKBC shoreward by decreasing the onshore bottom Ekman current.A weak Kuroshio Current(KC)can move the eastern boundary of the NKBC shoreward by increasing the off shoreward geostrophic fl ow.Furthermore,a strong(weak)southwestward wind,weak(strong)TWC,and strong(weak)KC can diminish(enhance)the intensity of the NKBC.Of the three factors,the wind plays the major role in infl uencing the NKBC.
基金Supported by the National Natural Science Foundation of China(41702359)China National Science and Technology Major Project(2016ZX05033003-003).
文摘Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact,causing complicated genesis and distribution of argillaceous sediments,as well as other issues.This paper investigates the spatial configuration of sand and mud in the sand bar reservoir,and analyzes its internal structure.Modern sand bar deposits in the Xiashan Lake,Shandong Province,China,were analyzed and compared with the sand bar reservoirs of the Member 2 of the Paleogene Shahejie Formation in the Banqiao Sag,China.The configurational mode of sand bar deposits was explored from the perspective of the spatial distribution and composition relationships between sand and mud.Based on the alternate deposition characteristics of sand and mud in the longitudinal direction,lacustrine nearshore sand bars can be divided into three sedimentary combination patterns:thin-sand and thin-mud interbed pattern,thick-mud thick-sand pattern,and thin-mud thick-sand pattern.Their mud components manifest as the deposition of fine-grained lithofacies of multiple genetic types.These include(semi-)deep lacustrine mud,sand and mud interbedded beach,argillaceous sediments in the water retention area behind the bar,and fall-silt seams that resulted from flood discharge.By summarizing the specific developmental locations and sequential relationships of each fine-grained argillaceous facies in modern sand bar deposits,a depositional process-based argillaceous sediment composition model is proposed.Based on this,this paper discusses the spatial configuration of sand bodies and argillaceous sediments in sand bar reservoirs,and introduces the typical stratigraphic structures of sand bars in two environments,i.e.,vertical superposition and lateral migration.In lacustrine nearshore sand bar reservoirs,the deposition and preservation degrees of mud mainly depend on three factors:accommodation space change,frequency of base-level cycles,and exposure-erosion time.These in turn influence the continuity and relative contents of sand and mud in reservoirs.The distribution of argillaceous sediments forms different orders of interlayers,which affects the heterogeneity and fluid percolation of sand bar reservoirs.Clarifying the space-matching relationship of sand and mud in sand bar deposits provides geological models and information parameters for the refined characterization and modeling of the internal configuration of sand bar reservoirs.Furthermore,this work offers guidance for the optimal adjustment of reservoir development strategies or the optimization of reservoir development plans.
文摘Pseudotolithus typus is one of the two commercially important Sciaenids off Benin nearshore waters mainly fished by beach seining. Unfortunately, since 1994, the production of this species has been decreasing, and increasingly more small-sized fishes are regularly harvested, while little is known about the species’ population structure and its life history. Therefore, population structure, probability of capture and size at first capture were investigated using length-frequency data of 1144 specimens sampled from beach seine hauls over a period of 18 months. A total of 54.3% of this population was immature, confirming the domination of smallsized fishes in the catches. Gonad maturation stages were also examined. Frequency distribution of oocyte size exhibited two cohorts of mature oocytes suggesting two spawning periods per year. Monthly averages of gonado-somatic index confirmed that P. typus spawned twice a year during the major warm season (March - May) and during the transition minor warm to minor cold season in October - November. Length at first capture (L75 = 22.76 cm) was smaller than the length at first sexual maturation (L50% = 23.6 cm) indicating a heavy pressure of the beach seine on this resource. To give each fish the chance of reproducing at least once in its lifetime to recruit into the stock, necessary measures such as the size-limit regulation by gradually increasing beach seine mesh size should be developed. Community-based management of the nearshore fishery could contribute to reducing fishing effort during the reproductive periods from February to May and from October to December each year.
文摘Ⅰ.INTRODUCTION The Republic of Maldives is an archipelago of some 1200 coral islands which clustered in 26 atolls in the central Indian Ocean (Figure 1). The total area of the county is 10,800 km^2, however its land area accounts for only 3% (298 km^2). Thus, the most of its resources are hidden in underwater. For a few thousands years tuna fishing has been the traditional industrial of the Maldives. Tourism becomes important in the national income only in the recent 20 years. Due to the coplexity of the underwater topography in the coral reef area, the investigation of the natural resources using conventional methods is difficult. To evaluate the potential applications of remote
基金financially supported in part by the National Science Council,Republic of China,under contract MOST 110-2221-E-006-183-supported by Taipower and RCETS offshore wind power team.
文摘As the increasing number of wind energy is integrated into the national power grid,analyses of wind energy are becoming increasingly more crucial.The interaction between the topography and the northeast(NE)monsoon brings abundant wind resources to the Taiwan Strait in autumn and winter.The offshore area has stronger and more stable wind resources,so deployment of offshore wind power is also actively being carried out.However,development of offshore wind power systems requires stricter evaluation and decision-making.Therefore,this study implements a multi-site measurement verification to establish the relationship between the wind resources of the nearshore wind turbine system and a potential offshore power site in Chanbin.In the absence of a wind turbine at a specific location,potential of offshore wind energy is analyzed through wind resources.The findings showed that although the distance between these two sites is substantial,the nearshore and offshore areas at Chanbin experience similar wind conditions,and nearshore wind turbine can respond well to changes in wind speed and generate power accordingly.Afterwards,on this basis,the offshore power potential was evaluated and compared with the nearshore wind turbine systems.The results suggested the advantages of offshore wind power.A further analysis of the differences between power generation on a monthly basis was carried out to determine the distribution of wind turbine operation modes and illustrate the influence of the NE monsoon.
文摘The severity of lightning strikes on offshore wind turbines built along coastal and nearshore regions can pose safety concerns that are often overlooked.In this research study the behavior of electrical discharges for wind turbines that might be located in the nearshore regions along the East Coast of China and Sea of Japan were characterized using a physics-based model that accounted for a total of eleven different geometrical and lightning parameters.Utilizing the electrical potential field predicted using this model it was then possible to estimate the frequency of lightning strikes and the distribution of electrical loads utilizing established semi-empirical relationships and available data.The total number of annual lightning strikes on an offshore wind turbine was found to vary with hub elevation,extent of cloud cover,season and geographical location.The annual lightning strike rate on a wind turbine along the nearshore region on the Sea of Japan during the winter season was shown to be moderately larger compared to the lightning strike frequency on a turbine structure on the East Coast of China.Short duration electrical discharges,represented using marginal probability functions,were found to vary with season and geographical location,exhibiting trends consistent with the distribution of the electrical peak current.It was demonstrated that electrical discharges of moderately long duration typically occur in the winter months on the East Coast of China and the summer season along the Sea of Japan.In contrast,severe electrical discharges are typical of summer thunderstorms on the East Coast of China and winter frontal storm systems along the West Coast of Japan.The electrical charge and specific energy dissipated during lightning discharges on an offshore wind turbine was found to vary stochastically,with severe electrical discharges corresponding to large electrical currents of long duration.
文摘Al-Nakheel beach is located northwest of Alexandria city,Egypt,along the Mediterranean coast.During the period from 1998 to 2003,seven detached breakwaters were constructed along Al-Nakheel beach to create a sheltered area for swimming.Unfortunately,the structures amplify rip currents,shoreline accretions,and erosions.The aim of this research is to track the variations of the rip currents within the study area and show the effects of the breakwaters on the shoreline.The research is based on the hydrodynamic and morphological data of the study area and uses the Delft3D hydrodynamical model combined with other data analysis tools to serve the model input.The data include measured sea-level observations in 2013,the ERA-interim wave datasets from 2015 to 2018 and wind data in 2018,bed morphologies,and Google Earth satellite images from 2010 to 2020.The model is calibrated on the basis of the available current measurements within the nearshore zone.Results show that the shoreline eroded at an average rate of about 0.9 m/yr.Moreover,pairs of vortices are formed behind the breakwaters with an average current velocity of 0.6 m/s.The predominant northwest waves induce rip currents on the leeside of the structures with velocities reaching 1.2 m/s,associated with the rip pulsation that extends offshore.The problem solution decision recommends the removal of the sand deposition on the leeside of the breakwaters by an average amount of 100000 m3/yr and the fencing of the safe area for swimming by a floating fence of 1000 m length and 65 m average width.
